Test Bank For Essential Cosmic Perspective, The, 9th Edition by Jeffrey O. Bennett Megan Donahue Nic by ACADEMIAMILL

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 1 A Modern View of the Universe Section 1.1 1) About where is our solar system located within the Milky Way Galaxy? A) at the center of the galaxy B) about 10 percent of the way from the center of the galaxy to the edge of the galactic disk C) about halfway from the center of the galaxy to the edge of the galactic disk D) near the far edge of the galactic disk E) in the halo of the galaxy above the galactic disk Answer: C 2) When we speak of the entire universe (as opposed to the observable universe), we mean ________. A) all the stars and galaxies that we can see with telescopes B) all material located within about 14 billion light-years of Earth C) the sum total of all matter and energy D) all the matter in galaxies, but not the spaces between the galaxies Answer: C 3) Which of the following is the smallest distance? A) Diameter of a typical planet B) 1 light-second C) 1 AU D) Diameter of a typical star Answer: A 4) Which of the following is the largest distance? A) Diameter of a typical galaxy B) Diameter of Pluto's orbit C) Distance to the nearest star (other than our Sun) D) 1 light-year Answer: A 5) Which of the following statements does not use the term light-year in an appropriate way? A) It's about 4 light-years from here to Alpha Centauri. B) It will take me light-years to complete this homework assignment. C) A light-year is about 10 trillion kilometers. D) It will take the Voyager spacecraft about 20,000 years to travel just 1 light-year. E) The Milky Way Galaxy is about 100,000 light-years in diameter. Answer: B

6) One light-minute is the distance that light travels in one minute. How far is this, in kilometers? (Recall that the speed of light is 300,000 km/s.) A) 300,000 km B) 18 million km C) 100 million km D) 1.08 billion km E) 9.46 trillion km Answer: B 7) One light-year is approximately ________. A) the distance from the Sun to Earth B) the speed at which Earth orbits the Sun C) 10 trillion kilometers D) the same as one regular year Answer: C 8) Light takes approximately one second to travel from Earth to the Moon. This means that the Moon is approximately ________. A) 1 astronomical unit from Earth B) 1 light-year from Earth C) 3000 kilometers from Earth D) 300,000 kilometers from Earth E) near the top of Earth's atmosphere Answer: D 9) Sunlight takes about 8.4 minutes to travel from the Sun to Earth. When NASA's New Horizons Spacecraft passed Pluto in 2015, it was about 32 AU from Earth. About how long did it take for transmitted images of Pluto to travel from the spacecraft to Earth? A) One Plutonian year B) 4-1/2 hours C) 2-1/4 days D) 3 weeks E) They arrived almost instantaneously. Answer: C 10) The Voyager 2 Spacecraft is currently on its way out of our solar system at a speed of about 50,000 kilometers per hour. It will reach the distance of the nearest star system (beyond our solar system) in about ________ years. A) 100 B) 1000 C) 10,000 D) 100,000 E) 1,000,000 Answer: D

11) Suppose we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest? A) The one that is farthest away B) The one that is reddest in color C) The one that is bluest in color D) The one that is closest to us E) The one that appears smallest in size Answer: A 12) Suppose we imagine the Sun to be about the size of a grapefruit. Which of the following best describes the size and distance of Earth on the same scale? A) Earth is the size of a tip of a ballpoint pen about 1 meter from the Sun. B) Earth is the size of a golf ball about 1 meter from the Sun. C) Earth is the size of a tip of a ballpoint pen about 15 meters from the Sun. D) Earth is the size of a golf ball about 15 meters from the Sun. E) Earth is the size of a marble about 25 miles from the Sun. Answer: C 13) Suppose we imagine the Sun to be about the size of a grapefruit. How big an area would the orbits of the eight planets of the solar system cover? A) The size of a typical dorm room B) The size of a typical campus building C) The size of a typical campus D) The size of a small city E) The size of a western state (e.g., Colorado) Answer: C 14) Which of the following best describes the Milky Way Galaxy? A) A spiral galaxy with a disk about 100,000 light-years in diameter B) A spiral galaxy with a disk about 1 billion kilometers in diameter C) A spiral galaxy with a disk about 1000 light-years in diameter D) A spherically shaped galaxy that is about 4 light-years in diameter E) A spherically shaped galaxy that is about 100,000 light-years in diameter Answer: A 15) If we use 1 millimeter to represent 1 light-year, about how large in diameter is the Milky Way Galaxy? A) 100 millimeters B) 100 meters C) 1 kilometer D) 100 kilometers E) 1 million millimeters Answer: B

16) How long would it take to count all the stars in the Milky Way Galaxy at a rate of one star per second? A) Several days B) Several weeks C) Several years D) Several thousand years E) Hundreds of thousands of years Answer: D 17) About how many galaxies are there in the observable universe? A) Roughly (within about a factor of 10) the same as the number of stars in our galaxy B) A few dozen C) A few thousand D) About as many as the number of grains of sand on all the beaches on Earth E) An infinite number Answer: A 18) If you represented each star by a grain of sand, about how much sand would it take to represent all the stars in the observable universe? A) All the sand in a typical playground sandlot B) All the sand on Miami Beach C) All the sand on the beaches of California D) One cubic meter of sand E) All the sand on all the beaches on Earth Answer: E 19) The distance of Mars from the Sun is about 1.5 AU. How far is this in kilometers? (You do not need a calculator to answer this question. You do need to know what an AU is, within a factor of 1000.) A) 1.5 150,000,000 km B) 1.5 150,000 km C) 150,000,000,000 / 1.5 km D) 150,000,000 / 1.5 km E) 1.5 150,000,000,000 km Answer: A 20) One light-year is the distance light travels in one year. The speed of light is about 300,000 km/s (3 × 105 km/s). How far is 1 light-year? A) 3 × 105 km B) 1.8 × 107 km C) 1.08 × 109 km D) 9.46 × 1012 km Answer: D

21) Light travels at a speed of 300,000 km/s. About how far is a light-year? A) 10 million meters B) 10 billion km C) 300,000 km D) 10 million km E) 10 trillion km Answer: E 22) Consider how the Moon moves through the Solar System and complete the following sentence. The Moon orbits the Sun ________. A) once a month B) once a year C) once a day Answer: B 23) Suppose you know the speed of a spacecraft in kilometers per second. How would you calculate its speed in kilometers per hour? A) Multiply by 60 and then multiply by 60 again. B) Divide by 60 and then divide by 60 again. C) Multiply by 24. D) Divide by 24. Answer: B 24) How many seconds are in one year? (Calculate this, do not look it up.) A) About 380 million (380,000,000, or 3.8 × 108) B) About 30 million (30,000,000, or 3 × 107) C) About 86 thousand (86,000, or 8.6 × 105) D) About 3600 (3.6 × 103) Answer: B 25) One light-hour is the distance light travels in one hour. The speed of light is about 300,000 km/s (3 × 105 km/s). If Jupiter is 0.72 light hours from the Sun, how far is this? A) 216 thousand km (2.16 × 105 km) B) 13 million km (1.3 × 107 km) C) 778 million km (7.78 × 108 km) D) 1.5 billion km (1.5 × 109 km) Answer: C 26) The planet Mars is, on average, about 228 million km from the Sun. How long does it take light from the Sun to reach Mars? (Recall that the speed of light is about 300,000 km/s.) A) About 8.4 minutes B) About 12.7 minutes C) About 1.52 light seconds D) About 1.52 hours Answer: B 5 Copyright © 2022 Pearson Education, Inc.

27) The Earth has a radius of about 6000 km. How long would it take for an object traveling at the speed of light to circle the Earth? (Recall that the speed of light is 300,000 km/s.) A) 1/300,000 of a second (0.0000033 s) B) 1/6000 of a second (0.000017 s) C) 1/8 of a second (0.0125 s) D) 1/2 of a second (0.5 s) Answer: C Section 1.2 1) Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case ________. A) we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2 B) we can't say anything about these galaxies except for their distances C) we are seeing Galaxy 1 as it looked at a later time in the history of the universe than Galaxy 2 Answer: A 2) Shortly after the Big Bang, the chemical composition of the universe was ________. A) almost entirely hydrogen and helium B) hydrogen only C) about equal amounts of all the elements D) about the same as it is today Answer: A 3) About what percentage of the original hydrogen and helium of the universe had been converted into heavier elements by the time our solar system was born? A) 20% B) 10% C) 50% D) 2% Answer: D 4) What is nuclear fusion? A) An explosion caused by putting together two volatile chemicals B) The process of splitting nuclei to produce energy C) The process of turning matter into pure energy D) The process of combining lightweight nuclei to make heavier nuclei E) A process that only occurs in bombs Answer: D

5) Earth is made mostly of metals and rocks. Where did most of the elements that make up these materials (carbon, silicon, iron, etc.) form? A) They were produced by the Big Bang. B) They were produced by chemical reactions in interstellar gas clouds. C) They were produced by stars. D) They were produced in our Sun. E) They were produced by nuclear fission of uranium and other radioactive materials in space. Answer: C 6) Why did Carl Sagan say that we are star stuff? A) The composition of most stars (mostly hydrogen and helium) is about the same as the composition of our bodies. B) Cosmic rays reaching Earth from distant astronomical sources may be one source of mutations that help evolution along. C) Nearly every atom from which we are made once (before the solar system formed) was inside of a star. D) Nearly every atom from which we are made was once inside our star, the Sun. E) Sagan thought that all of us have the potential to be movie (or TV) stars like he was. Answer: C 7) The Sun is made primarily of ________. A) hydrogen and oxygen B) hydrogen and helium C) carbon and nitrogen D) oxygen and carbon E) nearly equal portions of all the elements Answer: B 8) Our Sun formed ________ our galaxy formed. A) before B) at the same time that C) billions of years after D) within about 10 million years after Answer: C 9) In what sense are galaxies cosmic recycling plants? A) Every time one star dies, a new one of exactly the same size and mass is born. B) As a galaxy rotates, its stars cycle around the galaxy center again and again, each time returning to exactly where they started. C) New stars in galaxies form from gas that has been ejected by previous generations of stars. D) New galaxies are continuously being formed from the remains of older galaxies. Answer: C

10) On the scale of the cosmic calendar, in which the history of the universe is compressed to 1 year, when did the Sun and Earth form? A) January B) December C) September D) February Answer: C 11) On the scale of the cosmic calendar, in which the history of the universe is compressed to 1 year, how long has human civilization (i.e., since ancient Egypt) existed? A) About half the year B) About a month C) A few hours D) A few seconds E) Less than a millionth of a second Answer: D 12) On the scale of the cosmic calendar, in which the history of the universe is compressed into 1 year, when did the dinosaurs become extinct? A) In late December B) In late November C) In late October D) In late September E) In late August Answer: A 13) On the scale of the cosmic calendar, in which the history of the universe is compressed into 1 year, when did Kepler and Galileo first discover that we live on a planet in a solar system? A) 1 second ago B) 1 day ago C) 1 week ago D) December 25 E) December 30 Answer: A 14) On the scale of the cosmic calendar, in which the history of the universe is compressed into 1 year, how long is the average human life span? A) 0.2 millisecond B) 0.2 second C) 2 seconds D) 2 minutes E) 2 hours Answer: B

15) Your textbook discusses the cosmic calendar, a model of the history of the universe scaled to a single year. The length of time represented by one month on this cosmic calendar is therefore closest to ________. A) 1 billion years. B) 1 1000 years. C) 10 million years. D) 10 billion years. E) 1 million years. Answer: A 16) What made most of the oxygen nuclei in the solar system? A) Stars B) Nothing makes elements—oxygen has always been present in the universe. C) The Big Bang D) Our Sun E) High energy collisions of dust and cosmic rays Answer: A 17) Astronomer Alan says the universe is expanding at one rate and Astronomer Wendy says it is expanding at a faster rate. All other things being equal, which astronomer would say that the universe is older? A) Wendy B) Alan C) Neither Answer: B 18) Astronomers have used observations from the Hubble Space Telescope to measure the rate at which the universe is expanding, and have estimated the age of the universe from that measured rate. Suppose the expansion turns out to be faster than current measurements indicate. In that case, our new estimate for the age of the universe would be ________. A) Unaffected B) Younger (less time between now and the Big Bang) C) Older (more time between now and the Big Bang) Answer: B 19) About how long does it take our solar system to complete one orbit around the center of the Milky Way Galaxy? A) 10,000 years B) 1 million years C) 230 million years D) 4-1/2 billion years E) 14 billion years Answer: C

20) What do astronomers mean when they say the universe is expanding? A) Everything in the universe is gradually growing in size. B) Average distances are increasing between most galaxies. C) Average distances are increasing between most stars. D) The universe is expanding from a single point. Answer: B 21) How do scientists estimate the age of the universe? A) They look up the answer in a book or they Google it. B) They measure the abundances of radioactive elements in meteorites, and use their half-lives to calculate the age of the meteorites, which are the oldest solids in the solar system. C) They measure the speeds and distances of galaxies, and calculate the time it took for them to travel that distance (away from us). D) They make a guess: no one really knows how old the universe is. E) They measure how fast the Sun is losing energy, and how much energy it has left to lose. Answer: C 22) According to astronomers, approximately how old is the universe? A) 14 billion years B) 14 trillion years C) Infinite D) 14 million years Answer: A 23) According to current scientific estimates, when did the Big Bang occur? A) About 4.5 billion years ago B) About 20 billion years ago C) About 65 million years ago D) About 14 billion years ago E) About 10 billion years ago Answer: D

Section 1.3 1) Approximately how fast is a person located at the Earth's equator moving around Earth's axis due to the rotation of the Earth? A) 17,000 km/hr B) 1700 km/hr C) 170 km/hr D) 17 km/hr E) Not moving at all Answer: B 2) Earth's rotation causes a person at the North Pole to ________ relative to the center of the Earth. A) move at a speed of about 1670 km/hr B) spin in place once each year C) remain completely stationary D) spin in place once each day Answer: D 3) The ecliptic plane is ________. A) the plane of Earth's orbit around the Sun B) the plane of the Moon's orbit around Earth C) the plane of our solar system's orbit around the Milky Way Galaxy D) a flat disk of material that lies between the Sun and Earth E) the plane defined by Earth's equator Answer: B 4) We say that Earth has an axis tilt of 23-1/2° because this is the angle between Earth's ________. A) rotation axis and a line perpendicular (vertical) to the ecliptic plane B) rotation axis and the star Polaris C) equator and rotation axis D) rotation axis and north pole E) rotation axis and magnetic axis Answer: A

5) Patterns of stars in constellations hardly change in appearance over times of even a few thousand years. Why? A) Stars are fixed and never move. B) Stars move, but they move very slowly—only a few kilometers in a thousand years. C) Although most stars move through the sky, the brightest stars do not, and these are the ones that trace the patterns we see in the constellations. D) The stars in our sky actually move rapidly relative to us—thousands of kilometers per hour— but are so far away that it takes a long time for this motion to make a noticeable change in the patterns in the sky. E) Stars within a constellation move together as a group, which tends to hide their actual motion and prevent the pattern from changing. Answer: D 6) Which of the following correctly lists the described speeds from slowest to fastest? A) Earth's orbital speed about the Sun Earth's speed of rotation on its axis Earth's orbital speed about the Sun typical speeds of stars in the local solar neighborhood relative to us the speed of our solar system orbiting the center of the Milky Way Galaxy the speeds of very distant galaxies relative to us B) typical speeds of stars in the local solar neighborhood relative to us Earth's speed of rotation on its axis Earth's orbital speed about the Sun the speed of our solar system orbiting the center of the Milky Way Galaxy the speeds of very distant galaxies relative to us C) Earth's speed of rotation on its axis Earth's orbital speed about the Sun the speed of our solar system orbiting the center of the Milky Way Galaxy the speeds of very distant galaxies relative to us typical speeds of stars in the local solar neighborhood relative to us D) Earth's orbital speed about the Sun the speeds of very distant galaxies relative to us Earth's speed of rotation on its axis typical speeds of stars in the local solar neighborhood relative to us the speed of our solar system orbiting the center of the Milky Way Galaxy E) typical speeds of stars in the local solar neighborhood relative to us the speed of our solar system orbiting the center of the Milky Way Galaxy Earth's orbital speed about the Sun the speeds of very distant galaxies relative to us Earth's speed of rotation on its axis Answer: A

7) What evidence leads astronomers to conclude that most of the Milky Way's mass consists of a mysterious dark matter? A) We observe many dark clouds of gas that block the light of stars behind them. B) The galaxy's rotation indicates that it must contain much more matter than we can observe with our telescopes. C) Observations indicate that most stars are dimmer than the Sun, so we say they are "dark." D) Stars are separated from one another by vast distances, and therefore most places in the galaxy would be dark to our eyes. Answer: B 8) Most of the mass in the Milky Way Galaxy is located ________. A) in the halo (above/below the disk) B) within the disk C) in the stars in the spiral arms D) in the gas and dust E) in the central bulge of the galaxy Answer: A 9) The amount and distribution of matter in the Milky Way Galaxy is determined by ________. A) counting the number of stars in the galaxy B) determining the amount of gas and dust in the galaxy C) studying where stars are located in the Milky Way D) studying the rotation of the galaxy E) adding together the mass of the galaxy's stars and gas Answer: D 10) What evidence leads astronomers to conclude that the universe contains a mysterious dark energy? A) The expansion of the universe is accelerating with time. B) The gravity of distant galaxies is stronger than that of galaxies nearby. C) Studies of galactic motion indicate that there is more matter in the universe than we can account for with stars and gas. D) Stars shine much more brightly than we would expect from nuclear fusion. E) The existence of such dark energy is the only way to account for evil in the universe. Answer: A 11) From the fact that virtually every galaxy is moving away from us and more distant galaxies are moving away from us at a faster rate than closer ones, we conclude that ________. A) the Milky Way Galaxy is expanding B) we are located at the center of the universe C) even nearby galaxies will eventually be moving faster than the speed of light D) the universe is expanding E) the universe is shrinking Answer: D

12) By studying distant galaxies in the 1920s, Hubble made the following important discovery that led us to conclude that the universe is expanding. A) All galaxies contain billions of stars, and all galaxies have spiral shapes. B) All galaxies were born at the same time, and all will die at the same time. C) All galaxies outside the Local Group are moving away from us, and the farther away they are, the faster they're going. D) All galaxies outside the Local Group are orbiting the Local Group. E) Galaxies are in motion throughout the universe, with about equal numbers moving toward us and away from us. Answer: C 13) Imagine that we put a raisin cake into the oven, with each raisin separated from the others by 1 cm. An hour later, we take it out and the distances between raisins are 3 cm. If you lived in one of the raisins and watched the other raisins as the cake expanded, which of the following would you observe? A) All raisins would be moving away from you at the same speed. B) More distant raisins would be moving away from you faster. C) More distant raisins would be moving away from you more slowly. D) It depends: If you lived in a raisin near the edge of the cake, you'd see other raisins moving away from you, but they'd be coming toward you if you lived in a raisin near the center of the cake. E) The raisins would be expanding too, so you'd never notice any changes in the cake. Answer: B 14) Recall the raisin cake model of the universe and its analogy to our expanding universe. Suppose you measure the recession velocity (the speed at which any object is moving away from us) of Galaxy A to be 2000 km/s and the recession velocity of Galaxy B to be 6000 km/s. What can you conclude about the relative distances of these two galaxies? A) Galaxy A is 3 times as far from us as Galaxy B. B) Galaxy B is 3 times as far from us as Galaxy A. C) Galaxy A is 6 times as far from us as Galaxy B. D) Galaxy B is 6 times as far from us as Galaxy A. E) The relative distances cannot be determined from the information in this problem. Answer: B 15) The reason that we observe more distant galaxies to be moving away from us at higher speeds than nearby galaxies is that ________. A) the more distant galaxies were flung outward faster by the Big Bang B) the more distant galaxies are smaller and less massive, so they can move faster C) the nearby galaxies are slowed by our own galaxy's gravitational pull D) there is more space to expand between us and the distant galaxies Answer: D

16) We observe that most galaxies are moving away from us. If we could (somehow) communicate with an observer in a distant galaxy, what would that observer say about what it sees? A) Most galaxies are moving away from me, except for yours. B) Most galaxies are moving away from me, including yours. C) Most galaxies are moving away from you, and about half are moving towards me. Answer: B 17) The farthest galaxies visible in Hubble Space Telescope photos are about ________ lightyears away. A) 1 million B) 12 million C) 1 billion D) 12 billion E) 12 trillion Answer: D 18) Our solar system is located about 27,000 light-years from the galactic center. About how far does our solar system travel in one orbit? A) 54,000 light-years B) 85,000 light-years C) 100,000 light-years D) 170,000 light-years Answer: D 19) You observe two distant galaxies (well outside our Local Group of galaxies). You find that Galaxy W is moving away from us at a speed of 35,000 km/s and Galaxy X is moving away from us at a speed of 70,000 km/s. What can you say about the distances to those galaxies? A) Galaxy W is four times as far as Galaxy X. B) Galaxy W is twice as far as Galaxy X. C) She can't say anything about the distances to Galaxy W or X. D) Galaxy X is four times as far as Galaxy W. E) Galaxy X is twice as far as Galaxy W. Answer: B

Short Answer Questions 1) The speed of light is 300,000 km/s. How far is a light-year? Be sure to show all work clearly on your calculations. Answer: 1 light-year = (speed of light) × (1 yr) =

= 9,460,000,000,000 km 2) Earth's actual diameter is about 12,800 kilometers. What is Earth's diameter in a 1-to-10 billion scale model solar system? Show your work clearly. Answer: Scaled radius of Earth = actual radius/1010 = 6,378 km/1010 = 6,378 × 105 cm/1010 = 6.378 × 108 cm/1010 = 6.378 × 10−2 cm = 0.6 mm - This is about the size of the tip of a (fine tip) ballpoint pen. Reading Quiz Questions 1) Which of the following is a general difference between a planet and a star? A) Stars shine with energy released by nuclear fusion while planets shine primarily with light reflected from stars. B) Stars are found in galaxies but planets are not part of galaxies. C) Stars are made of gas and planets are made of rock. D) Stars are stationary while planets orbit stars. Answer: A 2) Our solar system consists of ________. A) the Sun and all the objects that orbit it B) the Sun and the planets, and nothing else C) a few hundred billion stars, bound together by gravity D) the Sun and several nearby stars, as well as the planets and other objects that orbit these stars Answer: A 3) A typical galaxy is a ________. A) collection of millions or billions of stars, bound together by gravity and orbiting a common center B) large, glowing ball of gas powered by nuclear energy C) nearby object orbiting a planet D) relatively small, icy object orbiting a star E) system consisting of one or a few stars orbited by planets, moons, and smaller objects Answer: A 16 Copyright © 2022 Pearson Education, Inc.

4) Which of the following best describes what we mean by the term universe? A) The sum total of all matter and energy B) A vast collection of stars that number as many as the grains of sand on all the beaches on Earth C) All the galaxies in all the superclusters D) Our Milky Way Galaxy Answer: A 5) An astronomical unit (AU) is ________. A) any very large unit, such as a light-year B) the average distance between Earth and the Sun C) the current distance between Earth and the Sun D) the average distance between any planet and the Sun Answer: B 6) A light-year is ________. A) about 10 trillion kilometers B) the time it takes light to reach the nearest star C) the time it takes light to travel around the Sun D) about 300,000 kilometers per second Answer: A 7) A television advertisement claiming that a product is light-years ahead of its time does not make sense because ________. A) it doesn't specify the number of light-years B) it uses "light-years" to talk about time, but a light-year is a unit of distance C) a light-year is an astronomically large unit, so a product could not possibly be so advanced D) light-years can only be used to talk about light Answer: B 8) The term observable universe refers to ________. A) the portion of the universe that we have so far photographed through telescopes B) the portion of the universe that can be seen by the naked eye C) the portion of the universe that is not hidden from view by, for example, being below the horizon D) the portion of the universe that we can see in principle, given the current age of the universe Answer: D 9) On a scale where the distance from Earth to the Sun is about 15 meters, the distance from Earth to the Moon is ________. A) small enough to fit within your hand B) about 1 meter C) about 5 meters D) about 30 meters Answer: A 17 Copyright © 2022 Pearson Education, Inc.

10) On a scale where the Sun is about the size of a grapefruit and the Earth is about 15 meters away, how far away are the nearest stars besides the Sun? A) 100 meters B) About the distance across 50 football fields C) About the distance across the state of Delaware D) About the distance across the United States Answer: D 11) The number of stars in the Milky Way Galaxy is approximately ________. A) a few hundred B) a few hundred thousand C) a few hundred billion D) a few hundred million Answer: C 12) What do astronomers mean by the Big Bang? A) The event that marked the beginning of the expansion of the universe B) A gigantic explosion that blew all the galaxies in the universe to smithereens C) The explosion of a massive star at the end of its life D) The event that marked the birth of our solar system Answer: A 13) What do we mean when we say that the universe is expanding? A) Everything in the universe is gradually growing in size. B) Within galaxies, average distances between star systems are increasing with time. C) The statement is not meant to be literal; rather, it means that our knowledge of the universe is growing. D) Average distances between galaxies are increasing with time. Answer: D 14) Based on observations of the universal expansion, the age of the universe is about ________. A) 14,000 years B) 14 million years C) 14 billion years D) The universe is younger than this. Answer: C 15) If the 14 billion year history of the universe were compressed to one year, and "now" is exactly midnight December 31, approximately how long ago were your grandparents born? A) 0.15 second ago B) 1 second ago C) 1 minute ago D) 1 hour ago Answer: C

16) What is the ecliptic plane? A) The plane of Earth's orbit around the Sun B) The plane of Earth's equator C) The plane of the Sun's equator D) The plane of the Milky Way Galaxy Answer: A 17) How long does it take the Earth to complete one orbit around the Sun? A) One year B) One day C) One month D) One week E) The time it takes Earth to orbit the Sun changes significantly from one orbit to the next. Answer: A 18) What is the "raisin cake analogy" to the expanding universe intended to explain? A) That as a raisin cake expands, every raisin moves away from every other raisin, just as galaxies move away from each other in an expanding universe B) That raisins, like galaxies, expand in size as the cake or universe expands C) That from within the raisin cake, you would see other raisins moving away from you only if you were on the central raisin, just as you see galaxies moving away only if you are in the center of the universe D) That the universe heats up as it expands, just as the raisin cake heats up as it bakes Answer: A Concept Quiz Questions 1) Which of the following has your "cosmic address" in the correct order? A) You, Earth, solar system, Local Group, Local Supercluster, Milky Way Galaxy, universe B) You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe C) You, Earth, Local Group, Local Supercluster, solar system, Milky Way Galaxy, universe D) You, Earth, solar system, Local Group, Milky Way Galaxy, Local Supercluster, universe E) You, Earth, Milky Way Galaxy, solar system, Local Group, Local Supercluster, universe Answer: B 2) When we look at an object that is 1,000 light-years away we see it ________. A) as it was 1,000 years ago B) as it was 1,000 light-years ago C) as it is right now, but it appears 1,000 times dimmer D) looking just the same as our ancestors would have seen it 1,000 years ago Answer: A

3) Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case ________. A) Galaxy 1 must be twice as big as Galaxy 2 B) we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2 C) we are seeing Galaxy 1 as it looked at a later time in the history of the universe than Galaxy 2 D) Galaxy 2 must be twice as old as Galaxy 1 Answer: B 4) Could we see a galaxy that is 20 billion light-years away? (Assume that we mean a "lookback time" of 20 billion years.) A) No, because it would be beyond the bounds of our observable universe. B) Yes, if we had a big enough telescope. C) No, because a galaxy could not possibly be that far away. D) Yes, we have already detected galaxies at that distance. Answer: A 5) Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes what the planets would look like? A) The planets are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the rest planets are spread much farther apart. B) The planets are all much smaller than the Sun and are spread out evenly over a distance about the length of a large classroom. C) The planets are all much smaller than the Sun. Four planets are located within a few centimeters of the Sun, and four planets are located at distances ranging up to about a meter. D) The planets range in size from about the size of a marble to the size of a baseball. They are spread out over a region about the size of a football field. Answer: A 6) If you could count stars at a rate of about one per second, how long would it take to count all the stars in the Milky Way Galaxy? A) Several days B) Several weeks C) Several years D) Several thousand years Answer: D 7) The total number of stars in the observable universe is about ________. A) 100 billion B) the same as the number of grains of sand in a school sandbox C) the same as the number of grains of sand on all the beaches on Earth D) the same as the number of atoms that make up the Earth Answer: C

8) Using the ideas discussed in your text, in what sense are we "star stuff"? A) The overall chemical composition of our bodies is about the same as that of stars. B) Movie stars and other people are all made of the same stuff, so we all have the potential to be famous. C) Nearly every atom from which we are made was once inside of a star. D) We could not survive without light from our star, the Sun. Answer: C 9) How are galaxies important to our existence? A) Without galaxies, there could not have been a Big Bang. B) Without galaxies, the universe could not be expanding. C) Deep in their centers, galaxies created the elements from which we are made. D) Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist. Answer: D 10) If we imagine the history of the universe compressed into one year, with the present as the stroke of midnight at the very end of that year, dinosaurs became extinct ________. A) about 6 months ago B) about 3 weeks ago C) yesterday morning D) about an hour ago Answer: C 11) Relative to the age of the universe, how old is our solar system? A) It is about 1% as old as the universe. B) It is between about 5% and 10% as old as the universe. C) It is about one-third the age of the universe. D) It is nearly the same age as the universe. Answer: C 12) How do the speeds at which we are moving with Earth's rotation and orbit compare to the speeds of more familiar objects? A) Earth's rotation carries most people around the axis faster than a commercial jet travels, and Earth's orbit carries us around the Sun faster than the Space Station orbits Earth. B) Earth's rotation carries most people around the axis at about the speed of a commercial jet, and Earth's orbit carries us around the Sun at about the speed of a military jet. C) Earth's rotation carries most people around the axis at about the speed of a car on the freeway, and Earth's orbit carries us around the Sun at about the speed of a commercial jet. D) Earth's rotation carries most people around the axis at about the speed at which the Space Station orbits Earth, and Earth's orbit carries us around the Sun at nearly the speed of light. Answer: A

13) Why do the patterns of the stars in our sky look the same from year to year? A) Because the stars in the constellations are so far away. B) Because the stars in the constellations are not moving. C) Because the stars in the constellations all move at the same speeds and in the same directions, so they don't change their relative positions. D) Because the stars in the constellations move so slowly — typically about the speed of a snail — that their motions are not noticeable. Answer: A 14) Where is our solar system located within the Milky Way Galaxy? A) Very near the center of the galaxy B) At the far edge of the galaxy's visible disk C) Roughly halfway between the center and the edge of the visible disk of the galaxy D) In the halo of the galaxy Answer: C 15) Consider a raisin cake expanding uniformly in an oven. Viewed from one of the raisins, you would see ________. A) all other raisins moving away from you, with more distant raisins moving faster B) all other raisins moving away from you, with more distant raisins moving slower C) all other raisins moving away from you at the same speed D) all raisins, including your own, growing in size as the cake expands Answer: A 16) Astronomers infer that the universe is expanding because distant galaxies all appear to ________. A) be growing in size B) be moving away from us, with more distant ones moving faster C) be made mostly of dark matter D) rotate rapidly Answer: B 17) Which statement about motion in the universe is not true? A) The mysterious dark matter is the fastest-moving material in the universe. B) Some stars in the Milky Way Galaxy are moving toward us and others are moving away from us. C) Except for a few nearby galaxies, all other galaxies are moving away from us. D) Your speed of rotation around Earth's axis is faster if you live near the equator than if you live near the North Pole. Answer: A

Visual Quiz Questions 1) Each box in this figure represents a different level of structure in our universe. Each box is labeled with one of the numbers 1–5. Which box represents the Milky Way Galaxy?

A) 1 B) 2 C) 3 D) 4 E) 5 Answer: C

2) What does this photograph show?

A) It is a picture of our own Milky Way Galaxy. B) It is a picture of the Andromeda galaxy, located about 2.5 million light-years away. C) It is a picture of a cloud of gas known as the Orion Nebula. D) It is a picture of our own solar system. E) It is a picture of a young star in the process of being born. Answer: B 3) This painting represents the Sun and planets (and two dwarf planets) of our solar system. What is not to scale in this painting?

A) The sizes of the planets are not correctly scaled compared to each other or the Sun. B) The distances between the planets are not shown to scale. C) The Sun is too big compare to the planets. D) Everything is correctly scaled, but the planets are shown in the wrong order from the Sun. E) Neither distances nor sizes are correctly scaled. Answer: B

4) What is the significance of this photograph?

A) It shows the first person ever to land on Mars. B) It shows a person standing on the most distant world ever visited by a human being. C) It shows the first person ever to go into space. D) It was taken Jan. 1, 2000, to commemorate the turn of the millennium. Answer: B 5) Suppose we made a scale model of our Milky Way Galaxy in which the disk of the galaxy is the size of a football field. Which (if any) diagram represents the Sun on the same scale? A)

D) The Sun on this scale would be about two feet in diameter and too big to show on the screen. E) The Sun on this scale would be microscopic and too small to see on the screen. Answer: E

6) These photos show two different astronomical objects. Which object is bigger, and by about how much?

A) Object 2 is more than a trillion times as large as Object 1. B) Object 2 is approximately 1,000 times as large as Object 1. C) Object 2 is about 10 times as large as Object 1. D) Object 1 is about 10 times as large as Object 2. E) Both objects are about the same size. Answer: A

7) This diagram represents Earth's rotation and orbit. What do we call the flat blue plane shown in this diagram? A) The solar plane B) The ecliptic plane C) Earth's axis D) The galactic plane E) An astronomical unit Answer: B 8) Notice that Earth's axis is shown with an arrowhead in this diagram. What does the arrow point to? A) The Sun B) The ecliptic plane C) The center of the Milky Way Galaxy D) Polaris, the North Star E) The Northern lights Answer: D 26 Copyright © 2022 Pearson Education, Inc.

9) These diagrams show a raisin cake before it is put in the oven and again one hour later after it has expanded during baking. Suppose you lived in Raisin 3 (the raisin labeled "3"). What would you have noticed about Raisin 2 during baking?

A) Raisin 2 is moving away from you at a speed of 4 cm/hr. B) Raisin 2 always stays in the same place but gets bigger in size. C) Raisin 2 is moving away from you at a speed of 2 cm/hr. D) Raisin 2 is moving away from you at a speed of 6 cm/hr. E) Raisin 2 is moving toward you at a speed of 2 cm/hr. Answer: C 10) Nearly all of the objects that you can see in this photograph are ________.

A) planets B) stars C) galaxies D) astronomical units Answer: C

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

The figure above shows the sizes of Earth and the Moon to scale; the scale used is 1 cm = 4000 km. Using what you've learned about astronomical scale in this chapter, answer the following questions. (Hint: If you are unsure of the answers, you can calculate them using the given data.) Earth—Sun distance = 150,000,000 km Diameter of Sun = 1,400,000 km Earth—Moon distance = 384,000 km Diameter of Earth = 12,800 km 1) If you wanted to show the distance between Earth and the Moon on the same scale, about how far apart would you need to place the two photos? A) 10 centimeters (about the width of your hand) B) 1 meter (about the length of your arm) C) 100 meters (about the length of a football field) D) 1 kilometer (a little more than a half mile) Answer: B 2) Suppose you wanted to show the Sun on the same scale. About how big would it need to be? A) 3.5 centimeters in diameter (the size of a golf ball) B) 35 centimeters in diameter (a little bigger than a basketball) C) 3.5 meters in diameter (about 11-1/2 feet across) D) 3.5 kilometers in diameter (the size of a small town) Answer: C 28 Copyright © 2022 Pearson Education, Inc.

3) About how far away from Earth would the Sun be located on this scale? A) 3.75 meters (about 12 feet) B) 37.5 meters (about the height of a 12-story building) C) 375 meters (about the length of four football fields) D) 37.5 kilometers (the size of a large city) Answer: C 4) Could you use the same scale to represent the distances to nearby stars? Why or why not? Answer: No. The nearest stars would not fit on Earth using this scale. The total distance to the nearest star would wrap around the Earth about 2.5 times! Chapter Review Questions 1) Briefly describe the major levels of structure (such as planet, star, galaxy) in the universe. 2) Define astronomical unit and light-year. 3) Explain the statement The farther away we look in distance, the further back we look in time. 4) What do we mean by the observable universe? Is it the same thing as the entire universe? 5) Using techniques described in the chapter, put the following into perspective: the size of our solar system; the distance to nearby stars; the size and number of stars in the Milky Way Galaxy; the number of stars in the observable universe. 6) What do we mean when we say that the universe is expanding, and how does expansion lead to the idea of the Big Bang and our current estimate of the age of the universe? 7) In what sense are we "star stuff"? 8) Use the cosmic calendar to describe how the human race fits into the scale of time. 9) Briefly explain Earth's daily rotation and annual orbit, defining the terms ecliptic plane and axis tilt. 10) Briefly describe our solar system's location and motion within the Milky Way Galaxy. 11) Why do scientists suspect that most of our galaxy's mass consists of dark matter? Briefly describe the mystery of dark matter and dark energy. 12) What key observations lead us to conclude that the universe is expanding? Use the raisin cake model to explain how these observations imply expansion.

Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. Example: I walked east from our base camp at the North Pole. Solution: The statement does not make sense because east has no meaning at the North Pole–all directions are south from the North Pole. 13) Our solar system is bigger than some galaxies. 14) The universe is billions of light-years in age. 15) It will take me light-years to complete this homework assignment! 16) Someday we may build spaceships capable of traveling a light-year in only a decade. 17) Astronomers discovered a moon that does not orbit a planet. 18) NASA will soon launch a spaceship that will photograph our Milky Way Galaxy from beyond its halo. 19) The observable universe is larger today than it was a few billion years ago. 20) Photographs of distant galaxies show them as they were when they were much younger than they are today. 21) At a nearby park, I built a scale model of our solar system in which I used a basketball to represent Earth. 22) Because nearly all galaxies are moving away from us, we must be located near the center of the universe.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 1 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 23) Which of the following correctly lists our "cosmic address" from small to large? A) Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe B) Earth, solar system, Local Group, Local Supercluster, Milky Way Galaxy, universe C) Earth, Milky Way Galaxy, solar system, Local Group, Local Supercluster, universe Answer: No Correct Answer Was Provided. 24) An astronomical unit is ________. A) any planet's average distance from the Sun B) Earth's average distance from the Sun C) any large astronomical distance Answer: No Correct Answer Was Provided. 25) The star Betelgeuse is about 600 light-years away. If it explodes tonight, ________. A) we'll know because it will be brighter than the full Moon in the sky B) we'll know because debris from the explosion will rain down on us from space C) we won't know about it until about 600 years from now Answer: No Correct Answer Was Provided. 26) If we represent the solar system on a scale that allows us to walk from the Sun to Pluto in a few minutes, then ________. A) the planets are the size of basketballs and the nearest stars are a few miles away B) the planets are marble-size or smaller and the nearest stars are thousands of miles away C) the planets are microscopic and the stars are light-years away Answer: No Correct Answer Was Provided. 27) The total number of stars in the observable universe is roughly equivalent to ________. A) the number of grains of sand on all the beaches on Earth B) the number of grains of sand on Miami Beach C) infinity Answer: No Correct Answer Was Provided. 28) When we say the universe is expanding, we mean that ________. A) everything in the universe is growing in size B) the average distance between galaxies is growing with time C) the universe is getting older Answer: No Correct Answer Was Provided. 29) If stars existed but galaxies did not, ________. A) we would probably still exist anyway B) we would not exist because life on Earth depends on the light of galaxies C) we would not exist because we are made of material that was recycled in galaxies Answer: No Correct Answer Was Provided. 31 Copyright © 2022 Pearson Education, Inc.

30) Could we see a galaxy that is 50 billion light-years away? A) Yes, if we had a big enough telescope B) No, because it would be beyond the bounds of our observable universe C) No, because a galaxy could not possibly be that far away Answer: No Correct Answer Was Provided. 31) The age of our solar system is about ________. A) one-third of the age of the universe B) three-fourths of the age of the universe C) 2 billion years younger than the age of the universe Answer: No Correct Answer Was Provided. 32) The fact that nearly all galaxies are moving away from us, with more distant ones moving faster, helped us to conclude that ________. A) the universe is expanding B) galaxies repel each other like magnets C) our galaxy lies near the center of the universe Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 33) Group Discussion: What does a scientist look like? The purpose of this exercise is to help you identify preconceptions that you or others may have about science and scientists. a. Working independently, make a simple sketch of a professional scientist and write down five words that describe the scientist in your sketch. Then join with a group of two or three other students to share your sketches and word lists. b. Make a list of all the words the group wrote down, then rank them in order of how often they were used. c. Discuss any similarities, differences, or patterns you notice among the scientists described by the group members. d. Discuss whether the group members feel they have much in common with professional scientists. e. Discuss how feelings about what you have (or do not have) in common with scientists might affect your approach to scientific thinking.

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 34) Earth as a Planet. For most of human history, scholars assumed Earth was the center of the universe. Today, we know that Earth is just one planet orbiting the Sun, and the Sun is just one star in a vast universe. How did science make it possible for us to learn these facts about Earth? 35) Thinking About Scale. One key to success in science is finding a simple way to evaluate new ideas, and making a simple scale model is often helpful. Suppose someone tells you that the reason it is warmer during the day than at night is that the day side of Earth is closer to the Sun than the night side. Evaluate this idea by thinking about the size of Earth and its distance from the Sun in a scale model of the solar system. 36) Looking for Evidence. In this first chapter, we have discussed the scientific story of the universe but have not yet discussed most of the evidence that backs it up. Choose one idea presented in this chapter–such as the idea that there are billions of galaxies in the universe, or that the universe was born in the Big Bang, or that the galaxy contains more dark matter than ordinary matter–and briefly discuss the type of evidence you would want to see before accepting the idea. (Hint: It's okay to look ahead in the book to see the evidence presented in later chapters.) 37) A Human Adventure. Astronomical discoveries clearly are important to science, but are they also important to our personal lives? Defend your opinion. 38) Infant Species. In the last few tenths of a second before midnight on December 31 of the cosmic calendar, we have developed an incredible civilization and learned a great deal about the universe, but we also have developed technology through which we could destroy ourselves. The midnight bell is striking, and the choice for the future is ours. How far into the next cosmic year do you think our civilization will survive? Defend your opinion. 39) Group Activity: Counting the Milky Way's Stars. Work as a group to answer each part. Note: This activity works particularly well in groups of four students, with each student taking on one of the following roles: scribe: takes notes on the group's activities; proposer: suggests tentative explanations to the group; skeptic: points out weaknesses in proposed explanations; moderator: leads group discussion and makes sure everyone contributes. a. Work together to estimate the number of stars in the Milky Way from just these two facts: (1) the number of stars within 12 light-years of the Sun, which you can count in Appendix F, and (2) the total volume of the Milky Way's disk (100,000 light-years in diameter and 1000 light-years thick), which is about 1 billion times the volume of the region of your star count. b. Discuss how your value from part a compares to the value given in this chapter. Make a list of possible reasons why your technique may have underestimated or overestimated the actual number.

Investigate Further 40) Alien Technology. Some people believe that Earth is regularly visited by aliens who travel here from other star systems. For this to be true, how much more advanced than our own technology would the aliens' technology have to be? Write one to two paragraphs to give a sense of the technological difference. (Hint: The ideas of scale in this chapter can help you contrast the distance the aliens would have to travel with the distances we currently are capable of traveling.) 41) Raisin Cake Universe. Suppose that all the raisins in a cake are 1 centimeter apart before baking and 4 centimeters apart after baking. a. Draw diagrams to represent the cake before and after baking. b. Identify one raisin as the Local Raisin on your diagrams. Construct a table showing the distances and speeds of other raisins as seen from the Local Raisin. c. Briefly explain how your expanding cake is similar to the expansion of the universe. 42) The Hubble Extreme Deep Field. The photo that opens this chapter is called the Hubble Extreme Deep Field. Find this photo on the Hubble Space Telescope website. Learn how it was taken, what it shows, and what we've learned from it. Write a short summary of your findings. Answer: No Correct Answer Was Provided. 43) The Cosmic Perspective. Write a short essay describing how the ideas presented in this chapter affect your perspectives on your own life and on human civilization. Answer: No Correct Answer Was Provided. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 44) Distances by Light. Just as a light-year is the distance that light can travel in 1 year, we define a light-second as the distance that light can travel in 1 second, a light-minute as the distance that light can travel in 1 minute, and so on. Calculate the distance in both kilometers and miles represented by each of the following: a. 1 light-second b. 1 light-minute c. 1 light-hour d. 1 light-day 45) Moonlight and Sunlight. How long does it take light to travel from a. the Moon to Earth? b. the Sun to Earth? 46) Saturn versus the Milky Way. Photos of Saturn and photos of galaxies can look so similar that children often think the photos show similar objects. In reality, a galaxy is far larger than any planet. About how many times larger is the diameter of the Milky Way Galaxy than the diameter of Saturn's rings? (Data: Saturn's rings are about 270,000 km in diameter; the Milky Way is 100,000 light-years in diameter.)

47) Driving Trips. Imagine that you could drive your car at a constant speed of 100 km/hr (62 mi/hr), even across oceans and in space. How long would it take to drive a. around Earth's equator? (Earth's circumference ≈ 40,000 km) b. from the Sun to Earth? c. from the Sun to Pluto? (Pluto distance ≈ 5.9 × 109 km) d. to Alpha Centauri (4.4 light-years away)? 48) Faster Trip. Suppose you wanted to reach Alpha Centauri in 100 years. a. How fast would you have to go, in km/hr? b. How many times faster is the speed you found in part a than the speeds of our fastest current spacecraft (around 50,000 km/hr)? 49) Galaxy Scale. Consider the 1-to-1019 scale, on which the disk of the Milky Way Galaxy fits on a football field. On this scale, how far is it from the Sun to Alpha Centauri (real distance: 4.4 light-years)? How big is the Sun itself on this scale? Compare the Sun's size on this scale to the actual size of a typical atom (about 10—10 m in diameter). 50) Age of the Universe. Suppose we did not yet know the expansion rate of the universe, and two astronomers came up with two different measurements: Wendy measured an expansion rate for the universe that was 50% faster than the expansion rate Allan measured. Was the age of the universe that Allan inferred older or younger than the age that Wendy inferred? By how much? Explain. (Hint: Read the discussion of the raisin cake analogy carefully, and the answer should become clear.)

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 2 Discovering the Universe for Yourself Section 2.1 1) At midnight, on a clear and moonless night, the number of stars that are distinctly visible to the eye is in the range ________. A) 2000-5000 B) 20,000-50,000 C) 200,000-500,000 D) 2 million-5 million Answer: A 2) Which of the following best describes the modern definition of a constellation? A) A region of the celestial sphere B) A pattern of bright stars in the sky C) A Greek mythological figure D) A collection of stars that are near one another in space E) A group of stars that all lie at about the same distance from Earth Answer: A 3) While the historical definition of a constellation is "a pattern or figure of stars in the sky," the modern definition used by astronomers is ________. A) A group of stars in the sky that are all very close to each other. B) A specifically named and bordered region of the celestial sphere. C) Any grouping of very bright stars in our galaxy, often hosting a star cluster. D) No definition; astronomers no longer use the term constellation. Answer: B 4) The number of official constellations (as defined by the International Astronomical Union) is ________. A) 56 B) 88 C) 123 D) 205 Answer: B 5) The stars stay in "fixed" positions on the celestial sphere because they ________. A) are all located at precisely the same distance from Earth B) are so far away that our eyes don't notice their motions through space C) remain stationary relative to our solar system in space D) were given their names by ancient civilizations Answer: B

6) The celestial sphere is ________. A) the central spherical region of the Milky Way Galaxy, dense with stars B) a spherical galaxy, centered on the Sun C) a useful illusion used to map the stars and other objects in the sky D) the star-sphere discovered by the Greeks and other ancient civilizations which shows the physical location in space of the nearby stars E) another name for our spherical Sun Answer: C 7) Which of the following statements about the celestial sphere is not true? A) When we look in the sky, the stars all appear to be located on the celestial sphere. B) Earth is placed at the center of the celestial sphere. C) The celestial sphere does not exist physically. D) The "celestial sphere" is just another name for our universe. E) From any location on Earth, we can see only half the celestial sphere at any one time. Answer: D 8) What is the ecliptic? A) When the Moon passes in front of the Sun B) The Moon's apparent path along the celestial sphere C) The constellations commonly used in astrology to predict the future D) The Sun's daily path across the sky E) The Sun's apparent annual path around the celestial sphere Answer: E 9) What is the celestial equator? A) Another name for the ecliptic B) The path the Sun appears to trace through the constellations each year C) A projection of Earth's equator into space D) The technical name of the Sun's equator Answer: C 10) On the celestial sphere, the Sun ________. A) circles once each year along the path called the ecliptic B) stays always at the same fixed point among the stars C) circles daily around the celestial equator D) is the central object Answer: A 11) Which of the following statements about the celestial equator is true at all latitudes? A) It lies along the band of light we call the Milky Way. B) It represents an extension of Earth's equator onto the celestial sphere. C) It cuts the dome of your sky exactly in half. D) It extends from your horizon due east, through your zenith, to your horizon due west. E) It extends from your horizon due north, through your zenith, to your horizon due south. Answer: B 2 Copyright © 2022 Pearson Education, Inc.

12) What is the name of the path on the celestial sphere that goes through the constellations of the zodiac? A) The celestial equator B) The ecliptic C) The Milky Way D) The meridian E) The horizon Answer: A 13) The "Milky Way" in the night sky looks like a blurry circle of light in the sky because ________. A) we are seeing the stars and gas that lie in disk of our Milky Way Galaxy B) our Sun is located at the center of our galaxy C) the stars within this band of light are much farther away than other stars D) our rotating Earth blurs our view of stars in the Milky Way Galaxy Answer: A 14) When we look toward the constellation Sagittarius, we are looking ________. A) at the galaxy's central bulge B) toward Polaris, the "Pole Star" C) toward the Winter Triangle D) out toward the outer Milky Way Answer: A 15) When we look into the band of light in our sky that we call the Milky Way, can we see distant galaxies? Why or why not? (Assume we are looking with visible light telescopes.) A) Yes, distant galaxies appear as small, fuzzy patches of light within the Milky Way band. B) yes, but only when we look in the direction of the constellation Sagittarius C) no, because the stars, gas, and dust of the Milky Way block our view of more distant objects D) no, because galaxies exist only above and below the plane of the Milky Way E) no, because distant galaxies are too dim to be seen even with powerful telescopes Answer: C 16) Which of the following correctly describes the meridian in your sky? A) A half-circle extending from your horizon due east, through your zenith, to your horizon due west B) A half-circle extending from your horizon due north, through your zenith, to your horizon due south C) A half-circle extending from your horizon due east, through the north celestial pole, to your horizon due west D) The point directly over your head E) The boundary between the portion of the celestial sphere you can see at any moment and the portion that you cannot see Answer: B

17) You experience night-time when ________. A) the Moon blocks the Sun's light B) Earth is on the opposite side of the celestial sphere from the Sun C) you are located on the side of the Earth that faces away from the Sun D) you are located on the side of the Earth that faces toward stars Answer: C 18) If Earth's rotation slowed down so that it completed exactly one rotation about its axis in 100 hours (instead of 24), what would be the typical time interval between sunrise and sunset? A) 50 hours B) 100 hours C) 12 hours D) 25 hours E) 24 hours Answer: A 19) Why do we experience night and day on Earth? A) Earth rotates on its axis once every 24 hours. B) The Sun orbits Earth once every 24 hours. C) The Moon circles Earth once every 24 hours. D) The Sun moves around in a circle once every 24 hours, shining like a spotlight on Earth. Answer: A 20) Do all galaxies out beyond the Milky Way rise in the east and set in the west (if they aren't circumpolar)? A) Impossible to say for sure, since we haven't yet seen all of the galaxies in the universe. B) No C) Yes Answer: C 21) We can describe the position of an object in our local sky by stating its ________. A) altitude and meridian B) altitude and direction C) latitude and direction D) latitude and longitude E) meridian and longitude Answer: B 22) How many arcminutes are in 1°? A) 60 B) 360 C) 3600 D) 100 E) 10,000 Answer: A

23) How many arcseconds are in 1 arcminute? A) 60 B) 360 C) 3600 D) 100 E) 10,000 Answer: A 24) How many arcseconds are in 1°? A) 60 B) 360 C) 3600 D) 100 E) 10,000 Answer: C 25) If you hold your fist at arm's length, you will see it spanning an angle of about ________. A) 1 arcsecond B) 1° C) 10° D) 45° E) 90° Answer: C 26) The angular sizes of the Sun and Moon are about the same because ________. A) both objects have the same physical size B) both objects are located the same distance away C) the Sun is larger in size than the Moon by the same factor (about 400) that it is farther in distance D) their angular sizes are an illusion created by the apparent locations on the celestial sphere Answer: C 27) Which of the following statements does not use the term angular size or angular distance correctly? A) The angular size of the Moon is about 1/2 degree. B) The angular distance between those two houses in the distance is 30°. C) The angular distance between those two bright stars in the sky is about 2 meters. D) The angular size of the Sun is about the same as that of the Moon. E) You can use your outstretched hand to estimate angular sizes and angular distances. Answer: C

28) We can describe the location of a point on Earth's surface by stating its ________. A) altitude and meridian B) altitude and direction C) latitude and direction D) latitude and longitude E) meridian and longitude Answer: D 29) Is there any place on Earth where we can see stars rise in the west and set in the east (rather than rising in the east and setting in the west)? Why or why not? A) Yes, in the Southern Hemisphere, because the sky appears backward there B) Yes, on Earth's equator, because it is halfway between the poles C) No, because the rising and setting of stars is caused by Earth's west to east rotation D) No, because the stars that rise in the west and set in the east are too dim to be seen by the naked eye Answer: C 30) What is a circumpolar star? A) A star that rises in the east and sets in the west B) A star that appears to circle from the north celestial pole to the south celestial pole C) A star that always remains above your horizon D) A star that appears to make a full circle around us each day E) A star that is visible from the North or South pole Answer: C 31) Which of the following statements about circumpolar stars is true at all latitudes? A) They are the stars close to the north celestial pole. B) They always remain above your horizon. C) They make relatively small circles, traveling clockwise around the north celestial pole. D) Like all other stars, they rise in the east and set in the west. E) You cannot see them from the Southern Hemisphere. Answer: B 32) What makes the North Star, Polaris, special? A) It is the brightest star in the sky. B) It is the star straight overhead. C) It appears very near the north celestial pole. D) It is the star directly on your northern horizon. E) It can be used to determine your longitude on Earth. Answer: C

33) You are standing on Earth's equator. Which way is Polaris, the North star? A) 30 degrees up, due West B) On the northern horizon C) Directly overhead D) The answer depends on whether it's winter or summer. E) The answer depends on what time of day (or night) it is. Answer: B 34) By locating the north celestial pole (NCP) in the sky, how can you determine your latitude? A) The altitude of the NCP is the same as your latitude. B) The altitude of the NCP is your angular distance from the North Pole. C) The azimuth of the NCP is the same as your latitude. D) The azimuth of the NCP is the angular distance from the North Pole. E) The altitude of the NCP is the same as your distance from the North Pole. Answer: A 35) If you locate the north celestial pole in your local sky and measure its altitude, then you will know ________. A) your latitude and longitude B) your latitude and the direction that is due north for you C) your longitude and the direction that is due north for you D) your latitude and the local time E) your latitude, longitude, and local time Answer: B 36) If you see Polaris directly overhead, you must be very close to ________. A) the equator B) the South Pole C) the Tropic of Cancer D) the North Pole Answer: D 37) You are standing at the North Pole. Which way is Polaris, the North star? A) The answer depends on what time of day (or night) it is. B) The answer depends on whether it's winter or summer. C) Directly overhead D) 30 degrees up, due West E) On the northern horizon Answer: C 38) The constellation Orion is visible on winter evenings but not on summer evenings because of ________. A) blockage by the full moon B) the tilt of Earth's rotation axis C) the location of Earth in its orbit around the Sun D) the precession of Earth's rotation axis Answer: C 7 Copyright © 2022 Pearson Education, Inc.

39) Looking through your telescope tonight, you observe a distant galaxy called RXJ1800 and notice that it is very near in the sky to the bright star Vega. What can you conclude from this observation? A) RXJ1800 and Vega will both set in the west at about the same time. B) Vega orbits the center of mass of RXJ1800. C) Vega and RXJ1800 must be no more than a few light-years apart. D) If you observe them again in a few nights, RXJ1800 and Vega will be farther apart than they appear tonight. Answer: A 40) We see two stars separated by one degree on the celestial sphere. What can we infer about these stars? A) They are very close together in space. B) They have similar luminosities. C) They rise and set at about the same time. D) They were born about the same time. Answer: C 41) The line representing latitude 45 degrees north runs through the state of Michigan. In Michigan, when is the Sun is directly overhead, at your zenith? A) Every day B) Only on the spring and fall equinoxes C) Only on the summer solstice, noon D) Never Answer: D 42) Today the Sun appears to be located in the middle of the constellation Virgo. Therefore, tomorrow the Sun will be in the constellation ________. A) Libra B) Virgo C) Leo D) Sagittarius Answer: B 43) Has Polaris always been a good "North Star"? Why or why not? A) Yes, because stars stay fixed on the celestial sphere B) No, because it is a young star which formed only a few hundred years ago C) No, because Earth's axis slowly changes the direction it points D) No, because ancient people did not know how to describe directions on Earth Answer: C

44) Choose the answer that fills in the three blanks in the correct order: Earth rotates once each ________, Earth orbits the Sun once each ________, and the Moon orbits Earth about once each ________. A) day, year, month B) day, year, week C) year, day, month D) hour, day, year E) hour, day, month Answer: A 45) The reason we don't see stars in the daytime is because ________. A) the sky is too bright B) stars shine only at night C) there are no stars in the direction of the Sun D) stars disappear in the daytime Answer: A 46) Which of the following explains why the Big Dipper will look different 100,000 years from now than it does today? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: D 47) Which of the following explains why the stars of Orion's belt rise in the east and set in the west? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: A 48) Which of the following explains why, a million years from now, Alpha Centauri will no longer be the nearest star system to our own? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: D

49) Which of the following explains why the Sun appears to move gradually eastward along the path called the ecliptic on the celestial sphere? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: D 50) Which of the following explains why we see different constellations at different times of year? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: D 51) Which of the following explains why the stars visible in our sky just after sunset are different from those visible just before sunrise? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: A 52) Suppose you see a photo showing Jupiter half in sunlight and half in shadow (i.e., a firstquarter Jupiter). This photo might have been taken by ________. A) the Keck telescope, on Mauna Kea, Hawaii B) the Arecibo radio telescope in Puerto Rico C) the Hubble Space Telescope (which orbits Earth) D) the Juno spacecraft that is orbiting Jupiter Answer: D

Section 2.2 1) If it is midnight in New York, it is ________. A) daytime in Sydney, Australia B) midnight in Sydney, Australia C) midnight in Los Angeles D) midday in Rio de Janeiro, Brazil E) midnight everywhere Answer: A 2) Seasons on Earth are caused by ________. A) Earth's axis tilt B) Earth's varying distance from the Sun C) Earth's varying orbital speed around the Sun D) the gravitational influence of the Moon E) the Sun's gravity Answer: A 3) When it is summer in the Northern Hemisphere, it is ________ in the Southern Hemisphere. A) winter B) fall C) spring D) summer Answer: A 4) Why is it summer in the Northern Hemisphere when it is winter in the Southern Hemisphere? A) The Northern Hemisphere is "on top" of Earth and therefore receives more sunlight during the Northern Hemisphere summer. B) The Northern Hemisphere is tilted away from the Sun and receives more indirect sunlight during the Northern Hemisphere summer. C) The Northern Hemisphere is tilted toward the Sun and receives more direct sunlight during the Northern Hemisphere summer. D) It isn't: both hemispheres have the same seasons at the same time. E) The Northern Hemisphere is closer to the Sun than the Southern Hemisphere during the Northern hemisphere summer. Answer: C 5) It is summer in the Northern Hemisphere when ________. A) the Northern Hemisphere is located closer to the Sun than the Southern Hemisphere B) the Northern Hemisphere is tilted toward the Sun and the Southern Hemisphere is tilted away C) Earth is at its nearest point to the Sun along its orbit D) Earth's axis points toward the North Star, Polaris Answer: B

6) The Northern and Southern hemispheres have equal illumination from the Sun ________. A) on the June and December solstices B) on the March and September equinoxes C) on all four of the equinoxes and solstices D) only on the March equinox E) at all times Answer: B 7) Consider a set of hypothetical planets that are identical in their orbits and properties except they have different axis tilts. Which of the following axis tilts would give its planet the most extreme differences between their seasons? (Axis tilt is measured relative to a line drawn perpendicular to the planet's orbit.) A) 23.5 degrees B) 90 degrees C) 0 degrees D) 45 degrees Answer: B 8) Suppose that Earth's rotation axis were tilted by 45 degrees instead of 23.5 degrees. Which of the following would be true, and why? A) The seasons would be more extreme, because the Sun's rays would be more direct in summer and less direct in winter. B) The seasons would be more extreme, because the Earth's surface would be closer to the Sun in the summer and farther from the Sun in the winter. C) The seasons would be less extreme, because the Sun's rays would be less direct in summer and more direct in winter. D) The seasons would be less extreme, because the Earths' surface would be farther from the Sun in the summer and closer to the Sun in the winter. Answer: A 9) Suppose Earth's rotation axis were tilted by 45 degrees instead of 23.5 degrees. How would the number of daylight hours be different on December 21 in the United States (or any northern hemisphere country)? A) There would be more hours of daylight than we have with a 23.5 degree tilt. B) There would be fewer hours of daylight than we have with a 23.5 degree tilt. C) The number of daylight hours would be about the same as it is if its tilt were 23.5 degrees. Answer: B 10) Why is January a cold month in the northern United States? A) Earth is near its farthest point from the sun. B) There's more snow in January. C) The northern hemisphere is farther from the sun than the southern hemisphere. D) The northern hemisphere is tilted away from the sun. Answer: D

11) Which of the following explains why Polaris will no longer be the North Star 1,000 years from now? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: C 12) Which of the following explains why, about 13,000 years from now, Vega will be a better North Star than Polaris? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: C 13) If Earth rotated once every 48 hours (instead of 24 hours), but everything else was the same, which of the following statements would be false? A) There would still be summer and winter seasons. B) The length of the year would be longer. C) The Sun would appear to move across the sky at a slower rate. D) The length of a day would be longer. Answer: B 14) Earth is farthest from the Sun in July and closest to the Sun in January. During which Northern Hemisphere season is Earth moving fastest in its orbit? A) Winter B) Spring C) Summer D) Fall Answer: A

Section 2.3 1) The time from one new moon to the next is approximately ________. A) one week B) two weeks C) three weeks D) one month E) two months Answer: D 2) Which of the following is not the name of one of the phases of the Moon? A) First-quarter moon B) Third-quarter moon C) Half moon D) New moon E) Full moon Answer: C 3) We say that the Moon is gibbous when ________. A) it appears to be more than half illuminated, but not full B) it appears to be less than half illuminated, but not new C) it is exactly half illuminated D) we see a thin crescent of light E) the Moon is visible in the morning Answer: A 4) In which general direction should you look to see the Moon rise? A) North B) South C) East D) West E) It depends on the phase of the Moon. Answer: C 5) When we see a crescent moon, the rest of the face that we see is not completely dark because ________. A) it is partially facing toward the Sun B) it is slightly illuminated by sunlight reflected by Earth C) it is slightly illuminated by starlight D) it is slightly illuminated by the light of Earth's cities Answer: B

6) In which general direction should you look to see the Moon set? A) North B) South C) East D) West E) It depends on the phase of the Moon. Answer: D 7) Which of the following statements about the Moon is not true? A) The Moon goes through its cycle of phases in about a month. B) The Moon's orbit around Earth is tilted about 5° to the ecliptic plane. C) The Moon's distance from Earth varies during its orbit. D) The Moon is visible in our sky only at night. E) The Moon rotates once in the same amount of time that it takes to orbit around Earth. Answer: D 8) Why do we see essentially the same face of the Moon at all times? A) Because the other face points toward us only at new moon, when we can't see the Moon B) Because the Moon does not rotate C) Because the Moon's rotational and orbital periods are equal D) Because the Sun illuminates only one half of the Moon at a time E) Because the Moon has a nearly circular orbit around Earth Answer: C 9) Suppose you live on the Moon. When people on Earth see a first-quarter phase, what phase do you see for Earth? A) New Earth B) first-quarter Earth C) Frescent Earth D) Third-quarter Earth E) Full Earth Answer: D 10) Suppose it is a crescent moon, as seen from Earth. How would Earth appear to someone on the Moon at this time? A) The side of Earth facing the Moon is completely bright. B) The illumination of the Earth does not change, as viewed from the Moon. C) Half of the side of Earth facing the Moon is bright and half is dark. D) Most of the side of Earth facing the Moon is bright. Answer: D

11) Suppose you live on the Moon. About how long is a day (i.e., from sunrise to sunrise)? A) 23 hours 56 minutes B) 24 hours C) A month D) A year E) About 18 years Answer: C 12) If the Moon is setting at 6 A.M., the phase of the Moon must be ________. A) first quarter B) third quarter C) full D) new E) waning crescent Answer: C 13) If the Moon is setting at noon, then it rose at ________. A) 6 A.M. B) 9 A.M. C) noon D) 6 P.M. E) midnight Answer: E 14) If the Moon is setting at noon, the phase of the Moon must be ________. A) full B) first quarter C) third quarter D) waning crescent E) waxing crescent Answer: C 15) If the Moon is rising at midnight, the phase of the Moon must be ________. A) full B) first quarter C) third quarter D) waning crescent E) waxing crescent Answer: C 16) At approximately what time would a full moon be on your meridian? A) 6 A.M. B) 9 A.M. C) noon D) 6 P.M. E) midnight Answer: E 16 Copyright © 2022 Pearson Education, Inc.

17) At approximately what time would a first-quarter moon rise? A) 6 A.M. B) 9 A.M. C) Noon D) 6 P.M. E) Midnight Answer: C 18) Approximately when does a first-quarter moon set? A) Sunset B) Noon C) Midnight D) Sunrise Answer: C 19) Approximately when does a third-quarter moon rise? A) Sunset B) Noon C) Midnight D) Sunrise Answer: C 20) Approximately when does a third-quarter moon set? A) Sunset B) Noon C) Midnight D) Sunrise Answer: B 21) If the Moon rises around 3 A.M., its phase must be ________. A) full B) first quarter C) third quarter D) waning crescent E) waxing crescent Answer: D 22) Suppose you live in the United States and you see a crescent moon in your evening sky tonight. What will a friend in South America see tonight? A) A crescent moon B) Your friend won't see the Moon tonight, because in South America, it will be visible only in the morning. C) A gibbous moon D) A first-quarter moon Answer: A

23) You observe a full moon rising at sunset. What will you see 6 hours later? A) A full moon on or near your meridian B) Waning gibbous moon C) First-quarter moon D) A third-quarter moon Answer: A 24) If the Moon is full at midnight, what will its phase be 6 hours later? A) Full moon B) First-quarter moon C) New moon D) Third-quarter moon Answer: A 25) Tonight the Moon is full. Therefore, in one week, the Moon will be ________. A) full B) first quarter C) third quarter D) new Answer: C 26) You see a waxing crescent moon. You email your friend in New Zealand and ask her what moon phase she sees that night. She says ________. A) waxing crescent B) waning crescent C) waning gibbous D) waxing gibbous Answer: A 27) All of the following statements are true. Which one explains the reason why there is not a solar eclipse at every new moon? A) The nodes of the Moon's orbit precess with an approximately 18-year period. B) The orbital plane of the Moon is tilted by about 5° to the ecliptic plane. C) The Moon rotates synchronously with its orbit around Earth. D) The Moon's orbital period is slightly shorter than the time it takes for a cycle of phases. E) The Moon's orbital distance varies as it orbits around Earth. Answer: B 28) Which of the following would be true about solar eclipses if the Moon's orbital plane was exactly aligned with the ecliptic plane? A) Solar eclipses would be rarer. B) Solar eclipses would occur more often. C) Solar eclipses would last much longer. D) Solar eclipses would be both rarer and would last much longer. E) Solar eclipses would both occur more often and would last much longer. Answer: B 18 Copyright © 2022 Pearson Education, Inc.

29) If the plane of the Moon's orbit around the Earth was perfectly aligned with the ecliptic plane (instead of being tilted by about 5°), a solar eclipse would be visible on some parts of Earth ________. A) once a day B) never C) about once a month D) about once every six months E) about once a year Answer: C 30) The conditions required for a solar eclipse are ________. A) (1) the phase of the Moon must be new; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun B) (1) the phase of the Moon must be full; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun C) (1) the phase of the Moon can be either new or full; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun D) (1) the phase of the Moon must be new; (2) the Moon must be located at the nearest point in its orbit around Earth E) (1) the phase of the Moon must be full; (2) the Moon must be located at the nearest point in its orbit around Earth Answer: A 31) Why are lunar eclipses more commonly seen than solar eclipses? A) Lunar eclipses occur at night and are easier to see. B) The Moon goes around the Earth faster than the Earth goes around the Sun. C) Earth casts a bigger shadow than the Moon. D) The tilt of the Moon's axis is smaller than the Earth's. E) The Moon is much closer to Earth than to the Sun. Answer: C 32) The conditions required for a lunar eclipse are ________. A) (1) the phase of the Moon must be new; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun B) (1) the phase of the Moon must be full; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun C) (1) the phase of the Moon can be either new or full; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun D) (1) the phase of the Moon must be new; (2) the Moon must be located at the nearest point in its orbit around Earth E) (1) the phase of the Moon must be full; (2) the Moon must be located at the nearest point in its orbit around Earth Answer: B

33) In addition to the conditions required for any solar eclipse, what must also be true in order for you to observe a total solar eclipse? A) Earth must lie completely within the Moon's full shadow (umbra). B) Earth must lie completely within the Moon's partial shadow (penumbra). C) Earth must be near aphelion in its orbit of the Sun. D) The Moon's full shadow (umbra) must touch the area where you are located. E) The Moon's partial shadow (penumbra) must touch the area where you are located. Answer: D 34) When only part of the Moon is covered by Earth's full shadow (umbra), we see a(n) ________. A) total lunar eclipse B) penumbral lunar eclipse C) partial lunar eclipse D) partial solar eclipse E) annular eclipse Answer: C 35) If a solar eclipse occurs when the Moon is relatively far from Earth, so that its full shadow (umbra) does not reach Earth, then people directly behind the full shadow will experience ________. A) a penumbral eclipse B) a total solar eclipse C) a partial solar eclipse D) an annular eclipse E) no eclipse Answer: D 36) During a lunar eclipse, the Moon's phase must be ________. A) first quarter B) third quarter C) full D) new Answer: C 37) During a solar eclipse, the Moon's phase must be ________. A) first quarter B) third quarter C) full D) new Answer: D

38) Imagine that you are on the Moon while your friend experiences a total solar eclipse on Earth. What do you see? A) You also see a solar eclipse, except with the Sun completely covered by the Earth. B) You see a relatively small shadow on an otherwise full Earth. C) You see a full Earth, just as you would if there were no eclipse at this time. D) You cannot see the Earth because it is blocked by the Sun. Answer: B 39) When are eclipse seasons? A) In the spring and fall B) In the summer and winter C) When the nodes of the Moon's orbit are nearly aligned with the Sun D) When Earth and the Sun are aligned with one another E) During an eclipse Answer: C 40) What effect does the precession of the Moon's nodes have on eclipses? A) It causes us to have lunar eclipses exactly every 6 months. B) It causes eclipses to occur a little less often than they would if the nodes did not precess. C) It causes eclipses to occur a little more often than they would if the nodes did not precess. D) Without this precession, eclipses could never occur. E) Without this precession, eclipses would occur every month. Answer: C 41) What is the saros cycle? A) The roughly 6-month period between eclipse seasons B) The approximately 18-year, 11-day cycle over which the pattern of eclipses repeats C) The average time between total solar eclipses D) The average time between a total solar eclipse and a total lunar eclipse E) The 26,000 year cycle over which Earth's axis sweeps out a cone in space Answer: B 42) Ancient people who knew the saros cycle could ________. A) completely predict the details of all eclipses B) completely predict the details of solar eclipses, but not lunar eclipses C) completely predict the details of lunar eclipses, but not solar eclipses D) predict the date and time of the next total solar eclipse that would be visible at their location E) predict when lunar and solar eclipses would occur, but not necessarily whether the eclipse would be partial or total, or exactly where it would be visible Answer: E 43) Which of the following explains why the Moon rises in the east and sets in the west? A) Earth rotates once each day. B) Earth orbits the Sun once each year. C) The direction of Earth's axis in space precesses with a period of about 26,000 years. D) Stars appear to move randomly relative to our Sun in the local solar neighborhood. E) The universe is expanding. Answer: A 21 Copyright © 2022 Pearson Education, Inc.

Section 2.4 1) Which of the following objects was not recognized as a planet in ancient times? A) Mercury B) Mars C) Jupiter D) Saturn E) Neptune Answer: E 2) What happens during the apparent retrograde motion of a planet? A) The planet rises in the west and sets in the east. B) The planet appears to move westward with respect to the stars over a period of weeks to months. C) The planet moves backward through the sky over the course of a night. D) The planet moves backward in its orbit around the Sun. E) The planet moves through constellations that are not part of the zodiac. Answer: B 3) What causes the apparent retrograde motion of the planets? A) It is an illusion created as we pass by a planet in our orbit (or the planet passes by us). B) It occurs when the planets reverse the direction of their orbits around the Sun. C) It is caused by the motion of planets around small circles that in turn go around bigger circles. D) It is an illusion created by our lack of depth perception in space. E) It is something we see only for planets that orbit the Sun in the opposite direction of Earth. Answer: A 4) Which of the following objects never appears to exhibit retrograde motion in our sky? A) The Sun B) Venus C) Mars D) Jupiter E) Saturn Answer: A 5) Which of the following statements about parallax is not true? A) You can demonstrate parallax simply by holding up a finger and looking at it alternately from your left and right eyes. B) The existence of stellar parallax is direct proof that Earth orbits the Sun. C) Measurement of stellar parallax allows us to determine distances to nearby stars. D) Observing stellar parallax requires only a single photograph taken through a powerful telescope. E) Ancient astronomers were unable to detect stellar parallax and used the absence of observed parallax as an argument in favor of an Earth-centered universe. Answer: D

6) Which of the following stars would exhibit the largest amount of stellar parallax? A) The star that is nearest to us B) The star that is farthest from us C) The star that is brightest in our sky D) The star that is dimmest in our sky E) The star that is moving at the highest speed relative to Earth Answer: A 7) We can't detect stellar parallax with naked-eye observations. Which of the following would make parallax easier to observe? A) Increasing the size of Earth's orbit B) Speeding up Earth's rotational motion C) Slowing down Earth's rotational motion D) Speeding up the precession of Earth's axis E) Getting away from streetlights Answer: A 8) Why were ancient peoples unable to detect stellar parallax? A) They did not look for it. B) They could not see distant stars. C) They did not have the ability to measure very small angles. D) They did not observe for long enough periods of time. E) They did detect it, but they rejected the observations. Answer: C 9) The parallax of two stars is reported in a star catalog. Which star is farther? A) The one with the larger amount of parallax B) You can't tell, since parallax has nothing to do with distance. C) The one with the smaller amount of parallax Answer: C 10) Which of the following planets cannot be seen with the naked eye? A) Venus B) Mars C) Jupiter D) Saturn E) Neptune Answer: E

Reading Quiz Questions 1) About how many stars are visible to the naked eye on a clear, dark night away from city lights? A) A few dozen B) A couple thousand C) Several million D) A few hundred billion Answer: B 2) What do astronomers mean by a constellation? A) A constellation is a region in the sky as seen from Earth. B) A constellation is a group of stars related through an ancient story. C) A constellation is any random grouping of stars in the sky. D) A constellation is a group of stars that are all located in about the same place in space. Answer: A 3) What is the ecliptic? A) The path the Sun appears to trace around the celestial sphere each year B) The Sun's daily path from east to west in our sky C) The path traced by the Moon's shadow on Earth during a solar eclipse D) A half-circle extending from your horizon due north, through your zenith, to your horizon due south Answer: A 4) What is the celestial sphere? A) The celestial sphere is a representation of how the entire sky looks as seen from Earth. B) The celestial sphere is a model that shows the true locations in space of the Sun and a few thousand of the nearest stars. C) The celestial sphere is a model of how the stars are arranged in the sky relative to our Sun, which is in the middle of the sphere. D) It represents a belief in an Earth-centered universe, and hence is no longer considered to have any use. Answer: A 5) What do we mean when we talk about the Milky Way in our sky? A) The patchy band of light that outlines the plane of the Milky Way Galaxy as seen from Earth. B) The whitish patch of light we see when we look toward the center of the Milky Way Galaxy. C) The spiral-shaped galaxy in which we live. D) The bright stars of the constellations that lie along the ecliptic in our sky. Answer: A

6) Which of the following correctly describes the meridian in your local sky? A) A half-circle extending from your horizon due east, through your zenith, to your horizon due west B) A half-circle extending from your horizon due east, through the north celestial pole, to your horizon due west C) A half-circle extending from your horizon due north, through your zenith, to your horizon due south D) The point directly over your head Answer: C 7) The point directly over your head is called ________. A) the meridian B) the zenith C) the north celestial pole D) the North Star Answer: B 8) Which of the following celestial objects do not rise in the east and set in the west? (Assume that all of these objects are visible from your location on Earth, and that none of them are circumpolar.) A) Stars B) The Sun C) The Moon D) Galaxies E) All of these objects rise in the east and set in the west. Answer: E 9) Which of the following statements does not use the term angular size or angular distance correctly? A) The angular distance between those two houses in the distance is 30 degrees. B) The angular distance between those two bright stars in the sky is about 2 meters. C) The angular size of the Sun is about the same as that of the Moon. D) You can use your outstretched hand against the sky to estimate angular sizes and angular distances. Answer: B 10) Stars that are visible in the local sky on any clear night of the year, at any time of the night, are called ________. A) bright B) seasonal C) circumpolar D) celestial Answer: C

11) We describe a location on Earth's surface by stating its ________. A) altitude and direction (or azimuth) B) meridian and longitude C) latitude and direction D) latitude and longitude Answer: D 12) If you are located in the Northern Hemisphere, which of the following correctly describes a relationship between the sky and your location? A) The altitude of the north celestial pole equals your latitude. B) The altitude of the celestial equator equals your latitude. C) The altitude of the north celestial pole equals your longitude. D) The longitude of the north celestial pole is circumpolar, and therefore crosses your zenith at the meridian. Answer: A 13) Which of the following best describes why we have seasons on Earth? A) The tilt of Earth's axis causes different portions of the Earth to receive more or less direct sunlight at different times of year. B) Earth's elliptical orbit means we are closer to the Sun and therefore receive more intense sunlight at some times of year than at others. C) The tilt of Earth's axis causes the Northern Hemisphere to be closer to the Sun than the Southern Hemisphere in summer, and vice versa in winter. D) The varying speed of Earth in its orbit around the Sun gives us summer when we are moving fastest and winter when we are moving slowest. Answer: A 14) Each choice describes how a few astronomical phenomena are related to time periods. Which list is entirely correct? (Careful: some lists are partially correct.) A) Earth's rotation defines a day. The cycle of the Moon's phases takes about a month. Earth's orbit defines a year. Earth's cycle of axis precession takes 26,000 years. B) Earth's rotation defines a day. The cycle of the Moon's phases takes about a week. Earth's orbit defines a year. Earth's cycle of axis precession defines a month. C) Earth's rotation defines a day. The Sun's rotation defines a week. The Moon's rotation defines a month. Earth's orbit defines a year. D) Earth's rotation defines a day. The Saros cycle of eclipses defines a month. Earth's orbit defines a year. Earth's cycle of axis precession takes 26,000 years. Answer: A 26 Copyright © 2022 Pearson Education, Inc.

15) If we have a new moon today, when we will have the next full moon? A) In about two weeks B) In about one week C) In about a month D) In about six months Answer: A 16) We cannot see a new moon in our sky because ________. A) it is obscured by Earth's shadow B) no sunlight is illuminating the Moon C) a new moon is quite near the Sun in the sky D) it is above the horizon during the daytime Answer: C 17) The Moon always shows nearly the same face to Earth because ________. A) the Moon does not rotate B) sunlight always hits the same face of the Moon C) the Moon rotates once in the same amount of time that it takes Earth to orbit the Sun once D) the Moon rotates once in the same amount of time that it takes the Moon to orbit Earth once Answer: D 18) Lunar eclipses can occur only when the phase of the Moon is ________. A) new B) first quarter C) full D) third quarter Answer: C 19) What is the Saros cycle? A) The 26,000-year cycle of the Earth's precession B) The roughly 18-year cycle over which the pattern of eclipses repeats C) The roughly one-month cycle of lunar phases in the sky D) The annual cycle of the seasons Answer: B 20) During the time that a planet is in its period of apparent retrograde motion ________. A) the planet moves backwards (clockwise as viewed from above Earth's north pole) in its orbit of the Sun B) the planet appears to rise in the west and set in the east, rather than the usual rising in the east and setting in the west C) over many days or weeks, the planet moves westward relative to the stars, rather than the usual eastward relative to the stars D) the planet is getting closer to the Sun in its orbit Answer: C

21) What is stellar parallax? A) It is the daily rise and set of the stars. B) It describes the fact that stars are actually moving relative to one another, even though to our eyes the stars appear fixed in the constellations. C) It is the slight back-and-forth shifting of star positions that occurs as we view the stars from different positions in Earth's orbit of the Sun. D) It is the change in the set of constellations that we see at different times of year in the evening sky. Answer: C 22) If a star's distance from Earth increased, its parallax shift would ________. A) decrease B) increase C) not change Answer: A Concept Quiz Questions 1) Which of the following statements about the celestial sphere is not true? A) The Earth is placed at the center of the celestial sphere. B) When we look in the sky, the stars all appear to be located on the celestial sphere. C) The celestial sphere is another name for our universe. D) The celestial sphere does not exist physically. Answer: C 2) The Andromeda Galaxy is faintly visible to the naked eye in the constellation Andromeda. Suppose instead it were located in the same direction in space as the center of the Milky Way Galaxy (but still at its current distance). How would it appear to the eye in that case? A) We could not see it at all. B) It would look about the same but would be in the constellation Sagittarius instead of Andromeda. C) It would be much brighter because it would be illuminated by the many stars in the center of our galaxy. D) It would look about the same, but it would be harder to pick out because its cloud-like appearance would make it blend in with the cloud-like appearance of the Milky Way in our sky. Answer: A 3) An angle of 1 arcsecond is ________. A) about the width of your fist held at arm's length B) about the width of a finger held at arm's length C) less than the thickness of a human hair held at arm's length D) slightly more than the width of a basketball held at arm's length Answer: C

4) When traveling north from the United States into Canada, you'll see the North Star (Polaris) getting ________. A) brighter B) dimmer C) higher in the sky D) lower in the sky Answer: C 5) Suppose you use the Southern Cross to determine that the south celestial pole appears 40 degrees above your horizon. Then you must be located at ________. A) latitude 40 degrees north B) latitude 50 degrees south C) latitude 40 degrees south D) longitude 40 degrees Answer: C 6) Suppose you are facing north and you see the Big Dipper close to your northern horizon, with Polaris (and the Little Dipper) above it. Where will you see the Big Dipper in six hours? A) To the right of Polaris; that is, 90 degrees counterclockwise from its current position B) To the left of Polaris; that is, 90 degrees clockwise from its current position C) Directly above Polaris D) Still in the same place, below Polaris Answer: A 7) In any particular place on Earth, certain constellations are visible in the evening only at certain times of the year because ________. A) our evening view of space depends on where Earth is located in its orbit around the Sun B) during some times of year, some constellations drop below the southern horizon C) some constellations are circumpolar D) on any particular night, we can only see stars that are directly opposite (180 degrees away from) the Sun in the sky Answer: A 8) The Sun's path, as viewed from the equator, is highest in the sky on ________. A) the December solstice B) the March and September equinoxes C) the June solstice D) the day when Earth is closest to the Sun Answer: B

9) Suppose Earth's axis tilt was significantly greater than its current 23.5 degrees, but Earth's rotation period and orbital period were unchanged. Which statement below would not be true? A) Summers and winters would be more severe (for example, hotter and colder, respectively) than they are now. B) The region of Earth where the Sun does not rise on the winter solstice would be larger (extending farther south) than it is now. C) The length of each season (for example, the number of days from the summer solstice to the fall equinox) would be significantly longer than it is now. D) Polaris would not be our North star. Answer: C 10) If our year were twice as long (that is, if Earth took twice as many days to complete each orbit around the Sun), but Earth's rotation period and axis tilt were unchanged, then ________. A) stars would take twice as long to rise and set B) the cycle of precession would take 13,000 years instead of 26,000 years C) the four seasons would each be twice as long as they are now D) the Earth would not have seasons Answer: C 11) How does Earth's varying distance from the Sun affect our seasons? A) It doesn't; Earth's orbital distance plays no significant role in the seasons. B) It makes summer warmer in the Northern Hemisphere than in the Southern Hemisphere. C) It is responsible for the fact that the seasons are opposite in the Northern and Southern hemispheres. D) It causes the seasons to be more extreme than they would be if the Earth's distance from the Sun were always the same. Answer: A 12) Suppose you live in the United States and you see a crescent moon in your evening sky tonight. What will a friend in South America see tonight? A) Your friend will see a gibbous moon. B) Your friend will also see a crescent moon. C) Your friend will see a first-quarter moon. D) Your friend won't see the Moon tonight because it is up only in the morning. Answer: B 13) Suppose it is full moon. What phase of Earth would someone on the Moon see at this time? A) Full Earth B) New Earth C) First-quarter Earth D) Earth does not go through phases as seen from the Moon. Answer: B

14) It's 6 a.m. and the Moon is at its highest point in your sky (crossing the meridian). What is the Moon's phase? A) New B) First quarter C) Full D) Third quarter Answer: D 15) You observe a full Moon rising at sunset. What will you see at midnight? A) A full moon high in the sky B) A first-quarter moon C) A waning gibbous moon D) A third-quarter moon Answer: A 16) All the following statements are true. Which one explains the reason that there is not a solar eclipse at every new moon? A) The nodes of the moon's orbit precess with an 18-year period. B) The orbital plane of the Moon is tilted slightly (by about 5 degrees) to the ecliptic plane. C) The Moon is only about one-fourth as large as Earth in diameter. D) The Moon goes through a complete cycle of phases about every 29-1/2 days. Answer: B 17) For most of history, the lack of observable stellar parallax was interpreted to mean that ________. A) stars must all lie at the same distance from Earth, on the celestial sphere B) stars were too far away for parallax to be measured with available technology C) Earth is stationary at the center of the universe D) Galileo's theories of the universe were essentially correct Answer: C 18) During the period each year when we see Mars undergoing apparent retrograde motion in our sky, what is really going on in space? A) Mars is moving around the Sun in the opposite direction from which Earth is moving around the Sun. B) Earth and Mars are getting closer together. C) Earth is catching up with and passing by Mars in their respective orbits. D) Earth and Mars are on opposite sides of the Sun. Answer: C 19) Suppose you see a photo showing Jupiter half in sunlight and half in shadow (that is, a first quarter Jupiter). This photo might have been taken by ________. A) a spacecraft orbiting Jupiter B) the Hubble Space Telescope (which orbits Earth) C) the Keck telescope on Mauna Kea, Hawaii D) the Arecibo radio telescope in Puerto Rico Answer: A 31 Copyright © 2022 Pearson Education, Inc.

Visual Quiz Questions 1) This diagram represents a simplified model of the celestial sphere. The unlabeled circle that is highlighted in purple represents ________.

A) the celestial equator B) the meridian C) the ecliptic D) the spring equinox Answer: A 2) This diagram represents a person's local sky. What does the red semicircle represent?

A) The horizon B) The meridian C) The zenith D) The celestial equator Answer: B

3) What is the approximate latitude and longitude of the South American location marked by the black dot on this diagram?

A) Latitude = 15ºS, longitude = 45ºW B) Latitude = 30ºW, longitude = 60ºN C) Latitude = 15ºN, longitude = 45ºW D) Latitude = 15ºS, longitude = 75ºW Answer: A

4) Diagrams like this one are commonly used in discussions of seasons and they can be quite useful. However, this diagram greatly exaggerates ________. A) the size of Earth relative to the size of Earth's orbit around the Sun B) the size of the Sun relative to the size of Earth's orbit around the Sun C) the amount by which Earth's orbit differs from a perfect circle D) all of the answers listed E) only the first and third choices Answer: D

5) Which position in this diagram represents Earth on the day that we have the longest amount of daylight in the continental United States? A) 1 B) 2 C) 3 D) 4 Answer: B 6) Which position in this diagram represents Earth at the beginning of spring for the Southern Hemisphere? A) 1 B) 2 C) 3 D) 4 Answer: C

7) Which photo shows what we call a first-quarter moon? (Note: Assume these photos were taken in the Northern Hemisphere.) A) 1 B) 2 C) 3 D) 4 Answer: B 8) Which photo shows what we call a gibbous moon? (Note: Assume these photos were taken in the Northern Hemisphere.) A) 1 B) 2 C) 3 D) 4 Answer: C

9) This multiple exposure photograph shows the apparent retrograde motion of Mars. To make this picture, the photographer needed to combine individual photos of Mars taken over a period of ________.

A) one full night B) about one hour C) about 3 nights D) several months Answer: D 10) What is this a picture of?

A) A total solar eclipse B) A total lunar eclipse C) The saros cycle D) A full moon Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Use this schematic seasons diagram to answer the questions below. 1) Which of the four labeled points (A through D) represents the day with the most hours of daylight for the Northern Hemisphere? A) A B) B C) C D) D Answer: B 2) Which of the four labeled points represents the day with the most hours of daylight for the Southern Hemisphere? A) A B) B C) C D) D Answer: D 3) Which of the four labeled points represents the beginning of spring for the Southern Hemisphere? A) A B) B C) C D) D Answer: C

4) The diagram exaggerates the sizes of Earth and the Sun relative to the orbit. If Earth were correctly scaled relative to the orbit in the figure, how big would it be? A) About half the size shown B) About 2 millimeters across C) About 0.1 millimeter across D) Microscopic Answer: D 5) Given that Earth's actual distance from the Sun varies by less than 3% over the course of a year, why does the diagram look so elliptical? A) It correctly shows that Earth is closest to the Sun at points A and C and farthest at points B and D. B) The elliptical shape is an effect of perspective, since the diagram shows an almost edge-on view of a nearly circular orbit. C) The shape of the diagram is meaningless and is done only for artistic effect. Answer: B

Use this diagram (based on Figure 2.14) to answer the questions below. 6) As viewed from Earth, in which zodiac constellation does the Sun appear to be located on April 21? A) Leo B) Aquarius C) Libra D) Aries Answer: D 7) If the date is April 21, what zodiac constellation will be visible on your meridian at midnight? A) Leo B) Aquarius C) Libra D) Aries Answer: C 8) If the date is April 21, what zodiac constellation will you see setting in the west shortly after sunset? A) Scorpius B) Pisces C) Taurus D) Virgo Answer: C

Chapter Review Questions 1) What are constellations? How did they get their names? 2) Suppose you were making a model of the celestial sphere with a ball. Briefly describe all the things you would need to mark on your celestial sphere. 3) On a clear, dark night, the sky may appear to be "full" of stars. Does this appearance accurately reflect the way stars are distributed in space? Explain. 4) Why does the local sky look like a dome? Define horizon, zenith, and meridian. How do we describe the location of an object in the local sky? 5) Explain why we can measure only angular sizes and angular distances for objects in the sky. What are arcminutes and arcseconds? 6) What are circumpolar stars? Are more stars circumpolar at the North Pole or in the United States? Explain. 7) What are latitude and longitude? Does the local sky vary with latitude? Does it vary with longitude? Explain. 8) What is the zodiac, and why do we see different parts of it at different times of year? 9) Suppose Earth's axis had no tilt. Would we still have seasons? Why or why not? 10) Briefly describe key facts about the solstices and equinoxes. 11) What is precession? How does it affect our view of the sky? 12) Briefly describe the Moon's cycle of phases. Can you ever see a full moon at noon? Explain. 13) Why do we always see the same face of the Moon? 14) Why don't we see an eclipse at every new and full moon? Describe the conditions needed for a solar or lunar eclipse. 15) What do we mean by the apparent retrograde motion of the planets? Why was it difficult for ancient astronomers to explain but easy for us to explain? 16) What is stellar parallax? How did an inability to detect it support the ancient belief in an Earth-centered universe?

Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 17) The constellation Orion didn't exist when my grandfather was a child. 18) When I looked into the dark lanes of the Milky Way with my binoculars, I saw a cluster of distant galaxies. 19) Last night the Moon was so big that it stretched for a mile across the sky. 20) I live in the United States, and during a trip to Argentina I saw many constellations that I'd never seen before. 21) Last night I saw Jupiter in the middle of the Big Dipper. (Hint: Is the Big Dipper part of the zodiac?) 22) Last night I saw Mars move westward through the sky in its apparent retrograde motion. 23) Although all the known stars rise in the east and set in the west, we might someday discover a star that will rise in the west and set in the east. 24) If Earth's orbit were a perfect circle, we would not have seasons. 25) Because of precession, someday it will be summer everywhere on Earth at the same time. 26) This morning I saw the full moon setting at about the same time the Sun was rising. Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 2 Reading and Concept Quizzes in the Study at www.MasteringAstronomy.com. 27) Two stars that are in the same constellation ________. A) must both be part of the same cluster of stars in space B) must both have been discovered at about the same time C) may actually be very far away from each other Answer: No Correct Answer Was Provided. 28) The north celestial pole is 35° above your northern horizon. This tells you that you are at ________. A) latitude 35°N B) longitude 35°E C) latitude 35°S Answer: No Correct Answer Was Provided.

29) Beijing and Philadelphia have about the same latitude but different longitudes. Therefore, tonight's night sky in these two places will ________. A) look about the same B) have completely different sets of constellations C) have partially different sets of constellations Answer: No Correct Answer Was Provided. 30) In winter, Earth's axis points toward the star Polaris. In spring, the axis points toward ________. A) Polaris B) Vega C) the Sun Answer: No Correct Answer Was Provided. 31) When it is summer in Australia, the season in the United States is ________. A) winter B) summer C) spring Answer: No Correct Answer Was Provided. 32) If the Sun rises precisely due east, ________. A) you must be located at Earth's equator B) it must be the day of either the March or the September equinox C) it must be the day of the June solstice Answer: No Correct Answer Was Provided. 33) A week after full moon, the Moon's phase is ________. A) first-quarter B) third-quarter C) new Answer: No Correct Answer Was Provided. 34) The fact that we always see the same face of the Moon tells us that the Moon ________. A) does not rotate B) rotates with the same period that it orbits Earth C) looks the same on both sides Answer: No Correct Answer Was Provided. 35) If there is going to be a total lunar eclipse tonight, then you know that ________. A) the Moon's phase is full B) the Moon's phase is new C) the Moon is unusually close to Earth Answer: No Correct Answer Was Provided.

36) When we see Saturn going through a period of apparent retrograde motion, it means ________. A) Saturn is temporarily moving backward in its orbit of the Sun B) Earth is passing Saturn in its orbit, with both planets on the same side of the Sun C) Saturn and Earth must be on opposite sides of the Sun Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 37) Cultural Constellations. Many cultures have created their own sets of constellations that differ from those used officially in astronomical research. Learn about the constellations of a particular culture of interest to you. How do the pattern of your chosen constellation(s) relate to the official constellations listed in Appendix H? Which set of patterns makes more sense to you personally? 38) Group Discussion: Sharing the Sky. Astronomers around the world are fond of saying "we all share the same sky." Gather in groups of two to four students to discuss the meaning of this statement. a. Give each group member a chance to describe the similarities and differences you would expect between the sky you see during a 24-hour period and the sky seen by someone on the opposite side of the world, or on the other side of the equator. b. Discuss whether you think that people making independent studies of the sky in different locations would come to similar conclusions about how the universe works. Would their conclusions be more accurate if they share perspectives with people from other places? Why or why not? c. Discuss whether the skies that people saw 2000 years ago differ in any significant ways from the skies we see today. d. Do you think that people living 2000 years from now will have experiences of the sky that are similar to your own? Why or why not?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 39) Earth-Centered or Sun-Centered? For each of the following, decide whether the phenomenon is consistent or inconsistent with a belief in an Earth-centered system. If consistent, describe how. If inconsistent, explain why, and also explain why the inconsistency did not immediately lead people to abandon the Earth-centered model. a. The daily paths of stars through the sky b. Seasons c. Phases of the Moon d. Eclipses e. Apparent retrograde motion of the planets 40) Shadow Phases. Many people incorrectly guess that the phases of the Moon are caused by Earth's shadow falling on the Moon. How would you convince a friend that the phases of the Moon have nothing to do with Earth's shadow? Describe the observations you would use to show that Earth's shadow isn't the cause of phases. 41) Earth-Centered Language. Many common phrases reflect the ancient Earth-centered view of our universe. For example, although we now know that day and night arise from Earth's rotation, we speak of "sunrise" or "sunset" as though it were the Sun moving around us daily. Identify other common phrases that imply an Earth-centered viewpoint. Do you think this language creates any difficulties in teaching science? Why or why not? 42) A Flat Earth? A few relatively famous people have recently made the claim that the Earth is flat. Working in small groups, first find out the basis on which they make these claims, then make a list of key observations that refute the flat-Earth claims. Based on what you learn, how you can tell which websites discussing flat-Earth claims are scientifically valid and which are not? What lessons might the flat-Earth claims contribute to the more general issue of "fake news" in our modern society? 43) Group Activity: Lunar Phases and Time of Day. Make a copy of the diagram below representing the Moon's orbit as seen from above Earth's North Pole. Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39; you may also find it useful to watch the video "Moon Phases, Part 2."

a. Label each of the eight Moon positions with the phase that it represents. b. What time of day corresponds to each of the four tick marks on Earth? Label each tick mark accordingly. c. Why doesn't the Moon's phase change during the course of one night? Explain your reasoning. d. At what times of day would a full moon be visible to someone on Earth? Write down when a full moon rises and explain why it appears to rise at that time. e. At what times of day would a third-quarter moon be visible to someone on Earth? Write down when a third-quarter moon sets and explain why it appears to set at that time. f. At what times of day would a waxing crescent moon be visible to someone on Earth? Write down when a waxing crescent moon rises and explain why it appears to rise at that time. Investigate Further 44) New Planet. A planet in another solar system has a circular orbit and an axis tilt of 35°. Would you expect this planet to have seasons? If so, would you expect them to be more extreme than the seasons on Earth? If not, why not? 45) Your View of the Sky. a. What are your latitude and longitude? b. Where does the north (or south) celestial pole appear in your sky? c. Is Polaris a circumpolar star in your sky? Explain.

46) View from the Moon. Suppose you lived on the Moon, in which case you would see Earth going through phases in your sky. Assume you live near the center of the face that looks toward Earth. a. Suppose you see a full Earth in your sky. What phase of the Moon would people on Earth see? Explain. b. Suppose people on Earth see a full moon. What phase would you see for Earth? Explain. c. Suppose people on Earth see a waxing gibbous moon. What phase would you see for Earth? Explain. d. Suppose people on Earth are viewing a total lunar eclipse. What would you see from your home on the Moon? Explain. 47) View from the Sun. Suppose you lived on the Sun (and could ignore the heat). Would you still see the Moon go through phases as it orbits Earth? Why or why not? 48) Farther Moon. Suppose the distance to the Moon were twice its actual value. Would it still be possible to have a total solar eclipse? Why or why not? 49) Smaller Earth. Suppose Earth were smaller. Would solar eclipses be any different? What about lunar eclipses? Explain. 50) Project: Observing Planetary Motion. Find out what planets are currently visible in your evening sky. At least once a week, observe these planets and draw a diagram showing their positions relative to stars in a zodiac constellation. How long does it take to notice the "wandering" features of planetary motion? Explain. 51) Project: Eclipse Trip. Find details about a future total solar eclipse that you may be able to observe. Create a plan for a trip to see the eclipse, including details of where you will view it, how you will get there, and what you should expect to see.

Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 52) Arcminutes and Arcseconds. There are 360° in a full circle. a. How many arcminutes are in a full circle? b. How many arcseconds are in a full circle? c. The Moon's angular size is about ½°. What is this in arcminutes? In arcseconds? 53) Find the Sun's Diameter. The Sun has an angular diameter of about 0.5° and an average distance from Earth of about 150 million km. What is the Sun's approximate physical diameter? Compare your answer to the actual value of 1,390,000 km. 54) Find a Star's Diameter. Estimate the diameter of the supergiant star Betelgeuse, using its measured angular diameter of about 0.5 arcsecond and distance of about 600 light-years. Compare your answer to the size of our Sun and the Earth–Sun distance. 55) Eclipse Conditions. The Moon's precise equatorial diameter is 3476 km, and its orbital distance from Earth varies between 356,400 km and 406,700 km. The Sun's diameter is 1,390,000 km, and its distance from Earth ranges between 147.5 and 152.6 million km. a. Find the Moon's angular size at its minimum and maximum distances from Earth. b. Find the Sun's angular size at its minimum and maximum distances from Earth. c. Based on your answers to parts a and b, is it possible to have a total solar eclipse when the Moon and Sun are both at their maximum distances? Explain.

