Astronomy 2017 08 by rguzmane

EXCLUSIVE TOTAL ECLIPSE ATLAS

p. 54

AUGUST 2017

The world’s best-selling astronomy magazine

AUGUST 21, 2017

Everything you need to know • Step-by-step viewing guide

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Vol. 45 • Issue 8

• 20 viewing hot spots • Navigating the sky on eclipse day • Best video and photo strategies

You and Your Shadow... Tele Vue-60 Sun, Moon, You, Tele Vue. Spectacular!

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TV-85 Eclipse Image by Dennis diCicco, processing by Sean Walker.

ADVERTORIAL

SPECTACULAR

TOTALITY PHASES

TOTALITY By Dave Henry and Ken Sklute

The mind of even experienced photographers can be a whirl of chaos in the moments before totality begins. Here’s a handy guide to getting your best shots.

Safety Never look at the sun without accredited and approved solar filtration over your eyes. Permanent, irreversible eye damage and/or blindness can result in seconds. Never point your camera into the sun without a special solar filter. Not using a solar filter at eclipse magnifications will ruin your camera in seconds. Never improvise, modify or use general photography neutral density (ND) filters regardless of how many stops they are. Buy an approved solar filter. They’re relatively inexpensive and are designed for the task.

The partial phases are easy. The solar filter is on the entire time and there’s no need to bracket exposures. As you get closer to totality, you may want to begin bracketing your exposures. If you have one of the newer Canon EOS bodies that have a built-in intervalometer, set it to take a photo every minute during the partial phases. Be sure to keep centering the sun in your frame (using the LCD screen, of course). When you’re setting up, remember to tape all your lens rings down and occasionally recheck your zoom and focus.

Planning is everything

This diamond ring, Baily’s beads and totality

For most of the country there will be less than 2-1/2 minutes of spectacular total eclipse photography. Even the smallest details can cost valuable seconds. For example, what will you do with the solar filter once it’s removed? You need to plan for that.

At first contact, the east edge of the moon appears to touch the west edge of the sun disk. At this moment, the eclipse has begun. You need the solar filter in place even though the sun is slowly being obscured by the moon. This phase will last about an hour and 20 minutes. About 15 seconds before second contact, you will see the diamond ring effect where the

moon almost completely covers the sun. About five seconds before second contact occurs, you will begin to see Baily’s beads. The moment Baily’s beads disappear, quickly remove the solar filter and switch your camera to take longer, bracketed exposures to capture the sun’s corona. Shoot like crazy. You’ll have less than 2-1/2 minutes and you don’t want to miss anything. When Baily’s beads reappear, quickly replace the solar filter. Wait for the camera and lens to stop vibrating, then continue shooting continuously for a couple of minutes. Once a sliver of the sun’s disk appears, you can return to shooting a frame a minute until the eclipse ends in about an hour and 25 minutes. Lastly, remember to take a moment to view totality with your eyes (and approved solar glasses). Only your eyes can see the full dynamic range of the corona, something that a photograph can’t quite do justice to…yet.

FIRST CONTACT: The east edge of the moon touches the west edge of the sun. At second contact, when the moon’s west edge touches the sun’s west edge, totality begins.

FIRST DIAMOND RING: About 15 seconds before second contact, you will see the diamond ring effect where the moon almost completely covers the sun.

BAILY’S BEADS: About five seconds before totality, there are still a few tiny rays of sunlight peeking between the valleys of the craters on the moon.

LAST DIAMOND RING: A sliver of the sun’s disc reappears, marking the end of totality. A © DAVE HENRY: Canon 50D DSLR camera, EF 800mm f/5.6L lens B-D © FABIO PIGNATA: Canon 300D (EOS Digital Rebel) on a telescope

Canon has the ideal equipment for capturing once-in-a-lifetime solar eclipse images. EOS 80D Double Lens Solar Eclipse Kit

For more shooting tips and to purchase Canon’s exclusive Solar Eclipse Bundles, go to usa.canon.com/eclipse.

AUGUST 2017 SABERS, ROYER, DRUCKMÜLLER, AND PADILLA

VOL. 45, NO. 8

ON THE COVER

CONTENTS

A deep coronal shot shows the March 2016 solar eclipse captured from the island of Bangka in Indonesia.

