THe Sun

Lesson 1

The Sun

On January 20, 2005, satellites that carried cell phone and cable signals suddenly shut down. They had been struck by a burst of energy. Where did this energy come from?

296

5 ES 5.a. Students know the Sun, an average star, is the central and largest body in the solar system and is composed primarily of hydrogen and helium.

ENGAGE

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How do the sizes of Earth and the Sun compare?

Materials

Purpose To study the size difference between Earth and the Sun.

Procedure Use Numbers What proportion does the size of Earth have to the size of the Sun?

Use Numbers What would the diameter of the

• meter stick

Sun be if the diameter of Earth was 0.5 cm?

• ruler

Make a Model Use appropriate tools to design

• colored pencils

a model of earth and the Sun to this scale.

How many Earths would it take to cover the length of the model Sun’s diameter?

Draw Conclusions

• clear tape Step

Diameter

The Sun

1,390,000 kilometers

Communicate Explain why this model does,

Earth

12,760 kilometers

or does not, show an accurate comparison between the diameters of the Sun and Earth.

Step

Explore More How does the Moon’s diameter compare with that of Earth? Do research to answer this question and make a model to represent the difference in their sizes.

5 IE 6.f. Select appropriate tools (e.g., thermometers, meter sticks, balances, and graduated cylinders) and make quantitative observations.

297 EXPLORE

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â–ś Main Idea 5 ES 5.a The Sun is a star made of hydrogen and helium.

The Sun is located at the center of the solar system and is also its largest object.

â–ś Vocabulary star , p. 299 astronomical unit , p. 299 fusion , p. 302

Sun

-Glossary @

www.macmillanmh.com

â–ś Reading Skill Draw Conclusions BSfb 1ZcSa

1]\QZcaW]\a

Earth

Earth and the Sun are shown here on a scale of 1 centimeter = 50,000 kilometers.

At this size, Earth and the Sun are 2,992 centimeters (about 98 feet) apart.

298 EXPLAIN

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What is the Sun?

Finding the Sun’s Mass

The Sun is a star. A star is an object that produces its own energy, including heat and light. The planets and the other objects in the solar system are not stars because they do not produce their own light.

It is impossible to measure the weight of the Sun. After all, the Sun cannot be put on a scale.

The stars that produce the most energy make about ten million times more energy than the Sun. The least-productive stars make only one-hundreth as much energy as the Sun. The Sun is an average-sized star and the largest object in the solar system.

The Sun’s diameter is about 1,390,000 kilometers (863,706 miles). If the Sun were a hollow ball, more than a million Earths could fit inside it. The Sun looks larger than the other stars that can be seen in the night sky because it is much closer to Earth.

The mean, or average, distance between the Sun and Earth is 149,591,000 kilometers (92,960,000 miles). This number is known as one astronomical (as•truh•NAH•mi•kulh) unit (AU). The closest stars to the solar

system are found in the Alpha Centauri star system. They are about 271,931 AUs away.

However, you can measure the mass of the Sun, or the amount of matter in it. The mass of the Sun can be calculated if you know two facts. The first fact is the length of time it takes for a planet to make one trip around the Sun (for Earth, that is 365.24 days). The second is the distance between the planet and the Sun (for Earth, that is 149,591,000 kilometers).

Using this information, scientists have calculated the Sun’s mass to be 2 million trillion trillion kilograms.

That’s 2,000,000,000,000,000,000, 000,000,000,000 kilograms! This is 745 times greater than the mass of all the other objects in the solar system put together. As a matter of fact, the mass of the Sun makes up 99.8% of all the mass in the solar system.

Quick Check Draw Conclusions Why are the

planets not stars?

Critical Thinking Why are

astronomical units used to measure distances rather than kilometers?

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What are the parts of the Sun? The Sun is a huge sphere made up mostly of two very light gases, hydrogen and helium. About 71% of the Sun’s mass is made up of hydrogen.

Another 27% is made up of helium.

Other materials, such as oxygen and carbon, make up the remaining 2% of the Sun’s mass.