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 3 The Science of Astronomy Section 3.1 1) People of central Africa learned to predict rainfall patterns by tracking rainfall amounts and ________. A) recording the seasonal changes in average temperature B) observing the path of the planets across the sky C) observing the length of the lunar cycle D) observing the orientation of the crescent Moon relative to the horizon E) observing the location of the Moon relative to the Sun in the sky Answer: D 2) Which of the following hypotheses best explains the success of the central African rainfall prediction technique of observing the waxing crescent Moon? A) When the Moon is aligned in a U-shape, it can hold more water, so there is more rain. When it is tilted, it can hold less, so the weather is drier. B) When the Moon is in Capricorn, there is always more tempestuous weather, while when in Pisces, it is just plain rainy. C) Clouds cover part of the Moon's surface, so the smaller the crescent, the more likely it is to rain. D) The Moon's orientation varies seasonally, and so does the weather. E) The Moon causes the tides and affects the weather. Answer: D 3) The names of the seven days of the week are based on the ________. A) seven naked-eye objects that appear to move among the constellations B) seven planets closest to the Sun C) seven brightest stars in the prominent constellation Orion D) most popular Norse gods E) seven largest constellations of the ancient world Answer: A 4) Historians trace the origins of our dividing a day into 24 hours to ________. A) the druids of Stonehenge B) the ancient Egyptians C) the Mayans D) the Aztecs E) the Babylonian astronomer, Meton Answer: B

5) At the Sun Dagger in New Mexico, a dagger-shaped beam of sunlight pierced a spiral ________. A) every day at noon B) at noon on the summer solstice C) at sunset on the spring equinox D) at noon on the day of full Moon each month E) during the totality of a total solar eclipse Answer: B 6) The Metonic cycle is the ________. A) 29-1/2-day period of the lunar cycle B) 12-month period of a lunar calendar C) 19-year period over which the lunar phases occur on about the same dates D) 18-year, 11-day period over which the pattern of eclipses repeats E) period between successive Easters Answer: C 7) How did the Egyptians use "star clocks" to estimate the time? A) They catalogued where particular stars appeared in the sky at various times of night throughout the year. B) They counted the number of stars visible at different times of night. C) They observed shadows cast by large obelisks blocking starlight. D) They measured the angular distance between the Moon and the brightest star in the sky. E) They created a catalog of where and when different planets would appear in particular locations among the constellations. Answer: A 8) In science, when we state that a measurement has "uncertainty," we mean ________. A) we don't know the exact value of the measurement, but we can be very confident that it lies within some well-determined range B) we are uncertain of exactly what it is that we are measuring C) the measurement was unsuccessful, and we still have no idea what its true value might be D) the measurement may or may not be correct, and we can say nothing more about its validity Answer: A

Section 3.2 1) How did Eratosthenes estimate the size of Earth in 240 B.C.? A) By observing the duration of a solar eclipse B) By measuring the size of Earth's shadow on the Moon in a lunar eclipse C) By comparing the maximum altitude of the Sun in two cities at different latitudes on the summer solstice D) By sending fleets of ships around Earth E) We don't know how he did it since all his writings were destroyed. Answer: C 2) Why did Ptolemy have the planets orbiting Earth on "circles upon circles" in his model of the universe? A) To explain why more distant planets take longer to make a circuit through the constellations of the zodiac B) To explain the fact that planets sometimes appear to move westward, rather than eastward, relative to the stars in our sky C) To explain why the Greeks were unable to detect stellar parallax D) To properly account for the varying distances of the planets from Earth E) To explain why Venus goes through phases as seen from Earth Answer: B 3) Which of the following was an important reason why most ancient Greeks rejected the notion that the Earth orbits the Sun? A) They could not measure how big the Earth was. B) They weren't as smart as we are. C) They believed that the Sun is a God. D) They could not measure small changes in the positions of stars that occur as Earth orbits the Sun. Answer: D 4) During the Dark Ages in Europe, the scientific work of the ancient Greeks was preserved and further developed primarily by scholars in ________. A) Baghdad (Iraq) B) Athens (Greece) C) Rome (Italy) D) Mumbai (India) E) Beijing (China) Answer: A

5) Which person below developed a system for predicting planetary positions that remained in use for some 1500 years? A) Tycho Brahe B) Copernicus C) Kepler D) Galileo E) Ptolemy Answer: E 6) Tonight Mars is in the portion of its orbit where we see it undergoing apparent retrograde motion. Which statement is true? A) Mars will be relatively bright in the night sky. B) Mars will rise in the west and set in the east. C) Mars will be visible in the night sky, but will appear much fainter than it does at other times. D) Mars will not be visible because it is above the horizon only in the daytime. Answer: A 7) Where was the Sun in Ptolemy's model of the universe? A) At the center B) Slightly offset from the center C) Between Earth and the Moon's orbit D) Between the orbits of Venus and Mars E) At the outer edge, beyond Saturn's orbit Answer: D 8) When did humans first confirm that Earth is not the center of the universe? A) About 400 years ago B) About 2000 years ago C) Around the time that early humans acquired language D) We haven't; there is still considerable scientific debate about whether Earth is the center of the universe. Answer: A 9) Which of the following statements can in principle be tested by scientific experiment(s)? A) War is morally justified. B) Picasso was the best artist of his generation. C) A supernatural being created the world. D) The locations of the Sun and planets among the constellations at your birth predict your personality and health. Answer: D

Section 3.3 1) The Greek philosopher Plato asserted that all heavenly objects move in perfect circles at constant speeds around the Earth. Which of the following observations most directly challenged this model? A) The apparent retrograde motion of planets B) The changing size of the Sun as the Earth gets closer and farther away C) Solar eclipses D) Seasonal changes in weather E) The differences in the lengths of shadows cast at different latitudes Answer: A 2) In terms of the history of science, we give special credit to the ancient Greeks because as far as is known, they ________. A) were the first to seek natural explanations for what they observed B) were the first to make written records of observations C) were the first to be able to predict eclipses D) were the first to write books E) were the most technologically advanced civilization Answer: A 3) Which person below wrote a book, published in 1543 (the year of his death), suggesting that Earth and other planets orbit the Sun? A) Tycho Brahe B) Copernicus C) Kepler D) Galileo E) Ptolemy Answer: B 4) Which person below was the first to prove that comets lie beyond Earth's atmosphere? A) Tycho Brahe B) Copernicus C) Kepler D) Galileo E) Aristotle Answer: A 5) Which person below discovered that the orbits of planets are ellipses? A) Tycho Brahe B) Copernicus C) Kepler D) Galileo E) Ptolemy Answer: C

6) Which person below did the following? He tried fitting perfect circles to Tycho's data, but in doing so found discrepancies of up to 8 arc minutes. Because he was confident that Tycho's data had uncertainties of only 1 arc minute, he abandoned perfect circles, which led him to a model using elliptical orbits. A) Galileo B) Newton C) Copernicus D) Kepler Answer: D 7) Which person below discovered that Jupiter has moons? A) Tycho Brahe B) Aristotle C) Kepler D) Galileo E) Ptolemy Answer: D 8) Which person below created a model of the solar system that put the Sun in the center, but that was not very accurate because he assumed that the orbits of the planets must be perfect circles? A) Galileo B) Newton C) Copernicus D) Kepler E) Tycho Answer: C 9) Which person below angered the Pope with his assertion that the Earth moved around the Sun? A) Galileo B) Copernicus C) Kepler D) Tycho Answer: A 10) The point along a planet's orbit where it is closest to the Sun is called the orbit's ________. A) perihelion B) aphelion C) eccentricity D) semimajor axis E) period Answer: A

11) Kepler's second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, implies that ________. A) a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun B) a planet's period does not depend on the eccentricity of its orbit C) planets that are farther from the Sun move at slower average speeds than nearer planets D) the period of a planet does not depend on its mass E) planets have circular orbits Answer: A 12) Kepler's third law, p2 = a3, implies that ________. A) a planet's orbital period does not depend on the eccentricity of its orbit B) all orbits with the same semimajor axis have the same period C) the orbital period of a planet does not depend on its mass D) planets that are farther from the Sun move at slower average speeds than nearer planets E) All of the above are correct. Answer: E 13) In its original form, Kepler's third law states that p2 = a3. What units must p and a use? A) p must be years and a must be astronomical units. B) p must be months and a must be astronomical units. C) p must be years and a must be kilometers. D) p must be days and a must be miles. E) p must be months and a must be kilometers. Answer: A 14) According to Kepler's third law (p2 = a3), a hypothetical planet that is twice as far from the Sun as Earth should have an orbital period of ________. A) exactly 1/2 Earth year B) exactly 2 Earth years C) between 1 and 2 Earth years D) between 2 and 3 Earth years E) It depends on the planet's mass. Answer: D 15) According to Kepler's third law (p2 = a3), an asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to ________. A) 2 astronomical units B) 4 astronomical units C) 8 astronomical units D) 16 astronomical units E) It depends on the asteroid's mass. Answer: B

16) According to Kepler's third law (p2 = a3), if a planet were discovered with an average distance from the Sun of 100 AU, its period would be ________. A) 10,000 years B) 1000 years C) Not enough information to say. D) 1 million years Answer: B 17) According to Kepler's third law (p2 = a3), how does a planet's mass affect its orbit around the Sun? A) A planet's mass has no effect on its orbit around the Sun. B) A more massive planet must have a larger semimajor axis. C) More massive planets orbit the Sun at higher average speed. D) More massive planets must have more circular orbits. Answer: A 18) Imagine that Earth were instantly replaced in its orbit by a speck of dust. Which statement best describes the subsequent orbital motion of that piece of dust? A) The dust particle will spiral into the Sun. B) The dust particle will be ejected from the solar system. C) The dust particle will continue in the same orbit as the Earth did, orbiting the Sun in 1 year. D) The dust particle will move to a smaller orbit and orbit the Sun in less than 1 year. E) The dust particle will move to a larger orbit and orbit the Sun in more than 1 year. Answer: C 19) Suppose an astronaut is working outside the Space Station and lets go off the handholds, so she is no longer attached to the Space Station in any way. Which of the following correctly explains what will happen? A) Orbital speed does not depend on mass, so she will remain very close to the Space Station. B) Her lower mass means she'll orbit much slower, so the Space Station will race rapidly away from her. C) Her lower mass means she'll orbit much faster, so she will rapidly race ahead of the Space Station. D) Because she is no longer attached to the orbiting Space Station, she'll rapidly lose altitude and fall back to Earth. Answer: A 20) Which of the following statements about Kepler's laws is true? A) Kepler's laws provide mathematical descriptions of the motion of the planets. B) Kepler's laws explain how gravity is responsible for keeping planets in orbit around the Sun. C) Kepler's laws tell us the precise sizes and distances of all the planets. D) All of the above are true. Answer: A

21) Which of the following statements best describes the accomplishments of these three people? A) Newton collected the data, Tycho provided the model in the form of laws, Kepler explained the model in terms of gravity. B) Tycho collected the data, Kepler provided the model in the form of laws, Newton explained the model in terms of gravity. C) Kepler collected the data, Tycho provided the model in the form of laws, Newton explained the model in terms of gravity. D) Tycho collected the data, Newton provided the model in the form of laws, Kepler explained the model in terms of gravity. Answer: B 22) Which of the following was not observed by Galileo? A) Craters on the Moon B) Stellar parallax C) Sunspots D) Jupiter's moons E) Phases of Venus Answer: B 23) In the Ptolemaic model of the solar system, which of the following phases could Venus exhibit? A) New and crescent phases only B) Gibbous and full phases only C) All phases D) Venus would not have phases in the Ptolemaic model. Answer: A 24) Which of the following phases does Venus actually display as viewed from Earth? A) New and crescent phases only B) Gibbous and full phases only C) All phases D) Venus does not exhibit phases. Answer: C 25) When we see Venus in its new phase, what phase would Earth be in as seen by a hypothetical person living on Venus? A) Full B) New C) First quarter D) Third quarter E) waning crescent Answer: A

26) Which of the following observations provided direct proof that Earth is not the center of all motion in the universe? A) The apparent retrograde motion of the planets B) The phases of the Moon C) Eclipses of the Sun D) Galileo's observation of stars in the Milky Way E) Galileo's observations of the moons of Jupiter Answer: E 27) Consider a set of ellipses that all have the same semimajor axis length. Which statement is true? A) The ellipse with the largest distance between its foci has the greatest eccentricity. B) The ellipse with the smallest distance between its foci has the greatest eccentricity. C) All the ellipses must also have the same eccentricity. D) All the ellipses must also have the same semiminor axis length. E) All the ellipses must be identical. Answer: A Section 3.4 1) Which of the following statements about scientific models is true? A) A model tries to represent all aspects of nature. B) A model tries to represent only one aspect of nature. C) A model can be used to explain and predict real phenomena. D) All models that explain nature well are correct. E) All current models are correct. Answer: C 2) What do scientists mean by verifiable observations? A) Statements that a person can, in principle, verify for himself or herself B) Statements that anyone would agree are obvious C) Observations that can be interpreted in only one way D) Observations that a model does not have to predict E) Observations that support a scientific theory Answer: A 3) What is meant by a hypothesis? A) A natural phenomenon that requires explanation B) A tentative explanation for a phenomenon that can be tested with observations or experiments C) A confirmed explanation for a natural phenomenon D) A pseudoscientific idea E) A historical theory that has been proved inaccurate Answer: B

4) What is meant by Occam's Razor? A) The idea that a well-designed experiment can help us decide between two competing models B) The idea that scientific models should not invoke supernatural explanations C) The idea that scientists should prefer the simpler of two models that agree equally well with observations D) The fine line between science and pseudoscience E) The shaving implement of a medieval scholar Answer: C 5) Which of the following statements expresses what we mean by a scientific theory? A) A simple model that explains a wide variety of phenomena and that has survived repeated tests B) An explanation for a physical phenomenon, an explanation that hasn't been tested yet C) An educated guess D) A hypothesis Answer: A 6) Which of the following is not necessary of a good scientific theory? A) A scientific theory must be proven true beyond all doubt to be accepted. B) A scientific theory should be based on natural processes and should not invoke the supernatural or divine. C) A scientific theory must explain a wide variety of phenomena observed in the natural world. D) A scientific theory must make testable predictions that, if found to be incorrect, could lead to its own modification or demise. Answer: A 7) Why do scientists consider Einstein's General Theory of Relativity to be a better theory of gravity than Newton's theory of gravity? A) Einstein's gravity makes correct predictions in a few cases where Newton's theory does not. B) The two theories always make very different predictions, and only Einstein's theory works. C) Newton's theory was never useful, so it had to be replaced by something. D) Einstein's theory is newer, and scientists always prefer newer theories. Answer: A 8) The ancient goal of astrology was to A) understand the origin of Earth. B) make a more accurate model of the universe. C) predict the passing of the seasons. D) predict human events. E) antagonize astronomers. Answer: D

9) Most horoscopes give advice such as "today is a good day to try new things." Is this a valid scientific prediction? A) No. The statement is too vague to be objectively tested. B) No. It is never a good day to try new things. C) Yes. You can try something new and see if the outcome is good. D) Yes. It is always a good day to try new things. E) No. This statement is not true for everyone. Answer: A 10) An astrologer makes 100 predictions and 90 of them turn out to be true. Would this support the scientific validity of astrology? A) Only if the 90 correct predictions are significantly higher than what we would expect by chance B) Yes, since 90 out of 100 is a very high number of correct predictions C) No, since the astrologer got 10 predictions wrong D) Only if the astrologer can clearly explain how they made their predictions E) Only if the astrologer used all of the planets to make their predictions Answer: A 11) There are 12 astrological "Sun signs," spaced evenly through the year. A person's astrological Sun sign is based on the constellation the Sun is in on the calendar day they were born (to be technical, if they were born on the same date about 2000 years ago). What is the chance that a person will correctly guess another person's Sun sign by random chance? A) About 1 in 12 B) Zero: it would be impossible to guess correctly randomly. C) About 1 in 100 D) About 1 in a million E) About 1 in 2 Answer: A 12) Which one of the following statements is testable by scientific methods? A) Picasso was a better artist than Rembrandt. B) Childhood vaccinations do not affect the rate of autism. C) If Robert Kennedy had not been killed, he would have become president of the United States. D) The universe was created by God. Answer: B

13) Suppose that a study finds a strong positive correlation between acupuncture treatments and recovery of patients from, say, cocaine addiction. However, also assume that there is no known mechanism of action (i.e., how acupuncture could cure addiction) that can explain the correlation. Is it possible that acupuncture is responsible for the patients' recovery? A) No. If there is no plausible mechanism of action, then acupuncture cannot be responsible for their healing. B) Yes. Just because we don't understand the mechanism doesn't mean the process does not occur. C) No. Acupuncture is not accepted by most medical doctors; therefore, it isn't effective. D) Yes. If the patients got better, then the acupuncture must be effective. Answer: B 14) Suppose that a study finds a strong positive correlation between acupuncture treatments and recovery of patients from, say, cocaine addiction. However, also assume that there is no known mechanism of action (i.e., how acupuncture could cure addiction) that can explain the correlation. Can we conclude that acupuncture is definitely responsible for the patients' recovery? A) No. Acupuncture may be responsible for the healing, or it may not. Correlation does not necessarily imply causation. B) Yes. If the study was run by qualified M.D.s, then we should respect their findings that acupuncture cured these patients. C) No. Acupuncture is hippie, new age stuff, and is not respected by reputable doctors. D) Yes. The patients stated afterwards that they knew it had helped, and these people know their own bodies better than we do. Answer: A 15) Which scientists played a major role in overturning the ancient idea of an Earth-centered universe, and about when? A) Copernicus, Kepler, and Galileo; about 400 years ago B) Aristotle and Copernicus; about 400 years ago C) Newton and Einstein; about 100 years ago D) Huygens and Newton; about 300 years ago E) Aristotle and Plato; about 2000 years ago Answer: A

Short Answer Questions 1) Why was a knowledge of the stars so important to Polynesians? Answer: The Polynesian people live on a group of widely separated islands in the South Pacific. Knowledge of the stars allowed navigators to determine their latitude and direction, both essential for traveling the large distances from island to island. 2) Describe how Eratosthenes first measured the size of Earth over 2000 years ago. Answer: Eratosthenes used measurements of the angle of the Sun in the sky at noon on the summer solstice in two places in Egypt. It was directly overhead in Syene and cast no shadows. In Alexandria, however, there was a slight shadow, indicating that the Sun was 7 degrees away from overhead. Eratosthenes concluded that Alexandria lies at a latitude 7 degrees north of Syene. The circumference of Earth is then the distance between Syene and Alexandria divided by the fraction of the circle (7/360) that the two cities span. 3) Give a scientific explanation of the success of the central African rainfall-prediction technique of observing the waxing crescent Moon. Can the Moon's phase cause a change in rainfall? Answer: The Moon's orientation varies seasonally, and so does the weather, so the orientation and the weather are correlated, but one does not cause the other. 4) Suppose you think you know the answer to a scientific question. Is it scientifically valid to look only for evidence to support your answer? Why or why not? Answer: No, you must look for all evidence relating to your question, whether that evidence supports or refutes it. Looking only for supportive evidence is often called "cherry picking" of data to support an idea because it ignores evidence that may refute it. Reading Quiz Questions 1) What practical value did astronomy offer to ancient civilizations? A) It helped them keep track of time and seasons, and it was used by some cultures for navigation. B) It allowed them to predict eclipses with great accuracy. C) It helped them understand our cosmic origins. D) It helped them find uses for ancient structures like Stonehenge. Answer: A 2) Scientific thinking is ________. A) based on everyday ideas of observation and trial-and-error experiments B) completely different from any other type of thinking C) a difficult process that only a handful of people can do well D) an ancient mode of thinking first invented in Egypt Answer: A

3) The names of the 7 days of the week are based on ________. A) the names of the seven planets closest to the Sun B) the seven most prominent constellations in the summer sky C) the names of prophets in the Bible D) the seven naked-eye objects that appear to move among the constellations Answer: D 4) The fact that the lunar phases repeat on the same solar dates about every 19 years (the Metonic cycle) can be used to ________. A) keep lunar calendars approximately synchronized with solar calendars B) predict the future orientation of the Earth's axis in space C) keep the dates of solstices and equinoxes about the same from year to year D) predict the dates of future eclipses Answer: A 5) Ptolemy was important in the history of astronomy because he ________. A) developed a model of the solar system that made sufficiently accurate predictions of planetary positions to remain in use for many centuries B) developed the first scientific model of the universe C) was the first to create a model of the solar system that placed the Sun rather than the Earth at the center D) was the first to believe that all orbits are perfect circles Answer: A 6) The ancient Greeks get a lot of attention for their contributions to science because ________. A) they were the first people known to try to explain nature with models based on reason and mathematics, without resorting to the supernatural B) the books of every other culture were lost in the destruction of the library of Alexandria C) they were the first people to realize that Earth is a planet orbiting the Sun D) they were the only ancient culture that kept written records of their astronomical observations Answer: A 7) What do we mean by a geocentric model of the universe? A) A model designed to explain what we see in the sky while having the Earth located in the center of the universe B) A model designed to explain what we see in the sky while having the Earth orbit the Sun C) The name given to sphere-shaped models that show all the constellations as they appear in our sky on the celestial sphere D) A model of the Milky Way Galaxy that has our solar system located at its center Answer: A

8) What was the Ptolemaic model? A) An Earth-centered model of planetary motion published by Ptolemy B) The Earth-centered model of the cosmos in which the Earth was surrounded by seven perfect spheres, one each for the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn C) The first scientific model to successfully predict solar and lunar eclipses D) A Sun-centered model of planetary motion published by Ptolemy Answer: A 9) The great contribution of Nicholas Copernicus was to ________. A) create a detailed model of our solar system with the Sun at the center B) prove that the Earth is not the center of the universe C) discover the laws of planetary motion D) discover the law of gravity Answer: A 10) The great contribution of Tycho Brahe was to ________. A) observe planetary positions with sufficient accuracy so that Kepler could later use the data to discover the laws of planetary motion B) discover four moons orbiting Jupiter, thereby lending strong support to the idea that the Earth is not the center of the universe C) offer the first detailed model of a Sun-centered solar system, thereby beginning the process of overturning the Earth-centered model of the Greeks D) discover that planets orbit the Sun in elliptical orbits with varying speed Answer: A 11) Which of the following was not observed by Galileo? A) Stellar parallax B) Mountains and valleys on the Moon C) Four moons orbiting Jupiter D) Phases of Venus Answer: A 12) Which of the following statements about an ellipse is not true? A) The focus of an ellipse is always located precisely at the center of the ellipse. B) A circle is considered to be a special type of ellipse. C) The semimajor axis of an ellipse is half the length of the longest line that you can draw across an ellipse. D) An ellipse with a large eccentricity looks much more elongated (stretched out) than an ellipse with a small eccentricity. Answer: A

13) Which of the following is not one of, nor a direct consequence of, Kepler's Laws? A) The force of attraction between any two objects decreases with the square of the distance between their centers. B) As a planet moves around its orbit, it sweeps out equal areas in equal times. C) The orbit of each planet about the Sun is an ellipse with the Sun at one focus. D) More distant planets orbit the Sun at slower speeds. E) A planet or comet in a noncircular orbit travels faster when it is nearer to the Sun and slower when it is farther from the Sun. Answer: A 14) Scientific models are used to ________. A) present the scale of the solar system to the general public B) make specific predictions that can be tested through observations or experiments C) make miniature representations of the universe D) prove that past paradigms no longer hold true Answer: B 15) Which of the following claims can be tested by scientific means? A) People born when the Sun appears in the constellation Leo have larger average incomes than other people. B) Abraham Lincoln's final thoughts were about the fate of his country. C) God exists. D) Blue is the best color for walls. Answer: A 16) In science, a broad idea that has been repeatedly verified so as to give scientists great confidence that it represents reality is called ________. A) a paradigm B) a hypothesis C) a Ptolemaic model D) a theory Answer: D

Concept Quiz Questions 1) Suppose the planet Uranus were much brighter in the sky, so that it was as easily visible to the naked eye as Jupiter or Saturn. Which one of the following statements would most likely be true in that case? A) A week would have 8 days instead of 7. B) Its brightness would make it possible to read by starlight at night. C) Its gravity would cause the tides to be much higher than they actually are. D) The discovery that the Earth is a planet going around the Sun would have come hundreds of years earlier. E) Its slow motion through the sky would have led it to be named after the Goddess of Procrastination. Answer: A 2) How does a 12-month lunar calendar differ from our 12-month solar calendar? A) It has about 11 fewer days. B) It does not have seasons. C) Its new year always occurs in February instead of on January 1. D) It uses a 23-hour rather than a 24-hour day. Answer: A 3) Which of the following best describes a set of conditions under which archaeoastronomers would conclude that an ancient structure was used for astronomical purposes? A) The structure has numerous features that align with the Sun's path at special times of year and cultural heritage claimed that the rulers were descendants of the Sun. B) They find that, looking out from the center of the building, there are two windows that align with the rise and set points of two bright stars. C) The structure consists of lines in the desert that make patterns visible only from high above. D) The structure has the same dome shape as modern astronomical observatories. Answer: A 4) How did the Ptolemaic model explain the apparent retrograde motion of the planets? A) The planets moved along small circles that moved on larger circles around the Earth. B) The planets sometimes stopped moving and then reversed to move backward along their circular orbits. C) The model showed that apparent retrograde motion occurs as Earth passes by another planet in its orbit of the Sun. D) The planets resided on giant spheres that sometimes turned clockwise and sometimes turned counterclockwise. Answer: A

5) When Copernicus first created his Sun-centered model of the universe, it did not lead to substantially better predictions of planetary positions than the Ptolemaic model. Why not? A) Copernicus used perfect circles for the orbits of the planets. B) Copernicus placed the planets in the wrong order going outward from the Sun. C) Copernicus misjudged the distances between the planets. D) Copernicus placed the Sun at the center but did not realize that the Moon orbits the Earth. Answer: A 6) Earth is farthest from the Sun in July and closest to the Sun in January. During which Northern Hemisphere season is Earth moving fastest in its orbit? A) Spring B) Summer C) Fall D) Winter Answer: D 7) According to Kepler's third law (p2 = a3), how does a planet's mass affect its orbit around the Sun? A) A planet's mass has no effect on its orbit around the Sun. B) More massive planets orbit the Sun at higher average speed. C) More massive planets must have more circular orbits. D) A more massive planet must have a larger semimajor axis. Answer: A 8) All the following statements are true. Which one follows directly from Kepler's third law (p2 = a3)? A) Venus orbits the Sun at a slower average speed than Mercury. B) Venus is more massive than Mercury. C) Venus takes longer to rotate than it does to orbit the Sun. D) Venus has a thicker atmosphere than Mercury. Answer: A 9) Suppose a comet orbits the Sun on a highly eccentric orbit with an average (semimajor axis) distance of 1 AU. How long does it take to complete each orbit, and how do we know? A) 1 year, which we know from Kepler's third law B) It depends on the eccentricity of the orbit, as described by Kepler's second law. C) It depends on the eccentricity of the orbit, as described by Kepler's first law. D) Each orbit should take about 2 years because the eccentricity is so large. Answer: A 10) Galileo challenged the idea that objects in the heavens were perfect by ________. A) showing that heavy objects fall at the same rate as lighter objects B) observing sunspots on the Sun and mountains on the Moon C) proving Kepler's laws were correct D) inventing the telescope Answer: B 19 Copyright © 2022 Pearson Education, Inc.

11) Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun? A) Phases of Venus B) Four moons of Jupiter C) Patterns of shadow and sunlight near the dividing line between the light and dark portions of the Moon's face D) The Milky Way is composed of many individual stars. Answer: A 12) Which of the following is not consistent with the major hallmarks of science? A) Science consists of proven theories that are understood to be true explanations of reality. B) Scientific explanations should be based solely on natural causes. C) Science progresses through the creation and testing of models that explain observation as simply as possible. D) A scientific model must make testable predictions. Answer: A 13) Which of the following is not part of a good scientific theory? A) A scientific theory cannot be accepted until it has been proven true beyond all doubt. B) A scientific theory must make testable predictions that, if found to be incorrect, could lead to its own modification or demise. C) A scientific theory must explain a wide variety of phenomena observed in the natural world. D) A scientific theory should be based on natural processes and should not invoke the supernatural or divine. Answer: A 14) Only one of the statements that follow uses the term theory in its correct, scientific sense. Which one? A) Einstein's theory of relativity has been tested and verified thousands of times. B) Evolution is only a theory, so there's no reason to think it really happened. C) I have a new theory about the cause of earthquakes, and I plan to start testing it soon. D) I wrote a theory that is 152 pages long. Answer: A 15) Which of these hypothetical observations (none of them are real) would force us to reconsider our modern, Sun-centered view of the solar system? A) We discover a small planet beyond Saturn that rises in the west and sets in the east each day. B) We discover an Earth-sized planet orbiting the Sun beyond the orbit of Pluto. C) We find that we are unable to measure any parallax for a distant galaxy. D) We discover that the universe is actually contracting, not expanding. Answer: A

Visual Quiz Questions 1) Central Africans learned long ago to use observations of the waxing crescent moon (once each month) to predict when the rainy season was coming. Use the graph for Central Africa. In what month(s) does this region get about 200 millimeters of rainfall?

A) April and August B) July C) February and October D) June and July E) March through June Answer: A

2) Each of these photos shows an ancient structure used for astronomical purposes. Which one is located in the United States? A)

Answer: D

3) This figure shows the circle on circle motion of a planet in the Ptolemaic model. At which point(s) is the planet in the middle of its period of retrograde motion in our sky?

A) Point 1 only B) Point 2 only C) Point 3 only D) Points 1 and 3 Answer: B 4) This figure shows the circle on circle motion of a planet in the Ptolemaic model. At which point(s) is the planet in the middle of its period of retrograde motion in our sky?

A) 1 B) 2 C) 3 D) 4 Answer: D

5) What, if anything, is wrong with the planetary orbit shown?

A) The Sun is not at one focus, as Kepler's first law requires. B) The shape of the orbit is not an ellipse, as Kepler's first law requires. C) The orbital path violates Kepler's third law. D) There is nothing wrong with this orbit; it is fine as shown. Answer: A 6) This diagram shows a planet at four points in its orbit around the Sun. At which of the points shown is it traveling slowest in its orbit? (The planet is not real, as all the planets of our solar system have orbits much more circular than the one shown.)

A) 1 B) 2 C) 3 D) 4 Answer: D

7) Assume you knew nothing else about the planets but what is shown in this diagram. What could you conclude?

A) The square of a planet's period in years is equal to the cube of its average distance from the Sun in AU. B) Earth takes less than a third as long to orbit the Sun as Mars. C) The outer planets are more massive than the inner planets. D) Saturn orbits the Sun faster than any other planet. Answer: A

8) This diagram shows a graphical interpretation of Kepler's third law. Suppose there were a planet in our solar system that orbited the Sun with an average speed of 11 km/s. In terms of its average distance, this planet would be located ________.

A) between Jupiter and Saturn B) beyond the orbit of Saturn C) between Venus and Mars D) between Mars and Jupiter E) It is impossible to determine from the information given. Answer: A 9) Look carefully at this telescopic photo of the Moon. All the following statements are true. Which one is proved by the fact that the line dividing the dark and bright regions is not perfectly straight?

A) The Moon's surface is not perfectly smooth but rather has mountains and valleys. B) The Moon goes around the Earth. C) This is a first-quarter moon. D) Some parts of the Moon's surface are darker in color than others. Answer: A

10) Study this diagram, which shows why we see phases of Venus, as first observed by Galileo. When should we expect to see a full Venus in our night sky?

A) Never B) At midnight, when Venus is on the opposite side of its orbit from Earth C) At midnight, when Venus is on the same side of its orbit from Earth D) Only when Earth is at the opposite side of the Sun from what is shown in this diagram Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Use the information in the graphs (from Figure 3.16) to answer the following questions. 1) Approximately how fast is Jupiter orbiting the Sun? A) This cannot be determined from the information provided. B) 20 km/s C) 10 km/s D) A little less than 15 km/s Answer: D 28 Copyright © 2022 Pearson Education, Inc.

2) An asteroid with an average orbital distance of 2 AU will orbit the Sun at an average speed that is ________. A) a little slower than the orbital speed of Mars B) a little faster than the orbital speed of Mars C) the same as the orbital speed of Mars Answer: A 3) Uranus, not shown on graph b, orbits about 19 AU from the Sun. Based on the graph, its approximate orbital speed is between about ________. A) 20 and 25 km/s B) 15 and 20 km/s C) 10 and 15 km/s D) 5 and 10 km/s Answer: D 4) Kepler's third law is often stated as p2 = a3. The value a3 for a planet is shown on ________. A) the horizontal axis of graph a B) the vertical axis of graph a C) the horizontal axis of graph b D) the vertical axis of graph b Answer: A 5) On graph a, you can see Kepler's third law (p2 = a3) from the fact that ________. A) the data fall on a straight line B) the axes are labeled with values for p2 and a3 C) the planet names are labeled on the graph Answer: A 6) Suppose graph a showed a planet on the red line directly above a value of 1000 AU3 along the horizontal axis. On the vertical axis, this planet would be at ________. A) 1000 years2 B) 10002 years2 C) years2 D) 100 years Answer: A 7) Suppose graph a showed a planet on the red line directly above a value of 1000 AU3 along the horizontal axis. How far does the planet orbit from the Sun?” A) 10 AU B) 100 AU C) 1000 AU D) AU Answer: A 29 Copyright © 2022 Pearson Education, Inc.

Chapter Review Questions 1) In what way is scientific thinking natural to all of us, and how does modern science build upon this everyday type of thinking? 2) Why did ancient peoples study astronomy? Describe the astronomical origins of our day, week, month, and year. 3) What is a lunar calendar? How can it be kept roughly synchronized with a solar calendar? 4) What do we mean by a model in science? Briefly summarize the Greek geocentric model. 5) What do we mean by the Ptolemaic model? How did this model account for the apparent retrograde motion of planets in our sky? 6) What was the Copernican revolution, and how did it change the human view of the universe? 7) What is an ellipse? Define its foci, semimajor axis, and eccentricity. 8) State and explain the meaning of each of Kepler's laws of planetary motion. 9) Describe the three hallmarks of science and explain how we can see them in the Copernican revolution. What is Occam's razor? Why doesn't science accept personal testimony as evidence? 10) What is the difference between a hypothesis and a theory in science? Science or Nonscience? Decide whether the claim made in each of the following statements could be evaluated scientifically or falls into the realm of nonscience. Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 11) The Yankees are the best baseball team of all time. 12) Several kilometers below its surface, Jupiter's moon Europa has an ocean of liquid water. 13) My house is haunted by ghosts who make the creaking noises I hear each night. 14) There are no lakes or seas on the surface of Mars today. 15) Dogs are smarter than cats. 16) Children born when Jupiter is in the constellation Taurus are more likely to be musicians than other children. 17) Aliens can manipulate time so that they can abduct and perform experiments on people who never realize they were taken. 30 Copyright © 2022 Pearson Education, Inc.

18) Newton's law of gravity works as well for explaining the orbits of planets around other stars as it does for explaining the orbits of planets in our own solar system. 19) God created the laws of motion that were discovered by Newton. 20) A huge fleet of alien spacecraft will land on Earth and introduce an era of peace and prosperity on January 1, 2035. Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 3 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 21) In the Greek geocentric model, the retrograde motion of a planet occurs when ________. A) Earth is about to pass the planet in its orbit around the Sun B) the planet actually goes backward in its orbit around Earth C) the planet is aligned with the Moon in our sky Answer: No Correct Answer Was Provided. 22) Which of the following was not a major advantage of Copernicus's Sun-centered model over the Ptolemaic model? A) It made significantly better predictions of planetary positions in our sky. B) It offered a more natural explanation for the apparent retrograde motion of planets in our sky. C) It allowed calculation of the orbital periods and distances of the planets. Answer: No Correct Answer Was Provided. 23) When we say that a planet has a highly eccentric orbit, we mean that ________. A) it is spiraling in toward the Sun B) its orbit is an ellipse with the Sun at one focus C) in some parts of its orbit it is much closer to the Sun than in other parts Answer: No Correct Answer Was Provided. 24) Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law, ________. A) Earth travels faster in its orbit around the Sun in July than in January B) Earth travels faster in its orbit around the Sun in January than in July C) it is summer in January and winter in July Answer: No Correct Answer Was Provided. 25) According to Kepler's third law, ________. A) Mercury travels fastest in the part of its orbit in which it is closest to the Sun B) Jupiter orbits the Sun at a faster speed than Saturn C) all the planets have nearly circular orbits Answer: No Correct Answer Was Provided.

26) Tycho Brahe's contribution to astronomy included ________. A) inventing the telescope B) proving that Earth orbits the Sun C) collecting data that enabled Kepler to discover the laws of planetary motion Answer: No Correct Answer Was Provided. 27) Galileo's contribution to astronomy included ________. A) discovering the laws of planetary motion B) discovering the law of gravity C) making observations and conducting experiments that dispelled scientific objections to the Sun-centered model Answer: No Correct Answer Was Provided. 28) Which of the following is not true about scientific progress? A) Science progresses through the creation and testing of models of nature. B) Science advances only through the scientific method. C) Science avoids explanations that invoke the supernatural. Answer: No Correct Answer Was Provided. 29) Which of the following is not true about a scientific theory? A) A theory must explain a wide range of observations or experiments. B) Even the strongest theories can never be proved true beyond all doubt. C) A theory is essentially an educated guess. Answer: No Correct Answer Was Provided. 30) When Einstein's theory of gravity (general relativity) gained acceptance, it demonstrated that Newton's theory had been ________. A) wrong B) incomplete C) really only a guess Answer: No Correct Answer Was Provided.

Inclusive Astronomy Use these questions to reflect on participation in science. 31) Group Discussion: Ancestral Astronomy. No matter what your background, you had ancestors who watched the sky and observed how celestial objects move through it. a. Working independently, choose a particular branch of your ancestry to explore, then gather historical information dating back as far as possible (ideally at least several centuries) about how and why your ancestors made use of their observations of the sky. b. Gather in small groups (two to four students) and take turns sharing what you learned through your research. Be clear about the ancestral group you have chosen and the time period your research covers. c. Make a list of the major uses of astronomical knowledge that your group members found, categorizing the uses as practical, ceremonial/religious, or other. Which uses were most common? Do you see any noticeable differences among the cultures? d. Discuss how cultural or geographical factors may have influenced the astronomical knowledge of these different ancestral groups. The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 32) What Makes It Science? Choose a single idea in the modern view of the cosmos discussed in Chapter 1, such as "The universe is expanding," or "We are made from elements manufactured by stars," or "The Sun orbits the center of the Milky Way Galaxy once every 230 million years." a. Describe how this idea reflects each of the three hallmarks of science, discussing how it is based on observations, how our understanding of it depends on a model, and how that model is testable. b. Describe a hypothetical observation that, if it were actually made, might cause us to call the idea into question. Then briefly discuss whether you think that, overall, the idea is likely or unlikely to hold up to future observations. 33) The Importance of Ancient Astronomy. Why was astronomy important to people in ancient times? Discuss both the practical importance of astronomy and the importance it may have had for religious or other traditions. Which do you think was more important in the development of ancient astronomy: its practical or its philosophical role? Defend your opinion. 34) The Impact of Science. The modern world is filled with ideas, knowledge, and technology that developed through science and application of the scientific method. Discuss some of these things and how they affect our lives. Which of these impacts do you think are positive? Which are negative? Overall, do you think science has benefited the human race? Defend your opinion. 35) Astronomy and Astrology. Why do you think astrology remains so popular around the world even though it has failed all scientific tests of its validity? Do you think this popularity has any social consequences? Defend your opinions.

36) Group Activity: Galileo on Trial. Conduct a mock trial in which you consider the following three pieces of evidence: (1) observations of mountains and valleys on the Moon; (2) observations of moons orbiting Jupiter; (3) observations of the phases of Venus. Note: This activity works particularly well in groups of four or more students: • One student takes the role of Galileo, arguing in favor of the idea that Earth orbits the Sun. • One student takes the role of prosecutor, arguing against the idea that Earth orbits the Sun. • The remaining students serve as a jury and render a verdict after hearing the arguments and rebuttals from Galileo and the prosecutor. Investigate Further 37) Earth's Shape. It took thousands of years for humans to deduce that Earth is spherical. For each of the following alternative models of Earth's shape, identify one or more observations that you could make for yourself that would invalidate the model. a. A flat Earth b. A cylindrical Earth [which was actually proposed by the Greek philosopher Anaximander (c. 610—546 B.C.)] c. A football-shaped Earth 38) Copernican Players. Using a bulleted list format, make a one-page "executive summary" of the major roles that Copernicus, Tycho, Kepler, and Galileo played in overturning the ancient belief in an Earth-centered universe. 39) Influence on History. Based on what you have learned about the Copernican revolution, write a one- to two-page essay about how you believe it altered the course of human history. 40) Cultural Astronomy. Choose a culture of particular interest to you, and research the astronomical knowledge and accomplishments of that culture. Write a two- to three-page summary of your findings. 41) Astronomical Structures. Choose an ancient astronomical structure of interest to you (e.g., Stonehenge, Templo Mayor, Pawnee lodges), and research its history. Write a two- to three-page summary of your findings. If possible, also build a scale model of the structure or create detailed diagrams to illustrate how the structure was used.

Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 42) Method of Eratosthenes. You are an astronomer on planet Nearth, which orbits a distant star. It has recently been accepted that Nearth is spherical in shape, though no one knows its size. One day, while studying in the library of Alectown, you learn that on the equinox your sun is directly overhead in the city of Nyene, located 1000 km due north of you. On the equinox, you go outside in Alectown and observe that the altitude of your sun is 80°. What is the circumference of Nearth? (Hint: Apply the technique used by Eratosthenes to measure Earth's circumference.) 43) Eris Orbit. The dwarf planet Eris orbits the Sun every 557 years. What is its average distance (semimajor axis) from the Sun? How does its average distance compare to that of Pluto? 44) Halley Orbit. Halley's comet orbits the Sun every 76.0 years and has an orbital eccentricity of 0.97. a. Find its average distance (semimajor axis). b. Halley's perihelion distance is approximately 90 million km. Approximately what is its aphelion distance?

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 4 Making Sense of the Universe Section 4.1 1) Which of the following is an example in which you are traveling at constant speed, but not at constant velocity? A) Rolling freely down a hill in a cart, traveling in a straight line B) Driving backward at exactly 50 km/hr C) Driving around in a circle at exactly 100 km/hr D) Jumping up and down exactly 60 times per minute E) none of the above Answer: C 2) Which of the following correctly states the value and units of the acceleration of gravity on Earth? A) 9.8 m/s2 B) 9.8 m/s C) 9.8 km/s2 D) 9.8 m2/s E) 9.8 km/s Answer: A 3) Momentum is defined as ________. A) mass times speed B) mass times velocity C) force times velocity D) mass times acceleration E) force times acceleration Answer: B 4) If an object's velocity is doubled, its momentum is ________. A) halved B) unchanged C) doubled D) quadrupled E) dependent on its acceleration Answer: C 5) As long as an object is not gaining or losing mass, a net force on the object will cause a change in ________. A) acceleration B) direction C) weight D) speed E) velocity Answer: E 1 Copyright © 2022 Pearson Education, Inc.

6) If your mass is 60 kilograms on Earth, what would your mass be on the Moon? A) 10 pounds B) 10 kilograms C) 360 kilograms D) 60 kilograms E) 60 pounds Answer: D 7) In which of the following cases would you feel weightless? A) while walking on the Moon B) while falling from an airplane with your parachute open C) while traveling through space in an accelerating rocket D) while falling from a roof E) none of the above Answer: D 8) Under what conditions is an object weightless? (Ignore effects of air resistance.) A) when it is in free-fall B) when it is on the Moon C) when it is detached from Earth's surface (such as in an airplane) D) when it is moving in at constant velocity Answer: A 9) Astronauts are weightless inside the International Space Station because ________. A) the station and the astronauts are constantly falling toward Earth. B) the station has rockets that fire to counteract Earth's gravity. C) there is no gravity in space. D) the station is too far from Earth for gravity to be noticeable. Answer: A 10) You are standing on a scale in an elevator and notice that your weight is lower than your normal weight. What do you conclude is occurring? A) The elevator is accelerating upward. B) The elevator is moving at a constant velocity upward. C) The elevator is accelerating downward. D) The elevator is moving at a constant velocity downward. E) Your diet is working. Answer: C 11) Two bowling balls with different masses are dropped from the same height. How do their accelerations compare? A) The heavier bowling ball accelerates faster. B) They both fall with the same acceleration. C) The lighter bowling ball accelerates faster. Answer: B

12) You conduct the following three ball drops, in each case measuring the time it takes for the ball to fall to the ground; the mass is the mass of the ball and the height is the height from which you drop the ball: Ball Drop 1. Mass 0.5 kilograms, height 20 meters Ball Drop 2. Mass 5.0 kilograms, height 20 meters Ball Drop 3. Mass 0.5 kilograms, height 30 meters Which pair of ball-drops will best test whether mass affects the acceleration of gravity? A) Ball drops 2 and 3 B) Ball drops 1 and 3 C) Ball drops 1 and 2 Answer: C 13) How could you test the hypothesis that the acceleration of gravity does not depend on mass? (Ignore effects of air resistance.) A) Drop two objects with the same mass from the same height. B) Drop two objects with the same mass from different heights. C) Drop two objects with different masses from the same height. D) Drop two objects with different masses from different heights. Answer: C 14) Suppose you drop a feather and a hammer on the Moon from the same height at the same time. What will happen? A) The feather will hit the ground first. B) They will hit the ground at the same time. C) The hammer will hit the ground first. D) They will float at the height you release them. Answer: B 15) Suppose you drop a 10-pound weight and a 5-pound weight on the Moon, both from the same height at the same time. What will happen? A) The 10-pound weight will hit the ground before the 5-pound weight. B) Both will hit the ground at the same time. C) Both weights will float freely, since everything is weightless on the Moon. Answer: B 16) If a net force is applied to an object, what is guaranteed to change? A) The object's momentum B) The object's speed C) The object's direction of motion D) The object's mass E) The object's weight Answer: A

17) Which of the following is not a conserved quantity? A) Energy B) Momentum C) Angular momentum D) Radiation Answer: D 18) Radiative energy is ________. A) heat energy B) energy from nuclear power plants C) energy carried by light D) energy used to power home radiators E) energy of motion Answer: C 19) What does temperature measure? A) The average mass of particles in a substance B) The average size of particles in a substance C) The average kinetic energy of particles in a substance D) The total number of particles in a substance E) The total potential energy of particles in a substance Answer: C Section 4.2 1) A basketball player jumps to make a basket and remains in the air for a moment. A sportscaster then remarks that she has "defied gravity." Which of the following accurately describes the situation? A) The player did stay in the air in spite of the Law of Gravitation, but a single counterobservation is not enough to warrant revisiting a theory that usually works. B) The player produced enough force with her legs to accelerate upward and remains above ground only until the acceleration of gravity brought her back down. C) The player can "defy gravity" because the Universal Law of Gravitation makes an exception for basketball players. D) The player has defied gravity, so scientists must go back into the lab to refine their theory. Answer: B 2) Suppose an object is moving in a straight line at 50 miles/hr. According to Newton's first law of motion, the object will ________. A) continue to move in a straight line at 50 miles/hr forever, no matter what happens B) continue to move in a straight line at 50 miles/hr until it is acted upon by a net force C) eventually slow down and come to a stop D) continually slow down, but never quite come to a complete stop Answer: B

3) You observe an object to be moving in a straight line at a constant speed. What can you conclude? (Assume the object does not have any engines or other power source.) A) The net force acting on the object is zero. B) No forces of any kind are acting on the object. C) The only force acting on the object is gravity. D) The only force acting on the object is air resistance. E) Some unseen force must be keeping the object in motion. Answer: A 4) An astronaut in space swings a ball attached to a string in a circular motion. If the string suddenly breaks, how will the ball move? A) It will move in a straight line in whichever direction it was moving when the string broke. B) It will continue to move in the same circular path it had been following before the string broke. C) It will instantly come to a stop. D) It will move toward the astronaut. E) It will move in a large elliptical path around the astronaut. Answer: A 5) Consider Newton's second law states, often written as force = mass × acceleration. Based on this law, what property can you determine if you observe the acceleration of an object with a known mass? A) The net force acting on the object B) The strength of gravity acting on the object C) The current velocity of the object D) The current location of the object Answer: A 6) Consider Newton's second law states, often written as force = mass × acceleration. If a known force is applied to an object with a known mass, what does this law predict for the object's acceleration? A) Acceleration = mass × force B) Acceleration = mass / force C) Acceleration = force / mass D) Newton's second law is irrelevant for solving this problem. Answer: C 7) The idea that we live in a universe (literally, "one story"), in which the same law of gravity applies both on Earth and in space, was established through the work of ________. A) Newton B) Copernicus C) Kepler D) Galileo Answer: A

8) Which person realized the laws of gravity applied to objects both on Earth and in space? A) Newton B) Copernicus C) Kepler D) Galileo Answer: A 9) The Earth exerts a gravitational force on a person standing on the surface. The person also exerts a gravitational force on the Earth. Based on Newton's third law of motion, how do these two forces compare? A) The forces exerted by the Earth and the person are the same. B) The Earth exerts a much stronger force than the person. C) The person exerts a much stronger force than the Earth. D) The Earth exerts a slightly stronger force than the person. E) The person exerts a slightly stronger force than the Earth. Answer: A 10) How does a rocket launch upward? Choose the statement that correctly answers the question. A) By expelling gas downward, the rocket is propelled upward. B) Expelling gas downward, which by pushing against the ground, propels the rocket upward. Answer: A Section 4.3 1) The source of energy that powers the Sun is ________. A) chemical potential energy of hydrogen B) mass energy released by nuclear fusion C) gravitational potential energy of the contraction of the gas cloud that formed the Sun D) kinetic energy of the orbital motion of the Sun E) thermal energy of the hydrogen atoms in the Sun Answer: B 2) Angular momentum depends upon ________. A) mass and velocity B) mass, velocity, and radius C) force and radius D) force, velocity, and radius E) momentum and angular velocity Answer: B

3) Which law explains why a skater can spin faster by pulling his arms closer to his body, or spin slower by spreading his arms out? A) The law of gravity B) Newton's third law of motion C) The law of conservation of momentum D) The law of conservation of angular momentum E) The law of conservation of energy Answer: D 4) Suppose the Sun were to suddenly shrink in size but its mass remained the same. According to the law of conservation of angular momentum, what would happen? A) The Sun's angular size in our sky would increase. B) The Sun's rate of rotation would slow. C) The Sun's rate of rotation would remain the same. D) The Sun rate of rotation would increase. Answer: D 5) Which of the following is the standard international unit for measuring energy? A) Kelvin B) Joule C) Watt D) Newton E) Meter Answer: B 6) Gasoline can be used to power cars because it has ________. A) gravitational potential energy B) chemical potential energy C) electrical potential energy D) kinetic energy E) radiative energy Answer: B 7) Which of the following has the most kinetic energy? A) A 4-ton truck moving 20 km/hr B) A 3-ton truck moving 30 km/hr C) A 2-ton truck moving 40 km/hr D) A 1-ton truck moving 50 km/hr E) A, B, C, and D all have the same kinetic energy. Answer: C 8) Which of the following represents the smallest range of temperatures? A) 50-100° Kelvin B) 50-100° Celsius C) 50-100° Fahrenheit D) They all represent the same range in temperature. Answer: C 7 Copyright © 2022 Pearson Education, Inc.

9) On a hot day, molecules of air ________ than on a cold day. A) move faster on average B) move slower on average C) are more massive D) are less massive E) contain more atoms Answer: A 10) The amount of gravitational potential energy released as an object falls depends on ________. A) its mass, the distance it falls, and the acceleration of gravity B) its mass and its speed at the time it begins falling C) its mass and its speed when it hits the ground D) only its mass and the acceleration of gravity E) only the acceleration of gravity Answer: A 11) In the formula E = mc2, what does E represent? A) The kinetic energy of a moving object B) The radiative energy carried by light C) The gravitational potential energy of an object held above the ground D) The mass-energy or potential energy stored in an object's mass E) The electric charge of the object Answer: D 12) According to Einstein's equation, E = mc2, which of the following statements is true? A) Mass can be turned into energy, but energy cannot be turned back into mass. B) It takes a large amount of mass to produce a small amount of energy. C) A small amount of mass can be turned into a large amount of energy. D) Mass can be turned into energy if it is accelerated to the speed of light. E) One kilogram of mass represents 1 joule of energy. Answer: C 13) Which of the following statements correctly describes the law of conservation of energy? A) An object always has the same amount of energy. B) Energy can change between many different forms, such as potential, kinetic, and thermal, but it is ultimately destroyed. C) Energy can change between many different forms, such as potential, kinetic, and thermal, but the total quantity of energy in the universe never changes. D) The fact that you can fuse hydrogen into helium to produce energy means that helium can be turned into hydrogen to produce energy. E) It is not really possible for an object to gain or lose potential energy because energy cannot be destroyed. Answer: C

14) Where does your body get the energy it uses to make your heart beat? A) It comes from the radiative energy of the sunlight that hits your skin. B) It comes from the chemical potential energy of the food you eat. C) It comes from the thermal energy of the water you drink. D) It comes from the kinetic energy of the molecules in the air that you breathe in. E) It is created by your brain during the time that you rest or sleep. Answer: B 15) Based on fundamental laws of motion and gravity, which of the following best explains why Kepler's second law (planets move faster in the parts of their orbit that are closer to the Sun and slower when they are farther from the Sun) is true? A) A planet's angular momentum must be conserved as it moves around its orbit. B) The speed of a planet at any point in its orbit depends on its temperature, which varies with distance from the Sun. C) The strength of gravity is inversely proportional to the square of the distance between two objects. D) The gravitational influence of other planets determines the speed of any particular planet's orbit. Answer: A 16) As an interstellar gas cloud shrinks in size, the law of conservation of angular momentum predicts it will ________. A) heat up B) slow down in its rotation C) cool off D) continue shrinking E) rotate faster Answer: E 17) How does a comet's orbital angular momentum vary over its orbit? A) Its angular momentum is greatest when the comet is closest to the Sun. B) Its angular momentum is greatest when the comet is farthest away from the Sun. C) Its angular momentum is the same throughout its orbit. Answer: C 18) When is a comet's orbital speed at its maximum? A) When it is closest to the Sun B) When it is farthest from the Sun C) Its orbital speed does not change. Answer: A 19) If a spinning star gets larger in diameter, what happens to its rotation rate? A) It increases. B) It will not change. C) It decreases. Answer: C 9 Copyright © 2022 Pearson Education, Inc.

20) When a rock is held above the ground, we say it has some gravitational potential energy. When we let it go, it falls and we say the gravitational potential energy is converted to kinetic energy. Finally, the rock hits the ground (and stays there). What has happened to the energy? A) The rock keeps the energy inside it in the form of mass-energy. B) The energy goes into the ground and, as a result, the orbit of Earth about the Sun is slightly changed. C) It is transformed back into gravitational potential energy. D) The energy goes to producing sound and to heating the ground, rock, and surrounding air. Answer: D Section 4.4 1) The orbital period of a geosynchronous satellite is ________. A) the same as Earth's precise rotation period B) the same as the Moon's precise orbital period around Earth C) the same as Earth's orbital period around the Sun D) about 12 years E) about 26,000 years Answer: A 2) Newton's version of Kepler's third law states: p2 =

× a3

In this equation, what does a represent? A) The orbital period B) The average distance between the two objects C) The masses of the two objects D) The universal gravitational constant Answer: B 3) Newton's version of Kepler's third law states: p2 = In this equation, what does G represent? A) The orbital period B) The average distance between the two objects C) The masses of the two objects D) The universal gravitational constant Answer: D

× a3

4) Newton's version of Kepler's third law states: p2 =

× a3

According to this, what observational information does one need in order to calculate the combined mass of a planet and its moon? A) The orbital period and the density of the two objects B) The average distance between the two objects and the orbital period C) The radius of the two planets in meters and the average distance between them D) It is impossible to determine the mass of any astronomical object. Answer: B 5) Newton's version of Kepler's third law states: p2 =

× a3

Solve this equation to find the combined mass of a planet and its satellite, given the orbital period and average separation. A) M1 + M2 = 4Gπ2 × B) M1 + M2 =

C) M1 + M2 =

D) M1 + M2 =

Answer: D 6) Suppose that Earth rotated once every 48 hours (instead of 24 hours), but Earth's orbit and the Moon's distance were still the same (and their masses were still the same). Which of the following statements would be true? A) Along coastlines, the time between one high tide and the next would be longer. B) The length of the year would be longer. C) Along coastlines, the time between one high tide and the next would be shorter. D) The Moon's orbital period would be longer. E) There would be more days in each year. Answer: A

7) Consider the following three hypothetical planets orbiting a star with the same mass as the Sun (one solar mass): Planet X: one Earth mass and 1 AU from the star Planet Y: two Earth masses and 1 AU from the star Planet Z: two Earth masses and 2 AU from the star The shortest orbital period belongs to (Ignore very small differences in orbital period that might be attributed to the planet masses alone.) A) Planet X alone B) Planet Y alone C) Planet Z alone D) Planets X and Y, which have about the same orbital period E) Planets Y and Z, which have about the same orbital period F) all three planets, since they all have about the same orbital period Answer: D 8) Consider a star with 2 identical planets, both with nearly circular orbits, except the orbit of Planet A is closer to the star than the orbit of Planet B. Which of the following statements is true? A) Planet A is moving slower than Planet B. B) Planet A moves with the same speed as Planet B. C) Planet A is moving faster than Planet B. Answer: C 9) How does a rocket take off? A) Its rocket engines push against the launch pad, propelling the rocket upward. B) It converts mass-energy to kinetic energy. C) It achieves lift from its wings in the same way that airplanes do. D) Hot gas shoots out from the back of the rocket and, by conservation of momentum, the rocket moves in the opposite direction. E) The hot rocket exhaust expands the air beneath the rocket, propelling it forward. Answer: D 10) A comet has an elliptical orbit around the Sun. Its total orbital energy is ________. A) greatest when it is farthest from the Sun B) greatest when it is closest to the Sun C) the same throughout its orbit Answer: C 11) According to the universal law of gravitation, the force due to gravity is ________. A) directly proportional to the square of the distance between objects B) inversely proportional to the square of the distance between objects C) directly proportional to the distance between objects D) inversely proportional to the distance between objects E) not dependent on the distance between objects Answer: B

12) According to the universal law of gravitation, if the masses of both attracting objects double, then the gravitational force between them will ________. A) not change at all B) increase by a factor of 2 C) decrease by a factor of 2 D) increase by a factor of 4 E) decrease by a factor of 4 Answer: D 13) Which orbital shapes are possible under the force of gravity? A) Ellipses only B) Ellipses and spirals C) Ellipses, parabolas, and hyperbolas D) Ellipses, spirals, and parabolas E) Spirals, circles, and squares Answer: C 14) Which of the following shapes is not an allowed trajectory of an object orbiting a star? (Assume no gas or dust is affecting the object's orbit.) A) A hyperbola B) A parabola C) A spiral D) An ellipse Answer: C 15) Where is the center of mass of a binary system consisting of two stars with different masses? A) The center of the more massive star B) The center of the less massive star C) The point halfway in between the two stars D) A point between the two stars that is closer to the more massive star E) A point between the two stars that is closer to the less massive star Answer: D 16) What information is needed to calculate the mass of Jupiter? A) The orbital period and distance of Jupiter's orbit around the Sun B) The orbital period and distance of one of Jupiter's moons C) The orbital speed of one of Jupiter's moons D) The Sun's mass and how Jupiter's speed changes during its elliptical orbit around the Sun E) The Sun's mass and the average distance of Jupiter from the Sun Answer: B

17) Gravity follows an inverse square law. This means that if the distance between two masses is decreased by a factor of 4, the gravitational force between those two masses ________. A) increases by a factor of 16 B) increases by a factor of 4 C) increases by a factor of 2 D) decreases by a factor of 4 E) decreases by a factor of 16 Answer: A 18) The gravitational force between two objects can be described using the equation Fg = G M1 M2 / d2. In this equation, what does d represent? A) The universal gravitational constant B) The density of the smaller object C) The distance between the two objects D) The diameter of the larger object Answer: C 19) The gravitational force between two objects can be described using the equation Fg = G M1 M2 / d2. In this equation, what does G represent? A) The universal gravitational constant B) The density of the smaller object C) The distance between the two objects D) The gravitational mass of the larger object Answer: A 20) The gravitational force between two objects can be described using the equation Fg = G M1 M2 / d2. According to this equation, if the distance between two objects increases, what happens to the gravitational force between them? A) The force increases. B) The force decreases. C) The force drops instantly to zero. D) The gravitational force is not affected by distance. Answer: B 21) Imagine we've discovered a planet orbiting another star at an average distance of 1 AU with an orbital period of 6 months. The planet has a moon that orbits the planet at the same distance as our Moon, but it takes 2 months to complete an orbit. What can we infer about this planet? A) It is more massive than Earth. B) It is less massive than Earth. C) It has the same mass as Earth. D) We cannot answer the question without knowing the mass of the star. E) We cannot answer the question without knowing the mass of the moon. Answer: B

22) A planet is orbiting a star. Which of the following statements is true for the acceleration and gravitational forces in this situation? A) The acceleration of the planet is much more than the acceleration of the star, and the gravitational force on the planet is much more than the gravitational force on the star. B) The acceleration of the planet is much more than the acceleration of the star, but the gravitational force on the star is the same but opposite the gravitational force on the planet. C) The gravitational force on the star is much smaller than the gravitational force on the planet, but the accelerations are equal and opposite. Answer: B 23) If the Sun instantaneously shrunk dramatically in size but retained the same mass, what would happen to the Earth? A) Earth's orbit would be unchanged. B) Earth would gradually spiral into the shrunken Sun. C) Earth would be ejected from the solar system. D) Earth would be rapidly sucked into the shrunken Sun. Answer: A 24) If we found a solar system where the central star's mass was double that of the Sun, what would be the period a planet orbiting 1 AU from the central star? A) More than a year B) Less than a year C) About a year D) Impossible to say, since we need to know the mass of the planet to predict its period Answer: B 25) What would happen if a rocket were launched into space with a speed greater than Earth's escape velocity? A) It would travel away from Earth into the solar system. B) It would fall back to the Earth. C) It would enter into orbit around the Earth. D) It would reach the orbit of the Moon, but could go no farther. E) It is not possible to reach speeds that high. Answer: A 26) Which of the following best describes why Earth has tides? A) Earth gets stretched out because the gravitational force from the Moon is stronger on parts of the Earth that are nearer to the Moon. B) Earth gets stretched out because the Moon pulls from one side, while the Sun pulls from the other. C) Earth's sea level changes constantly because of rainfall. D) Earth bulges near its equator because it is spinning. E) Air pressure from the atmosphere pushes on the surface of the ocean. Answer: A

27) At which lunar phase(s) are tides most pronounced (e.g., the highest high tides)? A) First quarter B) New Moon C) Full Moon D) Both new and full Moons E) Both first and third quarters Answer: B 28) At which lunar phase(s) are tides least pronounced (e.g., the lowest high tides)? A) First quarter B) New Moon C) Full Moon D) Both new and full Moons E) Both first and third quarters Answer: E 29) The escape velocity for a 100-kg object on Earth is about 11 km/s. What is the escape velocity of a 50-kg object on the surface of Earth? A) 11 km/s B) 22 km/s C) 5.5 km/s D) 44 km/s E) 2.75 km/s Answer: A 30) Which of the following caused the Moon to show (nearly) the same face to the Earth at all times? A) Tidal friction B) Spring tides C) Conservation of energy D) Atmospheric drag E) Gravitational encounters Answer: A Short Answer Question 1) You are alone in space and your tether brakes and you are floating motionless relative to your spaceship, which is located a frustrating 10 meters away. Your spacesuit has no jet pack and you have no air to spare. All you have is your wrench. How can you return to your ship? Answer: Throw the wrench in the opposite direction (utilizing the conservation of momentum). With a 1-lb (2.2 kg) wrench and a 30-mph (13 m/s) throw, you'll be back in a minute.

Reading Quiz Questions 1) Which of the following describes a velocity (as opposed to a speed)? A) 20 kilometers per hour, headed north B) 300,000 kilometers per second C) 9.8 meters per second squared (m/s2) D) 15 newtons E) 5 light-years Answer: A 2) The acceleration of gravity on Earth is approximately 10 m/s2 (more precisely, 9.8 m/s2). If you drop a rock from a tall building, about how fast will it be falling after 3 seconds? A) 30 m/s B) 10 m/s C) 30 m/s2 D) 10 m/s2 E) 20 m/s Answer: A 3) Momentum is defined as ________. A) mass multiplied by velocity B) mass multiplied by speed C) force multiplied by velocity D) mass multiplied by acceleration Answer: A 4) Which of the following examples describes a situation where a car is experiencing a net force? A) The car is holding constant speed around a curve. B) The car is holding constant speed down a straight hill because the driver is applying the brakes. C) The car is moving at constant speed in a straight line. D) The car is stopped on a hill. Answer: A 5) Suppose you lived on the Moon. Which of the following would be true? A) Your weight would be less than your weight on Earth, but your mass would be the same as it is on Earth. B) Both your weight and your mass would be less than they are on Earth. C) Your mass would be less than your mass on Earth, but your weight would be the same as it is on Earth. D) Both your weight and your mass would be the same as they are on Earth. Answer: A

6) In which of the following cases would you feel weightless? A) While falling from a roof B) While parachuting from an airplane C) While accelerating downward in an elevator D) While walking on the Moon Answer: A 7) Which of the following statements is not one of Newton's Laws of Motion? A) What goes up must come down. B) The rate of change of momentum of an object is equal to the net force applied to the object. C) In the absence of a net force acting on it, an object moves with constant velocity. D) For any force, there always is an equal and opposite reaction force. Answer: A 8) Newton's Second Law of Motion tells us that the net force applied to an object equals its ________. A) mass multiplied by acceleration B) mass multiplied by energy C) momentum multiplied by velocity D) mass multiplied by velocity Answer: A 9) Suppose that two objects collide. Which of the following things is not necessarily the same both before and after the collision? (In other words, which quantity is not conserved according to the laws of physics?) A) The total temperature of the objects B) The total momentum of the objects C) The total angular momentum of the objects D) The total energy of the objects Answer: A 10) When a spinning ice skater pulls in his arms, he spins faster because ________. A) his angular momentum must be conserved, so reducing his radius must increase his speed of rotation B) there is less friction with the air C) there is less friction with the ice D) there exists an unbalanced reaction force Answer: A 11) The energy attributed to an object by virtue of its motion is known as ________. A) kinetic energy B) potential energy C) radiative energy D) mass-energy Answer: A

12) Radiative energy is ________. A) energy carried by light B) heat energy C) energy from nuclear power plants D) energy of motion Answer: A 13) Absolute zero is ________. A) 0 Kelvin B) 0º Celsius C) 0° Fahrenheit D) 100º Celsius Answer: A 14) What does temperature measure? A) The average kinetic energy of particles in a substance B) The average mass of particles in a substance C) The total potential energy of particles in a substance D) The total amount of heat in a substance Answer: A 15) In the formula E = mc2, what does E represent? A) The mass-energy, or potential energy stored in an object's mass B) The kinetic energy of a moving object C) The radiative energy carried by light D) The gravitational potential energy of an object held above the ground E) The electric field produced by a charge Answer: A 16) According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them ________. A) decreases by a factor of 9 B) increases by a factor of 9 C) decreases by a factor of 3 D) increases by a factor of 3 Answer: A 17) What is the difference between a bound orbit and an unbound orbit around the Sun? A) An object on a bound orbit follows the same path around the Sun over and over, while an object on an unbound orbit approaches the Sun just once and then never returns. B) A bound orbit is an orbit allowed by the universal law of gravitation, and an unbound orbit is not. C) An object on a bound orbit has a gravitational attraction to the Sun, while an object on an unbound orbit does not. D) A bound orbit is circular, while an unbound orbit is elliptical. Answer: A 19 Copyright © 2022 Pearson Education, Inc.

18) Why is Newton's version of Kepler's third law so useful to astronomers? A) It can be used to determine the masses of many distant objects. B) It allows us to calculate distances to distant objects. C) It tells us that more-distant planets orbit the Sun more slowly. D) It explains why objects spin faster when they shrink in size. Answer: A 19) What do we mean by the orbital energy of an orbiting object (such as a planet, moon, or satellite)? A) Orbital energy is the sum of the object's kinetic energy and its gravitational potential energy as it moves through its orbit. B) Orbital energy is the object's kinetic energy as it moves through its orbit. C) Orbital energy is a measure of the object's speed as it moves through its orbit. D) Orbital energy is the amount of energy required for the object to leave orbit and escape into space. Answer: A 20) Which statement must be true for a rocket to travel from Earth to another planet? A) It must attain escape velocity from Earth. B) It must carry a lot of extra fuel. C) It must have large engines. D) It must be launched from space, rather than from the ground. Answer: A 21) Approximately where is it currently high tide on Earth? A) On the portion of Earth facing directly toward the Moon and on the portion of Earth facing directly away from the Moon B) Only on the portion of the Earth facing directly toward the Moon C) Wherever it is currently noon D) Anywhere that ocean water laps up on the shore Answer: A

Concept Quiz Questions 1) Which of the following represents a case in which you are not accelerating? A) Driving in a straight line at 100 kilometers per hour B) Going from 0 to 100 kilometers per hour in 10 seconds C) Slamming on the brakes to come to a stop at a stop sign D) Driving 100 kilometers per hour around a curve Answer: A 2) Suppose you drop a 10-pound weight and a 5-pound weight on the Moon, both from the same height at the same time. What will happen? A) Both will hit the ground at the same time. B) The 10-pound weight will hit the ground before the 5-pound weight. C) The 5-pound weight will hit the ground before the 10-pound weight. D) Both weights will float freely because everything is weightless on the Moon. Answer: A 3) Why are astronauts weightless in the Space Station? A) Because the Space Station is constantly in free-fall around the Earth B) Because the Space Station is traveling so fast C) Because there is no gravity in space D) Because the Space Station is moving at constant velocity Answer: A 4) A net force acting on an object will always cause a change in the object's ________. A) momentum B) speed C) mass D) direction Answer: A 5) Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground? A) It is the same. B) It is greater. C) It is less. D) You are weightless. Answer: A 6) The planets never travel in a straight line as they orbit the Sun. According to Newton's second law of motion, this must mean that ________. A) a force is acting on the planets B) the planets are always accelerating C) the planets have angular momentum D) the planets will eventually fall into the Sun Answer: A 21 Copyright © 2022 Pearson Education, Inc.

7) Suppose the Sun were suddenly to shrink in size but that its mass remained the same. According to the law of conservation of angular momentum, what would happen? A) The Sun would rotate faster than it does now. B) The Sun's rate of rotation would slow. C) The Sun's angular size in our sky would stay the same. D) This could never happen because it is impossible for an object to shrink in size without an outside torque. Answer: A 8) Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight? A) The ball's gravitational potential energy is greatest at the instant when the ball is at its highest point. B) The ball's gravitational potential energy is greatest at the instant it returns to hit the ground. C) The ball's gravitational potential energy is always the same. D) The ball's gravitational potential energy is greatest at the instant the ball leaves your foot. Answer: A 9) Suppose you heat an oven to 400°F (about 200°C) and boil a pot of water. Which of the following explains why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven? A) The water can transfer heat to your arm more quickly than the air. B) The water has a higher temperature than the oven. C) The molecules in the water are moving faster than the molecules in the oven. D) The oven has a higher temperature than the water. Answer: A 10) Which of the following scenarios involves energy that we would typically calculate with Einstein's formula E = mc2? A) A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium. B) An object accelerated to a great speed has a lot of kinetic energy. C) A mass raised to a great height has a lot of gravitational potential energy. D) A burning piece of wood produces light and heat, therefore giving off radiative and thermal energy. Answer: A 11) A rock held above the ground has potential energy. As the rock falls, this potential energy is converted to kinetic energy. Finally, the rock hits the ground and stays there. What has happened to the energy? A) The energy goes to producing sound and to heating the ground, rock, and surrounding air. B) The energy goes into the ground, and as a result, the orbit of the Earth about the Sun is slightly changed. C) The rock keeps the energy inside it in the form of mass-energy. D) It is transformed back into gravitational potential energy. Answer: A 22 Copyright © 2022 Pearson Education, Inc.

12) Suppose that the Sun shrank in size but that its mass remained the same. What would happen to the orbit of the Earth? A) Earth's orbit would be unaffected. B) The size of Earth's orbit would shrink, and it would take less than one year to orbit the Sun. C) Earth's orbit would expand, and it would take more than one year to orbit the Sun. D) Earth would change from a bound orbit to an unbound orbit and fly off into interstellar space. Answer: A 13) Imagine another solar system, with a star of the same mass as the Sun. Suppose a planet with a mass twice that of Earth (2MEarth) orbits at a distance of 1 AU from the star. What is the orbital period of this planet? A) 1 year B) 6 months C) 2 years D) It cannot be determined from the information given. Answer: A 14) Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet's year (orbital period) compare to Earth's year? A) The planet's year would be shorter than Earth's. B) The planet's year would be longer than Earth's. C) The planet's year would be the same as Earth's. D) An orbit at a distance of 1 AU would not be possible around a star more massive than the Sun. Answer: A 15) Newton showed that Kepler's laws are ________. A) natural consequences of the law of universal gravitation B) seriously in error C) actually only three of seven distinct laws of planetary motion D) the key to proving that Earth orbits our Sun Answer: A 16) Each of the following lists two facts. Which pair of facts can be used with Newton's version of Kepler's third law to determine the mass of the Sun? A) Earth is 150 million km from the Sun and orbits the Sun in one year. B) Mercury is 0.387 AU from the Sun and Earth is 1 AU from the Sun. C) The mass of Earth is 6 × 1024 kg and Earth orbits the Sun in one year. D) Earth rotates in one day and orbits the Sun in one year. Answer: A

17) When space probe Voyager 2 passed by Saturn, its speed increased (but not due to firing its engines). What must have happened? A) Saturn must have lost a tiny bit of its orbital energy. B) Voyager 2 must have dipped through Saturn's atmosphere. C) Saturn's rotation must have sped up slightly. D) Saturn must have captured an asteroid at precisely the moment that Voyager 2 passed by. Answer: A 18) Suppose that a lone asteroid happens to be passing Jupiter on an unbound orbit (well above Jupiter's atmosphere and far from all of Jupiter's moons.) Which of the following statements would be true? A) The asteroid's orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on. B) Jupiter's gravity would capture the asteroid, making it a new moon of Jupiter. C) Jupiter's gravity would suck in the asteroid, causing it to crash into Jupiter. D) There is no way to predict what would happen. Answer: A 19) Which of the following best describes the origin of ocean tides on Earth? A) Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth. B) The Moon's gravity pulls harder on water than on land because water is less dense than rock. C) Tides are caused by the 23.5-degree tilt of the Earth's rotational axis to the ecliptic plane. D) Tides are caused on the side of the Earth nearest the Moon because the Moon's gravity attracts the water. Answer: A 20) At which lunar phase(s) are tides most pronounced (for example, the highest high tides)? A) Both new and full moons B) Both first and third quarters C) Full moon only D) New moon only E) Third-quarter moon only Answer: A 21) Which of the following best explains why the Moon's orbital period and rotation period are the same? A) The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period. B) The Moon was once closer to Earth, but the force of gravity got weaker as the Moon moved farther away. C) The law of conservation of angular momentum ensured that the Moon must have the same amount of rotational angular momentum as it has of orbital angular momentum. D) The equality of the Moon's orbital and rotation periods is an extraordinary astronomical coincidence. Answer: A 24 Copyright © 2022 Pearson Education, Inc.

Visual Quiz Questions 1) Which person is weightless during the activity shown? A)

Answer: A

2) Which of the following statements about the force attracting these two galaxies is true?

A) It is the same force that causes an apple to fall to the ground. B) It is a force unlike any force that we ever experience on Earth. C) It is a mysterious force, whose nature remains completely unknown to scientists. D) The force will get weaker as time passes. Answer: A

3) The diagram shows a planet at four positions in its orbit. At which position does it have the greatest angular momentum? A) 1 B) 2 C) 3 D) 4 E) The angular momentum is the same at all four points. Answer: E 4) The diagram shows a planet at four positions in its orbit. At which position does it have the greatest gravitational potential energy? A) 1 B) 2 C) 3 D) 4 E) The gravitational potential energy is the same at all four positions. Answer: C

5) The diagram shows a planet at four positions in its orbit. At which position does it have the greatest total orbital energy? (Orbital energy is the sum of the planet's kinetic and gravitational potential energy.) A) 1 B) 2 C) 3 D) 4 E) The total orbital energy is the same at all four positions. Answer: E 6) Which of the paths shown represent unbound orbits?

A) 1 only B) 2 only C) 3 only D) Both 2 and 3 E) There is no such thing as an unbound orbit. Answer: D

7) Suppose you are aboard a rocket that is orbiting Earth in the low, circular orbit shown. If you want to escape from Earth and head to the Moon or Mars along the "escape" path shown, what do you need to do?

A) Fire the rocket engine in your direction of travel, so that you gain speed. B) The only way to end up on the "escape" path is to first return to Earth, then launch your rocket with escape velocity. C) Turn the rocket around, and fire the engine so that you lose speed. D) Throw some excess supplies overboard, so that your rocket becomes less massive. Answer: A

8) Which of the following correctly shows tidal bulges on Earth when the Moon is in the position shown? A)

Answer: A

9) In which position(s) of the Moon do we experience the highest high tides? A) 1 B) 2 C) 3 D) 4 E) 1 and 3 F) 2 and 4 Answer: E 10) In which position(s) of the Moon do we experience the lowest low tides? A) 1 B) 2 C) 3 D) 4 E) 1 and 3 F) 2 and 4 Answer: E

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

The figure above, based on Figure 4.19, shows how the Moon causes tides on Earth. Note that the North Pole is in the center of the diagram, so the numbers 1 through 4 label points along Earth's equator. 1) What do the three black arrows represent? A) The tidal force Earth exerts on the Moon B) The Moon's gravitational force at different points on Earth C) The direction in which Earth's water is flowing D) Earth's orbital motion Answer: B 2) Where is it high tide? A) point 1 only B) point 2 only C) points 1 and 3 D) points 2 and 4 Answer: C 3) Where is it low tide? A) point 1 only B) point 2 only C) points 1 and 3 D) points 2 and 4 Answer: D

4) What time is it at point 1? A) Noon B) Midnight C) 6 a.m. D) Cannot be determined from the information in the figure Answer: D 5) The light blue ellipse represents tidal bulges. In what way are these bulges drawn inaccurately? A) There should be only one bulge rather than two. B) They should be aligned with the Sun rather than the Moon. C) They should be much smaller compared to Earth. D) They should be more pointy in shape. Answer: C Chapter Review Questions 1) Define speed, velocity, and acceleration. What are the units of acceleration? What is the acceleration of gravity? 2) Define momentum and force. What do we mean when we say that momentum can be changed only by a net force? 3) What is free-fall, and why does it make you weightless? Briefly describe why astronauts are weightless in the International Space Station. 4) State Newton's three laws of motion. For each law, give an example of its application. 5) Describe the laws of conservation of angular momentum and conservation of energy. Give an example of how each is important in astronomy. 6) Define kinetic energy, radiative energy, and potential energy, with at least two examples for each. 7) Define and distinguish temperature and thermal energy. 8) What is mass-energy? Explain the formula E = mc2. 9) Summarize the universal law of gravitation both in words and with an equation. 10) What is the difference between a bound and an unbound orbit? 11) Under what conditions can we use Newton's version of Kepler's third law to calculate an object's mass, and what quantities must we measure in order to complete the calculation? 12) Explain why orbits cannot change spontaneously, and how a gravitational encounter can cause a change. How can an object achieve escape velocity? 32 Copyright © 2022 Pearson Education, Inc.

13) Explain how the Moon creates tides on Earth. Why do we have two high and low tides each day? 14) How do the tides vary with the phase of the Moon? Why? Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 15) I've never been to space, so I've never experienced weightlessness. 16) Suppose you could enter a vacuum chamber (a chamber with no air in it) on Earth. Inside this chamber, a feather would fall at the same rate as a rock. 17) If an astronaut goes on a space walk outside the Space Station, she will quickly float away from the station unless she has a tether holding her to the station. 18) I used Newton's version of Kepler's third law to calculate Saturn's mass from orbital characteristics of its moon Titan. 19) If the Sun were magically replaced with a giant rock that had precisely the same mass, Earth's orbit would not change. 20) The fact that the Moon rotates once in precisely the time it takes to orbit Earth once is such an astonishing coincidence that scientists probably never will be able to explain it. 21) Venus has no oceans, so it could not have tides even if it had a moon (which it doesn't). 22) If an asteroid passed by Earth at just the right distance, Earth's gravity would capture it and make it our second moon. 23) When I drive my car at 30 miles per hour, it has more kinetic energy than it does at 10 miles per hour. 24) Someday soon, scientists are likely to build an engine that produces more energy than it consumes.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 4 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 25) A car is accelerating when it is ________. A) traveling on a straight, flat road at 50 miles per hour B) traveling on a straight uphill road at 30 miles per hour C) going around a circular track at a steady 100 miles per hour Answer: No Correct Answer Was Provided. 26) Compared to their values on Earth, on another planet your ________. A) mass and weight would both be the same B) mass would be the same but your weight would be different C) weight would be the same but your mass would be different Answer: No Correct Answer Was Provided. 27) Which person is weightless? A) A child in the air as she plays on a trampoline B) A scuba diver exploring a deep-sea wreck C) An astronaut on the Moon Answer: No Correct Answer Was Provided. 28) Consider the statement "There's no gravity in space." This statement is ________. A) completely false B) false if you are close to a planet or moon, but true in between the planets C) completely true Answer: No Correct Answer Was Provided. 29) To make a rocket turn left, you need to ________. A) fire an engine that shoots out gas to the left B) fire an engine that shoots out gas to the right C) spin the rocket clockwise Answer: No Correct Answer Was Provided. 30) Compared to its angular momentum when it is farthest from the Sun, Earth's angular momentum when it is nearest to the Sun is ________. A) greater B) less C) the same Answer: No Correct Answer Was Provided. 31) The gravitational potential energy of a contracting interstellar cloud ________. A) stays the same at all times B) gradually transforms into other forms of energy C) gradually grows larger Answer: No Correct Answer Was Provided. 34 Copyright © 2022 Pearson Education, Inc.

32) If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be ________. A) twice as strong B) half as strong C) one-quarter as strong Answer: No Correct Answer Was Provided. 33) According to the law of universal gravitation, what would happen to Earth if the Sun were somehow replaced by a black hole of the same mass? A) Earth would be quickly sucked into the black hole. B) Earth would slowly spiral into the black hole. C) Earth's orbit would not change. Answer: No Correct Answer Was Provided. 34) If the Moon were closer to Earth, high tides would ________. A) be higher than they are now B) be lower than they are now C) occur three or more times a day rather than twice a day Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 35) The Dual Power of Knowledge. Einstein's discovery that energy and mass are equivalent has led to technological developments that are both beneficial and dangerous. List as many of these developments as you can, categorizing them as positive, negative, or neutral. Overall, do you think the human race would be better or worse off if we had never discovered that mass is a form of energy? Defend your opinion. 36) Group Discussion: Hidden Figures. The 2017 movie Hidden Figures (inspired by the 2016 book by Margot Lee Shetterly) popularized the contributions of Katherine Johnson, Dorothy Vaughan, and Mary Jackson to America's space program. a. Form groups of three students. Within your group, decide who will research each of the three "hidden figures" listed above, learning about her scientific specialty, how this specialty relates to human understanding of the laws of motion and gravity, and how her work contributed to putting astronauts in space. b. After completing your individual research, report to the other members of your group on what you have learned. c. Discuss: In what sense were these individuals pioneers? Is there more than one way in which they can be considered pioneers?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 37) Testing Gravity. Scientists are constantly trying to learn whether our current understanding of gravity is complete or must be modified. Describe how the observed motion of spacecraft headed out of the solar system (such as the Voyager spacecraft) can be used to test the accuracy of our current theory of gravity. 38) How Does the Table Know? Thinking deeply about seemingly simple observations sometimes reveals underlying truths that we might otherwise miss. For example, think about holding a golf ball in one hand and a bowling ball in the other. To keep them motionless, you must actively adjust the tension in your arm muscles so that each arm exerts a different upward force that exactly balances the weight of each ball. Now, think about what happens when you set the balls on a table. Somehow, the table exerts exactly the right amount of upward force to keep the balls motionless, even though their weights are very different. How does a table "know" to make the same type of adjustment that you make consciously when you hold the balls motionless in your hands? (Hint: Think about the origin of the force pushing upward on the objects.) 39) Perpetual Motion Machines. Every so often, someone claims to have built a machine that can generate energy perpetually from nothing. Why isn't this possible according to the known laws of nature? Why do you think claims of perpetual motion machines sometimes receive substantial media attention? 40) Group Activity: Your Ultimate Energy Source. Work as a group to answer each part.Note: You may wish to do this activity using the same four roles described in Chapter 1, Exercise 39. a. According to the law of conservation of energy, the energy your body is using right now had to come from somewhere else. Work in groups to make a list going backwards in time describing how the energy you are using right now has proceeded through time. b. For each item on the group's list, identify the energy as kinetic energy, gravitational potential energy, chemical potential energy, electrical potential energy, mass-energy, or radiative energy. Investigate Further 41) Weightlessness. Astronauts are weightless when in orbit in the Space Station. Are they also weightless during launch to the station? How about during their return to Earth? Explain. 42) Einstein's Famous Formula. a. What is the meaning of the formula E = mc2? Define each variable. b. How does this formula explain the generation of energy by the Sun? c. How does this formula explain the destructive power of nuclear bombs?

43) The Gravitational Law. a. How does quadrupling the distance between two objects affect the gravitational force between them? b. Suppose the Sun were somehow replaced by a star with twice as much mass. What would happen to the gravitational force between Earth and the Sun? c. Suppose Earth were moved to one-third of its current distance from the Sun. What would happen to the gravitational force between Earth and the Sun? 44) Allowable Orbits? a. Suppose the Sun were replaced by a star with twice as much mass. Could Earth's orbit stay the same? Why or why not? b. Suppose Earth doubled in mass (but the Sun stayed the same as it is now). Could Earth's orbit stay the same? Why or why not? 45) Head-to-Foot Tides. You and Earth attract each other gravitationally, so you should also be subject to a tidal force resulting from the difference between the gravitational attraction felt by your feet and that felt by your head (at least when you are standing). Explain why you can't feel this tidal force. 46) Space Elevator. Some people have proposed using a "space elevator" to reach orbit high above Earth. Learn about the concept and write a short report on how it works, what advantages it would have over rockets, and whether it is feasible. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 47) Energy Comparisons. Use the data in Table 4.1 to answer each of the following questions. a. Compare the energy of a 1-megaton H-bomb to the energy released by a major earthquake. b. If the United States obtained all its energy from oil, how much oil would be needed each year? c. Compare the Sun's annual energy output to the energy released by a supernova. 48) Fusion Power. No one has yet succeeded in creating a commercially viable way to produce energy through nuclear fusion. However, suppose we could build fusion power plants using the hydrogen in water as a fuel. Based on the data in Table 4.1, how much water would we need each minute to meet U.S. energy needs? Could such a reactor power the entire United States with the water flowing from your kitchen sink? Explain. (Hint: Use the annual U.S. energy consumption to find the energy consumption per minute, and then divide by the energy yield from fusing 1 liter of water to figure out how many liters would be needed each minute.)

49) Understanding Newton's Version of Kepler's Third Law. Find the orbital period for the planet in each case. (Hint: The calculations for this problem are so simple that you will not need a calculator.) a. A planet with twice Earth's mass orbiting at a distance of 1 AU from a star with the same mass as the Sun. b. A planet with the same mass as Earth orbiting at a distance of 1 AU from a star with four times the Sun's mass. 50) Using Newton's Version of Kepler's Third Law. a. Calculate Earth's approximate mass from the fact that the Moon orbits Earth in an average time of 27.3 days at an average distance of 384,000 kilometers. (Hint: The Moon's mass is only about 1/80 of Earth's.) b. Calculate Jupiter's approximate mass from the fact that its moon Io orbits every 42.5 hours at an average distance of 422,000 kilometers. c. Calculate the orbital distance for a planet that has an orbital period of 63 days around a star with the mass of the Sun. d. Calculate the combined mass of Pluto and its moon Charon from the fact that Charon orbits Pluto every 6.4 days with a semimajor axis of 19,700 kilometers. e. Calculate the orbital period of a spacecraft in an orbit 300 kilometers above Earth's surface. f. Calculate the approximate mass of the Milky Way Galaxy from the fact that the Sun orbits the galactic center every 230 million years at a distance of 27,000 light-years. (As discussed in Chapter 15, this calculation actually tells us only the mass of the galaxy within the Sun's orbit.)

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 5 Light and Telescopes Section 5.1 1) If a material is transparent, then it ________. A) reflects light well B) absorbs light well C) transmits light well D) scatters light well E) emits light well Answer: C 2) Grass appears green because ________. A) it emits green light and absorbs other colors B) it absorbs green light and emits other colors C) it transmits green light and emits other colors D) it reflects green light and absorbs other colors Answer: D 3) Everything looks red through a red filter because ________. A) the filter emits red light and absorbs other colors B) the filter absorbs red light and emits other colors C) the filter transmits red light and absorbs other colors D) the filter reflects red light and transmits other colors Answer: C 4) A wave has peaks and troughs that can move matter up and down when the wave interacts with matter. The frequency of a wave is ________. A) the number of peaks passing by any point each second B) the speed at which a wave moves through space C) the distance between two adjacent peaks of a wave Answer: A 5) The wavelength of a wave is ________. A) how strong the wave is B) the distance between a peak of the wave and the next trough C) the distance between two adjacent peaks of the wave D) the distance between where the wave is emitted and where it is absorbed E) equal to the speed of the wave times the wave's frequency Answer: C

6) How are wavelength, frequency, and energy related for photons of light? A) Longer wavelength means lower frequency and lower energy. B) Longer wavelength means higher frequency and lower energy. C) Longer wavelength means higher frequency and higher energy. D) Longer wavelength means lower frequency and higher energy. E) There is no simple relationship because different photons travel at different speeds. Answer: A 7) From lowest energy to highest energy, which of the following correctly orders the different regions of electromagnetic radiation? A) Infrared, visible light, ultraviolet, x-rays, gamma rays, radio B) Radio, infrared, visible light, ultraviolet, x-rays, gamma rays C) Visible light, infrared, x-rays, ultraviolet, gamma rays, radio D) Gamma rays, x-rays, visible light, ultraviolet, infrared, radio E) Radio, x-rays, visible light, ultraviolet, infrared, gamma rays Answer: B 8) From lowest frequency to highest frequency, which of the following correctly orders the different regions of electromagnetic radiation? A) Infrared, visible light, ultraviolet, x-rays, gamma rays, radio B) Radio, infrared, visible light, ultraviolet, x-rays, gamma rays C) Visible light, infrared, x-rays, ultraviolet, gamma rays, radio D) Gamma rays, x-rays, visible light, ultraviolet, infrared, radio E) Radio, x-rays, visible light, ultraviolet, infrared, gamma rays Answer: B 9) From shortest wavelength to longest wavelength, which of the following correctly orders the different regions of electromagnetic radiation? A) Infrared, visible light, ultraviolet, x-rays, gamma rays, radio B) Radio, infrared, visible light, ultraviolet, x-rays, gamma rays C) Visible light, infrared, x-rays, ultraviolet, gamma rays, radio D) Gamma rays, x-rays, visible light, ultraviolet, infrared, radio E) Radio, x-rays, visible light, ultraviolet, infrared, gamma rays Answer: D 10) Which of the following statements about x-rays and radio waves is not true? A) X-rays have shorter wavelengths than radio waves. B) X-rays and radio waves are both forms of light, or electromagnetic radiation. C) X-rays have higher frequency than radio waves. D) X-rays have higher energy than radio waves. E) X-rays travel through space faster than radio waves. Answer: E

11) Which of the following statements about x-rays and radio waves is true? A) X-rays have the same wavelengths as radio waves. B) X-rays have the same frequency as radio waves. C) X-rays have the same energy as radio waves. D) X-rays travel through space at the same speed as radio waves. Answer: D 12) Red light has a lower energy per photon than blue light. Therefore, red light has ________. A) higher frequency, shorter wavelength than blue light B) lower frequency, longer wavelength than blue light C) lower frequency, shorter wavelength than blue light D) higher frequency, longer wavelength than blue light Answer: B 13) Photons behave like ________. A) waves B) particles C) both waves and particles D) neither waves nor particles Answer: C 14) Why can't we see radio waves? A) Radio waves have wavelengths too long for the eye to detect. B) Radio waves are sound waves, so we hear them. C) Radio waves fade away before they can reach our eyes. D) We do see radio waves, but we interpret them as the color red. E) Radio waves have too low energy to be detected by any means. Answer: A 15) The visible light portion of the electromagnetic spectrum has wavelengths ranging from about 400 to 700 nanometers (nm). Which of the following statements is true? A) Blue light has wavelength of about 400 nm, red light has wavelength of about 700 nm. B) Blue light has wavelength of about 700 nm, red light has wavelength of about 400 nm. C) Blue light and red light can both have wavelengths that may be anywhere between 400 and 700 nm. D) Blue light and red light both have wavelengths of about 550 nm. Answer: A 16) Which of the following best describes the sizes of atoms? A) Atoms are so small that millions of them could fit across the period at the end of this sentence. B) Atoms are too small to see by eye, but can be seen with a handheld magnifying glass. C) Most atoms are about a millionth of a meter (1 micrometer) in diameter. D) Atoms are roughly the same size as typical bacteria. Answer: A

17) What is a molecule? A) A group of two or more atoms bound together B) A particle that is part of an atomic nucleus C) The smallest known particle in nature D) An atom that has lost or gained an electron so that it is electrically charged E) A form of an atom that has more or less neutrons than normal Answer: A 18) The diameter of a typical atom is about ________ the diameter of its nucleus. A) the same as B) 10 times C) 100 times D) 1/10 of E) 100,000 times Answer: E 19) What is the overall electrical charge of an atom with 6 protons, 6 neutrons, and 5 electrons? A) +17 B) −5 C) +7 D) +1 E) +6 Answer: D 20) An iron atom has an atomic number of 26 and an atomic mass number of 56. If it is neutral, how many protons, neutrons, and electrons does it have? A) 26 protons, 30 neutrons, 26 electrons B) 26 protons, 30 neutrons, 30 electrons C) 26 protons, 56 neutrons, 26 electrons D) 13 protons, 43 neutrons, 13 electrons E) 13 protons, 56 neutrons, 13 electrons Answer: A 21) A gold atom has an atomic number of 79 and an atomic mass number of 197. If it is neutral, how many protons, neutrons, and electrons does it have? A) 79 protons, 118 neutrons, 79 electrons B) 79 protons, 118 neutrons, 118 electrons C) 79 protons, 118 neutrons, 39 electrons D) 118 protons, 79 neutrons, 118 electrons E) 118 protons, 39 neutrons, 118 electrons Answer: A

22) Oxygen has atomic number 8. How many times must an oxygen atom be ionized to create an O+5 ion, and how many electrons will the ion have? A) It must be ionized three times; it will have five electrons. B) It must be ionized five times; it will have five electrons. C) It must be ionized five times; it will have three electrons. D) It doesn't have to be ionized; it just needs to gain five protons. E) It doesn't have to be ionized; it already has only three electrons. Answer: C 23) If a proton inside the nucleus of an atom suddenly turned into a neutron, while the atom retained its original number of electrons, what properties of the atom would change? A) Only its atomic number B) Only its atomic mass number C) Only its electrical charge D) Both its atomic number and atomic mass number, but not its electrical charge E) Both its atomic number and electrical charge, but not its atomic mass number Answer: E 24) How does the spectrum of a molecule differ from the spectrum of an atom? A) A molecule does not have spectral lines due to electrons changing energy levels. B) A molecule has additional spectral lines due to changes in its rotational and vibrational energies. C) Molecules only have spectral lines at ultraviolet wavelengths. D) Most atoms only have spectral lines at infrared wavelengths. E) An atom has a wider range of spectral lines than molecules. Answer: B 25) Which of the following describes the light that can be detected from a person? A) The person reflects many wavelengths of visible light and emits infrared light. B) The person emits many wavelengths of visible light and reflects infrared light. C) The person emits a few narrow wavelengths of visible light based on the elements that make up the human body. D) The person reflects a few narrow wavelengths of visible light based on the elements that make up the human body. Answer: A 26) We know how fast a distant galaxy is moving away from us on the basis of its ________. A) mass B) color C) spectrum D) age E) luminosity Answer: C

27) We can see other people because people ________. A) emit thermal radiation B) emit visible light C) emit infrared light D) reflect visible light E) reflect infrared light Answer: D Section 5.2 1) Which of the following is an example of reﬂection or scattering? A) Red light hits a red sweatshirt. B) Visible light does not pass through a black wall. C) Blue light hits a red sweatshirt. D) Light comes from your computer screen. Answer: A 2) Which statement correctly describes units that can be used to measure energy and power? A) Energy is measured in joules and power is measured in joules per second. B) Energy and power are both measured in units of joules. C) Energy and power are both measured in units of watts. D) Energy is measured in watts and power is measured in watts per second. E) Energy is measured in watts and power is measured in newtons. Answer: A 3) How much energy is needed to power a 100-watt light bulb for 1 second? A) 6000 joules B) 100 joules C) 1 joule D) 100 watts E) 6000 watts Answer: B 4) We can see each other in the classroom right now because we ________. A) emit visible light. B) emit thermal radiation C) emit infrared light D) reflect visible light E) reflect infrared light Answer: D 5) Which statement about photons is true? A) An infrared photon has less energy than an x-ray photon, but travels at the same speed. B) An infrared photon has less energy than an x-ray photon, and travels more slowly. C) An infrared photon has more energy than an x-ray photon, and travels more quickly. D) An infrared photon has more energy than an x-ray photon, but travels at the same speed. Answer: A 6 Copyright © 2022 Pearson Education, Inc.

6) Which of the following statements about electrical charge is true? A) Two negative charges will attract each other. B) Two positive charges will attract each other. C) A positive charge and a negative charge will repel each other. D) A positive charge and a negative charge will attract each other. Answer: D 7) When a neutral atom loses an electron, we say that it becomes ________. A) vaporized B) dissociate C) ionized D) an isotope E) a plasma Answer: C 8) An electron-volt is ________. A) the charge of one electron B) the energy of one electron C) the energy jump between the first and second energy levels of hydrogen D) an amount of energy much smaller than a joule E) an amount of energy much larger than a joule Answer: D 9) What do we see when white light passes through a cool cloud of gas? A) Visible light B) Infrared light C) Thermal radiation D) An absorption line spectrum E) An emission line spectrum Answer: D 10) When an electron in an atom goes from a higher energy level to a lower energy level, the atom may ________. A) emit a photon of a specific wavelength B) absorb a photon of a specific wavelength C) absorb several photons of a specific wavelength D) emit a photon of any wavelength E) absorb a photon of any wavelength Answer: A

11) An electron in an atom can go from a lower energy level to a higher energy level if the atom ________. A) emits a photon of a specific wavelength B) absorbs a photon of a specific wavelength C) emits several photons of a specific wavelength D) emits a photon of any wavelength E) absorbs a photon of any wavelength Answer: B 12) When an electron drops to a lower energy level in an atom, but no other interactions take place ________. A) the atom may emit a photon of light of a specific wavelength B) the total energy of the atom remains unchanged C) the atom must slow its speed moving through space D) the atom must increase its speed moving through space E) the electron must become slightly more massive Answer: A 13) What must be true in order for an atom to absorb a photon? A) The photon must have energy matching the difference in energy between two energy levels in the atom. B) The atom must have lost all of its electrons. C) The photon must have enough energy to remove an electron from the atom. D) A or C E) B or C Answer: D 14) Which of the following objects does not produce a spectrum that is a close approximation to a thermal radiation spectrum? A) A hot, transparent gas B) A star C) A filament in an ordinary (incandescent) light bulb D) You E) A planet Answer: A

15) The diagram above represents energy levels in a hydrogen atom. Each level is labeled with its energy (above the ground state of Level 1) in units of electron/volts (eV). The labeled transitions represent an electron moving between energy levels. Which transition represents an electron that absorbs a photon with 10.2 eV of energy? A) A B) B C) C D) D E) E Answer: B 16) The diagram above represents energy levels in a hydrogen atom. Each level is labeled with its energy (above the ground state of Level 1) in units of electron/volts (eV). The labeled transitions represent an electron moving between energy levels. Which transition represents the electron that emits a photon with the highest energy? A) A B) B C) C D) D E) E Answer: A 17) The diagram above represents energy levels in a hydrogen atom. Each level is labeled with its energy (above the ground state of Level 1) in units of electron/volts (eV). The labeled transitions represent an electron moving between energy levels. Which transition represents an electron that is breaking free of the atom? A) A B) B C) C D) D E) E Answer: E 9 Copyright © 2022 Pearson Education, Inc.

18) The diagram above represents energy levels in a hydrogen atom. Each level is labeled with its energy (above the ground state of Level 1) in units of electron/volts (eV). The labeled transitions represent an electron moving between energy levels. Which transition, as shown, is not possible? A) A B) B C) C D) D E) E Answer: D 19) Thermal radiation is defined as ________. A) radiation produced by a hot object B) radiation in the infrared part of the spectrum C) radiation that depends only on the emitting object's temperature D) radiation in the form of emission lines from an object E) radiation that is felt as heat Answer: C 20) Which of the following statements about thermal radiation is always true? A) A hot object emits more x-rays than a cool object. B) A hot object emits more radio waves than a cool object. C) A hot object emits more total radiation than a cool object. D) A hot object emits more total radiation per unit surface area than a cool object. E) A hot object emits less total radiation than a cool object. Answer: D 21) A gas heated to millions of degrees would emit ________. A) mostly radio waves B) mostly x-rays C) mostly ultraviolet light D) an equal amount of all wavelengths of light E) no light because it is too hot Answer: B 22) You are heating two chunks of metal of the same size and shape. One is made of lead and is heated to 400 K. The other is made of iron and is heated to 350 K. Which of the following statements apply to the thermal radiation the two chunks emit? A) The two spectra peak at the same wavelength. B) The spectra cannot be compared because they come from different materials. C) The lead spectrum peak is at a shorter wavelength than the iron spectrum peak. D) The lead spectrum peak is at a longer wavelength than the iron spectrum peak. Answer: C

23) You are heating two chunks of metal of the same size and shape. One is made of lead and is heated to 400 K. The other is made of iron and is also heated to 400 K. Which of the following statements apply to the thermal radiation the two chunks emit? A) The two spectra peak at the same wavelength. B) The spectra cannot be compared because they come from different materials. C) The lead spectrum peak is at a shorter wavelength than the iron spectrum peak. D) The lead spectrum peak is at a longer wavelength than the iron spectrum peak. Answer: A 24) Which of the following stars has the hottest surface temperature? A) The blue star B) The orange star C) The yellow star D) The red star Answer: A 25) Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.) A) The red star is more massive than the blue star. B) The blue star is more massive than the red star. C) The red star is farther away than the blue star. D) The blue star has a hotter surface temperature than the red star. E) The red star has a hotter surface temperature than the blue star. Answer: D 26) From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 121.6 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 121.8 nm. What can we conclude? A) The star is moving toward us. B) The star is moving away from us. C) The star is getting hotter. D) The star is getting colder. E) The "star" actually is a planet. Answer: B 27) We have obtained spectra of two hydrogen gas clouds and are studying an emission line that has a laboratory wavelength of 656.3 nm. This emission line appears in Cloud A's spectrum with a wavelength of 660.1 nm and in Cloud B's spectrum at 670.2 nm. What can we conclude about these clouds? A) They are both moving toward us, and Cloud A is moving faster than Cloud B. B) They are both moving away from us, and Cloud A is moving faster than Cloud B. C) They are both moving away from us, and Cloud B is moving faster than Cloud A. D) They are both moving toward us, and Cloud B is moving faster than Cloud A. Answer: C

28) One of the absorption lines of hydrogen has a rest wavelength of 656 nm. Suppose you observe this line in four different stars, and find this line at the wavelengths show below. Which wavelength represents the star that is moving toward Earth the fastest? A) 630 nm B) 656 nm C) 670 nm D) 640 nm Answer: A 29) If a hydrogen emission line appears at 656 nm in the laboratory, what can we say about a cloud of hydrogen gas, with an emission line at 680 nm? A) It is receding away from us. B) It is moving toward us. C) It is neither receding nor approaching us. D) There is not enough information to say anything about the cloud's motion. Answer: A 30) The spectrum of Star A has an absorption line of hydrogen at 660.0 nm. The spectrum of Star B has an absorption line at 666 nm. The wavelength of this transition in the laboratory is 656 nm. What can I say about Star A and Star B? A) Both stars are moving away from me, Star A is faster than Star B. B) Both stars are moving toward me, Star A is faster than Star B. C) Both stars are moving toward me, Star B is faster than Star A. D) Both stars are moving away from me, Star B is faster than Star A. Answer: D 31) If one object has a large redshift and another object has a small redshift, what can we conclude about these two objects? A) The one with the large redshift is moving toward us faster than the one with the small redshift. B) The one with the large redshift is moving away from us, and the one with the small redshift is moving toward us. C) The one with the large redshift is moving away from us faster than the one with the small redshift. D) The one with the large redshift is hotter and therefore is putting out more radiation. E) The one with the large redshift is redder in color than the other one. Answer: C 32) You observe the same spectral line in two stars that are identical in every way except that one rotates faster than the other. How does the spectral line differ between the two? A) There is no difference. B) The line in the faster rotating star is blueshifted. C) The line in the faster rotating star is redshifted. D) The line in the faster rotating star is broader. E) The line in the faster rotating star is narrower. Answer: D 12 Copyright © 2022 Pearson Education, Inc.

33) One star is emitting mostly visible light, and another star is emitting mostly infrared light. Which star is hotter? A) The temperature also depends on the radius of the star, so one can't decide based on the information provided. B) Both stars are the same temperature. C) The star emitting visible light. D) The star emitting infrared light. Answer: C 34) Which of the following stars is the hottest? A) A blue star B) An orange star C) A yellow star D) A green star E) A red star Answer: A 35) When an atom's electrons fall down to lower energy levels in a thin cloud of hot gas, what is produced? A) Thermal radiation B) An absorption line spectrum C) An emission line spectrum D) An infrared spectrum E) New interstellar compounds Answer: C 36) We know the Sun is primarily made from hydrogen and helium on the basis of its ________. A) luminosity B) spectrum C) age D) color E) mass Answer: B 37) One star is emitting primarily visible light, and another star is emitting primarily infrared light. Which star is hotter? A) There is not enough information to answer the question. B) Both stars are the same temperature. C) The star emitting visible light is hotter. D) The star emitting infrared light is hotter. Answer: C

38) Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color? A) It is moving away from us. B) Its surface is cooler than the surface of the Sun. C) It is much more massive than the Sun. D) It is much brighter than the Sun. Answer: B 39) Four different objects have spectra that peak in the wavelength regions listed below. Which peak wavelength region is associated with the coldest of the four objects? A) X-rays B) Visible light C) Infrared D) Ultraviolet Answer: A 40) Which of the following objects would produce an emission line spectrum? A) A hot, low-density neon gas B) A star like our Sun C) A light bulb D) The Earth Answer: A 41) We can see the Moon because it ________. A) emits visible light B) emits thermal radiation C) reflects infrared light D) reflects visible light E) glows through radioactive decay Answer: D 42) Which of the following observational techniques is most appropriate for measuring Doppler shifts? A) Spectroscopy (taking a spectrum) B) Imaging (taking a picture) C) Timing (measuring how the amount of light changes with time) Answer: A 43) If two objects are the same size, but one object has a temperature 3 times as hot (in Kelvin) as the other object, the hotter object emits ________. A) 3 times as much energy B) 9 times as much energy C) 12 times as much energy D) 81 times as much energy E) 27 times as much energy Answer: D 14 Copyright © 2022 Pearson Education, Inc.

44) Hydrogen has an absorption line at a rest wavelength of 656.28 nm. This line is shifted to 656.50 nm in the spectrum of a star. How fast is the star moving? Hint: The Doppler shift formula is = where the speed of light is c ≈ 300,000 km/s A) about 100 km/s away from us. B) about 100 km/s toward us. C) about 1000 km/s away from us. D) about 1000 km/s toward us. Answer: A 45) Suppose that an ion has an absorption line at a rest wavelength of 1000.0 nm. This line is shifted to 1000.1 nm in the spectrum of a star. How fast is the star moving? Hint: The Doppler shift formula is = where the speed of light is c ≈ 300,000 km/s A) about 300 km/s away from us. B) about 300 km/s toward us. C) about 3000 km/s away from us. D) about 3000 km/s toward us. Answer: A 46) Which of the following could not be determined by an observation that only uses spectroscopy? A) The chemical composition of a distant star B) The speed at which a distant galaxy is moving away from us C) The surface temperature of a distant star D) The rotation rate of a distant star E) The angular size of a distant galaxy Answer: E

Section 5.3 1) What is the purpose of the lens in an eye? A) To bend light entering the eye so that it is focused onto the retina B) To collect light to send to the brain to be interpreted C) To interpret the light collected by the eye as colors D) To adjust the amount of light entering the eye so it is not too much or too little E) To determine what color the eye will be Answer: A 2) How do the light-collecting area and best possible angular resolution of telescope with a 10meter diameter mirror compare to that of a telescope with a 5-meter diameter mirror? A) The 10-meter telescope has double the light collecting area, and its angular resolution is better by a factor of 2. B) The 10-meter telescope has 4 times the light collecting area, and its angular resolution is better by a factor of 2. C) The 10-meter telescope has 4 times the light collecting area, and its angular resolution is better by a factor of 4. D) The 10-meter telescope has 10 times the light collecting area, and its angular resolution is better by a factor of 5. Answer: B 3) How does the light-collecting area of a telescope with a 10-meter diameter mirror compare to that of a telescope with a 5-meter diameter mirror? A) The 10-meter telescope has 2 times the light collecting area. B) The 10-meter telescope has 4 times the light collecting area. C) The 10-meter telescope has 10 times the light collecting area. Answer: B 4) How does the best possible angular resolution of a telescope with a 10-meter diameter mirror compare to that of a telescope with a 5-meter diameter mirror? A) The 10-meter telescope's angular resolution is better by a factor of 2. B) The 10-meter telescope's angular resolution is better by a factor of 4. C) The 10-meter telescope's angular resolution is better by a factor of 10. Answer: A 5) Suppose the angular separation of two stars is smaller than the angular resolution of your eyes. How will the stars appear to your eyes? A) You will not be able to see these two stars at all. B) The two stars will look like a single point of light. C) The two stars will appear to be touching, looking rather like a small dumbbell. D) You will see two distinct stars. E) You will see only the larger of the two stars, not the smaller one. Answer: B

6) Suppose two stars are separated in the sky by 0.1 arcseconds. If you take a picture of them with the SOAR telescope, which has an angular resolution of 0.6 arcsecond, what will you see? A) One point of light that is the blurred image of both stars B) Two separate points of light C) Nothing at all Answer: A 7) If you want to see the image formed by a telescope, you should place your eye at the location of the telescope's ________. A) focus B) primary mirror C) secondary mirror D) central hole in the primary mirror E) Cassegrain Answer: A 8) Which of the following is one important reason why most large astronomical telescopes are reflecting telescopes rather than refracting telescopes? A) Reflecting telescopes have their heaviest component (the mirror) at the bottom rather than the top of the telescope's tube. B) Reflecting telescopes take up less space than refracting telescopes. C) Reflecting telescopes are taller than refracting telescopes. D) For a mirror and lens of the same diameter, a mirror will collect more light. Answer: A 9) What do astronomers mean by light pollution? A) Light pollution refers to pollution caused by light industry as opposed to heavy industry. B) Light pollution refers to harmful gases emitted by common street lights. C) Light pollution refers to light used for human activities that brightens the sky and hinders astronomical observations. D) Light pollution refers to the lights that must be used inside major observatories and that make it difficult for astronomers' eyes to adapt to darkness. E) Light pollution is another name for sunlight, which makes it impossible to see stars in the daytime. Answer: C 10) What causes stars to twinkle? A) It is intrinsic to the stars–their brightness varies as they expand and contract. B) variations in the absorption of light at different depths in Earth's atmosphere C) variable absorption by interstellar gas along the line of sight to the star D) bending of light rays by turbulent motions of air in Earth's atmosphere E) the inability of the human eye to focus on small points of light Answer: D

11) What causes stars to twinkle? A) Stars constantly vary in brightness as they expand and contract. B) Interstellar gas along the line of sight to the star absorbs different amounts of radiation. C) The human eye has difficulty seeing faint objects. D) Moving gases in Earth's atmosphere randomly bend light rays from stars. Answer: D 12) What is the purpose of adaptive optics? A) To improve the angular resolution of telescopes in space B) To reduce the distorting effects of atmospheric turbulence for telescopes on the ground C) To increase the collecting area of telescopes on the ground D) To increase the magnification of telescopes on the ground E) To allow several small telescopes to work together like a single larger telescope Answer: B 13) Which of the following is not a good reason to place an observatory on a remote mountain to? A) Reduce the impact of light pollution B) Reduce the twinkling caused by Earth's atmosphere C) Allow study of infrared light D) Allow observations at ultraviolet and x-ray wavelengths Answer: D 14) Which of the following wavelength regions cannot be studied at all with telescopes on the ground? A) Radio B) Infrared C) X-rays D) Both radio and x-rays E) Both infrared and x-rays Answer: C 15) Earth's atmosphere is most transparent to all wavelengths of ________ light. A) infrared B) visible C) ultraviolet D) x-ray E) both visible and ultraviolet Answer: B 16) What is the best reason to put a visible-light telescope in space instead of on the ground? A) The telescope is above the atmosphere so the light does not get distorted by turbulent air. B) A space telescope is closer to the source of the light, so it can make a clearer image. C) Space telescopes are not affected by earthquakes. D) It is easier to launch very large space telescopes into space than to find places for them on the ground. Answer: A 18 Copyright © 2022 Pearson Education, Inc.

17) Radio telescopes are generally ________ than visible-light telescopes. A) much larger B) much smaller C) much more expensive D) located at much higher altitudes Answer: A 18) The largest diameter telescopes are used to observe ________. A) radio waves B) infrared light C) visible light D) ultraviolet light E) x-rays Answer: A 19) What does the technique of interferometry allow? A) It allows two or more telescopes to obtain a total light-collecting area much larger than the total light-collecting area of the individual telescopes. B) It allows two or more telescopes to obtain the angular resolution of a single telescope much larger than any of the individual telescopes. C) It allows us to determine the chemical composition of stars. D) It allows astronomers to make astronomical observations without interference from light pollution. E) It allows the same telescope to make images with both radio waves and visible light. Answer: B 20) Astronomers sometimes make use of "neutrino telescopes," which are typically located deep underground. What are neutrinos? A) A type of light-weight subatomic particle B) A very high-energy form of light C) A very low-energy form of light D) A type of wave predicted to exist by Einstein's general theory of relativity Answer: A 21) Are cosmic rays a form of light? A) No, they consist of high-energy subatomic particles, not of electromagnetic waves. B) Yes, they are light waves with higher energy than gamma rays. C) Yes, they are light waves with lower energy than radio waves. D) Yes, they are the name we give to all rays of light that come from the cosmos. Answer: A

22) What are gravitational waves? A) A type of energy that is different from light and that has been detected from sources such as merging neutron stars and black holes B) A form of light with higher energy than gamma rays C) A form of light with lower energy than radio waves D) The name we give to electromagnetic waves that come from astronomical objects that have gravity Answer: A 23) Which technology was used by the Event Horizon Telescope project to obtain the first image of a black hole? A) Gravitational wave detection B) Adaptive optics C) Interferometry D) High-speed time monitoring Answer: C 24) Which of the following telescopes is best suited for studying the hottest intergalactic gas (10 million K) in a cluster of galaxies? A) Very Large Array Radio Telescope B) Hubble Space Telescope (UV, optical, and some infrared) C) Chandra X-ray Telescope D) Herschel Infrared Telescope Answer: C 25) Which of the following observational techniques is most appropriate for measuring Doppler shifts? A) Spectroscopy (taking a spectrum) B) Imaging (taking a picture) C) Time monitoring (measuring how the amount of light changes with time) Answer: A

Reading Quiz Questions 1) From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation? A) Gamma rays, X rays, ultraviolet, visible light, infrared, radio B) Infrared, visible light, ultraviolet, X rays, gamma rays, radio C) Radio, infrared, visible light, ultraviolet, X rays, gamma rays D) Gamma rays, X rays, visible light, ultraviolet, infrared, radio Answer: A 2) Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond? A) They have a frequency of 2 hertz. B) They have a frequency of 4 hertz. C) We can calculate the wavelength of the ripples from their frequency. D) They have a wavelength of two cycles per second. Answer: A 3) Which forms of light are lower in energy and frequency than the light that our eyes can see? A) Infrared and radio B) Ultraviolet and X rays C) Visible light D) Infrared and ultraviolet Answer: A 4) When considering light as made up of individual "pieces," each characterized by a particular amount of energy, the pieces are called ________. A) photons B) wavicles C) gamma rays D) frequencies Answer: A 5) Suppose you know the frequency of a photon and the speed of light. What else can you determine about the photon? A) Its wavelength and energy B) Its temperature C) Its acceleration D) The chemical composition of the object that emitted it Answer: A

6) Suppose you built a scale-model atom in which the nucleus is the size of a tennis ball. About how far would the cloud of electrons extend? A) Several kilometers B) A few meters C) Several centimeters D) To the Sun Answer: A 7) Which of the following best describes the fundamental difference between two different chemical elements (such as oxygen and carbon)? A) They have different numbers of protons in their nucleus. B) They have different atomic mass numbers. C) They have different numbers of electrons. D) They have different names. Answer: A 8) Consider an atom of carbon in which the nucleus contains 6 protons and 7 neutrons. What is its atomic number and atomic mass number? A) Atomic number = 6; atomic mass number = 13 B) Atomic number = 6; atomic mass number = 7 C) Atomic number = 13; atomic mass number = 6 D) Atomic number = 7; atomic mass number = 13 Answer: A 9) A red shirt is red because it ________. A) reflects red light but absorbs other colors B) transmits red light C) emits red light only D) absorbs red light but reflects other colors Answer: A 10) Suppose you look at a detailed spectrum of visible light from some object. How can you decide whether it is an emission line spectrum or an absorption line spectrum? A) An emission line spectrum consists of bright lines on a dark background, while an absorption line spectrum consists of dark lines on a rainbow background. B) An emission line spectrum consists of a long bright line, while an absorption line spectrum consists of a long dark line. C) The only way to decide is to make a graph of the intensity of the light at every wavelength, and then analyze the graph carefully. D) The emission line spectrum is produced by electrons jumping up in energy level, while the absorption line spectrum is produced by electrons jumping down in energy level. Answer: A

11) An atom that has fewer electrons than protons is called a/an ________. A) ion B) molecule C) solid D) plasma Answer: A 12) Thermal radiation is defined as ________. A) radiation with a spectrum whose shape depends only on the temperature of the emitting object B) radiation produced by an extremely hot object C) radiation that is felt as heat D) radiation in the form of emission lines from an object Answer: A 13) According to the laws of thermal radiation, hotter objects emit photons with ________. A) a shorter average wavelength B) a lower average frequency C) a lower average energy D) a higher average speed Answer: A 14) Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you? A) The wavelengths of spectral lines in the star's spectrum B) The peak energy of the star's thermal radiation C) The Doppler shift of the star's spectrum D) Whether the star's spectrum has more emission lines or more absorption lines Answer: A 15) The spectra of most galaxies show redshifts. This means that their spectral lines ________. A) have wavelengths that are longer than normal B) always are in the red part of the visible spectrum C) have wavelengths that are shorter than normal D) have a higher intensity in the red part of the spectrum Answer: A 16) What does angular resolution measure? A) The angular size of the smallest features that the telescope can see. B) The brightness of an image. C) The size of an image. D) The number of electromagnetic waves captured by an image. Answer: A

17) Which of the following statements best describes the two principle advantages of telescopes over eyes? A) Telescopes can collect far more light with far better angular resolution. B) Telescopes can collect far more light with far greater magnification. C) Telescopes collect more light and are unaffected by twinkling. D) Telescopes have much more magnification and better angular resolution. Answer: A 18) What is the purpose of interferometry? A) It allows two or more small telescopes to achieve the angular resolution of a much larger telescope. B) It allows two or more small telescopes to achieve a larger light-collecting area than they would have independently. C) It is designed to prevent light pollution from interfering with astronomical observations. D) It reduces the twinkling of stars caused by atmospheric turbulence. Answer: A 19) What do astronomers mean by light pollution? A) Light pollution is light from human sources that makes it difficult to see the stars at night. B) Light pollution is a type of air pollution created by lightweight gases such as hydrogen and helium. C) Light pollution means contamination of light caused by chemicals in the Earth's atmosphere. D) Light pollution is a term used to describe the appearance of the sky in regions that are crowded with stars. Answer: A 20) The stars in our sky twinkle in brightness and color because of ________. A) turbulence in the Earth's atmosphere B) rapid changes in the brightness and colors of stars caused by changes in their spectra C) light pollution D) the bubbling and boiling of gases on the surfaces of stars Answer: A 21) Which of the following wavelength regions can be studied with telescopes on the ground? A) Radio, visible, and very limited portions of the infrared and ultraviolet regions B) All light with wavelengths longer than ultraviolet wavelengths C) All light with wavelengths shorter than infrared wavelengths D) Infrared, visible, and ultraviolet light Answer: A

22) Why are astronomers interested in building observatories capable of detecting neutrinos, cosmic rays, and gravitational waves? A) These things are not forms of light, and therefore can provide different types of information than light about objects that emit them. B) These things are the highest energy forms of light, even more energetic than gamma rays, and therefore can tell us about explosive processes in the universe. C) These things should in principle be much easier to detect than light, which means we could build these observatories cheaply. D) These things are emitted from the same objects that emit x-rays, but unlike x-rays they can be detected with observatories on the ground. Answer: A Concept Quiz Questions 1) Which of the following best describes why we say that light is an electromagnetic wave? A) The passage of a light wave can cause electrically charged particles to move up and down. B) Light can be produced only by electric or magnetic appliances. C) Light is produced only when massive fields of electric and magnetic energy collide with one another. D) The term electromagnetic wave arose for historical reasons, but we now know that light has nothing to do with either electricity or magnetism. Answer: A 2) Gamma rays have a small ________. A) wavelength B) energy C) frequency D) mass Answer: A 3) Which of the following statements about x-rays and radio waves is not true? A) X-rays travel through space faster than radio waves. B) X-rays have shorter wavelengths than radio waves. C) X-rays and radio waves are both forms of light, or electromagnetic radiation. D) X-rays have higher frequency than radio waves. Answer: A

4) Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different isotopes of the same element? A) Atom 1: nucleus with seven protons and eight neutrons, surrounded by seven electrons Atom 2: nucleus with seven protons and seven neutrons, surrounded by seven electrons B) Atom 1: nucleus with six protons and eight neutrons, surrounded by six electrons Atom 2: nucleus with seven protons and eight neutrons, surrounded by seven electrons C) Atom 1: nucleus with eight protons and eight neutrons, surrounded by eight electrons Atom 2: nucleus with eight protons and eight neutrons, surrounded by seven electrons D) Atom 1: nucleus with four protons and five neutrons, surrounded by four electrons Atom 2: nucleus with five protons and five neutrons, surrounded by four electrons Answer: A 5) Which of the following statements is true of green grass? A) It absorbs red light and reflects green light. B) It absorbs red light and emits green light. C) It transmits all colors of light except green. D) It means the lawn is healthy. Answer: A 6) Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space? A) The cloud is cool and lies between you and a hot star. B) The cloud is extremely hot. C) The cloud is visible primarily because it reflects light from nearby stars. D) The cloud is cool and dense, so that you cannot see any objects that lie behind it. Answer: A 7) Which of the following statements about electrons is not true? A) Electrons orbit the nucleus rather like planets orbiting the Sun. B) Within an atom, an electron can have only particular energies. C) An electron has a negative electrical charge. D) Electrons have little mass compared to protons or neutrons. E) Electrons can jump between energy levels in an atom only if they receive or give up an amount of energy equal to the difference in energy between the energy levels. Answer: A 8) No object produces a perfect thermal radiation spectrum, but many objects produce close approximations. Which of the following would not produce a close approximation to a thermal radiation spectrum? A) A hot, thin (low-density, nearly transparent) gas B) A filament in a standard (incandescent) light bulb C) A star D) You Answer: A

9) Which of the following statements about thermal radiation is always true? A) A hot object emits more radiation per unit surface area than a cool object. B) A cold object produces more total infrared and radio emission per unit surface area than a hot object. C) A hot object produces more total infrared emission than a cooler object. D) All the light emitted by hot object has higher energy than the light emitted by a cooler object. Answer: A 10) Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color? A) Its surface is cooler than the surface of the Sun. B) It is much brighter than the Sun. C) It is much more massive than the Sun. D) It is moving away from us. Answer: A 11) Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude? A) The star is moving toward us. B) The star is moving away from us. C) The star is getting hotter. D) The star is getting colder. Answer: A 12) Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude? A) Star X is moving away from us faster than Star Y. B) Star Y is moving away from us faster than Star X. C) Star X is hotter than Star Y. D) Star X is moving away from us and Star Y is moving toward us. E) Star X is coming toward us faster than Star Y. Answer: A 13) Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true? A) The total amount of light in the spectrum tells us the star's radius. B) The peak of the star's thermal emission tells us its temperature; hotter stars peak at shorter (bluer) wavelengths. C) We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals. D) Shifts in the wavelengths of spectral lines compared to the wavelengths of those same lines measured in a laboratory on Earth can tell us the star's speed toward or away from us. Answer: A

14) The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see? A) The photo will seem to show only one star rather than two. B) The two stars will appear to be touching, looking rather like a small dumbbell. C) The stars will not show up at all in your photograph. D) You will see two distinct stars in your photograph. Answer: A 15) The light-collecting area of an 8-meter telescope is ________ times that of a 2-meter telescope. A) 16 B) 4 C) 8 D) 6 Answer: A 16) Which of the following is not an advantage of the Hubble Space Telescope over groundbased telescopes? A) It is closer to the stars. B) Stars do not twinkle when observed from space. C) It can observe infrared and ultraviolet light, as well as visible light. D) It never has to close because of cloudy skies. Answer: A 17) The Chandra X-ray Observatory must operate in space because ________. A) X rays do not penetrate Earth's atmosphere B) X rays are too dangerous to be allowed on the ground C) X-ray telescopes require the use of grazing incidence mirrors D) it was built by NASA Answer: A 18) Which of the following is always true about images captured with x-ray telescopes? A) They are always shown with colors that are not the true colors of the objects that were photographed. B) They always are made with adaptive optics. C) They show us light with extremely long wavelengths compared to the wavelengths of visible light. D) They always have high angular resolution. E) They are always pretty. Answer: A 19) Astronomers have begun to build instruments to detect "cosmic messengers" that are not forms of light, such as neutrinos, cosmic rays, and gravitational waves, because they ________. A) provide information about distant objects that we cannot obtain from light B) provide higher angular resolution than we can obtain with light C) are unaffected by the turbulence of Earth's atmosphere D) can allow us to see beyond the horizon of the observable universe Answer: A 28 Copyright © 2022 Pearson Education, Inc.