FEATURES 20 COVER STORY Get ready for E-Day

44 Sky This Month

The actions you take before the celestial lineup can help everything run smoothly August 21.

Totality comes to America. MARTIN RATCLIFFE AND ALISTER LING

MICHAEL E. BAKICH

26 A step-by-step guide to the Great American Eclipse

46 StarDome and Path of the Planets RICHARD TALCOTT; ILLUSTRATIONS BY ROEN KELLY

68 Video strategies for eclipse day

COLUMNS Strange Universe 10

Forget the point-and-shoot option — video mode is your camera’s most valuable feature on August 21. MICHAEL E. BAKICH

70 Expert tips on imaging

Don’t miss a thing as you watch the magnificent sky drama unfold. RICHARD TALCOTT

52 Navigating the sky

Tried-and-true techniques for photographing a total solar eclipse, from cameras to smartphones. MIKE REYNOLDS

32 What weather should you expect?

There’s so much more in the sky during the eclipse than the Sun and Moon. Here’s how to make sure you’ll see it all.

74 Let the countdown to 2024 begin

Make your best guess more than a roll of the dice come the big day. JAY ANDERSON

38 20 hot spots to view the eclipse People will view the spectacle from thousands of locations. Here are some you should consider. MICHAEL E. BAKICH

MICHAEL E. BAKICH

Let’s do this all over again in seven years — with two more minutes of totality!

54 Astronomy’s atlas of totality

MICHAEL E. BAKICH

Viewing the upcoming eclipse is all about totality. Here’s how to position yourself under the Moon’s inner shadow. MICHAEL E. BAKICH; MAPS BY MICHAEL ZEILER

76 Do you speak “eclipse”? Totality, arcminutes, chromosphere . . . it’s easy to get lost in technical terms. We’re here to help. MICHAEL E. BAKICH

ONLINE FAVORITES Go to www.Astronomy.com for info on the biggest news and observing events, stunning photos, informative videos, and more. 4

A ST R O N O M Y • AUG UST 2017

Our BrandNew 2017 Eclipse Page All the news you can use!

Pluto Globe Astronomy presents the first-ever Pluto globe!

Picture of the Day Gorgeous photos from our readers.

News The latest updates from the science and the hobby.

BOB BERMAN

Binocular Universe 78 PHIL HARRINGTON

Secret Sky 80 STEPHEN JAMES O’MEARA

For Your Consideration 82 JEFF HESTER

Observing Basics 84 GLENN CHAPLE

QUANTUM GRAVITY Snapshot 8 Astro News 12

IN EVERY ISSUE From the Editor 6 Astro Letters 9 New Products 85 Advertiser Index 86 Reader Gallery 88 Breakthrough 90 Astronomy (ISSN 0091-6358, USPS 531-350) is published monthly by Kalmbach Publishing Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Periodicals postage paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to Astronomy, P.O. Box 62320, Tampa, Fla. 33662-2320. Canada Publication Mail Agreement #40010760.

Are YOU Prepared? The 2017 Great American Solar Eclipse will be one of the most awe-inspiring events our solar system has to offer. On Monday, August 21st, 2017 the Moon will pass in front of the Sun presenting the U.S. with a Total Solar Eclipse. TENS OF MILLIONS of people will be able to experience this event simply by stepping outside and looking at the Sun with the correct solar gear! Meade’s new EclipseView™ Line of white-light, solar safe telescopes and binocular are the best instruments available from Meade for viewing the Sun and the upcoming Solar Eclipse!

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FROM THE EDITOR BY DAV I D J. E I C H E R Editor David J. Eicher Art Director LuAnn Williams Belter

Join me in Costa Rica

EDITORIAL

Managing Editor Kathi Kube Senior Editors Michael E. Bakich, Richard Talcott Associate Editors Alison Klesman, John Wenz Copy Editors Dave Lee, Elisa R. Neckar Editorial Assistant Nicole Kiefert ART

Graphic Designer Kelly Katlaps Illustrator Roen Kelly Production Specialist Jodi Jeranek CONTRIBUTING EDITORS