Most of the energy that the Sun produces is formed in its core. At its core, the Sun has a temperature of 10 million to 20 million degrees Celsius.

The pressure is more than 1 billion times greater than the air pressure at sea level on Earth.

The radiation layer, which is next to the core, moves the energy produced in the core in every direction. It can take millions of years for energy to move out of this layer.

In the convection layer, gases with different energies move in circles in a way similar to air with different densities. Energy moves out of this layer in about a week.

The photosphere is the visible surface of the Sun. It is not a solid surface, but rather a layer of gases. The photosphere is cooler than the core. Its temperature is about 5,730°C (10,346°F).

The next layer of the Sun is the chromosphere, or the inner layer of the Sun’s atmosphere. When it can be seen, it looks like a red circle around the Sun. The corona is the outermost layer of the Sun’s atmosphere. The corona takes on different shapes around the Sun depending on changes in the temperature of the photosphere.

photosphere

corona

chromosphere

core

radiation layer convection layer

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Solar Flares Solar flares are bursts of heat and energy that stretch out from the corona and chromosphere into space. Sometimes this energy disrupts satellites, interfering with TV, radio, and cell phone communication systems.

Energy from solar flares also causes displays of different-colored lights in the upper atmosphere. These lights are called the aurora borealis (uh•RAW•uh bawr•ee•AL•is), or northern lights. The northern lights are most often seen in Alaska, Canada, and the northern United States. They are only seen in the southern United States when the Sun releases large amounts of energy.

Solar flares are also sometimes associated with sunspots. Sunspots, or dark spots on the Sun, are regions of the photosphere that have a lower temperature than the surrounding regions.

The Parts of the Sun Make a Model Use modeling clay to make a model of the Sun that includes all of the layers.

Be careful. Using a plastic knife, cut away a quarter of your Sun so you can see into it.

Add sunspots and solar flares to the surface of your Sun. Communicate Write a description of your Sun. Include a color key to identify the layers.

Quick Check Draw Conclusions Why does it

take millions of years for energy that moves in every direction to leave the radiation layer? solar flare

Critical Thinking Which three

layers of the Sun can be seen?

Reading Diagrams sunspot

What is the layer of the Sun between the core and the convection layer called?

Clue: Find the labels on the diagram for the core and for the convection layer, and look for the name of the layer between them.

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mass. However, inside of the Sun hydrogen particles smash together to make helium. This smashing together of particles is called fusion (fyew•zhuhn) . A little bit of mass is lost when hydrogen particles combine to make helium. According to Einstein’s equation, that little bit of mass is changed into energy. We see this energy as light and heat, as well as other kinds of energy that cannot be seen.

How does the Sun produce energy?

More than 100 years ago, Albert Einstein discovered a relationship between energy and mass. He expressed the discovery in what has become one of the most famous equations in science:

E = mc2 The E stands for energy. The m stands for mass. The c represents the speed of light. The little 2 over the c means that the speed of light is squared, or multiplied by itself. This equation tells us that a little bit of mass can be changed into a lot of energy.

Quick Check Draw Conclusions What happens

when hydrogen particles collide?

Critical Thinking What would

happen if all of the hydrogen in the Sun turned into helium?

As you learned earlier in this lesson, the Sun is mostly made up of hydrogen. Hydrogen has very little Fusion

2

3

1

1 Particles of hydrogen move

throughout the Sun.

Reading Diagrams 2 Two particles of hydrogen collide.

3 One particle of helium is formed and

energy is released.

What happens to hydrogen particles in the Sun during fusion?

Clue: Starting on the left, follow what happens to the hydrogen particles.

302 EXPLAIN

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Summarize the Main Idea The Sun is a star and the largest object in the solar system. (pp. 298–299)

The Sun produces energy when hydrogen combines to form helium and energy. (pp. 300–302)

Think, Talk, and Write Main Idea What is the largest object in the solar system?

Vocabulary An object in the solar system that produces heat and light is a .