Visual Quiz Questions

1) The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. Which labeled transition represents an electron that absorbs a photon with 10.2 eV of energy? A) A B) B C) C D) D E) E Answer: B 2) The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. Suppose that an electron in a hydrogen atom absorbs 10.2 eV of energy, so that it moves from level 1 to level 2. What typically happens next? A) The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy. B) The electron jumps to level 3 as soon as it absorbs any additional energy. C) The electron remains in level 2 until it absorbs an additional 10.2 eV of energy. D) A different electron drops into level 1, because it is now unoccupied. Answer: A

3) Assume the woman in the figure uses her prism to look at a spectrum of light coming from the object(s) shown. In which case will she see a continuous rainbow of thermal radiation? A) Case 1 B) Case 2 C) Case 3 D) Case 4 Answer: A 4) In which case will the woman see a rainbow of color interrupted by a few dark absorption lines? A) Case 1 B) Case 2 C) Case 3 D) Case 4 Answer: B 5) In which case will the woman see a just a spectrum that is almost entirely black except for few bright emission lines? A) 1 B) 2 C) 3 D) 4 Answer: C

6) Suppose you decide to make a graph of intensity against wavelength for the spectrum shown here. Which of the following shows what the graph will look like?

Answer: B

7) This photo shows the visible light spectrum of the Sun. Why does it have all those dark lines on it?

A) The dark lines represent wavelengths of light at which atoms near the Sun's surface absorb radiation from the hotter solar interior. B) The dark lines come from sunspots on the Sun, which are dark in color. C) The dark lines are caused by Doppler shifts. D) The dark lines are not real, but rather are artifacts of the photographic process used to record the spectrum. Answer: A 8) This figure shows idealized thermal radiation spectra from several stars and a human. Based on this graph, at about what wavelength does a 15,000 K star emit its most intense light?

A) About 100 nanometers B) About 1,000 nanometers C) About 20 nanometers D) About 100,000 nanometers Answer: A

9) Consider the spectra of the four objects shown beneath the laboratory spectrum. Based on these spectra, what can you conclude about Object 1? A) It is moving away from us. B) It is composed mostly of hydrogen, helium, and iron. C) It is a star with a thin upper atmosphere. D) It is a hot object, with a temperature above 1 million K. E) It is moving toward us. Answer: A 10) Now consider Object 2. What can you say about Object 2 in comparison to Object 1? A) Object 2 is moving away from us faster than Object 1. B) Object 2 contains more hydrogen than Object 1. C) Object 1 had a higher temperature than Object 2. D) Object 2 is moving toward us while Object 1 is moving away from us. Answer: A 11) The first telescopic photo shows what appears to be a single star. The second photo shows the same object, now revealed to be two distinct stars. What is the difference between the two photos?

A) The second photo has better (smaller) angular resolution than the first photo. B) The second photo was taken with a telescope that has greater light-collecting area. C) The second photo was taken by two telescopes rather than one. D) The second photo comes from a radio telescope, whereas the first photo comes from a visiblelight photo. Answer: A

12) What kinds of light are these telescopes designed to detect?

A) Radio waves B) X-rays C) Infrared and visible light D) Ultraviolet light E) Light with extremely short wavelengths Answer: A End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Refer to the numbered features on the above graph, which is a schematic spectrum of the planet Mars. 1) Which of the six numbered features represents emission lines? Answer: 1 2) Which of the six numbered features represents absorption lines? Answer: 5

3) Which portion(s) of the spectrum represent(s) reflected sunlight? A) 1 only B) 2, 3, and 4 C) 3 and 6 D) The entire spectrum Answer: B 4) What does the wavelength of the peak labeled 6 tell us about Mars? A) Its color B) Its surface temperature C) Its chemical composition D) Its orbital speed Answer: B 5) What feature(s) of this spectrum indicate(s) that Mars appears red in color? A) The wavelength of the peak labeled 3 B) The wavelength of the peak labeled 6 C) The fact that the intensity of region 4 is higher than that of region 2 D) The fact that the peak labeled 3 is higher than the peak labeled 6 Answer: C Chapter Review Questions 1) Define wavelength, frequency, and speed for light waves. If light has a long wavelength, what can you say about its frequency? Explain. 2) What is a photon? In what way is a photon like a particle? In what way is it like a wave? 3) List the different forms of light in order from lowest to highest energy. Is the order the same from lowest to highest frequency? from shortest to longest wavelength? 4) Briefly describe the structure and size of an atom. How big is the nucleus compared to the entire atom? 5) Define atomic number and atomic mass number. Under what conditions are two atoms different isotopes of the same element? 6) What is electrical charge? Will an electron and a proton attract or repel one another? How about two electrons? 7) What are the four major ways in which light and matter can interact? Give an example of each from everyday life. 8) Describe the conditions that lead to each of the three basic types of spectra. Which type is the Sun's spectrum, and why?

9) Why do atoms emit or absorb light of specific wavelengths? How does this fact allow us to determine the chemical composition of a distant object? 10) Describe two ways in which the thermal radiation spectrum of an 8000 K star would differ from that of a 4000 K star. 11) Describe the Doppler effect for light and what we can learn from it. What does it mean to say that radio waves are blueshifted? 12) What are the two key properties of a telescope, and why is each important? Also distinguish between refracting and reflecting telescopes.

13) List at least three ways Earth's atmosphere can hinder astronomical observations. How can adaptive optics help? 14) Besides light, what other types of "cosmic messengers" can astronomers now observe? Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 15) If you could view a spectrum of the light reflecting off a blue sweatshirt, you'd find the entire rainbow of color (looking the same as a spectrum of white light). 16) Because of their higher frequency, x-rays must travel through space faster than radio waves. 17) Two isotopes of the element rubidium differ in their number of protons. 18) If the Sun's surface became much hotter (while the Sun's size remained the same), the Sun would emit more ultraviolet light but less visible light than it currently emits. 19) If you could see infrared light, you would see a glow from the backs of your eyelids when you closed your eyes. 20) If you had x-ray vision, then you could read this entire book without turning any pages. 21) If a distant galaxy has a substantial redshift (as viewed from our galaxy), then anyone living in that galaxy would see a substantial redshift in a spectrum of the Milky Way Galaxy. 22) Thanks to adaptive optics, telescopes on the ground can now make ultraviolet images of the cosmos. 23) Thanks to interferometry, a properly spaced set of 10-meter radio telescopes can achieve the angular resolution of a single 100-kilometer radio telescope. 24) If you lived on the Moon, you'd never see stars twinkle. 36 Copyright © 2022 Pearson Education, Inc.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 5 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 25) Why is a sunflower yellow? A) It emits yellow light. B) It absorbs yellow light. C) It reflects yellow light. Answer: No Correct Answer Was Provided. 26) Compared to red light, blue light has higher frequency and ________. A) higher energy and shorter wavelength B) higher energy and longer wavelength C) lower energy and shorter wavelength Answer: No Correct Answer Was Provided. 27) Radio waves are ________. A) a form of sound B) a form of light C) a type of spectrum Answer: No Correct Answer Was Provided. 28) Compared to an atom as a whole, an atomic nucleus is ________. A) very tiny but has most of the mass B) quite large and has most of the mass C) very tiny and has very little mass Answer: No Correct Answer Was Provided. 29) Some nitrogen atoms have seven neutrons and some have eight neutrons; these two forms of nitrogen are ________. A) ions of each other B) phases of each other C) isotopes of each other Answer: No Correct Answer Was Provided. 30) The set of spectral lines that we see in a star's spectrum depends on the star's ________. A) atomic structure B) chemical composition C) rotation rate Answer: No Correct Answer Was Provided. 31) A star whose spectrum peaks in the infrared is ________. A) cooler than our Sun B) hotter than our Sun C) larger than our Sun Answer: No Correct Answer Was Provided. 37 Copyright © 2022 Pearson Education, Inc.

32) A spectral line that appears at a wavelength of 321 nm in the laboratory appears at a wavelength of 328 nm in the spectrum of a distant object. We say that the object's spectrum is ________. A) redshifted B) blueshifted C) whiteshifted Answer: No Correct Answer Was Provided. 33) How much greater is the light-collecting area of a 6-meter telescope than that of a 3-meter telescope? A) Two times B) Four times C) Six times Answer: No Correct Answer Was Provided. 34) The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is ________. A) larger B) closer to the stars C) above Earth's atmosphere Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 35) A Telescope Near You. For your current residence, your birthplace, or your home town, find the location of the nearest ground-based, visible-light telescope with a mirror larger than about 2 meters in diameter. What is this telescope used for? Is it open to the public? Discuss whether or how you think this telescope may benefit your community. 36) Pair Discussion: The Curies. The married couple Marie and Pierre Curie were pioneers in the study of matter. a. Working independently, learn about the Nobel Prizes the Curies won, the reasons for those prizes, and the differing roles Marie and Pierre assumed in carrying out their research. Also, find the overall fraction of Nobel Prizes in science that have been awarded to women. b. Pair up with another student, one of you talking about Marie Curie and the other about Pierre Curie. Take turns describing what each scientist did to help earn their Nobel Prizes. Then discuss whether you think they both deserved the Nobel Prizes they received, and how well you think they worked together and supported each other. c. Discuss the fraction of Nobel Prizes that have been awarded to women. Does it seem surprising to you? Why or why not?

37) Pair Discussion: The Herschels. William and Caroline Herschel– brother and sister–were pioneers in using large telescopes to study the night sky. a. Working independently, find out when the Herschels lived, the kinds of telescopes they had at their disposal, and the major accomplishments credited to each of them. b. Pair up with another student, and decide which one of you will focus on William and which one on Caroline. Then take turns describing the major accomplishments of each sibling. c. Discuss the relationship between William and Caroline Herschel. Were they equal partners? Did they have similar opportunities to make major astronomical discoveries? Why or why not? The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 38) Elements in Space. Astronomers claim that objects throughout the universe are made of the same chemical elements that exist here on Earth. Given that most of these objects are so far away that we can never hope to visit them, why are astronomers so confident that the objects are made from the same set of chemical elements, rather than completely different substances? 39) The Changing Limitations of Science. Review the box "Extraordinary Claims: We Can Never Learn the Composition of Stars," which gives an example of how new discoveries can change the apparent limitations of science. Today, other questions seem beyond the reach of science, such as the question of how life began on Earth. Do you think such questions will ever be answerable through science? Defend your opinion. 40) Technology-Driven Science. Choose one technology described in this chapter and summarize how its development (or improvement) has allowed us to learn more about the universe. Then discuss how we might expect this technology to improve further during the next few decades, and identify at least one currently unanswered question about the universe that will likely be answered with the help of the improved technology. 41) Group Activity: Which Telescope? You represent a research group that wishes to observe matter around a black hole; assume that the matter is emitting photons at all wavelengths. You have the opportunity to make your observations with one of the following four telescopes: • A radio telescope, 300 meters in diameter, located in Puerto Rico • An infrared telescope, 2 meters in diameter, on a spacecraft in orbit around Earth and observing at a wavelength of micrometers • An infrared telescope, 10 meters in diameter, equipped with adaptive optics, located on Mauna Kea in Hawaii and observing at a wavelength of micrometers (10−5 m) • An x-ray telescope, 2 meters in diameter, located at the South Pole Discuss the pros and cons of each telescope for this observing task, then come to a group consensus in which you rank the four choices from best to worst. Compare your rankings to those of other groups in your class. Note: You may wish to do this activity using the same four roles described in Chapter 1, Exercise 39.

Investigate Further 42) Atomic Terminology Practice I. a. The most common form of iron has 26 protons and 30 neutrons. For a neutral atom of this form of iron, state the atomic number, atomic mass number, and number of electrons. b. Consider the following three atoms: Atom 1 has seven protons and eight neutrons; atom 2 has eight protons and seven neutrons; atom 3 has eight protons and eight neutrons. Which two are isotopes of the same element? c. Oxygen has atomic number 8 and its most common isotope 16O (atomic mass number 16). How many neutrons are in an atom of 16O? If this atom loses 5 electrons through ionization, how many electrons remain? 43) Atomic Terminology Practice II. a. What are the atomic number and atomic mass number of fluorine atoms with nine protons and ten neutrons? If we could add a proton to a fluorine nucleus, would the result still be fluorine? What if we added a neutron to a fluorine nucleus? Explain. b. The most common isotope of gold has atomic number 79 and atomic mass number 197. How many protons and neutrons does the gold nucleus contain? If it is electrically neutral, how many electrons does it have? If it is triply ionized (three electrons lost), how many electrons does it have? c. Uranium has atomic number 92. Its most common isotope is 238U (atomic mass number 238), but the form used in nuclear bombs and nuclear power plants is 235U (atomic mass number 235). How many neutrons are in each of these two isotopes of uranium?

44) Energy Level Transitions. The following labeled transitions represent an electron moving between energy levels in hydrogen. Answer each of the following questions and explain your answers.

a. Which transition could represent an atom that absorbs a photon with 10.2 eV of energy? b. Which transition could represent an atom that emits a photon with 10.2 eV of energy? c. Which transition represents an electron that is breaking free of the atom? d. Which transition, as shown, is not possible? e. Would transition A represent emission or absorption of light? How would the wavelength of the emitted or absorbed photon compare to that of the photon involved in transition C? Explain. 45) Orion Nebula. Viewed through a telescope, much of the Orion Nebula looks like a glowing cloud of gas. What type of spectrum would you expect to see from the glowing parts of the nebula? Why? 46) The Doppler Effect. In hydrogen, the transition from level 2 to level 1 has a rest wavelength of 121.6 nm. Suppose you see this line at a wavelength of 120.5 nm in Star A, at 121.2 nm in Star B, at 121.9 nm in Star C, and at 122.9 nm in Star D. Which stars are coming toward us? Which are moving away? Which star is moving fastest relative to us? Explain your answers without doing any calculations. 47) Spectral Summary. Clearly explain how studying an object's spectrum can allow us to determine each of the following properties of the object. a. The object's surface chemical composition b. The object's surface temperature c. Whether the object is a low-density cloud of gas or something more substantial d. The speed at which the object is moving toward or away from us

48) Your Microwave Oven. A microwave oven emits microwaves that have just the right wavelength to cause energy level changes in water molecules. Use this fact to explain how a microwave oven cooks your food. Why doesn't a microwave oven make a plastic dish get hot? Why do some clay dishes get hot in the microwave? Why do dishes that aren't themselves heated by the microwave oven sometimes still get hot when you heat food on them? (Note: It's not a good idea to put empty dishes in a microwave.) 49) Image Resolution. What happens if you take a photograph from a newspaper, magazine, or book and blow it up to a larger size? Can you see more detail than you could before? Explain clearly, and relate your answer to the concepts of magnification and angular resolution in astronomical observations. 50) Really Big Telescopes. Learn about one of the projects to build a very large telescope, such as the Giant Magellan Telescope, the Thirty Meter Telescope, or the European Extremely Large Telescope. Write a short report about the telescope's current status and potential capabilities. 51) A Lunar Observatory. Some people have proposed building an astronomical observatory on the Moon. Research the pros and cons of this idea, considering it both in isolation and in the context of plans for a human return to the Moon. If it were up to you, would you recommend that Congress begin funding a program to develop such an observatory? Defend your opinion. 52) Project: Twinkling Stars. Using a star chart, identify five to ten bright stars that should be visible in the early evening. On a clear night, observe each of these stars for a few minutes. Note the date and time, and for each star record the following information: approximate altitude and direction in your sky, brightness compared to other stars, color, and how much the star twinkles compared to other stars. Study your record. Can you draw any conclusions about how brightness and position in your sky affect twinkling? Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 53) Thermal Radiation Laws. a. Find the emitted power per square meter and wavelength of peak intensity for a 3000 K object that emits thermal radiation. b. Find the emitted power per square meter and wavelength of peak intensity for a 50,000 K object that emits thermal radiation. 54) Hotter Sun. Suppose the surface temperature of the Sun were about 12,000 K, rather than 6000 K. a. How much more thermal radiation would the Sun emit? b. What would happen to the Sun's wavelength of peak intensity? c. Do you think it would still be possible to have life on Earth? Explain.

55) Doppler Calculations. In hydrogen, the transition from level 2 to level 1 has a rest wavelength of 121.6 nm. Find the speed and direction (toward or away from us) for a star in which this line appears at wavelength a. 120.5 nm. b. 121.2 nm. c. 121.9 nm. d. 122.9 nm. 56) Hubble's Field of View. Large telescopes often have small fields of view. For example, the Hubble Space Telescope's (HST's) advanced camera has a field of view that is roughly square and about 0.06° on a side. a. Calculate the angular area of the HST's field of view in square degrees. b. The angular area of the entire sky is about 41,250 square degrees. How many pictures would the HST have to take with its camera to obtain a complete picture of the entire sky?

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 6 Formation of the Solar System Section 6.1 1) How much of the solar system's total mass is contained in the Sun? A) About half B) About 90% C) About 95% D) About 99.8% E) Exactly 100% Answer: D 2) If we could combine all the planets together, their total mass would be about ________ the Sun's mass. A) 1/1000 of B) 1/10 of C) the same as D) double E) half of Answer: A 3) Where does nuclear fusion occur in the Sun? A) On the surface B) In a layer just below the surface C) Deep in its core D) In a layer just above the visible surface E) All of the above Answer: C 4) Which planet has the most extreme differences between its daytime and nighttime temperatures? A) Mercury B) Venus C) Earth D) Mars E) Jupiter Answer: A 5) Which planet is most similar in size and mass to Earth? A) Mercury B) Venus C) Mars D) Jupiter E) Neptune Answer: B 1 Copyright © 2022 Pearson Education, Inc.

6) What is surprising about Earth's Moon? A) It is surprisingly large in comparison to the size of its planet. B) It orbits surprisingly far away from Earth. C) It has a surprisingly large number of craters. D) The fact that it lacks a significant atmosphere. Answer: A 7) Which of the following indicates that past conditions on Mars may have been suitable for life? A) There are very large extinct volcanoes on Mars. B) Mars has two small Moons, Phobos, and Deimos. C) There are dried up riverbeds, rock-strewn floodplains, and minerals that form in water. D) Mars has polar caps. E) Mars has been studied by numerous spacecraft, including both orbiters and landers. Answer: C 8) Which planet is orbited by the four "Galilean moons" known individually as Io, Europa, Ganymede, and Callisto? A) Saturn B) Uranus C) Mars D) Jupiter E) Neptune Answer: D 9) The most massive planet in our solar system is ________. A) Saturn B) Uranus C) Mars D) Jupiter E) Neptune Answer: D 10) Uranus's large axis tilt causes it to ________. A) have extreme seasonal variations B) be very hot C) be very cold D) have very short days and nights E) keep one side facing the Sun at all times Answer: A

11) Neptune's largest moon, Triton, orbits in a direction opposite to the direction in which Neptune rotates. Which of the following is most likely implied by this fact? A) Triton experiences very strong tidal forces. B) Triton probably formed as the result of a giant impact. C) Triton probably was captured into orbit by Neptune. D) Triton probably formed in its current orbit around Neptune. E) Triton probably has a rocky, asteroid-like composition. Answer: C 12) Which statement about Pluto is not true? A) Its surface temperature is very cold. B) It is made mostly of rock and ice. C) It is both smaller and less massive than Earth. D) It is the most massive object in the Kuiper belt. E) It was visited by the New Horizons spacecraft in 2015. Answer: D 13) Which of the following factors was very important to the decision to classify Pluto as a dwarf planet rather than a "regular" planet? A) Its small size and mass B) Its large distance from the Sun C) Its composition of ice and rock D) Its relatively large moon, Charon Answer: A 14) In what region of the solar system is Pluto found? A) The asteroid belt B) The Kuiper belt C) The Oort cloud D) The terrestrial planet region Answer: B 15) Which planet has the highest average surface temperature and why? A) Mercury, because it is closest to the Sun B) Mercury, because of its dense carbon dioxide atmosphere C) Venus, because of its dense carbon dioxide atmosphere D) Mars, because of its red color E) Jupiter, because it is so big Answer: C 16) Other than Earth, which of the following has visible polar caps? A) Mercury B) Venus C) The Moon D) Mars E) Jupiter Answer: D 3 Copyright © 2022 Pearson Education, Inc.

17) Which of the following worlds could an astronaut visit without the need for a spacesuit (and survive)? A) Mercury B) Venus C) The Moon D) Mars E) None of the above; an astronaut would need a spacesuit to survive a visit to any world in the solar system (aside from Earth). Answer: E 18) Which of the following planets has a ring system? A) Jupiter B) Saturn C) Uranus D) Neptune E) All of the above Answer: E 19) Which planet experiences the strongest gravitational force from the Sun? A) Mercury B) Earth C) Jupiter D) Saturn E) Neptune Answer: A Section 6.2 1) Which of the following is not an observed pattern of motion in our solar system? A) Most planets orbit the Sun at the same speed. B) All planets orbit the Sun in the same direction. C) Most planetary orbits lie nearly in the same plane. D) Most planets rotate in the same direction in which they orbit. E) Almost all moons orbit their planet in the same direction as the planet's rotation. Answer: A 2) Which of the following is not a characteristic of all the terrestrial planets? A) They are smaller than the jovian planets. B) They have solid, rocky surfaces. C) They are located closer to the Sun than the jovian planets. D) They have substantial atmospheres. E) They have higher densities than the jovian planets. Answer: D

3) Which of the following is not a characteristic of the jovian planets? A) They have higher average densities than the terrestrial planets. B) They have thick atmospheres. C) They are primarily made of hydrogen, helium, and hydrogen compounds. D) They are located further from the Sun than the terrestrial planets. E) They have rings. Answer: A 4) Which of the following best described the major ingredients of the jovian planets? A) Rocky minerals and water B) Hydrogen, helium, and hydrogen compounds C) Rock and metal D) Hydrogen compounds and carbon dioxide E) Hydrogen and helium only Answer: B 5) Where are most asteroids found? A) Between the orbits of Mars and Jupiter B) Between the orbits of Jupiter and Saturn C) In the Oort cloud D) Inside the orbit of Earth E) Between the orbits of Earth and Mars Answer: A 6) The Oort cloud is ________. A) a roughly spherical region larger than the orbit of Pluto that may contain a trillion comets B) a region in the same plane as the planets that contains hundreds of thousands of comets C) a circular region between the orbits of Mars and Jupiter that contains most known asteroids D) the cloud of gas from which the solar system formed E) a vast cloud of gas that encircles the solar system at a great distance from the Sun Answer: A 7) Which of the following is farthest from the Sun? A) Pluto B) Neptune C) An asteroid in the asteroid belt D) A comet in the Kuiper belt E) A comet in the Oort cloud Answer: E 8) What is the major difference between asteroids and comets? A) Asteroids are rocky and comets are icy. B) Asteroids are low in density and comets are high in density. C) Asteroids never have tails and comets always have tails. D) Asteroids are smaller than comets. E) Asteroids are larger than comets. Answer: A 5 Copyright © 2022 Pearson Education, Inc.

9) Astronomers estimate the total number of comets in the solar system to be about ________. A) 100 million B) 1 billion C) 10 billion D) 100 billion E) 1 trillion Answer: E 10) Which of the following is not an exception to the general patterns in the solar system? A) The "backward" rotation of Venus B) The relatively large size of Earth's Moon compared to Earth C) The fact that Saturn has rings D) The extreme axis tilt of Uranus E) The "backward" orbit of Triton around Neptune Answer: C 11) What is unusual about the planet Venus? A) It rotates in a direction opposite to the direction of its orbit. B) It orbits the Sun faster than it should give the size of its orbit. C) It orbits the Sun in a direction opposite that of all the other planets. D) It does not orbit the Sun in the same plane as the other planets. E) It rotates extremely rapidly around its axis. Answer: A 12) Which of the following is a feature of our solar system that should be predicted by a successful theory of solar system formation? A) The age of our solar system B) The fact that all the planets in our solar system orbit the Sun in the same direction C) The fact that there are exactly four terrestrial planets and exactly four jovian planets D) The fact that Earth has a 23-1/2° axis tilt E) The fact that Jupiter has the most known moons in the solar system Answer: B 13) The "close encounter hypothesis" suggested that the planets formed after a near-collision between our Sun and another star. If this hypothesis were correct, which of the following would be true? A) Planetary systems would be very rare. B) Planetary systems would be very common. C) Most planetary systems would have their jovian planets closer to their stars and their terrestrial planets farther from their stars. D) Most planetary systems would have the same number of planets as our own. E) All planetary systems would be at least 4 billion years old. Answer: A

14) Which of the following is not a pattern of motion in our Solar System? A) Most planets rotate in the same direction they orbit. B) Most planetary orbits lie in the same plane. C) Most planets orbit in the same direction. D) Almost all large moons orbit their planet in the same direction as the planet's rotation. E) The planets orbit the Sun in a direction opposite that of the Sun's rotation. Answer: E 15) Which of the following statements best explains why all the planets orbit the Sun in the same direction and in nearly the same plane? A) The planets formed from a disk of rotating gas, and their orbits therefore orbit as this gas did. B) The Sun's rotation spun out the planets as it formed. C) No one knows: planets form randomly, so it's a puzzle why they orbit with such a pattern. D) The Sun's gravity is strongest as its equator, so it pulled all the planets into this orbital alignment. Answer: A 16) What is our best hypothesis for why all the planets in our solar system orbit in the same direction as the Sun rotates? A) The planets and Sun formed from the same, single, rotating gas cloud. B) It's a complete coincidence. C) The planets were pulled out of the Sun by a major interaction with another star. D) Almost everything in our Galaxy rotates in the same direction. E) The Sun did not initially rotate, but the planets gravity caused it to start rotating in the direction in which the planets orbit. Answer: A 17) About what percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium? A) 0 percent B) 0.1 percent C) 2 percent D) 20 percent E) 80 percent Answer: C 18) The very first generation of star systems in the universe must have been born from gas that consisted entirely of hydrogen and helium (and no other elements). Which of the following statements is most likely to have been true about these first-generation star systems? A) They had terrestrial planets but no jovian planets. B) They did not have any planets or asteroids or comets. C) They had asteroids and comets but no large planets. D) They did not have and disks of gas around them as they formed. Answer: B

19) According to the nebular theory, what are asteroids and comets? A) Leftover planetesimals that never accreted into planets B) Chunks of rock or ice that condensed long after the planets had formed C) The shattered remains of collisions between moons D) The shattered remains of collisions between planets E) Chunks of rock or ice that have been expelled from the planets by volcanoes Answer: A 20) We know that Earth has water. However, according to our theory of solar system formation, the inner solar system was too hot for hydrogen compounds like water to condense. What do we conclude? A) Water arrived on Earth at a time when it rained throughout the inner solar system. B) Earth's water likely was brought here by asteroids or comets that formed beyond the frost line. C) Our theory of solar system formation will need modification because it is unable to account for the existence of water on Earth. D) Earth's water probably originated through chemical reactions among the rock and metal of Earth's interior. Answer: B Section 6.3 1) Where did most elements heavier than hydrogen and helium come from? A) They were produced in the Big Bang. B) They evolved from hydrogen and helium shortly after the Big Bang. C) They were produced by stars. D) They were produced inside interstellar gas clouds. E) All of the above Answer: C 2) Have astronomers ever seen a gas cloud that looks like it contains planetary systems that are in the process of forming? A) Yes, there are many such clouds, including the Orion Nebula. B) Yes, but only the original cloud that formed our own solar system. C) Yes, but only in distant galaxies, not in our own Milky Way. D) No, there is no evidence that any interstellar clouds are currently giving birth to stars. Answer: A 3) Which of the following is most important in causing a cloud of gas to collapse to form a star and planets? A) Gravity pulls all the gas inward. B) Pressure from other gas clouds pushes the gas inward. C) Opposite charges in the gas attract. D) Some gas is sent outward, causing the rest to move inward to conserve momentum. E) Pressure from light from nearby stars pushes the gas inward. Answer: A

4) Why did the solar nebula heat up as it collapsed? A) Nuclear fusion occurring in the core of the forming Sun produced energy that heated the nebula. B) As it shrank in size, gravitational potential energy was converted to thermal energy. C) It was heated by radiation from nearby stars. D) The shock wave from a nearby supernova heated the gas. E) Collisions among planetesimals generated friction and heat. Answer: B 5) If an interstellar gas cloud shrinks in size, what does the law of conservation of energy predict it will do? A) Heat up B) Spin slower C) Cool off D) Continue shrinking E) Spin faster Answer: A 6) According to our theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size? A) The two laws of thermal radiation B) The law of conservation of angular momentum C) The law of universal gravitation D) The law of conservation of energy Answer: D 7) If an interstellar gas cloud shrinks in size, what does the law of conservation of angular momentum predict it will do? A) Heat up B) Spin slower C) Cool off D) Continue shrinking E) Spin faster Answer: E 8) According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size? A) Einstein's law that E = mc2 B) The law of conservation of angular momentum C) Kepler's first law of planetary motion D) The law of universal gravitation Answer: B

9) Why did the solar nebula flatten into a disk? A) The interstellar cloud from which the solar nebula formed was originally somewhat flat. B) The force of gravity from the Sun pulled the material downward into a flat disk. C) As the nebula cooled, the gas and dust settled onto a disk. D) It flattened as a consequence of collisions between particles in the spinning nebula, changing random motions into more orderly ones. E) The force of gravity from the planets pulled the material downward into a flat disk. Answer: D 10) Which of the following observations of an extrasolar planet system would be inconsistent with what we expect from the nebular theory of solar system formation? A) A system which has two terrestrial planets close in and two jovian planets farther out B) A system in which some planets have small moons orbiting in a direction opposite to the planet's rotation C) A system in which some planets rotate in a direction opposite to their orbits D) A system in which all the planets orbit in completely different planes Answer: D 11) According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane? A) The original solar nebula happened to be disk shaped by chance. B) Any planets that once orbited in the opposite direction or a different plane were ejected from the solar system. C) The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk. D) The Sun formed first, and as it grew in size it spread into a disk, rather like the way a ball of dough can be flattened into a pizza by spinning it. E) It is a coincidence, as we would expect that most other solar systems would not have all their planets orbiting in such a pattern. Answer: C 12) Which of the following ingredients was least abundant in the solar nebula? A) Metal B) Rock C) Hydrogen compounds D) Hydrogen E) Helium Answer: B 13) Which of the following lists the ingredients of the solar nebula from highest to lowest percentage of mass of the nebula? A) Hydrogen and helium gas, hydrogen compounds, rocks, metals B) Hydrogen compounds, hydrogen and helium gas, rocks, metals C) Hydrogen and helium gas, hydrogen compounds, metals, rocks D) Hydrogen compounds, hydrogen and helium gas, metals, rocks E) Hydrogen compounds, rocks, metals, hydrogen and helium gas Answer: A 10 Copyright © 2022 Pearson Education, Inc.

14) About what percentage of the mass of the solar nebula consisted of hydrogen and helium gas? A) 0.5 percent B) 5 percent C) 50 percent D) 98 percent E) 100 percent Answer: D 15) What happened during the accretion phase of the early solar system? A) Atoms of hydrogen and helium gas bonded together and solidified. B) Particles grew by colliding and sticking together. C) The solar nebula differentiated into metals inside of the frost line and ices beyond. D) Large planetesimals captured atmospheres from the solar nebula. E) Earth gained its oceans from icy planetesimal capture. Answer: B 16) Beyond the frost line of the solar system, temperatures were low enough for ________. A) metals to condense into solid form B) rocks to condense into solid form C) hydrogen compounds to condense into solid ices D) asteroids to form E) hydrogen and helium to condense into ice Answer: C 17) The frost line of the solar system was located approximately between ________. A) the Sun and the present-day orbit of Mercury B) the present-day orbits of Mercury and Venus C) the present-day orbits of Mars and Jupiter D) the present-day orbits of Venus and Earth E) the present-day orbits of Uranus and Neptune Answer: C 18) What do we mean by the frost line when we discuss the formation of planets in the solar nebula? A) It is another way of stating the temperature at which water freezes into ice. B) It is a particular distance from the Sun, beyond which the temperature was low enough for ices to condense. C) It marks the special distance from the Sun at which hydrogen compounds become abundant; closer to the Sun, there are no hydrogen compounds. D) It is the altitude in a planet's atmosphere at which snow can form. Answer: B

19) Why are the inner planets made of denser materials than the outer planets? A) The Sun's gravity pulled denser materials toward the inner part of the solar nebula, while lighter gases escaped more easily. B) Denser materials were heavier and sank to the center of the nebula. C) In the inner part of the nebula only metals and rocks were able to condense because of the high temperatures, whereas hydrogen compounds, although more abundant, were only able to condense in the cooler outer regions. D) When the solar nebula formed a disk, materials naturally segregated into bands, and in our particular solar system, the denser materials settled nearer the Sun, while lighter materials are found in the outer part. E) In the beginning, when the protoplanetary disk was spinning faster, centrifugal forces flung the lighter materials toward the outer parts of the solar nebula. Answer: C 20) Why did terrestrial planets form in the inner solar system and jovian planets in the outer solar system? A) As the solar nebula shrank, it settled into a spinning disk and separated into individual planets. B) Denser, heavier materials, such as rocks and metals, settled to the center of the nebula, and therefore, planets that formed there were more likely to be made primarily from rock and metal. C) In the inner part of the nebula, only metals and rocks were able to condense because of the high temperatures, whereas hydrogen compounds, although more abundant, were only able to condense in the cooler outer regions. Answer: C 21) According to our present theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system? A) The solid material that accreted in the outer solar system included ices, while the solid material of the inner solar system consisted only less abundant metal and rock. B) There was more time for accretion in the outer solar system before the solar wind cleared the nebula away. C) The gas in the outer solar system contained a larger proportion of rock, metal, and hydrogen compound than the gas in the inner solar system. D) Gravity was stronger in the outer solar system, allowing more solid material to collect. Answer: A 22) Which of the following is the origin of most of the large moons around the jovian planets? A) They are captured asteroids. B) They are captured comets. C) They are captured planets. D) They were formed by condensation and accretion in a disk of gas around the planet. E) They were formed by giant impacts. Answer: D

23) The nebular theory predicts that the young Sun should have been rotating quite rapidly, but the Sun rotates slowly today. Can this fact be explained by the nebular theory? A) Yes; the young Sun's solar wind would have carried away angular momentum, slowing the Sun's rotation. B) Yes, objects always slow their rotations over time. C) No, it is a complete mystery as to why the Sun would rotate slowly today. Answer: A 24) According to our theory of solar system formation, why does the Sun rotate slowly today? A) The Sun once rotated much faster, but it transferred angular momentum to charged particles caught in its magnetic field and then blew the particles away with its strong solar wind. B) The Sun once rotated much faster, but it transferred angular momentum to the planets during the parts of their orbits where they come closest to the Sun. C) The Sun once rotated much faster, but it lost angular momentum due to internal friction. D) The Sun once rotated much faster, but it lost angular momentum because everything slows down with time. E) The Sun was born rotating slowly because the solar nebula had very little angular momentum. Answer: A 25) Hydrogen compounds in the solar nebula could condense into ice at temperatures of about 150 K. Suppose they instead could have condensed only at temperatures below 50 K? What would have been different in the solar nebula? A) The frost line would have been farther from the Sun. B) The frost line would have been closer to the Sun. C) Terrestrial planets would have formed outside the frost line. D) Jovian planets would have formed inside the frost line. Answer: A 26) Observations of young stars suggest that when the Sun was young, the solar wind ________. A) was weaker than it is today B) was stronger than it is today C) was about the same strength as it is today D) was nonexistent E) blew outward only along the Sun's poles Answer: B 27) The period we call the "heavy bombardment" was ________. A) the first few hundred thousand years of the solar system's history B) the most recent hundred million years of the solar system's history C) the first few hundred million years of the solar system's history D) a period of a few hundred million years that began when the solar system was about 1 billion years old E) the time during which an asteroid hit the Earth and caused the extinction of the dinosaurs Answer: C

28) What happened during the heavy bombardment? A) The planets of the solar system suffered many impacts. B) The planets collided with one another. C) Planetesimals collided with one another and stuck together to form planets. D) A supernova disrupted a gas cloud, causing it to start collapsing to form the solar system. E) A large meteor collided with Earth, killing the dinosaurs. Answer: A 29) Which of the following is not evidence supporting the giant impact theory for the formation of the Moon? A) Computer simulations show that the Moon could really have formed in this way. B) The composition of the Moon is similar to that of Earth's outer layers. C) The Moon is depleted of easily vaporized materials, as we would expect from the heat of an impact. D) Scientists have found several meteorites that appear to be the remains of the object that caused the giant impact. Answer: D 30) What is the giant impact hypothesis for the origin of the Moon? A) The Moon originally was about the same size as Earth, but a giant impact blasted most of it away so that it ended up much smaller than Earth. B) The Moon formed just like Earth, from accretion in the solar nebula. C) The Moon formed from material blasted out of Earth's mantle and crust by the impact of a Mars-size object. D) The Moon formed when two gigantic asteroids collided with one another. Answer: C 31) Based on our current theory of Earth's formation, the water we drink likely comes from ________. A) ice that condensed in the solar nebula in the region where Earth formed B) chemical reactions that occurred in Earth's crust after Earth formed C) chemical reactions that occurred in Earth's core after Earth formed D) material left behind during the giant impact that formed the Moon E) water-bearing planetesimals that formed beyond the frost line and then impacted Earth Answer: E 32) According to our theory of solar system formation, why do we find some exceptions to the general rules and patterns of the planets? A) Our theory is not quite correct because it cannot explain these exceptions. B) Most of the exceptions are the result of giant impacts or close gravitational encounters. C) The exceptions probably represent objects that formed recently, rather than early in the history of the solar system. D) The exceptions probably represent objects that were captured by our solar system from interstellar space. E) The exceptions are probably the result of the Sun passing very close to another star billions of years ago. Answer: B 14 Copyright © 2022 Pearson Education, Inc.

33) What is the best explanation for how the solar nebula was cleared of debris? A) The strong solar wind of the young Sun blew away material not accreted by the planets. B) The planets accreted all the material around them, leaving no debris. C) All of the debris eventually fell into the Sun. D) The debris collapsed to form moons. E) The debris all disappeared through radioactive decay. Answer: A 34) Suppose the Sun had been born with less mass, making it a smaller, cooler star. Which of the following consequences would we expect according to the nebular theory? A) The frost line would have been farther from the Sun, so jovian planets could form only at greater distances than in our solar system. B) The frost line would have been closer to the Sun, so jovian planets could form at nearer distances than in our solar system. C) The planets would have formed just as they did for our actual Sun, but the weaker gravity of a smaller Sun would have allowed the planets to escape into interstellar space. D) There would have been no solar nebula in which material could condense to form planets. Answer: B 35) Suppose the Sun had been born with more mass, making it larger and hotter. Which of the following consequences would we expect according to the nebular theory? A) There would be no comets. B) Asteroids would have formed closer to the Sun. C) Jovian planets would have formed farther from the Sun. D) There would have been no solar nebula in which material could condense to form planets. Answer: C 36) The age of the solar system can be established by radiometric dating of ________. A) the oldest Earth rocks B) the oldest rocks on the Moon C) the oldest meteorites D) the atmosphere of Mars E) the oldest rocks on Jupiter's moon Io Answer: C 37) What is the most likely reason that there are no other jovian planets in our solar system beyond Neptune? A) Any planets forming beyond Neptune would have drifted out of the solar system due to the weakness of the Sun's gravity at this distance. B) There was no material to create planetesimals beyond the orbit of Neptune. C) By the time planetesimals grew to a large enough mass to capture hydrogen and helium gas from the solar nebula, the gas had been cleared by the solar wind. D) Any planet forming beyond Neptune's orbit would have been scattered outside of the solar system by gravitational encounters. E) Formation of another planet was prevented by orbital resonances with Neptune. Answer: C 15 Copyright © 2022 Pearson Education, Inc.

38) Consider the five facts listed below. The nebular theory of the formation of the solar system successfully accounts for four of these facts, while one can be considered to be just a coincidence. Which fact is a coincidence? A) Our solar system has an equal number of terrestrial and jovian planets. B) The planets all orbit around the Sun in nearly circular orbits in nearly the same plane. C) The planets divide into two major types, terrestrial and jovian. D) The solar system has many small bodies, and these are concentrated in the regions known as the asteroid belt, Kuiper belt, and the Oort cloud. E) There are many impact craters on the Moon. Answer: A 39) How do astronomers explain the fact that some planetary systems (besides our own) have jovian-size planets that orbit very close to their stars? A) The planets likely formed farther out, then migrated inward. B) The solar nebula theory must be wrong because jovian planets cannot be that close. C) Jovian planets must be objects from outside the system that were captured. D) Jovian planets must be created by collisions of terrestrial planets. E) The observations must have been misinterpreted. Answer: A 40) Which of the following measurements of other solar systems would require us to change our current solar system formation theory? A) The age of another solar system is significantly older than our solar system. B) The planets in other solar systems mostly orbit their central stars in the same plane and same direction as the other planets in that solar system. C) Some stars have no planets. D) Some stars have many planets. E) Many other stars have planets orbiting in many different directions and at many different angles. Answer: E

Section 6.4 1) Comets are made mostly of ________. A) rock B) hydrogen gas C) rock and metal D) metal E) rock and ice Answer: E 2) The age of our solar system is approximately ________. A) 10,000 years B) 3.8 million years C) 4.5 million years D) 4.5 billion years E) 14 billion years Answer: D 3) How do we know how old the solar system is? A) By measuring the rate of the expansion of the universe B) We estimate the age based on how fast the terrestrial planets cooled and solidified. C) By radiometric dating of meteorites D) By measuring how much mass the Sun has lost through fusion over time Answer: C 4) Uranium-238 decays into lead-206 with a half-life of 4.5 billion years. Suppose you found a rock in which only 1/4 of the original uranium-238 remained (the other ¾ having become lead206). How old would the rock be? A) 9 billion years B) 4.5 billion years C) 2.25 billion years D) 13.5 billion years Answer: A 5) Potassium-40 decays to argon-40 has a half-life of 1.25 billion years. Suppose you find a rock that has only 1/8 of its original potassium-40 still remaining. How old is the rock? A) 3.75 billion years B) 5.25 billion years C) 2.5 billion years D) 1.25 billion years E) 4.5 billion years Answer: A

6) Why do Earth rocks have much younger ages than most meteorites? A) Earth formed billions of years after most meteorites formed. B) The rocks solidified long after the formation of the solar nebula. C) The atoms that make up Earth rocks are generally younger than the atoms that make up meteorites. D) Most meteorites come from other planetary systems that formed before our solar system. Answer: B 7) What is the half-life of a radioactive isotope? A) The amount of time for half of a sample of the isotope to decay into a different element or isotope B) The amount of time for half of a sample of the element to decay into nothing C) Half of the total time that the isotope has been in existence D) Half of the amount of that element in the universe E) Half of the age of the solar system Answer: A 8) If a radioactive isotope with a half-life of 5 hours is injected into your bloodstream for medical imaging purposes, how many hours do you have to wait before the amount of this isotope in your body is 1/16 its original amount? A) 15 B) 10 C) 25 D) 5 E) 20 Answer: E Short Answer Questions 1) Describe at least two things that make Earth unique in the solar system? Answer: Possible answers: It is the only planet with an oxygen-rich atmosphere and abundant liquid water on its surface. Its surface temperature is such that water can exist in three phases: solid, liquid, and gaseous. Compared to its size, Earth also has a very large moon. It is the only planet with plate tectonics. It is the only planet we know of that harbors life. 2) Identify at least three patterns of motion or planetary arrangement/location that a theory of solar system formation should be able to explain. Answer: Answers may include: 1. Planets orbit in the same direction. 2. Orbital direction is the same direction as the Sun's spin. 3. Most planets spin in the same direction that they orbit. 4. Bigger planets are in the outer solar system. 5. Large planets have many moons. 6. Planets lie in approximately the same plane. 3) List at least three of the notable exceptions to the general patterns of the solar system. Answer: Several possibilities: (a) The rotational axes of Uranus and Pluto are substantially tilted. (b) Venus rotates backward, that is, clockwise. (c) Unlike other terrestrial planets, Earth has a large moon. (d) Some of the moons of the jovian planets orbit in the opposite direction of their planets' rotation. 18 Copyright © 2022 Pearson Education, Inc.

4) List at least two of the notable exceptions to the general patterns of the solar system. Answer: Several possibilities: The rotational axes of Uranus and Pluto are substantially tilted. Venus rotates backward relative to its orbit. Earth has a surprisingly large Moon. Pluto has a moon that is almost as large as itself. Triton orbits "backward" relative to Neptune's rotation. Many small moons of the jovian planets orbit in the opposite direction of Jupiter's rotation. 5) A scientific theory must produce testable predictions that are then evaluated when data are available. Describe at least two predictions of the nebular theory that can be tested through observations of other planetary systems. Answer: Possible answers include: Planets should be common around other stars; most or all planets should orbit in the same direction and nearly the same plane around their star; rocky worlds should be closer to their stars and icy worlds farther away; all planetary systems should have "leftovers" like asteroids and comets. 6) Suppose the entire solar nebula had cooled to a very low temperature before the solar wind cleared it away. Do you think Earth would be the same? Why or why not? Answer: Ices would have condensed in the inner solar system, significantly increasing the size and mass (or possibly number) of terrestrial planets. Water and other hydrogen compounds would be much more abundant. 7) Suppose the planet Jupiter had never formed. How do you think the distribution of asteroids and comets in our solar system would be different? Explain. Answer: There would likely be no asteroid belt because without Jupiter's gravitational effects, the material in that region could have accreted into a single planet. There also would likely be few comets in the Oort cloud because many of those comets were presumably flung into Oort cloud orbits by gravitational encounters with Jupiter. Reading Quiz Questions 1) Which of the following lists the planets of our solar system in the correct order from closest to farthest from the Sun? A) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune B) Mercury, Earth, Venus, Mars, Jupiter, Saturn, Neptune, Uranus C) Mercury, Venus, Mars, Earth, Saturn, Jupiter, Neptune, Uranus D) Earth, Mars, Mercury, Venus, Jupiter, Saturn, Uranus, Neptune Answer: A 2) Suppose you view the solar system from high above Earth's North Pole. Which of the following statements about planetary orbits will be true? A) All the planets orbit counterclockwise around the Sun. B) The inner planets orbit the Sun counterclockwise, whereas the outer planets orbit the Sun clockwise. C) All the planets except Uranus orbit the Sun counterclockwise; Uranus orbits in the opposite direction. D) The inner planets orbit the Sun clockwise, whereas the outer planets orbit the Sun counterclockwise. Answer: A 19 Copyright © 2022 Pearson Education, Inc.

3) Which of the following statements about our Sun is not true? A) The Sun's diameter is about 5 times that of Earth. B) The Sun is a star. C) The Sun contains more than 98% of all the mass in our solar system. D) The Sun is made mostly of hydrogen and helium. Answer: A 4) Which of the following statements about Mars is not true? A) We could survive on Mars without spacesuits, as long as we brought oxygen in scuba tanks. B) We have landed robotic spacecraft on its surface. C) It has mountains that are taller than the tallest mountains on Earth. D) Its surface is frozen today, but evidence indicates it had flowing water in the distant past. Answer: A 5) The planet in our solar system with the highest average surface temperature is ________. A) Venus B) Mercury C) Earth D) Neptune Answer: A 6) The terrestrial planets in our solar system are ________. A) Mercury, Venus, Earth, and Mars B) Jupiter, Saturn, Uranus, and Neptune C) Pluto and Eris D) Mars, Jupiter, Saturn, Uranus, and Neptune Answer: A 7) The jovian planets in our solar system are ________. A) Jupiter, Saturn, Uranus, and Neptune B) Mercury, Venus, Earth, and Mars C) Pluto and Eris D) Io, Europa, Ganymede, and Callisto Answer: A 8) When we say that jovian planets contain significant amounts of hydrogen compounds except, we mean all the following chemicals except ________. A) carbon dioxide B) water C) ammonia D) methane Answer: A

9) In essence, the nebular theory holds that ________. A) our solar system formed from the collapse of an interstellar cloud of gas and dust B) nebulae are clouds of gas and dust in space C) the planets each formed from the collapse of its own separate nebula D) the planets formed as a result of a near-collision between our Sun and another star Answer: A 10) According to modern science, what was the approximate chemical composition of the solar nebula? A) 98% hydrogen and helium, 2% everything else B) 50% hydrogen and helium, 50% everything else C) 98% hydrogen, 2% helium D) Roughly equal proportions of hydrogen, helium, water, and methane Answer: A 11) The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did the elements heavier than hydrogen and helium come from? A) They were produced by stars that lived and died before our solar system was born. B) They were produced by gravity in the solar nebula as it collapsed. C) They have been present in the universe since its birth. D) They were made by chemical reactions in interstellar gas. Answer: A 12) According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size? A) It got hotter, its rate of rotation increased, and it flattened into a disk. B) Its mass, temperature, and density all increased. C) It gained energy, it gained angular momentum, and it flattened into a disk. D) Its gas clumped up to form the terrestrial planets, nuclear fusion produced heavy elements to make the jovian planets, and central temperatures rose to more than a trillion Kelvin. Answer: A 13) Which of the following types of material can condense into what we call ice at low temperatures? A) Hydrogen compounds B) Hydrogen and helium C) Rock D) Metal Answer: A

14) According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant? A) Hydrogen and helium gas; hydrogen compounds; rock; metal B) Hydrogen compounds; hydrogen and helium gas; metal; rock C) Hydrogen and helium gas; rock; metal; and hydrogen compounds D) Hydrogen; water; methane; and helium Answer: A 15) In the context of the formation of planets in the solar nebula, the frost line marks the distance from the Sun beyond which ________. A) the temperature was low enough for hydrogen compounds to condense into ices B) the temperature was low enough for solid rock to condense from the gas C) hydrogen compounds were particularly abundant D) planets could be cold enough to have snow Answer: A 16) What do we mean by accretion in the context of planet formation? A) The growth of planetesimals from smaller solid particles that collided and stuck together B) The formation of moons around planets C) The solidification of ices, rocks, and metal from the gas of the solar nebula D) The growth of the Sun as the density of gas increased in the center of the solar nebula Answer: A 17) According to the nebular theory of solar system formation, what are asteroids and comets? A) Leftover planetesimals that never accreted into planets B) The shattered remains of collisions between planets C) Chunks of rock or ice that condensed after the planets and moons finished forming D) Chunks of rock or ice that were expelled from planets by volcanoes Answer: A 18) What do we mean by the period of heavy bombardment in the context of the history of our solar system? A) The first few hundred million years after the planets formed, which is when most impact craters were formed B) The time before planetesimals finished accreting into planets, during which time many growing planetesimals must have shattered in collisions C) The time during which heavy elements condensed into rock and metal in the solar nebula D) The period about 65 million years ago when an impact is thought to have led to the extinction of the dinosaurs Answer: A

19) What is the giant impact hypothesis for the origin of the Moon? A) The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object. B) The Moon formed when two gigantic asteroids collided with one another. C) The Moon originally was about the same size as Earth, but a giant impact blasted most of it away so that it ended up much smaller than Earth. D) The Moon formed just like the Earth, from accretion in the solar nebula. Answer: A 20) Consider a radioactive substance with a half-life of 10 years. If you start with 1 kilogram of this substance, after 20 years, ________ of the radioactive substance will remain. A) 0.25 kilogram B) none C) 0.75 kilogram D) 0.5 kilogram Answer: A 21) According to modern scientific dating techniques, approximately how long ago did Earth and the other planets of our solar system form? A) 4.5 billion years B) 10,000 years C) 4.5 million years D) 14 billion years Answer: A Concept Quiz Questions 1) Compared to the distance between Earth and Mars, the distance between Jupiter and Saturn is ________. A) much larger B) about the same C) much smaller D) just slightly less Answer: A 2) How is Einstein's famous equation, E = mc2, important in understanding the Sun? A) It explains the fact that the Sun generates energy to shine by losing some 4 million tons of mass each day. B) It explains why the Sun has a magnetic field strong enough to influence the atmospheres of the planets. C) It explains why the Sun's surface temperature is about 6,000°C. D) It explains why the Sun is so massive. Answer: A

3) Venus has a higher average surface temperature than Mercury. Why? A) Because its surface is heated by an extreme greenhouse effect B) Because it is closer to the Sun C) Because its surface is covered with hot lava from numerous active volcanoes D) Because its slow rotation gives it more time to heat up in sunlight Answer: A 4) Which planet listed below has the most extreme seasons? A) Uranus B) Mars C) Earth D) Jupiter Answer: A 5) Which of the following is not a major pattern of motion in the solar system? A) Nearly all comets orbit the Sun in same direction and roughly the same plane. B) Most of the solar system's large moons orbit in their planet's equatorial plane. C) The Sun and most of the planets rotate in the same direction in which the planets orbit the Sun. D) All of the planets orbit the Sun in the same direction; counterclockwise as viewed from above Earth's north pole. Answer: A 6) Which of the following is not a major difference between the terrestrial and jovian planets in our solar system? A) Terrestrial planets contain large quantities of ice and jovian planets do not. B) Terrestrial planets orbit much closer to the Sun than jovian planets. C) Terrestrial planets are higher in average density than jovian planets. D) Jovian planets have rings and terrestrial planets do not. Answer: A 7) The following statements are all true. Which one counts as an "exception to the rule" in being unusual for our solar system? A) The diameter of Earth's Moon is about 1/4 that of Earth. B) Venus does not have a moon. C) Jupiter has a small axis tilt. D) Saturn has no solid surface. Answer: A 8) According to the nebular theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size? A) The law of conservation of energy B) The law of conservation of angular momentum C) Newton's third law D) The two laws of thermal radiation Answer: A 24 Copyright © 2022 Pearson Education, Inc.

9) According to the nebular theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size? A) The law of conservation of angular momentum B) The law of conservation of energy C) The law of universal gravitation D) Einstein's law E = mc2 Answer: A 10) According to the nebular theory of solar system formation, which of the following best explains why the solar nebula ended up with a disk shape as it collapsed? A) As the nebula shrank and rotated faster, collisions between orbiting particles caused it to flatten into a disk. B) The nebula was fairly flat to begin with, and retained this flat shape as it collapsed. C) The force of gravity pulled material that was spherically distributed downward into a flat disk. D) the law of conservation of energy Answer: A 11) What is the primary basis on which we divide the ingredients of the solar nebula into the four categories hydrogen/helium, hydrogen compounds, rock, and metal? A) The temperatures at which various materials can condense from gaseous form to solid form B) The atomic mass numbers of various materials C) The locations of various materials in the solar nebula D) The amounts of energy required to ionize various materials Answer: A 12) According to the nebular theory of solar system formation, what key difference in their early formation explains why the jovian planets ended up so different from the terrestrial planets? A) The terrestrial planets formed inside the frost line of the solar nebula and the jovian planets formed beyond it. B) The jovian planets formed in a region with a much higher density of hydrogen and helium gas. C) The terrestrial planets accreted from rock and metal, while the jovian planets were formed by giant balls of pure hydrogen and helium gas. D) The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal. Answer: A

13) Many meteorites appear to have formed very early in the solar system's history. How do these meteorites support the nebular theory's scenario for the formation of the terrestrial planets? A) The appearance and composition of these meteorites is just what we'd expect if metal and rock condensed and accreted as the nebular theory suggests. B) The sizes of these meteorites are just what we'd expect if metal and rock condensed and accreted as the nebular theory suggests. C) The overall composition of these meteorites is just what we believe the composition of the solar nebula to have been: mostly hydrogen and helium. D) The appearance and composition of these meteorites matches what we observe in comets today, suggesting that they were once pieces of icy planetesimals. Answer: A 14) According to our present theory of solar system formation, how did Earth end up with enough water to make oceans? A) The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars. B) The water was brought to the forming Earth by planetesimals that accreted near Earth's orbit. C) The water was formed by chemical reactions among the minerals in the Earth's core. D) Earth formed in the relatively narrow region of the solar nebula in which liquid water was plentiful. Answer: A 15) What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits? A) Some moons have orbits that are backward (compared to their planet's rotation) or highly inclined to their planet's equator. B) Some moons have a composition that differs from the composition of the planets. C) Astronomers have observed moons being captured. D) Some moons are surprisingly large in size. Answer: A 16) Which of the following is not a line of evidence supporting the idea that our Moon formed as a result of a giant impact? A) The Pacific Ocean appears to be a large crater, probably the one made by the giant impact. B) Computer simulations show that the Moon could really have formed through a giant impact. C) The Moon's average density suggests it is made of rock much more like that of the Earth's outer layers than that of the Earth as a whole. D) The Moon has a much smaller proportion of easily vaporized materials than Earth. Answer: A

17) About 2% of our solar nebula consisted of elements besides hydrogen and helium. However, the very first generation of star systems in the universe probably consisted only of hydrogen and helium. Which of the following statements is most likely to have been true about these firstgeneration star systems? A) There were no comets or asteroids in these first-generation star systems. B) Jovian planets in these first-generation star systems had clouds made of water and other hydrogen compounds. C) These first-generation star systems typically had several terrestrial planets in addition to jovian planets. D) Rings are made of rock and ice, which require elements besides hydrogen and helium, and thus could not have existed in star systems made of pure hydrogen and helium. Answer: A 18) Suppose you find a rock that contains 10 micrograms of radioactive potassium-40, which has a half-life of 1.25 billion years. By measuring the amount of its decay product (argon-40) present in the rock, you conclude that there must have been 80 micrograms of potassium-40 when the rock solidified. How old is the rock? A) 3.75 billion years B) 1.25 billion years C) 2.5 billion years D) 5.0 billion years Answer: A 19) How do scientists determine how long ago Earth first formed? A) Radiometric dating of meteorites B) Radiometric dating of Moon rocks C) Radiometric dating of the oldest Earth rocks D) Models of planetary formation tell us how long it took Earth to grow to its present size. Answer: A

Visual Quiz Questions 1) In this perspective view of the solar system, the sizes of the planets are ________ relative to the sizes of their orbits.

A) exaggerated about 1,000 times B) correctly scaled C) exaggerated about 10 times D) exaggerated about 100 million times Answer: A

2) Which pair of photos shows Earth correctly scaled in comparison to the Sun? A)

Answer: A

3) Which pair of photos below shows Earth correctly scaled in comparison to Jupiter? A)

Answer: A

4) What planet is this, and how do you know?

A) Saturn because of its colors and bright, wide rings B) Saturn because it is the only planet with rings C) Jupiter because it is the biggest planet and has the biggest rings D) Neptune because it has the brightest rings of any planet E) Jupiter because of its colors and bright, wide rings Answer: A 5) What object is shown in this photo?

A) Mars B) Venus C) Mercury D) Ganymede Answer: A

6) In this photograph, the large and bright object in the sky is ________.

A) a comet B) an asteroid C) a meteor D) the northern lights Answer: A 7) This sequence of paintings shows how a large gas cloud can collapse to become a much smaller, spinning disk of gas. What law explains why cloud spins faster as it shrinks in size?

A) The law of conservation of energy B) The universal law of gravitation C) The law of conservation of angular momentum D) Kepler's third law E) Newton's second law of motion Answer: C

8) What is the significance of this image?

A) It shows an actual disk of material orbiting another star, providing strong evidence the planets really do form in such disks. B) It shows an artist's conception of what our solar system might have looked like when the planets were first forming. C) It proves that jovian planets form farther from their stars than terrestrial planets. D) The large gap visible in the image represents the frost line of a young planetary system, demonstrating that such a line really exists. Answer: A 9) This diagram represents the solar nebula early in its history and shows the location of the frost line. Suppose you discover an object that is made of metal, rock, and ice. In which of the four regions shown in the diagram did it form?

A) Region 1 B) Region 2 C) Region 3 D) Region 4 Answer: D

10) You find a rock containing radioactive potassium-40 and its decay product argon-40. You assume that all the argon-40 was made from radioactive decay of potassium-40. The rock now has twice as much argon-40 as potassium-40; that is, 2/3 of the original potassium-40 has decayed into argon-40 while 1/3 remains in the rock. Based on this graph, about how old is the rock? A) 1 billion years B) 1.25 billion years C) 2 billion years D) 2.5 billion years E) 3 billion years Answer: C

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

The graph shows the radioactive decay of uranium-235 to lead-207. (Uranium-235 also decays by another pathway, not shown.) 1) Compare the graph above to Figure 6.26, which shows the decay of potassium-40. Which element is more radioactive (undergoes radioactive decay more quickly)? A) Uranium-235 B) Potassium-40 C) Both are equally radioactive. Answer: A 2) What fraction of the original uranium-235 should be left after 3.5 billion years? A) 1/2 B) 1/4 C) 1/8 D) 1/32 E) 1/64 Answer: D

3) You find a mysterious rock on the ground and determine that 60% of its uranium-235 has been converted into lead-207. What is the most likely origin of the rock, based on its radiometric age? A) It's older than our solar system, so it must have come from another solar system. B) It's a meteorite dating back to the formation of the solar system. C) It's a volcanic rock nearly a billion years old. D) It was just formed this year during the eruption of a nearby volcano. Answer: C Chapter Review Questions 1) Briefly describe the layout of the solar system as it would appear from beyond the orbit of Neptune. 2) For each of the objects in the solar system tour (pages 140—149), describe at least two features that you find interesting. 3) Briefly describe the four major features of our solar system that provide clues to how it formed. 4) What are the basic differences between terrestrial and jovian planets? Which planets fall into each group? 5) What is the nebular theory, and why is it widely accepted by scientists today? 6) What do we mean by the solar nebula? What was it made of, and where did it come from? 7) Describe three key processes that led the solar nebula to take the form of a spinning disk. What evidence supports this scenario? 8) Describe the four categories of materials in the solar nebula by their condensation properties and abundance. Which ingredients condensed inside and outside the frost line? 9) Briefly describe the process by which terrestrial planets are thought to have formed. 10) How was the formation of the jovian planets similar to that of the terrestrial planets? How was it different? Why did the jovian planets end up with many moons? 11) What are asteroids and comets, and how did they come to exist? How and why are they different? 12) What was the heavy bombardment, and when did it occur? 13) What is the leading hypothesis for the Moon's formation? What evidence supports this hypothesis? 14) Briefly explain the technique of radiometric dating. What is a half-life? How do we use radiometric dating to determine the age of the solar system? 36 Copyright © 2022 Pearson Education, Inc.

Surprising Discoveries? Suppose we found a solar system with the property described. (These are not real discoveries.) In light of what you've learned about the formation of our own solar system, decide whether the discovery should be considered reasonable or surprising. Explain your reasoning. 15) A solar system has five terrestrial planets in its inner solar system and three jovian planets in its outer solar system. 16) A solar system has four large jovian planets in its inner solar system and seven small terrestrial planets in its outer solar system. 17) A solar system has ten planets that all orbit the star in approximately the same plane. However, five planets orbit in one direction (e.g., counterclockwise), while the other five orbit in the opposite direction (e.g., clockwise). 18) A solar system has 12 planets that all orbit the star in the same direction and in nearly the same plane. The 15 largest moons in this solar system orbit their planets in nearly the same direction and plane as well. However, several smaller moons have highly inclined orbits around their planets. 19) A solar system has six terrestrial planets and four jovian planets. Each of the six terrestrial planets has at least five moons, while the jovian planets have no moons at all. 20) A solar system has four Earth-size terrestrial planets. Each of the four planets has a single moon that is nearly identical in size to Earth's Moon. 21) A solar system has many rocky asteroids and many icy comets. However, most of the comets orbit in the inner solar system, while the asteroids orbit in far-flung regions much like the Kuiper belt and Oort cloud of our solar system. 22) A solar system has several planets similar in composition to the jovian planets of our solar system but similar in mass to the terrestrial planets of our solar system. 23) A solar system has several terrestrial planets and several larger planets made mostly of ice. (Hint: What would happen if the solar wind started earlier or later than in our solar system?) 24) Radiometric dating of the oldest meteorites from another solar system shows that they are a billion years younger than rocks from the terrestrial planets of the same system.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 6 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 25) How many of the planets orbit the Sun in the same direction as Earth does? A) A few B) Most C) All Answer: No Correct Answer Was Provided. 26) The nebular theory holds that ________. A) our solar system formed from the collapse of an interstellar cloud of gas and dust B) each planet formed from the collapse of its own separate nebula C) the planets formed as a result of a near-collision between our Sun and another star Answer: No Correct Answer Was Provided. 27) The solar nebula was 98% ________. A) rock and metal B) hydrogen compounds C) hydrogen and helium Answer: No Correct Answer Was Provided. 28) Which of the following did not occur during the collapse of the solar nebula? A) Spinning faster B) Heating up C) Concentrating denser materials nearer the Sun Answer: No Correct Answer Was Provided. 29) What is Jupiter's main ingredient? A) Rock and metal B) Hydrogen compounds C) Hydrogen and helium Answer: No Correct Answer Was Provided. 30) Which of the following lists the major steps of solar system formation in the correct order? A) Collapse, accretion, condensation B) Collapse, condensation, accretion C) Accretion, condensation, collapse Answer: No Correct Answer Was Provided. 31) Leftover ice-rich planetesimals are called ________. A) comets B) asteroids C) meteorites Answer: No Correct Answer Was Provided.

32) What's unusual about our Moon? A) It's the only moon that orbits a terrestrial planet. B) It's by far the largest moon in the solar system. C) It's surprisingly large relative to the planet it orbits. Answer: No Correct Answer Was Provided. 33) Are there any exceptions to the rule that planets rotate with small axis tilts and in the same direction as they orbit the Sun? A) No B) Venus is the only exception. C) Venus and Uranus are exceptions. Answer: No Correct Answer Was Provided. 34) About how old is the solar system? A) 4.5 million years B) 4.5 billion years C) 4.5 trillion years Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 35) Group Discussion: Who Named the Planets? The names of the five planets that can be seen with the naked eye have been in use in the western world for thousands of years. However, beginning with the discoveries of Uranus in 1781 and Neptune in 1846, scientists needed to find names for planets and other newly discovered objects. a. Working in small groups, find out how Uranus and Neptune came to have their current names in English. Do you think these name choices made sense? Do you think the process that led to these names was "fair"? Why or why not? b. Each member of your group should learn about the names of Uranus and Neptune in two other languages, at least one of which is non-European. Discuss the similarities and differences you find among the names in different languages. c. Find out what names were considered for Pluto after its discovery in 1930, who suggested the name "Pluto," and how it came to be official. Are you surprised about who suggested the name? d. Find out how newly discovered objects (such as moons and asteroids) and surface features (such as those recently identified on Mars, Ceres, and Pluto) get their official names today. Do you think this process is appropriate? Make a list of other possibilities that might be considered (for example, allowing the discoverers to choose names or choosing through public, online competitions). If your group were in charge, would you change the current naming process in any way?

36) Group Discussion: Solar Origin Stories. Ancient cultures understood the immense importance of the Sun and told many stories about its origins. This chapter has told a different origin story, based on the nebular theory, which scientists consider to be supported by a wide body of evidence. a. Working independently, learn about an origin story for the Sun from a culture different from your own, taking the time necessary to understand the value and purpose of that story for the culture that told it. b. Gather in small groups and take turns sharing the origin stories you learned about. c. Make a list of notable similarities and differences among the origin stories your group learned about, then discuss any commonalities you see in the roles the stories played in their cultures. d. Discuss the similarities and differences between the ancient origin stories and the nebular theory. What do you think are the value and purpose of the nebular theory to our own culture? e. Discuss the potential value of the ancient origin stories to our own culture. What do we learn by seeking them out and retelling them? The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 37) Planetary Priorities. Suppose you were in charge of developing and prioritizing future planetary missions for NASA. What would you choose as your first priority for a new mission, and why? 38) Explaining the Past. Test the nebular theory against each of the three hallmarks of science discussed in Chapter 3. Be as detailed as possible in explaining whether the theory does or does not satisfy these hallmarks. Use your explanations to discuss whether it is really possible for science to inform us about how our solar system formed. Defend your opinion. 39) Unanswered Questions. As discussed in this chapter, the nebular theory answers many but not all questions about the origin of our solar system. Choose one important but unanswered question about the origin of our solar system and write two or three paragraphs in which you discuss how we might answer this question in the future. Be as specific as possible, focusing on the type of evidence necessary to answer the question and how the evidence could be gathered. What are the benefits of finding answers to this question?

40) Group Activity: A Cold Solar Nebula. The excess gas of the solar nebula is presumed to have been cleared away (by the solar wind) at a time when the frost line was located between the orbits of Mars and Jupiter, but study of planets around other stars suggests that gas may be cleared out earlier or later in other solar systems. In this activity, you'll consider how our solar system might have turned out differently if the excess gas of the solar nebula had not been cleared away until the entire disk of gas had cooled to 50 K.Note: You may wish to do this activity using the same four roles described in Chapter 1, Exercise 39. a. Make a list of ingredients that will condense at 50 K. b. Make a list of ways in which the terrestrial planets might have turned out differently under this alternative formation scenario. c. Repeat part b for the jovian planets. d. Discuss the likelihood that your predicted changes would match the actual characteristics of this alternative solar system. e. Come up with additional "what if" scenarios, discussing various other ways in which the planets might have turned out differently. Investigate Further 41) True or False. Decide whether each statement is true or false, and explain why. a. On average, Venus has the hottest surface temperature of any planet in the solar system. b. Our Moon is about the same size as moons of the other terrestrial planets. c. The weather conditions on Mars today are much different than they were in the distant past. d. Moons cannot have atmospheres, active volcanoes, or liquid water. e. Saturn is the only planet in the solar system with rings. f. Neptune orbits the Sun in the opposite direction of all the other planets. g. If Pluto were as large as the planet Mercury, we would classify it as a terrestrial planet. h. Asteroids are made of essentially the same materials as the terrestrial planets. i. When scientists say that our solar system is about 4½ billion years old, they are making a rough estimate based on guesswork about how long it should have taken planets to form. 42) Planetary Tour. Based on the brief planetary tour in this chapter, which planet besides Earth do you think is the most interesting, and why? Defend your opinion clearly in two or three paragraphs. 43) Patterns of Motion. In one or two paragraphs, summarize the orderly patterns of motion in our solar system and explain why their existence should suggest that the Sun and the planets all formed at one time from one cloud of gas, rather than as individual objects at different times. 44) Solar System Trends. Study the planetary data in Table 6.1 to answer each of the following. a. Notice the relationship between distance from the Sun and surface temperature. Describe the trend, explain why it exists, and explain any notable exceptions to the trend. b. The text says that planets can be classified as either terrestrial or jovian. Describe in general how the columns for density, composition, and distance from the Sun support this classification. c. Describe the trend you see in orbital periods and explain the trend in terms of Kepler's third law. d. Which column tells you which planet has the shortest days? Are there notable differences in the length of a day for the different types of planets? Explain. e. Which planets would you expect not to have seasons? Why? 41 Copyright © 2022 Pearson Education, Inc.

45) Two Kinds of Planets. The jovian planets differ from the terrestrial planets in a variety of ways. Using phrases or sentences that members of your family would understand, explain why the jovian planets differ from the terrestrial planets in each of the following: composition, size, density, distance from the Sun, and number of satellites. 46) An Early Solar Wind. Suppose the solar wind had cleared away the solar nebula before the seeds of the jovian planets could gravitationally draw in hydrogen and helium gas. How would the planets of the outer solar system be different? Would they still have many moons? Explain your answer in a few sentences. 47) History of the Elements. Our bodies (and most living things) are made mostly of water (H2O). Summarize the "history" of a typical hydrogen atom from its creation to Earth's formation. Do the same for a typical oxygen atom. (Hint: Which elements were created in the Big Bang, and where were the others created?) 48) Rocks from Other Solar Systems. Many "leftovers" from planetary formation were likely ejected from our solar system, and the same has presumably happened in other star systems. Given that fact, should we expect to find meteorites that come from other star systems? How rare or common would you expect them to be? (Be sure to consider the distances between stars.) Suppose that we did find a meteorite identified as a leftover from another stellar system. What could we learn from it? 49) Current Spacecraft Mission. Find a list of current interplanetary spacecraft missions. Choose one to learn about in detail and write a one- to two-page summary of the mission's basic design, goals, and status. 50) Dating the Past. Radiometric dating is used in many branches of science. For example, it is used to determine ages of fossils that help us learn the history of life on Earth and ages of relics that teach us about the rise of civilization. Research one use of radiometric dating outside of astronomy, writing a short report on how studies are conducted (such as what materials are dated and what radioactive elements are used) and what these studies have concluded. 51) Lucky to Be Here? Considering the overall process of solar system formation, do you think formation of a planet like Earth was likely? Could random events in the early history of the solar system have prevented our being here today? What implications do your answers have for the possibility of finding planets with Earth-like conditions around other stars? Defend your opinions.

Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 52) Radiometric Dating. You are dating rocks by their proportions of parent isotope potassium40 (half-life 1.25 billion years) and daughter isotope argon-40. Find the age for each of the following. a. A rock that contains equal amounts of potassium-40 and argon-40 b. A rock that contains three times as much argon-40 as potassium-40 53) Lunar Rocks. You are dating Moon rocks based on their proportions of uranium-238 (halflife of about 4.5 billion years) and its ultimate decay product, lead. Find the age for each of the following. a. A rock for which you determine that 55% of the original uranium-238 remains, while the other 45% has decayed into lead b. A rock for which you determine that 63% of the original uranium-238 remains, while the other 37% has decayed into lead 54) Carbon-14 Dating. The half-life of carbon-14 is about 5700 years. a. You find a piece of cloth painted with organic dye. By analyzing the dye, you find that only 77% of the carbon-14 originally in the dye remains. When was the cloth painted? b. A well-preserved piece of wood found at an archaeological site has 6.2% of the carbon-14 it must have had when it was living. Estimate when the wood was cut. c. Is carbon-14 useful for establishing Earth's age? Why or why not? 55) What Are the Odds? The fact that all the planets orbit the Sun in the same direction is cited as support for the nebular hypothesis. Imagine that there's a different hypothesis in which planets can be created orbiting the Sun in either direction. Under this hypothesis, what is the probability that eight planets would end up traveling in the same direction? (Hint: It's the same as the probability of flipping a coin eight times and getting all heads, then multiplied by two since the planets could end up traveling in either direction.)

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 7 Earth and the Terrestrial Worlds Section 7.1 1) In order of size from smallest to largest, the five terrestrial worlds are ________. A) Mercury, Venus, Earth, Moon, Mars B) Mercury, Moon, Venus, Earth, Mars C) Moon, Mercury, Venus, Earth, Mars D) Moon, Mercury, Mars, Venus, Earth E) Mercury, Moon, Mars, Earth, Venus Answer: D 2) Which of the following properties is used to distinguish between the core, mantle, and crust of a planet? A) Geological activity B) Temperature C) Rock strength D) Density E) Color Answer: D 3) The lithosphere of a planet is the layer that consists of ________. A) material above the crust B) material between the crust and the mantle C) the rigid rocky material of the crust and uppermost portion of the mantle D) the softer rocky material of the mantle E) the lava that comes out of volcanoes Answer: C 4) Why do terrestrial planet cores contain mostly metal? A) The entire planets are made mostly of metal. B) Metals condensed first in the solar nebula and the rocks then accreted around them. C) Metals are denser than rocks, so they sank to the center when the interiors were molten. D) Radioactivity created metals in the core from the decay of uranium. E) Convection in the mantle carried the metals to the core. Answer: C 5) Which of the following worlds have the thinnest lithospheres? (Hint: The answer is the same no matter whether you think of "thinnest" in actual depth in kilometers or as a proportion of the planet's radius.) A) Earth and the Moon B) Venus and the Moon C) Mercury and Venus D) Earth and Mars E) Earth and Venus Answer: E 1 Copyright © 2022 Pearson Education, Inc.

6) Which of the following best describes differentiation in planetary geology? A) Gravity separates molten materials according to density. B) Different types of minerals form a conglomerate rock. C) One planet's surface evolves differently from another planet's surface. D) One part of a planet's surface evolves differently from another part of the same planet's surface. E) Dense materials condense at higher temperatures than less dense materials. Answer: A 7) Which of the following must be true for differentiation to occur in a planet? A) The planet must have a rocky surface. B) The planet must be made of both metal and rock. C) The planet must have an atmosphere. D) The planet must be geologically active, that is, have volcanoes, planetquakes, and erosion from weather. E) The planet must have a molten interior. Answer: E 8) Which internal energy source(s) produce(s) heat by converting gravitational potential energy into thermal energy? A) Accretion B) Differentiation C) Radioactivity D) Both accretion and differentiation E) All three of accretion, differentiation, and radioactivity Answer: D 9) Which internal energy source is the most important in continuing to heat the terrestrial planets today? A) Accretion B) Differentiation C) Radioactivity D) Tidal heating Answer: C 10) What are the three main sources of internal heat for terrestrial planets? A) Conduction, differentiation, and accretion B) Accretion, differentiation, and radioactivity C) Accretion, differentiation, and eruption D) Convection, differentiation, and eruption E) Conduction, convection, and eruption Answer: B

11) Which of the following best describes convection? A) Rocks sink in water. B) Warm material expands and rises while cool material contracts and falls. C) Warm material gets even warmer and cool material gets even cooler. D) A liquid separates according to density, such as oil and water separating in a jar. E) Bubbles of gas move upward through a liquid of the same temperature. Answer: B 12) What is necessary for convection to occur in a substance? A) The substance must be subjected to a strong magnetic field. B) Dense material must be added to the substance. C) The substance is strongly shaken or disturbed by a strong wind. D) The substance is strongly cooled from underneath. E) The substance is strongly heated from underneath. Answer: E 13) What is the main process by which heat flows upward through the lithosphere? A) Conduction B) Convection C) Radiation D) Accretion E) Differentiation Answer: A 14) Heat escapes from a planet's surface into space by thermal radiation. In which wavelength range do planets radiate most of their light? A) Infrared B) Radio C) Visible D) Ultraviolet E) X-rays Answer: A 15) Which terrestrial world has the strongest magnetic field? A) Mars B) Earth C) the Moon D) Venus E) Mercury Answer: B

16) Why does Earth have the strongest magnetic field among the terrestrial worlds? A) It is the only one that has a metallic core. B) It rotates much faster than any other terrestrial world. C) It is the only one that has both a convecting core region and reasonably rapid rotation. D) It is by far the largest terrestrial world. E) It is the most volcanically active world. Answer: C 17) What conditions are thought to be necessary for a terrestrial planet to have a strong magnetic field? A) Aa molten metallic core only B) Fast rotation only C) A rocky mantle only D) Both a molten metallic core and reasonably fast rotation E) Both a metal core and a rocky mantle Answer: D 18) Approximately how large (across) is an impact crater compared to the size of the impactor? A) The same size B) 10–20 percent larger C) 10 times larger D) 100 times larger E) 1000 times larger Answer: C 19) An impact crater that is 10 kilometers across was probably made by the impact of an object about ________ across. A) 10 meters B) 100 meters C) 1 kilometer D) 10 kilometers E) 100 kilometers Answer: C 20) Volcanism is more likely on a planet that ________. A) is closer to the Sun B) is struck often by meteors and solar system debris C) has high internal temperature D) doesn't have an atmosphere or oceans Answer: C

21) How does the lava that forms a steep-sided volcano (a stratovolcano) compare to the lava that forms a shallow-sloped volcano (a shield volcano)? A) The lava is thicker (higher viscosity) for the steep-sided stratovolcano. B) The lava is runnier (lower viscosity) for the steep-sided stratovolcano. C) The lava comes from deeper in Earth's mantle for the steep-sided stratovolcano. D) The lava comes from a very shallow layer of Earth's crust for the steep-sided stratovolcano. E) The lava contains more metal for the steep-sided stratovolcano. Answer: A 22) Which factor below determines the steepness of a volcano? A) How easily the lava flows B) The temperature of the lava C) The duration of the eruption D) The age of the volcano E) The volume of lava Answer: A 23) What caused Earth's lithosphere to fracture into plates? A) Impacts of asteroids and planetesimals B) Internal temperature changes that caused the crust to expand and stretch C) Convection of the underlying mantle D) Tidal forces from the Moon and Sun E) Volcanism, which produced heavy volcanoes that bent and cracked the lithosphere Answer: C 24) Which of the following best describes tectonics? A) The creation of bowl-shaped depressions by asteroids or comets striking a planet's surface B) The eruption of molten rock from a planet's interior to its surface C) The disruption of a planet's surface by internal stresses D) The wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather Answer: C 25) A planet is most likely to have volcanic and tectonic activity if it has ________. A) low surface gravity B) high surface gravity C) low internal temperature D) high internal temperature E) a dense atmosphere Answer: D

26) What can we conclude when we see a region of a planet that is not as heavily cratered as other regions? A) There is little volcanic activity to create craters. B) The planet is rotating very slowly and only one side was hit by impactors. C) The planet formed after the age of bombardment and missed out on getting hit by leftover planetesimals. D) The surface in the region is older than the surface in more heavily cratered regions. E) The surface in the region is younger than the surface in more heavily cratered regions. Answer: E 27) Which of the following best describes why the smaller terrestrial worlds have cooler interiors than the larger ones? A) They were cooler when they formed. B) The smaller ones are farther from the Sun. C) They have relatively fewer radioactive elements. D) They have relatively more surface area compared to their volumes. E) They had more volcanic eruptions in the past, which released their internal heat. Answer: D 28) Which of the following surface features may result from tectonics? A) Mountains B) Valleys C) Volcanos D) Cliffs E) All of the above Answer: E 29) What would happen to Earth's temperature if you painted the entire surface of the Earth black? A) Its average temperature would go up. B) Its average temperature would go down. C) Its temperature would not change. Answer: A 30) What would happen to Earth's temperature if you painted the entire surface of the Earth white? A) Its temperature would not change. B) Its average temperature would go down. C) Its average temperature would go up. Answer: B

31) Which terrestrial world has the highest average surface temperature? A) Mercury B) Venus C) the Moon D) Mars E) Earth Answer: B 32) Which terrestrial world has the greatest difference in temperature between its "no greenhouse" temperature and its actual temperature? A) Mercury B) Venus C) Earth D) the Moon E) Mars Answer: B 33) Why does Venus have such a great difference in temperature between its "no greenhouse" temperature and its actual temperature? A) It has a slow rotation. B) It is so close to the Sun. C) It has a large amount of carbon dioxide in its atmosphere. D) It has a high level of volcanic activity. E) It has no cooling effects from oceans. Answer: C 34) Venus has a higher average surface temperature than Mercury. Why? A) Because its surface is covered with hot lava from numerous active volcanoes B) Because its slow rotation gives it more time to heat up in sunlight C) Because it is closer to the Sun D) Because its surface is heated by an extreme greenhouse effect Answer: D 35) Rank these planets in order of the strength of the greenhouse effect on the planet, from the weakest to the strongest greenhouse effect. A) Mars, Mercury, Earth, Venus B) Mercury, Venus, Earth, Mars C) Mercury, Earth, Mars, Venus D) Mercury, Mars, Earth, Venus E) Mars, Earth, Venus, Mercury Answer: D

36) What are greenhouse gases? A) Gases that absorb visible light B) Gases that absorb ultraviolet light C) Gases that absorb infrared light D) Gases that emit visible light E) Gases that transmit infrared light Answer: C 37) How does the greenhouse effect work? A) Greenhouse gases transmit visible light, allowing it to heat the surface, but then absorb infrared light emitted by the surface, trapping the heat near the surface. B) The higher pressure of an atmosphere at lower altitudes traps heat more effectively. C) Greenhouse gases are ionized by sunlight, making them heat up their surroundings. D) Greenhouse gases absorb x-rays and ultraviolet light from the Sun, which then heat the atmosphere and the surface. E) Greenhouse gases absorb infrared light from the Sun, which then heats the atmosphere and the surface. Answer: A 38) Why does increasing the amount a greenhouse gas increase the temperature of a planet? A) More greenhouse gas means that air molecules are heavier on average. B) More greenhouse gas means more absorption of visible light from the Sun. C) More greenhouse gas means higher atmospheric pressure. D) More greenhouse gas means more absorption of infrared light emitted by the planet. Answer: D 39) Of the four gases CO2, H2O, N2, and O2, which are greenhouse gases? A) Only CO2 B) CO2 and H2O C) CO2 and N2 D) All except O2 E) All four Answer: B 40) Which of the following is not a greenhouse gas? A) Water (H2O) B) Molecular oxygen (O2) C) Carbon dioxide (CO2) D) Methane (CH4) Answer: B

41) What would Earth's average surface temperature be if it had no greenhouse effect? A) Below the freezing point of water B) Slightly above the freezing point of water C) About 10°C D) The same temperature as it is with the greenhouse effect E) Slightly warmer than it is with the greenhouse effect Answer: A 42) By about how much does the greenhouse effect change the temperature of Earth? A) 30 K B) 5 K C) −16 K D) 500 K Answer: A 43) What kind of thermal radiation does Earth emit? A) Infrared light B) Visible and ultraviolet light C) Infrared and visible light D) Infrared, visible, and ultraviolet light E) Visible light Answer: A 44) Earth's stratosphere is heated primarily by which process? A) Convection from the Earth's surface B) Absorption of infrared light by greenhouse gases C) Absorption of visible light by ozone D) Absorption of ultraviolet light by ozone E) Absorption of infrared sunlight Answer: D 45) Which of the following gases absorbs ultraviolet light best? A) Carbon dioxide B) Nitrogen (N2) C) The oxygen we breathe (O2) D) Hydrogen E) Ozone (O3) Answer: E 46) Which of the following planets has a stratosphere? A) Mercury B) Venus C) Earth D) Mars E) All of the above Answer: C 9 Copyright © 2022 Pearson Education, Inc.

47) In which layer of Earth's atmosphere is ultraviolet light absorbed? A) Exosphere B) Thermosphere C) Stratosphere D) Troposphere Answer: C 48) Why is the sky blue? A) Air molecules scatter blue light more effectively than red light. B) The gases in Earth's atmosphere emit blue light. C) The Sun mainly emits blue light. D) The atmosphere transmits mostly blue light. E) Because of the way light is reflected off of the oceans. Answer: A 49) Why are sunsets and sunrises red? A) The Sun emits more red light when it's near the horizon. B) Sunlight must pass through more atmosphere to reach our eyes at those times, so more blue light is scattered away. C) Sunlight must pass through more atmosphere to reach our eyes at those times, which means it passes through a larger volume of red air molecules. D) The lower temperatures of morning and evening (compared to midday) make the sky redder in color. Answer: B 50) Which of the following would lead to a warmer temperature for a planet? A) A decrease in the planet's reflectivity B) A decrease in the planet's amount of greenhouse gases C) A decrease in the brightness of the Sun D) A decrease in the number of volcanic eruptions on the planet Answer: A 51) Venus is much hotter than the Earth. Which of the following explains most of this temperature difference? A) Venus has much more carbon dioxide in its atmosphere. B) Venus's clouds have a very high reflectivity. C) Venus rotates backward compared to its orbital rotation. D) The sunlight reaching Venus is more concentrated because of its closer distance to the Sun. Answer: A 52) All of the following statements are true. Which one provides strong observational support for the claim that greenhouse gases make a planet warmer than it would be otherwise? A) Venus has a higher average temperature than Mercury. B) Earth is the only planet with an ozone layer in its atmosphere. C) Earth has a higher average temperature than Mars. D) Mercury is much hotter than the Moon. Answer: A 10 Copyright © 2022 Pearson Education, Inc.

53) Which of the following statements about the greenhouse effect is true? A) Without the naturally occurring greenhouse effect, Earth would be too cold to have liquid oceans. B) A weak greenhouse effect operates on Mars. C) The burning of fossil fuels increases the greenhouse effect on Earth because of the release of carbon dioxide. D) One result of an increased greenhouse effect on Earth may be an increased number of severe storms. E) All of the above are true. Answer: E 54) Which of the following gases in Earth's atmosphere is not primarily a product of volcanic outgassing? A) Water (H2O) B) Nitrogen (N2) C) Oxygen (O2) D) Carbon dioxide (CO2) Answer: C Section 7.2 1) How were the relatively few craters that we see within the lunar maria formed? A) By impacts that occurred before those that formed most of the craters in the lunar highlands B) By impacts that occurred after those that formed most of the craters in the lunar highlands C) By the same large impactor that led to the formation of the maria D) They are volcanic in origin, rather than from impacts. E) They are sinkholes that formed when sections of the maria collapsed. Answer: B 2) How did the relatively smooth regions on the Moon known as the lunar maria form? A) Large impacts fractured the Moon's lithosphere, allowing lava to fill the impact basins. B) The early bombardment created heat that melted the lunar surface in the regions of the maria. C) Volatiles escaping from the Moon's interior heated and eroded the surface in the regions of the maria. D) The giant impact that created the Moon left smooth areas that we call the maria. E) The maria are the result of gradual erosion by micrometeorites striking the Moon. Answer: A 3) Left undisturbed, the footprints left on the Moon by the Apollo astronauts will likely ________. A) already have been erased by erosion B) remain visible for a few more decades C) remain visible for millions of years D) remain permanently visible on the Moon Answer: C

4) The Caloris Basin on Mercury covers a large region of the planet and contains relatively few smaller craters. From this, we conclude that ________. A) erosion destroyed most of the smaller craters that formed on the basin B) Mercury's atmosphere prevented smaller objects from hitting the surface C) only very large impactors hit Mercury's surface in the past D) the Caloris Basin formed toward the end of the heavy bombardment E) the Caloris Basin was formed by a volcano Answer: D 5) Which of the following is the best explanation for the tremendous cliffs on Mercury? A) They were probably carved in Mercury's early history by running water. B) They were probably formed by tectonic stresses when the entire planet shrank as its core cooled. C) They probably formed when a series of large impacts hit Mercury one after the other. D) They are almost certainly volcanic in origin, carved by flowing lava. E) They represent one of the greatest mysteries in the solar system, as no one has suggested a reasonable hypothesis for their formation. Answer: B 6) In what form does water exist on the Moon? A) There is water ice in craters near the poles. B) There are small pools of liquid water just beneath the surface. C) There are shallow lakes of liquid water in the deepest craters. D) There is water ice in the bright regions of the lunar maria. E) There is no water in any form on the Moon. Answer: A Section 7.3 1) Valles Marineris is a ________. A) large valley on the Moon B) vast plain on Mars C) huge series of cliffs on Mercury D) large canyon on Mars E) large canyon on Venus Answer: D 2) The polar caps on Mars are composed of ________. A) frozen carbon dioxide only B) water ice only C) both frozen carbon dioxide and water ice D) frozen hydrogen E) salt deposits Answer: C

3) Which of the following does not provide evidence that Mars once had large amounts of liquid water on its surface? A) The presence of what looks like dried-up riverbeds B) The presence of impact craters that appear to have formed in mud C) The vast canal system described by Percival Lowell D) The presence of minerals, dry clay, and sedimentary rock that form in water E) Some very old craters that appear to have been eroded by rain Answer: C 4) Rovers sent to Mars have discovered ________. A) minerals in Martian rocks that can only form in liquid water B) clear evidence that life once existed on Mars C) Mars has more craters than previously thought D) small pockets of liquid water lying just beneath the Martian soil Answer: A 5) Based on current evidence, when is/was liquid water abundant on the surface of Mars? A) Only before about 3 billion years ago B) Only during the first 1 million years of Mars's existence C) Water comes and goes, with the most recent water flows occurring a few thousand years ago. D) Only during the most recent 1 billion years of Mars's history Answer: A 6) Which of the following worlds show evidence of dried up rivers and lake beds? A) the Moon B) Mercury C) Venus D) Mars E) All of the above Answer: D 7) How might Mars's weakened magnetic field have allowed for major changes in its climate? A) Atmospheric gases were left vulnerable to being stripped into space by solar wind particles. B) The heat combined with the magnetic field and disappeared with it. C) Mars has actually heated up since the magnetic field weakened, since the solar rays no longer have such a dense layer to get through. D) They are completely unrelated; there is no possible influence. Answer: A

8) Which of these observations helped test the idea that Mars' atmosphere thinned due to interactions with the solar wind? A) The MAVEN orbiter measured present-day gas loss from Mars' atmosphere. B) The Curiosity rover measured the carbon content of rocks on Mars' surface. C) Astronomers used spectrographs on the Keck telescope to measure the density of Mars' atmosphere. D) Geologists measured the carbon content of Martian rocks that were transported to Earth by asteroid impacts. Answer: A 9) Suppose that Mars were located at the same distance from the Sun as Earth, but was otherwise the same. Would it still be colder than Earth? Why or why not? A) Yes, because Mars has fewer clouds than Earth B) Yes, because Mars has a much weaker greenhouse effect than Earth C) Yes, because Mars has less gravity than the Earth D) No, because with the same distance from the Sun, the two planets would have the same temperature Answer: B 10) Why does Mars have more extreme seasons than Earth? A) Because it is farther from the Sun B) Because it has a larger axis tilt C) Because it has a more elliptical orbit D) Because it has more carbon dioxide in its atmosphere Answer: C 11) Why is Mars red? A) It is made primarily of the red rock known as reddite. B) Its surface rocks were rusted by oxygen. C) Its atmosphere scatters blue light more effectively than red light. D) Its surface is made of ices that absorb blue light. E) Its surface is made of ices that absorb red light. Answer: B 12) All the following statements about Mars are true. Which one might be the cause of a significant loss of atmospheric gas to space? A) The rock on Mars is probably red because of chemical reactions with oxygen that had been released into the atmosphere through the outgassing of water molecules. B) Mars lost its global magnetic field, leaving the atmosphere vulnerable to the solar wind. C) The axis tilt of Mars is thought to change significantly with time. D) Mars probably once had a much higher density of greenhouse gases in its atmosphere than it does today. Answer: B

Section 7.4 1) Which of the following could explain why Venus does not have a strong magnetic field? A) It does not have a metallic core. B) Its rotation is too slow. C) It is too close to the Sun. D) It is too large. E) It has too thick an atmosphere. Answer: B 2) How have we been able to construct detailed maps of surface features on Venus? A) By studying Venus from Earth with powerful telescopes B) By studying Venus with powerful optical telescopes on spacecraft that were sent to orbit Venus C) By making computer models of geological processes on Venus D) By using radar from spacecraft that were sent to orbit Venus E) By landing spacecraft on the surface for close-up study Answer: D 3) Which two geological processes appear to have been most important in shaping the present surface of Venus? A) Impacts and volcanoes B) Impacts and tectonics C) Tectonics and erosion D) Volcanoes and tectonics E) Volcanoes and erosion Answer: D 4) Why can't astronomers study the surface of Venus with visible light telescopes? A) Venus' thick atmosphere prevents us from seeing the surface. B) We do not have telescopes with good enough angular resolution. C) Venus doesn't reflect any visible light. Answer: A 5) Spacecraft have landed on all the terrestrial worlds except ________. A) Mercury B) Venus C) Moon D) Mars E) Spacecraft have landed on all of the terrestrial worlds. Answer: E

6) Why does Earth's atmosphere contain much less carbon dioxide than Venus's atmosphere? A) Earth's volcanoes did not outgas as much carbon dioxide as those on Venus. B) Most of Earth's carbon dioxide was lost to space during the heavy bombardment. C) Chemical reactions with other gases destroyed the carbon dioxide and replaced it with the nitrogen that is in the atmosphere now. D) Most of Earth's carbon dioxide dissolved in the oceans, where it became incorporated into carbonate rocks. E) Earth formed farther from the Sun, and there was less carbon dioxide at great distances in the solar nebula. Answer: D 7) Venus has a high reflectivity because of its ________. A) light-colored rocks B) snow C) clouds D) dust storms E) volcanic ash Answer: C 8) All of the statements below are true. Which one gives the primary reason why the surface of Venus today is some 450°C hotter than the surface of Earth? A) Venus is only about 73 percent as far from the Sun as Earth. B) Venus has a much stronger greenhouse effect than Earth. C) Venus has a much higher reflectivity than Earth. D) Venus has a higher atmospheric pressure than Earth. Answer: B 9) Venus may have started with an ocean's worth of water. If so, where is its water now? A) The original water remains vaporized in the atmosphere due to Venus's intense heat. B) Most of the water is frozen beneath the surface. C) Most of the water combined with rocks in chemical reactions. D) The water was lost when ultraviolet light broke apart water molecules and the hydrogen escaped to space. E) The water changed to carbon dioxide through chemical reactions. Answer: D 10) In science, "positive feedback" is a term that applies to ________. A) a process undergoing a self-reinforcing cycle that amplifies some initial effect B) commentary that reflects a high opinion of a scientist's work C) feedback that has a positive electrical charge D) a process that can only continue as long as most scientists continue to support it Answer: A

11) Mars' atmosphere is mostly carbon dioxide. Why does it not experience a runaway greenhouse effect like Venus? A) Mars is protected by its magnetic field. B) Mars does not have enough additional water vapor to magnify the warming. C) Mars' atmosphere is too thin. D) Mars has a CO2 cycle like Earth that regulates the amount of carbon dioxide. Answer: C Section 7.5 1) What process has played the greatest role in determining the arrangement of the continents on Earth? A) Impact cratering B) Volcanism C) Plate tectonics D) Erosion E) Acid rain Answer: C 2) Which of the following is not evidence for plate tectonics on Earth? A) Some continental boundaries fit together like pieces of a jigsaw puzzle. B) Similar rocks and fossils are found in different continents. C) High ocean ridges between the continents D) The existence of volcanoes E) Earthquakes Answer: D 3) On average, approximately how fast do plates move with plate tectonics on Earth? A) A few centimeters per year B) A few millimeters per century C) A few centimeters per century D) They do not move at all, except during earthquakes. E) A few kilometers per hour Answer: A 4) According to current understanding of plate tectonics, which of the following is true about Earth's seafloors? A) They are built from rocks that are older than the rocks found on the continents. B) They represent the thickest regions of Earth's crust. C) Their material is almost completely recycled over a time period of about 200 million years. D) They should be covered with numerous impact craters dating to the time of the heavy bombardment. Answer: C

5) Ridges in the middle of the ocean are places where ________. A) one plate slides under another, returning older crust to the mantle B) hot mantle material rises upward, creating volcanic islands C) hot mantle material rises upward and spreads sideways, pushing the plates apart D) plates push together, creating ocean mountain chains E) plates slip sideways relative to one another Answer: C 6) Deep trenches in the ocean mark places where ________. A) one plate slides under another, returning older crust to the mantle B) plates pull apart, leaving great rifts in the crust C) hot mantle material rises upward and spreads sideways, pushing the plates apart D) plates push together, creating ocean mountain chains E) plates slip sideways relative to one another Answer: A 7) What is the main factor that makes Earth more geologically active than the other terrestrial planets? A) It is larger, so it has retained its internal heat for longer. B) It is farthest from the Sun, so it receives less light. C) It has a large Moon, so it is heated by tidal forces. D) It has far more radioactive material than other planets. E) It formed much later than the other planets. Answer: A 8) A planet with a higher reflectivity will do which of the following? A) Reflect more light and absorb less light B) Reflect less light and absorb more light C) Emit more light D) Emit higher energy light E) Transmit more light Answer: A 9) Which of the following can act like a long-term "thermostat" that helps keep Earth's average temperature fairly stable? A) Radioactive elements trapped in the Earth's mantle B) Heat stored in the Earth's magnetosphere C) Heat stored in the Earth's liquid core D) The carbon dioxide cycle that moves carbon dioxide between Earth's atmosphere, oceans, and rock Answer: D

10) Considering just the effects of the carbon dioxide cycle, if the Earth were to warm up a bit, what would happen? A) More evaporation and rainfall would reduce the atmospheric CO2 levels, and the greenhouse effect would weaken. B) More evaporation and rainfall would increase the atmospheric CO2 levels, and the greenhouse effect would strengthen. C) Carbonate materials would form in the oceans more rapidly, the atmospheric CO2 content would decrease, and the greenhouse effect would strengthen. D) There would be a runaway greenhouse effect, with the Earth becoming ever hotter until the oceans evaporated (as may have happened on Venus). E) The ice caps would melt and cool the Earth back to its normal temperature. Answer: A 11) Earth has gone in and out of numerous ice ages over the past couple million years. Which of the following was generally true during all those ice ages? A) The atmospheric carbon dioxide concentration was much higher than it is today. B) The atmospheric carbon dioxide concentration was much lower than it is today. C) The continents were closer together than they are today. D) The continents were farther apart than they are today. E) There were much larger mammals than there are today. Answer: B 12) Global warming is causing Earth to have less total sea ice. This, in turn, causes ________. A) Earth to absorb more total sunlight, heating our planet even more B) Earth to reflect more sunlight, counteracting the effects of global warming C) Earth's oceans to get heavier, lowering sea level Answer: B 13) Where did the molecular oxygen in Earth's atmosphere come from? A) Photosynthesis by living organisms B) The breakdown of water molecules by sunlight C) Outgassing from volcanoes D) Evaporation from the oceans E) Chemical reactions with surface rocks Answer: B 14) Which of the following is an expected consequence of global warming? A) More extreme weather events, including extreme winter storms B) Ocean water becoming more acidic C) An increase in sea level D) Reduced ice coverage in the Arctic Ocean E) All of the above are expected consequences of global warming. Answer: B

15) Why does the burning of fossil fuels increase the greenhouse effect on Earth? A) The heat from the flames warms the planet. B) Burning fossil fuels releases carbon dioxide into the atmosphere. C) Burning fossil fuels depletes the amount of ozone, thereby warming the planet. D) Burning fossil fuels produces infrared light, which is then trapped by existing greenhouse gases. Answer: B 16) Climate models support the claim that human activity is causing the currently observed global warming because ________. A) the models can perfectly predict all aspects of today's climate B) climate models that include contributions by human activity agree much better with actual data than models that consider only natural factors C) the models are very sophisticated, with thousands of equations, and this gives scientists confidence that the models must be correct D) the models predict that warming will continue in the future Answer: B 17) Which of the following describes the most convincing evidence in support of the idea that human activity is causing climate change on Earth? A) Polls show that a majority of Americans agree that this is the case. B) The vast majority of scientists say so. C) The known science behind the greenhouse effect predicts that warming should be occurring as the carbon dioxide concentration rises, and the average temperature is rising as expected. D) There is no other known process besides the burning of fossil fuels that can lead to any change in Earth's average temperature. Answer: C 18) The Sun is gradually increasing in brightness as it ages. Why isn't this considered to be an explanation for global warming? A) A change in the Sun's brightness would not be expected to have any effect on Earth's average temperature. B) The scientists are covering up this potentially valid explanation. C) The amount of energy the Earth receives from the Sun remains constant regardless of what the Sun does. D) The Sun is increasing in brightness much too slowly to be causing the current warming. Answer: D 19) If the amount of polar ice decreases, what would happen, and why? A) Cooling, because melted ice cools things off B) Warming, because more sunlight is reflected C) Cooling, because more sunlight is reflected D) Warming, because more sunlight is absorbed Answer: D

20) Given the rate at which human activity is increasing atmospheric carbon dioxide levels, why can't we expect the natural carbon dioxide cycle to prevent global warming? A) It operates too slowly. B) It only affects the rate at which carbon dioxide circulates within the atmosphere, not the total amount of carbon dioxide in the atmosphere. C) The natural carbon dioxide cycle no longer operates. D) The carbon dioxide cycle can only affect natural carbon dioxide, not the carbon dioxide released through human activity. Answer: A 21) In the greenhouse effect, what is the direct cause of extra heating of the Earth's surface? A) Additional carbon dioxide makes the atmosphere more transparent to infrared light, allowing the sun to more directly heat the surface. B) Additional carbon dioxide makes the atmosphere more opaque to infrared light, trapping more of the infrared light emitted by Earth. C) Additional carbon dioxide makes the atmosphere more dense, so heat passes through it more slowly. D) Additional carbon dioxide makes the atmosphere emit more infrared light which gets trapped near the surface of the Earth. Answer: B

22) Refer to the figure above. What can you conclude from the data shown on this graph alone? A) The carbon dioxide concentration varies naturally, but is much higher today than it has been in the past 800,000 years. B) Human activity has caused the carbon dioxide concentration to rise and fall many times in the past 800,000 years. C) Changes in the carbon dioxide concentration are the causes of ice ages. D) If current trends continue, carbon dioxide will soon be the most abundant gas in Earth's atmosphere. Answer: A

23) Refer to the figure above. Today's carbon dioxide concentration is about ________ that at any other time in the past 800,000 years. A) 2 % higher than B) 45% higher than C) double D) 400 times Answer: B 24) In what ways is Earth different from the other terrestrial planets? A) Its lithosphere is broken into plates that move around. B) It has a much higher percentage of oxygen in its atmosphere. C) Most of its surface is covered with liquid water. D) Life can be found almost everywhere on its surface. E) All of the above are true. Answer: E Short Answer Questions 1) Describe the three sources of internal heat of the terrestrial planets. Answer: Accretion is heat generated by the agglomeration of planetesimals when the planet was formed. Differentiation is heat generated by the energy released as dense objects fall toward the center of a planet during the formation of the core of a planet. Radioactive decay generates heat by releasing nuclear energy when an unstable (radioactive) isotope decays into a more stable element. 2) Explain how we can estimate the geological age of a planetary surface from its number of impact craters. Answer: Even though impacts still occur today, the vast majority of craters formed during the bombardment period that ended around 3.8 billion years ago. A surface region that is still saturated with craters must have remained essentially undisturbed for the last 3.8 billion years. In contrast, a surface region that has few craters indicates that the original craters must have been "erased" by other geological processes since then. 3) List at least three things that make Earth unique among the terrestrial planets. Answer: Many possible answers, including: It is the only planet with an oxygen-rich atmosphere; it is the only planet with an ozone layer; it is the only planet with surface liquid water; it is the only planet with a surface that has been significantly altered by plate tectonics; its climate has been stable enough for liquid water to persist for billions of years; it has a very large Moon relative to its size; it is the only planet we know of that harbors life. 4) What evidence suggests that Mercury contracted within about a billion years after it formed? Answer: The surface of Mercury is marked by long, high cliffs. Such features result from tectonic compression, but there are no corresponding features due to tectonic stretching. This suggests the whole planet contracted as it rapidly cooled in its early history. We can date the contraction from the age of the volcanic flows on its surface: volcanic (and all geologic) activity probably came to an abrupt halt as a result of the planet's contraction. 22 Copyright © 2022 Pearson Education, Inc.

5) Earth and Venus both presumably had similar gases outgassed from their volcanoes. Briefly explain how their atmospheres ended up so different. Answer: On Venus, water and carbon dioxide remained in the atmosphere. Over time, ultraviolet light split the water molecules and the hydrogen escaped to space. Thus, Venus has no more water today and an atmosphere thick with carbon dioxide. On Earth, water condensed to rain and eventually formed the oceans. Carbon dioxide was absorbed in the oceans and is now locked up in carbonate rocks. Thus, most of the water on Earth remains in the oceans, and most of the carbon dioxide is in rocks, leaving a much thinner atmosphere than that of Venus. 6) Why did Earth retain most of its water while Venus and Mars lost theirs? Answer: The basic answer is that Earth was at just the right distance to retain water as liquid. Venus lost its water because it was too hot. At its closer proximity to the Sun, Venus was warm enough to keep all its water in gaseous form in the atmosphere. When the runaway greenhouse effect became prominent, Venus became even warmer and the water vapor escaped into space. Mars was far enough from the Sun that it was cold enough for the water vapor to freeze out of the atmosphere, resulting in thick polar caps. 7) Why does Earth have so little carbon dioxide in its atmosphere, when Earth should have outgassed about as much of it as Venus? Answer: The answer to this question is that Earth has oceans. Carbon dioxide can dissolve in water, and the oceans actually contain much more carbon dioxide than the atmosphere. However, most of the carbon dioxide is locked up in rocks on the seafloor. Rainfall erodes rocks on Earth's surface. These rocks react with dissolved carbon dioxide in the oceans to form carbonate minerals, which fall to the ocean floor. 8) Why does Earth have so much more oxygen (O2) than Venus or Mars? Answer: The answer to this question is simply that Earth has life. Photosynthesis supplies oxygen to the atmosphere by converting CO2 to O2. Oxygen is removed from the atmosphere through oxidation processes such as fire and rust. Therefore, Earth originally developed its oxygen atmosphere when photosynthesis added oxygen at a rate greater than it could be removed.

Reading Quiz Questions 1) Suppose we use a baseball to represent Earth. On this scale, the other terrestrial worlds (Mercury, Venus, the Moon, and Mars) would range in size approximately from that of ________. A) a golf ball to a baseball B) a dust speck to a golf ball C) a dust speck to a basketball D) a golf ball to a beach ball Answer: A 2) From center to surface, which of the following correctly lists the interior layers (defined by density) of a terrestrial world? A) Core, mantle, crust B) Mantle, core, crust C) Mantle, crust, core D) Core, crust, lithosphere Answer: A 3) What do we mean when we say that the terrestrial worlds underwent differentiation? A) When their interiors were molten, denser materials sank toward their centers and lighter materials rose toward their surfaces. B) The five terrestrial worlds all started similarly but ended up looking quite different. C) Their surfaces show a variety of different geological features resulting from different geological processes. D) They lost interior heat to outer space. Answer: A 4) A terrestrial world's lithosphere is ________. A) a layer of relatively strong, rigid rock, encompassing the crust and part of the mantle B) a thin layer of rock that lies between the mantle and crust C) the interior region in which the planet's magnetic field is generated D) a layer of hot, molten rock encompassing the core and part of the mantle Answer: A 5) The two most important processes in heating the interiors of the terrestrial worlds are: A) (1) heat deposited by the process of formation (2) heat released by radioactive decay. B) (1) heat deposited by the process of formation (2) heat that came from the gravitational potential energy of incoming planetesimals. C) (1) heat from convection (2) heat from thermal radiation. D) (1) volcanism (2) tectonics. Answer: A

6) Which of the following is an example of convection? A) Warm air expanding and rising while cooler air contracts and fall. B) Different kinds of material separating by density, like oil and water. C) Rocks sinking in water. D) Gas bubbling upward through a liquid. Answer: A 7) What is a magnetosphere? A) A region of space around a planet in which the planet's magnetic field can trap charged particles B) The layer of a planet in which its magnetic field is generated C) The uppermost layer of any planetary atmosphere D) The region in a planet's atmosphere in which auroras occur Answer: A 8) The processes responsible for virtually all surface geology are ________. A) impact cratering, volcanisms, tectonics, and erosion B) convection, conduction, and radiation C) accretion, differentiation, and radioactive decay D) eruptions, lava flows, and outgassing Answer: A 9) In the context of planetary geology, what do we mean by outgassing? A) The release by volcanism of gases that had been trapped in a planetary interior B) The loss of atmospheric gas to outer space C) Another name for a volcanic eruption D) The evaporation of water that adds water vapor (a gas) to an atmosphere Answer: A 10) Which of the following is not an example of tectonics? A) The gradual disappearance of a crater rim as a result of wind and rain. B) The formation of a cliff when the lithosphere shrinks. C) The slow movement of Earth's lithospheric plates. D) The stretching of the crust by underlying mantle convection. Answer: A 11) Suppose we represent Earth with a basketball. On this scale, most of the air in Earth's atmosphere would fit in a layer that is ________. A) about the thickness of a sheet of paper B) about an inch thick C) about 6 inches thick D) about a half-inch thick Answer: A

12) Why is the sky blue (on Earth)? A) Because molecules scatter blue light more effectively than red light B) Because the Sun emits mostly blue light C) Because molecules scatter red light more effectively than blue light D) No one knows - this is one of the great mysteries of science Answer: A 13) Which of the following is the most basic definition of a greenhouse gas? A) A gas that absorbs infrared light B) A gas that makes a planet much hotter than it would be otherwise, even in small amounts C) A gas that keeps warms air from rising, and therefore warms the surface D) A gas that reflects a lot of sunlight Answer: A 14) Which of the following best describes the lunar maria? A) Relatively smooth, flat plains on the Moon B) Densely cratered regions on the Moon C) Mountainous regions on the Moon D) Frozen oceans of liquid water on the Moon Answer: A 15) Why does the Moon have a layer of "powdery soil" on its surface? A) It is the result of countless tiny impacts by small particles striking the Moon. B) Recent, large impacts shattered lunar rock to make this soil. C) It is made by the same processes that make powdery sand on Earth. D) It exists because the Moon accreted from powdery material after a giant impact blasted the Earth. Answer: A 16) What observational evidence supports the idea that Mercury once shrank by some 20 kilometers in radius? A) The presence of many long, tall cliffs B) The presence of many impact craters C) The characteristics of the Caloris Basin D) Mercury's unusually high density Answer: A 17) Which of the following is not a key line of evidence supporting the hypothesis that Mars once had abundant liquid water on its surface? A) The canals of Mars mapped by Percival Lowell B) Small, rounded pebbles found in places that look like dry riverbeds C) Chemical analysis of minerals found in what appear to be ancient lakebeds D) The eroded rims of ancient craters Answer: A

18) Scientists suspect that Mars once had abundant liquid water on its surface. For this to have been true, early Mars must have had ________ than Mars today. A) a much higher atmospheric pressure and much stronger greenhouse effect B) a larger mass and radius C) a smaller axis tilt and less elliptical orbit D) larger polar caps and more dust storms Answer: A 19) All of the statements below are true. Which one gives the primary reason why the surface of Venus today is some 450°C hotter than the surface of Earth? A) Venus has a much stronger greenhouse effect than Earth. B) Venus is only about 73% as far from the Sun as Earth. C) Venus has a much higher reflectivity than Earth. D) Venus has a higher atmospheric pressure than Earth. Answer: A 20) What do we mean by a runaway greenhouse effect? A) A greenhouse effect that keeps getting stronger until all of a planet's greenhouse gases are in its atmosphere B) This is presumably what happened on Venus. C) A greenhouse effect that heats a planet so much that its surface rock melts D) A process that heats a planet's surface, but that doesn't require the presence of greenhouse gases Answer: A 21) On average, how fast do the plates move on the Earth? A) A few centimeters per year B) A few millimeters per century C) About 1 mile per hour D) A few kilometers per year Answer: A 22) In the context of plate tectonics, what is a subduction zone? A) A place where a seafloor plate is sliding under a continental plate. B) A place where two plates are slipping sideways against one another. C) A place where two plates are pulling apart. D) A place where two continental plates are colliding. Answer: A 23) What is the importance of the carbon dioxide (CO2) cycle? A) It regulates the carbon dioxide concentration of our atmosphere, keeping temperatures moderate. B) It makes the growth of continents possible. C) It allows for an ultraviolet-absorbing stratosphere. D) It will prevent us from suffering any consequences from global warming. Answer: A 27 Copyright © 2022 Pearson Education, Inc.

24) Earth has been gradually warming in recent decades, and very strong evidence indicates that the cause of this warming is ________. A) human activities that are increasing the concentration of greenhouse gases in Earth's atmosphere B) the increase in forest fires during recent years C) a gradual brightening of the Sun D) the fact that our politicians spout a lot of hot air Answer: A 25) Based on all we know about the terrestrial worlds, what single factor appears to play the most important role in a terrestrial planet's geological destiny? A) Its size B) Its composition C) Its distance from the Sun D) Whether or not it has liquid water Answer: A Concept Quiz Questions 1) The cores of the terrestrial worlds are made mostly of metal because ________. A) metals sunk to the centers a long time ago when the interiors were molten throughout B) the terrestrial worlds as a whole are made mostly of metal C) the core contained lots of radioactive elements that decayed into metals D) over billions of years, convection gradually brought dense metals downward to the core Answer: A 2) The reason that small planets tend to lose interior heat faster than larger planets is essentially the same as the reason that ________. A) a large baked potato takes longer to cool than a small baked potato B) gas bubbles form and rise upward in boiling water C) Earth contains more metal than the Moon D) thunderstorms tend to form on hot summer days Answer: A 3) Suppose we had a device that allowed us to see Earth's interior. If we looked at a typical region of the mantle, what would we see happening? A) Not much: on human time scales, the mantle looks like solid rock. B) Hot molten rock rising upward throughout the mantle and cool, solid rock falling downward C) A rapid, up and down churning of the material in the mantle D) Dense metals falling downward and low-density rock rising upward Answer: A

4) Scientists suspect that Mars once had a global magnetic field. Assuming this is true, which of the following could explain why Mars today lacks a global magnetic field like that of Earth? A) Mars's interior has cooled so much that its molten core layer no longer undergoes convection. B) Mars rotates much slower than the Earth. C) The Martian core is made of rock, while Earth's core is made of metal. D) Mars is too far from the Sun to have a global magnetic field. Answer: A 5) What are the two geological features that appear to set Earth apart from other terrestrial worlds in our solar system? A) Plate tectonics and a high level of erosion B) A dense core and plate tectonics C) Significant volcanism and tectonics D) Mantle convection and a thick atmosphere Answer: A 6) Which of the following general statements about Earth's atmosphere is not true? A) The nitrogen and oxygen in Earth's atmosphere keep the surface pleasantly warm. B) Gas high in the atmosphere absorbs dangerous X rays from the Sun. C) Without the relatively rare gas called ozone, Earth's surface would be bathed in dangerous ultraviolet light from the Sun. D) The oxygen in our atmosphere was released by living organisms. Answer: A 7) Which of the following best describes how the greenhouse effect works? A) A planet's surface absorbs visible sunlight and returns this absorbed energy to space as infrared light. Greenhouse gases slow the escape of this infrared radiation, which thereby heats the lower atmosphere. B) Greenhouse gases absorb X rays and ultraviolet light from the Sun, and this absorbed radiation then heats the atmosphere and the surface. C) Greenhouse gases absorb infrared light coming from the Sun, and this absorbed sunlight heats the lower atmosphere and the surface. D) The greenhouse effect is caused primarily by ozone, which absorbs ultraviolet light and thereby makes the atmosphere much hotter than it would be otherwise. Answer: A 8) Suppose that Earth's atmosphere had no greenhouse gases. Then Earth's average surface temperature would be ________. A) well below the freezing point of water B) about the same as it is now C) slightly cooler, but still above freezing D) slightly warmer, but still well below the boiling point of water Answer: A

9) Most of the Moon's surface is densely covered with craters, but we find relatively few craters within the lunar maria. What can we conclude? A) The maria formed after the heavy bombardment ended. B) The maria formed within the past 1 billion years. C) The regions of the maria were hit by fewer impacts than the densely cratered regions. D) Erosion affects the maria more than it affects other regions of the Moon. Answer: A 10) Which of the following best describes the geological histories of the Moon and Mercury? A) Early in their histories, they suffered many impacts and experienced some volcanism and tectonics, but they now have little geological activity at all. B) Impact cratering is the only major geological process that has affected their surfaces. C) All four geological processes were important in their early histories, but only tectonics still reshapes their surfaces today. D) Impact cratering shaped these worlds early in their histories. Then, during the past few million years, they were reshaped by episodes of volcanism and tectonics. Answer: A 11) What makes us think that Mars must once have had an atmosphere that was warmer and had higher surface pressure? A) The atmosphere is too cold and thin for liquid water today, yet we see evidence that water flowed on the surface in the past. B) We think it for purely theoretical reasons, based on calculations showing that the Sun has brightened with time. C) The presence of inactive volcanoes on Mars tells us that there must once have been a lot of outgassing, and hence a thicker atmosphere. D) The fact that parts of Mars have a lot of craters tell us that Mars must once have been much warmer. Answer: A 12) All the following statements about Mars are true. Which one might have led to a significant loss of atmospheric gas to space? A) Mars lost any global magnetic field that it may once have had. B) The axis tilt of Mars is thought to change significantly with time. C) Outgassed water molecules are split apart, and the oxygen then reacts chemically with surface rock on Mars. D) Mars probably once had a much higher density of greenhouse gases in its atmosphere than it does today. Answer: A

13) Many scientists suspect that Venus has a stronger and thicker lithosphere than Earth. If this is true, which of the following could explain it? A) The high surface temperature that has "baked out" all the liquid water from Venus's crust and mantle B) The smaller size of Venus, which has allowed it to lose much more internal heat than Earth C) The slow rotation of Venus D) The apparent lack of plate tectonics on Venus Answer: A 14) All the following statements about Venus are true. Which one offers evidence of a global repaving about a billion years ago? A) Venus has relatively few impact craters and these craters are distributed fairly evenly over the entire planet. B) Venus has many circular features, called coronae, which appear to be tectonic in origin. C) Venus's largest features are three elevated regions that look somewhat like continents. D) Venus appears to lack any water that could lubricate the flow of rock in its crust and mantle. Answer: A 15) Which of the following best explains what scientists think happened to outgassed water vapor on Venus? A) Ultraviolet light split the water molecules, and the hydrogen then escaped to space. B) Water was removed from the atmosphere by chemical reactions with surface rock. C) It is frozen as water ice in craters near the poles. D) It turned into carbon dioxide by reacting with nitrogen in Venus's atmosphere. Answer: A 16) Why are there fewer large impact craters on Earth's seafloor than on the continents? A) Seafloor crust is younger than continental crust, so it has had less time in which to suffer impacts. B) The oceans slow large impactors and prevent them from making craters. C) Erosion erases impact craters must faster on the ocean bottom than on land. D) Most impacts occur on the land. Answer: A 17) Which two factors are most important to the existence of plate tectonics on Earth? A) Mantle convection and a thin lithosphere B) Oxygen in the atmosphere and mantle convection C) The existence of life and oxygen in the atmosphere D) Earth's liquid outer core and solid inner core Answer: A

18) Why does Earth have so little carbon dioxide in its atmosphere compared to Venus? A) Earth has just as much carbon dioxide as Venus, but most of it is locked up in carbonate rocks rather than being free in the atmosphere. B) Earth's volcanoes outgassed far less carbon dioxide than those on Venus. C) Earth once had a lot of carbon dioxide, but it was lost to space during the heavy bombardment early in our solar system's history. D) Chemical reactions turned Earth's carbon dioxide into nitrogen. Answer: A 19) Which two factors are critical to the existence of the carbon dioxide (CO2) cycle on Earth? A) Plate tectonics and liquid water oceans B) Life and atmospheric oxygen C) Life and active volcanism D) Active volcanism and active tectonics Answer: A 20) Suppose Earth were to cool down a little. How would the carbon dioxide cycle tend to restore temperatures to normal? A) Cooler temperatures lead to slower formation of carbonate minerals in the ocean, so carbon dioxide released by volcanism builds up in the atmosphere and strengthens the greenhouse effect. B) Cooler temperatures cause volcanoes to become more active, so they release more carbon dioxide into the atmosphere than they do when temperatures are warmer. C) Cooler temperatures allow carbon dioxide to form rain and rain out of the atmosphere. D) Cooler temperatures mean more ice and more erosion, which somehow makes the planet warm up. Answer: A 21) Which of the following correctly lists two key pieces of evidence that, together, indicate that we should expect human activity to cause global warming? A) (1) Carbon dioxide tends to make planets warmer than they would be otherwise. (2) Measurements demonstrate that human activity is raising the carbon dioxide concentration in the atmosphere. B) (1) The carbon dioxide cycle regulates Earth's climate. (2) Human activity has disrupted the carbon dioxide cycle. C) (1) The burning of fossil fuels is a form of human activity. (2) Human activity is always bad for the environment. D) (1) We can learn about past climate from ice cores. (2) Ice cores show that Earth naturally has cooler and warmer periods. Answer: A

22) The choices describe four hypothetical planets. Which one would you expect to have the hottest interior? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) A) Size: twice as big as Earth Distance from Sun: same as Mercury Rotation rate: once every 6 months B) Size: same as the Moon Distance from Sun: same as Mars Rotation rate: once every 10 days C) Size: same as Mars Distance from Sun: same as Earth Rotation rate: once every 18 hours D) Size: same as Venus Distance from Sun: same as Mars Rotation rate: once every 25 hours Answer: A 23) The choices describe four hypothetical planets. Which one's surface would you expect to be most crowded with impact craters? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) A) Size: same as the Moon Distance from Sun: same as Mars Rotation rate: once every 10 days B) Size: twice as big as Earth Distance from Sun: same as Mercury Rotation rate: once every 6 months C) Size: same as Mars Distance from Sun: same as Earth Rotation rate: once every 18 hours D) Size: same as Venus Distance from Sun: same as Mars Rotation rate: once every 25 hours Answer: A

24) The choices describe four hypothetical planets. Which one would you expect to have the most features of erosion? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) A) Size: same as Venus Distance from Sun: same as Mars Rotation rate: once every 25 hours B) Size: same as the Moon Distance from Sun: same as Mars Rotation rate: once every 10 days C) Size: same as Mars Distance from Sun: same as Earth Rotation rate: once every 18 hours D) Size: twice as big as Earth Distance from Sun: same as Mercury Rotation rate: once every 6 months Answer: A Visual Quiz Questions 1) This photo was taken from orbit around some planet. What planet is it, and how do you know?

A) Mars because we see dried up riverbeds B) The Moon because it has craters C) Venus because of its yellowish color D) Mercury because we see gigantic cliffs Answer: A

2) These four photos show features of Earth that change with time, some fast and some slow. Which of these features is a direct result of the fact that Earth has a global magnetic field? A)

Answer: A

3) These four photos show features of Earth that change with time, some fast and some slow. Which one of these features is being shaped primarily by the process we call tectonics? A)

Answer: D

4) Which of the four labeled arrows in this photo of the full moon points to one of the lunar maria?

A) Arrow 1 B) Arrow 2 C) Arrow 3 D) Arrow 4 Answer: A 5) This image shows two tall volcanoes on Venus. Why is it yellow?

A) The yellow color is arbitrary because this image was created with radar data rather than visible light. B) Lava from volcanoes on Venus is yellow rather than the red of lava on Earth. C) The camera used to take this photograph had a yellow filter on it. D) Venus is yellow all over, apparently as a result of some sort of sulfurous dust that coats its surface. Answer: A

6) What is the significance of the yellow lines on this map of Earth?

A) They represent boundaries between the plates that make up Earth's lithosphere. B) They represent borders between continents. C) The yellow lines are lined everywhere by chains of volcanoes. D) The yellow lines represent the locations of deep trenches. Answer: A 7) This diagram represents the conveyor-like action of plate tectonics on Earth. Which numbered position represents a place where new crust is emerging on the seafloor?

A) Position 1 B) Position 2 C) Position 3 D) Position 4 Answer: B

8) What does this figure tell us?

A) The current level of carbon dioxide in our atmosphere is higher than it has been at any time during the past 800,000 years. B) Earth is now warmer than it has been at any time during the past 800,000 years. C) The current level of carbon dioxide in our atmosphere can be attributed to natural changes in Earth's climate. D) The level of carbon dioxide in our atmosphere changes randomly with time, so there is no way to predict how it will change during the next century. E) The current level of carbon dioxide in the atmosphere and the global average temperature are both higher today than at any other time during the past 800,000 years. Answer: A

9) On this graph, the black curve represents actual temperature measurements, the red curve represents models of the climate that include human emissions of greenhouse gases, and the blue curve represents models of the climate that include only natural factors but do not include human emissions of greenhouse gases. What is the key message that can be read from this graph?

A) Models support the conclusion that human emissions are driving global warming. B) Different climate models give different predictions about how much global warming should be occurring. C) Climate models can successfully reproduce Earth's climate for the first half of the 20th century, but after that, they are unable to account for actual temperature data. D) Although some models support the idea that global warming is caused by human activity, other models do not and the cause therefore remains controversial. Answer: A

10) This figure summarizes the geological histories of the terrestrial worlds. Based on this figure, what can you conclude?

A) The most important factor in a planet's geological history is its size. B) The most important factor in a planet's geological history is its distance from the Sun. C) We can trace almost all the key properties of a planet's geology back to the number of impacts it suffered during the heavy bombardment. D) Earth is the only planet in the inner solar system capable of harboring life. Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Refer to this image of Mercury from MESSENGER to answer the following questions. 1) Label 1a lies on the rim of a large crater, and label 1b lies on the rim of a smaller one. Which crater must have formed first? A) Crater 1a B) Crater 1b C) Cannot be determined Answer: A 2) The region around 2b has far fewer craters than the region around 2c) The crater floor at 2a is also flat and smooth, without many smaller craters on it. Why are regions 2a and 2b so smooth? A) Few small craters ever formed in these regions. B) Erosion erased craters that once existed in these regions. C) Lava flows covered craters that once existed in these regions. Answer: C 3) A tectonic ridge appears to connect points 3a and 3b, crossing several craters. From its appearance, we can conclude that it must have formed ________. A) before the area was cratered B) after the area was cratered C) at the same time the area was cratered Answer: B 42 Copyright © 2022 Pearson Education, Inc.

4) Rank the following features in order from oldest to youngest: a. the tectonic ridge from 3a to 3b b. crater 1a c. the smooth floor of crater 1b Answer: b, c, a Chapter Review Questions 1) Describe the core-mantle-crust structures of the terrestrial worlds. What is a lithosphere? What is differentiation? 2) Why did the terrestrial worlds undergo differentiation? Why have larger worlds retained more internal heat than smaller ones? 3) Why does Earth have a global magnetic field? What is the magnetosphere? 4) Define the four major geological processes, giving examples of features on Earth shaped by each process. 5) How do crater counts tell us the age of a surface? Explain why the Moon has so many more craters than Earth. 6) What is outgassing, and how did it lead to the existence of Earth's atmosphere and oceans? 7) Describe the key ways in which the atmosphere affects Earth. What is the greenhouse effect, and how does it work? 8) Briefly summarize the geological histories of the Moon and Mercury. How did the lunar maria form? How are Mercury's great cliffs thought to have formed? 9) Choose at least three features on the global map of Mars (Figure 7.23), and explain the nature and likely origin of each. 10) Explain why liquid water is not stable on Mars today, but why we nonetheless think it flowed there in the distant past. 11) Describe the leading hypothesis for how Mars lost much of its atmosphere some 3 billion years ago, and identify the role played by Mars's size. 12) Describe the basic geology of Venus. Why is it surprising that Venus lacks plate tectonics? What might explain this lack? 13) What do we mean by a runaway greenhouse effect? Explain why this process occurred on Venus but not on Earth. 14) Describe four ways in which Earth is unique among the terrestrial worlds, and how each is important to life. 43 Copyright © 2022 Pearson Education, Inc.

15) Describe the conveyor-like action of plate tectonics, and how it changes the arrangement of the continents with time. 16) What is the carbon dioxide cycle, and why is it so crucial to life on Earth? 17) Briefly summarize the evidence linking human activity to global warming. What are its potential consequences? 18) Based on Figure 7.51, summarize the roles of planetary size and distance from the Sun in explaining the histories of the terrestrial worlds. Surprising Discoveries? Suppose we were to make the following discoveries. (These are not real discoveries.) In light of your understanding of planetary geology, decide whether the discovery should be considered reasonable or surprising. (In some cases, both views can be defended.) Explain your answer clearly, ideally in terms of fundamental properties of size, distance from the Sun, and rotation rate. 19) New photographs reveal sand dunes on Mercury. 20) A new orbiter observes a volcanic eruption on Venus. 21) Radiometric dating of rocks brought back from one lunar crater shows it formed only 10 million years ago. 22) A new orbital photograph of Mars shows a crater bottom filled with a lake of liquid water. 23) Clear-cutting in the Amazon rain forest on Earth exposes terrain that is as heavily cratered as the Moon. 24) Drilling into the Martian surface, a robotic spacecraft discovers liquid water a few meters beneath the slopes of a Martian volcano. 25) Seismic studies on Earth reveal a "lost continent" that held great human cities just a few thousand years ago but is now buried beneath the Atlantic seafloor. 26) We find a planet in another solar system that has an Earth-like atmosphere with plentiful oxygen but no life of any kind. 27) We find a planet in another solar system that has Earth-like plate tectonics; the planet is the size of the Moon and orbits 1 AU from its star. 28) We find evidence that during dinosaur times, when Earth had no polar ice caps, the atmosphere had more carbon dioxide than it does today.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 7 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 29) Which heat source continues to contribute to Earth's internal heat? A) Accretion B) Radioactive decay C) Sunlight Answer: No Correct Answer Was Provided. 30) In general, what kind of terrestrial planet would you expect to have the thickest lithosphere? A) A large planet B) A small planet C) A planet located far from the Sun Answer: No Correct Answer Was Provided. 31) Which of a planet's fundamental properties has the greatest effect on its level of volcanic and tectonic activity? A) Size B) Distance from the Sun C) Rotation rate Answer: No Correct Answer Was Provided. 32) Which describes our understanding of flowing water on Mars? A) It was never important. B) It was important once, but no longer. C) It is a major process on the Martian surface today. Answer: No Correct Answer Was Provided. 33) What do we conclude if a planet has few impact craters of any size? A) The planet was never bombarded by asteroids or comets. B) Its atmosphere stopped impactors of all sizes. C) Geological processes have erased craters. Answer: No Correct Answer Was Provided. 34) How many of the five terrestrial worlds are considered "geologically dead"? A) None B) Two C) Four Answer: No Correct Answer Was Provided. 35) Which terrestrial world has the most atmospheric gas? A) Venus B) Earth C) Mars Answer: No Correct Answer Was Provided. 45 Copyright © 2022 Pearson Education, Inc.

36) Which of the following is a strong greenhouse gas? A) Nitrogen B) Carbon dioxide C) Oxygen Answer: No Correct Answer Was Provided. 37) The oxygen in Earth's atmosphere was released by ________. A) volcanic outgassing B) the CO2 cycle C) life Answer: No Correct Answer Was Provided. 38) Where is most of the CO2 that has outgassed from Earth's volcanoes? A) In the atmosphere B) Escaped to space C) Locked up in rocks Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 39) Group Discussion: The Global Climate Change Conversation. The Intergovernmental Panel on Climate Change (IPCC) was set up in 1988 by the United Nations and the World Meteorological Organization to provide policy makers around the world with scientific assessments of climate change, its impacts and risks, and options for adaptation and mitigation. a. Working independently, visit the IPCC website and make a list of basic facts about how members of the IPCC are chosen, how the IPCC conducts its work, and how often it produces reports. b. Gather into small groups and take turns sharing what you learned about the IPCC, compiling a group list of key facts that builds on each individual's findings. c. You will have noticed that IPCC reports have both scientists and non-scientists as contributors. Do you think the distribution of this work is done in a way that makes sense? If so, explain why, and if not, explain what you would do differently. d. Look for a few media reports about the IPCC. Do these reports accurately describe how the IPCC works? Are there important claims in these media reports that either are incorrect or should have been explained more clearly? e. Overall, do you think that IPCC reports represent issues relating to climate change in a fair way? To what extent do you think these reports should influence policy?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 40) What Is Predictable? Briefly explain why much of a planet's geological history is destined from its birth, and discuss the level of detail that is predictable. For example, was Mars's general level of volcanism predictable? Could we have predicted a mountain as tall as Olympus Mons or a canyon as long as Valles Marineris? Explain. 41) Worth the Effort? Politicians often argue over whether planetary missions are worth the expense involved. If you were in Congress, would you support more or fewer missions? Why? 42) Skeptic Claims on Global Warming. A small, vocal group of people still dispute that humans are causing global warming. Do some research to find the basis of their claims. Then defend or refute their findings based on your own studies and your understanding of the hallmarks of science discussed in Chapter 3. Note: You may find it useful to visit globalwarmingprimer.com, which features a free online primer (written by one of the authors of this textbook) about global warming and many of the skeptic claims. 43) Unanswered Questions: Mars. Choose one important but unanswered question about Mars's past, and write two or three paragraphs discussing how we might answer this question in the future. Be as specific as possible, focusing on the type of evidence necessary to answer the question and on how the evidence could be gathered. What are the benefits of finding answers to this question? 44) Group Discussion: The Politics of Global Warming. Polls show that, today, political beliefs strongly influence whether a person accepts the scientific view of global warming presented in this chapter. Use this question to spur discussion of this political divide and how it might be bridged. a. The basic science of global warming is not new; the first scientist to investigate what would happen if we were to double Earth's atmospheric carbon dioxide concentration was Svante Arrhenius, working more than 100 years ago. Each group member should read about his work by doing a search on "Arrhenius and global warming." Discuss why he concluded that an increase in carbon dioxide would cause warming, and whether there was any political dimension to his work. b. Margaret Thatcher, generally considered to be one of the iconic founders of modern conservatism, was among the first global leaders to speak out on global warming. Each group member should read (or view) the speech she delivered to the United Nations on November 8, 1989. Briefly discuss her words and then discuss why so many people now consider global warming to have a political dimension, when it clearly did not (at least in Thatcher's view) at that time.

45) Group Activity: Moon Colony. Several nations are considering a permanent human presence on the Moon, and some private companies are also considering it. a. Working independently, each student should research at least one proposed plan for returning humans to the Moon, including an estimate of the costs for the plan. b. Form groups of three to four students and take turns reporting on your findings from part a. c. Considering what you learned from the research, as well as what you've learned in this textbook, make a list of potential scientific benefits of sending humans back to the Moon. Then make a separate list of any non-scientific (for example, economic, political, or educational) benefits that we might get from a Moon colony. d. Discuss how the colony might be supplied with food, water, and air. Are there resources on the Moon that you could use for any of these, or would they all need to be supplied from Earth? e. Come to a group consensus about whether the cost of returning to the Moon is worth it. If your group is in favor, describe specifics of how you think it should be done; for example, should it be done by individual nations, by an international effort, or by private companies? If your group is against, explain why. Investigate Further 46) Miniature Mars. Suppose Mars had turned out to be significantly smaller than its current size–say, the size of our Moon. How would this have affected the number of geological features due to each of the four major geological processes? Do you think Mars would still be a good candidate for harboring extraterrestrial life? Summarize your answers in two or three paragraphs. 47) Two Paths Diverged. Briefly explain how the different atmospheric properties of Earth and Venus can be explained by the fundamental properties of size and distance from the Sun. 48) Change in Formation Properties. Consider either Earth's size or its distance from the Sun, and suppose that it had been significantly different. Describe how this change might have affected Earth's subsequent history and the possibility of life on Earth. 49) "Coolest" Surface Photo. Visit the Astronomy Picture of the Day website, and search for archived images of the terrestrial worlds. Look at many of them, and choose the one you think is the "coolest." Write a short description of what it shows, and explain what you like about it. 50) Experiment: Planetary Cooling in a Freezer. Fill two small plastic containers of similar shape but different size with cold water and put both into the freezer at the same time. Every hour or so, record the time and your estimate of the thickness of the "lithosphere" (the frozen layer) in each container. How long does it take the water in each container to freeze completely? Describe the relevance of your experiment to planetary geology. Extra credit: Plot your results on a graph with time on the x-axis and lithospheric thickness on the y-axis. What is the ratio of the two freezing times?

51) Amateur Astronomy: Observing the Moon. Any amateur telescope has a resolution adequate to identify geological features on the Moon. The light highlands and dark maria should be evident, and shadowing is visible near the line between night and day. Try to observe the Moon near the first- or third-quarter phase. Sketch or photograph the Moon at low magnification, and then zoom in on a region of interest. Again sketch or photograph your field of view, label its features, and identify the geological process that created them. Look for craters, volcanic plains, and tectonic features. Estimate the size of each feature by comparing it to the size of the whole Moon (radius = 1738 kilometers). 52) Terraforming Mars. Some people have suggested that we might be able to engineer Mars in a way that would cause its climate to warm and its atmosphere to thicken. This type of planet engineering is called terraforming, because its objective is to make a planet more Earth-like and easier for humans to live on. Discuss possible ways to terraform Mars. Do any of these ideas seem practical? Do they seem like good ideas? Defend your opinions. 53) Global Warming Op-Ed. What, if anything, do you think we should be doing to alleviate the threat of global warming? Write a one-page editorial defending your opinion. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 54) Surface Area-to-Volume Ratio. Compare the surface area-to-volume ratios of a. the Moon and Mars. b. Earth and Venus. In each case, use your answer to discuss differences in internal heat on the two worlds. 55) Doubling Your Size. Just as the surface area-to-volume ratio depends on size, so can other properties. To see how, suppose that your size suddenly doubled; that is, your height, width, and depth all doubled. (For example, if you are 5 feet tall, you would become 10 feet tall.) a. By what factor has your waist size increased? b. How much more material will be required for your clothes? (Hint: Clothes cover the surface area of your body.) c. By what factor has your weight increased? (Hint: Weight depends on the volume of your body.) d. The pressure on your weight-bearing joints depends on how much weight is supported by the surface area of each joint. How has this pressure changed? 56) Plate Tectonics. Typical motions of one plate relative to another are 1 centimeter per year. At this rate, how long would it take for two continents 3000 kilometers apart to collide? What are the global consequences of motions like this?

57) Planet Berth. Imagine a planet, which we'll call Berth, orbiting a star identical to the Sun at a distance of 1 AU. Assume that Berth has eight times as much mass as Earth and is twice as large as Earth in diameter. a. How does Berth's density compare to Earth's? b. How does Berth's surface area compare to Earth's? c. Based on your answers to parts a and b, discuss how Berth's geological history is likely to have differed from Earth's.

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 8 Jovian Planet Systems Section 8.1 1) Which jovian planets have compositions dominated by hydrogen compounds such as methane, ammonia, and water? A) Uranus and Neptune B) Saturn and Uranus C) Jupiter and Neptune D) Saturn, Uranus, and Neptune E) Saturn and Neptune Answer: A

2) Based on the graph above, what would be the approximate radius of a hydrogen/helium planet with a mass one-tenth that of Jupiter? A) About 0.7 times the radius of Jupiter B) About 0.5 times the radius of Jupiter C) About the same as the radius of Jupiter D) About 1.1 times the radius of Jupiter Answer: A 3) Based on the graph above, a planet with twice the mass of Jupiter would have a radius that is ________. A) about twice the radius of Jupiter B) about 5% larger than the radius of Jupiter C) about half the radius of Jupiter D) about 10% smaller than the radius of Jupiter Answer: B 1 Copyright © 2022 Pearson Education, Inc.

4) Why is Saturn almost as large in radius as Jupiter despite its smaller mass? A) Jupiter's greater mass compresses it more, thus increasing its density. B) Saturn's rings make the planet look bigger. C) Saturn is farther from the Sun, thus cooler, and therefore less compact. D) Saturn has a larger proportion of hydrogen and helium than Jupiter, and is therefore less dense. E) Jupiter's strong magnetic field constrains its size. Answer: A 5) How much of Jupiter is made of material that is in a gaseous phase? A) Jupiter is entirely made of gas, all the way down to its center. B) Jupiter is entirely gaseous except for its rock core. C) Only about the outer 10% of Jupiter's interior is gaseous. D) Jupiter does not contain any gaseous phase material; it is all liquid or liquid metallic. Answer: C 6) Based on models, how does Jupiter's core compare in size and mass to Earth? A) It is about the same size and mass as Earth. B) It is about 10 times as large in both size and mass as Earth. C) It is about the same mass, but is 10 times as large in size as Earth. D) It is about the same size, but has about 10 times as much mass as Earth. E) Jupiter doesn't have a core–it is made entirely from hydrogen and helium. Answer: D 7) What is Jupiter's Great Red Spot? A) A giant storm that is about twice as wide as the planet Earth B) A giant crater on the surface of Jupiter C) A portion of strongly heated gas near the surface of Jupiter caused by a collision with a comet D) A huge patch of sulfur in Jupiter's atmosphere E) Reflected sunlight that is red for the same reason sunrises and sunsets are red on Earth Answer: A 8) Why is Jupiter denser than Saturn? A) Jupiter has a higher proportion of hydrogen compounds and rocks than Saturn. B) Jupiter's greater mass compresses its interior to a greater extent than that of Saturn. C) Jupiter has a much more massive core than Saturn. D) Jupiter has a greater proportion of helium compared to hydrogen than Saturn. Answer: B 9) Why is Neptune denser than Saturn? A) Neptune has a higher proportion of hydrogen compounds and rocks than Saturn. B) Neptune has a larger mass and stronger gravity than Saturn. C) Neptune has a much more massive core than Saturn. D) Neptune has a greater proportion of helium compared to hydrogen than Saturn. Answer: A

10) Which of the following statements is thought to be true of the jovian planets? A) All have cores of about the same mass, but differ in the amount of surrounding hydrogen and helium. B) The major differences between the planets can be explained by the different masses of their cores. C) Jupiter and Saturn are made mostly of ammonia while Uranus and Neptune are mostly methane. D) Jupiter and Saturn are made mostly of hydrogen while Uranus and Neptune are mostly helium. Answer: A 11) Refer to this figure from the textbook:

The Galileo spacecraft dropped a probe into Jupiter's atmosphere that survived to a depth of about 200 kilometers, or 0.3% of Jupiter's radius. Which is the deepest layer in which this probe was able to make measurements? A) The gaseous hydrogen layer B) The liquid hydrogen layer C) The metallic hydrogen layer D) The core Answer: A 3 Copyright © 2022 Pearson Education, Inc.

12) Why does Jupiter have several distinct cloud layers? A) The higher clouds are made of gaseous hydrogen and the lower clouds of liquid hydrogen. B) Different gases can condense at different altitudes in Jupiter's atmosphere. C) The atmospheric composition differs at different altitudes in Jupiter's atmosphere. D) The different cloud layers are a result of differing wind speeds. Answer: B 13) Jupiter's "striped" appearance is a result of ________. A) alternating bands of rising and falling air at different latitudes B) alternating bands of liquid and gaseous material at different latitudes C) changes in the atmospheric composition with latitude D) changes in the strength of Jupiter's magnetic field with latitude Answer: A 14) Why do Uranus and Neptune appear blue? A) Oceans that are visible through their atmospheres are blue. B) The nitrogen gas in their atmospheres absorbs red light. C) The methane gas in their atmospheres absorbs red light. D) Small dust grains preferentially scatter blue light. Answer: C 15) Why do most jovian moons show the same face to their planet? A) Because the moons once had atmospheres B) Because the entire solar nebula rotated in the same direction C) Because of the law of conservation of angular momentum D) Because of tidal forces acting on the moons E) No one knows; it is still a mystery. Answer: D 16) The largest Jovian moons have sizes comparable to Mercury. Why do they have an icy composition compared to Mercury's rocky composition? A) They are captured comets. B) They formed from hydrogen compounds expelled by the jovian planets. C) They experienced many more comet impacts during the heavy bombardment. D) They formed beyond the frost line, where ices were more abundant than metals and rock. Answer: D

Section 8.2 1) Where do scientists think that Jupiter's strong magnetic field is generated? A) In its rocky core B) In its metallic hydrogen layer C) In its liquid hydrogen layer D) In its gaseous hydrogen layer E) Above the cloudtops Answer: B 2) The moons of Jupiter are ________. A) all made of rock B) all made of ice C) made of a mixture of rock and ice D) all captured asteroids E) made mostly of hydrogen and helium gas Answer: C 3) Why are there no impact craters on the surface of Io? A) Io is too small to have experienced many impacts. B) Jupiter's strong gravity prevents impacts from hitting Io. C) All of Io's impact craters have been buried by lava flows. D) Any impact craters that once existed on Io were eroded by winds and rain. E) Io formed only recently, long after the heavy bombardment ended. Answer: C 4) What mechanism is most responsible for generating the internal heat of Io that drives volcanic activity? A) Accretion B) Radioactive decay C) Differentiation D) Tidal heating E) Bombardment Answer: D 5) What makes the surface of Io appear red and orange? A) Sulfur expelled by volcanic eruptions B) Rocks on the surface were rusted by oxygen. C) Clays on the surface formed in past lakes D) Reflection of Jupiter's light off of sheets of ice E) Io's thermal spectrum peaks in the red-orange part of the spectrum. Answer: A

6) Which of the following applies to Io? A) It is the most volcanically active body in the solar system. B) It is thought to have a deep, subsurface ocean of liquid water. C) It is the only moon in our solar system with an atmosphere thicker than Earth's atmosphere. D) It is the largest moon in the solar system. E) It is probably a captured Kuiper belt object. Answer: A 7) Which of the following applies to Europa? A) It is the most volcanically active body in the solar system. B) It is thought to have a deep, subsurface ocean of liquid water. C) It is the only moon in our solar system with an atmosphere thicker than Earth's atmosphere. D) It is the largest moon in the solar system. E) It is probably a captured Kuiper belt object. Answer: B 8) Which of the following applies to Ganymede? A) It is the most volcanically active body in the solar system. B) It is the only moon in our solar system with an atmosphere thicker than Earth's atmosphere. C) It is the largest moon in the solar system. D) It is probably a captured Kuiper belt object. Answer: D 9) Which of the following best describes the orbital resonance shared by Io, Europa, and Ganymede? A) Io completes four orbits in the same time it takes Europa to complete two orbits and Ganymede to complete one orbit. B) Io, Europa, and Ganymede each have the same orbital period around Jupiter. C) Io, Europa, and Ganymede all show the same face to Jupiter at all times. D) Io, Europa, and Ganymede are always oriented in a straight line. Answer: A 10) Which of the following best describes the surface of Europa? A) The surface is comprised of ice with many cracks in it. B) The surface is comprised of very smooth ice. C) The surface is covered by a liquid water ocean. D) The surface is rocky and dry. E) The surface is covered in liquid methane. Answer: A 11) Based on the given densities, which of these jovian moons contain the greatest percentage of rocky material and the smallest percentage of icy material? A) Callisto (density = 1.86 grams/cc) B) Europa (density = 2.97 grams/cc) C) Io (density = 3.57 grams/cc) D) Ganymede (density = 1.94 grams/cc) Answer: C 6 Copyright © 2022 Pearson Education, Inc.

12) Which of the following moons has the most substantial atmosphere? A) Titan B) Ganymede C) Io D) Europa E) Mimas Answer: A 13) What is the most abundant gas in Titan's atmosphere? A) Methane B) Nitrogen C) Hydrogen compounds D) Oxygen E) Argon Answer: B 14) Which of the following applies to Titan? A) It is the most volcanically active body in the solar system. B) It is thought to have a deep, subsurface ocean of liquid water. C) It is the only moon in our solar system with an atmosphere thicker than Earth's atmosphere. D) It is the largest moon in the solar system. E) It is probably a captured Kuiper belt object. Answer: C 15) Which of the following statements about Saturn's moon Titan is not true? A) It rains liquid methane and ethane. B) Its atmosphere contains abundant oxygen. C) Its temperature is too cold for liquid water to exist on its surface. D) Its surface is hidden from view by a thick atmosphere. E) It orbits Saturn. Answer: B 16) Which of the following describes a major similarity between Titan and Earth? A) Both have nearly identical atmospheric compositions of nitrogen and oxygen. B) Both have features of erosion due to a liquid, except on Titan it is liquid methane and ethane rather than liquid water. C) Both have many active volcanoes erupting with molten rock, except the rock is higher density on Titan. D) The two worlds have very similar surface temperatures and surface compositions. Answer: B

17) Which moon did the Huygens probe land on? A) Ganymede B) Callisto C) Europa D) Titan E) Triton Answer: D 18) What did the photographs from the Huygens probe reveal as it descended to the surface of Titan? A) Dry, featureless plains B) Rivers and lakes of liquid water C) A pockmarked surface covered with volcanos D) Features that look like river valleys and an ancient shoreline Answer: D 19) Why were scientists surprised to find evidence of subsurface liquid water on Enceladus? A) Enceladus was thought to be too far from the Sun to have a subsurface zone of liquid water. B) Enceladus was thought to be too small to have a subsurface zone of liquid water. C) Enceladus was not expected to have any water or ice in its composition. D) Scientists expect that Enceladus would have lost its liquid water to solar wind stripping by now. Answer: B 20) Why do astronomers suspect that Triton was a Kuiper belt object that was captured by Neptune? A) It orbits Neptune in the opposite direction of Neptune's rotation. B) It is too large to have been formed in the jovian nebula that formed Neptune. C) It has an atmosphere and a measurable greenhouse effect. D) It undergoes seasonal changes. E) It is colder than any other moon or planet. Answer: A 21) Which of the following applies to Triton? A) It is the most volcanically active body in the solar system. B) It is thought to have a deep, subsurface ocean of liquid water. C) It is the only moon in our solar system with an atmosphere thicker than Earth's atmosphere. D) It is the largest moon in the solar system. E) It is probably a captured Kuiper belt object. Answer: E

22) What is the most important reason why an icy moon is more likely to be geologically active than a rocky moon of the same size? A) Ice is less rigid and has a lower melting point than rock. B) Ice is colder than rock. C) Ice contains more radioactive elements than rock. D) Ice is affected by tidal forces to a greater extent than rock. E) Ice is less dense than rock. Answer: A 23) Which of the following statements about the rings of the four jovian planets is not true? A) All rings lie within two to three planetary radii of their planet. B) All the particle orbits are fairly circular and near their planet's equatorial plane. C) All have gaps and ringlets. D) All probably look much the same as they did when the solar system first formed. E) All are made of individual particles of rock or ice that orbit in accord with Kepler's laws: inner ring particles orbiting faster, and outer ring particles orbiting slower. Answer: D 24) Which of the jovian planets in our solar system have rings? A) Jupiter and Saturn only B) Saturn only C) Saturn, Uranus, and Neptune only D) Neptune only E) All four: Jupiter, Saturn, Uranus, and Neptune Answer: E 25) You are somewhere in the solar system. You can see Jupiter high in the sky, and it looks enormous. You can also see numerous nearby volcanoes, some that are currently erupting. Where are you? A) Mars B) Venus C) Europa D) Io Answer: D 26) You are somewhere in the solar system. It's much colder than Earth, and you are airborne in the planet's atmosphere, with blue skies around you. And while you can tell that your planet is rotating fairly rapidly, it is remaining daylight at all times, indicating a very large axis tilt (much larger than Earth's). Where are you? A) Saturn B) Uranus C) Mars D) Jupiter Answer: B

27) Why do almost all moons exhibit synchronous rotation in which they rotate with the same period as they orbit their planet? A) The moons formed this way, with the same rotational and orbital periods. B) Most jovian moons were formed out of their planet's nebula with the same orbital period. C) The moons probably once orbited farther away and more slowly, but friction with solar nebula gas caused their orbits to come closer to their planet, speeding them up. D) The moons probably once rotated faster, but tidal friction slowed their rotations to match their orbital periods. E) Synchronous rotation is caused by orbital resonances with other moons. Answer: D 28) Suppose you are head of NASA two decades from and have to make some budget cuts. Your agency has been planning four different missions to search for life in the solar system, and you need to cancel the least promising one. Which one do you cancel? A) A mission to dig beneath an ancient Martian river bed B) A mission to explore the ice geysers of Saturn's Moon Enceladus C) A mission designed to plunge deep beneath Jupiter's cloud layers D) A mission to drill through the icy surface of Jupiter's Moon Europa Answer: C Section 8.3 1) Why are Saturn's rings so thin? A) They are attached to Saturn's very thin equator. B) The "gap" moons shepherd the particles and maintain its thin profile. C) Any particle in the ring with an orbital tilt would collide with other ring particles. D) Solar radiation pressure keeps particles pressed into the rings. E) They formed from a flat sheet of material that broke apart. Answer: C 2) Which of the following best describes the composition of the particles that make up Saturn's rings? A) Largely water ice B) Shiny metallic grains C) Largely methane ice D) Dense rock E) Hydrogen and helium gas Answer: A 3) Planetary rings are ________. A) nearer to their planet than any of the planet's large moons B) orbiting in the equatorial plane of their planet C) composed of a large number of individual particles that orbit their planet in accord with Kepler's third law D) known to exist for all of the jovian planets in our solar system E) All of the above Answer: E 10 Copyright © 2022 Pearson Education, Inc.

Short Answer Questions 1) What's the best explanation for jovian planets farther from the Sun having less mass? Answer: The differences in the sizes of the jovian planets are due to their capturing different amounts of gas from the solar nebula, since their cores are all about the same size. Icy planetesimals took longer to accrete in the outer solar system because they were more spread out there. Thus, more distant jovian planets didn't have as much time as Jupiter to capture gas from the solar nebula before the nebula was cleared by the solar wind. 2) What do we mean by "ice geology"? Give an example illustrating why it is important in the outer solar system. Answer: Ice geology is the geology that can occur on icy worlds, which can occur at lower temperature than similar geology on rocky worlds. It is important in the outer solar system because it allows worlds to have active geology at smaller sizes than required for rocky worlds. This explains, for example, why Europa and Enceladus are geologically active despite being relatively small in size. Reading Quiz Questions 1) Which of the following is a general characteristic of the four jovian planets in our solar system? A) They are significantly lower in average density than are the terrestrial planets. B) They have very high levels of volcanic and tectonic activity. C) They are made predominantly of elements heavier than hydrogen and helium. D) They rotate more slowly than the terrestrial planets. Answer: A 2) Which of the following best describes the internal layering of Jupiter, from the center outward? A) core of rock, metal, and hydrogen compounds thick layer of metallic hydrogen layer of liquid hydrogen layer of gaseous hydrogen cloud layer B) core of rock and metal mantle of lower density rock upper layer of gaseous hydrogen cloud layer C) core of solid rock layer of solid metallic hydrogen layer of pure liquid hydrogen cloud layer D) core of liquid hydrogen compounds liquid hydrogen layer metallic hydrogen layer gaseous hydrogen layer cloud layer Answer: A 11 Copyright © 2022 Pearson Education, Inc.

3) Which of the following statements comparing the jovian interiors is not thought to be true? A) They all have the same exact set of internal layers, though these layers differ in size. B) They all have cores of roughly the same mass. C) They all have cores that contain at least some rock and metal. D) Deep inside them, they all have pressures far higher than that found on the bottom of the ocean on Earth. Answer: A 4) Overall, Jupiter's composition is most like that of ________. A) the Sun B) Earth C) a comet D) an asteroid Answer: A 5) Jupiter's colors come in part from its three layers of clouds. Which of the following is not the primary constituent of one of Jupiter's cloud layers? A) Clouds of sulfuric acid B) Clouds of water C) Clouds of ammonium hydrosulfide D) Clouds of ammonia Answer: A 6) How do typical wind speeds in Jupiter's atmosphere compare to typical wind speeds on Earth? A) They are much faster than hurricane winds on Earth. B) They are about the same as average winds on Earth. C) They are slightly faster than average winds on Earth. D) They are slightly slower than average winds on Earth. Answer: A 7) What is the Great Red Spot? A) A long-lived, high-pressure storm on Jupiter B) A hurricane that comes and goes on Jupiter C) A place where reddish particles from Io impact Jupiter's surface D) A region on Jupiter where the temperature is so high that the gas glows with red visible light Answer: A 8) What atmospheric constituent is responsible for the blue color of Uranus and Neptune? A) Methane B) Hydrogen C) Water D) Ammonia Answer: A

9) Jupiter's magnetic field is ________ Earth's magnetic field. A) about 20,000 times as strong as B) about the same strength as C) about twice as strong as D) much weaker than Answer: A 10) Which of the following statements about the moons of the jovian planets is true? A) Most of the moons have the potato-like shapes of asteroids, but a few are large enough to be spherical in shape. B) Even the biggest moons are smaller than any of the planets or dwarf planets in our solar system. C) All of the moons are barren and essentially airless, like our own Moon. D) The moons are made almost entirely of rock and metal. Answer: A 11) Which statement about Jupiter's moon Io is true? A) It is the most volcanically active body in our solar system. B) It is thought to have a deep, subsurface ocean of liquid water. C) It is the largest moon in the solar system. D) It is the only moon in the solar system with a thick atmosphere. Answer: A 12) What is tidal heating? A) A source of internal heat caused by varying tidal forces acting on a moon or other object B) A source of internal heat that occurs on all moons that are large enough to be spherical C) A source of surface heating caused by the sloshing of water or other liquids D) A source of surface heating caused by active volcanoes like those on Io Answer: A 13) Which moon has a thick atmosphere made mostly of nitrogen? A) Titan B) Triton C) Ganymede D) Europa Answer: A 14) The Huygens probe took numerous pictures as it descended to the surface of Saturn's moon Titan in 2005. What did the pictures show? A) Features or erosion, including what appeared to be dry river valleys and lakebeds B) Primitive life forms C) A densely cratered surface D) Lava flows of molten basalt Answer: A

15) Which of the following moons is considered likely to have a deep, subsurface ocean of liquid water? A) Europa B) Io C) Miranda D) Triton Answer: A 16) Which large jovian moon is thought to have been captured into its present orbit? A) Triton B) Callisto C) Titan D) Io Answer: A 17) Suppose you could float in space just a few meters above Saturn's rings. What would you see as you looked down on the rings? A) Countless icy particles, ranging in size from dust grains to large boulders B) A solid, shiny surface, looking much like a piece of a Blu-ray disk or DVD (or vinyl record album) but a lot bigger C) Dozens of large "moonlets" made of metal and rock, each a few kilometers across D) Long, solid strings of matter, each distinct from the next Answer: A 18) Which statement about planetary rings is not true? A) Saturn's rings formed along with its moons 4.6 billion years ago. B) All four jovian planets have rings. C) Individual ring particles orbit their planet in accord with Kepler's laws, so that particles closer in orbit faster than particles farther out. D) Rings are always located closer to a planet's surface than any large moons. Answer: A

Concept Quiz Questions 1) According to models of planetary interiors, the differences in mass among the four jovian planets (Jupiter, Saturn, Uranus, and Neptune) are due primarily to differences ________. A) in the amounts of material in the layers extending from the tops of their cores to their surfaces B) in their core masses C) in composition D) in density Answer: A 2) According to current models of solar system formation, why did Uranus and Neptune end up to be much less massive than Jupiter and Saturn? A) Particles in the solar nebula were more spread out at greater distances, so that accretion took longer and there was less time to pull in gas before the solar wind cleared the nebula. B) Ices were able to condense at the distance of Jupiter and Saturn, but only rock and metal could condense at the distances of Uranus and Neptune. C) The solar nebula had different chemical composition at different distances from the Sun, leading to the differences in mass. D) The size differences are thought to be a random coincidence. Answer: A 3) Jupiter and the other jovian planets are sometimes called "gas giants." In what sense is this term misleading? A) They actually contain relatively little material in a gaseous state. B) The materials they are made of are not the kinds of thing we usually think of as gases. C) They are not in any sense "giants." D) Actually, it's a great description because these worlds are big and gaseous throughout. Answer: A 4) What would happen to Jupiter if we could somehow double its mass? A) Its density would increase, but its diameter would barely change. B) Its density would decrease and its diameter would double. C) Its density would stay about the same and its volume would double. D) It would become a star, with nuclear fusion in its core. Answer: A 5) Why does Jupiter have three distinct layers of clouds? A) The three layers represent clouds made of gases that condense at different temperatures. B) Jupiter has three different types of wind, each of which makes a different type of cloud. C) The three layers reflect regions of Jupiter's atmosphere with different chemical compositions. D) Clouds form randomly, so on average there are always three layers. Answer: A

6) Which of the following best explains why we see horizontal "stripes" in images of Jupiter and Saturn? A) The light stripes are regions of high clouds, and the dark stripes are regions where we can see down to deeper, darker clouds. B) The dark and light stripes correspond to alternating bands of different chemical composition. C) There are three different color stripes corresponding to the three different types of clouds found on these planets. D) Dark stripes are in places with strong winds and light stripes are in places with weak winds. Answer: A 7) Uranus and Neptune have methane clouds but Jupiter and Saturn do not. Which factor explains why? A) Temperatures on Jupiter and Saturn are too high for methane to condense. B) Jupiter and Saturn do not contain any methane gas. C) The rapid rotation of Jupiter and Saturn prevents methane clouds from forming. D) The stronger gravity on Jupiter and Saturn pulls methane downward so that it can't form clouds. Answer: A 8) Which jovian planet has the most extreme seasonal changes, and why? A) Uranus, because of its extreme axis tilt B) Jupiter, because of its large mass C) Saturn, because it has an axis tilt similar to Earth D) Neptune, because of its varying distance from the Sun Answer: A 9) Why is the radiation so intense in the region that traces Io's orbit around Jupiter (the Io torus)? A) The region is full of gases that become ionized after they are released from volcanoes on Io. B) Io's gravity allows this region to capture huge numbers of charged particles from the solar wind. C) An orbital resonance between Io, Europa, and Ganymede makes the radiation intense. D) Jupiter's strong magnetic field makes the radiation intense everywhere, and the region around Io is no different than any other region. Answer: A 10) Which of the following is a key factor in explaining why many jovian moons have been more geologically active than the Moon or Mercury? A) Jovian moons contain much more ice that can melt or deform at lower temperatures than can the rock and metal that make up the Moon and Mercury. B) The jovian moons are considerably larger than the Moon and Mercury and therefore have retained much more internal heat. C) The jovian moons probably have far more internal heat generated by radioactive decay than do the Moon or Mercury. D) Because of their greater distances from the Sun, the jovian moons receive much less heat from the Sun. Answer: A 16 Copyright © 2022 Pearson Education, Inc.

11) All the following statements are true. Which one is most important in explaining the tremendous tidal heating that occurs on Io? A) Io orbits Jupiter on an elliptical orbit as a result of orbital resonances with other moons. B) Io is the closest to Jupiter of Jupiter's large moons. C) Io exhibits synchronous rotation, meaning that its rotation period and orbital period are the same. D) Io orbits Jupiter in the Io torus, and therefore has a surface that is bombarded by many charged particles. Answer: A 12) Which of the following is not a piece of evidence supporting the idea that Europa may have a subsurface ocean? A) Astronomers have detected small lakes of liquid water on Europa's surface. B) Europa has a magnetic field that appears to be induced by Jupiter's magnetic field. C) Photos of Europa's surface show regions that appear to consist of jumbled icebergs frozen in place. D) Europa's surface shows few impact craters. Answer: A 13) Which of the following is most unlikely to be found on Titan? A) Lakes of liquid water in the warmer equatorial regions B) Lakes of liquid methane ethane C) Rain or snow consisting of methane or ethane droplets or ice crystals D) Volcanic outgassing of methane and other gases Answer: A 14) What major feature of Saturn's moon Enceladus led scientists to suspect it might have a subsurface ocean? A) Fountains of ice spraying out from the surface into space B) Surface lakes of liquid methane or ethane C) Its large mass and size D) Its many active volcanoes Answer: A 15) What key evidence suggests that Triton is a captured moon? A) Triton orbits Neptune in a direction opposite that of Neptune's rotation. B) Triton is small and potato-shaped, which is common of captured moons. C) Triton is too large to have been formed in the "miniature solar nebula" thought to have surrounded Neptune in its early history. D) Triton appears to be made mostly of ice. Answer: A

16) Which statement about Saturn's rings is not true? A) The rings must look much the same today as they did shortly after Saturn formed. B) The large gap known as the Cassini Division is shaped by an orbital resonance with the moon Mimas, which orbits well outside the rings. C) Some features of the rings are shaped by small moons that actually orbit within the ring system. D) The rings are so thin that they essentially disappear from view when seen edge-on. Answer: A 17) According to current understanding, which of the following is required in order for a planet to have rings? A) The planet must have many small moons that orbit relatively close to the planet in its equatorial plane. B) The planet must be at least as massive as Saturn. C) The planet must orbit its star at a distance greater than Mars orbits the Sun. D) The planet must once have had a large moon that came too close to it, shattering the moon and creating the ring particles. Answer: A Visual Quiz Questions 1) Which of the following shows the four jovian planets correctly scaled in size? A)

Answer: A

2) Which of the following photos shows the planet Neptune? A)

Answer: A

3) What is the name of the feature indicated by the arrow in this photo?

A) The Great Red Spot B) The Io torus C) The Great Dark spot D) The Cassini Division Answer: A 4) According to this graph, a planet with 10 times the mass of Jupiter would have a radius about ________ as that of Jupiter.

A) the same B) 10 times as large C) 100 times as large D) 60% as large Answer: A

5) What are all the blue lines connecting to Jupiter supposed to represent in this picture?

A) Jupiter's magnetic field B) The solar wind C) Blue light reflected from methane clouds D) The orbits of some of Jupiter's many moons. Answer: A 6) What are all the black spots on this object?

A) Volcanoes on Jupiter's moon Io B) Methane lakes on Saturn's moon Titan C) Impact craters on Uranus's moon Miranda D) Wind streaks on Neptune's moon Triton E) Giant cliffs on the planet Mercury Answer: A

7) What is this object?

A) Jupiter's moon Europa B) Saturn's moon Titan C) Uranus's moon Miranda D) Neptune's moon Triton E) Jupiter's moon Callisto Answer: B 8) What is this object?

A) Jupiter's moon Europa B) Saturn's moon Titan C) Uranus's moon Miranda D) Neptune's moon Nereid E) Jupiter's moon Callisto Answer: A

9) What is this object?

A) Ice particles and water vapor are spraying out from the surface. B) A comet is impacting the surface. C) Pebble-size particles from Saturn's rings are raining down onto the surface. D) Sunlight is reflecting off clouds in Enceladus's atmosphere. Answer: A 10) This painting shows an artist's conception of what it would look like to be within Saturn's system of rings. Notice the many whitish "balls" visible in this painting. Based on what you have learned about rings, about how large are each of these "balls," on average?

A) About a size that you could hold in your arms B) About the size of a large asteroid C) About the size of Earth's Moon D) They are microscopic clusters of about 10 to 20 atoms each. Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Left: Approximate colors of Io in visible light; black spots are volcanoes that are active or have recently gone inactive. Right: Infrared thermal emission from Io; bright spots are active volcanoes. (Both images are from Galileo data and show the same face of Io, but taken at different times.) 1) What do the colors in the right image represent? A) The actual colors of Io's surface B) The colors we would see if we had infrared vision C) The intensity of the infrared light D) Regions of different chemical composition on the surface Answer: C 2) Which color in the right image represents the highest temperatures? A) Blue B) Green C) Orange D) Red E) White Answer: E 3) The right image was obtained when only part of Io was in sunlight. Based on the colors, which part of the surface was in sunlight? A) The left side B) The right side C) Only the peaks of the volcanoes Answer: B 24 Copyright © 2022 Pearson Education, Inc.

4) By comparing the two images, what can you conclude about Io's volcanoes? A) Every black spot in the visible image has a bright spot in the infrared image, so all of Io's volcanoes were active when the photos were taken. B) There are more black spots in the visible image than bright spots in the infrared image, so many of Io's volcanoes were inactive when the photos were taken. C) There are more bright spots in the infrared image than black spots in the visible image, so new eruptions must have started after the visible photo was taken. Answer: B Chapter Review Questions 1) Briefly describe how differences in composition among the jovian planets can be traced to their formation. 2) Why is Jupiter so much more dense than Saturn? Could a planet be smaller in size than Jupiter but greater in mass? Explain. 3) Briefly describe the interior structure of Jupiter and explain why it is layered in this way. How do the interiors of the other jovian planets compare to that of Jupiter? 4) Why does Jupiter have such a strong magnetic field? Describe a few features of Jupiter's magnetosphere. 5) Briefly describe Jupiter's cloud layers. How do the cloud layers help explain Jupiter's colors? Why are Saturn's colors more subdued? Why are Uranus and Neptune blue? 6) Briefly describe Jupiter's weather patterns and contrast them with those on the other jovian planets. What is the Great Red Spot? 7) Briefly describe how we categorize jovian moons by size. What is the origin of most of the medium and large moons? What is the origin of many of the small moons? 8) Describe key features of Jupiter's four Galilean moons and Enceladus. Explain the roles of tidal heating and orbital resonances in explaining these features. 9) Describe the atmosphere and surface features of Titan. 10) Why do we think Triton is a captured moon? How might its capture be relevant to its geological activity? 11) Briefly explain why icy moons can have active geology at much smaller sizes than rocky worlds. 12) What are planetary rings made of, and how do they differ among the four jovian planets? Briefly describe the effects of gap moons and orbital resonance on ring systems. 13) Explain why ring particles must be replenished over time, and where we think ring particles come from. 25 Copyright © 2022 Pearson Education, Inc.

Surprising Discoveries? Suppose someone claimed to make the following discoveries. (These are not real discoveries.) In light of what you've learned in this chapter, decide whether each discovery should be considered reasonable or surprising. Explain your reasoning. 14) Saturn's core is pockmarked with impact craters and dotted with volcanoes erupting lava. 15) Neptune's deep blue color is not due to methane, as previously thought, but instead is due to its surface being covered with an ocean of liquid water. 16) A jovian planet in another star system has a moon as big as Mars. 17) A planet orbiting another star is made primarily of hydrogen and helium and has approximately the same mass as Jupiter but the same size as Neptune. 18) A previously unknown moon orbits Jupiter outside the orbits of other known moons. It is the smallest of Jupiter's moons but has several large, active volcanoes. 19) A previously unknown moon orbits Neptune in the planet's equatorial plane and in the same direction that Neptune rotates, but it is made almost entirely of metals such as iron and nickel. 20) An icy, medium-size moon orbits a jovian planet in a star system that is only a few hundred million years old. The moon shows evidence of active tectonics. 21) A jovian planet is discovered in a star system that is much older than our solar system. The planet has no moons at all, but it has a system of rings as spectacular as the rings of Saturn. 22) Future observations discover rainfall of liquid water on Titan. 23) During a future mission to Uranus, scientists discover it is orbited by another 20 previously unknown moons. Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 8 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 24) Which lists the jovian planets in order of increasing distance from the Sun? A) Jupiter, Saturn, Uranus, Pluto B) Saturn, Jupiter, Uranus, Neptune C) Jupiter, Saturn, Uranus, Neptune Answer: No Correct Answer Was Provided. 25) Why does Neptune appear blue and Jupiter red? A) Neptune is hotter, which means bluer thermal emission. B) Methane in Neptune’s atmosphere absorbs red light. C) Neptune’s air molecules scatter blue light, much as Earth’s atmosphere does. Answer: No Correct Answer Was Provided. 26 Copyright © 2022 Pearson Education, Inc.

26) Why is Jupiter denser than Saturn? A) It has a larger proportion of rock and metal. B) It has a larger proportion of hydrogen. C) Its higher mass and gravity compress its interior. Answer: No Correct Answer Was Provided. 27) Some jovian planets give off more energy than they receive because of ________. A) fusion in their cores B) tidal heating C) ongoing contraction or differentiation Answer: No Correct Answer Was Provided. 28) The main ingredients of most moons of the jovian planets are ________. A) rock and metal B) frozen hydrogen compounds C) hydrogen and helium Answer: No Correct Answer Was Provided. 29) Why is Io more volcanically active than our moon? A) Io is much larger. B) Io has a higher concentration of radioactive elements. C) Io has a different internal heat source. Answer: No Correct Answer Was Provided. 30) What is unusual about Triton? A) It orbits its planet backward. B) It does not keep the same face toward its planet. C) It is the only moon with its own rings. Answer: No Correct Answer Was Provided. 31) Which moon shows evidence of rainfall and erosion by some liquid substance? A) Europa B) Titan C) Ganymede Answer: No Correct Answer Was Provided. 32) Saturn’s many moons affect its rings through ________. A) tidal forces B) orbital resonances C) magnetic field interactions Answer: No Correct Answer Was Provided. 33) Saturn’s rings ________. A) have looked basically the same since they formed along with Saturn B) were created long ago when tidal forces tore apart a large moon C) are continually supplied with new particles by impacts with small moons Answer: No Correct Answer Was Provided. 27 Copyright © 2022 Pearson Education, Inc.

Inclusive Astronomy Use these questions to reflect on participation in science. 34) Group Discussion: JUICE and International Collaboration. The European Space Agency's JUICE (for Jupiter Icy Moons Explorer) mission is designed to explore Jupiter's largest icy moons and to assess their potential for hosting life. a. Working independently, find some background information on the JUICE mission. List its main science objectives and its currently planned dates for launch and for arrival at Jupiter. b. The European Space Agency has 22 member nations that are providing the bulk of the funding for the mission. Should the funding provided by each nation be a factor in determining who gets to analyze the data? For example, should scientists from nations that provided more funding get access to the data before other scientists? c. The European Space Agency ultimately plans to share data from the JUICE mission widely, but other nations–particularly those in the developing world–may not have the financial resources to support their scientists in analyzing mission data. Should the European Space Agency try to support data analysis by scientists from nations that did not contribute to the mission funding? If so, how? If not, why not? d. Suppose that the mission finds valuable mineral resources on some of these moons. Who should own mineral rights to these resources? Why? The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 35) Europan Ocean. Scientists strongly suspect that Europa has a subsurface ocean, even though we cannot see through the surface ice. Briefly explain why scientists think this ocean exists. Is the "belief" in a Europan ocean scientific? Explain. 36) Breaking the Rules. As discussed in Chapter 7, the geological "rules" for the terrestrial worlds tell us that a world as small as Io should not have any geological activity. However, the Voyager images of Io's volcanoes proved that the old "rules" had been wrong. Based on your understanding of the nature of science [Section 3.4], should this be seen as a failure in the process of science? Defend your opinion. 37) Jovian Planet Mission. We can study terrestrial planets up close by landing on them, but jovian planets have no surfaces to land on. Suppose that you were in charge of planning a longterm mission to "float" in the atmosphere of a jovian planet. Describe the technology you would use and how you would ensure survival for any people assigned to this mission. 38) Jovian Moon Mission. Suppose you could choose any one jovian moon to visit. Which one would you pick, and why? What dangers would you face in your visit to this moon? What kinds of scientific instruments would you want to bring along for studies? 39) Unanswered Question. Choose one unanswered question about a jovian planet or moon. Write a few paragraphs discussing the question and the specific types of evidence needed to answer it. 28 Copyright © 2022 Pearson Education, Inc.

40) Group Activity: Comparing Jovian Moons. Compare the moons of Jupiter, drawing on the data in Appendix E.Note: You may wish to do this activity using the same four roles described in Chapter 1, Exercise 39. a. Collect data on Jupiter's four largest moons from Table E.3 in Appendix E and determine which moon has the greatest density. b. Use Table E.3 to determine what other solar system moon most resembles the moon from part a in mass, radius, and density. c. Propose a hypothesis about the composition of the moon from part a, based on its resemblance to the moon from part b, and examine potential concerns about the viability of the hypothesis. d. Use Table E.3 to determine whether there is a trend in density with orbital distance among the major moons of Jupiter; briefly describe any trends. e. Suggest a hypothesis that accounts for any trend found in part d, and discuss potential concerns with the hypothesis. f. Develop and describe an experiment that could test the hypotheses in parts c and e. Investigate Further 41) The Importance of Rotation. Suppose the material that formed Jupiter came together without any rotation so that no "jovian nebula" formed and the planet today wasn't spinning. How else would the jovian system be different? Think of as many effects as you can, and explain each in a sentence. 42) Comparing Jovian Planets. You can do comparative planetology armed only with telescopes and an understanding of gravity. a. The small moon Amalthea orbits Jupiter at about the same distance in kilometers as Mimas orbits Saturn, yet Mimas takes almost twice as long to orbit. From this observation, what can you conclude about how Jupiter and Saturn differ? Explain. b. Jupiter and Saturn are not very different in radius. When you combine this information with your answer to part a, what can you conclude? Explain. 43) Minor Ingredients Matter. Suppose the jovian planets' atmospheres were composed only of hydrogen and helium, with no hydrogen compounds at all. How would the atmospheres be different in terms of clouds, color, and weather? Explain. 44) Observing Project: Jupiter's Moons. Using binoculars or a small telescope, view the moons of Jupiter. Make a sketch of what you see, or take a photograph. Repeat your observations several times (nightly, if possible) over a period of a couple of weeks. Can you determine which moon is which? Can you measure the moons' orbital periods? Can you determine their approximate distances from Jupiter? Explain. 45) Observing Project: Saturn's Rings. Using binoculars or a small telescope, view the rings of Saturn. Make a sketch of what you see, or take a photograph. What season is it in Saturn's northern hemisphere? How far do the rings extend above Saturn's atmosphere? Can you identify any gaps in the rings? Describe any other features you notice.

Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 46) Disappearing Moon. Io loses about a ton (1000 kilograms) of sulfur dioxide per second to Jupiter's magnetosphere. a. At this rate, what fraction of its mass would Io lose in 4½ billion years? b. Suppose sulfur dioxide currently makes up 1% of Io's mass. When will Io run out of this gas at the current loss rate? 47) Ring Particle Collisions. Each ring particle in the densest part of Saturn's rings collides with another about every 5 hours. If a ring particle survived for the age of the solar system, how many collisions would it undergo? 48) Prometheus and Pandora. These two moons orbit Saturn at average distances of 139,350 and 141,700 kilometers, respectively. a. Using Newton's version of Kepler's third law, find their two orbital periods. Find the percent difference in their distances and in their orbital periods. b. Consider the two in a race around Saturn: In one Prometheus orbit, how far behind is Pandora (in units of time)? In how many Prometheus orbits will Pandora have fallen behind by one of its own orbital periods? Convert this number of periods back into units of time. This is how often the satellites pass by each other. 49) Orbital Resonances. Using the data in Appendix E, identify the orbital resonance relationship between Titan and Hyperion. (Hint: If the orbital period of one were 1.5 times that of the other, we would say that they were in a 3:2 resonance.) Which medium-size moon is in a 2:1 resonance with Enceladus? 50) Titanic Titan. What is the ratio of Titan's mass to that of all the other satellites of Saturn whose masses are listed in Appendix E? Calculate the strength of gravity on Titan compared to that on Mimas. Comment on how this affects the possibility of atmospheres on each. 51) Saturn's Thin Rings. Saturn's ring system is over 270,000 kilometers wide and approximately 50 meters thick. Assuming the rings could be shrunk down so that their diameter was the width of a dollar bill (6.6 centimeters), how thick would the rings be? Compare your answer to the actual thickness of a dollar bill (0.01 centimeter).

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 9 Asteroids, Comets, and Dwarf Planets Section 9.1 1) How can you identify an asteroid in a long exposure taken of stars through a telescope? (Assume the telescope is tracking the sky with Earth's rotation, so that stars appear as points of light.) A) The asteroid will be much brighter than the surrounding stars. B) The asteroid will be much dimmer than the surrounding stars. C) The asteroid will appear as a streak because of its motion relative to the stars. D) The asteroid will have a noticeable circular disk, rather than being just a point of light like the stars. E) The asteroid will be recognizable by its long, fuzzy tail. Answer: C 2) How can asteroids be distinguished from stars in telescope observations? A) Asteroids move relative to the stars. B) Asteroids are much dimmer than stars. C) Asteroids are much redder than stars. D) Asteroids are much brighter than stars. E) Asteroids are not spherical. Answer: A 3) Which of the following statements about comets and asteroids is true? A) Only asteroids collide with Earth. B) Comets are balls of ice and dust. C) Most of the trillions of comets in our solar system have tails. D) All asteroids lie in the asteroid belt between Mars and Jupiter. Answer: B 4) What do asteroids and comets have in common? A) They are leftover planetesimals from the era of planetary formation. B) They all formed beyond the frost line of the early solar system. C) They have very similar compositions of ice and rock. D) They are all much smaller than any moons. Answer: A 5) An icy leftover planetesimal orbiting the Sun is called a(n) ________. A) comet B) moon C) asteroid D) meteorite Answer: A

6) According to the nebular theory, what are the comets and asteroids? A) Chunks of rock or ice that condensed long after the planets had formed B) Chunks of rock or ice that have been expelled from the planets by volcanoes C) The shattered remains of collisions between moons D) The shattered remains of collisions between planets E) Leftover planetesimals that never accreted into planets Answer: E 7) Why do asteroids and comets differ in composition? A) Asteroids formed inside the frost line, while comets formed outside. B) Asteroids and comets formed at different times. C) Comets formed from the jovian nebula, while asteroids did not. D) Comets are much larger than asteroids. E) Asteroids are much larger than comets. Answer: A 8) How do comets differ from asteroids? A) Comets contain much larger proportions of ice than asteroids. B) Comets contain much smaller proportions of ice than asteroids. C) Comets are much larger in size than asteroids. D) Comets are much smaller in size than asteroids. Answer: A 9) Can an asteroid also be a dwarf planet? A) No; dwarf planets have different compositions from asteroids. B) No; asteroids are too big to be considered "dwarfs." C) Yes, if the asteroid is large enough for its gravity to have made it round. D) Yes, all asteroids are considered to be dwarf planets. Answer: C 10) When you see the bright flash of a meteor, what are you actually seeing? A) A star that has suddenly shot across the sky B) A bright star moving quickly past our solar system C) Emission of visible light from a particle that has not yet entered Earth's atmosphere D) The flash that occurs when a speeding rock from space hits the ground E) The glow from a pea-size particle and the surrounding air as the particle burns up in our atmosphere Answer: E 11) What is a meteorite? A) A streak of light caused by a star moving across the sky B) A streak of light caused by a small particle from space burning up in Earth's atmosphere C) A fragment of rock that has fallen to Earth's surface from space D) A small moon that orbits one of the jovian planets E) A comet that burns up in Earth's atmosphere Answer: C 2 Copyright © 2022 Pearson Education, Inc.

12) Why don't most of the particles that make meteors actually reach the surface of Earth? A) They are too small and burn up in the atmosphere. B) They reflect off the atmosphere and return to space. C) They are too small and are slowed to a stop in the atmosphere. D) They are deflected by the solar wind. E) They are deflected by the gravity of the Moon. Answer: A 13) What do we call a small piece of solar system debris that has fallen to the surface of Earth? A) Iridium B) A comet C) A meteor D) A meteorite E) A shooting star Answer: D 14) Which of the following would be the strongest clue that a rock you have found is a meteorite rather than a terrestrial rock? A) It contains a lot of iron. B) It is dark colored. C) It contains elements and isotopes in proportions that are rare on Earth but common in asteroids. D) It is too heavy for you to hold in your hand. Answer: C Section 9.2 1) How does the largest asteroid, Ceres, compare in size to other solar system worlds? A) It is larger than the planet Mars. B) It is larger than our Moon but smaller than Mercury. C) It is larger than Mercury but smaller than Mars. D) It is about a quarter the diameter of our Moon. E) It is about the size of the two moons of Mars. Answer: D 2) If we know the size of an asteroid, how can we determine its density? A) Comparing its reflectivity to the amount of light it reflects B) Looking for brightness variations as it rotates C) Determining its mass from its gravitational pull on a spacecraft, satellite, or planet D) Radar mapping E) Spectroscopic imaging Answer: C

3) Why aren't small asteroids spherical in shape? A) The strength of gravity of small asteroids is less than the strength of the rock. B) Small asteroids have odd shapes because they were all chipped off larger objects. C) Large asteroids became spherical because many small collisions chipped off pieces until only a sphere was left; this did not occur with small asteroids. Answer: A 4) Which of the following best explains the origin of metal-rich meteorites? A) They are leftover chunks of rock from the earliest period in the formation of the solar system. B) They are fragments of comets rather than of asteroids. C) They are fragments of the core of an asteroid that was shattered by a collision. D) They are fragments of rock chipped off the planet Mercury. E) They are fragments of rock chipped off the planet Mars. Answer: C 5) Which of the following best explains the origin of primitive meteorites? A) They are leftover chunks of rock from the earliest period in the formation of the solar system. B) They are fragments of comets rather than of asteroids. C) They are fragments of an asteroid that was shattered by a collision. D) They are fragments of rock chipped off the planet Mercury. E) They are fragments of rock chipped off the planet Mars. Answer: A 6) How can meteorites from the Moon or Mars have made it to Earth? A) Impacts on those worlds blasted rocks into space that eventually fell to Earth. B) Those worlds spin rapidly enough to have sent some rocks from their surfaces into space. C) The meteorites from the Moon and Mars were never actually part of those worlds; they are just rocks that formed in the same vicinities of the solar system. D) The solar wind gradually blew material off of the surfaces of these worlds, and once in space it collected together to make the meteorites. Answer: A 7) Why are collisions between asteroids in the asteroid belt rare? A) The average distance between asteroids is millions of kilometers. B) All asteroids orbit in perfect circular orbits at the same speed. C) Jupiter's gravity keeps asteroids apart. D) The gas surrounding the asteroids help them repel each other before colliding. E) There are only a few asteroids in the solar system. Answer: A 8) The total mass of all the asteroids in the asteroid belt combined is ________. A) less than that of any terrestrial planet B) about the same as that of Earth C) about twice that of Earth D) about the same as that of Jupiter E) more than that of all the planets combined Answer: A 4 Copyright © 2022 Pearson Education, Inc.

9) If all of the asteroids in the solar system were gathered into a single object, how big would it be once gravity compressed it? A) About half the diameter of Earth's Moon B) About the size of Earth's Moon C) About the size of the Earth D) About the size of a Neptune Answer: A 10) Where are the Trojan asteroids found? A) Orbiting Jupiter B) Along Jupiter's orbit, 60° ahead of and behind Jupiter C) In the center of the asteroid belt D) On orbits that cross Earth's orbit E) On orbits that cross Mars's orbit Answer: B 11) How do we know that there are large gaps in the average distances of asteroids from the Sun (within the asteroid belt)? A) We can see the gaps through telescopes. B) We can identify the gaps by looking for stellar occultations in which an asteroid passed in front of a star as seen from Earth. C) We have not actually detected any gaps, but theory says they must exist. D) We know the gaps must be present to explain how our spacecraft have successfully navigated the asteroid belt without suffering collisions. E) We notice gaps on graphs showing the distribution of asteroids with different orbital periods. Answer: E 12) What causes the large gaps in the asteroid belt (often called Kirkwood gaps)? A) Large asteroids that clear certain regions of the asteroid belt B) Tidal forces from Jupiter C) Tidal forces from the Sun D) Orbital resonances with Jupiter E) The competing gravitational tugs of Mars and Jupiter Answer: D 13) Gaps in the asteroid belt occur at distances where ________. A) the density of asteroids was once so high that collisions pulverized the asteroids into dust B) the period of an orbiting asteroid would be a simple fraction (like 1/3 or 1/4) of Jupiter's orbital period C) the period of an orbiting asteroid would be the same as Jupiter's orbital period D) the period of an orbiting asteroid would be the same as Mars's orbital period E) the orbit would take the asteroid beyond the "frost line" in the solar system Answer: B

14) This diagram shows the positions of about 150,000 asteroids on a single night.

What would be different if this figure were drawn accurately to scale? A) The dots that represent individual asteroids would have to be much smaller. B) The dots that represent individual asteroids would overlap each other. C) The dots should be farther from the Sun. Answer: A 15) According to the nebular theory, what is the asteroid belt? A) It is material left over from the interstellar cloud that never contracted with the rest of the gases to form the solar nebula. B) It consists of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet. C) It consists of objects that fragmented from the Sun during a catastrophic collision early in the formation of the solar system. D) It consists of planetesimals that formed between the orbits of Mars and Jupiter but which Jupiter's gravity prevented from becoming a planet. E) It consists of planetesimals formed in the outer solar system that were flung into distant orbits by encounters with the jovian planets. Answer: D

Section 9.3 1) A typical "shooting star" during a meteor shower is caused by a ________ entering Earth's atmosphere. A) boulder-size particle from an asteroid B) boulder-size particle from a comet C) pebble-size particle from an asteroid D) pebble-size particle from a comet E) microscopic particle of interstellar dust Answer: D 2) Comets are largely made out of ________. A) rock and ice B) hydrogen gas C) rock D) hydrogen compounds E) metal Answer: A 3) According to the nebular theory, how did the Kuiper belt form? A) It is material left over from the interstellar cloud that never contracted with the rest of the gases to form the solar nebula. B) It is made of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet. C) It consists of objects that fragmented from the Sun during a catastrophic collision early in the formation of the solar system. D) It is made of planetesimals between the orbits of Mars and Jupiter that never formed into a planet. E) It is made of planetesimals formed in the outer solar system that were flung into distant orbits by encounters with the jovian planets. Answer: B 4) According to the nebular theory, how did the Oort cloud form? A) It is material left over from the interstellar cloud that never contracted with the rest of the gases to form the solar nebula. B) It is made of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet. C) It consists of objects that fragmented from the Sun during a catastrophic collision early in the formation of the solar system. D) It is made of planetesimals between the orbits of Mars and Jupiter that never formed into a planet. E) It is made of planetesimals formed in the outer solar system that were flung into distant orbits by encounters with the jovian planets. Answer: E

5) Which of the following is furthest from the Sun? A) Pluto B) Neptune C) An asteroid in the asteroid belt D) A comet in the Kuiper belt E) A comet in the Oort cloud Answer: E 6) When do comets have tails? A) When they are relatively close to the Sun B) When they are close to a massive planet like Jupiter C) Only after a collision with a smaller object D) When they are young E) Comets always have tails. Answer: A 7) When a comet is in the inner solar system, what part of it points most directly away from the Sun? A) The denser side of its nucleus B) Its coma C) Jets of gas emerging from its nucleus D) Its tail Answer: D 8) A comets tails (especially its plasma tail) generally point ________. A) away from the Sun B) toward the Sun C) directly behind the comet along its orbit D) directly ahead of the comet along its orbit E) toward the location where the comet's inward trajectory first began Answer: A 9) Where did comets that are now in the Oort cloud originally form? A) Near the jovian planets B) Outside Neptune's orbit C) Inside Jupiter's orbit D) Within the solar nebula, but far outside the orbit of Pluto Answer: A 10) Where did comets that are now in the Kuiper belt originally form? A) In the asteroid belt B) Inside Jupiter's orbit C) Between the orbits of Jupiter and Neptune D) Near the distance at which they orbit today E) In the Oort cloud Answer: D 8 Copyright © 2022 Pearson Education, Inc.

11) A comet that has an extremely elliptical orbit most likely came from ________. A) the asteroid belt B) the Kuiper belt C) the Oort cloud D) the Trojan asteroids E) outside the solar system Answer: C 12) Approximately how many comets are thought to be in the Oort cloud? A) A thousand B) A million C) A billion D) A trillion E) A quintillion Answer: D 13) What evidence led astronomers to conclude that the Oort cloud is a spherical distribution of comets? A) The observation that comets enter the solar system from random directions B) Direct observation of comets orbiting the sun in the Oort cloud C) Astronomers did not draw that conclusion; the Oort cloud is shaped like a flat ring in the same plane as the planets. D) Observations of comets getting flung out by Jupiter's gravity in random directions Answer: A 14) Kepler's Third law relates a planet's orbital period and its average distance from the Sun (p2 = a3 ). If a new comet were discovered with an average distance from the Sun of 100 AU, its period would be ________. A) 1000 years B) 10,000 years C) 150 years D) 1 million years E) not enough information to say Answer: A

Section 9.4 1) Pluto's composition is most similar to that of a ________. A) terrestrial planet B) comet C) star D) jovian planet Answer: B 2) What is Charon? A) Pluto's largest moon B) The largest known asteroid C) The largest known comet D) One of the Galilean moons of Jupiter E) A moon of Neptune Answer: A 3) Based on its orbit, Pluto is a large member of ________. A) the asteroid belt B) the Kuiper belt C) the Oort cloud D) the moon system around Neptune E) an extrasolar planetary system Answer: B 4) Will Pluto eventually collide with Neptune? A) No, because Pluto's orbit is completely outside Neptune's orbit B) No, because Pluto's orbit is completely inside Neptune's orbit C) No, because Pluto's orbit never comes anywhere close to Neptune's orbit D) No, because the two planets have an orbital resonance that prevents them from getting close to each other E) Yes, it's likely that they will eventually. Answer: D 5) How is Pluto's moon system thought to have formed? A) From a giant impact B) By gravitational capture of passing asteroids C) By gravitational capture of passing comets D) By stealing them during a close encounter with Neptune Answer: A

6) What surprising discovery did the New Horizons spacecraft make during its 2015 flyby of Pluto? A) Pluto has the largest known volcano in the solar system. B) Pluto's surface consists mostly of rocky material. C) Pluto's surface shows signs of very recent geological activity. D) Pluto is an escaped moon of Neptune. E) All of the above Answer: C 7) What is the likely cause of the haze seen in photographs of Pluto's atmosphere taken by the New Horizons spacecraft? A) Ice particles erupting from geysers on Pluto's surface B) Hydrocarbon molecules captured from passing comets C) Condensation on the camera lens D) Ultraviolet solar radiation breaking down methane and nitrogen molecules Answer: D Section 9.5 1) Why was the Shoemaker-Levy 9 impact on Jupiter so important to astronomers? A) It dredged up material that allowed us to learn about Jupiter's interior. B) It wiped out the dinosaurs. C) It was the first clear evidence that impacts really occur. D) It confirmed our theory of solar system formation. E) It was the first event in modern history that was brighter than the full moon in the sky. Answer: A 2) On average, how often do impactors about 10 km in size, large enough to produce mass extinction, hit Earth? A) Once every century B) Once every thousand years C) Once every million years D) Once every hundred million years E) Once in Earth's history Answer: D 3) Which of the following was the first strong evidence for an asteroid impact being the cause of the extinction of the dinosaurs 65 million years ago (as well as 75% of all species alive at the time)? A) A worldwide layer rich in the element iridium that dates to that time B) The discovery of asteroid fragments in dinosaur bones dating to that time C) The fact that dinosaurs appear to have gone abruptly extinct at about that time D) Careful studies of lunar craters suggesting an unusually large number of impact at that time Answer: A

4) How can a large asteroid impact in one spot on Earth affect the climate of the entire Earth? A) The impact releases greenhouse gases that immediately make Earth warmer. B) The impact blasts a hole through Earth's mantle, allowing hot metal from the core to rise up and heat the world. C) The impact blasts debris into Earth's atmosphere that blocks sunlight, making Earth's surface cooler. D) The impact tears a hole in Earth's atmosphere, allowing heat energy to escape and thereby cooling our planet. Answer: C 5) A crater of the correct age to be from the impact thought to have caused the extinction of the dinosaurs was found in ________. A) the Yucatán Peninsula in Mexico B) Arizona C) Northern Africa D) Chelyabinsk, Russia E) Tunguska, Siberia Answer: A 6) If a major asteroid collision in the asteroid belt occurs once every 100,000 years on average, then how many major collisions have occurred over the approximately 4.5 billion year history of the solar system? A) About 45,000 B) About 4.5 million C) About 4.5 billion D) About 4500 Answer: A 7) Asteroid impacts large enough to cause mass extinction on Earth occur roughly once every 100 million years. Use that fact to estimate the probability that such an event will occur in your lifetime, which you can take to be approximately 100 years. What's your estimate of that probability? A) 1 in 100,000,000 B) 1 in 10,000 C) 1 in 1,000,000 D) 1 in 100,000,000,000 Answer: C 8) Assume that the average rate of 1-km-sized asteroids hitting the Earth is about 1 every million years. The chance of the Earth being hit by a 1-km-sized asteroid in the next 100 years is about ________. A) one in 100 million B) one in ten thousand C) inevitable, it has to happen sometime D) zero E) one in a million Answer: B 12 Copyright © 2022 Pearson Education, Inc.

Short Answer Questions 1) Describe some ways in which a meteorite can be distinguished from a terrestrial rock. Answer: Meteorites are usually covered with a dark, pitted crust from their fiery passage through the atmosphere. Some contain enough metal to attract a magnet hanging on a string. The isotopic ratios in meteorites differ from terrestrial rocks and they may also have a higher abundance of rare elements such as iridium than terrestrial rocks. 2) How are asteroid masses measured? Answer: Asteroid masses can be determined only in those cases where they have a moon or a spacecraft pass close by and feel its gravitational influence. The mass is then determined from Newton's version of Kepler's third law. 3) Why is the Kuiper belt flat but the Oort cloud spherical? Answer: The difference is that the comets in the Kuiper belt have not been scattered out by gravitational interactions with giant planets. Kuiper belt comets formed beyond the orbit of Neptune in the flattened solar nebula and their orbits have not been greatly changed. Oort cloud comets, however, formed within the orbit of the jovian planets and have been scattered out (or impacted other bodies in the solar system). The scattering was random so the orbits are in every direction and inclination, resulting in a spherical Oort cloud. 4) Describe at least three ways in which our solar system would be different if orbital resonances had never been important. Answer: There are many possible answers. For example, without orbital resonances: (1) Instead of the asteroid belt, the planetesimals in that region might have accreted into a single planet between Mars and Jupiter. (2) Comet orbits would not be nudged, so comets would not collide as frequently with Earth. (3) From the previous two ideas, Earth would not have been as heavily impacted. (4) Earth would not have received as many volatiles from the outer solar system. (5) Saturn's rings would not be broken into rings and gaps. (6) The asteroid belt would not have gaps. (7) Kuiper belt objects would not clump into orbital groups. (8) Pluto and other Kuiper belt objects would not be prevented from colliding with Neptune. (9) Io, Europa, and Ganymede would not be geologically active.

Reading Quiz Questions 1) Which of the following best describes the primary difference between asteroids and comets? A) Asteroids are rocky and comets are ice-rich. B) Comets are much larger than asteroids. C) Comets always have tails and asteroids never have them. D) Comets tend to orbit the Sun in the inner solar system, while asteroids tend to orbit much farther away. Answer: A 2) What is Eris? A) An icy object that orbits in the Kuiper belt and is more massive than Pluto B) The largest known asteroid C) A moon of Pluto D) An extrasolar planet ejected by another solar system and captured by ours Answer: A 3) A typical meteor is created by a particle about the size of a ________. A) pea B) baseball C) car D) basketball Answer: A 4) A rock found on Earth that crashed down from space is called a(n) ________. A) meteorite B) meteor C) asteroid D) impact Answer: A 5) Which statement about asteroids is not true? A) If we could put all the asteroids together, they would make an object about the size of Earth. B) Many but not all orbit the Sun in the asteroid belt. C) Some are more like loosely bound piles of rubble than solid chunks of rock. D) Most asteroids are not spherical in shape. Answer: A 6) The asteroid belt is located ________. A) between the orbits of Mars and Jupiter B) between the orbits of Earth and Mars C) between the orbits of Jupiter and Saturn D) beyond the orbit of Neptune Answer: A

7) What is Ceres? A) The largest known asteroid B) The first asteroid to have been visited by a spacecraft C) The largest moon of Pluto D) A dwarf planet that orbits the Sun in the Kuiper belt beyond the orbit of Pluto Answer: A 8) What do we mean by a primitive meteorite? A) A meteorite that is essentially unchanged since it first condensed and accreted in the solar nebula almost 4.6 billion years ago B) A meteorite that was discovered by primitive people C) A type of meteorite that is made mostly of high-density metals D) A meteorite that fell to Earth at least 4 billion years ago Answer: A 9) Among discovered meteorites, we have found some with all the following origins except ________. A) being a fragment from Comet Halley B) being a fragment from the surface of Mars C) being a fragment from the surface of the Moon D) being a fragment of a shattered asteroid Answer: A 10) Which statement is not thought to be true of all comets in our solar system? A) Comets always have tails. B) All comets are icy in composition. C) All comets orbit the Sun. D) All comets are leftover planetesimals that originally condensed beyond the frost line in the solar nebula. Answer: A 11) When a comet is within the inner solar system, its visible tails point ________. A) away from the Sun B) opposite the direction the comet is moving in its orbit C) perpendicular to the ecliptic plane D) always almost due north E) in the direction the comet is moving in its orbit Answer: A 12) When a comet passes near the Sun, part of it takes on the appearance of a large, bright ball from which the tail extends. This part is called the ________. A) coma B) nucleus C) plasma tail D) Oort core Answer: A 15 Copyright © 2022 Pearson Education, Inc.

13) Comets with orbits that take them through the inner solar system shed sand- to pebble-size particles that then follow the comet around its orbit. How do these particles affect Earth? A) They are the particles that produce meteor showers. B) They are the particles that produce the lights of auroras. C) They have been implicated in mass extinctions, including the extinction of the dinosaurs. D) On rare occasions, they can blanket our entire atmosphere with dust. Answer: A 14) Which of the following best distinguishes the Kuiper belt from the Oort cloud? A) Both are made up of many comets, but Kuiper belt comets orbit within a donut-shaped region just beyond the orbit of Neptune, while Oort cloud comets orbit much farther from the Sun and can have orbits of all inclinations. B) The Kuiper belt is made up of rocky asteroids, while the Oort cloud is made up of icy comets. C) The Kuiper belt is located between the orbits of Mars and Jupiter, while the Oort cloud lies far beyond Neptune. D) The Kuiper belt consists of only of very large comets (similar in size to Pluto), while the Oort cloud consists only of very small comets. Answer: A 15) Which of the following correctly states the number of comets that scientists estimate to be located in the Oort cloud and the number that have actually been observed in the Oort cloud (with telescopes)? A) Estimated number in Oort cloud: 1 trillion Observed in Oort cloud: zero B) Estimated number in Oort cloud: 1 million Observed in Oort cloud: 1,000 C) Estimated number in Oort cloud: 100,000 Observed in Oort cloud: 50 D) Estimated number in Oort cloud: 1 billion Observed in Oort cloud: 10,000 Answer: A 16) According to current evidence, Pluto is best described as ________. A) a large member of the Kuiper belt B) a terrestrial planet that is surprisingly far from the Sun C) a small jovian planet D) an escaped moon of Jupiter or Saturn Answer: A 17) What is Charon? A) The largest of Pluto's moons B) The largest known Kuiper belt comet C) The largest known asteroid D) A captured moon of Neptune Answer: A

18) Which of the following was a new discovery about Pluto by the New Horizons mission? A) Evidence of recent geological activity B) The existence of moons orbiting Pluto C) The fact that Pluto has an ice-rich composition D) The fact that Pluto is less massive than Eris Answer: A 19) What do we mean by a mass extinction? A) The extinction of a large fraction of the world's plant and animal species in a relatively short period of time B) The extinction of large animals, such as dinosaurs C) An extinction caused by the impact of an asteroid or comet D) The extinction of any species of plant or animal that has mass Answer: A 20) If the hypothesis tracing the extinction of the dinosaurs to an impact is correct, the dinosaurs died off largely because ________. A) of global climate effects initiated by dust and smoke that entered the atmosphere after the impact B) of injuries suffered from direct hits of pieces of the asteroid or comet C) radiation from iridium in the asteroid caused the dinosaurs to die of cancer D) the impact caused massive earthquakes worldwide Answer: A 21) Objects the size of the one that exploded over Chelyabinsk (Russia), causing significant damage and injuries to more than 1,000 people, probably hit Earth at least ________. A) once a century B) once a year C) once every 500,000 years D) once every 100 million years Answer: A Concept Quiz Questions 1) When you see the bright flash of a meteor, what are you actually seeing? A) The glow of heated air surrounding a small particle as it burns up in our atmosphere B) Emission of visible light from a particle that has not yet entered Earth's atmosphere C) A star that has suddenly shot across the sky D) The flash that occurs when a speeding rock from space hits the ground Answer: A 2) Which of the following statements best describes the size of the largest asteroid, Ceres? A) A little less than half the diameter of our Moon B) About the size of a terrestrial planet C) Smaller than the jovian planets but larger than the terrestrial planets D) No larger than a typical mountain on Earth Answer: A 17 Copyright © 2022 Pearson Education, Inc.

3) If we could put all the asteroids in the asteroid belt together, their total mass would be ________. A) much less than the mass of Mercury B) about the mass of Jupiter C) about the mass of Earth D) greater than the mass of Earth but less than the mass of Neptune Answer: A 4) Why didn't a planet form where the asteroid belt is now located? A) Gravitational tugs from Jupiter prevented material from collecting together to form a planet. B) There was not enough material in this part of the solar nebula to form a planet. C) There was too much rocky material to form a terrestrial planet, but not enough gaseous material to form a jovian planet. D) The temperature in this portion of the solar nebula was just right to prevent rock from sticking together. Answer: A 5) Gaps in the asteroid belt (often called Kirkwood gaps) are caused by ________. A) orbital resonances with Jupiter B) tidal forces from the Sun C) tidal forces from Jupiter D) the competing gravitational tugs of Mars and Jupiter Answer: A 6) In science fiction movies, spaceships are often shown dodging through large numbers of closely spaced, boulder-size objects. Which of the following real things in our solar system would look most like such science fiction dangers? A) The rings of Saturn B) The asteroid belt C) The atmosphere of Jupiter D) The Oort cloud Answer: A 7) Suppose you find a meteorite made almost entirely of metal. According to current science, which of the following statements must be true? A) Your meteorite is a fragment from the core of a large asteroid that shattered in a collision. B) Radiometric dating will show the age of your meteorite to date to the formation of our solar system. C) Your meteorite was blasted off the surface of Mars by an impact. D) Your meteorite is a fragment of an object from the Kuiper belt. Answer: A

8) Which of the following objects are probably not located in the same region of the solar system in which they originally formed? A) Oort cloud comets B) Kuiper belt comets C) Asteroids of the asteroid belt D) Pluto Answer: A 9) Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different? A) It would have only one tail instead of two. B) It would not have a coma. C) It would not have a nucleus. D) It would be much brighter in appearance. Answer: A 10) Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury every 125 years. What can we conclude? A) It has been on its current orbit for only a short time compared to the age of our solar system. B) It came from the Oort cloud. C) It came from the Kuiper belt. D) It has a coma and tail during most of each orbit. Answer: A 11) When we see a meteor shower, it means that ________. A) Earth is crossing the orbit of a comet B) the solar wind is unusually strong C) an Earth-approaching asteroid has recently come close to our planet D) you should duck and run for cover to avoid being blasted on the head by a rock from space Answer: A 12) Why won't Pluto collide with Neptune? A) Pluto orbits the Sun exactly two times for every three Neptune orbits. B) Pluto is always much farther from the Sun than Neptune. C) Pluto's orbit never comes anywhere close to Neptune's orbit. D) Actually, a collision of the two is inevitable within the next billion years. Answer: A 13) What is Pluto's moon Charon thought to have in common with our own Moon? A) It probably formed as a result of a giant impact. B) It has the same basic composition. C) It has the same approximate mass. D) It has the same average density. Answer: A

14) Which of the following is a real piece of evidence (from the New Horizons mission) pointing to recent or ongoing geological activity on Pluto? A) Surface regions that suggest glacial movement of frozen ices of nitrogen and methane B) Surface regions that show evidence of flooding by liquid water C) Crater rims showing evidence of erosion by rainfall D) Several towering volcanoes discovered on its surface Answer: A 15) Which of the following is not a piece of evidence supporting the idea that an impact caused the mass extinction that occurred 65 million years ago? A) Fossilized dinosaur bones contain fragments of rock from the impact. B) Unusually large abundances of iridium and other rare metals are found in a layer of clay that dates to 65 million years ago. C) A large impact crater along the coast of Mexico dates to 65 million years ago. D) Grains of quartz formed under high pressure are found in a layer of clay that dates to 65 million years ago. Answer: A 16) Which of the following best describes why scientists seek to identify even small asteroids that could potentially hit Earth? A) To try to prevent an impact that might destroy a town or city B) To try to prevent an impact that might cause the extinction of the human race C) To help us understand the origin of the solar system D) To allow us to capture the asteroids and use them for their resources Answer: A 17) Suppose that large jovian planets had never formed in our solar system. Which of the following would most likely be true? A) Neither the asteroid belt nor Oort cloud would exist. B) Earth would have suffered far fewer impacts. C) There would be a large empty region in our solar system between the orbit of Mars and the Kuiper belt. D) Earth would orbit much closer to the Sun. Answer: A

Visual Quiz Questions 1) This photo shows Comet Hale-Bopp in the night sky. Suppose you had taken another photograph from the same spot 10 minutes after this photo was taken. How would the scene have appeared at that time?

A) It would have looked virtually the same. B) We'd still see the same stars, but the comet would be out of sight, having passed below the horizon. C) We would see lots of smoke coming from the point where the comet crashed into the mountains. D) We'd still see the same stars, but the comet would have moved far enough so that we'd be able to see only its tails and not its coma above the horizon. Answer: A

2) Which photo shows an object that looks most like a typical asteroid? A)

Answer: A

3) Each white dot in this figure represents the location of a small body in our solar system. The donut-shaped ring of white dots represents the region of our solar system that we call ________.

A) the asteroid belt B) the Kuiper belt C) the Oort cloud D) the Sun's rings Answer: A

4) This graph shows the number of asteroids with different orbital periods. Notice the gap indicated by the downward-pointing black arrow. What does this graph tell us about this gap?

A) There are few if any asteroids at the indicated orbital period of about 4 years. B) There are more asteroids concentrated at the orbital period indicated by the arrow than at any other orbital period. C) Asteroids with an orbital period of about 4 years are all located very close together; so close that collisions occur frequently. D) There are exactly 495 asteroids with an orbital period of 4 years. Answer: A

5) A comet grows tails (plasma tail and dust tail) when it comes close to the Sun. Which of the following diagrams shows a comet's tails correctly oriented as they appear along its orbit? A)

Answer: A 6) Each white dot in this figure represents the location of a small body in our solar system. The donut-shaped ring of white dots just beyond Neptune's orbit represents the part of our solar system that we call ________.

7) The following images were all taken by spacecraft. Which one shows a comet? A)

Answer: A 8) This image shows Pluto photographed by the New Horizons spacecraft in 2015. What did scientists find most surprising when they saw this image?

A) The smooth areas and other features suggesting relatively recent geological activity B) The round shape C) The presence of numerous impact craters D) The fact that the entire face shown is sunlit in this photo Answer: A

9) What is the significance of the circular region marked in the image (with location identified on the map)?

A) It outlines the crater from the impact thought to have killed off the dinosaurs. B) It shows where the coastline of Mexico was located 65 million years ago. C) It shows the outline of the oldest known impact crater on Earth. D) Its colors indicate the ocean depth within the circle. Answer: A

10) This graph shows the frequency of impacts on Earth by objects of various sizes. According to this graph, objects large enough to cause a mass extinction hit Earth ________.

A) about once every 50 million years B) about once every 1,000 years C) about once in Earth's history D) about once every 500 million years Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

The graph above (Figure 9.29) shows how often impacts occur for objects of different sizes. The photo above shows Comet Tempel 1 moments before the Deep Impact spacecraft crashed into it. 30 Copyright © 2022 Pearson Education, Inc.

1) Estimate Comet Tempel 1's diameter, using the scale bar in the photo. Answer: About 5 km, though its unusual shape could lead to answers between 4 and 8 km. 2) According to the graph, how frequently do objects the size of Comet Tempel 1 strike Earth? A) Once in Earth's history B) About once every hundred million years C) About once every million years D) About once every thousand years Answer: B 3) Consider an object twice the size of Comet Tempel 1. What kind of damage would this object cause if it hit our planet? A) Mass extinction B) Widespread devastation and climate change C) Atmospheric explosion or a small crater Answer: A 4) Meteor Crater in Arizona is about 1.2 kilometers across. According to the graph, about how big was the object that made this crater? (Note: Be sure to read the axis labels carefully.) A) 1 meter B) 10 meters C) 100 meters D) 1 kilometer Answer: C 5) How often do objects big enough to create craters like Meteor Crater impact Earth? A) Once in Earth's history B) About once every ten thousand years C) About once every few million years D) About once every day, but most burn up in the atmosphere or land in the ocean Answer: B Chapter Review Questions 1) Briefly define asteroid, comet, dwarf planet, meteor, and meteorite. How did the discovery of Eris force astronomers to reconsider the definition of planet? 2) How large are asteroids? How does the total mass of all asteroids compare to the mass of a terrestrial world? 3) Distinguish between primitive meteorites and processed meteorites in terms of both composition and origin. 4) What do meteorites and spacecraft observations tell us about the geology of asteroids? 5) Where is the asteroid belt located, and why? Explain how orbital resonances with Jupiter affect the asteroid belt. 31 Copyright © 2022 Pearson Education, Inc.

6) What produces the coma and tails of a comet? What is the nucleus? Why do the tails point away from the Sun? 7) How are meteor showers linked to comets, and why do they recur at about the same time each year? 8) Describe the Kuiper belt and Oort cloud in terms of their locations and the orbits of comets within them. How did comets come to exist in these two regions? 9) Briefly describe Pluto and Charon. Why won't Pluto collide with Neptune? How do we think Charon formed? 10) Briefly describe the evidence suggesting that an impact caused the mass extinction that killed off the dinosaurs. How might the impact have led to the mass extinction? 11) How often should we expect impacts of various sizes on Earth? How serious a threat do we face from these impacts? 12) Briefly summarize the role of the jovian planets in shaping the orbits of small bodies in the solar system and in influencing life on Earth. Surprising Discoveries? Suppose someone claimed to make the following discoveries. (These are not real discoveries.) In light of what you've learned in this chapter, decide whether each discovery should be considered reasonable or surprising. Explain your reasoning. 13) A small asteroid that orbits within the asteroid belt has an active volcano. 14) Scientists discover a meteorite that, based on radiometric dating, is 7.9 billion years old. 15) An object that resembles a comet in size and composition is discovered orbiting in the inner solar system. 16) Studies of a large object in the Kuiper belt reveal that it is made almost entirely of rocky (as opposed to icy) material. 17) Astronomers discover a previously unknown comet that will be brightly visible in our night sky about 2 years from now. 18) A mission to Eris finds that it has lakes of liquid water on its surface. 19) Geologists discover a crater from a 5-kilometer object that impacted Earth more than 100 million years ago. 20) Archaeologists learn that the fall of ancient Rome was caused in large part by an asteroid impact in Asia. 32 Copyright © 2022 Pearson Education, Inc.

21) In another solar system, astronomers discover an object the size of Earth orbiting its star at the distance of the Kuiper belt. 22) Astronomers discover an asteroid with an orbit suggesting that it will impact Earth in the year 2064. Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 9 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 23) The asteroid belt lies between the orbits of ________. A) Earth and Mars B) Mars and Jupiter C) Jupiter and Saturn Answer: No Correct Answer Was Provided. 24) Jupiter nudges the asteroids through the influence of ________. A) tidal forces B) orbital resonances C) magnetic fields Answer: No Correct Answer Was Provided. 25) Can an asteroid be pure metal? A) No; all asteroids contain rock. B) Yes; it must have formed where only metal could condense in the solar nebula. C) Yes; it must be from the core of a shattered asteroid. Answer: No Correct Answer Was Provided. 26) Did a large terrestrial planet ever form in the region of the asteroid belt? A) No, because there was never enough mass there. B) No, because Jupiter prevented one from accreting. C) Yes, but it was shattered by a giant impact. Answer: No Correct Answer Was Provided. 27) What does Pluto most resemble? A) A terrestrial planet B) A jovian planet C) A comet Answer: No Correct Answer Was Provided. 28) How big an object causes a typical "shooting star"? A) A grain of sand or a small pebble B) A boulder C) An object the size of a car Answer: No Correct Answer Was Provided.

29) Which have the most elliptical and tilted orbits? A) Asteroids B) Kuiper belt comets C) Oort cloud comets Answer: No Correct Answer Was Provided. 30) Which are thought to have formed farthest from the Sun? A) Asteroids B) Kuiper belt comets C) Oort cloud comets Answer: No Correct Answer Was Provided. 31) About how often does a 1-kilometer object strike Earth? A) Every year B) Every million years C) Every billion years Answer: No Correct Answer Was Provided. 32) What would happen if a 1-kilometer object struck Earth? A) It would break up in the atmosphere without causing widespread damage. B) It would cause widespread devastation and climate change. C) It would cause a mass extinction. Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 33) Group Discussion: Who Owns the Asteroids? Within the next decade or two, it might become profitable for nations or private companies to mine asteroids in pursuit of rare minerals. Several private companies are already laying the groundwork for such mining. a. Gather in small groups (two to four students) and discuss whether nations and/or private companies should be able to claim ownership rights to minerals that they mine from an asteroid and bring to Earth. Make two lists, one of reasons why ownership should be allowed and one of why it shouldn't. b. Debate the pros and cons represented in your lists and then try to come to a group consensus on whether ownership should be allowed and, if so, what regulations it should be subject to. c. Make a list of ways in which asteroid mining might be used for scientific purposes. If the mining is done for commercial reasons, what obligation would the miners (nations or companies) have for also generating scientific value from their work?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 34) The Pluto Debate. Research the decision to demote Pluto to dwarf planet. In your opinion, is this a good example of the scientific process? Does it exhibit the hallmarks of science described in Chapter 3? Compare your conclusions to opinions you find about the debate, and describe how you think astronomers should handle this or similar debates in the future. 35) Life-or-Death Astronomy. In most cases, the study of the solar system has little direct effect on our lives. But the discovery of an asteroid or comet on a collision course with Earth is another matter. How should the standards for verifiable observations described in Chapter 3 apply in this case? Is the potential danger so great that any astronomer with any evidence of an impending impact should spread the word as soon as possible? Or is the potential for panic so great that even higher standards of verification ought to be applied? What kind of review process, if any, would you set in place? Who should be informed of an impact threat, and when? 36) Group Activity: Assessing Impact Danger. Work in small groups to assess the risks we face on Earth from meteorite and comet impacts as follows.Note: You may wish to do this activity using the same four roles described in Chapter 1, Exercise 39. a. Consider the question of the odds that human civilization will be destroyed by an impact during your lifetime. Determine the kinds of information you would need, develop a method for making the estimate, and write down your method. b. Analyze Figure 9.29 and determine whether it contains any of the necessary information. c. Apply your group's method to estimate the probability that civilization will be destroyed by an impact during your lifetime, which you can assume to be 100 years for the purpose of this exercise. d. Estimate the probability that an impact will cause "widespread devastation" somewhere on Earth during your lifetime. e. Finding near-Earth asteroids early greatly increases our chances of deflecting them. Given the probabilities from parts c and d and considering the damage these events would cause, decide as a group how much money per year should be spent on finding near-Earth asteroids and explain your reasoning. Investigate Further 37) The Role of Jupiter. Suppose that Jupiter had never existed. Describe at least three ways in which our solar system would be different, and clearly explain why. 38) Life Story of an Iron Atom. Imagine that you are an iron atom in a processed meteorite made mostly of iron. Tell the story of how you got to Earth, beginning from the time you were part of the gas in the solar nebula 4.6 billion years ago. Include as much detail as possible. Your story should be scientifically accurate but also creative and interesting. 39) Asteroids vs. Comets. Contrast the compositions and locations of comets and asteroids, and explain in your own words why they have turned out differently. 35 Copyright © 2022 Pearson Education, Inc.