Draw Conclusions What causes energy to be released inside the Sun? BSfb 1ZcSa

1]\QZcaW]\a

Critical Thinking How would Earth be

Make a Study Guide

affected if the Sun stopped producing energy?

Make a two-tab book (see p. 479). Use the titles shown. On the inside of each tab, draw conclusions about the title.

Test Practice All of the following are part of the solar system EXCEPT A the Sun. B Earth.

C the Moon.

D the stars.

Test Practice The Sun is made up of all of the following materials EXCEPT A hydrogen.

B helium.

C carbon.

D steam.

Writing Link

Math Link

Descriptive Writing

Earth’s Mass

Using what you have learned in this lesson, write about the Sun. Discuss the layers of the Sun, fusion, and the Sun’s size and mass.

The Sun’s mass is roughly 330,000 times Earth’s mass. If you made a model of the Sun with a mass that was 1,000 kilograms, what would be the mass of Earth in grams?

-Review Summaries and quizzes online @ www.macmillanmh.com 303 EVALUATE

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Draw Conclusions Scientists began recording data about sunspots in 1749.

After they collected years of data, scientists concluded that the number of sunspots increases and decreases during an 11-year cycle. From the beginning of the cycle, the number of sunspots tends to increase over a period of about five years to a maximum number. Over the next six years, the number of sunspots decreases to a minimum number. A new cycle begins when the number of sunspots increases.

▲ Scientists collect data about the number of sunspots that occur on the Sun.

Learn It When you draw conclusions, you look at all the facts and decide what can be based on those facts. Be careful not to “jump to conclusions,” or to draw conclusions that are not supported by the data.

Look at the chart. It lists the number of sunspots recorded each year beginning in 1750.

When scientists looked at the first two years of data, they could have concluded that the number of sunspots always decreased. However, in 1752, the number of sunspots increased.

This means that their conclusion was no longer supported by the data. They needed to collect more data and draw a new conclusion.

When you gather data, it is important to record it. Having a record of your data gives you the information that you need to be able to draw conclusions.

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Sunspots from 1750 to 1761 Year

Sunspots

1750

1,001

1751

572

1752

574

1753

368

1754

147

1755

115

1756

122

1757

389

1758

671

1759

648

1760

754

1761

1,030

Source: National Aeronautics and Space Administration

5 IE 6.h. Draw conclusions from scientific evidence and indicate whether further information is needed to support a specific conclusion.

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Try It Use the chart of sunspots from 1750 to 1761 to draw conclusions as you answer the following questions. ▶ In which year would you conclude that this cycle began? Why? ▶ If you were a scientist studying sunspots, in which years did you

observe changes in the number of sunspots that might make you question the existence of a cycle? Why? ▶ If you only had ten years of data, but you hypothesized that the

sunspot cycle was longer than ten years, what would you have to do before you could draw a conclusion?

Apply It This chart shows data about sunspots and solar flares from 1993 to 2004. Use it to draw conclusions as you answer the following questions. ▶ In which year do you conclude that an

11-year cycle began? How do you know? ▶ What can you conclude about the

frequency of sunspots between 1993 and 2004 compared to between 1750 and 1761? ▶ What can you conclude about the expected

sunspot activity in 2005 and 2006? ▶ Scientists recently began recording data

about the number of solar flares that occur every year. Their hypothesis was that solar flares increase and decrease on the same cycle as sunspots. Would you conclude that the recorded data supports this hypothesis?

Why?

Sunspots from 1993 to 2004 Year

Sunspots

Solar flares

1993

657

2,541

1994

359

1,066

1995

210

639

1996

103

280

1997

258

790

1998

769

2,423

1999

1,118

3,963

2000

1,433

4,474

2001

1,331

3,597

2002

1,245

3,223

2003

763

1,552

2004

486

728

Source: National Aeronautics and Space Administration and the National Oceanic and Atmospheric Administration

▶ What could you do to provide additional

support for your conclusion that solar flares increase and decrease on the same cycle as sunspots?

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