40) Comet Tails. Describe in your own words why comets have tails. Why do most comets have two distinct visible tails, and why do the tails go in different directions? Why is the third, invisible tail of small pebbles of interest to us on Earth? 41) Oort Cloud vs. Kuiper Belt. Explain in your own words how and why there are two different reservoirs of comets. Be sure to discuss where the two groups of comets formed and what kinds of orbits they travel on. 42) Rise of the Mammals. Suppose the impact 65 million years ago had not occurred. How do you think our planet would be different? For example, do you think that mammals still would eventually have come to dominate Earth? Would we be here? Defend your opinions. 43) Asteroid and Comet Missions. Learn about a current or planned space mission to study asteroids or comets. What are its scientific goals? Write a one- to two-page summary of your findings. 44) Impact Hazards. Many groups are searching for near-Earth asteroids that might impact our planet. They use something called the Torino Scale to evaluate the possible danger posed by an asteroid based on how well we know its orbit. What is this scale? What object has reached the highest level on this scale? What were the estimated chances of impact, and when? 45) Beneficial Asteroids. Learn about one of several efforts under way to mine asteroids for human benefit. How far along are the efforts? Discuss the issues that will determine if they succeed. 46) Project: Dirty Snowballs. If there is snow where you live or study, make a dirty snowball. (The ice chunks that form behind tires work well.) How much dirt does it take to darken snow? Find out by allowing your dirty snowball to melt in a container and measuring the approximate proportions of water and dirt afterward. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 47) Adding Up Asteroids. It's estimated that there are a million asteroids 1 kilometer across or larger. If a million asteroids 1 kilometer across were all combined into one object, how big would it be? How many 1-kilometer asteroids would it take to make an object as large as Earth? (Hint: You can assume they're spherical. The expression for the volume of a sphere is 4πr3/3, where r is the radius.) 48) Impact Energies. A relatively small impact crater 20 kilometers in diameter could be made by a comet 2 kilometers in diameter traveling at 30 kilometers per second (30,000 m/s). a. Assume that the comet has a total mass of 4.2 × 1012 kilograms. What is its total kinetic energy? (Hint: The kinetic energy is equal to ½mv2 where m is the comet's mass and v is its speed. If you use mass in kilograms and velocity in m/s, the answer for kinetic energy will have units of joules.) b. Convert your answer from part a to an equivalent in megatons of TNT, the unit used for nuclear bombs. Comment on the degree of devastation such a comet could cause if it struck a populated region on Earth. (Hint: One megaton of TNT releases 4.2 × 1015 joules of energy.) 36 Copyright © 2022 Pearson Education, Inc.

49) The "Near Miss" of Toutatis. The 5-kilometer asteroid Toutatis passed a mere 1.5 million kilometers from Earth in 2004. Suppose Toutatis were destined to pass somewhere within 1.5 million kilometers of Earth. Calculate the probability that this "somewhere" would have meant that it slammed into Earth. Based on your result, do you think it is fair to call the 2004 passage a "near miss"? Explain. (Hint: You can calculate the probability by considering an imaginary dartboard of radius 1.5 million kilometers in which the bull's-eye has Earth's radius, 6378 kilometers.) 50) Room to Roam. It's estimated that there are a trillion comets in the Oort cloud, which extends out to about 50,000 AU. What is the total volume of the Oort cloud, in cubic AU? How much space does each comet have in cubic AU, on average? Take the cube root of the average volume per comet to find the comets' typical spacing in AU. (Hint: For the purpose of this calculation, you can assume the Oort cloud fills the whole sphere out to 50,000 AU. The volume of a sphere is given by 4πr3/3 where r is the radius.) 51) Comet Dust Accumulation. A few hundred tons of comet dust is added to Earth daily from the millions of meteors that enter our atmosphere. Estimate the time it would take for Earth to get 0.1% heavier at this rate. Is this mass accumulation significant for Earth as a planet? Explain.

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 10 Other Planetary Systems Section 10.1 1) About how much brighter is a typical star than the light reflected by a planet orbiting around it? A) A hundred times brighter B) A thousand times brighter C) Ten thousand times brighter D) A million times brighter E) A billion times brighter Answer: E 2) Which of the following makes it very difficult to detect planets around other stars? A) Planets are constantly orbiting their stars, so we don't know where to point our telescopes to see them. B) Planets are typically at least a billion times fainter than their host stars. C) Planets give off only infrared light, not visible light. D) Planets orbit too far from their stars to be detected. Answer: B 3) The astrometric method seeks to detect planets by ________. A) precisely measuring distances to stars B) directly detecting the light of planets orbiting stars C) measuring small changes in the positions of stars on the sky D) precisely measuring the velocities of stars moving toward and away from us E) measuring small changes in the apparent brightness of stars Answer: C 4) The Doppler method seeks to detect planets by ________. A) precisely measuring distances to stars B) directly detecting the light of planets orbiting stars C) measuring small changes in the positions of stars on the sky D) precisely measuring the velocities of stars moving toward and away from us E) measuring small changes in the apparent brightness of stars Answer: D 5) The transit method seeks to detect planets by ________. A) precisely measuring distances to stars B) directly detecting the light of planets orbiting stars C) measuring small changes in the positions of stars on the sky D) precisely measuring the velocities of stars moving toward and away from us E) measuring small changes in the apparent brightness of stars Answer: E

6) The first planets around other stars were discovered ________. A) by Huygens, following his realization that other stars are Suns B) by Galileo following the invention of the telescope C) about a century ago D) in the 1990s E) in the 2010s Answer: D 7) With current technology, the Doppler method can be used to measure stellar motions that are as small as about ________. A) walking speed B) the speed at which continents move with plate tectonics C) the speed of cars on a freeway (with no traffic) D) the cruising speed of an airplane E) the orbital speed of Jupiter Answer: A 8) What do astronomers mean by the term "hot Jupiters"? A) Planets with masses and composition similar to what we would expect if Jupiter were hotter B) Massive planets that orbit stars that are more massive and hotter than our Sun C) Planets with masses similar to Jupiter, but that orbit very close to their central star D) Planets with masses similar to Jupiter, but compositions that are similar to Mercury E) Planets with masses and orbits similar to Jupiter but for which infrared observations indicate they are surprisingly hot in temperature Answer: C 9) What kind of planets are most easily detected using the Doppler method? A) High mass planets far from their host star B) Low mass planets far from their host star C) Low mass planets close to their host star D) High mass planets close to their host star E) Planets that have been ejected from their systems Answer: D 10) If an extrasolar planet suddenly became larger in radius, but kept the same mass and orbit, what would change in the observed Doppler shift of the star? A) Nothing. The radius of a planet does not affect the Doppler shift. B) The time between peaks in the velocity of the star would decrease. C) The peak velocity of the star would be faster. D) The shape of the velocity curve would become less symmetric. E) The lowest velocity of the star would be slower. Answer: A

11) If an extrasolar planet suddenly became larger in radius, but kept the same mass and orbit, what would change during an observed transit? A) The amount of starlight would have a larger dip during the transit. B) The amount of starlight would have a smaller dip during the transit. C) The time between transits would decrease. D) The time between transits would increase. E) Nothing. The radius of a planet does not affect the appearance of a transit. Answer: A 12) If an extrasolar planet suddenly became more massive, but kept the same radius and orbit, what would change during an observed transit? A) The amount of starlight would have a larger dip during the transit. B) The amount of starlight would have a smaller dip during the transit. C) The time between transits would decrease. D) The time between transits would increase. E) Nothing. The mass of a planet does not affect the appearance of a transit. Answer: E 13) Why do most extrasolar planets discovered by the Doppler method have orbits relatively close to their host stars? A) They transit more frequently and have thus been more likely to be detected in the short time we have been searching for them. B) More of the starlight is blocked by the planet when it transits the star. C) These close-in planets are easier to detect because they cause larger Doppler shifts. D) The closer to a star, the hotter and therefore brighter the planet is. E) Planets that are close to a star are heated up and therefore larger. Answer: C 14) Approximately how many extrasolar planets have been discovered to date? A) Tens B) Hundreds C) Thousands D) Millions E) Billions Answer: C 15) What kind of planet is most easily detected using the transit method? A) Large planets in edge-on orbits around small stars B) Large planets in face-on orbits around small stars C) Small planets in edge-on orbits around big stars D) Small planets in face-on orbits around big stars E) Earth-like planets in any orbit Answer: A

16) Which of the following planets in our solar system can we see occasionally transit across the face of the Sun? A) Mercury only B) Mercury and Venus C) Mercury, Venus, and Mars D) Mars, Jupiter, and Saturn E) All of the planets Answer: A 17) Viewed from afar, the transit of Earth would cause the Sun's brightness to dim by approximately ________. A) 10% B) 5% C) 1% D) 0.00001% E) 0.01% Answer: E 18) The Kepler mission discovered thousands of stars by using ________. A) the transit method B) the Doppler method C) the astrometric method D) direct detection E) gravitational lensing Answer: A 19) What must be true about the orbit of a planet discovered by the transit method? A) The planet must be closer to its star than Mercury is to the Sun. B) The planet must have a face-on orbit as seen from Earth. C) The planet must have an edge-on orbit as seen from Earth. D) The planet's orbit must be very close to circular. E) The planet's orbit must be very eccentric. Answer: C 20) Why have most extrasolar planets detected with the transit method been found with orbits fairly close to their host stars? A) They transit more frequently and are more likely to be detected in the short time we have been searching for them. B) More of the starlight is blocked by the planet when it transits the star. C) The wavelength shift of the star's spectrum is larger. D) The closer to a star, the hotter and therefore brighter the planet is. E) Planets that are close to a star are heated up and therefore larger. Answer: A

21) You use the Doppler method to discover a planet around a nearby star that is very similar to the Sun; the velocity curve that has a period of 6 months. What can you conclude about the planet's orbital distance? A) The planet's orbital distance is greater than 1 AU. B) The planet's orbital distance cannot be determined based on the information provided. C) The planet's orbital distance is less than 1 AU. D) The planet's orbital distance is exactly 1 AU. Answer: C 22) You have measured Doppler shifts to plot velocity curves for two otherwise identical stars. Star A has a period of 6 months and Star B has a period of 1 year. What can you say about the planets causing the motions of these stars? A) Star A's planet is more massive than Star B's planet. B) Star A's planet must orbit closer in than Star B's planet. C) It is impossible to say anything about the planets orbiting these stars. D) Star B must have a planet like Earth. Answer: B Section 10.2 1) If an extrasolar planet suddenly became more massive, but kept the same radius and orbit, what would change in the observed Doppler shift of the star? A) The peak velocity of the star would be faster. B) The time between peaks in the velocity of the star would decrease. C) The time between peaks in the velocity of the star would increase. D) The shape of the velocity curve would become less symmetric. E) Nothing. The mass of a planet does not affect the Doppler shift. Answer: A 2) A planet is detected via the Doppler method. What does the time between peaks of the stellar velocity tell us? A) The planet's size B) The planet's mass C) The planet's density D) The orbital period of the planet E) The orbital eccentricity of the planet Answer: D 3) How can the Doppler method be used to measure the orbital period of a planet? A) By measuring the speed at which the star orbits the mutual center-of-mass of the star and planet B) By measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak C) By measuring the asymmetries in the velocity curve D) By measuring the amount by which the starlight is reduced when the planet transits Answer: B

4) How can the Doppler method be used to estimate the average orbital distance of a planet's orbit? A) By measuring the speed at which the star orbits the mutual center-of-mass of the star and planet, and using Newton's theory of gravity B) By measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak, and using Newton's version of Kepler's Third law C) By measuring the asymmetries in the velocity curve D) By measuring the amount by which the starlight is reduced when the planet transits Answer: B 5) How can the Doppler method be used to measure the eccentricity of a planet's orbit? A) By measuring the speed at which the star orbits the mutual center-of-mass of the star and planet, and using Newton's theory of gravity B) By measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak, and using Newton's version of Kepler's Third law C) By measuring the asymmetries in the velocity curve D) By measuring the amount by which the starlight is reduced when the planet transits Answer: C 6) Why does the Doppler method only provide a measure of the minimum mass of a planet? A) Only a small part of the planet's motion is measured. B) Without a transit observation, the size and therefore density of the planet is unknown. C) We do not know the exact composition of the planet. D) The Doppler shift tells only part of a planet's orbital speed (the part toward and away from the observer). E) We do not have the technology to make a direct image of a planet yet. Answer: D 7) Current data suggest that ________ have at least one planet. A) about 1 in 1 million stars B) about 1% of all stars C) about 10% of all stars D) most stars E) 100% of all stars Answer: D 8) Which two methods can be combined to determine an extrasolar planet's density? A) Doppler and astrometric observations B) Doppler and transit observations C) Doppler and gravitational lensing observations D) Astrometric and gravitational lensing observations Answer: B

9) Which two quantities need to be measured in order to determine the density of an extrasolar planet? A) Mass and composition B) Orbital period and mass C) Radius and orbital period D) Radius and composition E) Mass and radius Answer: E 10) Current statistical evidence suggests that Earth-sized planets orbiting in the habitable zone are ________. A) extremely rare B) likely to exist around at least about 20% of all stars C) found around virtually all stars Answer: B 11) What type of observation can astronomers use to measure the composition of an extrasolar planet's atmosphere? A) Comparisons of a star's spectrum when a planet is in transit versus when it is eclipsed B) Measurements of the host star's velocity throughout an orbital cycle C) Measurement of how frequently the planet blocks the host star's light D) Combination of a transit observation and a Doppler shift measurement Answer: A 12) The planet HAT-P-32b has more than twice the radius of Jupiter, yet is only the same mass. It orbits its star more than a factor of ten closer than Mercury's orbit around the Sun. Which is the most plausible explanation for its large size? A) The mass measurement is mistaken, and it is actually about 10 times more massive than Jupiter. B) Planets that are close to a star are hotter, causing them to puff up. C) It is made of elements other than hydrogen and helium which do not compress under their own gravity. D) The hydrogen and helium gas compressed under their own gravity. Answer: B 13) The planet COROT-14b is only slightly larger than Jupiter, but is several times as massive. Which is the most plausible explanation for its similar size to Jupiter? A) The mass measurement is mistaken, and it is actually about 10 times more massive than Jupiter. B) Planets that are close to a star are hotter, causing them to puff up. C) It is made of elements other than hydrogen and helium which do not compress under their own gravity. D) The hydrogen and helium gas compressed under their own gravity to a higher density than Jupiter. Answer: D

14) What is a "super-Earth"? A) A rocky planet that is more massive than Earth B) A rocky planet that has more water than Earth C) A jovian planet that is approximately the same mass as Earth D) A jovian planet that has a solid surface E) A rocky planet that is closer to its host star than Earth is to the Sun Answer: A 15) A transiting extrasolar planet is observed to block 1% of its host star's light. How does the radius of this planet compare to the radius of the host star? A) The planet's radius is 0.1% of the host star's radius. B) The planet's radius is 1% of the host star's radius. C) The planet's radius is 10% of the host star's radius. D) The planet is the same size as the host star. Answer: C Section 10.3 1) How do we think the "hot Jupiters" around other stars were formed? A) They formed as jovian planets close to the star in the same orbits that they are seen today. B) They formed as dense, rocky planets close to the star in the same orbits that they are seen today. C) They formed as jovian planets beyond the frost line and then migrated inward. D) Many planets were formed around the star but coalesced into a single planet close in. E) They spun off from the young star when it was rapidly rotating. Answer: C 2) How does the theory of planetary migration in disks possibly account for the highly eccentric orbits discovered for some extrasolar planets? A) When migrating planets collide, they would move onto more eccentric orbits. B) When migrating planets pass close enough for a gravitational encounter, one may be flung from the system while the other is shifted to a highly elliptical orbit. C) A migrating planet would create waves in the planet forming disk, which would in turn lead to the formation of planets on highly elliptical orbits. D) When a planet migrates onto the surface of the star, the additional stellar mass would disrupt the orbits of the remaining planets. Answer: B 3) What would you expect to be different in a planetary system in which the nebular gas is blown into interstellar space by a stellar wind earlier than occurred in our solar system? A) No terrestrial planets would form. B) Jovian planets would be less massive because they had less time to gather hydrogen and helium gas. C) All planets would be more massive than Jupiter. D) Most of the planets would be destroyed by migration onto the central star. Answer: B 8 Copyright © 2022 Pearson Education, Inc.

4) Which of the following are true statements about the extrasolar planets found so far? A) Extrasolar planets have a much wider range of densities than the planets in the solar system. B) Extrasolar planets fall neatly into the terrestrial and jovian categories. C) Extrasolar planets all have nearly circular orbits. D) All of the above are correct. Answer: A 5) Which of the following hypothetical discovery would be most surprising given our current theory of how stars and planets are born? A) A star system with 7 planets, 2 of which rotate in a direction opposite to their orbital directions B) A star system with 5 planets, each orbiting in a different plane and in different directions C) A star system with a disk of gas but no planets D) A star system with 9 planets, in which 6 of the planets have no moons Answer: B 6) Which of the following hypothetical discoveries would be most surprising given our current theory of how stars and planets are born? A) A star system has 5 terrestrial planets and 3 jovian planets, with all the terrestrial planets orbiting in one direction all the jovian planets orbiting in the opposite direction. B) A star system has 12 planets, 3 of which do not seem to fit either the terrestrial or jovian categories. C) A star system has 20 planets. D) A star system with 7 planets, 2 of which rotate in a direction opposite to their orbital directions. Answer: A Short Answer Questions 1) Why is Jupiter (in our solar system) not considered to be a "hot Jupiter"? Answer: Hot Jupiters are Jupiter-like planets that migrated inward to orbit their stars at very close distances, which is what makes their surfaces hot. This large inward migration did not occur in our solar system, perhaps because the nebular gas was cleared by the solar wind before that much migration could occur. 2) State a testable prediction of the nebular theory that has been confirmed by observations of extrasolar planets. Does this confirmation mean the theory is completely correct? Answer: One key prediction of nebular theory is that planets should be common around stars, and this has been borne out by discoveries of extrasolar planets. But this does not mean that all aspects of the theory are correct, as they may be other details that will eventually require modification.

Reading Quiz Questions 1) What is an extrasolar planet? A) A planet that orbits a star that is not our own Sun B) A planet that is larger than the Sun C) A planet that is extra-large compared to what we'd expect D) A planet that is considered an "extra," in that it was not needed for the formation of its solar system Answer: A 2) The first confirmed detections of extrasolar planets occurred in ________. A) the 1990s B) the mid-17th century C) the 1920s D) 2009 Answer: A 3) All the following statements are true. Which one makes it possible to learn of the existence of extrasolar planets without seeing the planets themselves? A) Planets exert gravitational tugs on their stars that cause stars to orbit around the center of mass of their planetary systems. B) Planets reflect visible light from their stars. C) Planets emit infrared light. D) All the planets in a planetary system tend to orbit their star in the same direction and approximately the same plane. Answer: A 4) The astrometric method looks for planets with careful measurements of a star's ________. A) position in the sky B) brightness C) velocity toward or away from us D) distance from Earth Answer: A 5) The transit method searches for extrasolar planets by ________. A) monitoring stars for slight dimming that might occur as unseen planets pass in front of them B) obtaining high-resolution photographs of other star systems C) observing Doppler shifts in a star's spectrum caused by an unseen planet D) looking for slight back and forth shifts in a star's position in our sky Answer: A

6) If we use the Doppler method to measure the period with which a star alternately moves toward and away from us due to an orbiting planet, then we also know the ________. A) orbital period of the planet B) mass of the planet C) distance to the star D) radius of the planet Answer: A 7) Suppose we have determined the orbital period of a planet around its star. If we also know the mass of the star, then we can use the planet's orbital period and the star's mass to calculate ________. A) the planet's average orbital distance B) mass of the planet C) eccentricity of the planet's orbit D) radius of the planet Answer: A 8) Complete this statement: The larger the decrease in the star's brightness as a planet transits in front of its star, ________ of the planet. A) the larger the size (radius) B) the larger the mass C) the longer the orbital period D) the larger the orbital distance Answer: A 9) In which of the following cases can we determine the precise mass and density of an extrasolar planet? A) We have detected the planet with both the transit and Doppler methods. B) We have detected the planet with the Doppler method, but not any other method. C) We have detected the planet with the transit method, but not any other method. D) We have observed both transits and eclipses of the orbiting planet. Answer: A 10) What do we mean by a "hot Jupiter"? A) A planet that is Jupiter-like in size but orbits close to its star B) A planet that has a Jupiter-like orbit but is more massive and therefore has a higher internal temperature C) A planet that is Jupiter-like in Size but Earth-like in density D) A planet that has a Jupiter-like orbit but is made of high-melting point materials such as rock and metal Answer: A

11) What do we mean by a "super Earth"? A) A planet made of metal and rock that is larger in mass than Earth B) A planet that is more massive than Earth and also has surface oceans C) A planet with an Earth-like orbit that has more abundant life than Earth D) A planet similar in size to Earth but orbiting close to its star Answer: A 12) Overall, what do current data suggest about planetary types in other planetary systems? A) Planets come in a wider range of types than the planets in our solar system. B) All planets fall into the same terrestrial and jovian categories as the planets in our solar system. C) Jovian planets are common, while terrestrial planets are rare. D) Planets that fall into either the terrestrial or jovian categories are extremely rare outside of our own solar system. Answer: A 13) Overall, current data suggest that ________ of stars are orbited by one or more planets. A) at least about 70% B) approximately 1% C) approximately 20% D) no more than 30% Answer: A 14) Why were scientists surprised when they first discovered the existence of planets with Jupiter-like masses orbiting close to their stars (the "hot Jupiters")? A) The nebular theory predicts that jovian planets should only form at much larger distances from their stars. B) The surface temperatures of these planets seemed inexplicably high. C) They had expected to detect small, terrestrial planets before large, jovian planets. D) The orbits of these planets did not follow Kepler's laws of planetary motion. Answer: A 15) Which new process was added to the nebular theory of solar system formation to account for the existence of Jupiter-mass planets that orbit close to their stars (the "hot Jupiters")? A) Planets can migrate from the orbits in which they are born. B) In addition to the categories of terrestrial and jovian, there must be an "in-between" category of planet that has the mass of a jovian planet but the composition of a terrestrial planet. C) In some star systems, it is possible for jovian planets to form in the inner solar system and terrestrial planets to form in the outer solar system. D) Giant impacts can affect planets after they form. Answer: A

16) Which of the following might explain the lack of "water worlds" (planets made mostly of water or other hydrogen compounds) in our own solar system? A) In our solar system, the solar wind did not clear out gas until relatively late. B) There was not enough water in our solar system. C) Small worlds in our solar system formed only close to the Sun, where it was too hot for hydrogen compounds to condense. D) Water worlds can form only in systems in which all planets have highly elliptical (eccentric) orbits. Answer: A Concept Quiz Questions 1) From the viewpoint of an alien astronomer, how does Jupiter affect observations of our Sun? A) It causes the Sun to move in a small ellipse with an orbital period of about 12 years. B) It makes the Sun periodically get somewhat brighter. C) It makes the Sun appear dimmer when viewed with infrared light. D) It causes the Sun to move in a small ellipse in the sky, with the same ellipse repeated every night. Answer: A 2) Which of the following is a major reason why it so difficult to obtain direct images of extrasolar planets? A) The light of the planets is overwhelmed by the light from their star. B) Extrasolar planets give off light at different wavelengths than planets in our solar system. C) No telescope is powerful enough to detect the faint light from a distant planet. D) Telescopes are too busy with other projects. Answer: A 3) Suppose you are using the Doppler method to look for planets around another star. What must you do? A) Compare many spectra of the star taken over a period of many months or years. B) Compare many spectra of an orbiting planet taken over a period of many months or years. C) Compare the brightness of the star over a period of many months or years. D) Carefully examine a single spectrum of an orbiting planet. E) Carefully examine a single spectrum of the star. Answer: A 4) In general, which type of planet would you expect to cause the largest Doppler shift in the spectrum of its star? A) A massive planet that is close to its star B) A massive planet that is far from its star C) A low-mass planet that is close to its star D) A low-mass planet that is far from its star Answer: A

5) Consider a planet orbiting a Sun-like star that has been detected by the Doppler and that has an orbital period of one year. The larger the velocity changes measured for the star, the ________. A) larger the mass of the planet B) larger the radius of the planet C) smaller the mass of the planet D) smaller the radius of the planet Answer: A 6) Suppose a planet is discovered by the Doppler method and is then discovered to have transits. In that case, we can determine all the following about the planet except ________. A) its precise mass B) its density C) its physical size (radius) D) its rotation period E) its orbital period Answer: D 7) The transit method allows us in principle to find planets around ________. A) only a small fraction of stars that have planets B) all stars that have planets of any kind C) only stars of about the same mass and size as our Sun D) only stars located within about 100 light-years of Earth Answer: A 8) You observe a star similar to our own Sun in size and mass. This star moves slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet? A) The planet must be closer to the star than Earth is to the Sun. B) The planet must have a mass about the same as the mass of Jupiter. C) The planet must be farther from the star than Neptune is from the Sun. D) You do not have enough information to say anything at all about the planet. Answer: A 9) Which of the following will allow you to learn something about a transiting planet's atmospheric composition? A) Compare spectra obtained before and during an eclipse. B) Look for slight variations in the time between transits. C) Use the Doppler method to study the planet throughout a cycle from one transit to the next. D) Calculate the planet's size, and then use size to infer what its atmospheric composition must be. Answer: A

10) Based on everything you have learned about the formation of our solar system, which of the following statements is probably not true? A) Only a tiny percentage of stars are surrounded by spinning disks of gas during their formation. B) Within a star's planetary system, all its planets will tend to orbit in the same direction and approximately the same plane. C) Planets are common, and many or most stars have them. D) Other planetary systems will have far more numerous asteroids and comets than actual planets. Answer: A 11) To date, we've found few planets orbiting their stars at distances comparable to the distances of the jovian planets in our solar system. Why do astronomers think this is the case? A) We have not yet been searching for planets at such distances for a long enough time. B) Planets at such distances are extremely rare. C) No known method can detect planets at such large distances. D) Planets at such distances are probably low in mass. Answer: A 12) Current evidence suggests that some massive jovian planets orbit at close orbital distances to their stars. How do we think these planets ended up on these close orbits? A) These planets migrated inward after being born on orbits much farther from their stars. B) These planets were able to form close to their stars because their solar nebulas were cold in temperature. C) Despite their large masses, these planets are made of rock and metal and therefore could form in their inner solar systems. D) These planets were captured from other solar systems. Answer: A 13) Assuming that our ideas about how "hot Jupiters" ended up on their current orbits are correct, why didn't our own solar system end up with any hot Jupiters? A) Our solar nebula must have been blown into space shortly after the formation of the jovian planets. B) Our jovian planets must have migrated outward from inside the orbit of Mercury. C) Our solar nebula must have stuck around for an unusually long time after the formation of jovian planets. D) The existence of Earth and the other terrestrial planets prevented the jovian planets from migrating inward. Answer: A 14) Based on discoveries to date, which of the following conclusions is justified? A) Planetary systems are common and planets similar in size to Earth are also common. B) Although planetary systems are common, few resemble ours with terrestrial planets near the Sun and jovian planets far from the Sun. C) Planets are common, but planets as small as Earth are extremely rare. D) Most stars have one or more terrestrial planets orbiting within their habitable zones. Answer: A 15 Copyright © 2022 Pearson Education, Inc.

Visual Quiz Questions

1) The graph shows how a star's orbital speed varies with time because of the gravitational tug of an orbiting planet. These data were obtained by measuring ________. A) the precise wavelengths of spectral lines in the spectrum of the star B) the precise wavelengths of spectral lines in the spectrum of the orbiting planet C) the precise brightness of the star divided by the precise brightness of the planet D) the orbital period of the planet that is orbiting the star Answer: A 2) The graph shows how a star's orbital speed varies with time because of the gravitational tug of an orbiting planet. Based on these data, the planet's orbital period is about ________. A) 2 days B) 4 days C) 6 days D) 50 days Answer: B 3) This diagram shows the orbital path of the Sun around the center of mass of our solar system over a 65-year period as it would appear from a distance of 30 light-years. If aliens had constructed this graph at their home star system, they could learn all of the following except ________.

A) the fact that large, icy objects orbit the Sun in the Kuiper belt B) the fact that the Sun has more than two planets C) the mass and orbital period of Jupiter D) the orbital distance of Saturn Answer: A 4) This diagram represents a star with an orbiting planet that, as seen from Earth, periodically transits across the face of the star and disappears behind the star. If you measure the brightness of this system, at which point would it be brightest?

A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: A

5) This graph shows the brightness of a star over the course of a transit. Which of the following do we learn about the planet?

A) It is large enough to block about 2.5% of the star's light. B) It has an orbital period of less than 2 hours. C) It is about 2.5% as massive as the star. D) It is about 97.5% as bright as its star. Answer: A

6) This bar graph is based on statistical study of results from the Kepler mission. Which of the following conclusions is supported by the graph?

A) At least about 15% of stars have a planet similar in size to Earth. B) Most stars with an Earth-sized planet do not have any larger jovian planets orbiting far from their stars. C) Most stars have five planets. D) A star orbited by a super-Earth is likely also to be orbited by a mini-Neptune. Answer: A

7) Each dot on this graph represents an extrasolar planet detected over about a four-year period by the Kepler mission. Suppose the mission had been able to continue collecting data for many more years. How would you expect the graph to look different in that case?

A) Additional dots would be found further to the right. B) Additional dots would be found above the existing dots. C) Additional dots would be found further to the left. D) All the existing dots on the graph would move diagonally up and right. Answer: A

8) This graph plots planetary mass on the horizontal axis and planetary radius on the vertical axis. Which of the four points marked by one of the bold numbers 1 through 4 represents a planet with the greatest mass? A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: B 9) This graph plots planetary mass on the horizontal axis and planetary radius on the vertical axis. Which of the four points marked by one of the bold numbers 1 through 4 represents a planet with the greatest density? A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: D

10) This graph plots planetary mass on the horizontal axis and planetary radius on the vertical axis. Which of the four points marked by one of the bold numbers 1 through 4 represents a planet that has about the same composition as Earth but is larger in both size and mass? A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: C End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

This graph shows the periodic variations in the Doppler shift of a star caused by a planet orbiting around it. Positive velocities mean the star is moving away from Earth, and negative velocities mean the star is moving toward Earth. (You can assume that the orbit is viewed edgeon from Earth.) 1) How long does it take the star and planet to complete one orbit around their center of mass? Answer: about 4 days 2) What maximum velocity does the star attain? Answer: about 50 m/s

3) Match the star's position at points 1, 2, 3, and 4 in the plot with the descriptions below. a. headed straight toward Earth b. headed straight away from Earth c. closest to Earth d. farthest from Earth Answer: a. 2, b. 4, c. 3, d. 1 4) Match the planet's position at points 1, 2, 3, and 4 in the plot with the descriptions in question 3. Answer: a. 4, b. 2, c. 1, d. 3 5) What would be the most significant change in the plot if the planet were more massive? A) It would not change, because it describes the motion of the star, not the planet. B) The peaks and valleys would get larger (greater positive and negative velocities) because of larger gravitational tugs. C) The peaks and valleys would get closer together (shorter period) because of larger gravitational tugs. Answer: B Chapter Review Questions 1) Why are extrasolar planets hard to detect directly? 2) What are the two current major approaches to detecting extrasolar planets indirectly? 3) How can gravitational tugs from orbiting planets affect the motion of a star? Explain how alien astronomers could deduce the existence of planets in our solar system by observing the Sun's motion. 4) Briefly describe the astrometric method. What is the GAIA mission? 5) Briefly describe the Doppler method. Summarize the evidence that the planet orbiting 51 Pegasi is a hot Jupiter. 6) How does the transit method work? What was the Kepler mission? 7) Briefly summarize the planetary properties we can measure with current detection methods. 8) Why does the Doppler method generally allow us to determine only minimum planetary masses? In what cases can we be confident that we know precise masses? Explain. 9) How does the transit method tell us planetary size, and in what cases can we also learn mass and density? 10) How do the orbits of known extrasolar planets differ from those of planets in our solar system? Why are these orbits surprising? 23 Copyright © 2022 Pearson Education, Inc.

11) Summarize the current state of knowledge about extrasolar planet masses and sizes. Based on the evidence, is it likely that smaller planets or larger planets are more common? 12) Summarize the key features shown in Figure 10.13, and briefly describe the nature of planets that would fit each of the model regions shown on the graph. 13) What is planetary migration, and how may it account for the surprising orbits of many extrasolar planets? 14) How can scientists account for the fact that extrasolar planets seem to come in a wider range of types than the planets of our solar system? 15) Overall, does the nebular theory seem adequate for describing the origins of other planetary systems? Explain. 16) Based on current evidence, how common are planetary systems? Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 17) An extraterrestrial astronomer surveying our solar system with the Doppler method could discover the existence of Jupiter with just a few days of observation. 18) The fact that we have not yet discovered an Earth-size extrasolar planet in an Earth-like orbit tells us that such planets must be very rare. 19) Within the next few years, astronomers expect to confirm all the planet detections made with the astrometric and Doppler methods by observing transits of these same planets. 20) The infrared brightness of a star system decreases when a planet goes into eclipse. 21) Some extrasolar planets are likely to be made mostly of water. 22) Some extrasolar planets are likely to be made mostly of gold. 23) Current evidence suggests that there could be 100 billion or more planets in the Milky Way Galaxy. 24) It's the year 2025: The TESS mission has announced the discovery of numerous planets with Neptune-like orbits around their stars. 25) It's the year 2025: Astronomers have successfully obtained a high-resolution image of an Earth-size extrasolar planet, showing that it has oceans and continents. 26) It's the year 2040: Scientists announce that our first spacecraft to reach an extrasolar planet is now orbiting a planet in a planetary system located near the center of the Milky Way Galaxy. 24 Copyright © 2022 Pearson Education, Inc.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 10 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 27) Which method could detect a planet in an orbit that is face-on to Earth? A) Doppler method B) Transit method C) Astrometric method Answer: No Correct Answer Was Provided. 28) Which detection method(s) measure(s) gravitational tug of a planet on its star, allowing us to estimate planetary mass? A) The transit method only B) The Doppler method only C) The astrometric and Doppler methods Answer: No Correct Answer Was Provided. 29) Which one of the following can the transit method tell us about a planet? A) Its mass B) Its size C) The eccentricity of its orbit Answer: No Correct Answer Was Provided. 30) To determine a planet's average density, we can use ________. A) the transit method alone B) the astrometric and Doppler methods together C) the transit and Doppler methods together Answer: No Correct Answer Was Provided. 31) Based on the model types shown in Figure 10.13, a planet made almost entirely of hydrogen compounds would be considered a ________. A) terrestrial planet B) jovian planet C) "water world" Answer: No Correct Answer Was Provided. 32) Look at the dot for Jupiter in Figure 10.13, then at the red dot directly to Jupiter's left. Compared to the density of Jupiter, the density of the planet represented by that dot is ________. A) higher B) lower C) the same Answer: No Correct Answer Was Provided.

33) The term "super-Earth" means a planet that is ________. A) the size of Earth but with more water B) larger than Earth but on a close-in orbit that makes it much hotter than Earth C) similar in composition to Earth but larger in size Answer: No Correct Answer Was Provided. 34) What's the best explanation for the location of hot Jupiters? A) They formed closer to their stars than Jupiter did. B) They formed farther out like Jupiter but then migrated inward. C) The strong gravity of their stars pulled them in close. Answer: No Correct Answer Was Provided. 35) Based on computer models, when is planetary migration most likely to occur in a planetary system? A) Early in its history, when there is still a gaseous disk around the star B) Shortly after a stellar wind clears the gaseous disk away C) Late in its history, when asteroids and comets occasionally collide with planets Answer: No Correct Answer Was Provided. 36) Based on current data, planetary systems appear to be ________. A) extremely rare B) present around about 10% of all stars C) present around at least half of all stars Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 37) Group Discussion: Astronomy in Color. In 2015, a diverse group of scientists, including some international leaders in the study of extrasolar planets, started a blog called Astronomy in Color. Their blog states that they are "committed to increasing diversity by recognizing, confronting and removing the barriers to racial equity and inclusion." This discussion encourages you to reflect on why the scientists thought such a blog was necessary. a. Prior to the discussion, go to the Astronomy in Color blog, look at some of the posts, and choose one that you would like to read and discuss. b. Gather in groups of three and work together to make a list of reasons why some scientists are trying to draw attention to racial equity and inclusion in astronomy. c. For the benefit of the other members of your group, summarize the blog post you read and the issues it highlighted. d. Discuss what you learned from the blog posts. Are the issues the authors raised connected to broader issues in society? Are some of those issues unique to science in general or to astronomy in particular? e. What advice would your group give to the astronomical community that might help it to become more inclusive?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 38) When Is a Theory Wrong? As discussed in this chapter, in its original form the nebular theory of solar system formation does not explain the orbits of many known extrasolar planets, but it can explain them with modifications such as allowing for planetary migration. Does this mean the theory was "wrong" or only "incomplete" before the modifications were made? Explain.Be sure to look back at the discussion in Chapter 3 of the nature of science and scientific theories. 39) Unanswered Questions. As discussed in this chapter, we are only just beginning to learn about extrasolar planets. Briefly describe one important but unanswered question related to the study of planets around other stars. Then write two to three paragraphs in which you discuss how we might answer this question in the future. Be as specific as possible, focusing on the type of evidence necessary to answer the question and how the evidence could be gathered. What are the benefits of finding answers to this question? 40) Group Activity: Time to Move On. A common theme in science fiction is "leaving home" to find a new planet for humans to live on. Now that we know about thousands of planets, we can start imagining how to choose.Note: You may wish to do this activity using the same four roles described in Chapter 1, Exercise 39. a. Make a list of characteristics that you would look for in a planet that might make a good home. b. Examine the planets in Figure 10.13. Does this graph give enough information to determine which planets might make good homes, or poor ones? If not, what's missing? c. Suppose you also knew the orbital distance for each of the planets in Figure 10.13. Would that make it easier to find potential good homes? Why or why not? Investigate Further 41) Explaining the Doppler Method. Explain how the Doppler method works in terms an elementary school child would understand. It may help to use an analogy to explain the difficulty of direct detection and the general phenomenon of the Doppler shift. 42) Comparing Methods. What are the strengths and limitations of the Doppler and transit methods? What kinds of planets are easiest to detect with each method? Are there certain planets that each method cannot detect, even if the planets are very large? Explain. What advantages are gained if a planet can be detected by both methods? 43) No Hot Jupiters Here. How do we think hot Jupiters formed? Why didn't one form in our solar system? 44) Low-Density Planets. Only one planet in our solar system has a density less than 1 g/cm3, but many extrasolar planets do. Explain why in a few sentences. (Hint: Consider the densities of the jovian planets in our solar system, given in Figure 8.1.) 27 Copyright © 2022 Pearson Education, Inc.

45) Project: Detect an Extrasolar Planet for Yourself. Most colleges and many amateur astronomers have the equipment necessary to detect known extrasolar planets using the transit method. All that's required is a telescope 10 or more inches in diameter, a CCD camera system, and a computer system for data analysis. The basic method is to take exposures of a few minutes' duration over a period of several hours around the times of predicted transit, and to compare the brightness of the star being transited to that of other stars in the same CCD frame. For complete instructions, see the study area at www.MasteringAstronomy.com. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 46) Lost in the Glare. This exercise helps you consider how hard would it be for an alien astronomer to detect the light from planets in our solar system compared to the light from the Sun itself. a. Calculate the fraction of the total emitted sunlight that reaches Earth. (Hint: Imagine a sphere around the Sun the size of Earth's orbit [area = 4πa2], then calculate the fraction of that area taken up by the disk of Earth [area = 4πr2Earth] b. Earth reflects 29% of the sunlight that reaches it. Based on this fact and your answer from part a, find the ratio of the total amount of light emitted by the Sun to the amount reflected by Earth. What does this tell you about the difficulty of detecting a planet like Earth around another star? c. Would detecting Jupiter be easier or harder than detecting Earth? Comment on whether you think Jupiter's larger size or greater distance has a stronger effect on its detectability. You may neglect any difference in reflectivity between Earth and Jupiter. 47) Transit of TrES-1. The planet TrES-1, orbiting a distant star, has been detected by both the transit and the Doppler technique, so we can calculate its density and get an idea of what kind of planet it is. a. Using the method of Cosmic Calculations 10.1, calculate the radius of the transiting planet. The planetary transits block 2% of the star's light. The star that TrES-1 orbits has a radius of about 85% of our Sun's radius. b. The mass of the planet is approximately 0.75 times the mass of Jupiter, and Jupiter's mass is about 1.9 × 1027 kilograms. Calculate the average density of the planet. Give your answer in grams per cubic centimeter. Compare this density to the average densities of Saturn (0.7 g/cm3) and Earth (5.5 g/cm3). Is the planet likely to be terrestrial or jovian in nature? (Hint: To find the volume of the planet, use the formula for the volume of a sphere: V = 4πr3/3. Be careful with unit conversions.) 48) Planet Around 51 Pegasi. The star 51 Pegasi has about the same mass and luminosity as our Sun. It is orbited by a planet with an orbital period of 4.23 days and mass estimated to be 0.6 times the mass of Jupiter. Use Kepler's third law to calculate the planet's average distance (semimajor axis) from its star. (Hint: Because the mass of 51 Pegasi is about the same as the mass of our Sun, you can use Kepler's third law in its original form, p2 = a3[Section 3.3]. Be sure to convert the period into years before using this equation.)

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 11 Our Star Section 11.1 1) What two forces are balanced in what we call gravitational equilibrium? A) The electromagnetic force and gravity B) Outward pressure and the strong force C) Outward pressure and inward gravity D) The strong force and gravity E) The strong force and kinetic energy Answer: C 2) How does the Sun generate energy today? A) Nuclear fission B) Nuclear fusion C) Chemical reactions D) Gravitational contraction E) Gradually expanding in size Answer: B 3) How do we know how old the Sun is? A) From radiometric dating of solar system meteorites B) From Newton's version of Kepler's third law and the orbits of the planets C) From calculating its fuel supply and how fast it is using it up D) From its speed and distance from us E) From radiometric dating of particles in the solar wind Answer: A 4) Where in the Sun do fusion reactions happen? A) Core and radiation zone B) Only the core C) Everywhere inside the Sun Answer: B 5) Scientists in the 1800s suggested that the source of the Sun's energy might be gravitational contraction. What was the major flaw of this hypothesis? A) Contracting objects cool down rather than heat up. B) This process would power the Sun for only about 25 million years, but geologists already had evidence the Earth was much older than that. C) The Sun had been observed to be expanding, not contracting. D) The predicted amount of contraction should have been large enough for astronomers of that time to measure. Answer: B

6) What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse? A) Outward pressure due to hot gas B) The strong force between protons C) Electromagnetic repulsion between protons D) Neutrinos produced by nuclear fusion drag gas outward. Answer: A 7) Which of the following quantities is equal to the energy per second generated by fusion in the Sun's core? A) The force of gravity holding the Sun together B) The temperature of the Sun's core C) The temperature at the Sun's photosphere D) The luminosity of the Sun's photosphere Answer: D 8) Why isn't the Sun shrinking or expanding at present? A) Because the Sun has lived for billions of years B) Because the Sun is spinning so fast, the centrifugal forces keep the surface of the Sun supported against collapse. C) Because gas pressure balances gravity in the Sun D) Because the Sun is a solid substance Answer: C 9) Which of the following is the best answer to the question "Why does the Sun shine?" A) The Sun initially began generating energy through nuclear fusion as it formed, but today, it generates energy primarily through the sunspot cycle. B) The young Sun became hotter through gravitational contraction. Once the core was hot enough, nuclear fusion began and has kept the Sun shining ever since. C) The Sun initially began making energy through chemical reactions. These heated the interior enough to allow gravitational contraction and nuclear fusion to occur. D) As the Sun was forming, nuclear fusion reactions in the shrinking clouds of gas slowly became stronger and stronger, until the Sun reached its current luminosity. Answer: B 10) We say that the matter in the Sun's interior is a plasma, which mean it is ________. A) a low-density gas B) an ionized gas C) a thick liquid, like blood D) a freely flowing liquid, like water E) a very hot but electrically neutral gas Answer: B

11) The Sun's composition (by mass) is approximately ________. A) 100 percent hydrogen and helium B) 50 percent hydrogen, 25 percent helium, 25 percent other elements C) 70 percent helium, 28 percent hydrogen, 2 percent other elements D) 70 percent hydrogen, 28 percent helium, 2 percent other elements E) 98 percent hydrogen, 2 percent helium, and other elements Answer: D 12) What is the approximate average temperature of the surface of the Sun? A) 1 million K B) 580,000 K C) 58,000 K D) 5800 K E) 580 K Answer: D 13) What is the approximate temperature of the Sun's core? A) 5800 K B) 10,000 K C) 1 million K D) 15 million K E) 150 million K Answer: D 14) Which layer of the Sun do we see with our eyes? A) Photosphere B) Corona C) Chromosphere D) Convection zone E) Radiation zone Answer: A 15) The core of the Sun is ________. A) at the same temperature and density as the surface B) at the same temperature but denser than the surface C) hotter and denser than the surface D) constantly rising to the surface through convection E) composed of iron Answer: C

16) Based on its surface temperature of 5800 K, most photons that leave the Sun's surface lie in the ________ region of the electromagnetic spectrum. A) microwave B) infrared C) visible D) ultraviolet E) x-ray Answer: C 17) If the Sun's surface were cooler, how would its appearance change? A) It would appear more red. B) It would appear more blue. C) It would become bright white. D) It would stay the same. Answer: A 18) Order the interior layers of the Sun from hottest to coldest. A) Radiation zone, core, convection zone, photosphere B) Core, radiation zone, convection zone, photosphere C) Photosphere, convection zone, radiation zone, core D) Photosphere, convection zone, core, radiation zone Answer: B 19) Which of the following properties of the Sun tells us the rate at which energy is being generated in its core? A) Surface temperature B) Apparent brightness C) Mass D) Luminosity Answer: D 20) Which of the following statements is an inference from a model (rather than an observation)? A) The Sun emits neutrinos. B) The photosphere emits visible light. C) The photosphere is made out of mainly hydrogen and helium. D) The corona is hotter than the photosphere. E) The Sun's core is gradually turning hydrogen into helium. Answer: E

21) Which of the following statements about the Sun is an inference from a model, not an observation? A) The photosphere emits visible light. B) The Sun emits neutrinos. C) The corona is hotter than the photosphere. D) The convection zone is cooler than the radiation zone. Answer: D Section 11.2 1) How do today's human-built nuclear power plants on Earth generate energy? A) Chemical reactions B) Nuclear fusion C) Nuclear fission D) Converting kinetic energy into electricity E) Converting gravitational potential energy into electricity Answer: C 2) Which has a greater mass: four protons or a helium nucleus with two protons and two neutrons? A) Four protons B) The helium nucleus C) They have the same mass. Answer: A 3) What temperature is required to fuse hydrogen? A) Thousands of Kelvin B) Millions of Kelvin C) Billions of Kelvin D) Trillions of Kelvin E) Any temperature, as long as gravity is strong enough Answer: B 4) What is the primary product created by the fusion of hydrogen in the core of the Sun? A) Hydrogen compounds B) Plasma C) Carbon and oxygen D) Radioactive elements like uranium and plutonium E) Helium Answer: E

5) Which is the strongest of the fundamental forces in the universe? A) Strong force B) Weak force C) Electromagnetic force D) Gravitational force E) All four forces have the same strength. Answer: A 6) What is the only known force that can overcome the repulsion between two positively charged nuclei and bind them together in a single nucleus? A) The strong force B) The weak force C) The electromagnetic force D) The gravitational force E) The Coriolis force Answer: A 7) About how much mass does the Sun lose through nuclear fusion per second? A) 4 tons B) 4 million tons C) 600 tons D) 600 million tons E) None; mass is conserved. Answer: B 8) Suppose you put two protons near each other. Because of the electromagnetic force, what will the two protons do? A) Collide B) Remain stationary C) Attract each other D) Repel each other E) Join together to form a nucleus Answer: D 9) Which of the following best explains why nuclear fusion requires bringing nuclei extremely close together? A) Fusion can only proceed by the proton-proton chain and therefore requires that protons come close enough together to be linked up into a chain. B) Nuclei have to be very hot in order to fuse, and the only way to get them hot is to bring them close together. C) Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold. D) Nuclei are attracted to each other by the electromagnetic force, but this force is only strong enough to make nuclei stick when they are very close together. Answer: C

10) Consider two pairs of protons, one pair moving toward each other at a speed of 1000 km/s and the other at a speed of 10 km/s. Which pair of protons will get closer together before they repel each other? A) The pair moving toward each other at 1000 km/s/ B) The pair moving toward each other at 10 km/s C) There will be no difference because the protons in both pairs will collide with each other. D) There will be no difference because they will repel at the same distance regardless of their speeds. Answer: A 11) The first step in the proton-proton chain produces an antielectron, or positron. What happens to the positron? A) It slowly works its way to the Sun's surface, where it escapes into space. B) It rapidly escapes from the Sun, traveling into space at nearly the speed of light. C) It almost immediately annihilates with an electron, resulting in two gamma-ray photons. D) It quickly meets an ordinary electron, forming an electron-positron pair that remains stable. E) It joins with a nearby neutron to form a proton. Answer: C 12) Which of the following is the overall fusion reaction by which the Sun currently produces energy? A) 3 H ⇒ 1 Li + energy B) 3 He ⇒ 1 C + energy C) 4 H ⇒ 4 He + energy D) 6 H ⇒ 1 He + energy E) 4 H ⇒ 1 He + energy Answer: E 13) Why does the Sun's rate of fusion gradually rise over billions of years? A) The Sun becomes less efficient and must increase the rate of fusion to produce the same amount of energy. B) Fusion reactions decrease the overall number of particles in the core, causing the core to shrink, converting gravitational potential energy into thermal energy, and increasing the rate of fusion. C) The radiation produced by fusion reactions that is trapped in the core gradually raises the temperature, increasing the rate of fusion. D) The Sun gets heavier as it gets older, and the stronger inward pull of gravity increases the fusion rate. E) The rate of fusion is not rising; it is actually decreasing over time. Answer: B

14) In what way does our theory of nuclear fusion predict that the Sun should be different today than it was when fusion began about 4-1/2 billion years ago? A) The Sun's mass should be about 30% higher today. B) The Sun's mass should be about 30% lower today. C) The Sun's luminosity should be about 30% higher today. D) The Sun's radius should be about 30% higher today. E) The Sun's distance from Earth should be about 30% lower today. Answer: C 15) Why does the Sun emit neutrinos? A) Convection releases neutrinos, which random walk through the radiation zone. B) The Sun does not emit neutrinos. C) Neutrinos are a by-product of fusion in the Sun's core. D) Solar flares create neutrinos with magnetic fields. Answer: C 16) Which statement best describes what used to be called the solar neutrino problem? A) Theoretical models predict that neutrinos should be produced in the Sun, but no neutrinos had ever been observed to be coming from the Sun. B) Solar neutrinos were detected in fewer numbers than predicted by theoretical models. C) Theoretical models did not predict the production of neutrinos by the Sun, yet solar neutrinos were detected. D) Theoretical models predicted that all solar neutrinos should be destroyed before they arrive at Earth, yet neutrinos were detected on Earth. E) The neutrinos that were being detected from the Sun had much smaller masses than theoretical models could account for. Answer: B 17) Which of the following statements about neutrinos is not true? A) About a thousand trillion neutrinos are passing through your body every second. B) Neutrinos are created as a by-product of the proton-proton chain. C) Neutrinos have no electrical charge. D) Neutrinos have a tendency to pass through just about anything without interactions, making them very difficult to detect. E) The mass of a neutrino is 30 percent of the mass of an electron. Answer: E

18) The solar neutrino problem referred to the fact that, a couple decades ago, fewer neutrinos were being detected from the Sun than predicted by our theory of nuclear fusion. What was the solution to this problem? A) We learned that the Sun is generating energy by means other than nuclear fusion. B) We learned that the Sun is generating much less energy than we thought it was. C) We learned that our detectors were mistaking neutrinos for the particles known as cosmic rays. D) We learned that our detectors were detecting only one of three different types of neutrinos that reach us from the Sun. E) We learned that our detectors were not functioning properly. Answer: D 19) Suppose that, for some unknown reason, the core of the Sun suddenly became hotter. Which of the following best describes what would happen? A) Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and turn the Sun into a giant star. B) Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal. C) Higher temperature would cause the rate of fusion to fall, decreasing the internal pressure and causing the core to collapse until the rate of fusion returned to normal. D) The higher temperature would not affect the fusion rate, but would cause the core to expand and cool until the temperature returned to normal, with the core at a new, slightly larger size. Answer: B 20) What would happen to the core of the Sun if its temperature rose slightly? A) The rate at which fusion occurs would decrease, leading to a contraction of the core, which would in turn cause the temperature to rise even further. B) The rate at which fusion occurs would increase, leading to a contraction of the core, which would in turn cause the temperature to rise even further. C) The rate at which fusion occurs would increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down. D) The rate at which fusion occurs would decrease, leading to an expansion of the core, which would in turn cause the temperature to drop back down. Answer: C 21) When the temperature of the Sun's core goes up, what happens next? A) Fusion reactions slow down, core shrinks and heats. B) Fusion reactions speed up, core expands and cools. C) Fusion reactions speed up, the core shrinks and cools. D) Fusion reactions slow down, the core expands and heats. Answer: B

22) Suppose that, for some unknown reason, the core of the Sun suddenly became hotter and the rate of nuclear fusion thereby increased. What would happen next? A) The Sun would quickly run out of hydrogen, causing the temperature to return to its original value. B) The rate of fusion would almost instantly skyrocket, causing the Sun to explode. C) The temperature would continue to increase, causing higher and higher fusion rates. D) The core would expand, reducing the pressure and temperature, and the rate of fusion would decrease until it returned to its original level. Answer: D 23) What would happen in the Sun if the temperature of the core decreased? A) The fusion rate increases, then the core expands and cools. B) The fusion rate increases, then the core shrinks and heats. C) The fusion rate decreases, then the core shrinks and heats. D) The fusion rate decreases, then the core expands and heats. Answer: C 24) What would happen if the fusion rate in the core increased but the core could not expand? A) The Sun's core would heat and the rate of fusion would increase further. B) The Sun's core would reach a new equilibrium, but at a higher temperature. C) The Sun's core would reach a new equilibrium, but at a cooler temperature. D) The Sun's core would cool and the rate of fusion would decrease. Answer: A 25) Most of the energy produced in the Sun is released in the form of visible light from the photosphere. However, some energy is released from the upper layers of the solar atmosphere. Which of the following best describes where other forms of light are released? A) The chromosphere is the source of ultraviolet light, and the corona is the source of x-rays. B) The chromosphere is the source of infrared light, and the corona is the source of ultraviolet light. C) The chromosphere is the source of x-rays, and the corona is the source of radio waves. D) The convection zone is the source of ultraviolet light, and the upper photosphere is the source of x-rays. E) Radio waves can pass directly through the gas which allows us to see the core. Answer: A 26) What causes the bubbling pattern of granulation that we see in the Sun's photosphere? A) Underlying convection B) Sunspots C) Dark areas of the pattern have larger concentrations of carbon D) Dust particles E) Magnetic fields Answer: A

27) How do we know the interior structure of the Sun? A) From x-ray images of the Sun B) From mathematical models that use the laws of physics and the Sun's observed characteristics C) From probes sent below the surface of the Sun Answer: B 28) What have studies of sunquakes, or helioseismology, revealed? A) The Sun vibrates only on the surface. B) "Sunquakes" are caused by similar processes that create earthquakes on Earth. C) The Sun generates energy by nuclear fusion. D) Our mathematical models of the solar interior are fairly accurate. E) Neutrinos from the solar core reach the solar surface easily. Answer: D 29) Which of the following provides evidence to support models of how fusion occurs in the Sun's core? A) Solar neutrinos B) Solar flares C) Sun spots D) X-ray observations E) Careful study of the Sun's atmospheric structure Answer: A

30) This image shows the velocity of gas moving toward or away from us on the Sun's surface, as measured through Doppler shifts; the key indicates the measured velocity, with negative velocities indicating gas moving toward us and positive velocities away from us. Based on this map, about how fast is the sun rotating at its equator? (Hint: determine the speed at which equatorial gas is moving toward us on one side of the equator and away from us on the other.) A) About 200 m/s B) About 2000 m/s C) About 20,000 m/s D) The Sun is not rotating. Answer: B 31) This image shows the velocity of gas moving toward or away from us on the Sun's surface, as measured through Doppler shifts; the key indicates the measured velocity, with negative velocities indicating gas moving toward us and positive velocities away from us. What do the small-scale changes in the shading represent in this map? A) Vibrations of gas moving up or down at the solar surface B) Variations in the altitude of the solar surface C) Variations in the temperature of the photosphere D) Nothing; this is an artist's rendering of the sun. Answer: A

32) Which of the following is not a method astronomers use to determine the physical conditions inside the Sun? A) Observing x-ray images of the solar interior using satellites B) Building mathematical models that use the laws of physics C) Detecting solar neutrinos generated in the Sun's core D) Measuring Doppler shifts to observe solar vibrations Answer: A 33) Imagine that you are trying to stop neutrinos with a lead shield. How thick would you need to make this shield to ensure that it can stop an average neutrino? A) About one meter B) About 700,000 kilometers (the radius of the Sun) C) About 150 million kilometers (the size of an astronomical unit) D) About one light-year E) About 14 billion light-years (the size of the observable universe) Answer: D 34) Approximately how many neutrinos pass through your body each second? A) About a thousand trillion B) About one thousand C) About 1023 D) None; they are blocked by the Earth's atmosphere. Answer: A 35) About a thousand trillion neutrinos are passing through your body every second. Why don't they hurt you? A) Neutrinos interact with ordinary matter only through the weak force. B) Their masses are too low to cause any damage. C) They are traveling too slowly to cause any damage. D) Our immune systems release antibodies that counteract the damage the neutrinos cause. E) Actually, they do—neutrinos are the cause of many cancers. Answer: A

Section 11.3 1) To estimate the central temperature of the Sun, scientists ________. A) create a version of the Sun in a laboratory B) use computer models to predict interior conditions C) send probes to measure the temperature D) monitor changes in Earth's atmosphere Answer: B 2) The Sun is gradually increasing in luminosity as it ages. It is about 30% more luminous than it was when it was born. Why isn't this increase considered to be an explanation for global warming? A) The Sun is increasing in luminosity way too slowly, over many millions of years. B) What the Sun was doing millions of years ago is what determines Earth's temperature, since the Earth doesn't respond directly to what the Sun is doing today. C) The amount of energy the Earth receives from the Sun remains constant regardless of what the Sun does. D) The scientists are covering up this potentially valid explanation. Answer: A 3) Why are sunspots cooler than the surrounding solar surface? A) They are regions where convection carries cooler material downward. B) Strong magnetic fields slow convection and prevent hot plasma from entering the region. C) Magnetic fields trap ionized gases that absorb light. D) There is less fusion occurring there. E) Magnetic fields lift material from the surface of the Sun, cooling off the material faster. Answer: B 4) Why do sunspots appear dark? A) They are composed of different elements than the rest of the sun. B) They are regions that do not emit any radiation. C) They are regions that are significantly cooler than the rest of the photosphere. D) They are regions nearly devoid of gas. Answer: C 5) The intricate patterns visible in an x-ray image of the Sun generally show About A) extremely hot plasma flowing along magnetic field lines B) granulation on the photosphere C) helioseismological fluctuations D) structure within sunspots Answer: A

6) What are coronal holes? A) Regions on the photosphere where magnetic lines poke through, creating the cooler areas of the sunspots B) Areas of the corona where magnetic field lines project into space, allowing charged particles to escape the Sun, becoming part of the solar wind C) Holes in the corona of the Sun that allow us to see the photosphere D) Tunnels in the outer layers of the Sun through which photons can escape more quickly than through the radiation zone Answer: B 7) Which of the following statements about the sunspot cycle is not true? A) The number of sunspots peaks approximately every 11 years. B) With each subsequent peak in the number of sunspots, the magnetic polarity of the Sun is the reverse of the previous peak. C) The rate of nuclear fusion in the Sun peaks about every 11 years. D) The cycle is truly a cycle of magnetic activity, and variations in the number of sunspots are only one manifestation of the cycle. E) The number of solar flares peaks about every 11 years. Answer: C 8) What processes are involved in the sunspot cycle? A) Gravitational contraction of the Sun B) Wave motions in the solar interior C) Variations of the solar thermostat D) The winding of magnetic field lines due to differential rotation E) The interaction of the Earth's magnetic field with that of the Sun Answer: D 9) What observations characterize solar maximum? A) The Sun becomes much brighter. B) The Sun emits light of longer average wavelength. C) The Sun rotates faster at the equator. D) We see many sunspots on the surface of the Sun. Answer: D

10) Based on the above graph, the average time between maximums of the sunspot cycle is about ________. A) 110 years B) 11 years C) 1 year D) a few months Answer: B 11) Based on the above graph, which statement about the sunspot cycle is true? A) The period of the cycle is always exactly 11 years. B) Some solar minima (when the Sun has the fewest sunspots) have significantly fewer sunspots than others. C) Some solar maxima (when the Sun has the most sunspots) have significantly more sunspots than others. D) At least 1% of the Sun's surface is covered with sunspots at all times. Answer: C 12) While we can't completely rule out a connection between the sunspot cycle and weather cycles on Earth, most scientists doubt there is a significant effect because ________. A) the Sun's luminosity changes less than about 0.1% between minimum and maximums of the sunspot cycle B) the Sun is too far away to affect Earth's weather C) there are no known cycles in weather or climate that last as long as the sunspot cycle D) sunspots are linked to the Sun's magnetic field, which could not possibly have any effect on Earth Answer: A 13) We can rule out a connection between changes in the Sun's luminosity and the global warming that is currently occurring on Earth because ________. A) the Sun's luminosity has remained fairly steady even as Earth's temperature as increased B) the Sun is too far away to affect Earth's climate C) changes in the Sun's luminosity cannot occur on the time scale over which global warming has occurred D) Earth's atmosphere prevents changes in the Sun's luminosity from having any effect on Earth's surface Answer: A 16 Copyright © 2022 Pearson Education, Inc.

Short Answer Questions 1) Suppose someone tells you that the Sun generates its light and heat because it is a giant ball of fire. Would you agree? Why or why not? Answer: No. Fire is produced by chemical burning. The Sun could not possibly have generated chemical energy for billions of years because this process would have burned itself out long ago. The correct explanation is that the Sun generates its light and heat from nuclear fusion in its core. 2) Briefly explain how the Sun became hot enough for nuclear fusion. Answer: The Sun formed from a cloud of gas. As it contracted, its gravitational potential energy was converted to thermal energy. The Sun continued to contract until the core became hot enough to sustain nuclear fusion. 3) Briefly describe why the fact that we detect neutrinos coming from the Sun supports the idea that the Sun generates energy by nuclear fusion. Answer: Laboratory experiments and theory show that fusion produces neutrinos. Therefore, scientists predict that neutrinos should come from the Sun if fusion is occurring in its core. Theories predict how many and what type of neutrinos should be observed. Thus, the observations that confirm this prediction support the theory. Reading Quiz Questions 1) According to modern science, approximately how old is the Sun? A) 4 1/2 billion years B) 25 million years C) 10,000 years D) 400 million years Answer: A 2) The Sun will exhaust its nuclear fuel in about ________. A) 5000 AD B) 5 million years C) 5 billion years D) 50 billion years Answer: C 3) Which of the following correctly describes how the process of gravitational contraction can make a star hot? A) When a star contracts in size, gravitational potential energy is converted to thermal energy. B) Gravitational contraction involves nuclear fusion, which generates a lot of heat. C) Heat is generated when gravity contracts because gravity is an inverse square law force. D) Gravitational contraction involves the generation of heat by chemical reactions, much like the burning of coal. Answer: A

4) The source of energy that keeps the Sun shining today is ________. A) nuclear fission B) nuclear fusion C) gravitational contraction D) chemical reactions Answer: B 5) What two physical processes balance each other to create the condition known as gravitational equilibrium in stars? A) The strong force and the weak force B) Gravitational force and outward pressure C) Gravitational force and surface tension D) The strong force and the electromagnetic force Answer: B 6) Energy balance in the Sun refers to a balance between ________. A) the rate at which fusion generates energy in the Sun's core and the rate at which the Sun's surface radiates energy into space B) the mass that the Sun loses each second and the amount of mass converted into energy each second C) the force of gravity pulling inward and the force due to pressure pushing outward D) the amount of energy the Sun radiates into space and the amount of energy that reaches Earth Answer: A 7) When we say that the Sun is a ball of plasma, we mean that ________. A) the Sun is made of material that acts like a liquid acts on Earth B) the Sun is made of atoms and molecules C) the Sun consists of gas in which many or most of the atoms are ionized (missing electrons) D) the Sun is roughly the same color as blood Answer: C 8) What is the Sun's approximate composition (by mass)? A) 70% hydrogen, 28% helium, 2% other elements B) 100% hydrogen and helium C) 50% hydrogen, 25% helium, 25% other elements D) 90% dark matter, 10% ordinary matter Answer: A 9) From the center outward, which of the following lists the "layers" of the Sun in the correct order? A) Core, radiation zone, convection zone, photosphere, chromosphere, corona B) Core, radiation zone, convection zone, corona, chromosphere, photosphere C) Core, convection zone, radiation zone, corona, chromosphere, photosphere D) Core, corona, radiation zone, convection zone, photosphere, chromosphere Answer: A

10) What are the appropriate units for the Sun's luminosity? A) Watts B) Joules C) Newtons D) Kilograms Answer: A 11) The Sun's visible surface (that is, the surface we can see with our eyes) is called the ________. A) photosphere B) chromosphere C) corona D) core Answer: A 12) The Sun's average surface (photosphere) temperature is about ________. A) 5,800 K B) 1,000,000 K C) 1,000 K D) 37,000 K Answer: A 13) What is the solar wind? A) A stream of charged particles flowing outward from the surface of the Sun B) The uppermost layer of the Sun, which lies just above the corona C) The strong wind that blows sunspots around on the surface of the Sun D) The wind that causes huge arcs of gas to rise above the Sun's surface Answer: A 14) The fundamental nuclear reaction occurring in the core of the Sun is ________. A) nuclear fission B) radioactive decay C) nuclear fusion of hydrogen into helium D) nuclear fusion of helium to carbon Answer: C 15) The proton-proton chain is ________. A) the specific set of nuclear reactions through which the Sun fuses hydrogen into helium B) the linkage of numerous protons into long chains C) another name for the force that holds protons together in atomic nuclei D) an alternative way of generating energy that is different from the fusion of hydrogen into helium Answer: A

16) The overall result of the proton-proton chain is ________. A) 4 H becomes 1 He + energy B) 6 H becomes 1 He + energy C) p + p becomes 1 deuterium nucleus (2H) + energy D) individual protons are joined into long chains of protons Answer: A 17) To estimate the central temperature of the Sun, scientists ________. A) send probes to measure the temperature B) use hot gas to create a small Sun in a laboratory C) monitor changes in Earth's atmosphere D) use computer models to predict interior conditions Answer: D 18) Why are neutrinos so difficult to detect? A) They have a tendency to pass through just about any material without any interactions. B) They are extremely rare. C) They have no mass. D) No one knows; this is the essence of the "solar neutrino problem." Answer: A 19) The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about ________. A) a few hundred thousand years ago B) 3 days ago C) 100 years ago D) 1,000 years ago Answer: A 20) What happens to energy in the Sun's convection zone? A) Energy is transported outward by the rising of hot plasma and sinking of cooler plasma. B) Energy is produced in the convection zone by thermal radiation. C) Energy slowly leaks outward through the radiative diffusion of photons that repeatedly bounce off ions and electrons. D) Energy is produced in the convection zone by nuclear fusion. Answer: A 21) What do sunspots, solar prominences, and solar flares all have in common? A) They are all strongly influenced by magnetic fields on the Sun. B) They all have about the same temperature. C) They are all shaped by the solar wind. D) They all occur only in the Sun's photosphere. Answer: A

22) Which of the following is not a characteristic of the 11-year sunspot cycle? A) The sunspot cycle is steady, so that each 11-year cycle is nearly identical to every other 11year cycle. B) The likelihood of seeing solar prominences or solar flares is higher when sunspots are more common and lower when they are less common. C) The Sun's entire magnetic field flip-flops with each cycle, so that the overall magnetic cycle averages 22 years. D) The number of sunspots on the Sun at any one time gradually rises and falls, with an average of 11 years between the times when sunspots are most numerous. Answer: A 23) How is the sunspot cycle directly relevant to us here on Earth? A) Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment. B) The sunspot cycle strongly influences Earth's weather. C) The Sun's magnetic field, which plays a major role in the sunspot cycle, affects compass needles that we use on Earth. D) The brightening and darkening of the Sun that occurs during the sunspot cycle affects plant photosynthesis here on Earth. E) The sunspot cycle is the cause of recent global warming. Answer: A Concept Quiz Questions 1) In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot because of gravitational contraction. What was the major drawback to this idea? A) It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this. B) It predicted that the Sun would shrink noticeably as we watched it, but the Sun appears to be stable in size. C) It is physically impossible to generate heat simply by making a star shrink in size. D) It predicted that Earth would also shrink in size with time, which would make it impossible to have stable geology on our planet. Answer: A 2) When is/was gravitational contraction an important energy generation mechanism for the Sun? A) It was important when the Sun was forming from a shrinking interstellar cloud of gas. B) It is the primary energy generation mechanism in the Sun today. C) It has played a role throughout the Sun's history, but it was most important right after nuclear fusion began in the Sun's core. D) It is important during periods when the Sun is going from solar maximum to solar minimum. Answer: A

3) What do we mean when we say that the Sun is in gravitational equilibrium? A) There is a balance within the Sun between the outward push of pressure and the inward pull of gravity. B) The Sun maintains a steady temperature. C) The hydrogen gas in the Sun is balanced so that it never rises upward or falls downward. D) The Sun always has the same amount of mass, creating the same gravitational force. Answer: A 4) What do we mean when we say that the Sun is in energy balance? A) The amount of energy released by fusion in the Sun's core equals the amount of energy radiated from the Sun's surface into space. B) The Sun maintains a steady rate of energy output into space. C) The inward force of gravity balances the outward push of pressure. D) The amount of energy contained in the Sun's magnetic field is in balance with the amount of energy going into solar activity such as sunspots and solar flares. Answer: A 5) Which of the following is the best answer to the question, "Why does the Sun shine?" A) As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine. B) As the Sun was forming, nuclear fusion reactions in the shrinking clouds of gas slowly became stronger and stronger, until the Sun reached its current luminosity. C) The Sun initially began making energy through chemical reactions. These heated the interior enough to allow gravitational contraction and nuclear fusion to occur. D) The Sun initially began generating energy through nuclear fusion as it formed, but today it generates energy primarily through the sunspot cycle. Answer: A 6) How does the Sun's mass compare to Earth's mass? A) The Sun's mass is about 300,000 times the mass of the Earth. B) The Sun's mass is about 300 times the mass of the Earth. C) The Sun's mass is about 30 times the mass of the Earth. D) Both have approximately the same mass. Answer: A 7) Which of the following best describes why the Sun emits most of its energy in the form of visible light? A) Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light. B) Nuclear fusion in the Sun's core produces visible light photons. C) The visible light comes from energy level transitions as electrons in the Sun's hydrogen atoms jump between level 1 and level 2. D) The Sun's gas is on fire like flames from wood or coal, and these flames emit visible light. Answer: A

8) The Sun's surface seethes and churns with a bubbling pattern. Why? A) We are seeing hot gas rising and cool gas falling as a result of the convection that occurs beneath the surface. B) The Sun's surface is boiling. C) The churning gas is being stirred up by the strong solar wind. D) The churning is an illusion created by varying radiation; the gas on the Sun's surface is actually quite still. Answer: A 9) Which of the following correctly compares the Sun's energy generation process to the energy generation process in human-built nuclear power plants? A) The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei. B) Both processes involve nuclear fusion, but the Sun fuses hydrogen, while nuclear power plants fuse uranium. C) The Sun generates energy through nuclear reactions, while nuclear power plants generate energy through chemical reactions. D) The Sun generates energy through fission, while nuclear power plants generate energy through fusion. Answer: A 10) Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is ________. A) ejected into space in a solar wind B) ejected into space by solar flares C) converted to an amount of energy equal to 4 million tons times the speed of light squared D) reabsorbed as molecular hydrogen Answer: C 11) Which of the following best explains why nuclear fusion requires bringing nuclei extremely close together? A) Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold. B) Nuclei are attracted to each other by the electromagnetic force, but this force is only strong enough to make nuclei stick when they are close together. C) Nuclei have to be very hot in order to fuse, and the only way to get them hot is to bring them close together. D) Fusion can proceed only by the proton-proton chain, and therefore requires that protons come close enough together to be linked up into a chain. Answer: A 12) If the Sun's core suddenly shrank a little bit, what would happen in the Sun? A) The core would heat up, fusion rates would increase, the core would re-expand. B) The core would cool off and continue to shrink as its density increased. C) The density of the core would decrease, causing the core to cool off and expand. D) The core would heat up, causing it to radiate so much energy that it would shrink even more. Answer: A 23 Copyright © 2022 Pearson Education, Inc.

13) Which of the following choices is not a way by which we can study the inside of the Sun? A) We can send a space probe into the Sun's photosphere. B) We can probe the interior of the Sun by studying the vibrations in its photosphere. C) We can make a computer model of the Sun's interior that allow us to predict the observable properties of the Sun. D) We can study solar neutrinos. Answer: A 14) Why does the Sun emit neutrinos? A) Solar flares create neutrinos with magnetic fields. B) Fusion in the Sun's core creates neutrinos. C) Convection releases neutrinos, which random walk through the radiation zone. D) The Sun was born with a supply of neutrinos that it gradually emits into space. E) The Sun does not emit neutrinos. Answer: B 15) If the Sun suddenly stopped emitting neutrinos, what might we infer (after checking that our neutrino detectors were still operational)? A) Fusion reactions in the Sun have ceased within the past few minutes. B) Fusion reactions in the Sun ceased a few hundred thousand years ago. C) Fission reactions in the Sun have ceased. D) The Sun has exhausted its supply of neutrinos. Answer: A 16) A salesman attempts to convince you to purchase a "solar neutrino shield" to protect you and your family. (It's even "on sale!") Why do you turn down this excellent offer? A) Neutrinos rarely, if ever, interact with other matter. B) There's no such thing as a solar neutrino. C) Solar neutrinos are generated by solar winds, but we're in a solar minimum now, so the risk of damage is very low. D) The Earth's natural magnetic field already offers excellent protection against the onslaught of solar neutrinos. Answer: A 17) Why do sunspots appear dark in pictures of the Sun? A) They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere. B) They are too cold to emit any visible light. C) They are holes in the solar surface through which we can see through to deeper, darker layers of the Sun. D) They are extremely hot and emit all their radiation as X rays rather than visible light. Answer: A

18) How can we best observe the Sun's chromosphere and corona? A) The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes. B) The chromosphere is best observed with infrared telescopes and the corona is best observed with ultraviolet telescopes. C) The chromosphere and corona are both best studied with visible light. D) The chromosphere and corona are both best studied with radio telescopes. Answer: A 19) The intricate patterns visible in an X-ray image of the Sun generally show ________. A) helioseismological fluctuations B) a bubbling pattern on the photosphere C) extremely hot plasma flowing along magnetic field lines D) structure within sunspots Answer: C 20) How can we measure the strength of magnetic fields on the Sun? A) By looking for the splitting of spectral lines in the Sun's spectrum B) By observing the sizes of sunspots: Bigger sunspots mean a stronger field C) By observing auroras here on Earth D) Only by using sophisticated computer models because there are no observational ways of measuring magnetic field strength Answer: A 21) Satellites in low-Earth orbits are more likely to crash to Earth when the sunspot cycle is near solar maximum because ________. A) it is too dangerous to send the Space Shuttle to service satellites during solar maximum B) Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits C) of increased magnetic interference D) they are more likely to have their electronics "fried" by a solar flare during solar maximum Answer: B 22) We can essentially rule out the Sun as a cause of global warming over the past few decades because ________. A) the amount of incoming sunlight has decreased while Earth's average temperature has increased B) the amount of light coming from the Sun does not change over time scales of decades C) there is no evidence that the Sun can affect climate D) the number of sunspots on the Sun varies in an approximately 11-year cycle Answer: A

Visual Quiz Questions 1) The arrows in this diagram are meant to show how gravitational equilibrium works in the Sun. What do the different colors and different arrow lengths represent?

A) inward pointing green arrows represent gravity outward pointing red arrows represent pressure longer arrows represent a stronger push or pull B) inward pointing green arrows represent gravity outward pointing red arrows represent the solar wind longer arrows represent a stronger push or pull C) inward pointing green arrows represent conduction outward pointing red arrows represent radiation longer arrows represent greater intensity D) inward pointing green arrows represent downward convection outward pointing red arrows represent upward convection longer arrows represent stronger convection Answer: A 2) What layer of the Sun are we seeing in this photo?

A) Photosphere B) Chromosphere C) Corona D) Radiation zone Answer: A

3) The dark spots in this photo (such as the one indicated by the arrow) represent what we call ________.

A) sunspots B) convection zones C) coronal holes D) solar prominences E) Great Dark Spots Answer: A

4) Which photo pair shows Earth correctly scaled in comparison to the Sun? A)

5) This photograph shows a small portion of the Sun's photosphere. What is going on in the bright regions (such as the bright region indicated by the arrow)?

A) Hot gas is rising up from the solar interior. B) Cool gas is falling back down into the solar interior. C) The bright spots are regions of unusually intense magnetic fields. D) The bright spots are what we call sunspots. Answer: A

6) This x-ray image shows a loop of hot gas above the surface of the Sun. If we took a visible light photo that looked in the Sun's photosphere just under the two points where the loop of gas comes down (arrows), what would we find? A) Sunspots B) Bright prominences C) Coronal holes D) Radiation zones Answer: A

7) This x-ray image shows a loop of hot gas above the surface of the Sun. Suppose we took another photo looking at the same place 1 hour later. What would we see? A) The loop would look about the same as it does in this photo. B) The loop would have shot much higher up above the Sun's surface. C) The loop would have collapsed back down, so we would not see it anymore. D) The loop would have turned blue as the gas became hotter. Answer: A 8) What layer of the Sun are we seeing in this photograph, and in what wavelength band was it photographed?

A) Corona, photographed in x-rays B) Chromosphere, photographed in visible light C) Photosphere, photographed in visible light D) Convection zone, photographed in infrared light E) Radiation zone, photographed in x-rays Answer: A 9) Study this figure and its axis labels. What is this graph showing us?

A) The number of sunspots on the Sun tends to increase and decrease with an approximately 11year cycle. B) The latitude at which sunspots appear varies between 0 and 0.5 degrees. C) The intensity of Sunlight varies significantly over time, and reached an unusually high peak around 1960. D) The Sun pulsates much like a beating heart, but with each beat taking about a decade. Answer: A 30 Copyright © 2022 Pearson Education, Inc.

10) In terms of the global warming that has been occurring on Earth over the past few decades, what is the key message from this figure?

A) Changes in the Sun's energy output (irradiance) cannot explain the observed warming. B) The Sun's energy output (irradiance) tracks quite well with the observed warming trend. C) The Sun's energy output (irradiance) and Earth's global average temperature both vary in an 11-year cycle. D) Scientists have no way to explain the observed global warming trend. Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Figure 11.20b, repeated above, shows the latitudes at which sunspots appeared on the surface of the Sun since about 1900. Answer the following questions, using the information provided in the figure. 1) Which of the following years had the least sunspot activity? A) 1930 B) 1949 C) 1961 D) 1987 Answer: D 2) What is the approximate range in latitude over which sunspots appear? Answer: Sunspots appear over a range of 40°N latitude to 40°S latitude. 3) According to the figure, how do the positions of sunspots appear to change during one sunspot cycle? Do they get closer to or farther from the equator with time? Answer: Sunspots get closer to the equator in average position during a sunspot cycle. Individual sunspots are able to appear near the equator at any time, but sunspots spread across a wide range of latitudes at the beginning of the sunspot cycle, and the spread then narrows considerably by the end of the sunspot cycle. Chapter Review Questions 1) Briefly describe how gravitational contraction generates energy. When was it important in the Sun's history? Explain. 2) What two forces are balanced in gravitational equilibrium? What does it mean for the Sun to be in energy balance? 3) State the Sun's luminosity, mass, radius, and average surface temperature, and put the numbers in perspective. 32 Copyright © 2022 Pearson Education, Inc.

4) Briefly describe the distinguishing features of each of the layers of the Sun shown in Figure 11.4. 5) Distinguish between nuclear fission and fusion. Which one is used in nuclear power plants? Which one takes place in the Sun? 6) Why does nuclear fusion require high temperatures and pressures? 7) What is the overall nuclear fusion reaction in the Sun? Briefly describe the proton—proton chain. 8) Describe how a natural "solar thermostat" keeps the core fusion rate steady in the Sun. 9) Describe how energy generated by fusion makes its way to the Sun's surface. How long does it take? 10) How do mathematical models help us learn about the Sun, and what gives us confidence in the models? 11) What are neutrinos? What was the solar neutrino problem, and how was it solved? 12) What is solar activity? Describe sunspots, solar prominences, solar flares, and coronal mass ejections. 13) How do magnetic fields keep sunspots cooler than the surrounding plasma? Explain. 14) Why are the chromosphere and corona best viewed with ultraviolet and x-ray telescopes, respectively? Briefly explain how these regions are heated. 15) What is the sunspot cycle? Describe the leading model for explaining it. Does the sunspot cycle influence Earth's climate? Explain. Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 16) Before Einstein, gravitational contraction appeared to be a perfectly plausible mechanism for solar energy generation. 17) The solar wind usually flows outward from the Sun, but sometimes it turns around and flows backward. 18) If fusion in the solar core ceased today, worldwide panic would break out tomorrow as the Sun began to grow dimmer. 33 Copyright © 2022 Pearson Education, Inc.

19) Astronomers have recently photographed magnetic fields churning deep beneath the solar photosphere. 20) I wear a lead vest to protect myself from solar neutrinos. 21) There haven't been many sunspots this year, but there ought to be many more in about 5 years. 22) News of a solar flare caused concern among businesses involved in communication and electrical power generation. 23) By observing solar neutrinos, we can learn about nuclear fusion deep in the Sun's core. 24) If the Sun's magnetic field somehow disappeared, there would be no more sunspots on the Sun. 25) Scientists are currently building an infrared telescope designed to observe fusion reactions in the Sun's core. Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 11 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 26) Which of these groups of particles has the greatest mass? A) A helium nucleus with two protons and two neutrons B) Four electrons C) Four individual protons Answer: No Correct Answer Was Provided. 27) Which of these layers of the Sun is coolest? A) Core B) Radiation zone C) Photosphere Answer: No Correct Answer Was Provided. 28) X-ray images of the Sun generally show the ________. A) photosphere B) chromosphere C) corona Answer: No Correct Answer Was Provided. 29) Scientists estimate the central temperature of the Sun using ________. A) probes that measure changes in Earth's atmosphere B) mathematical models of the Sun C) laboratories that create miniature versions of the Sun Answer: No Correct Answer Was Provided. 34 Copyright © 2022 Pearson Education, Inc.

30) Sunspots appear darker than their surroundings because they ________. A) are cooler than their surroundings B) block some of the sunlight from the photosphere C) do not emit any light Answer: No Correct Answer Was Provided. 31) At the center of the Sun, fusion converts hydrogen into ________. A) plasma B) radiation and elements like carbon and nitrogen C) helium, energy, and neutrinos Answer: No Correct Answer Was Provided. 32) Solar energy leaves the core of the Sun in the form of ________. A) photons B) rising hot gas C) sound waves Answer: No Correct Answer Was Provided. 33) The fact that we observe neutrinos from the Sun provides direct evidence of ________. A) fusion in the Sun's core B) convection in the Sun's interior C) the existence of the solar wind Answer: No Correct Answer Was Provided. 34) What causes the cycle of solar activity? A) Changes in the Sun's fusion rate B) Changes in the organization of the Sun's magnetic field C) Changes in the speed of the solar wind Answer: No Correct Answer Was Provided. 35) Which of these things poses the greatest hazard to communication satellites? A) Photons from the Sun B) Solar magnetic fields C) Particles from the Sun Answer: No Correct Answer Was Provided.

Inclusive Astronomy Use these questions to reflect on participation in science. 36) Group Discussion: Arthur Walker, Scientist and Mentor. Arthur B. C. Walker Jr., an African-American scientist who spent much of his career at Stanford University, was a pioneer in developing the technology for taking ultraviolet and x-ray images of the Sun. a. Working independently, learn basic details of Dr. Walker's career, including when and where he earned his Ph.D., the name and occupation of his first graduate student, the purpose of the investigative commission he was appointed to in 1986, and the purpose of the award that now bears his name. b. Gather in small groups to discuss whether Dr. Walker was likely to have faced discrimination in his efforts to become a scientist. Be sure to consider the time period when he was earning his Ph.D. c. Within the group, share what you've learned about Dr. Walker's first graduate student, including what was posthumously revealed about the student's sexual orientation. Discuss why such a person might have considered Dr. Walker a particularly suitable mentor. d. Discuss what you learned about the 1986 commission. In addition to scientific and technical knowledge, what other skills do people on such a commission need to have? e. What is the purpose of the award that bears Dr. Walker's name, and who has won it to date? Does your group think this award is an appropriate way to honor him? Why or why not? The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 37) Inside the Sun. Scientists claim to know what is going on inside the Sun, even though we cannot directly observe the Sun's interior. What is the basis for these claims, and how are they aligned with the hallmarks of science outlined in Section 3.4? 38) The Solar Neutrino Problem. The earliest efforts to detect neutrinos from the Sun detected only about one-third of the number predicted by models of fusion in the Sun. This discrepancy became known as the solar neutrino problem but did not immediately cause scientists to abandon their fusion models. Instead, they focused on building better detectors and revising their theories about the properties of neutrinos. Eventually those improvements enabled solar-neutrino scientists to detect all of the neutrinos predicted by solar models. Explain how their decisionmaking process exemplified the hallmarks of science from Chapter 3. 39) The Role of the Sun. Briefly discuss how the Sun affects us here on Earth. Be sure to consider not only factors such as its light and warmth but also how the study of the Sun has led us to new understandings in science and to technological developments. Overall, how important has solar research been to our lives?

40) The Sun and Global Warming. Some people still claim that part or all of the global warming observed over the past century may be due to changes in the Sun, but the data in Figure 11.22 seem to rule that out (as do several other lines of evidence beyond those discussed in this text). Discuss how the people in your life talk about global warming, what information sources they view as credible, and whether they consult scientific data when making up their minds about the causes of global warming. 41) Group Activity: The Sun's Future. Working in small groups, discuss the following questions in light of what you have learned about how the Sun came to shine steadily with energy from fusion in its core.Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39. a. Will the Sun's core temperature go up or down after the core runs out of hydrogen for fusion? Why? b. If your group thinks the temperature will go up, decide what would ultimately stop the temperature from rising forever. If you think the temperature will go down, decide what could stop it from falling to absolute zero. c. Propose and describe an experiment or a set of observations that could test whether your answers to parts a and b are correct. Investigate Further 42) The End of Fusion I. Describe what would happen in the Sun if fusion reactions suddenly ceased. 43) The End of Fusion II. If fusion reactions in the Sun were to suddenly cease, would we be able to tell? If so, how? 44) A Really Strong Force. How would the interior temperature of the Sun be different if the strong force that binds nuclei together were ten times as strong? 45) Covered with Sunspots. Describe what the Sun would look like from Earth if the entire photosphere were the same temperature as a sunspot. 46) Inside the Sun. Describe how scientists determine what the interior of the Sun is like. Could we send a probe into the Sun to measure what is happening there? 47) Solar Energy Output. Observations over the past century show that the Sun's visible-light output varies by less than 1%, but its x-ray output can vary by a factor of ten or more. Explain why the changes in x-ray output can be so much larger than those in visible-light output. 48) An Angry Sun. A Time magazine cover once suggested that an "angry Sun" was becoming more active as human activity changed Earth's climate. It's certainly possible for the Sun to become more active at the same time that humans are affecting Earth, but is it possible that the Sun could be responding to human activity? Why or why not?

49) Research: Current Solar Weather. Daily information about solar activity is available at NASA's website www.spaceweather.com. Where are we in the sunspot cycle right now? When is the next solar maximum or minimum expected? Have there been any major solar storms in the past few months? If so, did they have any significant effects on Earth? Summarize your findings in a one- to two-page report. 50) Research: Solar Observatories in Space. Visit NASA's website for the Sun—Earth connection and explore some of the current and planned space missions designed to observe the Sun. Choose one mission to study in greater depth, and write a one- to two-page report on the status and goals of the mission and what it has taught or will teach us about the Sun. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 51) The Color of the Sun. Use Wien's law(see Cosmic Calculations 5.1) and the Sun's average surface temperature of about 5800 K to calculate the wavelength of peak thermal emission from the Sun. What color does this wavelength correspond to in the visible-light spectrum? Why do you think the Sun appears white or yellow to our eyes? 52) The Color of a Sunspot. Use Wien's law(see Cosmic Calculations 5.1) and the typical sunspot temperature of about 4000 K to calculate the wavelength of peak thermal emission from a sunspot. What color does this wavelength correspond to in the visible-light spectrum? How does this color compare with the overall color of the Sun? 53) Solar Mass Loss. Estimate how much mass the Sun will lose through fusion reactions during its 10-billion-year life. You can simplify the problem by assuming the Sun's energy output remains constant. Compare the amount of mass lost with Earth's mass. 54) Pressure of the Photosphere. The gas pressure of the photosphere changes substantially from its upper levels to its lower levels. Near the top of the photosphere, the temperature is about 4500 K and there are about 1.6 × 1016 gas particles per cubic centimeter. In the middle, the temperature is about 5800 K and there are about 1.0 × 1017 gas particles per cubic centimeter. At the bottom of the photosphere, the temperature is about 7000 K and there are about 1.5 × 1017 gas particles per cubic centimeter. Use the ideal gas law (Cosmic Calculations 11.1) to compare the pressures of each of these layers; explain the reason for the trend that you find. How do these gas pressures compare with Earth's atmospheric pressure at sea level? 55) The Lifetime of the Sun. The Sun's chemical composition was about 70% hydrogen when it formed, and about 13% of this hydrogen was available for eventual fusion in the core. (The rest remains in layers of the Sun where the temperature is currently too low for fusion.) a. Use these data and the Sun's mass to calculate the total mass of hydrogen available for fusion over the lifetime of the Sun. b. Combine your results from part a and the fact that the Sun fuses about 600 billion kg of hydrogen each second to calculate how long the Sun's initial supply of hydrogen can last. Give your answer in both seconds and years. c. Given that our solar system is now about 4.6 billion years old, when will we need to start worrying about the Sun running out of hydrogen for fusion? 38 Copyright © 2022 Pearson Education, Inc.

56) Solar Power Collectors. This problem leads you through the calculation and discussion of how much solar power can in principle be collected by solar cells on Earth. a. Imagine a giant sphere with a radius of 1 AU surrounding the Sun. What is the surface area of this sphere in square meters? (Hint: The formula for the surface area of a sphere is 4πr2.) b. Because this imaginary giant sphere surrounds the Sun, the Sun's entire luminosity of 3.8 × 1026 watts must pass through it. Calculate the power passing through each square meter of this imaginary sphere in watts per square meter. Explain why this number represents the maximum power per square meter that a solar collector in Earth orbit can collect. c. List several reasons why the average power per square meter collected by a solar collector on the ground will always be less than what you found in part b. d. Suppose you want to put a solar collector on your roof. If you want to optimize the amount of power you can collect, how should you orient the collector? (Hint: The optimal orientation depends on both your latitude and the time of year and day.)

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 12 Surveying the Stars Section 12.1 1) What are the standard units for luminosity? A) Watts B) Joules C) Newtons D) Kilograms E) Watts per second Answer: A 2) What is a star's luminosity? A) The apparent brightness of the star in our sky B) The surface temperature of the star C) The lifetime of the star D) The total energy that the star radiates each second Answer: D 3) What are the standard units for apparent brightness? A) Watts B) Joules C) Newtons D) Watts per second E) Watts per square meter Answer: E 4) What two things do we need to measure in order to determine a star's luminosity? A) Apparent brightness and distance B) Distance and mass C) Apparent brightness and temperature D) Apparent brightness and mass Answer: A 5) If we have measured a star's apparent brightness and distance, then we can easily calculate its ________. A) luminosity B) mass C) surface temperature D) radius E) lifetime Answer: A

6) Suppose the distance to a star was doubled but everything else about the star stayed the same. What would happen to the star's luminosity and apparent brightness? A) Luminosity is decreased by a factor of four and the apparent brightness is decreased by a factor of four. B) Luminosity is decreased by a factor of two and the apparent brightness is decreased by a factor of two. C) Luminosity remains the same, but the apparent brightness is decreased by a factor of two. D) Luminosity remains the same, but the apparent brightness is decreased by a factor of four. E) Luminosity is decreased by a factor of four, but the apparent brightness remains the same. Answer: D 7) Suppose the distance to a star was doubled but everything else about the star stayed the same. What would happen to the star's luminosity? A) It would decrease by a factor of 2. B) It would decrease by a factor of 4. C) It would increase by a factor of 2. D) It would increase by a factor of 4. E) It would remain the same. Answer: E 8) Suppose the distance to a star was doubled but everything else about the star stayed the same. What would happen to the star's apparent brightness in our sky? A) It would decrease by a factor of 2. B) It would decrease by a factor of 4. C) It would increase by a factor of 2. D) It would increase by a factor of 4. E) It would remain the same. Answer: B 9) Stars X and Y have the same luminosity, but star Y is 10 times as far from Earth as star X. How much brighter will star X appear in our sky than star Y? A) 10 times B) 100 times C) 1000 times D) 10,000 times E) 100,000 times Answer: B 10) Suppose that the Sun–Earth distance were 10 AU instead of 1 AU. Then the energy of sunlight received per square meter on Earth each second would be ________ it is today. A) 10 times as great as B) about the same as C) 1/100 as much as D) 100 times as great as E) 1/10 as much as Answer: C 2 Copyright © 2022 Pearson Education, Inc.

11) Suppose the star Sirius were moved to a distance 7 times closer to Earth than it is now. How would its apparent brightness change? A) It would be 7 times as bright. B) It would be 1/7 as bright. C) It would be 1/49 as bright. D) It would be 49 times as bright. Answer: D 12) Suppose the star Sirius were moved to a distance 7 times closer to Earth than it is now. How would its parallax angle change? A) It would stay the same. B) It would get smaller. C) It would get larger. Answer: C 13) You observe two stars that are identical to our Sun, but that are located at diﬀerent distances from Earth. Which star is the most luminous? A) They are both the same luminosity. B) The one that appears brightest in our sky is more luminous. C) The one that appears faintest in our sky is more luminous. D) There is no way to tell from the information given. Answer: A 14) Which of the following properties of stars is directly observed (i.e., it can be measured by a calibrated instrument on a telescope, from a single observation without a need for additional calculations)? A) Luminosity B) Radius C) Surface temperature D) Apparent brightness Answer: D 15) Star X has a smaller parallax angle than star Y. What can you conclude? A) Star X is nearer to Earth than star Y. B) Star X is farther from Earth than star Y. C) Star X is more luminous than star Y. D) 10 Star X is less luminous than star Y. E) Star X is smaller in radius than star Y. Answer: B

16) Suppose you measure the parallax angle for a particular star to be 0.1 arcseconds. What is the distance to this star? A) 10 light-years B) 10 parsecs, which is about 32.6 light-years C) 0.1 light-year D) 0.1 parsec, which is about 0.326 light-year E) Impossible to determine Answer: B 17) Suppose that you measure the parallax angle for a particular star to be 0.5 arcseconds. What is the distance to this star? A) 0.5 light-year B) 0.5 parsec, which is about 1.63 light-years C) 5 light-years D) 5 parsecs, which is about 16.3 light-years E) 2 parsecs, which is about 6.52 light-years Answer: E 18) Suppose that you measure the parallax angle for a particular star to be 0.1 arcseconds. What is the distance to this star? (Hint: A star at a distance of 3.26 light-years has a parallax angle of 1.0 arcseconds.) A) 0.1 light-years B) 0.326 light-years C) 10 light-years D) 32.6 light-years E) 3.26 light-years Answer: D 19) Star X has an apparent magnitude of 3, and star Y has an apparent magnitude of 8. What can we conclude? A) Star X appears brighter in the night sky than star Y. B) Star Y appears brighter in the night sky than star X. C) Star X is farther away from us than star Y. D) Star Y is farther away from us than star X. Answer: A 20) Star X has an apparent magnitude of 6, and star Y has an apparent magnitude of 2. How do they compare in observed brightness? A) Star X appears brighter in the night sky than star Y. B) Star Y appears brighter in the night sky than star X. C) Star X is farther away from us than star Y. D) Star Y is farther away from us than star X. Answer: B

21) A star's spectral type can be used to determine its ________. A) mass B) surface temperature C) luminosity D) core temperature E) radius Answer: B 22) How do we estimate the surface temperature of a star? A) By measuring the Doppler shifts of absorption lines in its chromosphere B) By obtaining its spectrum and classifying the spectral type C) By estimating its parallax D) By estimating its luminosity Answer: B 23) Which of the following correctly lists spectral types in order of decreasing temperature (from hottest to coolest)? A) MKGFABO B) OBAGFKM C) OBAFGKM D) ABFGKMO E) BAGFKMO Answer: C 24) Star X has spectral type B. Star Y has spectral type M. What can we conclude? A) Star X has a higher surface temperature than star Y. B) Star Y has a higher surface temperature than star X. C) Star X is more massive than star Y. D) Star Y is more massive than star X. Answer: A 25) Which stellar spectral type has the strongest molecular absorption lines in its visible light spectrum? A) O B) B C) G D) K E) M Answer: E 26) Which spectral type represents stars with the hottest surface temperatures? A) G B) M C) O D) A E) B Answer: C 5 Copyright © 2022 Pearson Education, Inc.

27) Which of the following stars has the hottest surface temperature? A) The blue star B) The orange star C) The green star D) The red star E) The yellow star Answer: A 28) Which of these stars is the bluest in color? A) O star B) G star C) M star D) B star Answer: A 29) Which spectral type represents stars with spectra that peak at the shortest ultraviolet wavelengths? A) O B) B C) G D) K E) M Answer: A 30) Which of the following statements about spectral types of stars is always true? A) A star with spectral type G has a lower interior temperature than a star with spectral type B. B) A star with spectral type G has a lower mass than a star with spectral type B. C) A star with spectral type G has a cooler surface temperature than a star with spectral type B. D) A star with spectral type G has a smaller radius than a star with spectral type B. E) All of the above are true. Answer: C 31) Which of the following people reorganized the spectral classification scheme into the one we use today and personally classified over 400,000 stars? A) Annie Jump Cannon B) Williamina Fleming C) Cecilia Payne-Gaposchkin D) Henry Draper E) Edward Pickering Answer: A

32) Which of the following people used the ideas of quantum mechanics to describe why the spectral classification scheme is in order of decreasing temperature? A) Annie Jump Cannon B) Williamina Fleming C) Cecilia Payne-Gaposchkin D) Henry Draper E) Edward Pickering Answer: C 33) Annie Jump Cannon became famous for ________. A) developing our modern system for classifying stars B) discovering the planet Uranus C) discovering the planet Neptune D) building the world's largest telescope Answer: A 34) Which of the following terms is given to a pair of stars that appear to change positions in the sky, indicating that they are orbiting one another? A) Visual binary B) Eclipsing binary C) Spectroscopic binary D) Double star E) None of the above Answer: A 35) Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts? A) Visual binary B) Eclipsing binary C) Spectroscopic binary D) Double star E) None of the above Answer: C 36) Besides mass, what else can be determined about the stars in an eclipsing binary system by observing only their light curve? A) Their luminosities B) Their surface temperatures C) Their radii D) Their distances from Earth Answer: C

37) How do we measure stellar masses? A) We measure their apparent brightness and distance (from parallax). B) We don't really know: stellar masses are based on an informed guess. C) We measure the orbital periods and velocities of stars in binary systems. D) We measure their density and radius. Answer: C 38) Astronomers generally can measure a star's mass if only it is a member of a binary star system. What characteristics of the stars must we know to measure the masses of the stars in a binary system? A) Their spectral types and their distance from Earth B) Their absolute magnitudes and their luminosities C) Their orbital period and average orbital distance D) Their luminosities and distance from Earth Answer: C 39) Suppose you see two main-sequence stars of the same spectral type. Star 1 is dimmer in apparent brightness than star 2 by a factor of 100. What can you conclude? (Neglect any effects that might be caused by interstellar dust and gas.) A) Without first knowing the distances to these stars, you cannot draw any conclusions about how their true luminosities compare to each other. B) The luminosity of star 1 is a factor of 100 less than the luminosity of star 2. C) Star 1 is 100 times more distant than star 2. D) Star 1 is 100 times nearer than star 2. E) Star 1 is 10 times more distant than star 2. Answer: E 40) Which two factors determine a star's luminosity? A) Radius and surface temperature B) Radius and distance from Earth C) Surface temperature and distance from Earth D) Mass and radius E) Mass and surface temperature Answer: A 41) Luminosity has units of energy per time. Apparent brightness has units of energy per time per area. Which of the following expressions correctly states the relationship between luminosity, distance, and apparent brightness (known as the "inverse square law for light")? A) luminosity = B) apparent brightness = C) apparent brightness = luminosity × 4π × (distance)2 D) distance = Answer: B 8 Copyright © 2022 Pearson Education, Inc.

42) The apparent brightness of an object is calculated as:

. If one knew the

luminosity and apparent brightness of a star that was too distant for a parallax measurement, what would be the best approach to determining its distance? A) Insert the values for luminosity and apparent brightness into the equation, then guess the value for the distance that satisfies the equation. B) Solve the equation for distance, then insert the values for luminosity and apparent brightness into the new equation. C) The distance cannot be determined. Answer: B Section 12.2 1) Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram? A) Surface temperature on the horizontal axis and luminosity on the vertical axis B) Mass on the horizontal axis and luminosity on the vertical axis C) Surface temperature on the horizontal axis and radius on the vertical axis D) Mass on the horizontal axis and stellar age on the vertical axis E) Interior temperature on the horizontal axis and mass on the vertical axis Answer: A 2) A star's position along the horizontal axis of an H-R diagram tells us all of the following except the star's ________. A) radius B) spectral type C) surface temperature D) surface color Answer: A 3) Which two quantities must you know in order to plot a star on an H-R diagram? A) Mass and lifetime B) Surface temperature and luminosity C) Mass and radius D) Apparent brightness and distance Answer: B 4) Which of the following stellar properties has the greatest range in values? A) Mass B) Radius C) Core temperature D) Surface temperature E) Luminosity Answer: E

5) Based on the H-R diagram shown above, what is the approximate surface temperature of an F star? A) 5000 K B) 6000 K C) 7000 K D) 12,000 K Answer: C 6) Based on the H-R diagram shown above, what is the approximate surface temperature of a B star? A) 6000 K B) 40,000 K C) 8000 K D) 20,000 K Answer: D

7) Based on the H-R diagram shown above, what is the spectral type of a main-sequence star with a luminosity 100 times greater than that of the Sun? A) O B) A C) G D) M Answer: B 8) Based on the H-R diagram shown above, what is the approximate luminosity of a ________. main-sequence M star? A) 10−6 times that of the Sun B) 0.01 times that of the Sun C) 1 times that of the Sun D) 10 times that of the Sun Answer: B 9) A main-sequence star is observed with a surface temperature of 3500 K and a luminosity 10−2 times that of the Sun. Based on the H-R diagram shown above, what is the approximate mass of this star? A) 0.2 times that of the Sun B) 0.5 times that of the Sun C) 0.9 times that of the Sun D) 1.5 times that of the Sun Answer: A 10) A star is observed with a surface temperature of 3000 K and a luminosity of 10−3 times that of the Sun. Based on the H-R diagram shown above, what is the approximate radius of this star? A) 0.1 solar radius B) 0.5 solar radius C) 1 solar radius D) The radius cannot be determined. Answer: A 11) A star is observed with a surface temperature of 3000 K and a luminosity of 105 times that of the Sun. Based on the H-R diagram shown above, what is the approximate radius of this star? A) 10 solar radii B) 102 solar radii C) 103 solar radii D) The radius cannot be determined. Answer: C

12) Based on the H-R diagram shown above, about how long does a main-sequence star of spectral type O spend fusing hydrogen into helium in its core? A) 1000 years B) 10,000 years C) 10 million years D) 100 million years E) 1 billion years Answer: C 13) Based on the H-R diagram shown above, about how long does a main-sequence star of spectral type G spend fusing hydrogen into helium in its core? A) 1000 years B) 10,000 years C) 1 million years D) 100 million years E) 10 billion years Answer: E 14) You have observed a star and classified it as a red giant. It has a surface temperature of 3000 K and a luminosity of 105 times that of the Sun. Can you determine its mass by plotting its position on an H-R diagram? A) Yes, its mass is 0.3 MSun. B) Yes, its mass is 3 MSun. C) Yes, its mass is 30 MSun. D) No, a red giant's mass cannot be determined from its position on the H-R diagram. Answer: D 15) You have observed a star and classified it as a white dwarf. It has a surface temperature of 3000 K and a luminosity of 10−3 times that of the Sun star based on its position in the H-R diagram. Can you determine its mass by plotting its position on an H-R diagram? A) Yes, its mass is 0.3 MSun. B) Yes, its mass is 3 MSun. C) Yes, its mass is 30 MSun. D) No, a white dwarf's mass cannot be determined from its position on the H-R diagram. Answer: D 16) On a Hertzsprung-Russell diagram, where would we find stars that are cool and dim? A) Upper right B) Lower right C) Upper left D) Lower left Answer: B

17) On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous? A) Upper right B) Lower right C) Upper left D) Lower left Answer: A 18) On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii? A) Upper right B) Lower right C) Upper left D) Lower left Answer: A 19) On a Hertzsprung-Russell diagram, where on the main sequence would we find stars that have the greatest mass? A) Upper right B) Lower right C) Upper left D) Lower left Answer: C 20) On a Hertzsprung-Russell diagram, where would we find red giant stars? A) Upper right B) Lower right C) Upper left D) Lower left Answer: A 21) On a Hertzsprung-Russell diagram, where would we find white dwarfs? A) Upper right B) Lower right C) Upper left D) V left Answer: D 22) Where do we find our Sun on the H-R diagram? A) Near the middle of the main sequence B) At the far upper left of the main sequence C) With the red giants D) At the far lower right of the main sequence E) With the white dwarfs Answer: A

23) How do stars on the main sequence obtain their energy? A) From chemical reactions B) From gravitational contraction C) By converting hydrogen to helium in their cores D) By converting helium to carbon, nitrogen, and oxygen E) From nuclear fission Answer: C 24) Which of the following is the most common type of main-sequence star? A) An O star B) An A star C) An F star D) An M star E) A G star Answer: D 25) Which main sequence stars have the lowest mass? A) Spectral type O B) Spectral type M C) Spectral type A D) Spectral type G E) Can't tell from information provided Answer: B 26) Which main sequence stars have the shortest lifetimes? A) Spectral type M B) Spectral type G C) Spectral type O D) Spectral type A E) Can't tell from information provided Answer: C 27) For main-sequence stars, which of the following is true about low-mass stars compared to high-mass stars? A) Low-mass stars are cooler and less luminous than high-mass stars. B) Low-mass stars are hotter and more luminous than high-mass stars. C) Low-mass stars are cooler but more luminous than high-mass stars. D) Low-mass stars are hotter but less luminous than high-mass stars. E) Low-mass stars have the same temperature and luminosity as high-mass stars. Answer: A 28) What does the luminosity of a main-sequence star tell us? A) The star's distance from us B) The rate at which it converts hydrogen to helium C) The star's radius D) The star's surface temperature Answer: B 14 Copyright © 2022 Pearson Education, Inc.

29) Star X is a supergiant of spectral type M. Star Y is a giant but of identical spectral type M. What can you conclude? A) Star X is more luminous and larger in radius than star Y. B) Star Y is more luminous and larger in radius than star X. C) Star X is hotter than star Y. D) Star Y is hotter than star X. Answer: A 30) The most fundamental property of a star is its ________. A) luminosity B) abundance of elements besides hydrogen and helium C) mass D) surface temperature E) radius Answer: C 31) The Sun's life time is 10 billion years. About how long is the lifetime of a star with a star has a mass of 10 MSun and a luminosity of 10,000 LSun? A) 1 million years B) 100 billion years C) 100 trillion years D) 10 million years Answer: D 32) The Sun's life time is 10 billion years. About how long is the lifetime of a star with a star has a mass of 0.1 MSun and a luminosity of 0.01 LSun? A) 1 billion years B) 100 million years C) 100 billion years D) 10 million years Answer: C

Section 12.3 1) Which of the following statements about an open star cluster is true? A) All stars in the cluster are approximately the same color. B) All stars in the cluster are approximately the same age. C) All stars in the cluster have approximately the same mass. D) There is an approximately equal number of all types of stars in the cluster. Answer: B 2) Which of the following is a safe assumption about all the stars in a star cluster? A) They all have approximately the same surface temperature. B) They are all approximately the same distance away from us. C) They all have approximately the same mass. D) They will all have approximately the same lifetimes. E) They all have approximately the same apparent brightness in our sky. Answer: B 3) You observe a star cluster with a main-sequence turnoff point at spectral type G (the same spectral type as the Sun). What is the approximate age of this star cluster? A) 10,000 years B) 4.6 billion years C) 10 billion years D) 100 billion years E) 10 million years Answer: C

4) The brightest main-sequence star in a cluster has a surface temperature of 30,000 K and a luminosity of about 104 LSun. Referring to the figure above as needed, what is the approximate age of the cluster? A) 107 years B) 109 years C) 1011 years D) 1013 years Answer: A 5) The brightest main-sequence star in a cluster has a surface temperature of 10,000 K and a luminosity of about 10 LSun. Referring to the figure above as needed, what is the approximate age of the cluster? A) 107 years B) 109 years C) 1011 years D) 1013 years Answer: B 17 Copyright © 2022 Pearson Education, Inc.

6) The youngest star clusters are ones in which their brightest main-sequence stars have spectral type ________. A) M B) B C) A D) O E) G Answer: D Reading Quiz Questions 1) What is the approximate chemical composition (by mass) with which all stars are born? A) 3/4 hydrogen, 1/4 helium, no more than about 2% heavier elements B) Half hydrogen and half helium C) 98% hydrogen, 2% helium D) 95% hydrogen, 4% helium, no more than 1% heavier elements Answer: A 2) The total amount of power (in watts, for example) that a star radiates into space is called its ________. A) apparent brightness B) absolute magnitude C) luminosity D) flux Answer: C 3) According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples? A) Its apparent brightness will decrease by a factor of 9. B) Its apparent brightness will increase by a factor of 9. C) Its apparent brightness will decrease by a factor of 3. D) Its apparent brightness will increase by a factor of 3. Answer: A 4) Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do? A) Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity. B) Determine both the star's distance and luminosity from its apparent brightness. C) Determine the distance to the star from its apparent brightness. D) Calculate the star's surface temperature if we know either its luminosity or its distance. Answer: A

5) If star A is closer to us than star B, then Star A's parallax angle is ________. A) larger than that of Star B B) smaller than that of Star B C) hotter than that of Star B D) fewer parsecs than that of Star B Answer: A 6) Star A has an apparent magnitude = 3 and star B has an apparent magnitude = 5. Which star is brighter in our sky? A) Star A B) Star B C) There is not enough information to answer the question. D) The two stars have the same brightness in our sky, but Star A is closer to us than Star B. Answer: A 7) From hottest to coolest, the order of the spectral types of stars is ________. A) OBAFGKM B) OBAGFKM C) ABFGKMO D) OMKGFBA E) ABCDEFG Answer: A 8) Our Sun is a star of spectral type ________. A) G B) F C) S D) M Answer: A 9) Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass? A) The star is a member of a binary star system. B) The star is of spectral type G. C) The star is of spectral type A. D) We know the star's luminosity and distance. Answer: A 10) Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts? A) Spectroscopic binary B) Eclipsing binary C) Visual binary D) Double star Answer: A

11) The axes on a Hertzsprung-Russell (H-R) diagram represent ________. A) luminosity and surface temperature B) mass and luminosity C) luminosity and apparent brightness D) mass and radius Answer: A 12) What can we infer, at least roughly, from a star's luminosity class? A) Its size (radius) B) Its mass C) Its age in years D) Its surface temperature Answer: A 13) On an H-R diagram, stellar radii ________. A) increase diagonally from the lower left to the upper right B) are greatest in the lower left and least in the upper right C) decrease from left to right D) are impossible to determine Answer: A 14) On an H-R diagram, stellar masses ________. A) can be determined for main sequence stars but not for other types of stars B) are greatest in the lower left and least in the upper right C) decrease from upper left to lower right D) are impossible to determine Answer: A 15) High-mass stars have ________ lifetimes than low-mass stars. A) much shorter B) slightly shorter C) much longer D) slightly longer Answer: A 16) On an H-R diagram, a red supergiant would be located in the ________. A) upper right B) upper left C) lower left D) lower right Answer: A

17) What is the common trait of all main-sequence stars? A) They generate energy through hydrogen fusion in their core. B) They are in the final stage of their lives. C) They are all spectral type G. D) They all have approximately the same mass. Answer: A 18) Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true? A) Earth would be inside the supergiant. B) The supergiant's surface temperature would be much hotter than the surface temperature of our Sun. C) Earth would fly off into interstellar space. D) The supergiant would appear as large as the full Moon in our sky. Answer: A 19) What is a white dwarf? A) It is the remains of a star that ran out of fuel for nuclear fusion. B) It is a main sequence star of spectral type F, which tends to look white in color. C) It is a type of star that produces energy by gravitational contraction. D) It is a star that follows a period-luminosity relation. Answer: A 20) Which of the following statements comparing open and globular star clusters is true? A) Stars in open clusters are relatively young, while stars in globular clusters are very old. B) Open clusters are found both in the disk and the halo of the galaxy, while globular clusters are found only in the halo. C) Globular clusters typically contain a few hundred stars, while open clusters typically contain tens to hundreds of thousands of stars. D) Open clusters contain only main-sequence stars, while globular clusters contain only giants. Answer: A 21) What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us? A) It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age. B) It is the point in a star cluster beyond which main sequence stars are not found, and it tells us the cluster's distance. C) It is the luminosity class of the largest star in a star cluster, and it tells us the cluster's age. D) It is the mass of the most massive star in the star cluster, and it tells us the cluster's size. Answer: A

Concept Quiz Questions 1) All stars are born with the same basic composition, yet stars can differ greatly in appearance. Which two factors are most important in determining the current appearance of a star? A) Mass and stage of life B) Luminosity and stage of life C) Age and location in the galaxy D) Mass and surface temperature E) Apparent brightness and luminosity Answer: A 2) Which units are appropriate for measurement of apparent brightness? A) Watts per square meter B) Watts C) Joules D) Newtons Answer: A 3) Star A is identical to Star B, but Star A is twice as far from us as Star B. Therefore ________. A) both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A B) both stars have the same luminosity, but the apparent brightness of Star B is twice that of Star A C) both stars have the same apparent brightness, but the luminosity of Star B is four times that of Star A D) both stars have the same luminosity, but the apparent brightness of Star A is four times that of Star B Answer: A 4) A star with a parallax angle of 1/20 arcsecond is ________. A) 20 parsecs (≈ 65.2 light-years) away B) 20 light-years away C) 1/20 parsec (≈ 0.163 light-year) away D) 10 parsecs (≈ 32.6 light-years) away Answer: A 5) A star's color is related to its surface temperature because ________. A) stars emit thermal radiation B) the colors of stars depend mainly on the emission lines in the spectra C) stars have absorption lines in their spectra D) the color of a star depends on its mass, and mass is related to surface temperature Answer: A

6) Which of the following statements about spectral types of stars is not generally true? A) The spectral type of a star can be used to determine its distance. B) The spectral type of a star can be used to determine its surface temperature. C) The spectral type of a star can be used to determine its color. D) The spectral type of a star can be determined by identifying lines in the star's spectrum. Answer: A 7) Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude? A) Rigel has a higher surface temperature than Sirius. B) Rigel has a higher core temperature than Sirius. C) Sirius has a higher core temperature than Rigel. D) Sirius has a higher surface temperature than Rigel. Answer: A 8) To calculate the masses of stars in a binary system, we must measure their ________. A) orbital period and average orbital distance B) spectral types and distance from Earth C) absolute magnitudes and luminosities D) luminosities and distance from Earth Answer: A 9) Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes significantly dimmer for about 2 hours. The most likely explanation is that ________. A) the star is a member of an eclipsing binary star system B) the star is a Cepheid variable C) the star is periodically ejecting gas into space, every 73 hours D) the star is a white dwarf Answer: A

The sketch below shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents the entire main sequence, while (c) and (d) represent only small parts of the main sequence.

10) Which group represents stars that are cool and dim? A) a B) b C) c D) d E) e Answer: D 11) Which group represents stars of the largest radii? A) a B) b C) c D) d E) e Answer: E 12) Which group represents the most common type of stars? A) b B) c C) d D) e Answer: C 13) Which group represents stars that are extremely luminous and emit most of their radiation as ultraviolet light? A) a B) b C) c D) d E) e Answer: C 24 Copyright © 2022 Pearson Education, Inc.

14) Which group represents stars with the longest main-sequence lifetimes? A) a B) b C) c D) d E) e Answer: D 15) Which group represents stars fusing hydrogen in their cores? A) a B) b C) c D) d E) e Answer: A 16) Which group represents stars that have no ongoing nuclear fusion? A) a B) b C) c D) d E) e Answer: B 17) You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star's ________. A) mass B) distance C) apparent brightness D) spectral type Answer: A 18) The approximate main-sequence lifetime of a star of spectral type O is ________. A) 3 million years B) 10,000 years C) 300 million years D) 10 billion years Answer: A 19) How did astronomers discover the relationship between spectral type and mass for main sequence stars? A) By measuring the masses and spectral types of main-sequence stars in binary systems B) By using computer models of hydrogen fusion and stellar structure C) By measuring stellar radii with powerful telescopes D) By comparing stars with the same spectral type but different luminosities Answer: A 25 Copyright © 2022 Pearson Education, Inc.

20) The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is the youngest? A) The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants. B) The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs. C) The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and supergiants. D) The diagram shows no main-sequence stars at all, but it has numerous supergiants and white dwarfs. Answer: A 21) The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is most likely to be located in the halo of our galaxy? A) The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants. B) The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs. C) The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and supergiants. D) The diagram shows no main-sequence stars at all, but it has numerous supergiants and white dwarfs. Answer: B

Visual Quiz Questions 1) This star map shows stars as we see them in our sky from Earth, centered around the constellation Canis Major. Larger dots represent brighter stars, and a few of the brightest stars are identified. From this view alone, what can you conclude about Sirius?

A) It has the greatest apparent brightness of any star in this region of the sky. B) It is the most luminous star in this region of the sky. C) It is the nearest star in this region of the sky. D) It is actually a binary star system in which the second star is a white dwarf. E) All of the above choices are true. Answer: A

2) Why do some of the bright stars (such as the one indicated by the arrow) in this photo have cross-shaped spikes over them?

A) The spikes are an artifact of photography through a telescope. B) The spikes are flares ejected from the surfaces of bright stars. C) Very bright stars tend to be slightly nonspherical in shape and therefore look like they have spikes in photos. D) The stars with spikes are actually binary star systems. Answer: A 3) All the stars in this photo are at about the same distance from Earth (some 25,000 light-years away). Which stars in this picture are the largest in size (radius)?

A) The bright red stars B) The blue/white stars that look largest on the photo C) The stars that have the spikes D) The dim red stars Answer: A

4) This graph shows how the apparent brightness of an eclipsing binary system changes with time. Which of the four labeled regions represents the system at a time when one star is eclipsing the other?

A) I B) II C) III D) IV E) Both II and IV F) Both I and II Answer: E

5) Study this H-R diagram. What is the spectral type of the star Sirius? (The red arrow helps you locate Sirius on the diagram.)

A) A B) 102 C) Main sequence D) Blue Answer: A

6) Study this H-R diagram. Which of the following stars is the most massive? (The red arrows help you locate these stars on the diagram.)

A) Beta Centauri B) Vega C) Bellatrix D) DX Cancri Answer: A

7) Study this H-R diagram. Which of the following stars is the largest in size (radius)? (The red arrows help you locate these stars on the diagram.)

A) Antares B) Canopus C) Alpha Centauri B D) Aldebaran Answer: A

8) Study this H-R diagram. Which of the following stars has (or had) the longest hydrogen fusing lifetime? (The red arrows help you locate these stars on the diagram.)

A) Barnard's star B) Alpha Centauri B C) Betelgeuse D) The Sun Answer: A

9) This photo shows an object located in the halo of our Milky Way galaxy. What kind of object is it? A) A globular cluster of stars B) An open cluster of stars C) A spiral galaxy D) A supergiant star E) A "beehive" cluster Answer: A 10) This photo shows an object located in the halo of our Milky Way galaxy. Notice the many bright red dots in the photograph. What are they? A) Red giant stars B) Cool, red main-sequence stars of spectral type M C) Old white dwarf stars that have turned red in color D) Massive supergiant stars E) Starspots Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

The figure above, similar to Figure 12.13, uses zoom-ins to compare the sizes of giant and supergiant stars to the sizes of Earth and the Sun 1) Suppose we wanted to represent all of these objects using the 1-to-10-billion scale from Chapter 1, on which the Sun is about the size of a grapefruit. Approximately how large in diameter would the star Aldebaran be on this scale? A) 40 centimeters (the size of a typical beach ball) B) 6 meters (roughly the size of a dorm room) C) 15 meters (roughly the size of a typical house) D) 130 meters (slightly larger than a football field) Answer: B 2) Approximately how large in diameter would the star Betelgeuse be on this same scale? A) 40 centimeters (the size of a typical beach ball) B) 6 meters (roughly the size of a dorm room) C) 130 meters (slightly larger than a football field) D) 3 kilometers (the size of a small town) Answer: D 3) Approximately how large in diameter would the star Procyon B be on this same scale? A) 10 centimeters (the size of a large grapefruit) B) 1 centimeter (the size of a grape) C) 1 millimeter (the size of a grape seed) D) 0.1 millimeter (roughly the width of a human hair) Answer: C

The H-R diagram above is identical to Figure 12.11. Answer the following questions based on the information given in the figure. 4) What are the approximate luminosity and lifetime of a star whose mass is 10 times that of the Sun? Answer: luminosity: about 10,000LSun; lifetime: slightly longer than 10 million years 5) What are the approximate luminosity and lifetime of a star whose mass is 3 times that of the Sun? Answer: luminosity: about 100LSun; lifetime: slightly shorter than 1 billion years 6) What are the approximate luminosity and lifetime of a star whose mass is twice that of the Sun? Answer: luminosity: about 10LSun; lifetime: approximately 1 billion years

Chapter Review Questions 1) Briefly explain how we can learn about the lives of stars even though their lives are far longer than human lives. 2) In what ways are all stars similar? In what ways can stars differ? 3) How is a star's apparent brightness related to its luminosity? Explain by describing the inverse square law for light. 4) How do we use stellar parallax to determine a star's distance, and how can we then determine its luminosity? 5) What do we mean by a star's spectral type, and how is it related to the star's surface temperature and color? Which types of stars are hottest and coolest in the spectral sequence OBAFGKM? 6) What are the three basic types of binary star systems? Why are eclipsing binaries so important for measuring masses of stars? 7) Draw a sketch of a Hertzsprung-Russell (H-R) diagram. Label the main sequence, giants, supergiants, and white dwarfs. Where on this diagram do we find stars that are cool and dim? Cool and luminous? Hot and dim? Hot and luminous? 8) What do we mean by a star's luminosity class? Briefly explain how we classify stars by spectral type and luminosity class. 9) What is the defining characteristic of a main-sequence star? Briefly explain why massive main-sequence stars are more luminous and have hotter surfaces than less massive mainsequence stars. 10) Which stars have longer lifetimes: massive stars or less massive stars? Explain why. 11) How do giants and supergiants differ from main-sequence stars? What are white dwarfs? 12) Why is a star's birth mass its most fundamental property? 13) Describe in general terms how open clusters and globular clusters differ in their numbers of stars, ages, and locations in a galaxy. 14) Explain why H-R diagrams look different for star clusters of different ages. How does the location of the main-sequence turnoff point tell us the age of the star cluster?

Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 15) Two stars that look very different must be made of different kinds of elements. 16) Two stars that have the same apparent brightness in the sky must also have the same luminosity. 17) Sirius looks brighter than Alpha Centauri, but we know that Alpha Centauri is closer because its apparent position in the sky shifts by a larger amount as Earth orbits the Sun. 18) Stars that look red-hot have hotter surfaces than stars that look blue. 19) Some of the stars on the main sequence of the H-R diagram are not converting hydrogen into helium. 20) The smallest, hottest stars are plotted in the lower left portion of the H-R diagram. 21) Stars that begin their lives with the most mass live longer than less massive stars because they have so much more hydrogen fuel. 22) Star clusters with lots of bright, blue stars of spectral types O and B are generally younger than clusters that don't have any such stars. 23) All giants, supergiants, and white dwarfs were once main-sequence stars. 24) Most of the stars in the sky are more massive than the Sun. Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 12 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 25) If the star Alpha Centauri were moved to a distance 10 times farther from Earth than it is now, its parallax angle would ________. A) get larger B) get smaller C) stay the same Answer: No Correct Answer Was Provided. 26) What do we need to measure in order to determine a star's luminosity? A) Apparent brightness and mass B) Apparent brightness and temperature C) Apparent brightness and distance Answer: No Correct Answer Was Provided. 38 Copyright © 2022 Pearson Education, Inc.

27) What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system? A) The time between eclipses and the average distance between the stars B) The period of the binary system and its distance from the Sun C) The velocities of the stars and the Doppler shifts of their absorption lines Answer: No Correct Answer Was Provided. 28) Which of these stars has the coolest surface temperature? A) An A star B) An F star C) A K star Answer: No Correct Answer Was Provided. 29) Which of these stars is the most massive? A) A main-sequence A star B) A main-sequence G star C) A main-sequence M star Answer: No Correct Answer Was Provided. 30) Which of these stars has the longest lifetime? A) A main-sequence A star B) A main-sequence G star C) A main-sequence M star Answer: No Correct Answer Was Provided. 31) Which of these stars has the largest radius? A) A supergiant A star B) A giant K star C) A supergiant M star Answer: No Correct Answer Was Provided. 32) Which of these stars has the greatest surface temperature? A) A main-sequence B star B) A supergiant A star C) A giant K star Answer: No Correct Answer Was Provided. 33) Which of these star clusters is youngest? A) A cluster whose brightest main-sequence stars are white B) A cluster whose brightest stars are red C) A cluster containing stars of all colors Answer: No Correct Answer Was Provided. 34) Which of these star clusters is oldest? A) A cluster whose brightest main-sequence stars are white B) A cluster whose brightest main-sequence stars are yellow C) A cluster containing stars of all colors Answer: No Correct Answer Was Provided. 39 Copyright © 2022 Pearson Education, Inc.

Inclusive Astronomy Use these questions to reflect on participation in science. 35) Research: Women in Astronomy. Until fairly recently, men greatly outnumbered women in professional astronomy. Nevertheless, many women made crucial discoveries in astronomy throughout history–including discovering the spectral sequence for stars. Choose a female astronomer from any time period and learn enough about her life and discoveries to write a oneto three-page scientific biography. 36) Discussion: Annie Jump Cannon's Disability. Annie Jump Cannon (discussed in Section 12.1) was one of the greatest astronomers of the 20th century, male or female. She also had a significant physical disability: a childhood disease had made her completely deaf by the time she reached adulthood. a. Gather in small groups to discuss the potential impacts of Annie Jump Cannon's deafness on her career. Begin the discussion by making a list of ways in which you think her deafness might have made a career in astronomy more challenging. b. Cannon's greatest contributions came from the fact that she visually classified the spectra of more than 400,000 stars during her lifetime. Discuss whether her deafness might have provided her with any advantages in this work and, if so, list what they might have been. c. When Cannon was considered for membership in the National Academy of Sciences in 1923, one of its members said he could not vote for Cannon because she was deaf. Why do you think someone would have voiced that objection in 1923? Discuss how and why scientists' views about physically disabled people have changed during the past century. The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 37) Classification. As discussed in the text, Annie Jump Cannon and her colleagues developed our modern system of stellar classification. Why do you think rapid advances in our understanding of stars followed so quickly on the heels of this effort? What other areas of science have had huge advances in understanding following an improved system of classification? 38) Snapshot of the Heavens. The beginning of the chapter likened the problem of studying the lives of stars to learning about human beings from a 1-minute glance at human life. What could you learn about human life by looking at a single snapshot of a large family, including babies, parents, and grandparents? How is the study of such a snapshot similar to what scientists do when they study the lives of stars? How is it different? 39) Life Spans of Stars. Scientists estimate the life span of a star by dividing the total amount of energy available for fusion by the rate at which the star radiates energy into space. Such calculations predict that the life spans of high-mass stars are shorter than those of low-mass stars. Describe one type of observation that can test this prediction and verify that it is correct.

40) Group Activity: Comparing Stellar Properties. The following activity makes use of Tables F.1 and F.2 in Appendix F. Before starting, split into two groups, one of which will gather data from Table F.1 and the other from Table F.2. a. Working in your separate groups, count and record the number of stars of each spectral type (OBAFGKM) and of each luminosity class (I, II, III, IV, V) in your assigned table. Ignore the white dwarfs. b. Working together, compare the counts of spectral types in the two tables. Are there any patterns you can identify? If so, develop a hypothesis that could explain them. c. Are there any patterns to the differences in the counts you found for the luminosity classes in the two tables? If so, develop a hypothesis that could explain them. d. Considering the data from both tables, identify the nearest star of each spectral type. Based on your results, discuss whether it is possible that there is an undiscovered star of spectral type O within 200 light-years of the Sun. Explain your reasoning. Investigate Further 41) Stellar Data. Consider the following data table for several bright stars. Mv is absolute magnitude, and mv is apparent magnitude. Use these data to answer the following questions, and include a brief explanation with each answer. (Hint: Remember that the magnitude scale runs backward, so brighter stars have smaller or more negative magnitudes.)

Star Aldebaran Alpha Centauri A Antares Canopus Fomalhaut Regulus Sirius Spica

Mv -0.2 +4.4 -4.5 -3.1 +2.0 -0.6 +1.4 -3.6

mv +0.9 0.0 +0.9 -0.7 +1.2 +1.4 -1.4 +0.9

Spectral Type K5 G2 M1 F0 A3 B7 A1 B1

Luminosity Class III V I II V V V V

a. Which star appears brightest in our sky? b. Which star appears faintest in our sky? c. Which star has the greatest luminosity? d. Which star has the least luminosity? e. Which star has the highest surface temperature? f. Which star has the lowest surface temperature? g. Which star is most similar to the Sun? h. Which star is a red supergiant? i. Which star has the largest radius? j. Which stars have finished fusing hydrogen in their cores? k. Among the main-sequence stars listed, which one is the most massive? l. Among the main-sequence stars listed, which one has the longest lifetime? 41 Copyright © 2022 Pearson Education, Inc.

42) Data Tables. Study the spectral types listed in Appendix F for the 20 brightest stars and for the stars within 12 light-years of Earth. Why do you think the two lists are so different? Explain. 43) Interpreting the H-R Diagram. Using the information in Figure 12.10, describe how Proxima Centauri differs from Sirius. 44) Parallax from Jupiter. Suppose you could observe stellar parallax from the orbit of Jupiter. How would it differ from the stellar parallax we observe from Earth? Would it be easier or more difficult to measure stellar distances? Explain. 45) An Expanding Star. Describe what would happen to the surface temperature of a star if its radius doubled in size with no change in luminosity. 46) Colors of Eclipsing Binaries. Figure 12.8 shows an eclipsing binary system consisting of a small blue star and a larger red star. Explain why the decrease in apparent brightness of the combined system is greater when the blue star is eclipsed than when the red star is eclipsed. 47) Visual and Spectroscopic Binaries. Suppose you are observing two binary star systems at the same distance from Earth. Both are spectroscopic binaries consisting of similar types of stars, but only one of the binary systems is a visual binary. Which of these star systems would you expect to have the greater Doppler shifts in its spectra? Explain your reasoning. 48) Life of a Star Cluster. Imagine you could watch a star cluster from the time of its birth to an age of 13 billion years. Describe in one or two paragraphs what you would see happening during that time. 49) Research: GAIA and Parallax. The European Space Agency's GAIA mission, launched in 2013, has measured parallax for more than a billion stars. Learn how this satellite can measure much smaller parallax angles than can be measured from the ground and how those measurements affect our knowledge of the universe. Write a one- to two-page report on your findings.

Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 50) The Inverse Square Law for Light. Use Earth's distance of about 150 million km from the Sun, the Sun's apparent brightness of about 1300 watts/m2, and the inverse square law for light to calculate the apparent brightness that we would measure for the Sun if we were located at the following positions. a. half Earth's distance from the Sun b. twice Earth's distance from the Sun c. five times Earth's distance from the Sun 51) The Luminosity of Alpha Centauri A. Alpha Centauri A lies at a distance of 4.4 light-years from Earth and has an apparent brightness in our night sky of 2.7 × 10-8 watt/m2. Recall that 1 light-year = 9.5 × 1015 m. a. Use the inverse square law for light to calculate the luminosity of Alpha Centauri A. b. Suppose you have a light bulb that emits 10 watts of visible light. How far away would you have to put the light bulb for it to have the same apparent brightness as Alpha Centauri A in our sky? (Hint: Use 10 watts as L in the inverse square law for light, and use the apparent brightness given above for Alpha Centauri A. Then solve for the distance.) 52) More Practice with the Inverse Square Law for Light. Use the inverse square law for light to answer each of the following questions. a. Suppose a star has the same luminosity as our Sun (3.8 × 1026 watts) but is located at a distance of 10 light-years from Earth. What is its apparent brightness? b. Suppose a star has the same apparent brightness as Alpha Centauri A (2.7 × 10-8 watt/m2) but is located at a distance of 200 light-years from Earth. What is its luminosity? c. Suppose a star has a luminosity of 8 × 1026 watts and an apparent brightness of 3.5 × 1012 watt/m2. How far away is it from Earth? Give your answer in both kilometers and light-years. d. Suppose a star has a luminosity of 5 × 1029 watts and an apparent brightness of 9 × 10-15 watts/m2. How far away is it from Earth? Give your answer in both kilometers and light-years. 53) Parallax and Distance. Use the parallax formula to calculate the distance to each of the following stars. Give your answers in both parsecs and light-years. a. Alpha Centauri: parallax angle of 0.7420 arcsecond b. Procyon: parallax angle of 0.2860 arcsecond 54) Radius of a Star. Sirius A has a luminosity of 26LSun and a surface temperature of about 9400 K. What is its radius? (Hint: See Cosmic Calculations 12.2.)

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 13 Star Stuff Section 13.1 1) Where do stars form and why? A) Stars form around giant planets because planets provide the "seeds" of star formation. B) Stars form in cold gas clouds because gravity has to be stronger than gas pressure. C) Stars form in warm dust clouds because the dust shields the protostars from radiation. D) Stars form in hot gas clouds because stars have to be hot to start fusion reactions. Answer: B 2) Which of the following accurately describes the density and temperature of molecular clouds compared to other interstellar clouds? A) Molecular clouds are relatively low in both density and temperature. B) Molecular clouds are relatively high in both density and temperature. C) Molecular clouds are relatively high in density and low in temperature. D) Molecular clouds are relatively low in density and high in temperature. Answer: C 3) Suppose there is a cloud containing interstellar dust between a star and us. How will the dust affect the light we see from the star? A) It makes the star appear dimmer and redder in color. B) It makes the star appear dimmer and bluer in color. C) It does not affect the star's brightness but makes it appear redder in color. D) It makes the star appear dimmer but does not affect the star's color. Answer: A 4) If you wanted to observe stars behind a molecular cloud, in what wavelength of light should you observe? A) Ultraviolet B) Visible C) Infrared D) X-ray E) Gamma ray Answer: C 5) The thermal pressure within a gas depends on ________. A) density only B) temperature only C) density and temperature D) composition E) gravity Answer: C

6) The strength of gravity within a molecular cloud depends on ________. A) density only B) temperature only C) density and temperature D) composition E) thermal pressure Answer: A 7) What condition is necessary in an interstellar gas cloud for it to begin collapsing? A) A low density B) A low temperature C) A high temperature D) A high heavy element content E) A low heavy element content Answer: B 8) Which of the following must be occurring in order for a molecular cloud to collapse and form stars? A) The inward pull of gravity must be stronger than the outward push of thermal pressure. B) The mass of the cloud must continually increase, thereby increasing the strength of gravity. C) The interior of the cloud must continually increase in temperature. D) The gas in the cloud must be supported by electron degeneracy pressure. Answer: A 9) About what is the smallest mass a newborn star can have? A) 0.01 times the mass of the Sun B) 0.08 times the mass of the Sun C) 0.8 times the mass of the Sun D) The mass of the Sun E) Twice the mass of the Sun Answer: B 10) The most massive stars have masses somewhere around ________. A) 5 solar masses B) 10 solar masses C) 30 solar masses D) 150 solar masses E) 3000 solar masses Answer: D 11) What eventually halts the gravitational collapse of an interstellar gas cloud that forms a brown dwarf rather than a true (main-sequence) star? A) The central object becoming hot enough to sustain nuclear fusion in its core B) Degeneracy pressure caused by the high density of electrons in the core C) Thermal pressure from the high core temperature D) The onset of convection in the object's outer layers Answer: B 2 Copyright © 2022 Pearson Education, Inc.

12) What happens to an object supported by degeneracy pressure as the object cools with time? A) The degeneracy pressure weakens and the object collapses. B) The degeneracy pressure strengthens and the object expands. C) The degeneracy pressure is unaffected by the temperature change, so the object remains stable. Answer: C 13) What prevents a brown dwarf from undergoing nuclear fusion? A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. B) There is not enough mass to maintain nuclear reactions in a self-sustaining way. C) The surface temperature never rises high enough for the radiation to be trapped and heat its interior to the temperature required for nuclear fusion. D) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. E) There are too many heavy elements and not enough hydrogen for fusion to occur in a self sustaining way. Answer: A 14) Why doesn't a brown dwarf become a star? A) It does not have enough mass for its core to get hot enough to start fusion reactions before degeneracy pressure prevents further collapse. B) It always has a companion star that is hotter, and therefore, the brown dwarf is more like a planet than a star. C) It does not have enough heavy elements to start fusion reactions. D) Its luminosity is not high enough to qualify as an official star. Answer: A 15) What is thought to prevent the formation of stars with masses larger than about 300 times that of our Sun? A) Molecular clouds do not have enough material to form such massive stars. B) Such massive stars would fragment into binary stars because of their rapid rotation. C) Such massive stars would generate so much light that radiation pressure would blow them apart. D) The onset of degeneracy pressure would prevent such massive stars from forming. Answer: C 16) Which statement accurately describes how our Sun fits into the mass range of stars? A) The Sun is completely average, with half of all stars being more massive than the Sun and half of all stars being less massive than the Sun. B) The Sun is near the bottom of the overall mass range. C) The Sun is near the top of the overall mass range. D) The Sun is near the middle of the overall mass range, but most stars are more massive than the Sun. E) The Sun is near the middle of the overall mass range, but most stars are less massive than the Sun. Answer: E 3 Copyright © 2022 Pearson Education, Inc.

17) Of the mass ranges below, which represents the most common stars? A) 0.08 to 0.5 MSun B) 0.5 to 2 MSun C) 2 to 10 MSun D) 10 to 150 MSun Answer: A 18) The most common main-sequence stars have spectral type ________. A) G B) A C) O D) M Answer: D 19) In order to remain stable, a star must have an internal balance between ________. A) gravity and pressure B) gravity and temperature C) temperature and pressure D) pressure and nuclear fusion E) nuclear fusion and chemical reactions Answer: A 20) Which of the following statements correct describes overall energy balance in a star? A) Gravity balances pressure. B) Energy generated by fusion in the core balances the energy emitted from the star's surface. C) Temperature balances light energy emitted at the photosphere. D) Energy in sunspots balances energy in magnetic fields. Answer: B 21) Why are main-sequence lifetimes shorter for more massive stars? A) They aren't; higher mass stars have longer lifetimes. B) Strong stellar winds cause higher mass stars to lose mass quickly. C) Higher core temperatures allow fusion to proceed much more rapidly. D) More massive stars are made of heavier elements that don't fuse as easily. Answer: C 22) Which of the following sequences correctly describes the stages of life (from beginning to end) for a low-mass star? A) Red giant, protostar, main-sequence, white dwarf B) Protostar, main-sequence, red giant, white dwarf C) White dwarf, main-sequence, red giant, protostar D) Protostar, main-sequence, white dwarf, red giant E) Protostar, red giant, main-sequence, white dwarf Answer: B

Section 13.2 1) What key event marks the transition of a protostar into a true (main-sequence) star? A) The onset of sustained nuclear fusion in its core B) The clearing of the gas from the surrounding gas cloud into interstellar space C) The moment when the luminosity first matches the luminosity of the lowest-mass main sequence stars D) The onset of a strong stellar wind Answer: A 2) What is the primary source of energy for protostars (that have not yet become hot enough for fusion in their cores)? A) Fission from concentrated radioactive elements B) High-energy photons from nearby stars C) Gravitational contraction D) The conversion of mass into energy in accord with E = mc2 Answer: C 3) What is the key distinction between protostars and true (main-sequence) stars? A) Protostars generate most of their energy from gravitational contraction, and stars generate it from nuclear fusion. B) Protostars are larger and more luminous than stars. C) Protostars have stronger magnetic fields than stars. D) Protostars are supported by thermal pressure, and stars are supported by degeneracy pressure. Answer: A 4) What happens to the rotation of a molecular cloud as it collapses to form a star? A) The rotation rate remains the same at all times. B) The rotation slows as the cloud collapses. C) The rotation rate increases as the cloud collapses. Answer: C 5) Why do disks form around young stars? A) The surrounding gas can only approach the star from a single direction. B) Collisions between gas particles flatten the rotating gas cloud. C) The rotation of the cloud causes gas to be spun outward from the central star. D) Intense winds from nearby massive stars flatten the gas cloud. Answer: B 6) Approximately how long does the protostellar stage last for a starlike our Sun? A) 300 years B) 30,000 years C) 100,000 years D) 30 million years E) 30 billion years Answer: D 5 Copyright © 2022 Pearson Education, Inc.

7) In general, the time it takes from when in interstellar cloud fragment first begins collapsing until it gives birth to a main-sequence star is ________. A) shorter for less massive stars B) longer for less massive stars C) about the same for all stars D) dependent on the rotation rate of the star Answer: B 8) Which stars spend the shortest amount of time as protostars? A) The most massive stars B) The least massive stars C) Mass doesn't matter, all stars spend about the same amount of time as protostars. Answer: A

9) The diagram above shows the life track of a 1 MSun protostar from the time it first begins to form until it reaches the main sequence, with four stages labeled. What is happening to the protostar's surface temperature and luminosity during Stage 1, when gravity assembles the protostar from a collapsing cloud? A) Its surface temperature and luminosity increase. B) Its surface temperature remains the same and its luminosity decreases. C) Its surface temperature and luminosity decrease. D) Its surface temperature decreases and its luminosity increases. E) Its surface temperature and luminosity remain the same. Answer: A

10) The diagram above shows the life track of a 1 MSun protostar from the time it first begins to form until it reaches the main sequence, with four stages labeled. What is happening to the protostar's surface temperature and luminosity during Stage 2, when it is undergoing convective contraction, and its life track moves almost straight down on the HR diagram? A) Its surface temperature and luminosity increase. B) Its surface temperature remains the same and its luminosity decreases. C) Its surface temperature and luminosity decrease. D) Its surface temperature decreases and its luminosity increases. E) Its surface temperature and luminosity remain the same. Answer: B 11) The diagram above shows the life track of a 1 MSun protostar from the time it first begins to form until it reaches the main sequence, with four stages labeled. What is happening to the protostar's surface temperature and luminosity during Stage 3, when it is undergoing radiative contraction and its life track moves up and to the left? A) Its surface temperature and luminosity increase. B) Its surface temperature remains the same and its luminosity decreases. C) Its surface temperature and luminosity decrease. D) Its surface temperature decreases and its luminosity increases. E) Its surface temperature and luminosity remain the same. Answer: A 12) The diagram above shows the life track of a 1 MSun protostar from the time it first begins to form until it reaches the main sequence, with four stages labeled. What is happening to the protostar's surface temperature and luminosity during Stage 4, when its life track moves straight down to join the main sequence? A) Its surface temperature and luminosity increase. B) Its surface temperature increases, and its luminosity decreases. C) Its surface temperature and luminosity decrease. D) Its surface temperature decreases, and its luminosity increases. E) Its surface temperature and luminosity remain the same. Answer: B 13) When discussing stellar lives, astronomers divide stars by mass into low-mass, intermediatemass, and high-mass stars. Which category has the longest lifetimes? A) Low-mass stars B) Intermediate-mass stars C) High-mass stars Answer: A 14) When discussing stellar lives, astronomers divide stars by mass into low-mass, intermediatemass, and high-mass stars. Which category includes a 25 MSun star? A) Low-mass stars B) Intermediate-mass stars C) High-mass stars Answer: C 7 Copyright © 2022 Pearson Education, Inc.

15) What can we learn about a star from a life track on an H-R diagram? A) How long ago it was born B) When it will die C) Where it is located D) What surface temperature and luminosity it will have at each stage of its life E) All of the above Answer: D 16) About what percentage of a star's total lifetime is spent on the main sequence? A) 10% B) 20% C) 50% D) 90% E) 100% Answer: D 17) What change slowly occurs during the main-sequence lifetime of a star? A) As the solar wind blows material into space, the decreasing mass reduces pressure in the core, which in turn reduces the fusion rate and the luminosity. B) As hydrogen is used up in the core, the fusion rate decreases and reduces the luminosity. C) It gathers more gas from interstellar space, increasing its mass and hence the luminosity. D) Its core temperature slowly increases, increasing the fusion rate and hence the luminosity. Answer: D 18) Why does a star grow larger in radius immediately after it exhausts its core hydrogen? A) The outer layers of the star are no longer gravitationally attracted to the core. B) Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward. C) Helium fusion in the core generates enough thermal pressure to push the upper layers outward. D) Helium fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward. Answer: B 19) What happens to a star after it exhausts its core hydrogen? A) Its core contracts but its outer layers expand. B) Its core expands but its outer layers contract. C) The entire star (both core and outer layers) contracts. D) The entire star (both core and outer layers) expands. Answer: A

20) What is happening deep inside a star while it expands into a subgiant? A) It is fusing hydrogen to produce helium in the core. B) It is fusing hydrogen to produce helium in a shell around the core. C) It is fusing helium to produce carbon in the core. D) It is fusing helium to produce carbon in a shell around the core. E) It is not fusing any element; it is contracting and heating up. Answer: B 21) How does a red giant compare to a main-sequence star of the same mass? A) The red giant has higher surface temperature and higher luminosity. B) The red giant has higher luminosity but lower surface temperature. C) The red giant has lower surface temperature and lower luminosity. D) The red giant lower luminosity but higher surface temperature. E) Both stars have the same mass and therefore have the same surface temperature and luminosity. Answer: B 22) Which of the following is required for helium fusion as compared to hydrogen fusion? A) Much higher temperature B) Much higher density C) A star of much greater mass D) A star that is much older in age Answer: A 23) How many helium nuclei fuse to make one carbon nucleus in the overall helium fusion reaction? A) 2 B) 3 C) 4 D) Varies depending on the type of carbon being made Answer: B 24) What is created by the fusion of three helium nuclei? A) Hydrogen B) Oxygen C) Carbon D) Nitrogen E) Iron Answer: C

25) What happens after the helium flash in the core of a star? A) The core quickly heats up and expands as helium fusion begins all at once throughout the core. B) The star breaks apart in a violent explosion. C) The core suddenly contracts because the helium disappears after being fused. D) The core stops fusing helium. E) The star starts to fuse helium in a shell outside the core. Answer: A 26) What will happen in the Sun immediately after it has exhausted its supply of hydrogen in its core? A) The helium core will shrink, heat, and start helium fusion reactions to produce carbon. B) With the core hydrogen used up, the Sun will no longer be able to generate energy in any way. C) The helium core will shrink and heat while hydrogen fusion begins in a shell around the core. D) The core will collapse, resulting in a supernova. Answer: C 27) The star Arcturus is a red giant that is easily visible in the night sky. Based on models of stellar evolution, what is happening to Arcturus as this stage of its life? A) It is increasing in size, and hydrogen fusion reactions are occurring in a shell around the core. B) It is stable in its size, and hydrogen fusion reactions are occurring in its core. C) It is decreasing in size, and hydrogen fusion reactions are occurring in its core. D) It is increasing in size, and hydrogen fusion reactions are occurring in its core. E) It is decreasing in size, and hydrogen fusion reactions are occurring in a shell around the core. F) It is stable in its size, and hydrogen fusion reactions are occurring in a shell around the core. Answer: A 28) How does a white dwarf compare to a main-sequence star of the same mass? A) The white dwarf has higher surface temperature and higher luminosity. B) The white dwarf has higher luminosity but lower surface temperature. C) The white dwarf has lower surface temperature and lower luminosity. D) The white dwarf has lower luminosity but higher surface temperature. E) The white dwarf and main-sequence star have the same mass and therefore have the same surface temperature and luminosity. Answer: D

29)

Refer to the H-R diagram above that shows the life track of a 1-solar-mass star, with various stages labeled with Roman numerals. A star at the point labelled iii is ________. A) a protostar B) on the main sequence C) a red giant D) experiencing shell fusion Answer: B 30) How will the Sun end its life? A) As a white dwarf B) As a white dwarf supernova C) As a massive star supernova D) As a neutron star or black hole Answer: A 31) Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission? A) Hydrogen B) Oxygen C) Silicon D) Iron E) Uranium Answer: D 32) When discussing stellar lives, astronomers divide stars by mass into low-mass stars (masses similar to the Sun or lower) and high-mass stars (masses more than about 8 times that of our Sun). Which category includes stars that die in supernova explosions? A) High-mass stars only B) Low-mass stars only C) They both die in supernova explosions. D) Neither: Supernovas only occur in binary star systems. Answer: A

33) During which of the following phases of life is a star's balance of pressure and gravity out of equilibrium? A) When it is on the main sequence B) When it is undergoing helium core fusion C) When it is a white dwarf D) When it is expanding as a red giant E) A star is never out of equilibrium. Answer: D 34) What kind of star is destined to die by supernova explosion? A) A brown dwarf B) A red giant C) A low mass star D) A high mass star Answer: D

35) Refer to the sketch above of an H-R diagram for a star cluster. What is the age of the cluster? A) Less than 1 billion years B) About 1 billion years C) About 2 billion years D) About 10 billion years E) More than 15 billion years Answer: D 36) Refer to the sketch above of an H-R diagram for a star cluster. Which statement about this cluster is true? A) It is probably located in the disk of the galaxy. B) It contains some stars that will soon undergo supernova explosions. C) It is probably located in a globular cluster. D) It is probably embedded in a molecular cloud in which new stars are being born. Answer: C

37) Refer to the sketch above of an H-R diagram for a star cluster. Consider the star to which the arrow points. How is it currently generating energy? A) By gravitational contraction B) By hydrogen shell burning around an inert helium core C) By core hydrogen fusion D) By core helium fusion combined with hydrogen shell burning E) By both hydrogen and helium shell burning around an inert carbon core Answer: B 38) Refer to the sketch above of an H-R diagram for a star cluster. Consider the star to which the arrow points. Which of the following statements about this star is true? A) It is somewhat more massive than the Sun. B) It is smaller in radius than the Sun. C) It has a lower luminosity than the Sun. D) Its surface temperature is higher than the Sun's. E) Its core temperature is lower than the Sun's. Answer: A Section 13.3 1) What do astronomers mean when they say that we are all "star stuff"? A) Life would be impossible without energy from the Sun. B) Earth formed at the same time as the Sun. C) Many of the elements from which we and Earth were made were created by stars. D) The Sun formed from the interstellar medium: the "stuff" between the stars. E) The universe contains billions of stars. Answer: C 2) When discussing stellar lives, astronomers divide stars by mass into low-mass, intermediatemass, and high-mass stars. Which category includes our Sun? A) The Sun is a low-mass star. B) The Sun is an intermediate-mass star. C) The Sun is a high-mass star. Answer: A 3) What happens to the core of a star after a planetary nebula occurs? A) It contracts from a protostar to a main-sequence star. B) It breaks apart in a violent explosion. C) It becomes a white dwarf. D) It becomes a neutron star. E) It can become either a neutron star or a black hole. Answer: C

Refer to the H-R diagram above that shows the life track of a 1-solar-mass star, with various stages labeled with Roman numerals. After all its life stages are completed, the remaining core of this star will be left behind as ________. A) a white dwarf made primarily of carbon and oxygen B) a white dwarf made primarily of hydrogen C) a neutron star D) a black hole E) a supernova Answer: A 5) High-mass stars fuse hydrogen into helium through the CNO cycle rather than solely by the proton-proton chain. Which property of the CNO cycle explains why high mass stars have much shorter lives than low mass stars? A) The CNO cycle is only possible when the abundance of CNO elements is very high. B) The CNO cycle is very fast at converting hydrogen to helium. C) The CNO cycle is very fast at converting hydrogen to carbon, nitrogen, oxygen (CNO). D) The CNO cycle is only possible when the star has lived for a very long time. Answer: B 6) Why don't low-mass stars have the CNO cycle occurring in their cores? A) The CNO cycle makes elements heavier than carbon, nitrogen, and oxygen. B) They don't have enough carbon, nitrogen, and oxygen. C) Their core temperatures are too low. Answer: C 7) Which element is the last to be produced by fusion in the cores of the most massive stars (just before their lives end in supernova explosions)? A) Iron B) Lead C) Oxygen D) Uranium E) Hydrogen Answer: A

8) Refer to the figure above showing the abundance of elements in the galaxy relative to hydrogen. What is the least abundant element with an atomic number less than iron's? A) Hydrogen B) Lithium C) Beryllium D) Nitrogen Answer: C 9) Refer to the figure above showing the abundance of elements in the galaxy relative to hydrogen. Based on our understanding of stellar lives, why does iron have a higher abundance than elements similar in atomic number? A) It is the end product of core fusion in massive stars. B) It has a higher density than other elements. C) It does not; this apparent higher abundance is due to iron's many spectral lines making it easier to find. D) The Big Bang created larger amounts of iron than of other elements with similar atomic number. Answer: A

10) Refer to the figure above showing the abundance of elements in the galaxy relative to hydrogen. What is the general trend in elemental abundance? A) Elements with more protons are less abundant. B) Elements with more protons are more abundant. C) Elements heavier than iron do not exist. D) Elements heavier than iron are relatively abundant. E) There is no apparent trend in the abundance of elements. Answer: A 11) Refer to the figure above showing the abundance of elements in the galaxy relative to hydrogen. Why are elements with even numbers of protons more abundant, on average, than elements with odd numbers of protons? A) Because elements are mainly made in reactions with helium nuclei B) Because when elements split in a fission reaction, they prefer to split with all the protons paired. C) There's no explanation, it's something of a mystery to be explained, or it may be a coincidence. D) Because elements are mainly made in reactions with hydrogen nuclei Answer: A 12) What happens to the core of a star if gravity is strong enough to overcome neutron degeneracy pressure? A) The core contracts and becomes a white dwarf. B) The core contracts and becomes a ball of neutrons. C) The core contracts and becomes a black hole. D) The star explodes violently, leaving nothing behind. E) Gravity is not able to overcome neutron degeneracy pressure. Answer: C 13) What types of stars end their lives with supernovae? A) All stars that are red in color B) All stars that are yellow in color C) High-mass stars that can continue to have core fusion until they have iron cores D) Stars that are similar in mass to the Sun E) Stars that have reached an age of 10 billion years Answer: C 14) After a high-mass star explodes in a supernova, what is left behind? A) Always a white dwarf B) Always a neutron star C) Always a black hole D) Almost always either a white dwarf or a neutron star E) Almost always either a neutron star or a black hole Answer: E

Section 13.4 1) Most of the carbon in your body was produced in ________. A) the Big Bang B) interstellar gas in the space between the stars C) red giant stars D) supernova explosions E) the solar nebula Answer: C 2) You discover a binary star system in which one member is a 15MSun main-sequence star and the other star is a 10MSun giant. Why should you be surprised, at least at first? A) It doesn't make sense to find a giant in a binary star system. B) The odds of ever finding two such massive stars in the same binary system are so small as to make it inconceivable that such a system could be discovered. C) The two stars in a binary system should both be at the same point in stellar evolution; that is, they should either both be main-sequence stars or both be giants. D) The two stars should be the same age, so the more massive one should have become a giant first. E) A star with a mass of 15MSun is too big to be a main-sequence star. Answer: D 3) How can the stars in a close binary system dramatically affect each other? A) The close orbits can allow tidal forces to rip one or both stars apart. B) Transfer of mass from one star to another can change how both stars evolve. C) Intense radiation from one star can heat the surface of the other star, causing it to undergo a supernova explosion. Answer: B Short Answer Questions 1) Briefly describe how a star forms. Answer: In cold, dense molecular clouds, gravity brings material together. As gas moves inward, it converts gravitational potential energy to thermal energy and warms up. Once the cloud becomes so dense that the thermal radiation cannot escape, the temperature rises rapidly, nuclear fusion begins, and the dense core becomes a protostar. As the cloud has collapsed from a large size to a small size, it must spin very fast to conserve angular momentum. This results in the formation of a protostellar disk around the protostar. Planets may form in this disk as the star continues to grow. Eventually stellar winds and jets clear away the surrounding gas and a newly formed star emerges. 2) Why does a cloud collapse rapidly at first, and then slow down as it gets denser? Answer: The self-gravity causes the cloud to collapse. Gravitational potential energy is turned to heat (through friction) and released as infrared light from the cloud. As the cloud continues to collapse and becomes smaller and denser, molecules collide more frequently and do not have time to release their excess energy as photons. The thermal energy in the cloud is trapped and its temperature rises. The rising temperature increases the pressure and slows down the collapse. 17 Copyright © 2022 Pearson Education, Inc.

3) Briefly summarize the stages of life for a low-mass star. Answer: [Note: For a "brief" summary, students need recognize only the key stages; additional details are included here for reference.] The protostar assembles from the molecular clouds, heats up from gravitational contraction, and begins hydrogen fusion in the core. The star settles onto the main sequence, where it will fuse hydrogen in its core for 10 billion years. When the core hydrogen is used up, the core contracts until it is degenerate, hydrogen fusion continues in a shell outside the core, and the outer layers expand and cool the star becomes a red giant. Helium fusion begins in the core, but since the core is degenerate, a helium flash takes place and rapidly spreads throughout the core. Helium fusion stabilizes, and the star moves left on the H-R diagram. Core helium is used up and helium begins fusing in a shell outside the core, with hydrogen still fusing in a shell above it. The outer layers expand, and the star again becomes a red giant. The star undergoes thermal pulses and loses its outer layers through a stellar wind. The core shrinks and heats up but is not able to fuse any more elements. The star becomes a planetary nebula as heat from the core blows away and heats up the gas left over from the red giant phase. Only the naked degenerate core is left, a white dwarf. 4) Briefly summarize the stages of life for a high-mass star. Answer: [Note: For a "brief" summary, students need recognize only the key stages; additional details are included here for reference.] The first stages are similar to those of a low-mass star, except that they happen over much shorter time periods. While on the main sequence, the star fuses hydrogen by the CNO cycle and remains at this stage only for several million years. In addition to helium fusion, high-mass stars also undergo alpha capture, which creates heavier elements by fusing a helium nucleus with an existing atom. After helium is used up in the core, the core contracts while helium and hydrogen fusion continue in outer shells. The core contracts until carbon ignition occurs, and the star moves left again on the H-R diagram while carbon fusion occurs in the core. The process continues for stars of still higher mass, zigzagging across the H-R diagram as heavier elements are fused in the core and used up as fuel. Each fusion stage requires less time until iron is finally produced in the core. Iron cannot be fused to produce energy, so the core collapses and pressures increase so that electrons and protons are converted to neutrons. A high quantity of neutrinos is released, which may help force the outer layers violently outward in an explosion called a supernova. Elements heavier than iron are created, the outer layers move away from the core at great velocities, and only a neutron star or black hole is left as a remnant. 5) Briefly explain why high-mass stars have shorter lifetimes than low-mass stars. Answer: [Note: For a "brief" summary, you may consider it sufficient for students to state that high-mass stars have much higher luminosities, which more than make up for their additional fuel.] High-mass stars have much more fuel for fusion, but they use it at a much greater rate, primarily because their hydrogen fusion proceeds through the CNO cycle rather than the protonproton chain.

Reading Quiz Questions 1) The interstellar clouds called molecular clouds are ________. A) the cool clouds in which stars form B) the clouds in which elements such as carbon, nitrogen, and oxygen are made C) the clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide D) the hot clouds of gas expelled by dying stars Answer: A 2) What is a protostar? A) A star that is still in the process of forming B) A star that has planets C) An intermediate-mass star D) A star in its final stage of life Answer: A 3) Most interstellar clouds remain stable in size because the force of gravity is opposed by ________ within the cloud. A) thermal pressure B) degeneracy pressure C) radiation pressure D) stellar winds Answer: A 4) Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds? A) Infrared B) Visible light C) Ultraviolet D) Blue light Answer: A 5) What kind of gas cloud is most likely to give birth to stars? A) A cold, dense gas cloud B) A hot, dense gas cloud C) A cold, low-density gas cloud D) A hot, low-density gas cloud Answer: A 6) Which of the following phenomena is not commonly associated with the star-formation process? A) Intense ultraviolet radiation coming from a protostar B) The formation of a spinning disk of material around a protostar C) Powerful "jets" shooting out along the rotation axis of a protostar D) Strong winds of particles blowing out into space from a protostar Answer: A 19 Copyright © 2022 Pearson Education, Inc.

7) When does a protostar become a main-sequence star? A) When the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space B) When a piece of a molecular cloud first begins to contract into a star C) When it becomes luminous enough to emit thermal radiation D) At the instant that the first hydrogen fusion reactions occur in the protostar's core Answer: A 8) Approximately what core temperature is required before hydrogen fusion can begin in a star? A) 10 million K B) 10,000 K C) 10 trillion K D) 10 billion K E) 1 billion K Answer: A 9) Which of the following stars spends the longest time in the protostellar phase of life? A) A 1 solar-mass star B) A 2 solar-mass star C) A 3 solar-mass star D) A 4 solar-mass star E) A 5 solar-mass star Answer: A 10) What is the approximate range of masses that newborn main-sequence stars can have? A) 0.1 to 150 solar masses B) 0.001 to 1500 solar masses C) 0.1 to 1500 solar masses D) 0.001 to 10 solar masses E) 0.1 to 10 solar masses Answer: A 11) The vast majority of stars in a newly formed star cluster are ________. A) less massive than the Sun B) very high-mass, type O and B stars C) red giants D) about the same mass as our Sun Answer: A 12) Which of the following statements about brown dwarfs is not true? A) Brown dwarfs eventually collapse to become white dwarfs. B) Brown dwarfs are supported against gravity by degeneracy pressure, which does not depend on the object's temperature. C) Brown dwarfs form like ordinary stars but are too small to sustain nuclear fusion in their cores. D) All brown dwarfs have masses less than about 8% that of our Sun. Answer: A 20 Copyright © 2022 Pearson Education, Inc.

13) What can we learn about a star from a life track on an H-R diagram? A) The surface temperature and luminosity the star will have at each stage of its life B) The star's age C) The star's current stage of life D) How the star's distance from Earth varies at different times in its life Answer: A 14) Which of the following lists the stages of life for a low-mass star in the correct order? A) Protostar, main-sequence star, red giant, planetary nebula, white dwarf B) Protostar, main-sequence star, red giant, supernova, neutron star C) Protostar, main-sequence star, planetary nebula, red giant D) Main-sequence star, white dwarf, red giant, planetary nebula, protostar Answer: A 15) What happens when a main-sequence star exhausts its core hydrogen fuel supply? A) The entire star shrinks in size. B) The core shrinks while the rest of the star expands. C) The core immediately begins to fuse its helium into carbon. D) The star becomes a neutron star. Answer: B 16) The primary source of energy for a star as it grows in size to become a red giant is ________. A) hydrogen fusion in the central core B) helium fusion in the central core C) hydrogen fusion in a shell surrounding the central core D) gravitational contraction Answer: C 17) The overall helium fusion reaction is ________. A) three helium nuclei fuse to form one carbon nucleus B) two helium nuclei fuse to form one beryllium nucleus C) two hydrogen nuclei fuse to form one helium nucleus D) four helium nuclei fuse to form one oxygen nucleus Answer: A 18) What is a helium flash? A) The sudden onset of helium fusion in the core of a low-mass star B) The ignition of helium shell fusion in a high-mass star with a carbon core C) A sudden brightening of a low-mass star, detectable from Earth by observing spectral lines of helium D) It is another name for the helium fusion reaction. Answer: A

19) What is a planetary nebula? A) Gas ejected from a low-mass star in the final stage of its life B) Gas created from the remains of planets that once orbited a dead star C) Interstellar gas from which planets are likely to form in the not-too-distant future D) The remains of a high-mass star that has exploded Answer: A 20) The ultimate fate of our Sun is to ________. A) become a white dwarf that will slowly cool with time B) explode in a supernova C) become a rapidly spinning neutron star D) become a black hole Answer: A 21) What is the CNO cycle? A) A set of steps by which four hydrogen nuclei fuse into one helium nucleus B) The process by which helium is fused into carbon, nitrogen, and oxygen C) The process by which carbon is fused into nitrogen and oxygen D) The set of fusion reactions that have produced all the carbon, nitrogen, and oxygen in the universe Answer: A 22) To predict whether a star will eventually fuse oxygen into a heavier element, what do you need to know about the star? A) Its mass B) Its luminosity C) How much oxygen it now has in its core D) Its overall abundance of elements heavier than helium Answer: A 23) Why is iron significant to understanding how a supernova occurs? A) Iron cannot release energy either by fission or fusion. B) Iron is the heaviest of all atomic nuclei, and thus no heavier elements can be made. C) Supernovae often leave behind neutron stars, which are made mostly of iron. D) The fusion of iron into uranium is the reaction that drives a supernova explosion. Answer: A 24) After a supernova explosion, the remains of the stellar core can be ________. A) either a neutron star or a black hole B) a neutron star only C) a black hole only D) a white dwarf, neutron star, or black hole Answer: A

25) Algol consist of a 3.7 MSun main-sequence star and a 0.8 MSun subgiant. Why does this seem surprising, at least at first? A) The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star. B) The two stars in a binary system should both be at the same stage of life; that is, they should either both be main-sequence stars or both be subgiants. C) It doesn't make sense to find a subgiant in a binary star system. D) A star with a mass of 3.7 MSun is too big to be a main-sequence star. Answer: A Concept Quiz Questions 1) Which two processes can generate energy to help a star maintain its internal thermal pressure? A) Nuclear fusion and gravitational contraction B) Nuclear fusion and nuclear fission C) Nuclear fusion and supernova D) Nuclear fission and supernova Answer: A 2) Our Sun is considered to be a ________. A) low-mass star B) intermediate-mass star C) high-mass star D) brown dwarf Answer: A 3) Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse? A) The cloud must radiate away much of its thermal energy. B) The cloud must trap most of its thermal energy. C) The cloud must collide with other clouds. D) New dust particles must continually be made in the cloud. Answer: A 4) Angular momentum plays an important role in star formation. Which of the following characteristics of a protostellar system is probably not strongly affected by the star's angular momentum? A) The onset of core hydrogen fusion B) The existence of protostellar jets C) The strength of protostellar winds D) The formation of a protostellar disk Answer: A

5) Generally speaking, a main-sequence star is ________ than it was during the time it was a protostar. A) hotter and dimmer B) hotter and brighter C) cooler and dimmer D) cooler and brighter Answer: A 6) Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true? A) A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage. B) All the stars in the cluster will be of about the same mass. C) All the stars in the cluster will become main-sequence stars at about the same time. D) All the stars in the cluster will have approximately the same luminosity and surface temperature. Answer: A 7) We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs. But if they do, then which of the following would be true? A) Brown dwarfs would outnumber all ordinary stars. B) Brown dwarfs would be responsible for most of the overall luminosity of our Milky Way Galaxy. C) Brown dwarfs would be extremely rare. D) Most of the brown dwarfs in the Milky Way Galaxy would be quite young in age. Answer: A 8) Where would a brown dwarf be located on an H-R diagram? A) Below and to the right of the lowest part of the main sequence B) Above and to the left of the highest part of the main sequence C) In the upper right corner of the H-R diagram D) In the lower left corner of the H-R diagram Answer: A 9) Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars? A) H-R diagrams of globular clusters B) H-R diagrams of open clusters C) Observing a low-mass star over many years D) Spacecraft observations of the Sun Answer: A

10) Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star? A) Fusion reactions are producing energy at a greater rate in the red giant. B) The red giant has a hotter core. C) The red giant's surface is hotter. D) The red giant is more massive. Answer: A This diagram represents the life track of a 1 solar mass star from its pre-main-sequence stages to just before its final death. Refer to the life stages labeled with roman numerals.

11) During which stage is the star's energy supplied by primarily by gravitational contraction? A) Stage II B) Stage III C) Stage V D) Stage VI E) Stage VIII Answer: A 12) During which stage does the star have an inert (non-fusing) helium core? A) Stage III B) Stage IV C) Stage VI D) Stage VII E) Stage VIII Answer: B 13) Which stage lasts the longest? A) Stage I B) Stage III C) Stage IV D) Stage VI E) Stage VIII Answer: B

14) During which stage does the star have an inert (non-fusing) carbon core surrounded by shells of helium and hydrogen fusion? A) Stage II B) Stage III C) Stage IV D) Stage VI E) Stage VIII Answer: E 15) What will happen to the star after stage VIII? A) Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf. B) It will continue to expand gradually until carbon fusion begins in its core. C) It will explode as a supernova and leave a neutron star or black hole behind. D) It will remain in stage VIII for about 10 billion years, after which its outer layers will shrink back and cool. Answer: A 16) Carbon fusion occur in high-mass stars but not in low-mass stars because ________. A) the cores of low-mass stars never get hot enough for carbon fusion B) the cores of low-mass stars never contain significant amounts of carbon C) only high-mass stars do fusion by the CNO cycle D) carbon fusion can occur only in the stars known as carbon stars Answer: A 17) Which of the following statements about various stages of core nuclear fusion (hydrogen, helium, carbon, and so on) in a high-mass star is not true? A) Each successive stage lasts for approximately the same amount of time. B) As each stage ends, the core shrinks and heats further. C) Each successive stage creates an element with a higher atomic number and atomic mass number. D) As each stage ends, the reactions that occurred in previous stages continue in shells around the core. Answer: A 18) Which event marks the beginning of a supernova? A) The sudden collapse of an iron core into a compact ball of neutrons B) The onset of helium fusion after a helium flash C) The beginning of neon fusion in an extremely massive star D) The sudden initiation of the CNO cycle Answer: A

19) Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye? A) Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime. B) We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky. C) Because the supernova destroys the star, Betelgeuse would suddenly disappear from view. D) Think back to the scale of our solar system (see Chapter 1) and the distances to stars. Even with a big cloud of gas expanding away from it, a star will still look like a point of light to the naked eye. Answer: A 20) Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen16, neon-20, and magnesium-24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case? A) At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions. B) The apparent pattern is thought to be a random coincidence. C) Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between. D) This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang. Answer: A 21) A spinning neutron star has been observed at the center of a ________. A) supernova remnant B) planetary nebula C) red supergiant D) protostar Answer: A 22) Which is more common: a star blows up as a supernova, or a star ejects a planetary nebula? A) Planetary nebulas are more common. B) Supernovae are more common. C) They both occur in about equal numbers. D) It is impossible to say. Answer: A

23) You discover a binary star system in which one star is a 15 MSun main-sequence star and the other is a 10 MSun giant. How do we think that a star system such as this might have come to exist? A) The giant must once have been the more massive star, but it is now less massive because it transferred some of its mass to its companion. B) Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main-sequence stars millions of years later than its less massive companion. C) The two stars probably were once separate, but became a binary when a close encounter allowed their mutual gravity to pull them together. D) The two stars are simply evolving normally and independently, and one has become a giant before the other. Answer: A

Visual Quiz Questions 1) This famous image from the Hubble Space Telescope shows what is sometimes called the "pillars of creation." Which of the following best describes what it shows?

A) The pillars are clouds of gas and dust in which many new stars are forming; the edges of the pillars are sculpted by ultraviolet radiation from stars outside the pillars. B) Each of the pillars is a cloud of gas that will give birth to a single star, which will emerge from the top of its pillar. C) There is a hot, young star at the top of each pillar that is shooting a jet of gas that forms the pillar below the star. D) There is a single star outside the frame at the bottom, and the pillars are clouds of accreting particles that will form planets orbiting the star. Answer: A 2) This photo shows gas associated with a protostar. What is this gas doing?

A) It is flowing outward in two opposite directions from the protostar. B) It is gas that is gradually accreting onto the protostar. C) It is part of a protostellar disk in which planets may someday form. D) It is gas blown off the protostar's surface as a protostellar wind. Answer: A

3) What is the main idea captured by this graph?

A) Low-mass stars are much more common than higher-mass stars. B) Low-mass stars are smaller and redder than higher-mass stars. C) Stars are best understood by dividing them into four categories by mass. D) Objects with mass below 0.08 MSun are brown dwarfs rather than true stars. Answer: A 4) In this diagram, red balls represent protons and gray balls represent neutrons. What reaction is being shown?

A) Fusion of helium into carbon B) Fusion of hydrogen into helium C) Fusion of carbon into oxygen D) The "iron catastrophe" that initiates a supernova Answer: A

5) This H-R diagram shows the life track of a 1 MSun star from the time it first becomes a mainsequence star. Which numbered point represents the star when it has both hydrogen-fusing and helium-fusing shells around an inert carbon core?

A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: D

6) This Hubble Space Telescope photo shows a planetary nebula. What is the white dot in the center (indicated by the arrow)?

A) A white dwarf B) A red giant star with a strong stellar wind C) A neutron star D) A protostar that will soon become a main-sequence star Answer: A

7) Suppose a particular star has a core that is undergoing several stages of fusion simultaneously, as shown in this diagram. Based on our understanding of stellar lives, the mass of this star is ________.

A) greater than 8 times the mass of the Sun. B) about 2 times the mass of the Sun. C) about the same mass as the Sun. D) less than 0.1 times the mass of the Sun. Answer: A

8) According to this diagram, how much more abundant is hydrogen in the universe than nitrogen?

A) Hydrogen is about 10,000 times as abundant as nitrogen. B) Hydrogen is about 30% more abundant than nitrogen. C) Hydrogen is about 10 times as abundant as nitrogen. D) Hydrogen is about 4 times as abundant as nitrogen. Answer: A 9) This photo shows the famous Crab Nebula. What is it?

A) An expanding cloud of remains from a star that died in a supernova B) A classic example of a planetary nebula C) A star that is right now undergoing a supernova explosion D) A star forming cloud that will eventually give birth to hundreds of stars Answer: A

10) The arrow in the photo on the left points to the location of the star that has exploded as a supernova in the photo on the right. From this photo pair alone, what can we conclude about the star that exploded? (Assume that we know the star was not a member of a binary system.)

A) It was a high-mass star with at least 8 times the mass of the Sun. B) It is now a black hole. C) It was a red giant star. D) Before the supernova, the star lived for at least a billion years. Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

This figure, similar to the left side of Figure 13.13, shows the future life stages of the Sun on an H-R diagram. Use the figure to answer the following questions. 1) What will the Sun's approximate luminosity be during the subgiant stage? Answer: Approximately 10 LSun 2) When the Sun is a red giant, what will its approximate surface temperature be? Answer: Approximately 3500 K 3) Just before the Sun produces a planetary nebula, what will its approximate luminosity be? Answer: Approximately 104 LSun

4) When the Sun becomes a white dwarf with a surface temperature similar to its current surface temperature, what will its luminosity be? Answer: Approximately 10-4 LSun Chapter Review Questions 1) What is a molecular cloud? Briefly describe the process by which a protostar forms from gas in a molecular cloud. 2) Why do protostars rotate rapidly? How can a close binary star system form? 3) Why does a spinning disk of gas surround a protostar? Describe key phenomena seen among protostars, such as strong stellar winds and jets. 4) What are the minimum and maximum masses for a star, and why do these limits occur? What is a brown dwarf? 5) What is degeneracy pressure, and how does it differ from thermal pressure? Explain why degeneracy pressure can support a stellar core against gravity even when the core becomes cold. 6) Briefly describe the Sun's life stages after it exhausts its core hydrogen. Discuss both the changes occurring in the Sun's core and the changes visible from outside the Sun. 7) Why does helium fusion require much higher temperatures than hydrogen fusion? Briefly explain why helium fusion in the Sun will begin with a helium flash. 8) What is a planetary nebula? What happens to the core of a star after a planetary nebula occurs? 9) What will happen to Earth as the Sun changes in the future? 10) What do we mean by a star's life track on an H-R diagram? Summarize the stages of the Sun's life track in Figure 13.13. 11) In broad terms, explain how the life of a high-mass star differs from that of a low-mass star. 12) Describe some of the nuclear reactions that can occur in high-mass stars after they exhaust their core helium. Why do these reactions occur in high-mass but not in low-mass stars? 13) Why can't iron be fused to release energy? 14) Summarize some of the observational evidence supporting our ideas about how the elements form in massive stars. 15) What event initiates a supernova, and why is a neutron star or black hole left behind? What observational evidence supports our understanding of supernovae? 37 Copyright © 2022 Pearson Education, Inc.

16) Why can the lives of close binary stars differ from those of single stars? Describe the Algol paradox and its resolution. Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 17) The iron in my blood came from a star that blew up more than 4 billion years ago. 18) I discovered stars being born within a patch of extremely low-density, hot interstellar gas. 19) Humanity will eventually have to find another planet to live on, because one day the Sun will blow up as a supernova. 20) I sure am glad hydrogen has a higher mass per nuclear particle than many other elements. If it had the lowest mass per nuclear particle, none of us would be here. 21) If the Sun had been born 4½ billion years ago as a high-mass star rather than as a low-mass star, Jupiter would have Earth-like conditions today, while Earth would be hot like Venus. 22) If you could look inside the Sun today, you'd find that its core contains a much higher proportion of helium and a lower proportion of hydrogen than it did when the Sun was born. 23) I just discovered a 3.5MSun main-sequence star orbiting a 2.5MSun red giant. I'll bet that red giant was more massive than the 3.5MSun star when it was a main-sequence star. 24) Globular clusters generally contain lots of white dwarfs. 25) After hydrogen fusion stops in a low-mass star, its core cools off until the star becomes a red giant. 26) The oxygen in my lungs comes from supernova explosions.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 13 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 27) Stars can form most easily in clouds that are ________. A) cold and dense B) warm and dense C) hot and low-density Answer: No Correct Answer Was Provided. 28) A brown dwarf is ________. A) an object not quite massive enough to be a star B) a white dwarf that has cooled off C) a starlike object that is less massive than Jupiter Answer: No Correct Answer Was Provided. 29) Which of these stars has the hottest core? A) A blue main-sequence star B) A red supergiant C) A red main-sequence star Answer: No Correct Answer Was Provided. 30) Which of these stars does not have fusion occurring in its core? A) A red giant B) A red main-sequence star C) A blue main-sequence star Answer: No Correct Answer Was Provided. 31) After the helium flash in a low-mass star, the star's luminosity ________. A) goes up. B) goes down C) stays the same Answer: No Correct Answer Was Provided. 32) What would stars be like if hydrogen had the smallest mass per nuclear particle? A) Stars would be brighter. B) All stars would be red giants. C) Nuclear fusion would not occur in stars of any mass. Answer: No Correct Answer Was Provided. 33) What would stars be like if carbon had the smallest mass per nuclear particle? A) Supernovae would be more common. B) Supernovae would never occur. C) High-mass stars would be hotter. Answer: No Correct Answer Was Provided.

34) What would you be most likely to find if you returned to the solar system in 10 billion years? A) A neutron star B) A white dwarf C) A black hole Answer: No Correct Answer Was Provided. 35) Which of these stars has the shortest life expectancy? A) An isolated 1MSun star B) A 1MSun star in a close binary system with a 0.8MSun star C) A 1MSun star in a close binary system with a 2MSun star Answer: No Correct Answer Was Provided. 36) What happens to the core of a high-mass star after it runs out of hydrogen? A) It shrinks and heats up. B) It shrinks and cools down. C) Helium fusion begins right away. Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 37) Connections to the Stars. In ancient times, many people believed that our lives were somehow influenced by the patterns of the stars in the sky. Modern science has not found any evidence to support this belief, but instead has found that we have a connection to the stars on a much deeper level: We are "star stuff." Discuss in some detail our real connections to the stars, as established by modern astronomy. Do you think these connections have any philosophical implications for how we view our lives and our civilization? Explain. 38) Group Discussion: Inclusion of Amateurs. Observations and careful record keeping by amateur observers of the sky have been enormously beneficial to professional researchers, and particularly to studies of variable and exploding stars. a. Section 13.3 discusses how historical supernova observations, particularly those made by the Chinese, have assisted modern research on supernova remnants. Should we consider those ancient observers to be amateurs or professionals? Is the distinction meaningful? Defend your opinion. b. The American Association of Variable Star Observers (AAVSO) is a large community that has made observations and kept records of stellar brightness variations, including supernova explosions, for more than a century. The vast majority of these observations were made by amateurs, not professionals. Do you think amateur observations can be trusted? Why or why not? c. Imagine you are a professional astronomer. How might you go about verifying that observations made by amateurs are sufficiently accurate to support professional research? d. What do you think of the term amateur in this context? What does it mean to you? Do you think it could be biasing your viewpoint on the work of amateur astronomers?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 39) Predicting the Sun's Future. Models of stellar evolution make detailed predictions about the fate of the Sun. Describe one piece of evidence that supports each of the following model predictions. a. The Sun cannot continue supplying Earth with light and heat forever. b. The Sun will become a red giant before the end of its life. c. The Sun will leave behind a white dwarf after it dies. 40) Predicting the Properties of Brown Dwarfs. Models of star formation predict that objects less massive than 0.08MSun become brown dwarfs instead of true hydrogen-fusing stars. Once they have formed, these objects cool because no fusion is occurring to replace the thermal energy lost from their surfaces. How would you expect the properties of brown dwarfs in an older star cluster to compare with those of brown dwarfs in a younger one? Propose an observing program that could test your hypothesis. 41) Group Activity: Comparing Models of Stars with Data. Work as a group to evaluate each of the following predictions.You will find it useful to study the star cluster data in Figures 12.10, 12.17, and 12.18. Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39. a. Type O stars have shorter lives than type G stars. b. Type K supergiant stars produce iron before they explode as supernovae. c. Type F stars become much more luminous near the ends of their lives than they were as main-sequence stars. d. Type O stars do not become more luminous near the ends of their lives but do become redder. e. Type M stars have longer lives than type K stars. f. Stars similar to the Sun reach a maximum size of about 100 solar radii during the red giant stage. g. Type K main-sequence stars will become red giants when their cores run out of hydrogen. h. Some stars become white dwarfs at the ends of their lives. i. White dwarfs cool with time but do not change much in radius.

Investigate Further Short-Answer/Essay Questions 42) Brown Dwarfs. How are brown dwarfs like jovian planets? In what ways are brown dwarfs like stars? 43) Homes to Civilization? We do not yet know how many stars have Earth-like planets, nor do we know the likelihood that such planets might harbor advanced civilizations like our own. However, some stars can probably be ruled out as candidates for advanced civilizations. For example, given that it took a few billion years for humans to evolve on Earth, it seems unlikely that advanced life would have had time to evolve around a star that is only a few million years old. For each of the following stars, decide whether you think it is possible that it could harbor an advanced civilization. Explain your reasoning in one or two paragraphs. a. 10MSun main-sequence star b. 1.5MSun main-sequence star c. 1.5MSun red giant d. 1MSun helium core-fusion star e. Red supergiant 44) Rare Elements. Lithium, beryllium, and boron are elements with atomic numbers 3, 4, and 5, respectively. Despite their being three of the five simplest elements, Figure 13.19 shows that they are rare compared to many heavier elements. Suggest a reason for their rarity. (Hint: Consider the process by which helium fuses into carbon.) 45) Future Skies. As a red giant, the Sun will have an angular size in Earth's sky of about 30°. What will sunset and sunrise be like? Do you think the color of the sky will be different from what it is today? Explain. 46) Research: Historical Supernovae. Historical accounts exist of supernovae in the years 1006, 1054, 1572, and 1604. Choose one of these supernovae and learn more about historical records of the event. Did the supernova influence human history in any way? Write a two- to three-page summary of your research findings. 47) Picturing Star Birth and Death. Photographs of stellar birthplaces (i.e., molecular clouds) and death places (e.g., planetary nebulae and supernova remnants) can be strikingly beautiful, but only a few such photographs are included in this chapter. Search the web for additional images. Look not only for photos taken in visible light, but also for those taken in other wavelengths. Put the photographs you find into a personal online journal, along with a oneparagraph description of what each photograph shows. Include at least 20 images. 48) Humanity in a.d. 5,000,000,000. Do you think it is likely that humanity will survive until the Sun begins to expand into a red giant 5 billion years from now? Why or why not?

Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 49) An Isolated Star-Forming Cloud. Isolated molecular clouds can have a temperature as low as 10 K and a particle density as great as 100,000 particles per cubic centimeter. What is the minimum mass that a cloud with these properties needs in order to form a star? 50) Density of a Red Giant. Near the end of its life, the Sun's radius will extend nearly to Earth's orbit. Estimate the volume of the Sun at that time using the formula for the volume of a sphere (V = 4πr3/3). Using that result, estimate the average matter density of the Sun at that time. How does that density compare with the density of water (1 g/cm3)? How does it compare with the density of Earth's atmosphere at sea level (about 10-3 g/cm3)? 51) Supernova Betelgeuse. The distance from Earth of the red supergiant Betelgeuse is approximately 600 light-years. If it were to explode as a supernova, it would be one of the brightest stars in the sky. Right now, the brightest star other than the Sun is Sirius, with a luminosity of 26LSun and a distance of 8.6 light-years. How much brighter in our sky than Sirius would the Betelgeuse supernova be if it reached a maximum luminosity of 1010LSun? 52) Construction of Elements. Using the periodic table in Appendix D, determine which elements are made by the following nuclear fusion reactions. (You can assume the total number of protons in the reaction remains constant.) a. Fusion of a carbon nucleus with another carbon nucleus b. Fusion of a carbon nucleus with a neon nucleus c. Fusion of an iron nucleus with a helium nucleus 53) Algol's Orbital Separation. The Algol binary system consists of a 3.7MSun star and a 0.8MSun star with an orbital period of 2.87 days. Use Newton's version of Kepler's third law to calculate the orbital separation of the system. How does that separation compare with the typical size of a red giant star?

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 14 The Bizarre Stellar Graveyard Section 14.1 1) What is a white dwarf? A) The exposed core of a dead star, supported by electron degeneracy pressure B) The exposed core of a dead star, supported by neutron degeneracy pressure C) A hot, but very small main-sequence star with a mass of less than 1.4 solar masses D) A cool and very small main-sequence star with a mass of less than 1.4 solar masses E) The name for the singularity at the center of a black hole Answer: A 2) How much would a teaspoon of white dwarf material weigh on Earth? A) The same as a teaspoonful of Earthlike material B) About the same as Mt. Everest C) About the same as Earth D) A few tons E) A few million tons Answer: D 3) Which of the following is closest in mass to a white dwarf? A) The Moon B) Earth C) Jupiter D) The Sun Answer: D 4) Which of the following is closest in size (radius) to a white dwarf? A) Earth B) A small city C) A football stadium D) A basketball E) The Sun Answer: A 5) Which of the following is always true about a 1.2-solar mass white dwarf compared to a 1.0 solar mass white dwarf? A) The more massive white dwarf has a larger radius. B) The more massive white dwarf has a smaller radius. C) The more massive white dwarf has a higher surface temperature. D) The more massive white dwarf has a lower surface temperature. E) The more massive white dwarf is supported by neutron degeneracy pressure, rather than electron degeneracy pressure. Answer: B

6) What is the ultimate fate of an isolated white dwarf? A) It will cool down and become gradually dimmer. B) As gravity overwhelms the electron degeneracy pressure, it will explode as a nova. C) As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova. D) As gravity overwhelms the electron degeneracy pressure, it will become a neutron star. E) The electron degeneracy pressure will eventually overwhelm gravity and the white dwarf will slowly evaporate. Answer: A 7) What kind of pressure prevents a white dwarf from collapsing? A) Neutron degeneracy pressure B) Electron degeneracy pressure C) Thermal pressure D) Radiation pressure Answer: B 8) What is the upper limit to the mass of a white dwarf? A) There is no upper limit. B) There is an upper limit, but we do not yet know what it is. C) About 2.8 solar masses D) About 1.4 solar masses E) About 1 solar mass Answer: D 9) Which of the following hypothetical observations would contradict current understanding of the nature of white dwarfs? A) Discovery of a white dwarf with a mass of 1.5 MSun B) Discovery of a white dwarf with a surface temperature of 6000 K C) Discovery of a white dwarf at the center of a planetary nebula D) Discovery of a white dwarf with a 1.5 MSun mass main-sequence companion Answer: A 10) In which wavelength regions is it easiest to identify and study the accretion disk around a white dwarf in a binary system? A) Visible and infrared light B) Infrared and radio light C) X-ray and ultraviolet light D) Gamma ray and x-ray light E) Radio and visible light Answer: C

11) Which of the following statements about novae is true? A) A star system that undergoes a nova may have another nova sometime in the future. B) A nova involves fusion taking place on the surface of a neutron star. C) A nova is the most powerful type of explosion ever seen in the universe. D) When a star system undergoes a nova, it brightens as much as a star system undergoing a supernova. E) A nova can occur on a single, isolated star. Answer: A 12) After our Sun dies, will it ever undergo a nova explosion? Why or why not? A) No, because it does not have a close binary companion B) No, because our Sun will become a neutron star, not a white dwarf C) Yes, because our Sun will become a white dwarf D) Yes, because all stars undergo novae explosions after they die Answer: A 13) You observe a nova. Based on current understanding, you can also conclude that you are observing ________. A) a close binary system in which one member is a white dwarf B) a close binary system in which one member is a neutron star C) the complete destruction of a white dwarf D) a close binary system in which both members are white dwarfs Answer: A 14) Observationally, a key distinction between a white dwarf supernova and a massive-star supernova is that the spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white dwarf supernova does not. Why don't we see prominent hydrogen lines in the spectrum of a white dwarf supernova? A) White dwarf supernovae occur so far away that their hydrogen lines become too dim to see. B) During a white dwarf supernova, all the white dwarf's hydrogen fuses instantly to make helium. C) White dwarfs are stellar corpses that contain little or no hydrogen, so they do not show hydrogen lines when they explode. D) The hydrogen lines of white dwarf supernovae are so redshifted that we cannot detect them. Answer: C

15) What does Einstein's general theory of relativity tell us about two white dwarfs orbiting one another very close together? A) They will emit gravitational waves that carry energy and angular momentum away from the system, causing the white dwarfs to gradually spiral inward toward each other and eventually merge. B) They will emit gravitational waves that carry energy and angular momentum toward the system, causing the white dwarfs to gradually spiral away from one another and eventually fly far apart. C) They will emit gravitational waves that carry energy and angular momentum away from the system, causing the white dwarfs to quickly spiral away from one another. D) They will orbit one another forever. Answer: A 16) Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit? A) The upper limit to a white dwarf's mass is something we have learned from observations, but no one knows why this limit exists. B) Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. C) White dwarfs get hotter with increasing mass, and above the 1.4-solar-mass limit, they would be so hot that even their electrons would melt. D) White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit. Answer: B 17) Which of the following is closest in size (radius) to a neutron star? A) Earth B) A city C) A football stadium D) A basketball E) The Sun Answer: B 18) How does a black hole form from a massive star? A) During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole. B) Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant. C) If enough mass is accreted by a white dwarf star so that it exceeds the 1.4-solar-mass limit, it will undergo a supernova explosion and leave behind a black-hole remnant. D) If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a black-hole remnant. E) A black hole forms when two massive main-sequence stars collide. Answer: A

19) Consider our Moon, a white dwarf, and a neutron star. Which of the following lists them in the correct order of size (diameter), from smallest to largest? A) Neutron star, Moon, white dwarf B) Moon, white dwarf, neutron star C) White dwarf, neutron star, Moon Answer: A 20) Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except ________. A) a brown dwarf B) a white dwarf C) a neutron star D) the core of a high-mass main-sequence star Answer: D 21) The surface of the neutron star RXJ2015 has a temperature of 10 million K. This neutron star emits radiation most strongly in ________. A) x-ray light B) visible light C) radio light D) infrared light Answer: A 22) If you were to come back to our Solar System in 8 billion years, what might you expect to find? A) a red giant star B) a white dwarf C) a rapidly spinning pulsar D) a black hole E) Everything will be pretty much the same as it is now. Answer: B

23)

The figure above shows how the luminosity of supernovae changes over time. About how long does it take a white dwarf supernova to decrease in luminosity by a factor of 100 from its peak? A) 300 days B) 200 days C) 100 days D) 25 days Answer: B 24) Consider a main-sequence star, a white dwarf, a neutron star, and the singularity of a black hole. Which of the following lists them in the correct order of increasing density (low to high)? A) Main sequence star, white dwarf, neutron star, black hole singularity B) Main sequence star, neutron star, white dwarf, black hole singularity C) Black hole singularity, main sequence star, white dwarf, neutron star D) Main sequence star, black hole singularity, neutron star, white dwarf Answer: A

Section 14.2 1) Which of the following is most likely to undergo a white dwarf supernova? A) A main-sequence star of spectral type O B) A main-sequence star like our Sun C) An isolated white dwarf (not in a binary system) D) A close binary system in which both stars are white dwarfs E) A pulsar Answer: D 2) How much would a paperclip made of neutron star material weigh on Earth? A) About the same as an actual paperclip B) A few tons C) About as much as Mt. Everest D) About as much as the Moon E) About as much as the Sun Answer: C 3) How might a pulsar appear to an observer? A) It may appear to flash several times per second or more with near perfect regularity. B) It may slowly get dimmer and brighter with a period ranging from several days to several weeks. C) It may appear to flash at random intervals. D) It may appear to change color very rapidly, from blue to red and back again, with near perfect regularity. E) Its spectrum may alternate between showing blueshifts and redshifts very rapidly with near perfect regularity. Answer: A 4) What is a pulsar? A) A star that alternately expands and contracts in size B) A rapidly rotating neutron star C) A neutron star or black hole that happens to be in a binary system D) A binary system that happens to be aligned so that one star periodically eclipses the other E) A star that is burning iron in its core Answer: B 5) What causes the pulses of a pulsar? A) Vibrations on the pulsar's surface B) As the pulsar rotates, beams of radiation along its magnetic axis sweep through space. C) The pulsar undergoes periodic explosions of nuclear fusion that generate strong emission. D) The pulsar is periodically eclipsed by an orbiting companion. E) The pulses are peaks and valleys of gravitational waves. Answer: B

6) What is the ultimate fate of an isolated pulsar (not in a binary system)? A) It will spin ever faster, becoming a millisecond pulsar. B) As gravity overwhelms the neutron degeneracy pressure, it will explode as a supernova. C) As gravity overwhelms the neutron degeneracy pressure, it will become a white dwarf. D) It will gradually cool, and it will become too dim to detect. E) It will gradually turn into a white dwarf. Answer: D 7) How do we know that pulsars must be very small in size (radius)? A) We have measured their radii directly in high-resolution telescope images. B) Their small sizes are inferred from careful study of their spectra. C) Some spin so rapidly that if they were larger in size, their surfaces would be moving faster than the speed of light. D) Only very small objects can beam radiation into space. E) This is only a theory that has not yet been confirmed by observations. Answer: C 8) You observe an x-ray burster. Based on current understanding, you can also conclude that you are observing ________. A) a close binary system in which one member is a white dwarf B) a close binary system in which one member is a neutron star C) a close binary system in which one member is a black hole D) a close binary system in which one member is a neutron star and the other is a black hole Answer: B Section 14.3 1) After a massive-star supernova, what is left behind? A) Always a white dwarf B) Always a neutron star C) Always a black hole D) Either a white dwarf or a neutron star E) Ether a neutron star or a black hole Answer: E 2) Which of the following correctly describes how light will be affected as it tries to escape from the vicinity of a massive object like a black hole? A) Light doesn't have mass; therefore, it is not affected by gravity. B) The light will be redshifted. C) The light will be blueshifted. D) The visible light will be redshifted, but higher frequencies, such as x-rays and gamma rays, will not be affected. Answer: B

3) Which of the following statements about black holes is true for an object falling into a black hole? A) From an outside observer's viewpoint, the object falls quickly through the event horizon. B) From an outside observer's viewpoint, light from the object will become increasingly blueshifted as it approaches the event horizon. C) In the object's reference frame, the object will slow down as it falls and come to a stop just before it reaches the event horizon. D) Once the object crosses the event horizon, it can no longer communicate with anything outside the black hole. Answer: D 4) Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? A) Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted. B) Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted. C) The clock will fall faster and faster, reaching the speed of light as it crosses the event horizon. D) The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes. Answer: A 5) Which of the following black holes has the largest event horizon? (Ignore any effects of rotation.) A) A 5 solar mass black hole B) A 10 solar mass black hole C) All black holes have the same size event horizon. Answer: B 6) Which of the following systems is most likely to contain a black hole? A) An x-ray binary in which the unseen companion has a mass 2 MSun B) An x-ray binary in which the unseen companion has a mass 10 MSun C) An x-ray binary that undergoes frequent x-ray bursts D) A binary system in which novae have been observed to occur E) A system that has recently undergone a white dwarf supernova Answer: B 7) Evidence indicates that many gamma-ray bursts are produced by ________. A) supernovae of very high-mass stars B) the explosion of a white dwarf C) bursts of fusion occurring on the surfaces of white dwarfs in binary systems D) bursts of fusion occurring on the surfaces of neutron stars in binary systems Answer: A

8) The figure above shows how the luminosity of supernovae changes over time. Which type of supernova is the most luminous one year after the explosion? A) Massive star supernova B) White dwarf supernova C) Impossible to tell from the graph Answer: A 9) What would happen if Jupiter was suddenly replaced by a black hole with the same mass as Jupiter? A) The orbits of the planets in our solar system would be unaffected. B) The other planets would slowly be pulled into Jupiter, but the Sun would be unaffected. C) The other planets and the Sun would slowly be pulled into Jupiter. D) The entire solar system would rapidly be sucked into the black hole. Answer: A 10) The formula for the Schwarzschild radius of a black hole of mass M is: Rs = 3 ×

What is the Schwarzschild radius of a 100 million-solar-mass black hole? A) 3 km B) 30 km C) 3000 km D) 300 million km E) 3 million km Answer: D Section 14.4 1) Evidence indicates that at least some gamma-ray bursts, including those detected with gravitational waves, are produced by ________. A) the merger of two neutron stars B) the explosion of a white dwarf C) bursts of fusion occurring on the surfaces of white dwarfs in binary systems D) bursts of fusion occurring on the surfaces of neutron stars in binary systems Answer: A 2) Some gamma-ray bursts last only a few seconds and do not appear to come from supernovae. What is the leading hypothesis for the origin of short these gamma-ray bursts? A) New stars forming in the Milky Way B) Bursts of fusion occurring on the surfaces of white dwarfs in binary systems C) Bursts of fusion occurring on the surfaces of neutron stars in binary systems D) The explosion of a white dwarf E) The mergers of two neutron stars Answer: E 10 Copyright © 2022 Pearson Education, Inc.

3) Two neutron stars in a close binary are predicted to spiral into each other and eventually merge because they lose orbital energy through ________. A) the emission of gravitational waves B) strong x-ray emission of their accretion disks C) friction as they orbit through the gas of a surrounding accretion disk D) the exchange of mass from one to the other Answer: A 4) Scientists have detected mergers of black holes that have spiraled into each other by ________. A) detecting gravitational waves from the merger B) observing distant systems that produce unusually strong gamma-ray emission C) observing distant systems that produce unusually strong radio emission D) detecting rapidly pulsating sources of gamma-ray emission Answer: A Short Answer Questions 1) Could our Sun ever undergo a nova or a white dwarf supernova event? Why or why not? Answer: No, because both events occur on white dwarfs in close binary systems. Even after our Sun becomes a white dwarf, such events won't occur because our Sun is not part of a close binary. 2) Why do white dwarf supernovae all have approximately the same maximum luminosity? Answer: White dwarf supernovae occur when the mass of the white dwarf has just exceeded 1.4 MSun. Since the mass is the same and the entire object—made of degenerate matter—explodes at once, the maximum luminosity is the same. 3) What would happen if a small piece (say the size of a paper clip) of neutron star material suddenly appeared on Earth? Answer: The extremely dense material could not be supported by the ordinary material on Earth, and it would plunge to the center of Earth under the action of gravity. Its momentum would carry it past the center, back to the other side, and it would continue to oscillate back and forth through Earth creating a small hole each time (that would rapidly fill with molten rock) until friction finally brought it to rest at the center of Earth. 4) Briefly describe what you would see if your friend plunged into a black hole. Assume you are watching from orbit of the black hole and have a telescope powerful enough so that you can see him clearly as he falls. Answer: As he approached the black hole, he would be stretched by tidal forces, his time would run slow, and light coming from him would be redshifted. The closer he got to the event horizon, the slower time would run. You would never see him cross the event horizon, but he would disappear from view when his light became redshifted out of the range of detection.

5) Why would Earth's orbit be unaffected were the Sun to suddenly become a black hole (with no change in its mass)? Answer: Earth's orbit (and those of the other planets) would remain unchanged since they are far enough away that Newton's law of gravity applies and the gravitational force depends only on the masses of the objects and the distance between them, not on their composition or density. Reading Quiz Questions 1) A white dwarf is ________. A) what most stars become when they die B) a precursor to a black hole C) an early stage of a neutron star D) a brown dwarf that has exhausted its fuel for nuclear fusion Answer: A 2) A typical white dwarf is ________. A) as massive as the Sun but only about as large in size as Earth B) as large in diameter as the Sun but only about as massive as Earth C) about the same size and mass as the Sun but much hotter D) as massive as the Sun but only about as large in size as Jupiter Answer: A 3) If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh ________. A) as much as a truck B) about 5 pounds C) as much as the entire Earth D) as much as an average person Answer: A 4) The maximum mass of a white dwarf is ________. A) about the mass of our Sun B) about 1.4 times the mass of our Sun C) limitless; there is no theoretical limit to the maximum mass of a white dwarf D) about 3 times the mass of our Sun Answer: B 5) What is an accretion disk? A) A disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole B) Any flattened disk in space, such as the disk of the Milky Way Galaxy C) A stream of gas flowing from one star to its binary companion star D) A disk of material found around every white dwarf in the Milky Way Galaxy Answer: A

6) According to our modern understanding, what is a nova? A) An explosion on the surface of a white dwarf in a close binary system B) The explosion of a massive star at the end of its life C) The sudden formation of a new star in the sky D) A rapidly spinning neutron star Answer: A 7) What would happen if a white dwarf gained enough mass to reach the 1.4 solar-mass white dwarf limit? A) The white dwarf would explode completely as a white dwarf supernova. B) The white dwarf would collapse in size, becoming a neutron star. C) The white dwarf would undergo a nova explosion. D) The white dwarf would collapse to become a black hole. Answer: A 8) A neutron star is ________. A) the remains of a star that died in a massive star supernova (if no black hole was created) B) the remains of a star that died by expelling its outer layers in a planetary nebula C) a star made mostly of elements with high atomic mass numbers, so that they have lots of neutrons D) an object that will ultimately become a black hole Answer: A 9) A typical neutron star is more massive than our Sun and about the size (radius) of ________. A) a small asteroid (10 km in diameter) B) Earth C) the Moon D) Jupiter Answer: A 10) If you had something the size of a sugar cube that was made of neutron star matter, it would weigh ________. A) about as much as a large mountain B) about 50 pounds C) as much as the entire Earth D) about as much as a truck Answer: A

11) Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? A) Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars. B) Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star. C) The life of a white dwarf is an ongoing battle between electron degeneracy pressure and neutron degeneracy pressure. D) In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure. Answer: A 12) Pulsars are thought to be ________. A) accreting white dwarfs B) rapidly rotating neutron stars C) unstable high-mass stars D) accreting black holes Answer: B 13) How is an x-ray burst (in an x-ray binary system) similar to a nova? A) Both involve explosions on the surface of stellar corpse. B) Both typically recur every few hours to every few days. C) Both are thought to involve fusion of hydrogen into helium. D) Both result in the complete destruction of their host stars. Answer: A 14) What is the basic definition of a black hole? A) An object with gravity so strong that not even light can escape B) A dead star that has faded from view C) Any object made from dark matter D) A compact mass that emits no visible light Answer: A 15) Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly ________. A) 0.5 solar masses B) 1.4 solar masses C) 3 solar masses D) 10 solar masses Answer: C 16) What do we mean by the event horizon of a black hole? A) It is the point beyond which neither light nor anything else can escape. B) It is the center of the black hole. C) It is the distance from the black hole at which stable orbits are possible. D) It is the place where x-rays are emitted from black holes. Answer: A 14 Copyright © 2022 Pearson Education, Inc.

17) Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). How would Earth's orbit change? A) Earth would almost instantly be sucked into oblivion in the black hole. B) Earth would orbit faster, but at the same distance. C) Earth would slowly spiral inward until it settled into an orbit about the size of Mercury's current orbit. D) It would not change; Earth's orbit would remain the same. Answer: D 18) What do we mean by the singularity of a black hole? A) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions. B) It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole. C) It is the edge of the black hole, where one could leave the observable universe. D) The term is intended to emphasize the fact that an object can become a black hole only once, and a black hole cannot evolve into anything else. Answer: A 19) What makes us think that the star system Cygnus X-1 contains a black hole? A) It emits x-rays as we expect from a system with an accretion disk, but the unseen star in the system is too massive to be a neutron star. B) No light is emitted from this star system, so it must contain a black hole. C) The fact that we see strong x-ray emission tells us that the system must contain a black hole. D) Cygnus X-1 is a powerful x-ray burster, so it must contain a black hole. Answer: A 20) The Schwarzschild radius of a black hole depends on ________. A) only the mass of the black hole B) the observationally measured radius of the black hole C) the way in which the black hole formed D) both the mass and chemical composition of the black hole Answer: A 21) Observational evidence indicates that at least some gamma ray bursts are produced by ________. A) the supernovas of very massive stars that leave behind black holes B) the central black hole of the Milky Way Galaxy C) the same types of close binary systems that produce x-ray bursts D) white dwarf supernovas in distant galaxies Answer: A

22) Suppose two neutron stars or two black holes are closely orbiting one another. What do scientists predict will eventually happen to them, and why? A) Their orbits will spiral inward until the two objects merge because of energy lost through gravitational waves. B) Their orbits will gradually grow larger because of the centrifugal force involved as they circle around each other. C) Their orbits will spiral inward as a result of friction with the surrounding gas until all the gas clears, after which their orbits will remain stable. D) The orbits would remain stable unless there were a third object orbiting along with them. Answer: A 23) When did scientists first detect gravitational waves from mergers of compact objects (pairs of neutron stars or black holes)? A) 2015 B) 1543 C) 1990 D) Gravitational waves have not yet been detected, though scientists hope to detect them soon. Answer: A 24) According to current models, where does the element gold come from? A) Mergers of neutron stars B) The supernova explosions of high-mass stars C) The late stages of fusion in low-mass stars D) The Big Bang Answer: A Concept Quiz Questions 1) Which of the following statements about degeneracy pressure is not true? A) Degeneracy pressure can continue to support an object against gravitational collapse even if the object becomes extremely cold. B) Degeneracy pressure arises from a quantum mechanical effect that we don't notice in our daily lives. C) Black holes form when gravity overcomes neutron degeneracy pressure. D) Degeneracy pressure can arise only from interactions among electrons. Answer: D 2) The more massive a white dwarf, the ________. A) smaller its radius B) higher its temperature C) larger its radius D) higher its luminosity Answer: A

3) Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit? A) Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. B) White dwarfs get hotter with increasing mass, and above the 1.4-solar-mass limit they would be so hot that even their electrons would melt. C) White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit. D) The upper limit to a white dwarf's mass is something we have learned from observations, but no one knows why this limit exists. Answer: A 4) The white dwarf that remains when our Sun dies will be mostly made of ________. A) hydrogen B) helium C) carbon D) neutrons Answer: C 5) Which statement about accretion disks is not true? A) The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass. B) The gas in the inner parts of the disk travels faster than the gas in the outer parts of the disk. C) The gas in the inner parts of the disk is hotter than the gas in the outer parts of the disk. D) Accretion disks are made primarily of hydrogen and helium gas. Answer: A 6) According to present understanding, a nova is caused by ________. A) hydrogen fusion on the surface of a white dwarf B) carbon fusion in the core of a white dwarf C) hydrogen fusion on the surface of a neutron star D) a white dwarf that gains enough mass to exceed the 1.4-solar-mass limit Answer: A 7) Which of the following is not true about differences between novae and supernovae? A) Supernovae eject gas into space, but novae do not. B) Novae are much less luminous than supernovae. C) Novae occur only in binary star systems, while supernovae can occur both among single stars and among binary star systems. D) The same star can undergo novae explosions more than once, but can undergo only a single supernova. Answer: A

8) Will our Sun ever undergo a white dwarf supernova explosion? Why or why not? A) No, because it is not orbited by another star. B) Yes, right at the end of its double shell-fusion stage of life. C) Yes, about a million years after it becomes a white dwarf. D) No, because the Sun's core will never be hot enough to fuse carbon and other heavier elements into iron. Answer: A 9) Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town? A) The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. B) It would rapidly sink to the center of Earth. C) The combined mass of Earth and the neutron star would cause the neutron star to collapse into a black hole. D) It would crash into Earth, throwing vast amounts of dust into the atmosphere that, in turn, would cool the Earth; this is probably what caused the extinction of the dinosaurs. Answer: A 10) Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather than some other type of star? A) Pulsars are easy to identify by their almost perfectly steady periods of pulsation. B) Pulsars are very bright and therefore easy to find. C) Several pulsars are located within a dozen light-years of our solar system, making them useful for finding our solar system. D) We're pretty sure that aliens will have only radio telescopes and not optical telescopes, so they'll have a better chance of seeing pulsars than ordinary stars. Answer: A 11) Which statement about pulsars is true? A) Pulsars can form only in close binary systems. B) All pulsars are neutron stars, but not all neutron stars are pulsars. C) Pulsars can "pulse" no more than about once a day. D) All neutron stars are pulsars. Answer: B 12) How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf? A) The accretion disk around a neutron star is much hotter and emits higher-energy radiation. B) The accretion disk around a neutron star is made mostly of helium, while the accretion disk around a white dwarf is made mostly of hydrogen. C) The accretion disk around a neutron star is more likely to give birth to planets. D) The accretion disk around a neutron star always contains much more mass. Answer: A 18 Copyright © 2022 Pearson Education, Inc.

13) Which statement about Schwarzschild radii is true? A) The Schwarzschild radius of a black hole can be defined only in binary systems. B) The more massive the black hole, the smaller the Schwarzschild radius. C) The Schwarzschild radius of a black hole depends only on its mass. D) The Schwarzschild radius is used to describe the size of neutron stars. Answer: C 14) Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? A) Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted. B) Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted. C) The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes. D) The clock will fall faster and faster, reaching the speed of light as it crosses the event horizon. Answer: A 15) Which of statement below about black holes is not true? A) A spaceship passing near a 10 solar-mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar-mass main-sequence star. B) We have strong observational evidence that black holes really exist. C) If you watch someone else fall into a black hole, you will never see the person cross the event horizon; you'll only see the person fade from view as the light he or she reflects (or emits) becomes more and more redshifted. D) If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon. Answer: A 16) When we see x-rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole? A) Intense x-ray bursts B) Spectral lines from the companion star that alternately shift to shorter and longer wavelengths C) Visible and ultraviolet light from the companion star D) Bright x-ray emission that varies on a time scale of a few hours Answer: A 17) Which of the following observatories is most likely to discover a black hole in a binary system? A) An x-ray observatory in space B) The Hubble Space Telescope C) An infrared observatory in space D) A radio telescope array on the ground Answer: A 19 Copyright © 2022 Pearson Education, Inc.

18) What types of events have scientists so far been able to detect with gravitational wave observatories, such as LIGO? A) X-ray bursts B) Supernovae C) Mergers of closely-orbiting pairs of neutron stars or black holes D) The gradual decay over many years of the orbits of binary neutron stars Answer: C 19) Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole. The black hole is surrounded by an accretion disk. Sometime within the next million years or so, the civilization's planet is likely to be doomed because ________. A) the red giant will probably supernova within the next million years B) jets of material shot out of the accretion disk will shoot down their planet C) the red giant star, which provides most of energy the civilization needs to exist, will soon be destroyed in the accretion disk D) tidal forces from the black hole will rip the planet apart. E) the planet's orbit will gradually decay, as it is sucked in by the black hole Answer: A 20) Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole. The black hole is surrounded by an accretion disk. One foolhardy day, a daring individual in their space force (let's call him Major Tom) decides to become the first of his species to cross the event horizon of the black hole. To add to the drama, he decides to go in wearing only a thin space suit, which offers no shielding against radiation, no cushioning against any forces, and so on. Which of the following is most likely to kill him first (or at least to start the process of killing him first)? A) X-rays from the accretion disk B) Tidal forces due to the black hole C) The crush of gravity at the singularity embedded within the black hole D) The sucking force from the black hole, which will cause his head to explode Answer: A

21) Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole. The black hole is surrounded by an accretion disk. Through a bizarre (and scientifically unexplainable) fluctuation in the space-time continuum, a copy of a book from that civilization arrives on your desk; it is titled Iguoonos: How We Evolved. In the first chapter, you learn that these beings evolved from organisms that lived 5 billion years ago. Which of the following statements should you expect to find as you continue to read this book? A) They evolved on a different planet in a different star system and moved to their current location. B) As a result of traumatic experiences to their evolutionary ancestors, they dislike television. C) Their immediate ancestors were chimpanzees. D) They believe that the presence of two stars in their system was critical to their evolution. E) They evolved from primitive wormlike creatures that had 13 legs, 4 eyes, and bald heads, thus explaining why such critters are now considered a spectacular delicacy. Answer: A Visual Quiz Questions 1) Sirius, the brightest star in the night sky, is actually a binary star system. Sirius A is mainsequence star and Sirius B is a white dwarf. Nearly all the visible light we see from Sirius comes from Sirius A. But when we photograph the system with x-ray light, as shown here, Sirius B is the brighter of the two stars. Why?

A) As a white dwarf, Sirius B is much hotter than Sirius A and thus emits more x-rays. B) As a white dwarf, Sirius B is too small to emit visible light but not too small to emit x-rays. C) Sirius B is brighter in x-rays because it is a nova. D) Sirius B is brighter in x-rays because it is a white dwarf supernova. Answer: A

2) Based on the curves shown here, which of the following statements best describes how we can distinguish a massive star supernova from a white dwarf supernova?

A) A white dwarf supernova is brighter at its peak and over a few months fades more steadily than a massive star supernova. B) For a few seconds, a white dwarf supernova is brighter than a massive star supernova, but after that the two look virtually identical. C) The spectrum of a massive star supernova has two major spectral lines, while a white dwarf supernova has only one. D) The two types of supernovae behave so similarly that we can only distinguish them by studying photographs of the systems taken before the explosions. Answer: A

3) Which of the following diagrams best represents the scale of Earth in comparison to a neutron star? A)

Answer: A

4) Which of the following represents the true shape of a black hole as you'd see it (or measure it) as you flew past it in a spaceship? A)

Answer: A

5) A spacecraft is on a trajectory that happens to be taking it near a black hole. Which diagram shows how the spacecraft's orbit will be affected? A)

Answer: A

6) This series of images shows the pulsar at the center of the Crab Nebula looking bright every 0.033 second. Based on these data and current theory of pulsars, what can we conclude?

A) The pulsar is a neutron star that makes one full rotation every 0.033 second. B) The pulsar is a neutron star whose magnetic field switches on and off every 0.033 second. C) The pulsar is part of a close binary star system in which the two stars complete an orbit every 0.033 second. D) The pulsar has an accretion disk that undergoes an x-ray burst every 0.033 second. Answer: A 7) This painting shows an accretion disk around a black hole in a close binary star system. What physical law explains why matter flowing from the companion star orbits rapidly as it nears the black hole?

A) The law of conservation of angular momentum B) Newton's third law of motion C) Kepler's second law of planetary motion D) Einstein's general theory of relativity Answer: A

8) A binary system that looks like the one depicted in this painting should shine brightly in xrays. Which one of the four labeled regions is the source of most of the x-rays?

A) Region I B) Region II C) Region III D) Region IV Answer: B 9) This graph shows data collected by a gamma ray telescope. What kind of event is it showing?

A) A gamma ray burst from a distant galaxy B) A burst of gamma rays from a flare on a blue supergiant star C) A burst of gamma rays from an explosion on the surface of a neutron star D) The on and off gamma-ray light changes of a pulsar Answer: A

10) This graph shows a gravitational wave signal recorded by the gravitational wave detectors (called LIGO) in two locations. What do models indicate was the cause of this signal?

A) The merger of two black holes in a distant galaxy B) A supernova in a distant galaxy C) The sudden explosion of an entire galaxy D) An x-ray burst on the surface of a neutron star Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy

Figure 14.5, repeated above, shows how the luminosities of supernovae change with time. Answer the following questions, using the information provided in the figure. 1) At peak brightness, the white dwarf supernova is approximately ________ times as luminous as the massive star supernova at peak brightness. A) 1.5 B) 3 C) 10 D) 100 Answer: B 2) The luminosity of the white dwarf supernova 175 days after it reaches peak brightness is about ________ of its luminosity at peak brightness. A) 30% B) 10% C) 3% D) 1% Answer: D

3) Approximately how many days does it take for a white dwarf supernova to decline to 10% of its peak brightness? A) 3 days B) 30 days C) 170 days D) 300 days Answer: B 4) Approximately how many days does it take for a massive star supernova to decline to 10% of its peak brightness? A) 10 days B) 30 days C) 100 days D) 300 days Answer: C 5) Approximately how many days does it take for a massive star supernova to decline to 1% of its peak brightness? A) 3 days B) 30 days C) 170 days D) 300 days Answer: D Chapter Review Questions 1) What is degeneracy pressure, and how is it important to white dwarfs and neutron stars? What is the difference between electron degeneracy pressure and neutron degeneracy pressure? 2) Describe the mass, size, and density of a typical white dwarf. How does the size of a white dwarf depend on its mass? 3) What happens to the electron speeds in a more massive white dwarf, and how does this idea lead to the white dwarf limit for mass? 4) What is an accretion disk? Describe how an accretion disk can provide a white dwarf with a new source of energy. 5) What is a nova? Describe the process that creates a nova and what a nova looks like. 6) What processes may cause a white dwarf supernova? Observationally, how do we distinguish white dwarf and massive star supernovae? 7) Describe the mass, size, and density of a typical neutron star. What would happen if a neutron star came to your hometown? 8) How do we know that pulsars are neutron stars? Are all neutron stars also pulsars? Explain. 30 Copyright © 2022 Pearson Education, Inc.

9) Explain how the presence of a neutron star can make a close binary star system appear to us as an x-ray binary. Why do some of these systems appear to us as x-ray bursters? 10) In what sense is a black hole like a hole in the observable universe? Define the event horizon and Schwarzschild radius. 11) What do we mean by the singularity of a black hole? How do we know that our current theories are inadequate to explain what happens at the singularity? 12) Suppose you are falling into a black hole. How will you perceive the passage of your own time? How will outside observers see time passing for you? Briefly explain why your trip is likely to be lethal. 13) Why do we think that black holes should sometimes be formed by supernovae? What observational evidence supports the existence of black holes? 14) What are gamma-ray bursts, and how do we think they are produced? 15) Why can emission of gravitational waves lead to mergers of white dwarfs, neutron stars, and black holes? What can result from such mergers? How and when were such mergers first detected? Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 16) The white dwarf at the center of the Helix Nebula has a mass three times the mass of our Sun. 17) I observed a white dwarf supernova occurring at the location of an isolated white dwarf (not a member of a binary system). 18) If you want to find a pulsar, you should look near the remnant of a supernova described by ancient Chinese astronomers. 19) Scientists have just learned that there is a 10MSun black hole lurking near Pluto's orbit. 20) If your spaceship flew within a few thousand kilometers of a black hole, you and your ship would be rapidly sucked into it. 21) We can detect black holes with x-ray telescopes because matter falling into a black hole emits x-rays after it smashes into the event horizon. 22) From your point of view, an object falling toward a black hole will never cross the event horizon. 31 Copyright © 2022 Pearson Education, Inc.

23) The best way to search for black holes is to look for small black circles in the sky. 24) Gamma-ray bursts are more likely to be observed in galaxies that are rapidly forming new stars than in galaxies containing only old stars. 25) Gravitational waves are best observed with the Hubble Space Telescope. Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 14 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 26) Which of these objects has the smallest radius? A) A 1.2MSun white dwarf B) A 0.6MSun white dwarf C) Jupiter Answer: No Correct Answer Was Provided. 27) What happens if a white dwarf reaches the 1.4MSun limit? A) It explodes as a white dwarf supernova. B) It collapses to become a neutron star. C) It collapses to become a black hole. Answer: No Correct Answer Was Provided. 28) If we see a nova, we know that we are observing ________. A) a rapidly rotating neutron star B) a gamma ray—emitting supernova C) a white dwarf in a binary system Answer: No Correct Answer Was Provided. 29) A pulsar is ________. A) an unstable high-mass star B) an accreting white dwarf C) a rapidly rotating neutron star Answer: No Correct Answer Was Provided. 30) What would happen if the Sun suddenly became a black hole without changing its mass? A) The black hole would quickly suck in Earth. B) Earth would gradually spiral into the black hole. C) Earth would remain in the same orbit. Answer: No Correct Answer Was Provided. 31) What makes us think that Cygnus X-1 contains a black hole? A) We can directly observe that one member of the system emits no light. B) The unseen object orbited by a luminous star is too massive to be a neutron star. C) The strong x-ray emission from the system means it must contain a black hole. Answer: No Correct Answer Was Provided. 32 Copyright © 2022 Pearson Education, Inc.

32) Viewed from a distance, how would a flashing red light appear as it fell into a black hole? A) It would appear to flash more quickly. B) Its flashes would appear bluer. C) Its flashes would shift to the infrared part of the spectrum. Answer: No Correct Answer Was Provided. 33) Which of these black holes exerts the weakest tidal forces on an object near its event horizon? A) A 10MSun black hole B) A 100MSun black hole C) A 106MSun black hole Answer: No Correct Answer Was Provided. 34) Current evidence indicates that most gamma-ray bursts come from ________. A) supernovae that leave a black hole behind B) unusually massive x-ray bursters C) the merger of two black holes Answer: No Correct Answer Was Provided. 35) Why do some pairs of neutron stars collide and merge? A) Occasionally a neutron star moving through space will collide head-on with another neutron star. B) Gravitational waves from close neutron star binary systems carry away orbital energy and angular momentum. C) Electromagnetic waves from pulsars carry away angular momentum. Answer: No Correct Answer Was Provided.

Inclusive Astronomy Use these questions to reflect on participation in science. 36) Black Holes in Popular Culture. Expressions such as "it disappeared into a black hole" are now common in popular culture. Give a few other examples of popular expressions in which the term black hole is used but is not meant to be taken literally. In what ways are these uses correct in their analogies to real black holes? In what ways are they incorrect? Why do you think such an esoteric scientific idea as that of a black hole has captured the public imagination? 37) Group Discussion: Graduate Students and Nobel Prizes. A few astronomers have had the opportunity to do Nobel Prize—winning research while still in graduate school. This discussion asks you to reflect on the reasons some of these people have actually received the Nobel Prize and others have not. a. The Extraordinary Claims box on page 377 briefly discusses Subrahmanyan Chandrasekhar, who won the 1983 Nobel Prize in Physics in part for his discovery in 1930 of the white dwarf limit. He did that work while still a graduate student, and at the time he was ridiculed by the famed astronomer Sir Arthur Stanley Eddington. Chandrasekhar, who was from India, thought that at least some of the ridicule may have been racially motivated. Do you find this possibility plausible? Why or why not? Do you think it could have played a role in the delay of more than 50 years between the time of Chandrasekhar's discovery and his eventual Nobel Prize? b. The Extraordinary Claims box and Section 18.2 discuss the work of Jocelyn Bell Burnell, who discovered the first pulsar in 1967 while working as a graduate student under the mentorship of Antony Hewish. Hewish had led work on the design and construction of the radio telescope that Burnell used in making her discovery. The 1974 Nobel Prize in Physics was awarded based on the pulsar discovery, but it was awarded only to Hewish rather than jointly to him and Burnell. Do you think Burnell should have shared the prize? Why or why not? In what sense could Hewish have been more deserving? Could cultural biases have influenced the Nobel Committee? Do you think similar cultural biases could still be influential today? Why or why not? The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 38) Too Strange to Be True? Despite strong theoretical arguments for the existence of neutron stars and black holes, many scientists rejected the possibility that such objects could exist until they were confronted with very strong observational evidence. Some people claim that this type of scientific skepticism demonstrates an unwillingness on the part of scientists to give up their deeply held scientific beliefs. Others claim that this type of skepticism is necessary for scientific advancement. What do you think? Defend your opinion. 39) Gravitational-Wave Detection. Go to the website for the Laser Interferometer Gravitational Observatory. Look up the detections of gravitational waves that it has made. How many detections have there been so far? What kinds of objects have made the detected waves? What are the approximate distances of those objects? Write a short report on what you learn.

40) Unanswered Questions. You have seen in this chapter that current theoretical models make numerous predictions about the nature of black holes but leave many questions unanswered. Briefly describe one important but unanswered question related to black holes. If you think it will be possible to answer this question in the future, describe how we could find an answer, being as specific as possible about the evidence needed. If you think the question will never be answered, explain why you think it is impossible to answer. 41) Group Activity: A Closer Look at Cygnus X-1. The close binary system Cygnus X-1 contains a supergiant of spectral type O and a black hole with a mass of about 15MSun. Consider this system and the artist's conception of it in Figure 14.15 as you work together as a group to do the following.Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39. a. Use the H-R diagram in Figure 12.10 to estimate the radius of the supergiant star. b. Use Cosmic Calculations 14.1 to estimate the Schwarzschild radius of the black hole. How much larger is the supergiant star than the black hole? c. The supergiant star in Figure 14.15 is drawn about 5 cm across. Use your result from part b to determine approximately how large (in radius) the black hole would be in this figure if it were drawn to scale. How far off is the figure from this approximate size? d. Discuss whether it is easy or difficult for matter to fall directly into a black hole of this size. e. Notice that the stream of matter from the supergiant star in Figure 14.15 is flowing off to the side of the black hole and onto an accretion disk, rather than straight into the black hole. Take turns proposing reasons the stream goes off to the side, and then come to a group consensus on the reason for this flow of matter. f. Given your prior results, discuss whether or not the rendering of Figure 14.15 is an "accurate enough" portrayal of the system. What, if anything, would your group do differently if you were asked to make an artist's rendering of the Cygnus X-1 system? Investigate Further Life Stories of Stars. Write a one- to two-page life story for the scenarios in the questions below. Each story should be detailed and scientifically correct but also creative. That is, it should be entertaining while at the same time showing that you understand stellar evolution. Be sure to state whether "you" are a member of a binary system. 42) You are a white dwarf of 0.8MSun. 43) You are a neutron star of 1.5MSun. 44) You are a black hole of 10MSun. 45) You are a white dwarf in a close binary system and are accreting matter from your companion star. 46) Census of Stellar Corpses. Which kind of object do you think is most common in our galaxy: white dwarfs, neutron stars, or black holes? Explain your reasoning.

47) Fate of an X-Ray Binary. The x-ray bursts that happen on the surface of an accreting neutron star are not powerful enough to accelerate the exploding material to escape velocity. Predict what will happen in an x-ray binary system in which the companion star eventually feeds over 3 solar masses of matter into the neutron star's accretion disk. 48) Why Black Holes Are Safe. Explain why the principle of conservation of angular momentum makes it very difficult to fall into a black hole. 49) Surviving the Plunge. The tidal forces near a black hole with a mass similar to that of a star would tear a person apart before that person could fall through the event horizon. Black hole researchers have pointed out that a fanciful "black hole life preserver" could help counteract those tidal forces. The life preserver would need to have a mass similar to that of an asteroid and would need to be shaped like a flattened hoop and placed around the person's waist. In what direction would the gravitational force from the hoop pull on the person's head? In what direction would it pull on the person's feet? Based on your answers, explain in general terms how the gravitational forces from the "life preserver" would help to counteract the black hole's tidal forces. 50) Black Holes. Andrew Hamilton, a professor at the University of Colorado, maintains a website with a great deal of information about black holes and what it would be like to visit one. Visit his site and investigate some aspect of black holes that you find particularly interesting. Write a short report on what you learn. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 51) Schwarzschild Radii. Calculate the Schwarzschild radius (in kilometers) for each of the following. a. A 108MSun black hole in the center of a quasar b. A 5MSun black hole that formed in the supernova of a massive star c. A mini—black hole with the mass of the Moon d. A mini—black hole formed when a super-advanced civilization decides to punish you (unfairly) by squeezing you until you become so small that you disappear inside your own event horizon 52) The Crab Nebula Pulsar Winds Down. Theoretical models of the slowing of pulsars predict that the age of a pulsar is approximately equal to p/(2r), where p is the pulsar's current period and r is the rate at which the period is slowing with time. Observations of the pulsar in the Crab Nebula show that it pulses 30 times per second, so p = 0.0333 second, but the time interval between pulses is growing longer by 4.2 × 10-13 second with each passing second, so r = 4.2 × 10-13 second per second. Using that information, estimate the age of the Crab Nebula pulsar. How does your estimate compare with the true age of the pulsar, which was born in the supernova observed in A.D. 1054?

53) A Water Black Hole. A clump of matter does not need to be extraordinarily dense in order to have an escape velocity greater than the speed of light, as long as its mass is large enough. You can use the formula for the Schwarzschild radius RS to calculate the volume 4πRS3/3 inside the event horizon of a black hole of mass M. What does the mass of a black hole need to be in order for its mass divided by its volume to be equal to the density of water (1 g/cm3)? 54) Energy of a Supernova. In a massive star supernova explosion, a stellar core collapses and forms a neutron star roughly 10 kilometers in radius. The gravitational potential energy released in such a collapse is approximately equal to GM2/r, where M is the mass of the neutron star, r is its radius, and the gravitational constant is G = 6.67 × 10-11 m3/(kg × s2). Using this formula, estimate the amount of gravitational potential energy released in a massive star supernova explosion. How does it compare to the amount of energy released by the Sun during its entire main-sequence lifetime? 55) Energy of a Black Hole Merger. Models indicate that the gravitational-wave signal shown in Figure 14.21 came from the merger of two black holes with masses of 29MSun and 36MSun (respectively), and resulted in a single black hole with a mass of 62MSun. The difference in total mass between the start and the finish of the merger corresponds to the amount of energy carried away in the form of gravitational waves. Use Einstein's formula E = mc2 to calculate this amount of energy. Be sure to put the mass in units of kilograms and the speed of light in meters per second, so that the resulting energy has units of joules. Compare your answer to the energy released by a supernova (from Problem 54) and to the energy released by the Sun during its entire main-sequence life.

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 15 Our Galaxy Section 15.1 1) What is the approximate diameter of the disk of the Milky Way? A) 100 light-years B) 1000 light-years C) 10,000 light-years D) 100,000 light-years E) 1,000,000 light-years Answer: D 2) The thickness of the disk of the Milky Way is about ________ the diameter of the disk. A) 1/10th of B) 1/1000th of C) 1/1,000,000th of D) the same as Answer: B 3) Approximately how far is the Sun from the center of the galaxy? A) 27 light-years B) 270 light-years C) 2700 light-years D) 27,000 light-years E) 27 million light-years Answer: D 4) Which of the following are typically found in the halo of our galaxy? A) Open star clusters B) Stars of spectral types O and B C) Globular star clusters D) Cold gas and dust E) All of the above Answer: C 5) Which of the following typically orbit within the disk of our galaxy? A) Stars of spectral types O and B B) Globular star clusters C) The Large and Small Magellanic Clouds D) Other galaxies Answer: A

6) Which of the following represent the oldest stars of the Milky Way? A) The Sun and other stars with similar mass B) O stars C) Red giant stars in spiral arms D) Cepheid variable stars E) Stars in globular clusters Answer: E 7) How did Harlow Shapley conclude that the Sun was not in the center of the Milky Way Galaxy? A) By looking at the shape of the "milky band" across the sky B) By mapping the distribution of stars in the galaxy C) By mapping the distribution of globular clusters in the galaxy D) By mapping the distribution of gas clouds in the spiral arms E) By looking at other nearby spiral galaxies Answer: C 8) Why can't we see the center of our galaxy with our eyes? A) We are in the center of the Milky Way. B) There are no stars in the center of the Milky Way, just a supermassive black hole. C) Interstellar dust and gas absorbs and scatters visible light before it can reach us from the center. D) The center of the Milky Way does not emit enough visible light. E) Stars are too densely spaced in the plane of our galaxy to see all the way to the center. Answer: C 9) Approximately how long does it take stars in our region of the Milky Way to complete an orbit around the center of the Milky Way Galaxy? A) 20,000 years B) 200,000 years C) 2 million years D) 200 million years E) 2 billion years Answer: D 10) Which of the following best describes the orbits of stars in the halo? A) Halo stars have orbits confined to a relatively thin plane. B) Halo stars have elliptical orbits, with random orientations. C) Halo stars have elliptical orbits, but all orbiting in the same direction. D) Some halo stars orbit around the galactic center but others never pass through the plane of the galactic disk. E) Halo stars orbit the centers of their globular clusters, but do not orbit the center of the galaxy. Answer: B

11) What observational evidence supports the conclusion that most of the mass of the Milky Way is in the form of dark matter? A) There is no observational evidence; it is only a theoretical idea based on computer models indicating that the Milky Way could not have formed unless it had much more mass than it contains in stars and gas. B) Although dark matter emits no visible light, we have detected it with radio telescopes. C) We can see the dark matter as dark blotches in the sky, such as the dark lanes that are visible within the Milky Way in the night sky. D) The orbital speeds of stars and gas clouds far from the galactic center are surprisingly high, suggesting that these stars and gas clouds are feeling gravitational effects from unseen matter. Answer: D 12) The average orbital speed of a star around the center of our galaxy depends primarily on ________. A) the mass of the Milky Way's central black hole B) the mass of the entire galaxy, including the halo C) whether the star is in the disk or halo of the galaxy D) the mass of the galaxy inside its orbit Answer: D 13) Which of the following best describes stars in the halo of our Galaxy? A) Young, red, and dim with low abundance of heavy elements B) Young, blue, and bright with high abundance of heavy elements C) Old, red, and dim with low abundance heavy elements D) Old, red, and dim with high abundance of heavy elements E) Old, red, and bright with low abundance of heavy elements Answer: C 14) How would you expect a star that formed recently in the disk of the galaxy to differ from one that formed early in the history of the disk? A) It should have a higher fraction of elements heavier than hydrogen and helium. B) It should orbit the galactic center at a much higher rate of speed. C) It should be higher in mass. D) It should be moving very fast relative to the Earth. Answer: A

Section 15.2 1) What does the interstellar medium consist of? A) Many individual stars of varying mass B) Intermediate mass stars C) Asteroids, comets, and planets D) Gas and dust Answer: D 2) What do astronomers typically refer to as "heavy elements"? A) Elements that are heavier than iron B) Elements that are heavier than carbon C) Elements that are heavier than uranium D) Elements besides hydrogen and helium Answer: D 3) How can we see through the interstellar medium? A) By observing in high-energy wavelengths such as x-rays and long wavelengths of light such as radio waves and infrared B) By observing only the brightest visible sources C) By using only the biggest telescopes D) By using telescopes above the Earth's atmosphere E) We cannot see through the interstellar medium. Answer: A 4) What is a shock front? A) A wave of pressure that moves faster than the speed of sound B) A wave of pressure that moves slightly slower than the speed of sound C) A wave of pressure that moves faster than the speed of light D) A wave of electromagnetic energy that can create electrical shocks E) The wave created when protons slam into electrons Answer: A 5) What are cosmic rays? A) Subatomic particles that travel close to the speed of light B) A form of light with shorter wavelength than gamma rays C) Fast-moving dust particles in the interstellar medium D) Any light waves from space Answer: A 6) Where are most elements heavier than hydrogen and helium made? A) In the gas between the stars B) In the cores of stars, in supernovae, and during neutron star mergers C) All elements were made about 5 minutes after the universe began. D) In the cool atmospheres of red giant stars E) In white dwarfs Answer: B 4 Copyright © 2022 Pearson Education, Inc.

7) What is the primary way in which stars with masses similar to the Sun ultimately return some of their material to the interstellar medium? A) By exploding as white dwarf supernovae B) Through jets they may have during the protostar stage C) Through planetary nebulae D) Through the winds they have during their main-sequence lives E) Stars with masses similar to the Sun do not recycle any material back into the interstellar medium. Answer: C 8) What is the primary way in which high-mass stars recycle material into the interstellar medium? A) Through stellar winds and supernova explosions B) Through the formation of planetary nebulae C) Through protostar formation D) Through stellar winds alone Answer: A 9) How are interstellar bubbles of hot, ionized gas made? A) By the collapse of a gas cloud to form stars B) By the ejection of planetary nebulae from low-mass stars C) By the winds of massive stars and supernovae explosions D) By collisions between the Milky Way and satellite dwarf galaxies E) By the rapidly rotating magnetic fields of pulsars Answer: C 10) Sound waves in the interstellar medium ________. A) cannot exist at all B) travel so slowly that they are undetectable C) cannot be heard by human ears, but do indeed travel through the gas D) travel extremely quickly and are therefore very loud Answer: C 11) Which of the following indicates the presence of high-mass stars in a region of recent star formation? A) Closely spaced low-mass stars B) Ionization nebulae C) Globular clusters D) Planetary nebulae Answer: B

12) How should we expect that the interstellar medium of the Milky Way will be different in 50 billion years? A) The total amount of gas will be much less than it is today. B) Thanks to the recycling of the star-gas-star cycle, the interstellar medium should look about the same in 50 billion years as it does today. C) The total amount of gas will be much greater, since many stars will undergo supernovae between now and then. D) The total amount of gas will be about the same, but it will contain a much higher percentage of elements heavier than hydrogen and helium. Answer: A 13) What produces the 21-cm line that we use to map out the Milky Way Galaxy? A) Atomic hydrogen B) Ionized hydrogen C) Molecular hydrogen D) Carbon monoxide E) Helium Answer: A 14) Where do most dust grains form? A) In supernovae B) In the winds of red giant stars C) In planetary nebulae D) In molecular clouds Answer: B

15) The image of our galaxy in radio emission from CO, mapping the distribution of molecular clouds, is closest to the image of our galaxy in ________.

A) radio emission from H atoms B) short wavelength infrared light from most of the stars C) visible light, which is closest to how the night sky appears from Earth D) x-rays from hot gas bubbles in the disk E) gamma ray from cosmic-ray collisions with gas atoms Answer: E 7 Copyright © 2022 Pearson Education, Inc.

16) Where does most star formation occur in the Milky Way today? A) In the halo B) In the bulge C) In the spiral arms D) In the galactic center E) Uniformly throughout the Galaxy Answer: C 17) Where would you least expect to find an ionization nebula? A) In the galactic disk B) Near a hot, young star C) In a spiral arm D) In the halo of our galaxy Answer: D 18) Which of the following provides the strongest evidence that halo stars are older, on average, than disk stars? A) Halo stars orbit in random directions, but disk stars have more ordered orbits. B) There are no blue halo stars. C) There are no red disk stars. D) Theories of galaxy formation tell us that the halo formed earlier than the disk. Answer: B 19) Suppose you were able to measure the composition of the first star that formed in the Milky Way's history. What would you expect it to have been made of at the time of its birth? A) 100% hydrogen B) 75% hydrogen, 25% helium, and less than 0.1% other elements C) 98% hydrogen, 2% helium, and less than 0.1% other elements D) 70% hydrogen, 28% helium, and 2% other heavy elements Answer: B

Section 15.3 1) Which of the following would you expect to be very common in globular clusters? A) High-mass main-sequence stars B) Low-mass main-sequence stars C) Supernova remnants D) X-ray binaries E) Supergiant stars Answer: B 2) Which of the following statements about the disk of the Milky Way is generally true? A) The typical age of disk stars is greater than that of halo stars. B) Disk stars are all younger than 5 billion years. C) Disk stars have a higher proportion of heavy elements, on average, than halo stars. D) Disk stars orbit around the Galactic center in orbits of random inclination and direction. E) The diameter of the disk is about 1 million times its thickness. Answer: C 3) Which of the following statements is generally true for stars in the halo? A) Halo stars all orbit the center of the galaxy in approximately the same plane. B) Halo stars always remain in the halo, never passing through the disk of the galaxy. C) All halo stars will end their main-sequence lives within the next 100 million years. D) Halo stars have a much smaller proportion of elements besides hydrogen and helium than our Sun. E) Halo stars come in a wide variety of ages. Answer: D 4) Why are stars no longer forming in the galactic halo? A) Frequent supernovae blew all the halo gas out into intergalactic space. B) There was never star formation in the halo; its stars were ejected from the disk. C) Only low-mass stars formed in the halo, so there were no stellar winds or supernovae to recycle gas. D) The cold molecular gas required for star formation is in the galactic disk. Answer: D 5) What evidence suggests that some of the stars in the halo of the Milky Way Galaxy came from mergers with other galaxies? A) Globular clusters are typically found only in the halo. B) Some halo stars with similar and distinct chemical compositions move together in organized streams. C) Some halo stars are older than our Galaxy. D) Halo stars have randomly oriented orbits. Answer: B

Section 15.4 1) The galactic center lies in the direction of which constellation? A) Orion B) The Big Dipper C) Leo D) Sagittarius E) Taurus Answer: D 2) Which of the following provides the strongest evidence to support the claim that there is a black hole at the center of our galaxy? A) We observe many sources of x-rays near the center of our galaxy. B) Infrared and radio observations show a large concentration of gas near the center of our galaxy. C) The motions of the gas and stars indicate that the galactic center has a mass millions of times that of the Sun within a region less than 1 light-year across. D) We observe a large, dark object that absorbs all light at the center of our galaxy. Answer: C 3) What is SgrA*? A) A source of bright x-ray emission coming from the entire constellation of Sagittarius B) A source of bright radio emission in the center of our galaxy C) A source that is bright in the visible wavelengths in the center of our galaxy D) The brightest star in the constellation Sagittarius E) The bulge at the center of our galaxy Answer: B 4) How do we study the region near the center of our own galaxy, the Milky Way? A) High-resolution images acquired with visible light telescopes B) Observations at radio, infrared and x-ray wavelengths C) We cannot directly observe the galactic center, so we infer its characteristics from theoretical models. D) We look at the centers of other galaxies and assume that our Milky Way's center is similar. E) We can study the galactic center only by observing gravitational waves. Answer: B 5) What is thought to be the origin of enormous x-ray flares that occasionally come from the direction of Sgr A*? A) X-ray binary systems that lie close to the galactic center B) Massive-star supernovae near the galactic center C) Comet-sized objects being torn apart by the tidal forces of the black hole near the galactic center D) Supernova shock waves plowing into dense regions of the interstellar medium near the galactic center Answer: C 10 Copyright © 2022 Pearson Education, Inc.

Short Answer Questions 1) Explain why, even though there are sound waves in space, it is still true that "no one can hear you scream" (assuming that the sound of your scream travels only through space, not through radio communication). Answer: Screams, and any sound that we make, are waves of gas atoms and molecules. We perceive sound when these waves of gas particles strike our eardrums and cause them to vibrate, but it takes many trillions of such particles to move them noticeably. In interstellar space, where the gas density is extremely low, there are too few (if any) collisions with our eardrums for us to hear sound. 2) Why do spiral arms tend to be blueish in color? Answer: They are regions of enhanced star formation, and in general, only young stars are blue. 3) Briefly describe how we can use the orbital characteristics of stars at many distances from the galactic center to determine the distribution of mass in the Milky Way. Answer: Using the orbital velocity law, related to Newton's version of Kepler's third law, we can determine the mass of the galaxy that lies within a particular orbit (and thus distance from the center) if we know the average orbital velocity of stars or clouds at that distance. Therefore, by applying the orbital velocity law to the orbits of stars at many distances from the galactic center, we can determine how much mass lies within each radius. 4) Briefly explain why stars that formed early in the history of the galaxy contain a smaller proportion of heavy elements than stars that formed more recently. Answer: The star-gas-star cycle gradually enriches the interstellar medium with heavy elements. Therefore, stars that formed early in the history of the galaxy were formed before much enrichment from supernova events could take place. Stars that formed more recently were formed from material that had been enriched by the many previous generations of stars. Reading Quiz Questions 1) How does the diameter of the disk of the Milky Way Galaxy compare to its thickness? A) The diameter is about 100 times as great as the thickness. B) The diameter and thickness are roughly equal. C) The diameter is about 10 times as great as the thickness. D) The diameter is about 100,000 times as great as the thickness. Answer: A 2) What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy? A) The galaxy's disk B) The galaxy's bulge C) A globular cluster D) The galaxy's halo Answer: B

3) The Sun's location in the Milky Way Galaxy is ________. A) near the galactic center B) in the galactic disk, roughly halfway between the center and the outer edge of the disk C) in the halo of the galaxy, about 27,000 light-years above the galactic disk D) at the outer edge of the galactic disk Answer: B 4) What do we mean by the interstellar medium? A) The gas and dust that lies in between the stars in the Milky Way galaxy B) The dust that fills the halo of the Milky Way galaxy C) The middle section of the Milky Way galaxy D) The name of an oracle who can channel messages from beings that live near the star called Vega Answer: A 5) What are the Magellanic Clouds? A) Two small galaxies that orbit the Milky Way Galaxy B) Two nebulae located in the disk of the Milky Way galaxy and visible only from the Southern Hemisphere C) Star-forming clouds found in the constellation Orion D) The clouds of dust and gas found interspersed in many places throughout the Milky Way Galaxy Answer: A 6) How do disk stars orbit the center of the galaxy? A) They all orbit in roughly the same plane and in the same direction. B) They have orbits randomly inclined and in different directions relative to the galactic center. C) They follow spiral paths along the spiral arms. D) They follow orbits that move up and down through the disk, typically taking them about 50,000 light-years above and below the disk on each orbit. Answer: A 7) How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path? A) By applying Newton's version of Kepler's third law (or the equivalent orbital velocity formula) to the Sun's orbit around the center of the Galaxy B) By counting the number of stars visible in this region of the galaxy C) By estimating the amount of gas and dust in between the stars D) By using the law of conservation of angular momentum to calculate the orbital speeds of nearby stars Answer: A

8) Elements heavier than hydrogen and helium constitute about ________ of the mass of the Milky Way's interstellar medium. A) 0.002 % B) 2 % C) 70 % D) 98% Answer: B 9) What do we mean by the star-gas-star cycle? A) It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium. B) It is the idea that stars in close binary systems can exchange gas with one another. C) It is the set of nuclear reactions by which heavy elements are produced in the cores of massive stars. D) It describes the orbits of the stars and interstellar medium around the center of the galaxy. Answer: A 10) What are cosmic rays? A) Subatomic particles that travel close the speed of light B) Another name for gamma rays and x-rays C) Fast moving dust particles in the interstellar medium D) The highest-energy form of light E) Lasers used as weapons by extraterrestrials Answer: A 11) The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with ________. A) radio telescopes observing at a wavelength of 21 centimeters B) ground-based visible-light telescopes C) space-based ultraviolet telescopes D) x-ray telescopes Answer: A 12) Interstellar dust consists mostly of ________. A) microscopic particles of carbon and silicon B) ozone "smog" C) hydrogen and helium atoms D) tiny grains of water ice E) the same tiny particles found in household dust Answer: A

13) Which of the following models best explains why our galaxy has spiral arms? A) The spiral arms are a wave of star formation caused by a wave of density propagating outward through the disk of the galaxy. B) The spiral arms are composed of groups of stars that are bound together by gravity and therefore always stay together as the galaxy rotates. C) The spiral arms were imprinted on the galaxy at its birth. Ever since, like a coiling rope, the spiral arms have been wound tighter with each galactic rotation. D) No model can explain the existence of the arms, which rotate with the galaxy like the fins of a giant pinwheel toy. Answer: A 14) What do we mean by a protogalactic cloud? A) A cloud of hydrogen and helium that contracts to become a galaxy B) A term once used historically to refer to any galaxy C) A cloud-like halo that surrounds the disks of spiral galaxies D) A cloud of gas that was once a galaxy Answer: A 15) Most stars in the Milky Way's halo are ________. A) very old B) found inside molecular clouds C) very young D) blue or white in color Answer: A 16) What is an ionization nebula? A) A region of hot, low-density gas surrounding a recent supernova B) A clump of gas that will soon give birth to a new star C) A colorful cloud of gas that glows because it is heated by light from nearby hot stars D) A name sometimes used to describe spiral galaxies besides the Milky Way Answer: C 17) Where does most star formation occur in the Milky Way Galaxy? A) In the spiral arms B) Everywhere throughout the galactic disk C) In the central bulge D) Within the halo Answer: A 18) What do halo stars do differently from disk stars? A) Halo stars orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane. B) Halo stars remain stationary, quite unlike disk stars that orbit the galactic center. C) Halo stars explode as supernovae much more frequently than disk stars. D) Halo stars orbit the center of the galaxy at much lower speeds than disk stars. Answer: A 14 Copyright © 2022 Pearson Education, Inc.

19) Based on observations, which of the following statements about stars in the Milky Way is generally true? A) The older the star, the lower its abundance of heavy elements B) The older the star, the bluer its color C) The older the star, the faster its orbital speed D) The younger the star, the higher its mass E) The less massive the star, the older it is Answer: A 20) What kind of object do we think lies in the center of the Milky Way Galaxy? A) A black hole of about 4 million solar masses B) A gigantic x-ray binary system C) A dense cluster of young, hot stars D) An enormous collection of dark matter, explaining why we detect no light at all from the galactic center Answer: A Concept Quiz Questions 1) If we could see our own galaxy from 2 million light-years away, it would appear ________. A) as a flattened disk with a central bulge and spiral arms, spanning a few degrees across the sky B) as a faintly glowing band of light stretching all the way around the sky C) to fill the sky with widely spaced stars D) like a single, dim star Answer: A 2) How does the interstellar medium affect our view of most of the galaxy? A) It prevents us from seeing most of the galactic disk with visible and ultraviolet light. B) It absorbs all wavelengths of light. C) It produces so much visible light that it blocks our view of anything beyond it. D) It has no effect on visible-light observations, but prevents us from studying the galactic center with radio waves or x-rays. Answer: A 3) Applying Newton's version of Kepler's third law (or the orbital velocity law) to the a star orbiting 40,000 light-years from the center of the Milky Way galaxy allows us to determine ________. A) the mass of the Milky Way Galaxy that lies within 40,000 light-years of the galactic center B) the total mass of the entire Milky Way Galaxy C) the mass of the black hole thought to reside in the center of the galaxy D) the percentage of the galaxy's mass that is made of dark matter Answer: A

4) How would you expect a star that formed recently in the disk of the galaxy to differ from one that formed early in the history of the disk? A) It should have a higher fraction of elements heavier than hydrogen and helium. B) It should be higher in mass. C) It should be much more luminous. D) It should orbit the galactic center at a much higher rate of speed. E) All of the above differences would be expected. Answer: A 5) Suppose a scientist holds a press conference at which he claims that 10% of the matter in the Milky Way is in the form of dust grains. Does his claim seem reasonable? Why or why not? A) The 10% figure is too high because there are not enough heavy elements to make that much dust. B) It is reasonable because we already know that interstellar dust obscures our view through the disk of the galaxy. C) The 10% figure is too low because most of the mass of the galaxy is in the form of interstellar dust. D) It seems reasonable as long as we assume that red giant stars, which produce dust grains in their stellar winds, are more common than we thought. Answer: A 6) The most common form of gas in the disk of the Milky Way galaxy is ________. A) atomic hydrogen gas B) molecular hydrogen C) gas in hot bubbles D) gas in stellar winds Answer: A 7) How should we expect the Milky Way's interstellar medium to be different in 50 billion years than it is today? A) The total amount of gas will be much less than it is today. B) The total amount of gas will be about the same, but the percentage of elements heavier than hydrogen and helium will have risen from the current 2% to more than 50%. C) The total amount of gas will be much greater because many stars will undergo supernovae between now and then. D) Thanks to the recycling of the star-gas-star cycle, the interstellar medium should look about the same in 50 billion years as it does today. Answer: A 8) Over time, the star-gas-star cycle leads the gas in the Milky Way to ________. A) have a greater abundance of heavy elements B) have a lower abundance of heavy elements C) become denser and have a greater abundance of heavy elements D) become denser and hotter Answer: A

9) Suppose you want to observe and study the radiation from gas inside an interstellar bubble created by a supernova. Which of the following observatories will be most useful? A) An x-ray telescope in space B) A visible-light telescope on a mountain summit C) An infrared telescope in space D) The Hubble Space Telescope Answer: A 10) If you could watch a time-lapse movie of the interstellar medium over hundreds of millions of years, what would you see? A) Gas that is often moving at high speed, particularly after one or more supernovae, and constantly changing form between molecular clouds, atomic hydrogen, and hot, ionized bubbles and superbubbles. B) Gas that changes only in very slow and steady ways, so that the movie would in fact be quite boring. C) The entire disk of the Milky Way would pulsate in and out as it contracts to form stars and then blows out in supernovae and then contracts to form stars again and so on. D) The movie would alternate back and forth between being very bright when there is a lot of gas and very dark when there is very little gas. Answer: A 11) All the following types of objects are found almost exclusively in the disk (rather than the halo) of the Milky Way except ________. A) globular clusters B) young stars C) x-ray binaries D) high-mass, red supergiant stars Answer: A 12) Red and orange stars are found evenly spread throughout the galactic disk, but blue stars are typically found ________. A) only in or near star-forming clouds B) in the halo C) only in the central bulge D) also evenly spread throughout the galactic disk Answer: A 13) Which of the following statements comparing halo stars to our Sun is not true? A) Most stars in the halo have either died or are in their final stages of life, while the Sun is only in about the middle of its lifetime. B) Most stars in the halo have cooler surface temperatures than the Sun. C) Most stars in the halo are less luminous than the Sun. D) Most stars in the halo contain a much lower percentage of heavy elements than the Sun. Answer: A

14) Most nearby stars move relative to the Sun at speeds below about 30 km/s. Suppose you observe a nearby star that is moving much faster than this (say, 300 km/s). Which of the following is a likely explanation for its high speed? A) It is probably a halo star that is currently passing through the disk. B) It is a very young star, recently formed. C) It has been pushed to high speed by the shock wave from a nearby supernova. D) It is a high mass star. Answer: A 15) What evidence suggests that most of the mass of the Milky Way is in the form of dark matter? A) The orbital speeds of stars far from the galactic center are surprisingly high. B) Although dark matter emits no visible light, we have detected its radio emissions. C) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk. D) Our view of distant galaxies is often obscured by dark blotches, which are presumably made of dark matter. Answer: A 16) Spiral arms appear bright because ________. A) they contain more hot young stars than other parts of the disk B) they contain far more stars than other parts of the galactic disk C) they contain more molecular clouds than other parts of the disk D) they are the only places where we find stars within the disk of the galaxy Answer: A 17) How did star formation likely proceed in the protogalactic cloud that formed the Milky Way? A) The stars that formed first could orbit the center of the galaxy in any direction at any inclination. B) The stars that formed first eventually settled into a galactic disk, circling the center of the galaxy. C) The protogalactic cloud gradually formed stars, starting from the center of the galaxy working outward. D) The protogalactic cloud gradually formed stars, starting from the outer edges of the spiral arms and working inward. Answer: A

18) If we could watch spiral arms from a telescope situated above the Milky Way over 500 million years, what would we see happen? A) Stars will move through the spiral arms, bunching up closer as they pass through. Young hot stars will form and die within the arms before having a chance to move out. B) The spiral arms will seem to "wind up," wrapping more and more tightly around the center of the Galaxy. C) The spiral arms will quickly dissipate and fade away, because they are a temporary phenomenon that should only last for a million years or so. D) The spiral arms will eventually unwind, as centripetal forces send the stars flying outward into intergalactic space. Answer: A 19) What is the best evidence for an extremely massive black hole in the center of the Milky Way? A) The orbits of stars in the center of the galaxy indicate that the presence of an approximately 4 million solar-mass object in a region no larger than our solar system. B) Huge amounts of x-rays are pouring out of the center of the galaxy. C) The center of our galaxy hosts a pulsar that is spinning so fast that it could only be a black hole. D) We observe stars vanishing in the center of the Galaxy as they are sucked into the black hole. Answer: A 20) Which of the following statements is not true of the object known as Sgr A* in the center of our Galaxy? A) It is by far the brightest source of visible light lying in the direction of the galactic center. B) It is thought to harbor a black hole of about 4 million solar masses. C) It is a source of x-ray emission that we have observed with telescopes in space. D) It is a source of bright radio emission. Answer: A

Visual Quiz Questions

1) This diagram represents an edge-on view of our Milky Way Galaxy. Of the four labeled points, which one is located in what we call the halo of the galaxy? A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: D 2) This diagram represents an edge-on view of our Milky Way Galaxy. Of the four labeled points, which one could represent the Sun's position in the galaxy? A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: A 3) This diagram represents an edge-on view of our Milky Way Galaxy. Of the four labeled points, which one is located closest to a place where evidence suggests we would find a 4 million solar-mass black hole? A) Point 1 B) Point 2 C) Point 3 D) Point 4 Answer: B

4) This photograph shows an interstellar bubble about 10 light-years in diameter. If you could photograph this same region about 100 years from now, how would you expect it to look different?

A) The bubble will be slightly larger. B) The bubble will be slightly smaller. C) The bubble will have burst as a supernova. D) The bubble's shape will have become much more like an oval rather than a sphere. Answer: A

5) This photograph shows x-ray emission from a supernova remnant. What is the source of the xrays?

A) Hot gas expanding outward from the site of a supernova B) Cold gas that will soon give birth to new stars C) Accretion disk around a black hole near the center of the supernova remnant D) Spots within the remnant where hot gas is crashing into and destroying planets Answer: A

6) What are the dark blobs (indicated by the red arrows) in this photograph from the Hubble Space Telescope?

A) Cold, dense molecular clouds in which stars are forming B) Warm atomic hydrogen gas, much like most of the gas in the galaxy C) Tall interstellar bubbles blown out by supernovae or stellar winds D) Jets of hot gas shot out from young binary star systems Answer: A

7) The top panorama shows our view of the Milky Way in all directions as it appears in visible light. The bottom panorama shows the same view, but in a different wavelength of light. What wavelength band are we seeing in the bottom photo, and how do you know?

A) Infrared light, because the dust that appears dark in the visible light photo glows in infrared light B) X-ray light, because only x-rays allow us to see through the disk of our galaxy C) Radio waves, because clouds of gas in the disk of our galaxy appear pinkish when we look at them with radio telescopes D) Infrared light, because clouds of gas and dust appear pinkish when we look at them with infrared telescopes Answer: A

8) Notice the well-defined spiral arms in this photograph of the galaxy M51. What makes the spiral arms so much brighter than regions between the arms?

A) The presence of many massive young stars in the spiral arms B) The presence of many old, red giant stars in the spiral arms C) The presence of many hot interstellar bubbles in the spiral arms D) The spiral arms are bright because nearly all the galaxy's stars are located within them. Answer: A 9) What law of nature explains why the galaxy began to rotate rapidly and flatten out as it shrunk in size?

A) The law of conservation of angular momentum B) Newton's universal law of gravitation C) Newton's third law of motion D) Einstein's special theory of relativity Answer: A

10) This figure shows observations that have allowed astronomers to determine the orbits of several stars around Sgr A* (the central object). What can we learn about Sgr A* by analyzing these orbits?

A) Its mass B) Its age C) Its chemical composition D) All of the above Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

These images show the central region of our galaxy in different wavelengths of light. Use these images to answer the following questions. 1) The image of radio emission uses different colors to represent different levels of intensity. Which color represents the brightest radio emission? Which color represents the lowest levels of brightness? Answer: Brightest: white; lowest levels of brightness: black/dark blue 2) The image of x-ray emission uses different colors to represent different levels of brightness. The dark blue color represents the least bright x-ray emission. Which color represents the brightest x-ray emission? Answer: White 3) How do regions showing strong radio emission from molecules look in the visible-light image? Are they bright or are they dark? Answer: Regions with strong radio emissions are dark in the visible-light image.

4) How do regions showing strong radio emission from molecules look in the infrared-light image? Are they bright or are they dark? Answer: Regions with strong radio emissions are dark in the infrared-light image. (Note: students may find this a bit difficult to see at the scale shown in the images, but the darkest infrared regions clearly correspond to strong radio emissions.) 5) Based on a comparison of the radio, infrared, and visible-light images, we can conclude that gas clouds containing molecules ________. A) absorb roughly equal amounts of infrared starlight and visible starlight B) absorb substantial amounts of visible starlight but no infrared starlight C) absorb infrared starlight less effectively than they absorb visible starlight Answer: C 6) Compare the radio and x-ray images. Can you conclude from this comparison that gas clouds containing molecules absorb x-ray light? Answer: Yes Chapter Review Questions 1) Draw simple sketches of our galaxy as it would appear face-on and edge-on. Identify the disk, bulge, halo, and spiral arms, and indicate the galaxy's approximate dimensions. 2) What are the Large and Small Magellanic Clouds, and the Sagittarius and Canis Major Dwarfs? 3) Describe and contrast stellar orbits in the disk, halo, and bulge of our galaxy. 4) How can we use orbital properties to learn about the mass of the galaxy? What have we learned? 5) Summarize the stages of the star—gas—star cycle in Figure 15.3. 6) What creates a bubble of hot, ionized gas? What happens to the gas in the bubble over time? 7) What are cosmic rays, and where are they thought to come from? 8) What do we mean by atomic hydrogen gas? How common is it, and how do we map its distribution in the galaxy? 9) Briefly summarize the different types of gas present in the disk of the galaxy, and describe how they appear when we view the galaxy in different wavelengths of light. 10) What are ionization nebulae, and why are they found near hot, massive stars? 11) How do we know that spiral arms do not rotate like giant pinwheels? What makes spiral arms bright? 28 Copyright © 2022 Pearson Education, Inc.

12) What triggers star formation within a spiral arm? How do we think spiral arms are maintained? 13) Briefly describe the characteristics that distinguish disk stars from halo stars. 14) What evidence suggests that the Milky Way formed from the merger of several smaller protogalactic clouds? 15) What is Sgr A*? What evidence suggests that it contains a massive black hole? Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 16) We did not understand the true size and shape of our galaxy until NASA launched satellites into the galactic halo, enabling us to see what the Milky Way looks like from the outside. 17) Planets like Earth probably didn't form around the first stars because there were so few heavy elements back then. 18) If I could see infrared light, the galactic center would look much more impressive. 19) Many spectacular ionization nebulae are seen throughout the Milky Way's halo. 20) The carbon in my diamond ring was once part of interstellar dust grains. 21) The Sun's velocity around the Milky Way tells us that most of our galaxy's dark matter lies near the center of the galactic disk. 22) We know that a black hole lies at our galaxy's center because numerous stars near it have vanished over the past several years, telling us that they've been sucked in. 23) If we could watch a time-lapse movie of a spiral galaxy over millions of years, we'd see many stars being born and dying within the spiral arms. 24) The star—gas—star cycle will keep the Milky Way looking just as bright in 100 billion years as it looks now. 25) Halo stars orbit the center of our galaxy much faster than the disk stars.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 15 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 26) What is the shape of the Milky Way's halo? A) Round like a ball B) Flat like a disk C) Flat like a disk but with a hole in the center Answer: No Correct Answer Was Provided. 27) Where are most of the Milky Way's globular clusters found? A) In the disk B) In the bulge C) In the halo Answer: No Correct Answer Was Provided. 28) Why do disk stars bob up and down as they orbit the galaxy? A) Because the gravity of other disk stars always pulls them toward the disk B) Because of friction with the interstellar medium C) Because the halo stars keep knocking them back into the disk Answer: No Correct Answer Was Provided. 29) How do we determine the Milky Way's mass outside the Sun's orbit? A) From the Sun's orbital velocity and its distance from the center of our galaxy B) From the orbits of halo stars near the Sun C) From the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun Answer: No Correct Answer Was Provided. 30) Which part of the galaxy contains the coldest gas? A) The disk B) The halo C) The bulge Answer: No Correct Answer Was Provided. 31) What is the typical percentage (by mass) of elements other than hydrogen and helium in stars that are forming right now in the vicinity of the Sun? A) 20% B) 2% C) 0.02% Answer: No Correct Answer Was Provided. 32) Which of these forms of radiation passes most easily through the disk of the Milky Way? A) Red light B) Blue light C) Infrared light Answer: No Correct Answer Was Provided. 30 Copyright © 2022 Pearson Education, Inc.

33) Where would you be most likely to find an ionization nebula? A) In the halo B) In the bulge C) In the disk Answer: No Correct Answer Was Provided. 34) Which kind of star is most likely to be found in the halo? A) An O star B) An A star C) An M star Answer: No Correct Answer Was Provided. 35) The best measurements of the mass of the black hole at the galactic center come from ________. A) the orbits of stars in the galactic center B) the orbits of gas clouds in the galactic center C) the amount of radiation coming from the galactic center Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 36) Group Discussion: Alternative Names for the Milky Way. Today, we call our galaxy the Milky Way Galaxy, after the band of light that appeared "milky" to the ancient Greeks. But other cultures had other names for that band of light. a. Working independently, learn at least three other names that have been used for the Milky Way and the stories behind those names. Then gather in small groups and share the names and stories that each of you found. b. Discuss and then vote on the name other than "Milky Way" that your group favors. What does your group think are the strengths of that name? c. Discuss the reasons your group's favorite name did not become widely used as the name of our galaxy, and make a list of cultural factors that may have favored the name "Milky Way Galaxy." Do you think some of those other names should become better known? Why or why not?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 37) Discovering the Structure of the Milky Way. The story of how we came to learn the structure of the Milky Way (see Special Topic, page 390) is an excellent demonstration of how science progresses. What features of the Milky Way's appearance in our sky led scientists to conclude that its width is much larger than its thickness? Why did they originally believe that the Sun was near the Milky Way's center? What key observations forced scientists to change their views about the location of the Sun within the Milky Way? 38) Formation of the Milky Way. Figure 15.18 outlines a basic model that accounts for some but not all of the features of the Milky Way. What observational evidence indicates that the Milky Way's protogalactic cloud contained virtually no elements other than hydrogen and helium? What evidence suggests that the halo stars formed first and disk stars formed later? What features of the Milky Way are not explained by this basic model? 39) Galactic Ecosystem. We have likened the star—gas—star cycle in our Milky Way to the ecosystem that sustains life on Earth. Here on our planet, water molecules cycle from the sea to the sky to the ground and back to the sea. Our bodies convert atmospheric oxygen molecules into carbon dioxide, and plants convert carbon dioxide back into oxygen molecules. How are the cycles of matter on Earth similar to the cycles of matter in the galaxy? How do they differ? Do you think the term ecosystem is appropriate in discussions of the galaxy? 40) Galaxy Stuff. In the chapters on stars, we learned why we are "star stuff." Explain why we are also "galaxy stuff." Does the fact that the entire galaxy was involved in bringing forth life on Earth change your perspective on Earth or on life? If so, how? If not, why not?

41) Group Activity Star Clusters and Milky Way Structure. Use the all-sky diagramin Appendix H and the information about globular and open clusters below to do the following.Note: You may wish to do this activity using the same four roles described in Chapter 1, Exercise 39. • Globular clusters are found in the following constellations: Aquarius, Aquila, Canes Venatici, Capricornus, Carina, Centaurus, Columba, Coma Berenices, Hercules, Hydra, Lepus, Lynx, Lyra, Musca, Ophiuchus, Pegasus, Puppis, Sagittarius, Scorpius, Sculptor, Serpens, Tucana, and Vela. • Open clusters with ages of 100 million years or less are found in the following constellations: Canis Major, Carina, Cassiopeia, Crux, Cygnus, Monoceros, Norma, Ophiuchus, Perseus, Puppis, Sagittarius, Scorpius, Scutum, Serpens, Taurus, and Vela. a. Split your group into two teams (e.g., two people each), with one team focusing on globular clusters and the other on open clusters. The members of each team should work together to locate on the all-sky map(Appendix H) the constellations in which their clusters are found and to identify patterns in these locations relative to the Milky Way's disk and relative to the galactic center. b. The full group should compare the locations of the two sets of clusters and describe the differences you've found. c. One member of the group should offer a hypothesis to explain the differences. Others can then suggest alternative hypotheses. d. Discuss the group's set of hypotheses and list possible observations that astronomers could perform to determine which hypothesis is more likely to be correct. Investigate Further 42) Unenriched Stars. Suppose you discovered a star made purely of hydrogen and helium. How old do you think it would be? Explain. 43) Enrichment of Star Clusters. The gravitational pull of an isolated globular cluster is rather weak–a single supernova explosion can blow all the interstellar gas out of a globular cluster. How might this fact relate to observations indicating that stars ceased to form in globular clusters long ago? How might it relate to the fact that globular clusters are deficient in elements heavier than hydrogen and helium? Summarize your answers in one or two paragraphs. 44) High-Velocity Star. The average speed of stars in the solar neighborhood relative to the Sun is about 20 km/s. Suppose you discover a star in the solar neighborhood that is moving at a much higher speed relative to the Sun, say, 200 km/s. What kind of orbit does this star probably have around the Milky Way? In what part of the galaxy does it spend most of its time? Explain. 45) Future of the Milky Way. Describe how the Milky Way would look from the outside if you could watch it for the next 100 billion years. How would its appearance change? 46) Orbits at the Galactic Center. Using the information in Figure 15.21, identify which two stars reach the highest orbital speeds. Explain how the orbits of those two stars illustrate Kepler's first two laws.

47) A Nonspinning Galaxy. How would the development of the Milky Way Galaxy have been different if it had collapsed from protogalactic clouds that had no net angular momentum? Describe how you think our galaxy would look today and explain your reasoning. 48) Gas Distribution in the Milky Way. Make a sketch of the gas distribution in the plane of the Milky Way, based on the photographs in Figure 15.11. In your sketch, map out where you would find molecular clouds, atomic hydrogen clouds, and bubbles of hot gas. Explain why each of those components of the interstellar medium is found in the location where you have drawn it. 49) Research: The Galactic Center. Search for recent images of the center of the Milky Way Galaxy, along with information about the massive black hole thought to reside there. Write a short report, with pictures, giving an update on current knowledge. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 50) Mass of the Milky Way's Halo. The Large Magellanic Cloud orbits the Milky Way at a distance of roughly 160,000 light-years from the galactic center and a velocity of about 300 km/s. Use these values in the orbital velocity formula to estimate the Milky Way's mass within 160,000 light-years from the center. 51) Mass of the Central Black Hole. Suppose you observed a star orbiting the galactic center at a speed of 1000 km/s in a circular orbit with a radius of 20 light-days. Calculate the mass of the object that the star was orbiting. 52) Mass of a Globular Cluster. Stars in the outskirts of a globular cluster are typically about 50 light-years from the cluster's center, which they orbit at speeds of about 10 km/s. Use these data to calculate the mass of a typical globular cluster. 53) Mass of Saturn. The innermost rings of Saturn orbit in a circle with a radius of 67,000 kilometers at a speed of 23.8 km/s. Use the orbital velocity formula to compute the mass contained within the orbit of those rings. Compare your answer with the mass of Saturn listed in Appendix E.

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 16 A Universe of Galaxies Section 16.1 1) Which of the following types of galaxies are closest to being spherical in shape? A) Spirals B) Ellipticals C) Irregulars Answer: B 2) Which of the following types of galaxies are typically reddest in color? A) Spirals B) Ellipticals C) Irregulars Answer: B 3) Which types of galaxies have a halo component? A) Spirals only B) Ellipticals only C) Irregulars only D) Both spirals and ellipticals Answer: D 4) Which types of galaxies have a clearly defined disk component? A) Spirals only B) Ellipticals only C) Irregulars only D) Both spirals and ellipticals Answer: A 5) How do elliptical galaxies typically compare to spiral galaxies? A) Elliptical galaxies are redder and rounder. B) Elliptical galaxies are redder and flattened. C) Elliptical galaxies are bluer and rounder. D) Elliptical galaxies are bluer and flattened. E) Elliptical galaxies are always much smaller. Answer: A 6) How does a lenticular galaxy differ from a spiral galaxy? A) It has no bulge. B) It has an elongated bulge resembling a bar more than a sphere. C) It is flatter in shape. D) It has no gas or dust. E) It has no spiral arms. Answer: E 1 Copyright © 2022 Pearson Education, Inc.

7) Which of the following is true of elliptical galaxies? A) They usually have significant, ongoing star formation. B) They usually contain abundant clouds of cool gas and dust. C) They are usually bluish in color. D) They are the most common type of galaxy in the central regions of galaxy clusters. Answer: D 8) Which of the following types of galaxies is the most common type of galaxy found in large clusters? A) Spirals B) Ellipticals C) Irregulars Answer: B 9) Which of the following is true about irregular galaxies? A) They are composed solely of old stars. B) They generally have significant bulge populations. C) They were more common when the universe was younger. D) They have reddish colors. E) They have well-defined spiral arms. Answer: C

10) The H-R diagram for stars plots color on the horizontal axis and luminosity on the vertical axis. If we make a similar diagram plotting color and luminosity for galaxies, as shown below, what general trend does it show?

A) Galaxies fill the diagram uniformly, indicating no correlation between luminosity and color. B) Galaxies form two main clumps on the diagram, one on the bluer, fainter side and one on the redder side, somewhat more luminous. C) Much as with stars, galaxies fall into several distinct groups representing normal galaxies, giant and supergiant galaxies, and dwarf galaxies. D) A strong trend for blue galaxies to be much more luminous on average than red galaxies. Answer: B 11) On a graph of luminosity versus color for galaxies, shown below, many galaxies form a clump known as the "blue cloud." Why are galaxies in the blue cloud blue? A) They contain hot, young stars that indicate active star formation. B) They are moving slower than galaxies in the red cloud. C) They contain lots of dust that cause the bluish color. D) They contain cold, dying stars that are fading to black. E) They are all moving toward us, causing them to be blueshifted. Answer: A

12) Why do spiral galaxies appear blue in color? A) The longer wavelengths emitted by these galaxies are absorbed by interstellar dust. B) Their rapid rotation causes a blueshift in the light they emit. C) They contain many white dwarfs, which are usually hot enough to appear blue. D) Their light output is dominated by hot, massive blue stars. Answer: D 13) Why do elliptical galaxies appear yellow or red in color? A) They contain many nebulae that glow red in color. B) Their population is dominated by old, low-mass stars and old, red giant stars. C) They are moving away from us so their light is highly redshifted. D) They contain vast amounts of dust that absorbs blue light. Answer: B 14) What kind of galaxy is the Milky Way? A) An irregular galaxy B) A spiral galaxy C) An elliptical galaxy Answer: C 15) The Sloan Digital Sky Survey includes many thousands of galaxies in its spectroscopic catalogs. How are the distances to most of these galaxies estimated? A) From their redshifts and the application of Hubble's Law B) By measuring Cepheid variable light curves C) By measuring their parallax angle as the Earth circles the Sun D) By measuring the light from white dwarf supernovae Answer: A 16) Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 22 km/s/million light-years. How fast would a galaxy 1000 million light-years away be receding from us? A) 22 km/s B) 22 million light-years/s C) 22,000 km/s D) 1000/22 km/s E) 0.22 times the speed of light Answer: C 17) Hubble's Law states that v = H0d, and current measurements indicate that H0 ≈ 22 kilometers per second per million light-years. About how far away is a galaxy with a redshift indicating that it is moving away from us at 2200 kilometers per second? A) 100 million light-years B) 200 million light-years C) 200 light-years D) 100 light-years Answer: A 4 Copyright © 2022 Pearson Education, Inc.

18) What observational evidence supports the idea that a collision between two spiral galaxies might lead to the formation of a single elliptical galaxy? A) Some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies. B) Elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies. C) Elliptical galaxies with stars and gas clouds that orbit differently from the other stars in the galaxy. D) There are giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies. E) All of the above are correct. Answer: E Section 16.2 1) The most massive galaxies in the universe are ________. A) ellipticals B) spirals C) lenticulars Answer: A 2) In astronomy, a standard candle is an object with a known ________. A) luminosity B) apparent brightness C) distance D) surface temperature Answer: A 3) Why are Cepheid variables important? A) Cepheid variables are stars that vary in brightness extremely rapidly as they rotate on their axes. B) Cepheid variables are stars that brighten and dim with a period that is directly related to the star's luminosity. C) Cepheids are a type of young galaxy that helps us understand how galaxies form. D) Cepheids are supermassive stars that we observe because they will soon undergo supernovae. Answer: B 4) Leavitt's law is a relationship between ________. A) a Cepheid variable star's period and luminosity B) a galaxy's distance and recession speed C) a galaxy's distance and redshift D) a main-sequence star's color and luminosity Answer: A

5) This figure shows the Cepheid period-luminosity relation. What is the approximate luminosity of a Cepheid star that varies in brightness with a period of 10 days? A) About 1000 times the luminosity of the Sun B) About 3000 times the luminosity of the Sun C) About 10,000 times the luminosity of the Sun D) About 30,000 times the luminosity of the Sun Answer: B 6) This figure shows the Cepheid period-luminosity relation. Suppose that a Cepheid with a period of 30 days has the same apparent brightness as a nearby star with a luminosity identical to our Sun. How many times farther away is the Cepheid? (Hint: First use the graph to find the Cepheid's luminosity, then apply the inverse square law for light.) A) The Cepheid is 10 times farther away than the nearby star. B) The Cepheid is 100 times farther away than the nearby star. C) The Cepheid is 10,000 times farther away than the nearby star. D) The Cepheid is actually 10 times closer than the nearby star. Answer: B 7) White dwarf supernovae are good standard candles for distance measurements because ________. A) all white dwarf supernovae have about the same peak luminosity B) all white dwarf supernovae occurred at about the same time in the history of the universe C) all galaxies have at least one white dwarf supernova each year D) white dwarf supernovae occur only among very massive stars E) all white dwarf supernovae start out bright and fade with time Answer: A

8) Nearly all galaxies contain Cepheid variable stars. Why, then, do we determine the most distant galaxy distances using white dwarf supernovae rather than Cepheids as standard candles? A) White dwarf supernovae are much more reliable standard candles than Cepheids. B) White dwarf supernovae can be observed in galaxies that are too far away for us to see individual Cepheids. C) White dwarf supernovae are more common than Cepheids. D) White dwarf supernovae can be detected with a single observation, while it takes many observations to measure a Cepheid's light curve. Answer: B 9) How did Edwin Hubble measure the distance to the Andromeda Galaxy? A) He measured its parallax. B) He used Cepheid variables in the Andromeda Galaxy. C) He deduced it from its redshift. D) He used white dwarf supernovae in the Andromeda Galaxy. Answer: B 10) Which of the following expresses the major idea of Hubble's Law? A) There must have been a Big Bang. B) All galaxies are moving away from us equally fast. C) The more distant a galaxy is from us, the faster it moves away from us. D) The closer a galaxy is to us, the faster it moves away from us. E) More distant galaxies appear younger. Answer: C 11) What is the most accurate way to determine the distance to a relatively nearby star (within the Milky Way)? A) Radar ranging B) Stellar parallax C) Using Cepheid variables D) Using white dwarf supernovae E) Applying Hubble's law Answer: B 12) What is the most accurate way to determine the distance to a relatively nearby galaxy? A) Radar ranging B) Parallax C) Using Cepheid variables D) Using white dwarf supernovae Answer: C

13) What is the most accurate way to determine the distance to a distant galaxy (a galaxy that is too far away for us to see individual stars)? A) Radar ranging B) Parallax C) Using Cepheid variables D) Using white dwarf supernovae Answer: D 14) Dr. X claims that the Hubble constant is 20 km/s/million light-years while Dr. Y claims it is 24 km/s/million light-years. Which statement below automatically follows? A) Dr. X concludes that the universe is expanding, but Dr. Y does not. B) Dr. X will conclude that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a slower speed than will Dr. Y. C) Dr. X will conclude that the universe is older than will Dr. Y. D) Dr. X believes that the universe will someday stop expanding, while Dr. Y believes it will expand forever. E) Dr. X will conclude that the universe contains more mass than will Dr. Y. Answer: C 15) What two quantities did Edwin Hubble compare for a sample of galaxies to discover the expansion of the universe? A) Velocity and distance B) Luminosity and distance C) Velocity and temperature D) Luminosity and temperature E) Age and distance Answer: A

16) This figure shows Hubble's law. If a galaxy is observed to be moving away from us at 30,000 (3 104) km/s, approximately how far away is it? (Hint: Be sure to read the axis labels carefully.)

A) 30,000 light-years B) 1400 million light-years C) 3000 million light-years D) 1400 light-years Answer: B 17) Which statement is true about the relationship between Hubble's constant and the age of the universe? A) The larger the value of Hubble's constant, the faster the universe is expanding and the younger the universe must be. B) The larger the value of Hubble's constant, the slower the universe is expanding and the younger the universe must be. C) The larger the value of Hubble's constant, the slower the universe is expanding and the older the universe must be. D) There is no relationship between the value of Hubble's constant and the age of the universe. Answer: A

18) Based on current estimates of the value of Hubble's constant, approximately how old is the universe? A) 10 billion years old B) 12 billion years old C) 14 billion years old D) 18 billion years old E) 20 billion years old Answer: C 19) You observe a galaxy that is 100 million light-years away. Which of the following do you see? A) The light from the galaxy as it is today, and it is blueshifted. B) The light from the galaxy as it is today, and it is redshifted. C) The light from the galaxy as it was 100 million years ago, and it is blueshifted. D) The light from the galaxy as it was 100 million years ago, and it is redshifted. E) Nothing: the galaxy lies beyond the cosmological horizon. Answer: D 20) Why can't we see past the cosmological horizon? A) Every galaxy in the entire universe (not just the observable universe) exists within the cosmological horizon, so there's nothing to see beyond it. B) It's impossible to look back to a time before the universe was born. C) We do not have telescopes big enough. D) The cosmological horizon is infinitely far away, and we can't see to infinity. Answer: B 21) Suppose you are observing a distant galaxy whose light has taken 12 billion years to reach us. What is the maximum age that this galaxy could have been when it emitted the light we are observing now? (Assume the age of the universe is about 14 billion years.) A) About 2 billion years old B) About 10 billion years old C) About 4 billion years old D) About 12 billion years old Answer: A 22) Stars X and Y both have the same apparent brightness, but star X is 10,000 times as luminous as star Y. How much farther away is star X than star Y? A) Star X is 10 times as far away as star Y. B) Star X is 100 times as far away as star Y. C) Star X is 10,000 times as far away as star Y. D) Star X is 10 times closer to us than star Y. Answer: B

23) Suppose you measure the brightness and period of a number of Cepheid variable stars in Galaxy A and Galaxy B. You ﬁnd that all the Cepheid variables in Galaxy A are approximately 25 times as bright (apparent brightness) as Cepheid variables with similar periods in Galaxy B. What can you conclude about the distances of these galaxies? A) Galaxy A is 25 times as far away as Galaxy B. B) Galaxy A is 5 times as far away as Galaxy B. C) Galaxy B is 25 times as far away as Galaxy A. D) Galaxy B is 5 times as far away as Galaxy A. Answer: D 24) Galaxy A and galaxy B formed at the same time. Galaxy A is much farther from us than galaxy B. Which of the following is true? A) Galaxy A will appear younger to us than galaxy B. B) Galaxy A will appear older to us than galaxy B. C) Galaxy A will appear to be the same age as galaxy B. Answer: A 25) Suppose that an object doubles its luminosity in 10 hours. What can we conclude? A) The object must be a quasar. B) The object must be a Cepheid variable star. C) The object is no more than about 10 light-hours across. D) The object must be very far away, making it one of the most luminous objects in the universe. E) The object is being orbited by another object with an orbital period of 10 hours. Answer: C Section 16.3 1) Which statement accurately describes how observations of distant galaxies help us learn about galaxy evolution? A) By observing galaxies with different lookback times, we learn how galaxies appeared at different stages of their evolution. B) We can observe the birth of galaxies. C) We can observe the evolution of a single galaxy over time. D) We can watch as two galaxies merge and view the result, helping us learn how mergers affect evolution. E) We can see what our galaxy used to look like and therefore theorize about the physical processes that led to its current appearance. Answer: A 2) In what sense do telescopes function as "time machines"? A) They allow us to observe individual stars and galaxies as they change with time. B) Some of the oldest telescopes are still in use today. C) They allow us to see distant objects as they were in the distant past. D) They allow us to see the Milky Way Galaxy as it was when it was much younger. Answer: C

3) Which of the following are the two key starting assumptions of theoretical models of galaxy evolution? A) (1) The beginning of the universe can be modeled as a giant supernova explosion and (2) this supernova created all the elements in the proportions we find them today. B) (1) Hydrogen and helium gas, along with dark matter, filled all of space and (2) some regions of the universe were slightly denser than others. C) (1) Hydrogen and helium gas, along with dark matter, filled all of space and (2) the distribution of this material was perfectly uniform everywhere. D) (1) Hydrogen gas, along with dark matter, filled all of space and (2) all the other elements came from stars. Answer: B 4) Consider a scale on which our entire Milky Way Galaxy is about the size (diameter) of a grapefruit. Which of the following best describes the size and distance of the Andromeda Galaxy on the same scale? A) A grapefruit about 3 meters away B) A grapefruit about 3 centimeters away C) A beach ball about the length of a football field away D) A peanut about 3 centimeters away E) A grapefruit about 3 kilometers away Answer: A 5) Which of the following protogalactic clouds is most likely to form an elliptical galaxy? A) A very low-density cloud with very little angular momentum B) A dense cloud with very little angular momentum C) A low-density cloud with quite a bit of angular momentum D) A very massive cloud with any density and a lot of angular momentum Answer: B 6) Which of the following protogalactic clouds is most likely to form a spiral galaxy? A) A very low-density cloud with very little angular momentum B) A dense cloud with very little angular momentum C) A low-density cloud with quite a bit of angular momentum D) A very massive cloud with any density and a lot of angular momentum Answer: C 7) What is one idea why a relatively dense protogalactic cloud more likely to produce an elliptical galaxy than a spiral galaxy? A) The force of gravity from the higher gas density can pull the material into a more spherical shape. B) The more frequent collisions between particles in the high-density gas randomize the particle orbits. C) The thickness of the dense cloud prevents a disk from forming. D) The higher gas density allows more rapid star formation, leaving little gas to form a disk. Answer: D

8) What observational evidence supports the hypothesis that elliptical galaxies are born from relatively dense protogalactic clouds? A) Elliptical galaxies have stars packed more densely together than spiral galaxies. B) Elliptical galaxies are generally larger than spiral galaxies. C) Even very distant elliptical galaxies tend to lack young, blue stars, indicating their stars formed early and rapidly. D) Elliptical galaxies have more and denser gas than spiral galaxies. E) The stars in elliptical galaxies are denser than those in spiral galaxies. Answer: C 9) How might two colliding spiral galaxies tend to create an elliptical galaxy? A) The orbits of the stars get randomized during the collision, while their gas disks collide and form stars. B) The collision creates a larger galaxy and elliptical galaxies are always larger. C) The gas in the disks of the galaxies is expelled into intergalactic space by gravitational interactions. D) The heat created by collisions between stars causes the disks to puff out into a spherical shape. Answer: A 10) What is a central dominant galaxy? A) A galaxy around which many other smaller galaxies orbit B) A giant spiral galaxy that exerts large tidal forces on other nearby galaxies C) A spiral galaxy from which many smaller galaxies form when it is stripped apart by tidal forces D) A giant galaxy with several bright clumps of stars at the center of a dense cluster E) A hypothesized galaxy type that no longer exists, but once dominated the structure of the universe Answer: D 11) Why are collisions between galaxies common, but collisions between stars rare? A) Stars are very small compared to the distances between them, but galaxies are not. B) Stars repel each other with stellar winds, but galaxies do not. C) Stars are much less common than galaxies, so there are fewer of them to collide. D) Stars do not survive as long as galaxies, so they have less time to collide. Answer: A 12) A starburst galaxy gets this name because ________. A) it contains far more x-ray bursters than our Milky Way Galaxy B) it has many stars bursting out of its disk toward intergalactic space C) it is forming stars so fast that the starburst phase of life must be temporary D) it contains so many stars that the galaxy's gravity cannot retain them in their orbits Answer: C

13) Why do we conclude that a starburst must represent only a temporary stage in galaxy evolution? A) We observe starbursts to last only a few years in any individual galaxy before the starburst ends. B) The star formation rate of a starburst would consume all available gas for star formation in a time much shorter than the age of the universe. C) We don't see any starbursts occurring in nearby galaxies. D) Galaxies with starbursts are all very far away, indicating that these starbursts occurred only very long ago. Answer: B 14) Starburst galaxies are best observed in which wavelength range? A) X-rays B) Ultraviolet C) Visible D) Infrared E) Gamma rays Answer: D 15) What evidence suggests that some small galaxies in our Local Group have undergone two or more starbursts in the past? A) We observe several small galaxies currently undergoing massive star formation. B) We see small galaxies in which many stars have one age and many others have another age that is billions of years older. C) We see evidence that small galaxies in our Local Group have experienced several collisions in the past. D) We see evidence that several small galaxies were shot out of larger galaxies in our Local Group during a period of starburst activity. Answer: B

Section 16.4 1) What is a quasar? A) A starlike object that actually represents a bright patch of gas in the Milky Way B) A very large galaxy thought to be formed by the merger of several smaller galaxies, resulting in a quick burst of star formation C) The name given to the largest objects in the Kuiper Belt D) The extremely bright center of a distant galaxy E) Another name for very bright stars of spectral type O Answer: D 2) How do we know that quasars are very distant objects? A) From their high luminosities B) From the fact that they can vary in luminosity in short time periods C) By observing Cepheid variables within them D) From their large redshifts E) By measuring their parallax angles Answer: D 3) Which of the following statements best supports the hypothesis that active galactic nuclei are powered by supermassive black holes? A) Orbits of gas clouds within them indicate billions of solar masses of material in a small volume of space. B) They are found in the centers of galaxies. C) They have jets and accretion disks. D) They emit radiation at all wavelengths, from the radio to the gamma rays. Answer: A 4) Which of the following provides observational evidence that quasars have power sources that are fairly small in size? A) Some quasars are more than a thousand times as luminous as the Milky Way. B) Quasars are always located very far away. C) Telescopic images show the very small power sources of quasars. D) The galaxies in which quasars are embedded often show disruption from the central energy source. E) Some quasars can change significantly in apparent brightness in just a few hours. Answer: E 5) According to the supermassive black hole hypothesis, how is the energy that powers active galactic nuclei produced? A) By nuclear fusion near the central black hole B) By magnetic fields that trap and accelerate charged particles C) By the impact of jets being shot out of the central black hole D) By converting the gravitational potential energy of infalling matter to kinetic energy and thermal energy E) By matter–antimatter annihilation Answer: D 15 Copyright © 2022 Pearson Education, Inc.

6) Quasars and other active galactic nuclei are often intense sources of x-rays. According to the supermassive black hole hypothesis, where are these x-rays produced? A) In hot gas in an accretion disk around the central black hole B) In ionization nebulae heated by supernovae near the black hole C) In dust-rich molecular clouds that are forming new stars near the black hole D) In the central black hole itself Answer: A 7) All of the following are true. Which of these gives evidence that quasars were more common when the universe was young than they are today? A) They are more common at very great distances. B) They are very bright. C) They are active galactic nuclei. D) We don't see them in every galaxy. Answer: A 8) Approximately what percentage of mass-energy of infalling matter can be converted to thermal energy when the matter is falling into a supermassive black hole? A) About the same as that converted by hydrogen fusion B) Much less than that converted by hydrogen fusion C) Much more that converted by hydrogen fusion Answer: C Short Answer Questions 1) Briefly describe how astronomers estimate the number of galaxies in the observable universe. Answer: Astronomers can count galaxies in small regions of the sky that have been photographed in great detail by powerful telescopes (e.g., with photos like the Hubble eXtreme Deep Field). They can then estimate the total number of galaxies in the observable universe by multiplying the number of galaxies in the small region of the sky by the number of such regions it would take to cover the entire sky. 2) Do individual galaxies expand in size as the universe expands? Why or why not? Answer: No, because they are bound together by their own gravity. 3) Explain why galaxy collisions are far more common than star-star collisions. Answer: Galaxies are much closer together, relative to their size, than stars are. If the Sun were made the size of a grapefruit, the nearest star would be on the other side of the continent. However, if the Milky Way (or any other galaxy) were made the size of a grapefruit, there would likely be another galaxy within a few feet of it. Thus, galaxy interactions are far more common than star-star interactions and must be taken into account when considering galaxy evolution.

4) In what sense are telescopes "time machines" that allow us to study the formation and evolution of galaxies? Answer: Telescopes see objects as they were when the light left them. For distant objects, this "lookback time" can be billions of years, which means in some cases we can literally see galaxies in the process of formation. Moreover, by looking to different distances (lookback times), we see other galaxies in various stages of life between formation and the present day. Reading Quiz Questions 1) Based on the number of galaxies visible in the Hubble eXtreme Deep Field (Figure 16.1 in your text), the estimated number of galaxies in our observable universe is at least ________. A) 100 billion B) 100 million C) 50,000 D) Infinity Answer: A 2) Which of the following is not one of the three major categories of galaxies? A) Globular galaxies B) Elliptical galaxies C) Spiral galaxies D) Irregular galaxies Answer: A 3) A standard candle is ________. A) a 7-cm-long wax candle B) a light source of known luminosity C) another name for a main-sequence star D) another name for a barred-spiral galaxy Answer: B 4) What is a Cepheid variable? A) A type of very luminous star that makes an excellent standard candle B) A bright source of variable x-ray emission, thought to harbor a supermassive black hole C) A main-sequence star of spectral type B5 D) A type of galaxy that varies in its light output Answer: A 5) What two observable properties of a Cepheid variable are directly related to one another? A) The period between its peaks of brightness and its luminosity B) The period between its peaks of brightness and its distance C) Its luminosity and its mass D) Its mass and its distance Answer: A

6) What does Hubble's law tell us? A) The more distant a galaxy, the faster it is moving away from us. B) The faster a spiral galaxy's rotation speed, the more luminous it is. C) The longer the period of a Cepheid variable, the greater its luminosity. D) For every force, there is an equal and opposite reaction force. Answer: A 7) Given that white dwarf supernovae are such good standard candles, why don't we use them to measure the distance to all galaxies? A) They are rare events, so we have observed them in only a tiny fraction of all galaxies. B) We cannot see them beyond a distance of about 100 million light-years. C) They can occur only in spiral galaxies, not elliptical galaxies. D) We would, but we don't have enough telescopes. Answer: A 8) When we use an analogy that represents the expanding universe with the surface of an expanding balloon, what does the inside of the balloon represent? A) The inside of the balloon does not represent any part of our universe. B) The center of the universe C) The entire universe D) Regions of the universe beyond the Milky Way Galaxy Answer: A 9) If we say that a galaxy has a lookback time of 1 billion years, we mean that ________. A) its light traveled through space for 1 billion years to reach us B) it is now 1 billion light-years away C) it was 1 billion light-years away when the light left the galaxy D) it is 400 million years old Answer: A 10) Cosmological redshift is the result of ________. A) the high speeds at which galaxies move within clusters B) the expansion of the universe C) very old, red stars in distant galaxies D) supermassive black holes Answer: B 11) Although the entire universe may be much larger than our observable universe, we can see only within our observable universe. The "boundary" of our observable universe is called ________. A) the cosmological horizon B) the Big Bang C) the lookback time D) the Hubble Deep Field Answer: A

12) Current estimates place the age of the universe at about ________. A) 10 billion years B) 10 million years C) 14 billion years D) 4 1/2 billion years Answer: C 13) Telescopes designed to study the earliest stages in galactic lives should be optimized for observations in ________. A) infrared light B) visible light C) radio waves D) x-rays Answer: A 14) Which of the following is an important starting assumption in models of galaxy formation? A) Some regions in the universe start out denser than others. B) Galaxies form first, then black holes. C) All galaxies start out as spiral galaxies. D) Black holes form first, seeding the formation of galaxies. Answer: A 15) Collisions between galaxies typically unfold over a period of ________. A) several days B) several months C) thousands of years D) hundreds of millions of years Answer: D 16) Current understanding holds that a galaxy's type (spiral, elliptical, or irregular) ________. A) may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies B) is always determined by the angular momentum of the protogalactic cloud that formed it C) is always determined by whether the galaxy is located in a cluster where collisions are likely or outside a cluster where collisions are less likely D) may either be a result of the mass of the protogalactic cloud that formed it or the result of the heavy element abundance in that cloud Answer: A 17) Why are collisions between galaxies more likely than collisions of stars within galaxies? A) Relative to their sizes, galaxies are much closer together than stars. B) Galaxies are much larger than stars. C) Galaxies travel through space much faster than stars. D) Galaxies have higher redshifts than stars. Answer: A

18) Which of the following is not a feature of central dominant galaxies? A) They're found in clusters of galaxies B) They are spiral galaxies C) They often have multiple galactic nuclei D) They are thought to form through the mergers of smaller galaxies Answer: B 19) Which of the following statements correctly explains why galaxy collisions should have been more common in the past than they are today? A) Galaxies were closer together in the past, because the universe was smaller. B) Galaxies were more active in the past and therefore would have collided with each other more frequently. C) Galaxies were much bigger in the past, because they had not contracted completely. D) Galaxies attracted each other more strongly in the past, because they had not yet turned most of their mass into stars. Answer: A 20) The distinguishing feature of a starburst galaxy is ________. A) a rate of star formation that may be 100 or more times greater than that in the Milky Way B) the presence of an unusually large number of binary star systems containing x-ray bursters C) a very large luminosity compared to the total luminosity of the Milky Way D) strong radio emission from "lobes" of material well outside the visible boundaries of the galaxy Answer: A 21) The unusually bright centers found in some galaxies are called ________. A) active galactic nuclei B) halos C) supermassive black holes D) starbursts Answer: A 22) According to current understanding, what is a quasar? A) An active galactic nucleus that is particularly luminous B) A very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster C) Any object with an extremely large redshift D) A galaxy with an unusually high rate of star formation Answer: A 23) Which of the following observational phenomena is probably not a direct consequence of the presence of a supermassive black hole? A) The energy output of quasars B) The radio emission from radio galaxies C) The huge jets seen emerging from the centers of some galaxies D) The large numbers of stars found in globular clusters Answer: D 20 Copyright © 2022 Pearson Education, Inc.

24) The mass of a supermassive black hole thought to power quasar is typically ________. A) 3 solar masses B) 10 solar masses C) 1 trillion solar masses D) 1 billion solar masses Answer: D 25) According to the model in which active galactic nuclei are powered by supermassive black holes, the high luminosity of an active galactic nucleus primarily consists of ________. A) light emitted by hot gas in an accretion disk that swirls around the black hole B) intense radiation emitted by the black hole itself C) the combined light of thousands of young, high-mass stars that orbit the black hole D) radio waves emitted from radio lobes found on either side of the galaxy we see in visible light Answer: A Concept Quiz Questions 1) In a photo like the Hubble eXtreme Deep Field (Figure 16.1 in your text), we see galaxies in many different stages of their lives. In general, which galaxies are seen in the earliest (youngest) stages of their lives? A) The galaxies that are farthest away B) The galaxies that have the most hot, young stars of spectral types O and B C) The galaxies that are the reddest in color D) The galaxies that are nearest to us Answer: A 2) The most basic difference between elliptical galaxies and spiral galaxies is that ________. A) elliptical galaxies lack anything resembling the disk of a spiral galaxy B) elliptical galaxies lack anything resembling the halo of a spiral galaxy C) spiral galaxies lack anything resembling the distribution of stars in an elliptical galaxy D) elliptical galaxies are very old and spiral galaxies are very young Answer: A 3) Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation? A) The distance to the galaxy B) The rotation rate of the galaxy C) The mass of the galaxy D) The name of the galaxy Answer: A

4) Why are white dwarf supernovae more useful than massive star supernovae for measuring cosmic distances? A) White dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak luminosities. B) We can see only white dwarf supernovae in distant galaxies, not massive star supernovae. C) White dwarf supernovae are much more common than massive star supernovae. D) White dwarf supernovae obey Leavitt's law, while massive supernovae do not. Answer: A 5) In 1924, Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way, thereby putting to rest the idea that it might have been a cloud within our own galaxy. What key observation enabled him to prove this? A) He observed individual Cepheid variable stars in Andromeda. B) He was able to measure the parallax of the Andromeda Galaxy. C) He found that the universe is expanding, and therefore concluded that Andromeda must lie outside our own galaxy. D) He was the first person ever to look through a telescope at the object we now call the Andromeda Galaxy. Answer: A 6) Assume that Hubble's constant is 22 kilometers per second per million light-years. Then we would expect a galaxy 100 million light-years away to be moving ________. (Assume the motion is due only to Hubble's law.) A) away from us at 2,200 km/s B) away from us at 220 km/s C) toward us at 2,200 km/s D) away from us at 22,000 km/s Answer: A 7) Does Hubble's law work well for galaxies within the Local Group? Why or why not? A) No, because galaxies in the Local Group are gravitationally bound together. B) No, because Hubble did not know the Local Group existed when he discovered his law. C) No, because we do not know the precise value of Hubble's constant. D) Yes, it works so well that we have never detected any measurable deviations from its predictions. Answer: A 8) What is the best way to determine a galaxy's redshift? A) Find the galaxy's apparent distance, and look up the redshift based on Hubble's Law. B) Find the color of the galaxy, and estimate its distance based on how red the galaxy is. C) Take a spectrum of the galaxy, and measure the difference in wavelength of spectral lines from the wavelengths of those same lines as measured in the laboratory. D) Measure the magnitude of the galaxy, estimate its distance, and calculate its redshift using Hubble's Law. Answer: C

9) Which statement below correctly describes the relationship between expansion rate and age for the universe? A) The faster the rate of expansion, the younger the age of the universe. B) The faster the rate of expansion, the older the age of the universe. C) Age is independent of the expansion rate. Answer: A 10) What does cosmological redshift do to light? A) Stretches its wavelength B) Makes it brighter C) Makes it slow down D) Makes all light infrared Answer: A 11) Why can't we see past the cosmological horizon? A) Beyond the cosmological horizon, we would be looking back to a time before the universe was born. B) We do not have big enough telescopes. C) The cosmological horizon is infinitely far away, and we can't see to infinity. D) Every galaxy in the entire universe (not just the observable universe) exists within the cosmological horizon, so there's nothing to see beyond it. Answer: A 12) We can study how galaxies evolve because ________. A) we can watch as they interact in real time B) the farther away we look, the further back in time we see C) galaxies are transparent to visible light D) we are really smart astronomers Answer: B 13) Which of the following statements is not an assumption used in models of galaxy formation? A) The very early universe had an almost perfectly uniform distribution of hydrogen and helium gas. B) Some regions in the universe were slightly more dense than others. C) The universe is expanding. D) Gas contracted to form the disks of galaxies before any stars were born. Answer: D 14) One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be ________. A) an irregular galaxy B) an elliptical galaxy C) a spiral galaxy D) a torn and incoherent galaxy Answer: C 23 Copyright © 2022 Pearson Education, Inc.

15) Which of the following phenomena is not thought to be a result of collisions or other interactions between galaxies? A) The presence of very large, central dominant galaxies in clusters of galaxies B) The fact that elliptical galaxies are more common in clusters of galaxies than outside clusters C) Starbursts D) The fact that spiral galaxies have both disk and halo components Answer: D 16) Interactions among galaxies also are thought to influence a galaxy's type in at least some cases. Which of the following does not support the idea that interactions can shape galaxies? A) The fact that more distant galaxies have larger redshifts. B) Computer modeling of collisions between galaxies. C) The fact that galaxies with distorted appearances are more common at great distances than nearby. D) The presence of features such as "tails" extending out of galaxies, bridges between galaxies, and rings of stars around galaxies. Answer: A 17) Observations indicate that over billions of years, galaxies in general tend to change from ________. A) smaller and bluer to larger and redder B) larger and redder to smaller and bluer C) smaller and redder to larger and bluer D) larger and bluer to smaller and redder Answer: A 18) Which is not a general characteristic of starburst galaxies? A) The observed features that cause us to classify a galaxy as a "starburst" galaxy must be only temporary phenomena in the galaxy's history. B) The galaxy's rate of star formation is many times higher than the rate of star formation in the Milky Way. C) Supernovae occur so frequently that their effects combine to drive a galactic wind that blows material into intergalactic space. D) The "starburst" is thought to be caused by the presence of a supermassive black hole in the galaxy's center. Answer: D 19) A quasar's spectrum is hugely redshifted. What does this large redshift tells us about the quasar? A) The composition of the quasar B) The distance to the quasar C) The mass of the quasar's central, supermassive black hole D) The type of host galaxy in which the quasar resides Answer: B

20) Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply? A) Active galactic nuclei tend to become less active as they age. B) Supermassive black holes existed only when the universe was young, and no longer exist today. C) Active galactic nuclei can form only at large distances from the Milky Way. D) The jets seen in many active galactic nuclei must cause them to move far away from us. Answer: A 21) Suppose we observe a source of x-rays that varies substantially in brightness over a period of a few days. What can we conclude? A) The x-ray source is no more than a few light-days in diameter. B) The x-ray source is a quasar. C) The x-ray source contains a black hole with an accretion disk. D) The x-ray source must have a strong, rapidly varying magnetic field. Answer: A 22) All of the following observations are real. Which one does not support the model in which active galactic nuclei are powered by accretion disks around massive black holes? A) The most luminous active galactic nuclei have huge redshifts. B) X-ray emission from active galactic nuclei can vary significantly in times as short as a few days. C) The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun. D) Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed. Answer: A 23) According to the model in which active galactic nuclei are powered by supermassive black holes, the energy released as light comes from ________. A) gravitational potential energy released by matter that is falling toward the black hole B) nuclear fusion in the accretion disk surrounding the black hole C) matter-antimatter annihilation occurring just outside the event horizon of the black hole D) jets emerging from the accretion disk Answer: A 24) The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that ________. A) galaxy formation and supermassive black hole formation must be related B) the black hole will eventually suck in the rest of the galaxy C) the biggest galaxies have the most luminous quasars D) quasars were more common 10 billion years ago than they are today Answer: A

Visual Quiz Questions 1) If you looked at the field of view seen in this Hubble Space telescope with your naked eye, about how big would it appear in the sky?

A) About the size of the Big Dipper B) About the size of the full Moon C) About the size of your little finger held at arm's length against the sky D) About the size of this period — . — viewed at arm's length against the sky Answer: D 2) Is this a photo of a spiral galaxy or an elliptical galaxy, and how do you know?

A) It is a spiral galaxy because we can see a dusty disk going across the center. B) It is a spiral galaxy, and we know because photos of this same galaxy from above show its spiral arms. C) It is an elliptical galaxy because it is elliptical in shape. D) It is an elliptical galaxy because it looks red/yellow in color. Answer: A

3) This photo shows the Large Magellanic Cloud, or LMC for short. Based on what you have learned in about the LMC from your text, which of the following statements about the LMC is not true?

A) Galaxies similar to the LMC are extremely rare. B) It is an irregular galaxy. C) It orbits the Milky Way Galaxy. D) Its color indicates active star formation. Answer: A 4) What is this a picture of?

A) A cluster of galaxies B) A globular cluster C) An elliptical galaxy D) The expanding universe Answer: A

5) Based on this diagram, "red sequence" galaxies are ________ than "blue cloud" galaxies.

A) redder and more luminous B) redder and more distant C) cooler and more distant D) more luminous and older Answer: A

6) Each dot on this graph represents an individual Cepheid variable star. Which of the following is true for a Cepheid that is 10,000 times as luminous as the Sun?

A) It varies gradually in brightness, with a peak in brightness about every 30 days. B) It orbits the center of the galaxy about every 30 days. C) It orbits its binary companion about every 30 days. D) It undergoes a massive flare about every 30 days. Answer: A

7) The data points in this diagram represent the measured speeds and distances of various galaxies, and the solid line represents a best fit to these data. The trend indicated by the solid line is known as ________.

A) Hubble's law B) Leavitt's law C) the inverse square law for light D) Kepler's third law Answer: A 8) This diagram shows several stages in a computer simulation of a collision between two galaxies. What is being simulated?

A) Two spiral galaxies merge to become an elliptical galaxy surrounded by debris. B) Two elliptical galaxies merge to become a spiral galaxy. C) Two galaxies collide, sending their stars flying off into space while their centers merge to become a supermassive black hole. D) Two spiral galaxies collide, ultimately merging to make a larger spiral galaxy. Answer: A 30 Copyright © 2022 Pearson Education, Inc.

9) The bright object in this photo is a quasar (named 3C 273). According to current understanding, about how big is the source of the bright light?

A) About the size of our solar system B) About a million light-years across C) About the size of the central bulge of the Milky Way Galaxy (that is, about 10,000 light-years across) D) About 500 light-years across Answer: A 10) This image, made with data from radio telescopes around the world, shows an object located in the galaxy M87. What is significant about this image?

A) It was the first direct image ever acquired of gas orbiting a supermassive black hole, providing very strong evidence that black holes really exist. B) It was the first image ever acquired of a gaseous disk in which planets are forming around a young star. C) It provided the first definitive proof that distant galaxies have halos like that of our own Milky Way. D) It was the first image of a distant galaxy acquired by the James Webb Space Telescope. Answer: A 31 Copyright © 2022 Pearson Education, Inc.

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Answer the questions below based on Figure 16.18, repeated here. 1) Which distance measurement technique is best suited to measuring objects at a distance of 10 million light-years? Answer: Cepheids 2) Which distance measurement technique is best suited to measuring objects at a distance of 10 light-years? Answer: Parallax 3) Which standard-candle technique is best for measuring the distances of very distant galaxies? Answer: White dwarf supernovae (distant standards)

Answer the questions below based on Figure 16.36, repeated here. 4) This image combines observations made with visible-light and radio telescopes. Which color in the image represents the radio emission? Answer: Purple to pinkish-white 5) What is the approximate distance from the far edge of one lobe to the far edge of the other? Answer: Approximately 2,500,000 light-years 6) What is the approximate size of the visible galaxy producing the jets? Answer: Approximately 200,000 light-years in diameter Chapter Review Questions 1) What are the three major types of galaxies, and how do their appearances differ? 2) Distinguish between spiral and elliptical galaxies in terms of the presence or absence of a disk component and halo component. How does this difference explain the lack of hot, young stars in elliptical galaxies? 3) Where are the blue cloud and the red sequence on a plot of the relationship between galaxy color and luminosity? On which part of the plot would you tend to find the most luminous galaxies? 4) How do galaxy types in clusters of galaxies differ from those in smaller groups and those of isolated galaxies? 5) What do we mean by a standard candle? Explain how we can use standard candles to measure distances. 33 Copyright © 2022 Pearson Education, Inc.

6) Summarize each of the major links in the distance chain. How does Leavitt's law make Cepheid variable stars important? Why are white dwarf supernovae so useful, even though they are quite rare? 7) Explain how Hubble used Leavitt's law to prove that the Andromeda Galaxy lies beyond the bounds of the Milky Way. 8) What is Hubble's law? Explain what we mean when we say that Hubble's constant is between 21 and 23 kilometers per second per million light-years. 9) What is the Cosmological Principle, and how is it important to our understanding of the universe? 10) How is the expansion of the surface of an inflating balloon similar to the expansion of the universe? Use the balloon analogy to explain why Hubble's constant is related to the age of the universe. 11) What do we mean by the lookback time to a distant galaxy? Briefly explain why lookback times are less ambiguous than distances for discussing objects very far away. 12) What do we mean by a cosmological redshift? How does our interpretation of a distant galaxy's redshift differ if we think of it as a cosmological redshift rather than as a Doppler shift? 13) What is the cosmological horizon, and what determines how far away it lies? 14) What do we mean by galaxy evolution? How do telescopic observations allow us to study galaxy evolution? 15) What are the starting assumptions for models of galaxy formation? Describe how a spiral galaxy is thought to form. 16) Describe two ways in which conditions in a protogalactic cloud might lead to the birth of an elliptical rather than a spiral galaxy. 17) Describe some of the consequences of galaxy collisions. Why were collisions more common in the past? 18) What is a starburst galaxy, and why would it tend to have a galactic wind? Explain how this idea leads to a model in which spiral and irregular galaxies are surrounded by an extended atmosphere of hot gas. 19) Define active galactic nuclei and quasars. How can we use variations in luminosity to set limits on the sizes of their emitting regions? 20) What evidence suggests that supermassive black holes really exist? 21) What is a radio galaxy? How can radio galaxies affect the gas surrounding them? 34 Copyright © 2022 Pearson Education, Inc.

22) What evidence suggests that central black holes are connected to the overall evolution of galaxies, and how is the connection thought to work? Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 23) If you want to find a lot of elliptical galaxies, you'll have better luck looking in clusters of galaxies than elsewhere in the universe. 24) Cepheids make good standard candles because they all have exactly the same luminosity. 25) After measuring the galaxy's redshift, I used Hubble's law to estimate its distance. 26) The center of the universe is more crowded with galaxies than any other place in the universe. 27) I'd love to live in one of the galaxies near our cosmological horizon, because then I could see the black void into which the universe is expanding. 28) If someone in a galaxy with a lookback time of 4½ billion years had a superpowerful telescope, that person could see our solar system in the process of its formation. 29) Galaxies that are more than 10 billion years old are too far away to see even with our most powerful telescopes. 30) If the Andromeda Galaxy someday collides and merges with the Milky Way, the resulting galaxy may be elliptical. 31) NGC 9645 is a starburst galaxy that has been forming stars at the same furious pace for some 10 billion years. 32) Astronomers proved that quasar 3C473 contains a supermassive black hole when they discovered that its center is dark.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 16 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 33) Which of these galaxies do we see at its oldest age? A) A galaxy in the Local Group B) A galaxy observed at a distance of 5 billion light-years C) A galaxy observed at a distance of 10 billion light-years. Answer: No Correct Answer Was Provided. 34) Which of these galaxies would you most likely find at the center of a large cluster of galaxies? A) A large spiral galaxy B) A giant elliptical galaxy C) A small irregular galaxy. Answer: No Correct Answer Was Provided. 35) According to Leavitt's law, we can determine the luminosity of a Cepheid in a distant galaxy by ________. A) measuring its parallax B) measuring its period of brightening and dimming C) measuring its recession speed Answer: No Correct Answer Was Provided. 36) Which kind of object is the best standard candle for measuring distances to extremely distant galaxies? A) A white dwarf B) A Cepheid variable star C) A white dwarf supernova. Answer: No Correct Answer Was Provided. 37) Why do virtually all the galaxies in the universe appear to be moving away from our own? A) We are located near where the Big Bang happened. B) We are located near the center of the universe. C) Expansion causes all galaxies to move away from nearly all others. Answer: No Correct Answer Was Provided. 38) When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was about ________. A) 10 billion years old B) 7 billion years old C) 4 billion years old Answer: No Correct Answer Was Provided.

39) Which of these statements expresses a key assumption in our most successful models for galaxy formation? A) The distribution of matter was perfectly uniform early in time. B) Some regions of the universe were slightly denser than others. C) Galaxies formed around supermassive black holes. Answer: No Correct Answer Was Provided. 40) The luminosity of a quasar is generated in a region the size of ________. A) the Milky Way B) a star cluster C) the solar system Answer: No Correct Answer Was Provided. 41) The primary source of a quasar's energy is ________. A) chemical energy B) nuclear energy C) gravitational potential energy Answer: No Correct Answer Was Provided. 42) Observations indicate that galaxies with more massive central black holes tend to also have ________. A) a greater mass of stars in their central bulges B) a greater overall luminosity C) a more elliptical shape Answer: No Correct Answer Was Provided.

Inclusive Astronomy Use these questions to reflect on participation in science. 43) Group Discussion: Leavitt's Law. This book follows the recommendation of the American Astronomical Society in referring to what was previously called the Cepheid "period-luminosity relation" as Leavitt's law. a. Working independently, do a search on "Leavitt's law" to learn about the history behind this name. b. Gather into small groups to share what you've learned and to discuss the reasons behind the change from "period-luminosity relation" to "Leavitt's law." Make a list of pros and cons of the change in terminology. c. Have each group member state which name ("period-luminosity relation" or "Leavitt's law") she or he prefers, and why. It might help to explain your assumptions about why the name of a graph might matter. d. Can you come to a group consensus about which term is preferable? If so, prepare a brief summary to explain your choice to others. If not, make a list of reasons for the disagreement. 44) Group Discussion: Who Gets to Use JWST? The James Webb Space Telescope (JWST), scheduled for launch after this book is published, is a joint project of NASA, the European Space Agency, and the Canadian Space Agency. Once in space, JWST will be the world's premier facility for many astronomical observations, including those relating to galaxy evolution. Demand for telescope time will be enormous, and the people in charge of the proposal process want to maximize the telescope's scientific productivity while simultaneously minimizing the impact of cultural biases on who gets access. a. Working independently, learn about the process of submitting proposals for observations with JWST. Then gather into small groups to share what you've learned. Identify procedures or processes that the JWST mission has put into place to make the review process fair. Be prepared to discuss whether you think those procedures and processes will result in a fair outcome and how you think they could be improved. b. Imagine that you are leading a group charged with reading the proposals and deciding what projects should be awarded telescope time. Who would you ask for advice to determine which proposals had the greatest scientific merit and whether those proposals were feasible, given the technological capabilities of JWST? c. Do you think there is a risk that the judgments of the people you consult might be culturally biased in any way? Make a list of potential cultural biases that could in principle affect their judgments. d. Overall, how would your group structure the process to minimize the effects of cultural bias? Do you think your process would be foolproof, or might there still be biases?

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 45) Deviations from Hubble's Law. Suppose you are measuring distances and velocities of galaxies in order to test Hubble's law. You find that 90% of the galaxies have velocities that are within 200 kilometers per second of the predictions of Hubble's law but 10% have velocities that deviate from the predictions by up to 1000 kilometers per second. Propose a hypothesis that would explain these deviations from Hubble's law, and outline a set of observations that could test your hypothesis. 46) The Case for Black Holes. Consider four sets of evidence for the existence of black holes: (1) observations of x-ray binary systems; (2) observations of gravitational waves from mergers of black holes; (3) observations of star orbits at the center of the Milky Way; (4) observations of the center of M87. For each case, briefly summarize the observational evidence and state the implied black hole mass (or masses). Then rank the sets in order of how compelling you find the evidence. Justify your opinions. 47) Black Holes and Galaxy Evolution. Astronomers do not yet know the cause of the relationship between the mass of a galaxy's supermassive black hole and the total mass of stars in its bulge (see Figure 16.35), but this chapter discussed the hypothesis that it arises because energetic outbursts from the black hole periodically disrupt a galaxy's star—gas—star cycle. Suggest possible observations that could be made to test this hypothesis. 48) Unanswered Questions. Briefly describe one important but unanswered question related to galaxy evolution. If you think it will be possible to answer that question in the future, describe how we might find an answer, being as specific as possible about the evidence necessary to answer the question. If you think the question will never be answered, explain why you think it is impossible to answer. 49) Group Activity: Counting Galaxies. The following activity is based on the Hubble eXtreme Deep Field in Figure 20.1. Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39. a. Working individually, estimate the number of galaxies in the image. b. Gather into small groups, where each member presents his or her method and estimate to the others. Do the estimates differ? By how much? c. Discuss any significant differences in the methods and the resulting estimates, with the goal of understanding the pros and cons of different estimation methods. d. As a group, come up with an estimation method that incorporates the best features of the team members' individual methods, and apply this method to come up with your group's final estimate for the number of galaxies in the image. Then use the fact that this image shows about 1/30,000,000 of the entire sky to come up with an estimate for the total number of galaxies in the observable universe. Compare your estimate with those of other groups in your class.

Investigate Further 50) Going Deep with Hubble. The Hubble eXtreme Deep Field in Figure 16.1 was chosen for observation in large part because it is a completely ordinary part of the sky. Why do you think astronomers would want to devote so much precious telescope time to observing totally ordinary regions of the sky in such great detail? Explain your reasoning. 51) Supernovae in Other Galaxies. In which type of galaxy would you be most likely to observe a massive star supernova, a giant elliptical galaxy, or a large spiral galaxy? Explain your reasoning. 52) Hubble's Galaxy Types. How would you classify the following galaxies using the system illustrated in Figure 16.7? Justify your answers. a. Galaxy M101 (Figure 16.2) b. Galaxy NGC 4594 (Figure 16.3) c. Galaxy NGC 1300 (Figure 16.4) d. Galaxy M87 (Figure 16.5) 53) Color and Luminosity. The luminosity of our Milky Way galaxy is about 1.5 × 1010LSun. Describe how the Milky Way's light output compares with those of the most luminous galaxies in the blue cloud, based on the information in Figure 16.8. Approximately how much more luminous than the Milky Way are the most luminous galaxies in the red sequence? 54) Cepheids as Standard Candles. Suppose you are observing Cepheids in a nearby galaxy. You observe one Cepheid with a period of 8 days between peaks in brightness and another with a period of 35 days. Use Figure 16.13 to estimate the luminosity of each star. 55) Galaxies at Great Distances. The most distant galaxies that astronomers have observed are much easier to see in infrared light than in visible light. Explain why that is the case. 56) Universe on a Balloon. In what ways is the surface of a balloon a good analogy for the universe? In what ways is this analogy limited? Explain why a miniature scientist living in a polka dot on the balloon would observe all other dots to be moving away, with more distant dots moving away faster. 57) Life Story of a Spiral. Imagine that you are a spiral galaxy. Describe your life history from birth to the present day. Your story should be detailed and scientifically consistent, but also creative. That is, it should be entertaining while at the same time incorporating current scientific ideas about the formation of spiral galaxies. 58) Life Story of an Elliptical. Imagine that you are an elliptical galaxy. Describe your life history from birth to the present. There are several possible scenarios for the formation of elliptical galaxies, so choose one and stick to it. Be creative while also incorporating scientific ideas that demonstrate your understanding.

Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 59) Cepheids in M100. Scientists using the Hubble Space Telescope have observed Cepheids in the galaxy M100. Here are the actual data for three Cepheids in M100: • Cepheid 1: luminosity = 3.9 × 1030 watts apparent brightness = 9.3 × 10-19 watt/m2 • Cepheid 2: luminosity = 1.2 × 1030 watts apparent brightness = 3.8 × 10-19 watt/m2 • Cepheid 3: luminosity = 2.5 × 1030 watts apparent brightness = 8.7 × 10-19 watt/m2 Compute the distance to M100 with data from each of the three Cepheids. Do all three distance computations agree? Based on your results, estimate the uncertainty in the distance you have found. 60) Distances from Hubble's Law. Imagine that you have obtained spectra for several galaxies and have measured the redshift of each galaxy to determine its speed away from us. Here are your results: • Galaxy 1: Speed away from us is 15,000 km/s. • Galaxy 2: Speed away from us is 20,000 km/s. • Galaxy 3: Speed away from us is 25,000 km/s. Estimate the distance to each galaxy from Hubble's law. Assume that H0 = 22 km/s/Mly 61) Your Last Hurrah. Suppose you fell into an accretion disk that swept you into a supermassive black hole. On your way down, the disk radiates 10% of your mass-energy, E = mc2 a. What is your mass in kilograms? (Recall that 1 kg = 2.2 pounds.) Calculate how much radiative energy will be produced by the accretion disk as a result of your fall into the black hole. b. Calculate approximately how long a 100-watt light bulb would have to shine to radiate this same amount of energy.

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 17 The Birth of the Universe Section 17.1 1) To date, physicists have investigated the behavior of matter and energy at temperatures as high as those that existed in the universe as far back as ________ after the Big Bang. A) 1 million years B) 300,000 years C) 300 years D) 3 minutes E) 10-10 second Answer: E 2) What is the main idea of the Big Bang theory? A) The universe formed from the collapse of a previous universe. B) All matter and energy in the universe was in an incredibly hot, dense state and space itself began expanding. C) The universe as we see it formed from the singularity in a black hole. D) A massive explosion about 14 billion years ago created all matter and energy that rushed out to fill the surrounding space. Answer: B 3) When we say that the electromagnetic and weak forces "freeze out" from the electroweak force at 10-10 seconds after the Big Bang, what do we mean? A) These forces are important only at temperatures below the freezing point of water—a temperature that the universe reached at an age of about 10-10 seconds. B) "Freezing out" was a term coined by particle physicists who think that the Big Bang theory is really cool. C) Prior to this time, the electromagnetic and weak forces could not be distinguished from each other, but they possessed separate identities following this time. D) Following this time, neither the electromagnetic nor the weak force was ever important in the universe again. E) Following this time, the electromagnetic and weak forces starting cooling the universe, which is why it is so cold today. Answer: C 4) What direct evidence do we have that the weak and electromagnetic forces were once unified as a single electroweak force? A) The most advanced telescopes are able to see back to this era in the universe. B) Detectors on Earth have received photons and high-energy particles from this era. C) Temperatures in the center of the Sun can reproduce the conditions during this era. D) Particle accelerators on Earth can recreate the conditions of this era and have produced particles predicted by the electroweak theory. E) We have no direct evidence of the electroweak force. Answer: D 1 Copyright © 2022 Pearson Education, Inc.

5) What happened to the quarks that existed freely during the particle era? A) They combined to make protons, neutrons, and their antiparticles. B) They froze out of the soup of particles at the end of the era. C) They evaporated. D) They combined to make electrons and neutrinos. E) They combined to make W and Z bosons. Answer: A 6) If the electromagnetic force is stronger than gravity, then why is it overpowered by gravity on large scales? A) The electromagnetic force only works on scales of about the size of an atomic nucleus. B) The electromagnetic force follows an inverse cube law with distance, rather than an inverse square law. C) Electrical charge is canceled out by mass. D) Most objects are electrically neutral. Answer: D 7) This figure shows the relative strength of the four fundamental forces at different temperatures. Based on this graph, at what temperature does the strong force become equal in strength to the electroweak force?

A) About 1015 K B) About 1027 K C) About 1032 K D) The strong force always remains distinct and stronger than the electroweak force at all temperatures. Answer: B 2 Copyright © 2022 Pearson Education, Inc.

8) Which force binds together protons and neutrons in a nucleus? A) Strong force B) Gravity C) Electromagnetic force D) Weak force Answer: A 9) Our current theories are unable to describe the conditions of the universe during the Planck era. About how long after the Big Bang did the Plank era end? A) 10-10 second B) 10-35 second C) 10-43 second D) 3 minutes E) 380,000 years Answer: C 10) Why can't current theories describe what happened during the Planck era? A) We do not yet have a theory that links quantum mechanics and general relativity. B) We do not understand the properties of antimatter. C) We do not know how much energy existed during that time. D) It was a time period from which we cannot receive radiation. E) The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant. Answer: A 11) If grand unified theories are correct, what caused inflation at the end of the GUT era? A) Gravity was an extremely weak force at this period in time. B) Large amounts of matter and antimatter annihilated at this time. C) There wasn't enough matter present to slow down the expansion at that time. D) The universe was too small and needed to grow quickly. E) An enormous amount of energy was released when the strong force froze out (became distinct) from the GUT force. Answer: E 12) Approximately how long after the Big Bang did the era of nucleosynthesis end, marking the time when the basic chemical composition of the universe was determined? A) 10-10 second B) 0.001 second C) 5 minutes D) 380,000 years E) 5 million years Answer: C

13) What kinds of atomic nuclei were present when fusion ceased at the end of the era of nucleosynthesis? A) Only hydrogen B) Only helium C) Hydrogen, helium, and trace amounts of deuterium and lithium D) Roughly equal amounts of each of the following: hydrogen, helium, deuterium, and lithium E) Nuclei of all the chemical elements Answer: C 14) Why did fusion cease only about 5 minutes after the Big Bang (at the end of the era of nucleosynthesis)? A) The density of the universe became too low. B) There was no longer any more hydrogen available for fusion reactions. C) Too many heavy elements were produced. D) Neutrinos carried off too much energy. Answer: A 15) What event made it possible for photons to begin to travel freely through the universe when the universe was about 380,000 years old? A) Magnetic fields had weakened to the point that they no longer interfered with light. B) The universe had expanded and cooled enough for electrons to combine with nuclei to form neutral atoms. C) Atomic nuclei were finally able to escape the plasma of the early universe. D) Atoms started to combine to make the first molecules. E) Fusion of hydrogen to make helium ceased. Answer: B 16) Which of the following happened first (after the Big Bang)? A) Molecules formed. B) Neutral atoms formed. C) Protons formed. D) Helium formed. Answer: C

17) Order these cosmological events in order from earliest to latest. A) Formation of the first atomic nuclei, formation of the first neutral atoms, formation of the first subatomic particles, formation of the first galaxies B) Formation of the first subatomic particles, formation of the first atomic nuclei, formation of the first neutral atoms, formation of the first galaxies C) Formation of the first galaxies, formation of the first neutral atoms, formation of the first atomic nuclei, formation of the first subatomic particles D) Formation of the first subatomic particles, formation of the first neutral atoms, formation of the first atomic nuclei, formation of the first galaxies E) Formation of the first neutral atoms, formation of the first subatomic particles, formation of the first atomic nuclei, formation of the first galaxies F) Formation of the first atomic nuclei, formation of the first subatomic particles, formation of the first neutral atoms, formation of the first galaxies Answer: B 18) According to the Big Bang theory, why do we live in a universe that is made of matter rather than antimatter? A) Einstein's famous equation E = mc2 tells us that energy can turn into matter, but does not tell us that it can turn into antimatter. B) GUT theories predict that under the conditions that prevailed in the early universe, the normal laws of physics would have been suspended so that only matter particles were created, and no particles of antimatter. C) The fact that we live in a universe made of matter is not surprising because antimatter has never been shown to exist for real. D) During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles. Answer: D 19) Which of the following observations is not a piece of evidence that lends support to aspects of the Big Bang theory? A) The darkness of the night sky B) The expansion of the universe C) The observed helium abundance in the universe D) The relative motions of galaxies in the Local Group Answer: D

Section 17.2 1) Which of the following lists the two key predictions of the Big Bang model that have been verified by observations? A) (1) the existence of the cosmic microwave background and (2) the amount of helium relative to hydrogen in the universe B) (1) the existence of the cosmic microwave background and (2) the existence of dark matter C) (1) the existence of the cosmic microwave background and (2) the near-critical density of the universe D) (1) the predominance of matter over antimatter and (2) the near-critical density of the universe E) (1) the predominance of matter over antimatter and (2) the large-scale structure of galaxies Answer: A 2) When did the photons in the cosmic microwave background first travel freely through the universe? A) The moment of the Big Bang B) About 10-10 second after the Big Bang C) About 5 minutes after the Big Bang D) About 380,000 years after the Big Bang E) At the time, the first stars began to shine in the universe. Answer: D 3) Why does the Big Bang theory predict that the cosmic microwave background should have an essentially perfect thermal radiation spectrum? A) This radiation came from the heat of the universe itself. B) The spectrum of pure hydrogen is a perfect thermal radiation spectrum. C) The spectrum of 75 percent hydrogen and 25 percent helium is a perfect thermal radiation spectrum. D) The light from all the stars and gas in the sky averaged over the entire universe is a perfect thermal radiation spectrum. E) The first stars that formed in the universe must all have had the same temperature. Answer: A 4) The cosmic microwave background is almost perfectly uniform in all directions, except for very small deviations in its temperature. What do scientists think these small deviations represent? A) Regions of slightly higher density that made it possible for galaxies to form B) Small increases in temperature caused by individual stars C) The warmer spots represent regular matter and the cooler spots represent dark matter. D) Regions of slightly higher helium abundance in the early universe E) Varying redshifts and blueshifts due to motions of gas in the early universe Answer: A

5) Suppose you repeated the famous COBE and Planck observations of the cosmic microwave background, with a slight different observational setup, to check their results. Which of the following observations would be surprising and contradict earlier findings? A) You find that cosmic microwave background has a temperature of 2.73 K. B) You find that cosmic microwave background has an almost perfect thermal spectrum. C) You find that cosmic microwave background contains redshifted emission lines of hydrogen and helium. D) You find that cosmic microwave background looks essentially the same in all directions. E) You find that cosmic microwave background has tiny temperature fluctuations at the level of about 1 part in 100,000. Answer: C 6) Approximately how long have cosmic microwave background photons been traveling through space? A) 5000 years B) 380,000 years C) 14 billion years D) It depends on which direction they come from. Answer: C 7) In what sense is the cosmic microwave background evidence for the Big Bang? A) Because Einstein predicted that the universe should be expanding B) Because this radiation would have been necessary to cause the Big Bang C) Because explosions are always associated with dangerous levels of radiation D) Because it was predicted to exist if the Big Bang really occurred Answer: D 8) Our Sun is made of about 28% helium (by mass). Where did this helium come from? A) Fusion in stars B) The Big Bang only C) Mostly from fusion in stars with a small contribution from the Big Bang D) Mostly from the Big Bang with a small contribution from fusion in stars E) Radioactive decay of heavier elements only Answer: D 9) Why did the Big Bang not produce a significant proportion of elements heavier than helium? A) High-energy photons did not affect helium, but blasted apart the nuclei of heavier elements as soon as they formed. B) By the time helium nuclei could survive, the temperature had become too low for heavier elements to form. C) They did, but radioactive decay caused these elements to disappear again. Answer: B

10) The spectrum of the cosmic microwave background peaks at a wavelength of about 1 mm, and the universe has a temperature of about 3 K. If the spectrum instead peaked at a wavelength of 10 millimeters, what would its temperature be? A) The same temperature of about 3 K B) Less than 3 K C) More than 3 K Answer: B Section 17.3 1) Why do scientists think tiny quantum ripples should have been present in the very early universe? A) The shock wave of the Big Bang caused ripples that expanded outward with time. B) The energy released when the strong force froze out of the GUT force caused shock waves that produced ripples in the universe. C) Matter and antimatter particles that spontaneously formed from high-energy photons caused disruptions in the radiation field. D) The annihilation of matter and antimatter particles caused tiny explosions that disrupted the radiation field. E) Quantum mechanics tells us that the energy fields at any point in space be continually fluctuating as a result of the uncertainty principle. Answer: E 2) What is hypothesized to have caused a sudden inflation of the early universe? A) The annihilation of matter and antimatter B) The separation of the electromagnetic and weak forces C) The "freezing out" of the strong force from the GUT force D) The energy released in the fusion of protons and neutrons to produce helium E) Giant quantum fluctuations Answer: C 3) The temperature variations of the cosmic microwave background observed by the Planck telescope agree well with our model predictions. This provides persuasive evidence in favor of what? A) Both the Big Bang and inflation B) Only the Big Bang, but not inflation C) Not the Big Bang, but inflation D) Neither the Big Bang nor inflation Answer: A

4) How does the hypothesis of inflation explain the near-uniformity of the cosmic microwave background? A) The expanding universe would have cooled. B) Matter expanded into regions of space that had no matter, and thus ended up at the same temperature. C) Matter was near the critical-density for a universal collapse, which smoothed out the differences in temperatures. D) Prior to rapid inflation, all regions of space were close enough to bounce radiation back and forth and reach the same temperature. Answer: D 5) Which of the following hypothetical observations would demonstrate that the inflation model was incorrect? A) The geometry of the universe is curved, not flat. B) The helium abundance in a galaxy is 29%. C) The rate of expansion of the universe has changed over time. D) Stars began to shine only a few hundred million years after the Big Bang. Answer: A 6) This chapter discusses the "critical density" of the universe. More generally, when we say that something is a "critical value" in science, we mean ________. A) a number that signifies some boundary or change B) a value that has been heavily criticized C) an idea, representing a value system, that is very important D) any number that has been very precisely measured Answer: A Section 17.4 1) The fact that the sky is dark at night proves that the universe cannot be ________. A) eternal and unchanging with an infinite number of stars B) expanding C) more than 20 billion years old D) infinite in size Answer: A

Short Answer Questions 1) Briefly explain how Hubble's discovery of a relationship between galactic distance and recession velocity led to the idea of the Big Bang. Answer: Hubble's discovery showed that the universe is expanding. If the universe is expanding, then logically it seems that it should have been smaller in the past. Extrapolating back in time, there must have been a time when everything was in one place—which we call the Big Bang. 2) Briefly describe two key pieces of evidence that support the Big Bang theory. Answer: The two key pieces of evidence that support the Big Bang theory are the cosmic microwave background and the observed helium content of the universe. The cosmic microwave background consists of photons arriving at Earth directly from the end of the era of nuclei. The radiation came from the heat of the universe and should have a thermal radiation spectrum with a peak wavelength corresponding to 3000 K, the temperature the universe was at the end of that era. Since the universe has expanded by a factor of about 1000 since that time, we observe the radiation with a peak wavelength of about a millimeter, corresponding to a temperature of 2.73K. The Big Bang theory predicts that the universe should have had a composition of 75 percent hydrogen and 25 percent helium by mass at the end of the era of nucleosynthesis. The Milky Way's helium fraction is about 28 percent, and no galaxy has a helium fraction lower than 25 percent. Reading Quiz Questions 1) In general, what happens to the density and temperature of a gas as it expands? A) It gets less dense and cooler. B) It gets denser and cooler. C) It gets less dense and hotter. D) It gets denser and hotter. Answer: A 2) In the distant past, the temperature of the universe was ________. A) hotter than it is today B) cooler than it is today C) absolute zero (0 K) D) 3 K Answer: A 3) What is antimatter? A) It consists of particles that are just like those of ordinary matter except with opposite properties, such as opposite charge. B) It is matter that we infer to be in space by its gravitational influence, but that we have not yet identified. C) It is a form of matter that has been hypothesized to exist but for which there is not yet any experimental evidence. D) It is the material that makes up a complete antiuniverse that is identical to our own except that it is made from antimatter instead of matter. Answer: A 10 Copyright © 2022 Pearson Education, Inc.

4) What happens when a particle of matter meets its corresponding antiparticle of antimatter? A) The combined mass of the two particles is completely transformed into energy (photons). B) They can form a complete atom. C) They fuse to make a heavier particle. D) The question makes no sense, because antimatter does not really exist. Answer: A 5) Experiments allow physicists today to reproduce (on very small scales) energy and temperature conditions thought to have prevailed in the early universe as far back in time as about ________. A) one ten-billionth (10-10) of a second after the Big Bang B) 380,000 years after the Big Bang C) 10-45 seconds after the Big Bang D) 10 billion years ago Answer: A 6) The four fundamental forces that operate in the universe today are ________. A) strong force, weak force, electromagnetic force, and gravity B) strong force, weak force, electric force, and magnetic force C) nuclear force, electromagnetic force, gravity, and tidal force D) nuclear force, gravity, electric force, and magnetic force Answer: A 7) What is the significance of Planck time? A) Before it, conditions were so extreme that our current understanding of physics is insufficient to predict what might have occurred. B) It is the time at which inflation is thought to have occurred. C) It is the time when the cosmic microwave background was released. D) It is the amount of time required for two protons to fuse to make deuterium. Answer: A 8) A grand unified theory (GUT) refers to a type of theory intended to unify ________. A) the strong force with the electromagnetic and weak forces B) gravity with the strong and weak forces C) the electromagnetic and weak forces D) all four forces together Answer: A 9) In terms of the "eras" that scientists use to describe different times in the history of the universe, we live in the ________. A) era of galaxies B) era of nucleosynthesis C) era of nuclei D) Planck era Answer: A

10) What do we mean by the term inflation? A) A sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe's first second of existence B) The expansion of the universe that we still observe today C) The sudden release of photons when a particle and antiparticle annihilate one another D) Quantum fluctuations by high speed, relativistic particles in a state of false vacuum that caused disturbances in the space–time continuum leading to the process described in the question to which this answer refers Answer: A 11) Which of the following statements correctly summarizes the events in the early universe according to the Big Bang theory? A) The universe began with the forces unified. During the first fraction of a second, the forces separated and there was a brief but important episode of inflation. Subatomic particles of both matter and antimatter then began to appear from the energy present in the universe. Most of the particles annihilated to make photons, but some became protons, neutrons, electrons, and neutrinos. The protons and neutrons underwent some fusion during the first three minutes, thereby determining the basic chemical composition of the universe. B) An episode of what we call inflation initiated the event of the Big Bang. Once the Big Bang got underway, particles and forces began to appear one by one. The forces produced protons, which fused to make hydrogen and helium until the universe was about 380,000 years old. Then gravity began to act, turning the hydrogen and helium into galaxies. C) Forces and various subatomic particles began to appear during the first second after the Big Bang. For reasons not understood, the particles were all made of ordinary matter and none were made of antimatter, thus explaining why we live in a universe made of matter. The particles underwent some fusion for the first 380,000 years after the Big Bang, at which time the first stars were born. D) The Big Bang began with the initiation of what we call inflation, which gradually slowed to the current expansion rate of the universe. Forces came to exist for a different reason, having to do with quantum fluctuations in the space–time continuum. Particles came to exist as a result of cracks made when forces froze. Once there were particles, gravity brought them together to make stars, and the stars then turned the particles into hydrogen, helium, and other elements. Answer: A 12) Which statement about the cosmic microwave background is not true? A) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. B) Its spectrum has the shape of an essentially perfect thermal radiation spectrum. C) With the exception of very small variations, it appears essentially the same in all directions in which we look into space. D) It is thought to be radiation that began its journey to our telescopes when the universe was about 380,000 years old. Answer: A

13) What is the approximate temperature of the universe (as a whole) today? A) 3K B) 3000K C) 300K D) The universe cannot be said to have a single temperature. Answer: A 14) The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they? A) (1) the existence and specific characteristics of the observed cosmic microwave background (2) the observed overall chemical composition of the universe B) (1) the early universe was hot and dense (2) we see distant galaxies as they were in the distant past C) (1) the episode of inflation thought to have occurred in the early universe (2) the separation of gravity and the other forces at the end of the Planck era D) (1) the universe is expanding (2) the observed ratio of spiral to elliptical galaxies in the universe Answer: A 15) Which of the following observations cannot be explained by the Big Bang theory, unless we assume that an episode of inflation occurred? A) The fact that the temperature of the cosmic microwave background is almost the same everywhere B) The fact that about 25% of the ordinary matter in the universe consists of helium C) The existence of the cosmic microwave background D) The fact that the universe is expanding Answer: A 16) The critical density of the universe is the ________. A) total density of matter and energy needed to give the universe a "flat" geometry (in spacetime) B) measured average density of matter in the universe C) density of matter necessary for stars and galaxies to form D) density value at which the total density of matter precisely equals the total density of antimatter Answer: A 17) Models of the Big Bang that include inflation predict that the overall geometry of the universe should be "flat" (in spacetime). This prediction ________. A) agrees with data found by studying the cosmic microwave background B) has been verified by observing the paths of light coming from distant galaxies C) has been shown to be incorrect by study of the expansion pattern of the universe D) cannot be tested at this time Answer: A

18) Which of the following statements cannot be tested by science today? A) Prior to the Planck time, our universe sprouted from another universe. B) Our universe is flat. C) The universe is 14 billion years old. D) The expansion of the universe is now accelerating. Answer: A 19) Olbers's paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question? A) Why is the sky dark at night? B) What would it be like to ride on a beam of light? C) How many stars are in the universe? D) Can we measure the position and momentum of an electron at the same time? Answer: A Concept Quiz Questions 1) How do we determine the conditions that existed in the early universe? A) We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size. B) We look all the way to the cosmological horizon, where we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang. C) The conditions in the very early universe must have been much like those found in stars today, so we learn about them by studying stars. D) We can only guess at the conditions, because we have no way to calculate or observe what they were. Answer: A 2) Why do scientists assume that the early universe was much hotter and denser than the universe of today? A) The fact that the universe is expanding implies that objects were closer together in the past, and compressing material makes it hotter and denser. B) All objects begin their existence in a hot and dense state. C) The fact that the universe is filled with stars and galaxies implies that matter must once have been hot to have made these objects. D) Observations of distant galaxies show that they are much hotter than galaxies of today, suggesting that the whole universe was hotter in the past. Answer: A 3) Why can't current theories describe what happened during the Planck era? A) We do not yet have a theory that links quantum mechanics and general relativity. B) We do not know how hot or dense the universe was during that time. C) We do not understand the properties of antimatter. D) The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant. Answer: A 14 Copyright © 2022 Pearson Education, Inc.

4) Which of the following statements best explains what we mean when we say that the electroweak and strong forces "froze out" at 10-38 second after the Big Bang? A) These two forces first became distinct at this time. B) These forces are important only at temperatures below the freezing point of water, which is a temperature that the universe reached at an age of about at 10-38 second. C) Freezing out was a term coined by particle physicists who think that the Big Bang theory is really cool. D) Following this time, neither the strong nor electroweak forces were ever important in the universe again. Answer: A 5) According to the Big Bang theory, how many forces, and which ones, operated in the universe during the GUT era? A) Two forces: gravity and a single force that later became the strong, weak, and electromagnetic forces B) One force that represented the unification of all four forces that operate today C) Three forces: gravity, the strong force, and the electroweak force D) Two forces: the strong force and the electroweak force Answer: A 6) Laboratory experiments conducted with particle accelerators confirm predictions made by the theory that unifies ________. A) the electromagnetic and weak forces into the electroweak force B) the strong, weak, and electromagnetic forces into the GUT force C) the unification of all four forces into a single "superforce" D) the strong and weak forces into the combined nuclear force Answer: A 7) What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old? A) The basic chemical composition of the universe had been determined. B) The proportions of dark matter and luminous matter had been determined. C) It marks the time at which the first stars formed. D) It marks the time at which the expansion of the universe had settled down to its current rate. Answer: A

8) According to the Big Bang theory, why do we live in a universe that is made of almost entirely of matter rather than antimatter? A) During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything was annihilated except the slight excess of matter particles. B) GUT theories predict that under the conditions that prevailed in the early universe, the normal laws of physics would have been suspended, so that only matter particles were created and no particles of antimatter. C) The fact that we live in a universe made of matter is not surprising, because antimatter has never been shown to exist for real. D) Einstein's famous equation E = mc2 tells us that energy can turn into matter but does not tell us that it can turn into antimatter. Answer: A 9) Which of the following is not an observed characteristic of the cosmic microwave background? A) It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe. B) It has a perfect thermal radiation spectrum. C) Its temperature is the same everywhere, except for small variations at the level of 1 part in 100,000. D) Its temperature is a little less than 3 Kelvin (3 degrees above absolute zero). Answer: A 10) In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times before about 380,000 years after the Big Bang. Why? A) Before that time, the universe was too crowded with stars. B) Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely. C) Before that time, the universe was dark so there was no light to illuminate anything. D) 380,000 years after the Big Bang marks the time when stars were first born, producing the light by which we can see the universe. Answer: B 11) If observations had shown that the cosmic microwave background was perfectly smooth (rather than having slight variations in temperature), then we would have no way to account for ________. A) the relationship between the strong and the weak force B) the fact that our universe is expanding C) how galaxies came to exist D) the existence of helium in the universe Answer: C

12) In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe? A) By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur. B) Helium fusion occurred, but the carbon nuclei that were made were later destroyed by the intense radiation in the early universe. C) Temperatures in the early universe were never above the roughly 100 million Kelvin required for helium fusion. D) No one knows; this is one of the major mysteries in astronomy. Answer: A 13) How does the hypothesis of inflation account for the existence of the "seeds" of density from which galaxies and other large structures formed? A) Inflation would have caused random, microscopic quantum fluctuations to grow so large in size that they became the seeds of structure. B) Inflation predicts that gravity would have been very strong and thereby would have concentrated mass into seeds. C) Inflation tells us that the universe should have a "flat" overall geometry, and this led to the flat disks of galaxies. D) Inflation predicts that temperatures and densities should have become nearly equal throughout the universe. Answer: A 14) Suppose that inflation did not occur. In that case, the fact that the cosmic microwave background has the same temperature in opposite directions of the sky would be considered ________. A) surprising, because those locations would never have been close enough to have any light or matter exchanged between them B) surprising, because we would not expect those locations to have the same age C) natural, because everything in the universe is naturally expected to have the same temperature D) natural, because quantum fluctuations in the early universe would have ensured that the whole universe had precisely the same temperature Answer: A 15) Which analogy best explains why inflation predicts that the overall geometry of the observable universe should appear to be flat? A) Earth is so big that it the part explored by an ant appears flat. B) As a balloon expands, dots that you have drawn on it become farther apart with time. C) If you stretch a wavy line infinitely, it becomes straight. D) No city on Earth is any more the "center" of Earth's surface than any other city. Answer: A

16) Suppose that the universe were infinite in both extent and age. In that case, we would expect the night sky to be ________. A) uniformly bright B) much larger C) filled with about 1,000 times as many stars D) expanding at a more rapid rate Answer: A 17) The Big Bang theory seems to explain how elements were formed during the first few minutes after the Big Bang. Which hypothetical observation (these are not real observations) would call our current theory into question? A) The discovery of a galaxy with a helium abundance of only 10% by mass B) The discovery of a star-like object made almost entirely of carbon and oxygen C) The discovery of a planet that with no helium in its atmosphere D) The discovery of a galaxy with 27% helium by mass Answer: A

Visual Quiz Questions

1) What does this graph show? A) It shows calculations indicating that the temperature of the universe began quite high but is now quite low. B) It shows that the temperature of the universe began quite low but is now quite high. C) It shows that the temperature of the universe has changed diagonally with time. D) It shows evidence that the Big Bang really happened. Answer: A 2) On this graph, the time corresponding to the point at the far lower right of the diagonal line represents ________. A) the age of the universe today, in seconds B) age of the universe at the time the cosmic microwave background was released C) the Planck time D) the amount of time required for nucleosynthesis in the early universe Answer: A

3) What does this diagram represent?

A) A particle and antiparticle colliding and converting all their mass into photons B) Two photons spontaneously turning into a particle and an antiparticle C) A blue electron and a red electron turning into to pink light rays D) A particle of ordinary matter and a particle of dark matter colliding and becoming two photons of dark energy Answer: A 4) Study this diagram that summarizes the eras of the universe. Which of the following statements is not true?

A) The electroweak era was the longest lasting of all the eras in the history of the universe. B) The total time during which the universe went through the Planck era, GUT era, electroweak era, and particle era was less than the time it takes you to blink your eyes. C) Whole atoms with both electrons and nuclei were not stable until the universe was about 380,000 years old. D) Most of the helium in the universe was produced before the universe was about five minutes old. Answer: A

5) Which of the following is not implied by this diagram?

A) There are six distinct forces known to operate in the universe, and a seventh force called the "super force" might also exist. B) At very high temperatures, the electromagnetic and weak forces are no longer distinct but instead act as a single electroweak force. C) At the current temperature of the universe, gravity is the weakest of the forces. D) At the current temperature of the universe, the strong force is the strongest of the forces. Answer: A

6) The data points on this graph represent the measured spectrum of the cosmic microwave background, while the solid curve represents a theoretically calculated thermal radiation spectrum for a temperature of 2.73 K. What is the significance of the near-perfect match between the data and the theoretical spectrum?

A) It shows that the cosmic microwave background has a thermal radiation spectrum, just as the Big Bang theory predicts it should. B) It shows that all objects in the universe emit thermal radiation. C) It tells us the average temperature of gas in the Milky Way Galaxy. D) It demonstrates that the universe must contain more dark matter than ordinary matter. Answer: A

7) This figure shows an all-sky map of the cosmic microwave background recorded by the Planck telescope. How long did this light travel through space before it reached the telescope? A) About 14 billion years B) About 380,000 years C) About a million years D) Depending on what portion of the map we're looking at, the light traveled for times between just a few minutes and a few billion years. Answer: A 22 Copyright © 2022 Pearson Education, Inc.

8) This figure shows an all-sky map of the cosmic microwave background recorded by the Planck mission. What do the dark and bright variations represent? A) Regions of the sky with very slightly different density at the time the radiation was emitted B) Regions of the sky with different proportions of hydrogen and helium at the time the radiation was emitted C) The present distribution of galaxies in the universe D) Regions of the sky with different amounts of dark energy Answer: A 9) This diagram represents what we call saddle-shaped geometry. In the context of this chapter, what is its significance?

A) It represents a two-dimensional analogy to one possible geometry for our universe. B) It shows what our universe really looks like if the density is less than the critical density. C) It shows the general shape of the cosmic microwave background. D) Its dark color is meant to indicate that dark energy and dark matter are the primary constituents of the universe. Answer: A

10) This graph is made from measurements of the cosmic microwave background (dots) and a model based on the hypothesis of inflation. What does it show?

A) Measurements of the separation between regions of different temperature (in the cosmic microwave background) agree with predictions made by the hypothesis of inflation. B) It shows that the temperature of the cosmic microwave background is about 3 Kelvin. C) It shows that some regions of the early universe must have been hundreds of times as dense as others. D) It shows that the universe has no center and no edges. Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

Answer the following questions based on Figure 17.1, which is repeated here. 1) What was the approximate temperature of the universe at an age of 1015 s? A) About 1 K B) About 100 K C) About 105 K D) About 1015 K Answer: B 2) What was the approximate temperature of the universe at an age of 5 minutes? A) About 300 K B) About 106 K C) About 109 K D) About 1012 K Answer: C 25 Copyright © 2022 Pearson Education, Inc.

3) How much cooler is the universe now (at an age of 4 × 1017 s) than it was at an age of 1 second? A) Its current temperature is one hundred-millionth (10-8) the temperature at an age of 1 second. B) Its current temperature is one hundred-thousandth (10-5) the temperature at an age of 1 second. C) Its current temperature is one-hundredth (10-2) the temperature at an age of 1 second. D) Its current temperature is one ten-billionth (10-10) the temperature at an age of 1 second. Answer: D Chapter Review Questions 1) Explain what we mean by the Big Bang theory. 2) What is antimatter? How were particle—antiparticle pairs created and destroyed in the early universe? 3) What are the four forces that operate in the universe today? Why do we think there were fewer forces operating in the early universe? 4) Make a list of the major eras in the history of the universe, summarizing the important events thought to have occurred during each era. 5) Why can't our current theories describe conditions that existed in the universe during the Planck era? 6) What are grand unified theories? According to these theories, how many forces operated during the GUT era? How are these forces related to the four forces that operate today? 7) What do we mean by inflation, and when do we think it occurred? 8) Why do we think there was slightly more matter than antimatter in the early universe? What happened to all the antimatter, and when? 9) How long did the era of nucleosynthesis last? Explain why this era was so important in determining the chemical composition of the universe. 10) When we observe the cosmic microwave background, at what age are we seeing the universe? How long have the photons in the background been traveling through space? Explain. 11) Briefly describe how the cosmic microwave background was discovered. How do the existence and nature of this radiation support the Big Bang theory? 12) How does the chemical abundance of helium in the universe support the Big Bang theory? Explain.

13) Describe three key questions about the universe that are answered by inflation and explain how inflation answers each of them. 14) What observational evidence supports the hypothesis of inflation? Be sure to explain how observations of the cosmic microwave background can tell us about the universe at the much earlier time when inflation occurred. 15) What is Olbers' paradox, and how is it resolved by the Big Bang theory? Test Your Understanding Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 16) According to the Big Bang theory, the early universe had nearly equal amounts of matter and antimatter. 17) According to the Big Bang theory, the cosmic microwave background was created when energetic photons ionized the neutral hydrogen atoms that originally filled the universe. 18) Observed characteristics of the cosmic microwave background can be explained by assuming that it comes from individual stars and galaxies. 19) According to the Big Bang theory, most of the helium in the universe was created by nuclear fusion in the cores of stars. 20) According to the hypothesis of inflation, large-scale structure in the universe may have originated as tiny quantum fluctuations. 21) According to the hypothesis of inflation, the "flat" geometry of the universe most likely arose by chance. 22) Inflation is a nice idea, but there are no known ways to test whether it really happened. 23) In the distant past, what is now the cosmic microwave background consisted primarily of infrared light. 24) The main reason the night sky is dark is that stars are so far away. 25) Patterns in the cosmic microwave background tell us about conditions in the early universe that ultimately led to galaxy formation.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 17 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 26) The current temperature of the universe as a whole is ________. A) absolute zero B) a few K C) a few thousand K Answer: No Correct Answer Was Provided. 27) The charge of an antiproton is ________. A) positive B) negative C) neutral Answer: No Correct Answer Was Provided. 28) When a proton and an antiproton collide, they ________. A) repel each other B) fuse together C) convert into two photons Answer: No Correct Answer Was Provided. 29) Which of the following does not provide strong evidence for the Big Bang theory? A) Observations of the cosmic microwave background B) Observations of the amount of hydrogen in the universe C) Observations of the ratio of helium to hydrogen in the universe. Answer: No Correct Answer Was Provided. 30) When the universe was 380,000 years old, its thermal radiation spectrum consisted mostly of ________. A) radio and microwave photons B) visible and infrared photons C) x-ray and ultraviolet photons Answer: No Correct Answer Was Provided. 31) Which of the following does inflation help to explain? A) The uniformity of the cosmic microwave background B) The amount of helium in the universe C) The temperature of the cosmic microwave background Answer: No Correct Answer Was Provided. 32) Which of the following does inflation help to explain? A) The origin of hydrogen B) The origin of galaxies C) The origin of atomic nuclei. Answer: No Correct Answer Was Provided. 28 Copyright © 2022 Pearson Education, Inc.

33) Which of these pieces of evidence supports the idea that inflation really happened? A) The enormous size of the observable universe B) The large amount of dark matter in the universe C) The apparently "flat" geometry of the universe. Answer: No Correct Answer Was Provided. 34) What is the earliest time from which we observe light in the universe? A) A few hundred million years after the Big Bang B) A few hundred thousand years after the Big Bang C) A few minutes after the Big Bang. Answer: No Correct Answer Was Provided. 35) Which of the following best explains why the night sky is dark? A) The universe is finite in size. B) The universe has a finite age. C) The distribution of matter in the universe is not uniform on very large scales. Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 36) Group Discussion: Astronomy and Technological Development. The stated mission of the International Astronomical Union (IAU), an organization of professional astronomers from around the world, is to "promote and safeguard the science of astronomy in all its aspects through international cooperation." As part of this mission, the IAU promotes astronomy as a means of broadly enhancing technological research and education in the developing world. a. Working independently, go to the website of the IAU's Office of Astronomy for Development (OAD) and learn about at least two of the activities it is supporting. b. Gather into small groups and tell each other about the OAD's activities. Make a list of impacts that those activities might have on the countries in which they are happening. c. How do you think the IAU should determine whether the OAD's efforts are successful? What processes would you recommend for deciding if or how particular activities should be changed? d. Within your group, briefly debate the relative merits for developing countries of spending money on astronomy versus spending money on sciences with more direct practical applications. Summarize the outcome of your debate.

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 37) Unanswered Questions. Briefly describe one important but unanswered question about the events that happened shortly after the Big Bang. If you think it will be possible to answer that question in the future, describe how we might find an answer, being as specific as possible about the evidence necessary to answer the question. If you think the question will never be answered, explain why you think it is impossible to answer. 38) Darkness at Night. Imagine that you were Johannes Kepler, pondering the darkness of the night sky without any knowledge of the Big Bang or the expanding universe. Come up with a hypothesis for the darkness of the night sky that would have been plausible in Kepler's time but does not depend on the Big Bang theory. Propose an experiment that scientists might be able to perform today to test that hypothesis. 39) The Moment of Creation. The time line of the universe discussed in this textbook takes us back only to within 10−43 second of creation, not to the moment of creation itself. Do you think it will ever be possible for science to consider the moment of creation, or to answer questions such as why the Big Bang happened? Defend your opinions. 40) Group Activity: Testing the Big Bang Theory. Listed below are five hypothetical observations that are not predicted by the Big Bang theory. For each one, imagine what would happen if it were actually observed–whether it could be explained with the existing Big Bang theory, could be explained with a revision to the Big Bang theory, or would force us to abandon the Big Bang theory. Write down your team's reasoning for each case. Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39. • Hypothetical observation 1: a star cluster with an age of 15 billion years • Hypothetical observation 2: a galaxy with an age of 10 million years • Hypothetical observation 3: a galaxy at a distance of 10 billion light-years whose spectrum is blueshifted • Hypothetical observation 4: a galaxy containing 90% hydrogen and 10% helium • Hypothetical observation 5: evidence for an increase in the cosmic microwave background temperature with time Investigate Further 41) Life Story of a Proton. Tell the life story of a proton from its formation shortly after the Big Bang to its presence in the nucleus of an oxygen atom you have just inhaled. Your story should be creative and imaginative, but it should also demonstrate your scientific understanding of as many stages in the proton's life as possible. You can draw on material from the entire book, and your story should be three to five pages long. 42) Creative History of the Universe. The story of creation as envisioned by the Big Bang theory is quite dramatic, but it is usually told in a fairly straightforward, scientific way. Tell the story more dramatically, in the form of a short story, play, or poem. Be as creative as you wish, but be sure to remain true to the science as it is understood today. 30 Copyright © 2022 Pearson Education, Inc.

43) Re-creating the Big Bang. Particle accelerators on Earth can push particles to extremely high speeds. When these particles collide, the amount of energy associated with the colliding particles is much greater than the mass-energy the particles have when at rest. As a result, these collisions can produce many other particles out of pure energy. Explain in your own words how the conditions that occur in particle accelerators are similar to the conditions that prevailed shortly after the Big Bang. Also, point out some of the differences between what happens in particle accelerators and what happened in the early universe. 44) Betting on the Big Bang Theory. If you had $100, how much money would you wager on the proposition that we have a reasonable scientific understanding of what the universe was like when it was 1 minute old? Explain your bet in terms of the scientific evidence presented in this chapter. 45) "Observing" the Early Universe. Explain why we will never be able to observe the era of nucleosynthesis through direct detection of the radiation emitted at that time. How do we learn about this era? 46) Element Production in the Big Bang. Nucleosynthesis in the early universe was unable to produce more than trace amounts of elements heavier than helium.Using the information in Figure 13.18, which shows the mass per nuclear particle for many different elements, explain why producing elements like lithium (3 protons), boron (4 protons), and beryllium (5 protons) was so difficult. 47) Evidence for the Big Bang. Make a list of at least seven observed features of the universe that are satisfactorily explained by the Big Bang theory and the hypothesis of inflation. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 48) Energy from Antimatter. The total annual U.S. power consumption is about 2 × 1020 joules. Suppose you could supply that energy by combining pure matter with pure antimatter. Estimate the total mass of matter—antimatter fuel you would need to supply the United States with energy for 1 year. How does that mass compare with the amount of matter in your car's gas tank? (A gallon of gas has a mass of about 3 kilograms.) 49) Temperature of the Universe. What will the temperature of the cosmic microwave background be when the average distances between galaxies are twice as large as they are today? (Hint: The peak wavelength of photons in the background will then also be twice as large as it is today.) 50) Uniformity of the Cosmic Microwave Background. The temperature of the cosmic microwave background differs by only a few parts in 100,000 across the sky. Compare that level of uniformity to the uniformity of the surface of a table that is 1 square meter. How big would the largest bumps on that table be if its surface were smooth to one part in 100,000? Could you see bumps of that size on the table's surface?

51) Daytime at "Night." According to Olbers' paradox, the entire sky would be as bright as the surface of a typical star if the universe were infinite in space, unchanging in time, and the same everywhere. However, conditions would not need to be quite that extreme for the "nighttime" sky to be as bright as the daytime sky. a. Using the inverse square law for light from Cosmic Calculations 12.1, determine the apparent brightness of the Sun in our sky. b. Using the inverse square law for light, determine the apparent brightness our Sun would have if it were at a distance of 10 billion light-years. c. From your answers to parts a and b, estimate how many stars like the Sun would need to exist at a distance of 10 billion light-years for their total apparent brightness to equal that of our Sun. d. Compare your answer to part c with the estimate of 1022 stars in our observable universe from Section 1.1. Use your answer to explain why the night sky is much darker than the daytime sky. How much larger would the total number of stars need to be for "night" to be as bright as day?

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 18 Dark Matter, Dark Energy, and the Fate of the Universe Section 18.1 1) Why is dark matter called "dark matter"? A) It does not interact strongly with light, but it does have gravity like other matter. B) It is made from black holes. C) It absorbs all light and exerts gravity. D) The name is misleading because it is pure energy rather than matter. Answer: A 2) What does Einstein's cosmological constant represent in his equations of general relativity? A) The value of the expansion rate of the universe B) The value of the acceleration of the universe C) The value that measures the strength of gravity across the universe D) The size of the cosmological horizon E) A repulsive force that can counteract gravity Answer: E Section 18.2 1) How do we know that there is much more mass in the halo of our galaxy than in the disk? A) There are so many globular clusters in the halo that their total mass is greater than the mass of stars in the disk. B) Stars and gas clouds in the outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass were concentrated in the disk. C) We have discovered that the halo is filled with an enormous number of brown dwarfs that have a combined mass much greater than the disk. D) Laboratory experiments have proven that the halo must be full of subatomic dark matter particles. Answer: B 2) What evidence suggests that the Milky Way contains dark matter? A) We observe stars and gas clouds far from the galactic center orbiting the galaxy at higher speeds than we would expect without dark matter. B) We see many lanes of dark material blocking out the light of stars behind them along the band of the Milky Way. C) We see many dark voids between the stars in the halo of the Milky Way. D) When we observe in different wavelengths, such as infrared or radio, we see objects that don't appear in visible-light observations. E) When we look at the galactic center, we are able to observe a large black hole that is composed of dark matter. Answer: A

3) Which of the following best describes the distribution of the dark matter in a spiral galaxy? A) Approximately spherical and about the same size as the galaxy halo B) Approximately spherical and about 10 times the size of the galaxy halo C) Flattened in a disk and about the same size as the stellar disk D) Flattened in a disk but about 10 times larger than the stellar disk E) Predominantly concentrated in the spiral arms Answer: B 4) How do we determine the amount of dark matter in elliptical galaxies? A) We measure the orbital velocities of star-forming gas clouds around the outer portions of the galaxy. B) We measure the range of speeds of collections of stars at different distances from the galactic center and determine how much mass is interior to their orbits. C) We count the number of stars in the galaxy and determine its volume, so that we can calculate the galaxy's density. D) We search for dark lanes of dust and black holes within the galaxy. E) We measure how fast the galaxy rotates as a whole. Answer: B 5) How are rotation curves of spiral galaxies determined for orbital distances beyond where starlight can be detected? A) By extrapolation of the measured rotation curve B) By observations of the 21 cm line of atomic hydrogen C) By observations of spectral lines emitted by dark matter D) By watching the galaxies rotate over a period of decades E) By measuring the broadening of the galaxy's absorption lines Answer: B 6) Why can't astronomers use the 21-cm line of neutral hydrogen gas to measure the masses of elliptical galaxies? A) All elliptical galaxies are too far away for us to detect the 21-cm line. B) The disorderly motion of the material in elliptical galaxies prevents us from measuring different velocities at different sides of the galaxy. C) Elliptical galaxies have little gas, so they do not have strong 21-cm line emission. D) Supermassive black holes in the center of elliptical galaxies disturb measurements of the 21cm line. Answer: C 7) We observe stars orbiting at distances of 25,000 light-years from the centers of Galaxy X and Galaxy Y. For this orbital distance, stars in Galaxy X have higher orbital speeds than stars in Galaxy Y. What can we conclude? A) Galaxy X contains more total mass within 25,000 light-years of its center than Galaxy Y. B) Galaxy Y contains more total mass within 25,000 light-years of its center than Galaxy X. C) Galaxy X contains more dark matter than Galaxy Y. D) Galaxy Y contains more dark matter than Galaxy X. E) The stars of Galaxy X are more massive than those of Galaxy Y. Answer: A 2 Copyright © 2022 Pearson Education, Inc.

8) Which of the following provides important evidence for the existence of dark matter in clusters of galaxies? A) Careful counts of the numbers of galaxies in clusters B) The relative proportions of spiral and elliptical galaxies in clusters C) The high temperature and distribution of gas between the galaxies in clusters D) The total luminosity in visible light coming from cluster galaxies Answer: C 9) Which of the following methods used to determine the mass of a cluster of galaxies does not depend on Newton's law of gravity? A) Measuring the orbital velocities of galaxies in the cluster B) Measuring the temperature of x-ray gas in the intracluster medium C) Measuring the amount of distortion caused by gravitational lensing Answer: C 10) How do x-ray measurements help us measure the amount of dark matter in galaxy clusters? A) The gravity of dark matter causes intracluster gas to be heated to very high temperatures, and the higher the temperature, the stronger the x-ray emission we will detect from the gas. B) Dark matter absorbs x-rays, so we can map the dark matter distribution by looking for absorption lines in x-ray spectra. C) Collisions between dark matter particles emit x-rays, allowing us to map dark matter with xray images. Answer: A

11)

This figure shows the x-ray emission from hot gas (red) in two colliding galaxy clusters and the distribution of mass found by gravitational lensing (blue). Which of the following three conclusions can be reasonably drawn from this image? I) The mass found by gravitational lensing in these colliding galaxy clusters is in a separate physical location from the hot gas that resulted from the collision. II) Dark matter does not strongly interact with regular matter, other than through gravity. III) Hot intracluster gas makes up the majority of the mass of galactic clusters. A) Only I B) I and II C) I and III D) I, II, and III Answer: B 12) Which of the following best describes what we mean by gravitational lensing? A) A massive object bends light beams that are passing nearby. B) A massive object scatters away the light of more distant objects. C) Gravity causes matter that would otherwise be dark to become visible. D) Telescope lenses are distorted by gravity. Answer: A 13) Which of the following is not evidence for dark matter? A) The flat rotation curves of spiral galaxies B) X-ray observations of hot gas in galaxy clusters C) Gravitational lensing around galaxy clusters D) The expansion of the universe Answer: D

14) Which of the following is an example of ordinary (baryonic) matter? A) You B) Photons of light C) Electrons and positrons produced by pair production D) Weakly interacting massive particles (WIMPs) E) Neutrinos Answer: A 15) Neutrinos travel at very high speeds (close to the speed of light). How does this fact imply that neutrinos cannot make up the bulk of the dark matter in galaxies? A) Their high speeds mean neutrinos cannot have much mass. B) Their high speeds tell us that neutrinos interact only through the weak force and gravity. C) Their speeds of neutrinos mean that neutrinos would escape from galaxies. Answer: C 16) Based on current evidence, which of the following is the most likely candidate to make up the majority of dark matter? A) Brown dwarfs B) Jupiter-size objects C) Weakly interacting massive particles (WIMPs) D) Faint red stars E) Black holes Answer: C 17) The more ordinary (baryonic) matter there is in the universe, the lower the ratio of deuterium to hydrogen. Therefore, if Harry measures a higher ratio of deuterium to hydrogen than Sally, Harry infers ________. A) the same density of ordinary matter as Sally B) a lower density of ordinary matter than Sally C) a higher density of ordinary matter than Sally Answer: B 18) Why do we expect WIMPs to be distributed throughout galactic halos, rather than settled into the galaxy's disk? A) WIMPs are lightweight enough that they have expanded out into the halo. B) WIMPs were produced by stars in the early stages of galaxy evolution and therefore are only found in globular clusters in the halo. C) WIMPS rarely interact with other particles and therefore cannot settle into galactic disks. D) Shock waves from generations of supernovae have blown the WIMPs out into the halo. E) WIMPs annihilate when they come into contact with ordinary matter, such as stars. Answer: C

19) Based on the observed amount of deuterium in the universe, we can conclude that ________. A) ordinary (baryonic) matter makes 75 percent of the mass of the universe B) neutrons outnumber protons 7 to 1 in the universe C) most of the deuterium that was created in the early universe has since been destroyed D) the density of ordinary (baryonic) matter is about 5 percent of the critical density E) the density of the universe equals the critical density Answer: D 20) Based on current evidence and models, visible, luminous matter (such as the stars within galaxies) amounts to approximately what percentage of the total mass and energy of the universe? A) Less than 1 percent B) 10 percent C) 25 percent D) 50 percent Answer: A 21) What is the approximate mass-to-light ratio for the inner region of the Milky Way Galaxy, in units of solar masses per solar luminosity? A) 1000 B) 600 C) 100 D) 6 E) 0.1 Answer: D 22) If a galaxy's overall mass-to-light ratio is 100 solar masses per solar luminosity, and its stars account for only 5 solar masses per solar luminosity, how much of the galaxy's mass must be dark matter? A) 100 percent B) 95 percent C) 80 percent D) 50 percent E) 5 percent Answer: B

Section 18.3 1) Galaxies sometimes have recession speeds that deviate somewhat from the exact speed predicted by Hubble's law. What do these so-called peculiar velocities reveal? A) Velocities due to the gravitational tugs of nearby galaxies or clusters of galaxies B) Deviations in the rate at which the universe has been expanding at different times in the past C) These velocities indicate serious discrepancies with Hubble's law and with our view of an expanding universe. D) These velocities indicate that the expansion rate differs for different directions in space. Answer: A 2) How do astronomers create three-dimensional maps of the universe? A) Through comparison of computer models of the structure formation with observations B) By measuring the sky positions and redshifts of many galaxies C) By measuring the sky positions and apparent brightnesses of many galaxies D) By measuring the colors and luminosities of many galaxies E) By carefully measuring the parallax of many galaxies Answer: B 3) Which of the following best describes how galaxies are distributed on large scales in the universe? A) Galaxies are uniformly distributed throughout space. B) Galaxies are randomly distributed throughout space. C) Galaxies are distributed in large, elongated chains radiating outward from a common center. D) Galaxies appear to be distributed in chains and sheets that surround great voids. E) Galaxies are distributed in a series of concentric spherical shells around a common center. Answer: D 4) If all the "dark matter" in the Universe were somehow instantaneously removed, which of the following would happen? A) The Solar System would fly apart. B) All the stars in the Milky Way would collapse into the central black hole. C) Clusters of galaxies would no longer be gravitationally bound together. D) Atoms would split into nuclei and free electrons. Answer: A

Section 18.4 1) Given the observed average distance between galaxies today, which statement is true? A) The faster the past expansion rate, the younger the age of the universe. B) The faster the past expansion rate, the older the age of the universe. C) The age of the universe depends only on the average distance between galaxies, not on the rate of expansion. Answer: A 2) Which model of the universe gives the youngest age for the present size of the universe? (Assume that the present expansion rate is the same for all of these models. The different models have different expansion histories.) A) A recollapsing universe B) A coasting universe C) A critical universe D) An accelerating universe E) All models give the same age. Answer: A 3) Why were astronomers in the 1990s surprised to learn that the expansion rate of the universe is getting faster with time? A) They did not expect the universe to be expanding at all. B) They assumed that the expansion rate should never change. C) They expected gravity to be slowing the expansion rate with time. Answer: C 4) Why isn't the space within our solar system or the Milky Way expanding according to Hubble's law? A) Hubble's law only applied early in the history of the universe. B) As we are inside our solar system and the Milky Way, we cannot observe their expansion. C) The universe is not old enough for the solar system or Milky Way to have begun their expansion. D) The gravity exerted by the solar system and the Milky Way is strong enough to hold them together against the expansion of the universe. Answer: D 5) Which of the following hypothetical universes would be the youngest, assuming that all are expanding at the same rate? A) The one that has the most dark matter B) The nearly empty universe with no dark matter C) The one that has the most dark energy D) All of these universes would have the same age. Answer: A

6) Based on current understanding, what exactly is causing the expansion of the universe to accelerate? A) WIMPs B) Neutrinos C) White dwarf supernovae D) Gravity E) We don't know, but we call it "dark energy." Answer: E

7) The graph above shows 4 models for how the average distance between galaxies could change with time, from the past (left) to now (middle) to the future (right-hand side). The graph also shows real data, based on white dwarf supernovae. Which model(s) predict(s) that galaxies are getting farther apart NOW? A) Accelerating B) Coasting C) Critical D) Recollapsing E) all of them Answer: E

8) The graph above shows 4 models for how the average distance between galaxies could change with time, from the past (left) to now (middle) to the future (right-hand side). The graph also shows real data, based on white dwarf supernovae. Which model(s) predict(s) that galaxies will eventually get closer together? A) Accelerating B) Coasting C) Critical D) Recollapsing E) all of them Answer: D 9) The graph above shows 4 models for how the average distance between galaxies could change with time, from the past (left) to now (middle) to the future (right-hand side). The graph also shows real data, based on white dwarf supernovae. Which model predicts that galaxies had the largest separations in the past? A) Accelerating B) Coasting C) Critical D) Recollapsing Answer: A 10) The graph above shows 4 models for how the average distance between galaxies could change with time, from the past (left) to now (middle) to the future (right-hand side). The graph also shows real data, based on white dwarf supernovae. Which model is most strongly supported by the data? A) Critical B) Accelerating C) Recollapsing D) Coasting Answer: B 11) Based on current evidence and models, the total amount of matter (both luminous matter and dark matter) represents approximately what percentage of the total mass and energy of the universe? A) About 1 percent B) About 10 percent C) About 30 percent D) About 50 percent E) 100 percent Answer: C 12) In a mass-energy census of the universe, what are the approximate proportions of normal matter, dark matter, and dark energy? A) 68% dark matter, 27% dark energy, 5% normal matter B) Mostly normal matter, with only trace amounts of dark matter and dark energy C) 27% dark matter, 68% dark energy, 5% normal matter D) 33% dark matter, 33% dark energy, 33% normal matter Answer: C 10 Copyright © 2022 Pearson Education, Inc.

Short Answer Questions 1) How do we know that there is an insignificant amount of dark matter in our solar system? Answer: We can measure the distribution of mass in the solar system through analysis of the orbital speeds of planets orbiting the Sun (i.e., making a rotation curve). This analysis tells us vast majority of the solar system's mass in the Sun, which means there cannot be much mass of any kind—including dark matter—in the rest of the solar system. Reading Quiz Questions 1) Which of the following best summarizes what we mean by dark matter? A) Matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light B) Matter that may inhabit dark areas of the cosmos where we see nothing at all C) Matter consisting of black holes D) Matter for which we have theoretical reason to think it exists, but no observational evidence for its existence Answer: A 2) Which of the following best summarizes what we mean by dark energy? A) It is a name given to whatever is causing the expansion of the universe to accelerate with time. B) It is the energy contained in dark matter. C) It is the energy of black holes. D) It is a type of energy that is associated with the "dark side" of The Force that rules the cosmos. Answer: A 3) The text states that luminous matter in the Milky Way seems to be much like the tip of an iceberg. This refers to the idea that ________. A) dark matter represents much more mass and extends much further from the galactic center than the visible stars of the Milky Way B) luminous matter emits white light, much like the light reflected from icebergs C) black holes are much more interesting than ordinary stars that give off light D) the expression "surface of a great sea of dark matter" does not really make any sense Answer: A 4) What is a rotation curve? A) A graph showing how orbital velocity depends on distance from the center for a spiral galaxy B) A precise description of the shape of a star's orbit around the center of the Milky Way Galaxy C) A curve used to decide whether a star's orbit places it in the disk or the halo of a spiral galaxy D) A graph that shows a galaxy's mass on the vertical axis and size on the horizontal axis Answer: A

5) What is the primary way in which we determine the mass distribution of a spiral galaxy? A) We construct its rotation curve by measuring Doppler shifts from gas clouds at different distances from the galaxy's center. B) We calculate its mass-to-light ratio. C) We apply Newton's version of Kepler's third law to the orbits of globular clusters in the galaxy's halo. D) We count the number of stars we can see at different distances from the galaxy's center. Answer: A 6) What do we mean when we say that the rotation curve for the Milky Way galaxy is "flat"? A) Gas clouds orbiting far from the galactic center have approximately the same orbital speed as gas clouds located further inward. B) The amount of light emitted by stars at different distances is about the same throughout the galaxy. C) The disk of a spiral galaxy is quite flat rather than spherical like the halo. D) All the galaxy's mass is concentrated in its flat, gaseous disk. Answer: A 7) Although we know less about dark matter in elliptical galaxies than in spiral galaxies, what does current evidence suggest? A) Elliptical galaxies probably contain about the same proportion of their mass in the form of dark matter as do spiral galaxies. B) Elliptical galaxies probably contain far less dark matter than spiral galaxies. C) Elliptical galaxies probably contain far more dark matter than spiral galaxies. D) Unlike the broad distribution of dark matter in spiral galaxies, elliptical galaxies probably contain dark matter only near their centers. Answer: A 8) Which of the following is not one of the three major strategies used to measure the mass of a galaxy clusters? A) Measuring the speeds of galaxies orbiting the cluster's center B) Studying x-ray emission from hot gas inside the cluster C) Observing how the cluster bends light from galaxies located behind it D) Measuring the temperatures of stars in the halos of the galaxies Answer: D 9) When we say that a cluster of galaxies is acting as a gravitational lens, what do we mean? A) It bends or distorts the light coming from galaxies located behind it. B) It magnifies the effects of gravity that we see in the cluster. C) It is an unusually large cluster that has a lot of gravity. D) The overall shape of the cluster is that of a lens. Answer: A

10) Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies? A) Dark matter is the dominant form of mass in both clusters and in individual galaxies. B) Dark matter is present between galaxies in clusters, but not within individual galaxies. C) Dark matter is present in individual galaxies, but there is no evidence that it can exist between the galaxies in a cluster. D) Within individual galaxies, dark matter is always concentrated near the galactic center, and within clusters it is always concentrated near the cluster center. Answer: A 11) What is the distinguishing characteristic of what we call ordinary (or baryonic) matter? A) It consists of atoms or ions with nuclei made from protons and neutrons. B) It emits a great deal of light. C) It can attract other matter through the force of gravity. D) It is made of subatomic particles that scientists call WIMPs. Answer: A 12) Measuring the amount of deuterium in the universe allows us to set a limit on ________. A) the density of ordinary (baryonic) matter the universe B) the total amount of mass in the universe C) the acceleration of the universe D) the current age of the universe Answer: A 13) What do we mean when we say that particles such as neutrinos or WIMPs are weakly interacting? A) They respond to the weak force but not to the electromagnetic force, which means they cannot emit light. B) The light that they emit is so weak that it is undetectable to our telescopes. C) They are only weakly bound by gravity, which means they can fly off and escape from galaxies quite easily. D) They interact with other matter only through the weak force and not through gravity or any other force. Answer: A 14) Which of the following best sums up current scientific thinking about the nature of dark matter? A) Most dark matter probably consists of weakly interacting particles of a type that we have not yet identified. B) Dark matter consists primarily of a mysterious form of energy that is causing the expansion of the universe to accelerate. C) There is no longer any doubt that dark matter is made mostly of WIMPs. D) Dark matter probably does not really exist, and rather indicates a fundamental problem in our understanding of gravity. Answer: A

15) When we speak of the large-scale structure of the universe, we mean ________. A) the overall arrangement of galaxies, clusters of galaxies, and superclusters in the universe B) the structure of any large galaxy C) the structure of any individual cluster of galaxies D) the overall shape of the observable universe Answer: A 16) The primary evidence that has led astronomers to conclude that the expansion of the universe is accelerating comes from ________. A) observations of white dwarf supernovae B) observations of the speeds of individual galaxies in clusters C) measurements of the rotation curve for the universe D) measurements of how galaxy speeds away from the Milky Way have increased during the past century Answer: A 17) Which of the following best sums up current scientific thinking about the nature of dark energy? A) Dark energy most likely consists of a form of photons that we can't see or detect. B) Dark energy is most likely made up of weakly interacting particles that do not interact with light. C) Dark energy probably exists, but we have little (if any) idea what it is. D) Dark energy is the source of the mind weapon used by Sith Lords in Star Wars. Answer: C 18) Based on evidence both from measurements of the acceleration of the expansion rate and from careful study of the cosmic microwave background, about what percentage of the universe's total mass and energy takes the form of ordinary atomic matter (protons, neutrons, and electrons)? A) 5% B) 0.5% C) 27% D) 68% Answer: A 19) According to current understanding, if the universe continues to expand forever, the last major source of light will come from ________. A) evaporation of black holes B) the last supernovas C) collisions between galaxies D) gamma-ray bursts Answer: A

Concept Quiz Questions 1) Why do we call dark matter "dark"? A) It emits no radiation that we have been able to detect. B) It is dark brown or dark red in color. C) It blocks out the light of stars in a galaxy. D) It contains large amounts of dark-colored dust. Answer: A 2) Although most astronomers assume dark matter really exists, there is at least one other possible explanation for the phenomena attributed to dark matter. What is it? A) There could be something wrong or incomplete with our understanding of how gravity operates on galaxy-size scales. B) The so-called dark matter is really just ordinary stars that are enshrouded in clouds of dust. C) We could just be having a hard time understanding the observations, because they involve very distant galaxies. D) There could be something wrong with our understanding of how atoms produce light. Answer: A 3) Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be different? A) The orbital speeds would fall off sharply with increasing distance from the galactic center. B) The orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant. C) The rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round. D) The rotation curve would look the same with or without the presence of dark matter. Answer: A 4) The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they tell us anything about where the dark matter is located within the galaxy? A) Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center. B) Yes, they tell us that dark matter is concentrated near the center of the galaxy. C) Yes, they tell us that dark matter is spread uniformly throughout the galactic disk. D) No, we cannot determine anything about the location of dark matter from the rotation curve. Answer: A 5) It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy. Why? A) Elliptical galaxies lack the atomic hydrogen gas that we use to determine orbital speeds at great distances from the centers of spiral galaxies. B) Elliptical galaxies contain much less dark matter than spiral galaxies, so it's much more difficult to measure. C) Stars in elliptical galaxies are dimmer, making them harder to study. D) We cannot observe spectral lines for elliptical galaxies. Answer: A 15 Copyright © 2022 Pearson Education, Inc.

6) How do we know that galaxy clusters contain a lot of mass in the form of hot gas that fills spaces between individual galaxies? A) We detect this gas with x-ray telescopes. B) We infer its existence by observing its gravitational effects on the galaxy motions. C) The hot gas shows up as bright pink in visible-light photos of galaxy clusters. D) We can observe the frictional effects of the hot gas in slowing the speeds of galaxies in the clusters. Answer: A 7) Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster? A) The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass. B) Temperature is always directly related to mass, which is why massive objects are always hotter than less massive objects. C) The temperature of the gas tells us the gas density, so we can use the density to determine the cluster's mass. D) The question is nonsense; gas temperature cannot possibly tell us anything about mass. Answer: A 8) How does gravitational lensing tell us about the mass of a galaxy cluster? A) Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it. B) The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law. C) The lensing broadens spectral lines, and we can use the broadening to "weigh" the cluster. D) Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster. Answer: A 9) If WIMPs really exist and make up most of the dark matter in galaxies, which of the following is not one of their characteristics? A) They travel at speeds close to the speed of light. B) They are subatomic particles. C) They can neither emit nor absorb light. D) They tend to orbit at large distances from the galactic center. Answer: A 10) Is space expanding within clusters of galaxies? Why or why not? A) No, because their gravity is strong enough to hold them together even while the universe as a whole expands. B) No, because the universe is not old enough yet for these objects to have begun their expansion. C) No, because expansion of the universe affects only empty space, not space in which matter is present. D) Yes, and that is why clusters tend to grow in size with time. Answer: A 16 Copyright © 2022 Pearson Education, Inc.

11) Which of the following statements about large-scale structure is probably not true? A) Clusters and superclusters appear to be randomly scattered about the universe, like dots sprinkled randomly on a wall. B) Galaxies and clusters have grown around tiny density enhancements that were present in the early universe. C) Voids between superclusters began their existence as regions in the universe with a slightly lower density than the rest of the universe. D) Many cluster and superclusters are still in the process of formation as their gravity gradually pulls in new members. Answer: A 12) Based on current evidence, a supercluster is most likely to have formed in regions of space where ________. A) the density of dark matter was slightly higher than average when the universe was very young B) there was an excess concentration of hydrogen gas when the universe was very young C) supermassive black holes were present in the very early universe D) the acceleration of the expansion was proceeding faster than elsewhere Answer: A 13) Imagine that it turns out that dark matter (not dark energy) is made up of an unstable form of matter and that all of it suddenly decays tomorrow into photons or other forms of energy. Based on current understanding, which of the following would begin to occur? A) Stars would begin to stop having nuclear fusion in their cores. B) Planetary systems would begin to expand and disperse. C) The galaxies in clusters would begin to fly apart. D) The expansion of the universe would begin coming to a halt. Answer: C 14) Based on current evidence, how does the actual average density of matter in the universe compare to the critical density? A) The actual average density of matter, even with dark matter included, is only about a quarter of the critical density. B) If we include dark matter, the actual average density of matter equals the critical density. C) The actual average density of matter less than 1% of the critical density. D) The actual density of average matter is about twice the critical density. Answer: A 15) Current evidence suggests the universe will continue to expand forever, but some people would prefer if we lived in a recollapsing universe that would eventually stop expanding and start contracting. Based on current understanding, which of the following would have to be true for our universe to fit a recollapsing model? A) Dark energy does not exist and there is much more matter than current evidence suggests. B) Dark energy is the dominant form of energy in the cosmos. C) The density of dark matter turns out to be greater than the density of dark energy. D) The total density of matter equals the critical density. Answer: A 17 Copyright © 2022 Pearson Education, Inc.

16) Scientists do not know what dark energy is, yet they claim that it is the dominant constituent of the mass-energy of the universe. What (if any) evidence supports this claim? A) There are two lines of evidence: (1) measurements of the accelerating expansion and (2) the universal geometry inferred from the cosmic microwave background. B) There are two lines of evidence: (1) the fact that the universe is expanding and (2) the observed ratio of deuterium to hydrogen. C) The only evidence comes from observations of white dwarf supernovae that indicate the expansion rate is accelerating. D) The claim comes from models of the Big Bang, but it is not backed up by any observational evidence. Answer: A 17) Which of the following statements best describes current understanding of the eventual fate of the universe? A) Although the accelerating expansion suggests that the universe will continue to expand forever, it is possible that future discoveries will indicate a different fate. B) The universe will continue to expand forever, because only gravity could reverse the expansion, and it is not strong enough to do so. C) The acceleration of the expansion will eventually lead to a Big Rip that will break all matter apart. D) The universe will gradually decay as it continues to expand, with protons eventually decaying and black holes ultimately evaporating, leaving the universe cold and dark. Answer: A

Visual Quiz Questions 1) Consider a spinning disk of pizza dough, as shown here. What would the rotation curve for the spinning dough look like?

Answer: A 2) This graph shows the rotation curves of four different spiral galaxies. Based on these curves, what do all four galaxies have in common?

A) Their most distant stars all orbit at about the same speed as stars located about 30,000 light-years from their centers. B) Their fastest-moving stars are always located within about 1,000 light-years of their centers. C) They all have supermassive black holes near their centers. D) All their stars take about 200 million years to complete a single orbit, no matter how far they are from the galactic center. Answer: A 20 Copyright © 2022 Pearson Education, Inc.

3) Notice the blue ovals (such as those indicated by the arrows) in this image of a galaxy cluster. The oval structures are not really located where they appear to be, but instead are multiple images of a single galaxy that lies directly behind the cluster. What do we call the process that creates these multiple images?

A) Gravitational lensing B) Cluster image distortion C) The arc effect D) Dark energy Answer: A

4) Notice the distorted galaxy images, such as the large arc-shaped structure, in this image of a galaxy cluster. What can astronomers learn by carefully measuring the distortions in this image?

A) The total mass of the cluster B) The amount of dark energy in the universe C) The precise distance to the galaxy cluster D) The age of the galaxy cluster Answer: A

5) This image shows a colliding pair of galaxy clusters known together as the Bullet Cluster. The blue region represents a map of the cluster's dark matter. How was this blue map made?

A) The blue region was inferred from studies of how the cluster causes gravitational lensing of objects located behind it. B) The blue region represents X-ray emission from hot gas within the cluster. C) The blue region represents previously unknown radio emission from the dark matter. D) The blue region comes from the combined light of many young stars drawn together by the cluster's dark matter. Answer: A

6) Study this graph, focusing on the red curve and reddish horizontal swath. Which statement correctly interprets what the graph shows?

A) The measured abundance of deuterium agrees with the theoretically predicted abundance only if we make the prediction with a model of the universe in which ordinary matter makes up about 5% of the critical density. B) The abundance of deuterium in the universe has rapidly decreased with time. C) The actual abundance of deuterium in the universe has never changed, but the predicted abundance has decreased with time. D) The abundance of deuterium in the universe is high in galaxies near the Milky Way but much lower in galaxies that are much farther away. Answer: A

7) This figure shows a "slice of the universe" from the Sloan Digital Sky Survey. What is the Sloan Great Wall (indicated by the arrow)?

A) A huge collection of galaxies extending a billion light-years in length B) A giant wall of hot gas extending a billion light-years in length C) Our cosmological horizon, the point beyond which we cannot see D) A hypothesized structure built of the particles responsible for creating dark energy in the universe Answer: A

8) These diagrams represent four possible models for the universe. Each model shows how the size of the observable universe changes with time. Of the four models, which one gives the universe the oldest age at present? A) Accelerating universe B) Coasting universe C) Critical universe D) Recollapsing universe E) The age of the universe would be the same no matter which model is correct. Answer: A 9) These diagrams represent four possible models for the universe. Which model presumes the existence of some type of dark energy in the universe? A) Accelerating universe B) Coasting universe C) Critical universe D) Recollapsing universe E) All four models assume the existence of dark energy. Answer: A

10) This graph shows how the average distances between galaxies changes with time in the four models for the universe, and also shows data points measured from white dwarf supernovae. Which of the following statements best describes what the data are telling us?

A) The data indicate that we live in an accelerating universe. B) The data prove beyond doubt that we live in an accelerating universe that will continue to expand forever. C) The data strongly suggest that our universe is made 95% of dark matter and only 5% of ordinary matter. D) The data prove beyond doubt that the universe will never collapse. Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

The schematic figure to the left shows a more complicated expansion history than the four idealized models shown in Figure 18.15. Answer the following questions, using the information given in this figure. 1) At time A, is the expansion of the universe accelerating, coasting, or decelerating? Answer: Accelerating 2) At time B, is the expansion of the universe accelerating, coasting, or decelerating? Answer: Accelerating 3) At time C, is the expansion of the universe accelerating, coasting, or decelerating? Answer: Coasting 4) At time D, is the expansion of the universe accelerating, coasting, or decelerating? Answer: Decelerating

Chapter Review Questions 1) Define dark matter and dark energy, and clearly distinguish between them. What types of observations have led scientists to propose the existence of each of these unseen influences? 2) Describe how orbital speeds in the Milky Way depend on distance from the galactic center. How does this relationship indicate the presence of large amounts of dark matter? 3) How do orbital speeds depend on distance from the galactic center in other spiral galaxies, and what does this tell us about dark matter in spiral galaxies? 4) How do we measure the masses of elliptical galaxies? What do these masses lead us to conclude about dark matter in elliptical galaxies? 5) Briefly describe the three different ways of measuring the mass of a cluster of galaxies. Do the results from the different methods agree? What do they tell us about dark matter in galaxy clusters? 6) What is gravitational lensing? Why does it occur? How can we use it to estimate the masses of lensing objects? 7) Briefly explain why the conclusion that dark matter exists rests on the assumption that we understand gravity correctly. Is it possible that our understanding of gravity is not correct? Explain. 8) In what sense is dark matter "dark"? Briefly explain why objects like you, planets, and even dim stars qualify as dark matter. 9) What evidence indicates that most of the matter in the universe cannot be ordinary (baryonic) matter? 10) Explain what we mean when we say that a neutrino is a weakly interacting particle. Why can't the dark matter in galaxies be made of neutrinos? 11) What do we mean by WIMPs? Why does it seem likely that dark matter consists of these particles, even though we do not yet know what they are? 12) Briefly describe the various large-scale structures of the universe, the role of dark matter in their formation, and why the largest structures probably reflect the density patterns of the early universe. 13) Describe and compare the four general patterns for the expansion of the universe: recollapsing, critical, coasting, and accelerating. What evidence supports the accelerating model and the existence of dark energy? 14) How do observations of the cosmic microwave background provide evidence for dark energy? 29 Copyright © 2022 Pearson Education, Inc.

15) Based on current evidence, what is the overall inventory of the mass-energy content of the universe? 16) What implications does the evidence for dark energy have for the fate of the universe? Does It Make Sense? Decide whether or not each of the following statements makes sense (or is clearly true or false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 17) Strange as it may sound, most of both the mass and the energy in the universe may take forms that we are unable to detect directly. 18) A cluster of galaxies is held together by the mutual gravitational attraction of all the stars in its galaxies. 19) We can estimate the total mass of a cluster of galaxies by studying the distorted images of galaxies whose light passes through the cluster. 20) Clusters of galaxies are the largest structures that we have so far detected in the universe. 21) The primary evidence for an accelerating universe comes from observations of young stars in the Milky Way. 22) There is no doubt remaining among astronomers that the fate of the universe is to expand forever. 23) Dark matter is called "dark" because it blocks light from traveling between the stars. 24) Dark energy is the energy associated with the motion of particles of dark matter. 25) Evidence that the expansion of the universe is accelerating comes from observations showing that the average distance between galaxies is increasing faster now than it was 5 billion years ago. 26) If dark matter consists of WIMPs, then we should be able to observe photons produced by collisions between these particles.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 18 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 27) Dark matter is inferred to exist because ________. A) we see lots of dark patches in the sky B) it explains how the expansion of the universe can be accelerating C) we can observe its gravitational influence on visible matter Answer: No Correct Answer Was Provided. 28) Dark energy has been hypothesized to exist in order to explain ________. A) observations suggesting that the expansion of the universe is accelerating B) the high orbital speeds of stars far from the center of our galaxy C) explosions that seem to create giant voids between galaxies Answer: No Correct Answer Was Provided. 29) Measurements of how orbital speeds depend on distance from the center of our galaxy tell us that stars in the outskirts of the galaxy ________. A) orbit the galactic center just as fast as stars closer to the center B) rotate rapidly on their axes C) travel in straight, flat lines rather than elliptical orbits Answer: No Correct Answer Was Provided. 30) Strong evidence for the existence of dark matter comes from observations of ________. A) our solar system B) the center of the Milky Way C) clusters of galaxies Answer: No Correct Answer Was Provided. 31) A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call ________. A) dark energy B) spiral density waves C) gravitational lensing Answer: No Correct Answer Was Provided. 32) Based on the observational evidence, is it possible that dark matter doesn't really exist? A) No, the evidence for dark matter is too strong for us to think it could be in error. B) Yes, but only if there is something wrong with our current understanding of how gravity should work on large scales. C) Yes, but only if all the observations themselves are in error. Answer: No Correct Answer Was Provided.

33) Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies? A) Subatomic particles that we have not yet been able to detect B) Swarms of relatively dim red stars C) Supermassive black holes Answer: No Correct Answer Was Provided. 34) Which region of the early universe was most likely to become a galaxy? A) A region whose matter density was lower than average B) A region whose matter density was higher than average C) A region with an unusual concentration of dark energy Answer: No Correct Answer Was Provided. 35) The major evidence for the idea that the expansion of the universe is accelerating comes from observations of ________. A) white dwarf supernovae. B) the orbital speeds of stars within galaxies C) the evolution of quasars Answer: No Correct Answer Was Provided. 36) Which of the following possible types of universe would not expand forever? A) A critical universe B) An accelerating universe C) A recollapsing universe Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 37) Group Discussion: Vera Rubin and the Nobel Prize. As of 2018, no one had yet received a Nobel Prize for any of the discoveries implying that dark matter exists. Vera Rubin would have seemed a likely candidate for such a prize, for reasons briefly noted in the Extraordinary Claims box on page 474. Unfortunately, however, she died in 2016, and Nobel Prizes can be awarded only to people who are still living. a. Working independently, read at least one article about whether Vera Rubin should have won a Nobel Prize. b. Gather into small groups and discuss the articles that you read. What are the arguments in favor of a Nobel Prize for Rubin? Did you come across anyone arguing that a Nobel Prize would not have been appropriate? c. Many eminent female astronomers in the 21st century already view Rubin as a pioneer and role model. Do you think receiving a Nobel Prize would have further increased her positive impact on women's participation in astronomy? Explain your reasoning. d. When considering candidates for the Nobel Prize, would it be appropriate for the Prize Committee to consider potential impacts of the award on diversity and inclusion in science? Make a list of the pros and cons of considering these impacts.

The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 38) Dark Matter. Overall, how convincing do you consider the case for the existence of dark matter? Write a short essay in which you explain what we mean by dark matter, describe the evidence for its existence, and discuss your opinion about the strength of the evidence. 39) The Nature of Dark Matter. Find and study recent reports on the possible nature of dark matter. Write a report or hold a group discussion on the latest ideas about what dark matter is made of. 40) Dark Energy. Overall, how convincing do you consider the case for the existence of dark energy? Write a short essay in which you explain what we mean by dark energy, describe the evidence for its existence, and discuss your opinion about the strength of the evidence. 41) Alternative Gravity. Suppose someone proposed a new theory of gravity that claimed to explain observations of motion in galaxies and clusters of galaxies without the need for dark matter. Briefly describe at least one other test that you would expect the new theory to be able to pass if it was, in fact, a better theory of gravity than general relativity, which is currently our best explanation of how gravity works.

42) Group Activity: Dark Matter and Distorted Galaxies. Study the gravitational lensing shown in Figure 18.8. Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39. a. Notice in Figure 18.8 how gravitational lensing causes the image of a background galaxy to shift to a position farther from the center of the cluster. Individually, draw simple sketches of how you'd expect the lensed image of a spherical galaxy to look. As a group, briefly discuss your sketches. Do they agree? If not, do you think that one prediction is better than the others? b. Draw a copy of the diagram below on a large piece of paper. Use a straight edge to make sure that the lines are straight and that they all intersect at the same place; the circle should be close to the point of intersection, as shown. Note that the point at which the lines intersect represents the center of a galaxy cluster, and the circle represents the true position and shape of a spherical galaxy at a much greater distance from Earth.

c. Now work together to determine the effect of the cluster's lensing shift on the galaxy's image as follows. Step 1: For each dot on the circle, draw another dot farther to the right along the same line, so that the distance between the two dots is equal to the length of the line labeled "lensing shift." Step 2: Connect the new dots to see the shape of the lensed image. d. How do your results from part c compare to the predictions you made in part a? How do the results compare with the lensed galaxy images in Figure 18.9? Discuss possible reasons for any discrepancies you find. Investigate Further 43) The Future Universe. Based on current evidence concerning the growth of structure in the universe, briefly describe what you would expect large-scale structures in the universe to look like about 10 billion years from now. 44) Dark Matter and Life. State and explain at least two reasons one might use to argue that dark matter is (or was) essential for life to exist on Earth. 45) Orbital Speed vs. Radius. For each of the following three hypothetical galaxies, draw a graph showing how orbital speed depends on distance from the galactic center. Make sure the horizontal axis has approximate distances labeled. a. a galaxy with all its mass concentrated at its center b. a galaxy with constant mass density within 20,000 light-years of its center, and zero density beyond that distance c. a galaxy with constant mass density within 20,000 light-years of its center, and beyond that an enclosed mass that increases proportionally with the distance from the center 34 Copyright © 2022 Pearson Education, Inc.

46) Dark Energy and Supernova Brightness. When astronomers began measuring the brightnesses and redshifts of distant white dwarf supernovae, they expected to find that the expansion of the universe was slowing down. Instead they found that it was speeding up. Were the distant supernovae brighter or fainter than expected? Explain why. (Hint: In Figure 18.16, the position of a supernova point on the vertical axis depends on its redshift. Its position on the horizontal axis depends on its brightness–supernovae seen further back in time are not as bright as those seen closer in time.) 47) What Is Dark Matter? Describe at least three possible constituents of dark matter. Explain how we would expect each to interact with light, and how we might go about detecting its existence. 48) Alternative Gravity. Suppose you wished to explain the rotation curves of galaxies without the need for dark matter. Would gravity at very large distances need to be stronger or weaker than expected with our current theory of gravity? Explain. 49) Photo Journal: Gravitational Lenses. Gravitational lensing occurs in numerous astronomical situations. Compile a catalog of examples from the web, with photos of lensed stars, quasars, and galaxies. Give a one-paragraph explanation of what is shown in each photo. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 50) White Dwarf M/L. What is the mass-to-light ratio of a 1MSun white dwarf with a luminosity of 0.001LSun? 51) Supergiant M/L. What is the mass-to-light ratio of a 30MSun supergiant star with a luminosity of 300,000LSun? 52) Solar System M/L. What is the mass-to-light ratio of the solar system? 53) Mass from Orbital Velocities. Study the graph of orbital speeds for the spiral galaxy NGC 7541, which is shown in Figure 18.4. a. Use the orbital velocity formula(see Cosmic Calculations 15.1) to determine the mass (in solar masses) of NGC 7541 enclosed within a radius of 30,000 light-years from its center. (Hint: 9.461 × 1015 m.) b. Use the orbital velocity formula to determine the mass of NGC 7541 enclosed within a radius of 60,000 light-years from its center. c. Based on your answers to parts a and b, what can you conclude about the distribution of mass in this galaxy?

54) Weighing a Cluster. A cluster of galaxies has a radius of about 5.1 million light-years (4.8 × 1022 m) and an intracluster medium with a temperature of 6 × 107 K. Estimate the mass of the cluster using the orbital velocity formula (Cosmic Calculations 15.1). Give your answer in both kilograms and solar masses. Suppose that the combined luminosity of all the stars in the cluster is 8 × 1012 LSun. What is the cluster's mass-to-light ratio?

The Essential Cosmic Perspective, 9e (Bennett et al.) Chapter 19 Life in the Universe Section 19.1 1) How do scientists study the history of life on Earth? A) By studying fossils of ancient life only B) By comparing DNA among living organisms only C) Both by studying fossils of ancient life and by using telescopes to study habitable worlds elsewhere D) Both by studying fossils of ancient life and comparing DNA among living organisms E) By using telescopes to study habitable worlds elsewhere only Answer: D 2) If scientists excavate two fossils at the Grand Canyon, one of which was found at a much deeper rock layer than the other, what can we assume about the fossils? A) The fossil found in a deeper layer is older. B) The fossil found in a deeper layer is younger. C) The fossil found in a deeper layer is not as well-preserved. D) The fossil found in a deeper layer has a higher carbon-12 abundance. Answer: A 3) What evidence leads scientists to conclude that life was present on Earth within a billion years of its formation? A) Such early existence of life is the only way to explain the variety of life-forms seen today. B) Fossil evidence of life dates back to this time. C) Studies of DNA indicate that life must have been present by that time. Answer: B

4) The figure above shows the geological time scale of Earth. Animals have been present on land for approximately ________ of the Earth's history. A) 1/10 B) 1/4 C) 1/2 D) 3/4 Answer: A 5) The figure above shows the geological time scale of Earth. Life has existed for ________ of the Earth's history. A) all B) about 90% C) about 50% D) about 25% Answer: B 6) The figure above shows the geological time scale of Earth. The time since dinosaurs went extinct (with the K-T event) represents approximately ________ of the Earth's history. A) 0.15% B) 1.5% C) 15% D) 50% Answer: B

7) The figure above shows the geological time scale of Earth. The K-T event that marks the extinction of the dinosaurs occurred approximately ________ years ago. A) 65 million B) 10 million C) 650 million D) 100 million Answer: A 8) About when did the extinction of the dinosaurs occur? A) 3.5 billion years ago B) 2 billion years ago C) 540 million years ago D) 65 million years ago E) Less than 1 million years ago Answer: D 9) What was the Cambrian explosion? A) The impact of the meteor that led to mass extinction of the dinosaurs B) The initial spark of lightning that created the first life-form from amino acids C) The eruption of the volcano known as Cambria on the ancient supercontinent of Pangaea D) A dramatic diversification of life that began about 542 million years ago E) The largest mass extinction in Earth's history Answer: D 10) Which of the following contributed to the gradual evolution of life via natural selection? A) Organisms tend to produce more offspring than the local environment can support. B) Individuals in a population vary in many heritable traits. C) Individuals with traits that help them survive and reproduce are more likely to pass those traits on to succeeding generations. D) All of the above are correct. Answer: D 11) Which of the following can cause mutations in living organisms? A) Natural selection B) A changing climate C) Reproduction D) Ultraviolet light and toxic chemicals E) The greenhouse effect Answer: D

12) The oldest carbon isotope evidence of life indicates that life on Earth arose at least ________. A) 4.5 billion years ago B) 3.95 billion years ago C) 2 billion years ago D) 542 million years ago E) 65 million years ago Answer: B 13) Which of the following living organisms most resemble the common ancestor of all life according to genetic testing? A) Bacteria such as E. coli B) Organisms living deep in the oceans around seafloor volcanic vents C) Plankton that use sunlight as an energy source through photosynthesis D) Viruses E) Stromatolites Answer: B 14) Why are relatively few details known about the life that existed on Earth prior to a few hundred million years ago? A) Nearly all life at that time was microscopic, making it much more difficult to identify. B) Older rocks are rarer than younger rocks because of geologic processes. C) Many rocks have been transformed by high heat and pressure, destroying any fossils they contained. D) All of the above are correct. Answer: D 15) Which of the following offers evidence to support the hypothesis that life arises relatively easily under the conditions that existed on the early Earth? A) Small animals like Tardigrades can survive exposure to the near-vacuum of space. B) Life is currently present in extreme environments like deep ocean volcanic vents. C) Life was present on Earth by about the time that the heavy bombardment ended. D) All organisms on Earth use DNA as their genetic material. Answer: C 16) Which of the following provides direct evidence that the chemical building blocks of life (such as amino acids and DNA bases) could have formed naturally under the conditions that were present on the early Earth? A) Fossil remains of life date to fairly early in Earth's history. B) These chemicals have been formed in laboratory experiments that recreate conditions of the early Earth. C) DNA studies show that all known life on Earth evolved from a common ancestor. D) We have found evidence of complex carbon molecules on Saturn's moon Titan. Answer: B

17) Which of the following provides evidence that all life on Earth shares a common ancestor? A) All life on Earth shares certain biochemical similarities, including use of DNA as its hereditary molecule. B) All life on Earth requires energy and nutrients to survive. C) All life on Earth requires liquid water to survive. D) All life on Earth shares similarities in appearance that could not possibly be a coincidence. Answer: A 18) What are the three key necessities for all life on Earth? A) (1) nutrients, (2) energy, (3) liquid water B) (1) liquid water, (2) carbon, (3) oxygen C) (1) nutrients, (2) liquid water, (3) oxygen D) (1) DNA, (2) mutations, (3) liquid water E) (1) DNA, (2) liquid water, (3) oxygen Answer: A 19) What is not necessary for all living organisms on Earth to survive? A) Energy B) Nutrients C) Oxygen D) Liquid water Answer: C 20) Which of the following statements about ozone (in Earth's stratosphere) is not true? A) The presence of ozone was crucial to the origin of life. B) If the ozone layer is depleted, we can expect the rate of mutations in land-based life-forms to increase significantly. C) Ozone absorbs ultraviolet light from the Sun. D) The human-made chemicals known as CFCs can cause a loss of ozone in the atmosphere. Answer: A

Section 19.2 1) Which of the following worlds is the one for which we have sent the most space missions to learn about the potential of life beyond the Earth? A) The Moon B) Venus C) Mars D) Europa E) Titan Answer: C 2) What evidence tells us that the so-called "Martian meteorites" actually came from Mars? A) Their chemical composition matches that of known Martian rocks. B) Their ages match the known age of Mars. C) Their color is the same as most Martian rocks. D) Their composition tells us they formed farther from the Sun than Earth. Answer: A 3) Which of the following explains why we do not consider the surface of Mars to be habitable today? A) Mars has too much carbon dioxide in its atmosphere. B) Mars is located far outside the Sun's habitable zone. C) The atmospheric pressure is too low for liquid water to be stable on the surface. D) Mars is bombarded too often with asteroids and comets. E) Mars has too little gravity for its surface to be habitable. Answer: C 4) Which of the following best describes the findings of the Viking landers in the experiments they conducted to search for life on Mars? A) Some experiments were potentially suggestive of life, but their results could also be explained by chemical reactions not associated with life. B) Absolutely no evidence indicating life was found in the Martian soil. C) The landers detected organic material and evidence for microbial organisms in the soil. D) The experiments failed to operate properly and therefore did not provide any results. Answer: A 5) Why didn't the Viking landers find organic molecules in the soil on Mars? A) The Martian soil contains perchlorate, which destroyed the organic molecules when heated during the experiments. B) There are no organic molecules on Mars because they were carried away by the solar wind. C) The Viking landers were not designed to detect organic molecules. D) Organic molecules exist too deep below the surface of Mars to be detected. Answer: A

Section 19.3 1) Which of the following gases, which we might be able to detect in infrared spectra, would be a strong indicator of life on another planet? A) Carbon dioxide B) Ozone C) Methane D) Water vapor E) Sulfuric acid Answer: B 2) Which of the following has been the most important for maintaining the Earth's stable climate over the time it took for large organisms to evolve? A) Impacts of water-bearing planetesimals B) The ending of the heavy bombardment C) Plate tectonics D) The tides E) Deep sea volcanic vents Answer: C 3) Why is a global magnetic field thought to be necessary for life to exist on the surface of a planet? A) A magnetic field shields the planet from harmful ultraviolet light. B) A magnetic field helps form ozone in the upper atmosphere. C) A magnetic field helps keep the planet's atmosphere from being stripped away by stellar winds. D) A magnetic field helps warm the planet's surface through the greenhouse effect. Answer: C 4) What defines the habitable zone around a star? A) The region around a star where rocky planets can form B) The region around a star where humans can survive C) The region around a star where liquid water can exist on planetary surfaces D) The region around a star where its ultraviolet radiation is too weak to destroy biological organisms on a planetary surface E) The region around a star outside of its hot, tenuous corona Answer: C 5) Jovian planets are thought to form beyond the frost line of their star systems. How, then, might it be possible for a large moon around a jovian planet to have a habitable surface with liquid water? A) The moon would need to be locked in synchronous rotation with its planet. B) The jovian planet would need to have migrated inward to the habitable zone of its star. C) The moon would need to have a magnetic field. D) The moon would need to have plate tectonics. E) The moon would need to have a high density. Answer: B 7 Copyright © 2022 Pearson Education, Inc.

Section 19.4 1) Which of the following best describes the goal of SETI (Search for Extraterrestrial Intelligence)? A) To detect signals originating from civilizations from outside the solar system B) To detect life of any kind, anywhere besides Earth C) To estimate the number of civilizations in the galaxy D) To find habitable planets around other stars Answer: A 2) In 1974, a radio message was sent out from the Arecibo observatory in Puerto Rico. About how far has it gotten by now? A) Just beyond our Solar System B) Not even to the nearest stars C) A small fraction of the distance across the Milky Way D) Almost to the center of the Milky Way E) Beyond the Milky Way, to the Andromeda galaxy Answer: C 3) Which of the following statements best reflects our current knowledge about the term flife in the equation Number of Civilizations = NHP × flife × fcivilization × fnow? A) The value of flife is either 0 or 1, but not anything in between. B) The value of flife is between 0 and 1. C) The value of flife is less than 0.0000001. D) The value of flife is equal to 1/2. E) The value of flife is greater than 0.9. Answer: B 4) What do we mean by fnow in the Drake equation (Number of Civilizations = NHP × flife × fcivilization × fnow)? A) The fraction of planets with civilizations on which the civilizations exist now B) The fraction of time since the Big Bang represented by the present era C) The fraction of all species ever to exist that we currently are aware of D) The fraction of planets in the galaxy on which a civilization could theoretically develop now E) The fraction of civilizations in the universe that currently are sending messages to us Answer: A

5) Which factor(s) in the Drake equation (Number of Civilizations = NHP × flife × fcivilization × fnow) can we estimate based on discoveries of extrasolar planets? A) NHP B) flife C) fcivilization D) fnow E) all of the above Answer: A Section 19.5 1) Which of the following best explains why an interstellar ramjet could, in theory, achieve continuous acceleration? A) It uses fuel that is more efficient than any other known fuel. B) It collects its fuel as it goes, rather than having to carry the weight of fuel along with it. C) It takes advantage of theoretically possible loopholes in Einstein's theory of relativity. D) It has such a large fuel tank that it will essentially never use up all the fuel it carries. E) Its speed always gets faster because time dilation changes the rate at which time flows. Answer: B 2) At about what fraction of the speed of light do our fastest current spacecraft travel? A) 1/2 B) 1/10 C) 1/100 D) 1/1000 E) 1/10,000 Answer: E 3) If we develop spacecraft that can take humans to nearby solar systems at a few percent of the speed of light, how long would it be before we could conceivably populate all habitable planets in the entire Milky Way? A) A few thousand years B) A few million years C) A few billion years D) We could never colonize the galaxy unless we had ships that could travel very close to the speed of light. Answer: B

4) Which of the following is not a possible solution to the question of why we have not yet found evidence of other civilizations? A) We are the only intelligent civilization to have ever arisen in the Milky Way. B) Of all of the intelligent civilizations in the Milky Way, none has chosen to create a galactic civilization. C) There is a galactic civilization, but we are currently unable to detect or recognize it. D) There is a galactic civilization, but it is being actively hidden from us. E) Given the current age of our galaxy, there has not been enough time for a galactic civilization to develop. Answer: E 5) Which of the following best describes Fermi's Paradox? A) Galactic civilizations seem forbidden by the laws of physics. B) Interstellar travel is possible yet would take an infinite amount of time because of relativistic time dilation. C) We would be unable to detect an Earthlike planet even at a distance of a few light-years. D) Reasonable assumptions predict that a galactic civilization should have already arisen in the Milky Way, yet we have absolutely no evidence for it. E) The Drake equation predicts that there should be no intelligent life in the Milky Way, yet we exist. Answer: D Short Answer Questions 1) Why is ozone so crucial to the continued well-being of life on Earth? Answer: Ozone (O3) absorbs ultraviolet photons from the Sun and prevents them from reaching the ground where these high-energy photons would harm biological life. 2) What evidence do we have that life arose fairly quickly on Earth? Answer: Because of the period of heavy bombardment, it would have been difficult for life to survive more than about 4 billion years ago. Combined with evidence from fossils of life 3.5 billion years ago and carbon isotope evidence dating back to 3.95 billion years, it seems that it only takes a few hundred million years for life to spring into existence. 3) Why do we generally rule out stars with masses more than a few times that of the Sun when we consider star systems where life could be possible? Answer: Their stellar lifetimes are too short to allow enough time for life to evolve.

Reading Quiz Questions 1) Fossil evidence points to the presence of life on Earth as far back as ________ ago. A) almost 4 billion years B) about 2.0 billion years C) about 545 million years D) about 65 million years Answer: A 2) What is the significance of stromatolites? A) They appear to be fossils of structures made by microbes long ago. B) They indicate that microbes in the distant past were much larger than bacteria of today. C) They show that the oxygen content of Earth's atmosphere was much smaller in the past. D) They are the earliest known fossils of animals. Answer: A 3) Why do scientists say that evolution is a "theory"? A) Because it explains a great deal about life and is supported by an enormous body of evidence B) Because they are not very confident that it really happened C) Because it's really just a guess about how life developed on Earth D) Because it is supported by only a small amount of evidence Answer: A 4) What is a mutation? A) A change in a living cell's DNA. B) A change in an organism that turns it into a different species. C) A change in the type of food an organism consumes. D) A change in the physical appearance of a living organism. Answer: A 5) Based on DNA studies, it seems that all life on Earth ________. A) shares a common ancestor B) belongs to one of just two kingdoms: plants and animals C) arose from one of five distinct ancestors that lived about 2 billion years ago D) requires oxygen to survive Answer: A 6) Which of the following is considered by biologists to be a likely place where life might have first arisen on Earth? A) In hot water near undersea volcanoes B) On meteorites that landed on Earth C) On land surfaces that got moderately heavy rainfall D) Deep in Earth's core Answer: A

7) How did oxygen (O2) get into Earth's atmosphere? A) It was released by life through the process of photosynthesis. B) It was captured from the solar nebula. C) It was outgassed from volcanoes. D) It came from chemical reactions with surface rocks. Answer: A 8) Which of the following is not considered crucial for life to exist on some world? A) A liquid, such as liquid water B) A source of energy that can be used by life C) A source of nutrients D) An atmosphere Answer: D 9) Which of the following best describes what we mean by a habitable world? A) A planet or moon that could support life, if any life happened to be on it B) A planet or moon with life C) A planet or moon that lies within its star's habitable zone D) A planet or moon on which humans could survive if we happened to go there Answer: A 10) Which of the following places is not generally considered a potential home for life in our solar system? A) Jupiter's atmosphere B) Mars C) Europa D) Titan Answer: A 11) The Sun's habitable zone ________. A) extends from some place a little beyond the orbit of Venus to some place near the orbit of Mars B) consists only of Earth, because Earth is the only planet known to be inhabited C) extends from the orbit of Earth to the orbit of Jupiter D) extends from just beyond the orbit of Mercury to just beyond Earth's orbit Answer: A 12) Why don't we expect to find life on planets orbiting high-mass stars? A) The lifetime of a high-mass star is too short. B) The stars are too hot to allow for life. C) Planets cannot have stable orbits around high-mass stars. D) The high-mass stars emit too much ultraviolet radiation. Answer: A

13) In the context of this chapter, what is an orphan planet? A) A planet-size object that does not orbit a star B) A planet orbiting a star that is not a member of a galaxy C) A planet that has microbial life but no larger organisms D) A planet with no moons, such as Mercury or Venus Answer: A 14) At present, what is the primary way that the search for extraterrestrial intelligence (SETI) is carried out? A) By using radio telescopes to search for signals from extraterrestrial civilizations B) By analyzing high-resolution images of nearby stars in search of evidence for structures that could not have developed naturally C) By searching for planets around distant stars D) By using x-ray telescopes to search for exhaust from interstellar spacecraft Answer: A 15) In the Drake equation (Number of Civilizations = NHP × flife × fciv × fnow), what do we mean by fnow? A) The fraction of planets with civilizations at the present time (as opposed to only in the past or future) B) The fraction of planets in the galaxy on which a civilization could theoretically develop right now C) The fraction of civilizations in the universe that currently are sending messages to us D) The fraction of all species ever to exist that we currently are aware of Answer: A 16) We have sent several spacecraft on trajectories that will ultimately take them into interstellar space (including Pioneer 10 and 11, Voyager 1 and 2, New Horizons). How long will it take these spacecraft to travel as far as the nearest stars? A) Tens of thousands of years B) A few hundred years C) A few decades D) Never, because they will rust and fall apart Answer: A 17) Einstein's theory of relativity tells us that travelers who make a high-speed trip to a distant star and back will ________. A) age less than people who stay behind on Earth B) age more than people who stay behind on Earth C) have more fun than people who stay behind on Earth D) never be able to make the trip within their lifetimes Answer: A

18) If there are other civilizations at present in the Milky Way Galaxy, which statement is almost undoubtedly true? A) They are far more technologically advanced than we are. B) They are anatomically much like us, with two arms, two legs, two eyes, and two ears. C) They have social structures that are completely different from our own; for example, different types of "family" units, and so on. D) For fun, they enjoy "buzzing" to Earth and temporarily abducting people, showing a clear preference for people located in less-developed rural areas. Answer: A Concept Quiz Questions 1) Why are fossils of early life on Earth more rare than fossils of plants and animals from the past few hundred million years? A) Early organisms lacked skeletons and other hard structures that are most likely to be fossilized. B) Life was far less abundant before a few hundred million years ago. C) Fossils could not form before there was oxygen in the atmosphere. D) We find fossils in sedimentary layers, and no sediments were deposited until just a few hundred million years ago. Answer: A 2) Which of the following best describes natural selection? A) It is the idea that the strong survive and the weak die off. B) It is a guess made by scientists about how life develops, but it has no hard evidence to support it. C) It is the idea that organisms with genetic traits that improve their ability to reproduce are more likely to pass those traits on to future generations. D) It is the idea that organisms naturally increase in complexity and intelligence with time. Answer: C 3) Which of the following is not key evidence in support of the idea that all life today shares a common ancestor? A) We have identified fossils of the first life forms that ever existed on Earth. B) All life uses DNA and the same genetic code. C) Mapping of gene sequences shows how life is all related. D) All life builds proteins from the same amino acids and uses ATP to store energy in cells. Answer: A

4) Which of the following best describes the predominant scientific view of the origin of life on Earth? A) We may never know precisely how life arose, but current evidence suggests that life probably can arise naturally under the conditions that prevailed on the early Earth. B) Life probably migrated to Earth from some other world. C) Life arose through a series of extremely unlikely chemical coincidences, making it seem almost miraculous that life ever came to exist at all. D) We can describe with great certainty the precise steps by which life arose on Earth. Answer: A 5) According to current science, why didn't oxygen begin to accumulate in the atmosphere for more than a billion years after life appeared on the Earth? A) Oxygen was removed from the atmosphere by chemical reactions with surface rocks as quickly as it was released by life. B) Early forms of animal life consumed the oxygen released by plants during the first billion years of life on Earth. C) Early life did not release oxygen, and oxygen releasing organisms didn't evolve for a billion years after the earliest life. D) Oxygen was removed from the atmosphere by dissolving in the ocean as quickly as it was released by life. Answer: A 6) When we analyze whether a world is a possible home to life, the key thing we look for is ________. A) the past or present existence of liquid water B) evidence of atmospheric oxygen C) the presence of organic molecules such as amino acids D) surface coloration changes that could indicate vegetative growth Answer: A 7) Which of the following best describes the current status of the evidence concerning whether life has ever existed on Mars? A) Mars probably once had a habitable surface, but we do not know if it had life. B) Clear evidence strongly suggests that life once existed on Mars. C) Clear evidence indicates that Mars never had conditions favorable to life. D) Although current evidence is mixed, ongoing studies should ensure that we will have a definitive answer to the question of whether life ever existed on Mars within about five years. Answer: A 8) Why is Europa considered a good candidate for the possible existence of life? A) Strong evidence suggests that it has a deep, subsurface ocean of liquid water. B) The Galileo spacecraft found strange seasonal changes on its surface that look like they could be due to life. C) It is located within our Sun's habitable zone. D) It has a thick atmosphere with a surface pressure greater than that on Earth. Answer: A 15 Copyright © 2022 Pearson Education, Inc.

9) In general, how does the size and location of a star's habitable zone depend on the star's mass? A) The smaller (less massive) the star, the smaller and the closer-in the habitable zone. B) The smaller (less massive) the star, the larger and the closer-in the habitable zone. C) The smaller (less massive) the star, the larger and the farther-out the habitable zone. D) The habitable zone is always about the same size, but its location moves inward for smaller stars. Answer: A 10) We are not yet capable of detecting life on planets around other stars. But as our technology develops, our first real chance of detecting such life will probably come from ________. A) examining spectral lines from the atmospheres of distant planets B) sending spacecraft to study the planets up close C) examining high-resolution images of the planets made by orbiting telescopes D) determining the orbital properties of the planets Answer: A 11) Some scientists speculate that super-Earths and water worlds might be habitable at greater distances from their stars than Earth-size planets. Why? A) Their larger sizes might allow them to retain hydrogen atmospheres. B) Their larger sizes mean they might have more of the ingredients needed for life. C) For the water worlds, at least, they are certain to have oceans no matter how far they are from a star. D) These planets may retain more internal heat than Earth, which might drive greater geological activity. Answer: A 12) Which of the following best describes how the Drake equation is useful? A) It helps us understand what we need to know to determine the likelihood of finding other civilizations. B) It has allowed us to determine the number of civilizations in the Milky Way Galaxy. C) It allows us to calculate the masses of planets orbiting other stars. D) It tells us what wavelengths of light will be most useful to examine in the search for extraterrestrial intelligence. Answer: A 13) In the Drake equation (Number of Civilizations = NHP × flife × fciv × fnow), we expect the term fciv to be small if ________. A) most civilizations destroy themselves within just a few hundred years of arising B) most of the civilizations that have ever existed are still out and about in the galaxy C) primitive life is common but intelligent life is rare D) most habitable planets never actually get life on them Answer: C

14) Suppose it turns out that one in 1 million stars has a planet that at some point in its history is home to an advanced civilization. Then the total number of civilizations that have arisen in our galaxy would be closest to ________. Assume there are about 100 billion stars in the Milky Way galaxy. A) 100,000 B) 10,000 C) 1,000 D) 100 Answer: A 15) Which of the following describes a major danger of interstellar travel at near-light speed? A) Atoms and ions in interstellar space will hit a fast-moving spacecraft like a flood of dangerous cosmic rays. B) Any interstellar journey will take much longer than the lives of the crew members. C) Time dilation will slow the heart beats of the crew to a dangerously low rate. D) Asteroid fields floating in interstellar space will present a navigational challenge. Answer: A 16) Which of the following statements about matter-antimatter engines is not true? A) Matter-antimatter reactions represent the most efficient possible reactions in terms of energy release. B) Spacecraft powered by matter-antimatter engines could probably reach speeds of more than half the speed of light. C) One of the major challenges to developing matter-antimatter engines is finding a way to store antimatter after it is produced. D) Matter-antimatter engines would be great in theory, but to date we have no evidence that antimatter even exists. Answer: D 17) Which of the following is not considered a potential solution to the question of why we lack any evidence of a galactic civilization? A) There is no galactic civilization because all civilizations destroy themselves before they achieve the ability to colonize the galaxy. B) The galactic civilization is deliberately avoiding contact with us. C) There is no galactic civilization because we are the first species ever to achieve the ability to study the universe. D) The galactic civilization probably is undetectable because they operate under different laws of physics from the ones we know. Answer: D

Visual Quiz Questions 1) What are the different colored horizontal layers that we see in this photo of a wall in the Grand Canyon?

A) They are sediments deposited at different times in the past, so that layers near the bottom are the oldest and layers near the top are the youngest. B) They are different types of volcanic rock that cooled at different rates after a single, large volcanic eruption. C) They formed as the Colorado River carved out the canyon, so that the layers near the top are the oldest and the layers at the bottom are the youngest. D) They got their coloration from ancient civilizations that painted the rock. Answer: A 2) Suppose you had a time machine and traveled back in time to Earth about 3 billion years ago. Based on studying this diagram of the geological time scale, what would have caused you the most difficulty as you tried to walk around?

A) A lack of breathable air B) The danger posed by carnivorous dinosaurs C) The possibility of being harmed by poisonous plants D) A lack of liquid water Answer: A 18 Copyright © 2022 Pearson Education, Inc.

3) This diagram shows the "tree of life" based on genetic studies of relationships between living organisms. Which statement about the tree of life is not true?

A) It shows that plants and animals are the two most dominant forms of life on Earth today. B) It shows that all organisms alive today bear genetic similarities that suggest they evolved from a common ancestor. C) It shows that, based on genetic relationships, there are three major branches of life on Earth. D) It shows that there is greater genetic diversity in microscopic organisms than among animals. Answer: A

4) This photo shows an undersea volcanic vent. What is it, and what is its significance to the study of the origin of life?

A) Genetic studies suggest that life may have originated around vents like this one. B) It is the place where we have found the oldest living organisms on Earth. C) It is the place where we have found the oldest fossils on Earth. D) It shows that fires can burn underwater. Answer: A

5) This photo shows apparatus used in an experiment in which materials thought to have been present on the early Earth were sparked with energy. What have we learned from this type of experiment?

A) These experiments have shown that the building blocks of life form easily and naturally under conditions that existed on the early Earth. B) These experiments have told us the precise composition of Earth's early atmosphere. C) These experiments have shown us how life originated on Earth. D) These experiments have provided strong evidence for the idea that life first arose near volcanic vents at the bottom of the ocean. Answer: A

6) These two diagrams contrast the habitable zones around the Sun and around a much lower mass star. They are shown to scale. Based on what you see here, what can you conclude about the possibility of finding life around the lower-mass star compared to finding life around a Sunlike star?

A) There is a higher probability that an orbiting planet will be in the habitable zone for a Sun-like star than for a lower-mass star. B) Sun-like stars must always have more life around them than lower-mass stars. C) A Sun-like star always has at least two habitable planets, while a lower-mass star may have only one habitable planet. D) There is virtually no chance of finding life around a lower-mass star. Answer: A

7) What does this graph tell us about humans compared to other animals?

A) Humans have a brain that is unusually large for an animal of our size. B) Humans have the largest brains of any animal. C) Unlike the brains of other animals, human brains cannot be described by a straight line. D) Based on averages determined from other animals, human brains are precisely the size we'd expect for animals of our weight. Answer: A 8) This photo shows a radio telescope that is being used in the search for life beyond Earth. How is it being used in this search?

A) It is used to listen for signals deliberately broadcast by another civilization. B) It is used to obtain spectra of planets around other stars so that we can look for chemicals, like oxygen, that might indicate the presence of life. C) It is used to make detailed radar maps of Mars, from which we may be able to determine whether cities ever existed on our planetary neighbor. D) It is used to communicate with spacecraft that we have launched toward distance stars in search of life on planets that my orbit them. Answer: A 23 Copyright © 2022 Pearson Education, Inc.

9) This painting shows a futuristic spacecraft powered by the detonation of small hydrogen bombs. If we actually had such a spacecraft, what would it allow us to do?

A) It would allow us to make a one-way trip to the nearest star besides the Sun in about a century. B) It would allow us to travel roundtrip to almost anywhere in the Milky Way Galaxy in just a few years of ship time. C) It would allow us to travel from Earth to Mars in less than an hour. D) It would allow us to travel up to several times faster than the speed of light. Answer: A 10) This photo shows a boy playing with sand on the beach. If we think about the grains of sand, how are they significant to the question of life beyond Earth?

A) There are about as many stars in the universe as there are grains of sand on all the beaches on Earth, so there are a lot of possible homes to life. B) There are about as many life-bearing planets in the universe as there are grains of sand on all the beaches on Earth. C) There are about as many habitable planets orbiting other stars in the universe as there are grains of sand on all the beaches on Earth. D) We think that life must always arise on or near an ocean, so this scene on the beach probably looks much like what we'd expect to find on any other planet with life on it. Answer: A

End-of-Chapter Questions Visual Skills Check Use the following questions to check your understanding of some of the many types of visual information used in astronomy.

This figure repeats Figure 19.3 of the geological time scale. Use it to answer the questions below. 1) List the following events in the order in which they occurred, from first to last. a. earliest humans b. earliest animals c. impact causes extinction of dinosaurs d. earliest mammals e. earliest plants living on land f. first time there is significant oxygen in Earth's atmosphere g. first life on Earth Answer: g, f, b, e, d, c, a 2) List the following time frames in order of how long they lasted, from longest to shortest. a. Hadean eon b. Proterozoic eon c. Paleozoic era d. Cretaceous period Answer: b, a, c, d

3) Which time frame(s) do we live in today? (More than one may apply.) A) Quaternary period B) Tertiary period C) Cenozoic era D) Phanerozoic eon E) Paleozoic era Answer: A, C, D 4) How long did the Cambrian explosion last? A) Less than 1 year B) About a decade C) About 10,000 years D) About 20 million years E) About 500 million years Answer: D 5) When did the heavy bombardment end? A) About 4.5 billion years ago B) Between about 4.3 and 4.5 billion years ago C) Between about 3.8 and 4.0 billion years ago D) Exactly 3.95 billion years ago Answer: C 6) How long have mammals been present on Earth? A) About 1 million years B) About 65 million years C) About 225 million years D) About 510 million years Answer: C Chapter Review Questions 1) What is astrobiology, and what type of research does it involve? 2) How do we study the history of life on Earth? Describe the geological time scale and a few of the major events along it. 3) Summarize the evidence pointing to an early origin of life on Earth. How far back in Earth's history did life exist? 4) Why is the theory of evolution so critical to our understanding of the history of life on Earth? Explain how evolution proceeds by natural selection, including what happens on the level of DNA. 5) How are laboratory experiments helping us study the origin of life on Earth? Explain.

6) Give a brief overview of the history of life on Earth. What evidence points to a common ancestor for all life? 7) Is it possible that life migrated to Earth from elsewhere? Explain. 8) Describe the range of environments in which life thrives on Earth. What are three basic requirements for life? 9) What is a habitable world? Which worlds in our solar system seem potentially habitable, and why? 10) Briefly summarize the current status of the search for life on Mars. 11) What do we mean by a star's habitable zone? What key factors have given Earth long-term surface habitability, and do they seem likely on other worlds? Explain. 12) What types of worlds might support surface habitability? What types of worlds might have subsurface habitability? Explain. 13) What is the Drake equation? Define each of its factors, and describe the current state of understanding about their potential values. 14) What is SETI? Describe the capabilities of current SETI efforts. 15) Why is interstellar travel so difficult? Describe a few technologies that might someday make it possible. 16) What is Fermi's paradox? Describe several potential solutions to the paradox, and the implications of each for our civilization. Fantasy or Science Fiction? Based on our present understanding of science, decide whether each of the following futuristic scenarios is plausible or whether it is unlikely to be possible. Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer. 17) The first human explorers on Mars discover the ruins of an ancient civilization, including remnants of tall buildings and temples. 18) The first human explorers on Mars drill a hole into a Martian volcano to collect a sample of soil from deep underground. On analyzing the soil, they discover that it holds living microbes resembling terrestrial bacteria but with a different biochemistry. 19) In 2050, a spacecraft lands on Europa and melts its way through the ice into the subsurface ocean. It finds numerous strange, living microbes, along with a few larger organisms that feed on the microbes.

20) It's the year 2075. A giant telescope on the Moon, consisting of hundreds of small telescopes linked together across a distance of 500 km, has just captured a series of images of a planet around a distant star that clearly show seasonal changes in vegetation. 21) A century from now, after completing a careful study of planets around stars within 100 light-years of Earth, astronomers discover that the most diverse life exists on a planet orbiting a young star that formed just 100 million years ago. 22) In 2040, a brilliant teenager working in her garage builds a coal-powered rocket that can travel at half the speed of light. 23) In the year 2750, we receive a signal from a civilization telling us that the Voyager 2 spacecraft recently crash-landed on its planet, which orbits a nearby star. 24) Crew members of the matter—antimatter spacecraft Star Apollo, which left Earth in the year 2165, return to Earth in the year 2450, looking only a few years older than when they left. 25) Aliens from a distant star system invade Earth with the intent to destroy us and occupy our planet, but we successfully fight them off when their technology proves no match for ours. 26) A single great galactic civilization exists. It originated on a single planet long ago but is now made up of beings from many different planets, assimilated into the galactic culture.

Quick Quiz Choose the best answer to each of the following. For additional practice, try the Chapter 19 Reading and Concept Quizzes in the Study Area at www.MasteringAstronomy.com. 27) Fossil evidence suggests that life on Earth arose ________. A) almost immediately after Earth formed B) within a few hundred million years after Earth formed C) about a billion years before the rise of the dinosaurs Answer: No Correct Answer Was Provided. 28) The theory of evolution is ________. A) a scientific theory, supported by extensive evidence B) one of several competing scientific models that all seem equally successful in explaining the nature of life on Earth C) a guess about how life changes with time Answer: No Correct Answer Was Provided.

29) Plants and animals are ________. A) the two major forms of life on Earth B) the only organisms that have DNA C) just two small branches of the diverse "tree of life" on Earth Answer: No Correct Answer Was Provided. 30) Which of the following is a reason why early living organisms on Earth probably could not have survived on the surface? A) The lack of an ozone layer B) The lack of oxygen for them to breathe C) The fact that these organisms were single-celled Answer: No Correct Answer Was Provided. 31) According to current understanding, a key requirement for life is ________. A) photosynthesis B) liquid water C) an ozone layer Answer: No Correct Answer Was Provided. 32) Which of the following worlds is not considered a reasonable candidate for harboring life? A) Europa B) Mars C) The Moon Answer: No Correct Answer Was Provided. 33) How does the habitable zone around a star of spectral type G compare to that around a star of spectral type M? A) It is larger. B) It is hotter. C) It is closer to its star. Answer: No Correct Answer Was Provided. 34) In the Drake equation, suppose that the term flife = ½. What would this mean? A) Half the stars in the Milky Way Galaxy have a planet with life. B) Half of all life-forms in the universe are intelligent. C) Half of the habitable worlds in the galaxy actually have life, while the other half don't. Answer: No Correct Answer Was Provided. 35) The amount of energy that would be needed to accelerate a large spaceship to half the speed of light is ________. A) about 100 times as much energy as is needed to launch the Space Shuttle B) more than 2000 times the current annual global energy consumption C) more than the amount of energy released by a supernova Answer: No Correct Answer Was Provided.

36) According to current scientific understanding, the idea that the Milky Way Galaxy might be home to a civilization millions of years more advanced than ours is ________. A) a virtual certainty B) extremely unlikely C) one reasonable answer to Fermi's paradox Answer: No Correct Answer Was Provided. Inclusive Astronomy Use these questions to reflect on participation in science. 37) The Turning Point. The end of this chapter presented the idea that humanity is now at a turning point, and that current generations have a greater responsibility for the future than did any previous generation. Do you agree with this assessment? If so, how can we ensure that we deal with this responsibility wisely, in a way that builds a better future for the entire human race? If not, why not? 38) Group Discussion: Who Speaks for Earth? Form small groups to discuss the issues that would arise if SETI were to receive a message from an alien civilization. a. The message would presumably be received first by a relatively small group of astronomers. Work together to write up a short protocol specifying what these scientists should do upon receiving the message. For example, should they announce the discovery immediately and share the message immediately? b. Responding to the message would make our existence known to the aliens. Is this a good idea? Make a list of pros and cons of sending a response. c. Assume that we have decided to send a response. Given that the response will represent the entire human race, who should write it, and what type of information should it offer about our species and our planet? The Process of Science These questions may be answered individually in short-essay form or discussed in groups, except where identified as group-only. 39) The Science of Astrobiology. The study of astrobiology is sometimes criticized as being the study of something for which we have no evidence, since we do not yet have evidence of life beyond Earth. Is astrobiology a science or speculation? Defend your opinion. 40) Astrobiology Funding. Imagine that you were a member of Congress and your job included deciding how much government funding to allocate to research in different areas of science. How would the amount you allotted to the search for life in the universe compare to the amount you allotted to research in other areas of astronomy and planetary science? Why? 41) Breakthrough Starshot. The "Breakthrough Starshot" initiative proposes to send a fleet of tiny, robotic spaceships to the Alpha Centauri star system. Learn about how this effort is intended to work, who is funding it, and what its goals are. Overall, do you think it is realistic? Do you think it is worthwhile? Defend your opinions.

42) Unanswered Questions. In a sense, this entire chapter was about one big, unanswered question: Are we alone in the universe? But as we attempt to answer this "big" question, there are many smaller questions that we might wish to answer along the way. Describe one currently unanswered question about life in the universe that we might be able to answer with new missions or experiments over the next couple of decades. What kinds of evidence will we need to answer the question? How will we know when it is answered? 43) Group Discussion: Solution to the Fermi Paradox. Discuss the various possible solutions to the question "Where are the aliens?" Can your group reach a consensus on which possibility is the most likely? If so, write a brief summary of why you chose this solution and what it means for our future. If not, record the number of group members supporting each possibility, and summarize the key points of disagreement. 44) Group Activity: Habitable Planets? Work in small groups to rank the four hypothetical planets described below in order from most likely to support life to least likely to support life. Assume the planets are all approximately the same size as Earth, and explain your reasons for each ranking.Note: You may wish to do this activity using the four roles described in Chapter 1, Exercise 39. Planet 1: orbits a star of spectral type B (approximately 10 solar masses) in a circular orbit within the habitable zone Planet 2: orbits a Sun-like star in a circular orbit at a distance twice Earth's orbital distance from the Sun Planet 3: orbits a star with a luminosity one-quarter the Sun's luminosity in a circular orbit at a distance one-half Earth's orbital distance from the Sun Planet 4: orbits a Sun-like star in an elliptical orbit, with its orbital distance ranging from 1 AU to 10 AU Investigate Further 45) Most Likely to Have Life. Suppose you were asked to vote in a contest to name the world in our solar system (besides Earth) "most likely to have life." Which world would you cast your vote for? Explain and defend your choice in a one-page essay. 46) Likely Suns. Study the stellar data for nearby stars given in Appendix F, Table F.1. Which star on the list would you expect to have the largest habitable zone? Which would have the second-largest habitable zone? If we rule out multiple-star systems, which star would you expect to have the highest probability of having a habitable planet? Explain your answers. 47) Is Life Common? Based on what you have learned in this book, do you think life will ultimately prove to be rare, common, or something in between? Write a one- to two-page essay explaining and defending your opinion. 48) What's Wrong with This Picture? Many science fiction stories have imagined the galaxy divided into a series of empires, each having arisen from a different civilization on a different world, that hold each other at bay because they are all at about the same level of military technology. Is this a realistic scenario? Explain. 31 Copyright © 2022 Pearson Education, Inc.

49) Aliens in the Movies. Choose a science fiction movie (or television show) that involves an alien species. Do you think aliens like those depicted could really exist? Write a one- to twopage critical review of the movie or show, focusing primarily on the question of whether it portrays the aliens in a scientifically reasonable way. Quantitative Problems Be sure to show all calculations clearly and state your final answers in complete sentences. 50) SETI Search. Suppose there are 10,000 civilizations broadcasting radio signals in the Milky Way Galaxy right now. On average, how many stars would we have to search before we would expect to hear a signal? Assume there are 500 billion stars in the galaxy. How would your answer change if there were only 100 civilizations instead of 10,000? 51) SETI Signal. Consider a civilization broadcasting a signal with a power of 10,000 watts. The Arecibo radio telescope, which is about 300 m in diameter, could detect this signal if it were coming from as far away as 100 light-years. Suppose instead that the signal is being broadcast from the other side of the Milky Way Galaxy, about 70,000 light-years away. How large a radio telescope would we need to detect this signal? (Hint: Use the inverse square law for light.) 52) Cruise Ship Energy. Suppose we have a spaceship about the size of a typical ocean cruise ship today, which means it has a mass of about 100 million kg, and we want to accelerate the ship to a speed of 10% of the speed of light. a. How much energy would be required? (Hint: You can find the answer simply by calculating the kinetic energy of the ship when it reaches its cruising speed; because 10% of the speed of light is still small compared to the speed of light, you can use this formula: kinetic energy = ½ × m × v2 .) b. How does your answer compare to total worldwide energy use at present, which is about 5 × 1022 joules per year? c. The typical cost of energy today is roughly 5¢ per 1 million joules. At this price, how much would it cost to generate the energy needed by this spaceship? 53) Matter—Antimatter Engine. Consider the spaceship from Problem 52. Suppose you want to generate the energy to get it to cruising speed using matter—antimatter annihilation. How much antimatter would you need to produce and take on the ship? (Hint: When matter and antimatter meet, they turn all their mass into energy equivalent to mc2.)