Bob Berman, Adam Block, Glenn F. Chaple, Jr., Martin George, Tony Hallas, Phil Harrington, Korey Haynes, Jeff Hester, Liz Kruesi, Ray Jayawardhana, Alister Ling, Steve Nadis, Stephen James O’Meara, Tom Polakis, Martin Ratcliffe, Mike D. Reynolds, Sheldon Reynolds, Erika Rix, Raymond Shubinski EDITORIAL ADVISORY BOARD

eyond this month’s exciting solar eclipse, billions of other objects in the sky will be visible for countless ages to come. And as an old friend, Bart Bok (1906–1983), used to say, “All the good stuff’s in the southern sky.” This was a little bit of an exaggeration, which Bart said with a twinkle in his eye, but the man who defined our Milky Way Galaxy was pretty well right. The Southern Hemisphere sky is loaded with numerous bright deep-sky objects that would be familiar to all of us if more than about 12 percent of humanity lived under it. To observe many of the southern sky’s greatest treasures, I invite you to join me for a spectacular trip to Costa Rica next spring. In conjunction with our tour partner, TravelQuest and its president Aram Kaprielian, I’ll be escorting a group of observers to that wonderful Central American country March 10–17, 2018, for the 15th annual Southern Sky Party. Armed with telescopes, we’ll spend five uninterrupted nights of dark-sky viewing at a star lodge near the Gulf of Nicoya on Costa Rica’s Pacific Coast. The evenings will

begin with Orion overhead and Canopus to the south, and as each hour progresses, we’ll get spectacular views of objects in Crux, Centaurus, Carina, and the Large Magellanic Cloud. The trip begins by flying into San José, a city of 288,000 and a reasonable two-and-a-half-hour flight from Miami. The following day, we’ll board a private

The deep southern Milky Way will glow extremely brightly for travelers on Astronomy’s 2018 Southern Sky Party trip to Costa Rica. TUNÇ TEZEL

motor coach for the journey to the star lodge. The observing location is set in a prime bird and wildlife habitat, and it is exclusively reserved for our group. Aside from nightly observing and nature viewing, there will be reading, card games, and socializing available to non-astronomers. And the lodge has a beautiful pool, breathtaking bay vistas

beyond, and buffet-style meals that will feature a delicious array of fresh ingredients. Stargazers can also count on regular cups of the local Costa Rican coffee, the area’s most celebrated export. Daytime activities will also be lots of fun. You can always sleep in and relax, or take a dip in the pool as you plan observing “hit lists” for the next night. Or you may wish to take a horseback ride, or explore the birds and wildlife that will surround us in the forest. The journey includes three daytime excursions: a day trip to the nearby macaw sanctuary, a half-day boat trip around the Bay of Nicoya, and a short overland journey to a spectacular overlook point to witness sunset. Among the creatures we will see near the lodge are crocodiles and monkeys. I invite you to go on the Southern Hemisphere observing run of your life with me to Costa Rica. You can find out more, and register, here: http:// astronomy.com/magazine/ trips-tours/2018-costa-rica

A ST R O N O M Y • AUG UST 2017

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QUANTUM GRAVITY

EVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH . . .

HOT BYTES >> TRENDING TO THE TOP

SWIFT ACTION An algorithm called PACMan could sort through over 1,000 Hubble Space Telescope proposals submitted for review annually.

CHILLY WEATHER Jupiter’s magnetic field caused the planet to develop a Great Cold Spot with temperatures 360° F (200° C) below its surroundings.

PROPER CREDIT Texas State University researchers determined that Charles Messier was the first to observe the Ring Nebula, recorded in his catalog as M57.

SNAPSHOT

Whatever you do, just look On August 21, millions of people will see the total eclipse of the Sun. Cutting a swath across the United States from the Oregon coast to the shores of Charleston Harbor, the eclipse stands to be the most viewed in history. People will swarm to the center line, each eager to witness one of nature’s grandest spectacles. As anyone who has seen an eclipse knows, there’s no way to completely describe it. It’s a surreal moment when the Moon’s shadow passes over you in the daytime, when temporary night washes over the landscape, and when you see weather and animals change behavior in response to planetary orbits. I’ll be with one of Astronomy’s tours, near Jackson Hole, Wyoming, and will look forward to exchanging eclipse stories with many of you after the event. For those of you who are lugging lots of imaging equipment along, however, I want to give you a word of caution: “Every eclipse lasts 8 seconds.” While that old saying in amateur astronomy is not true — this eclipse will last as long as 2 minutes, 41.6 seconds at maximum duration near Carbondale, Illinois — the point is that you’ll see zillions of images and video of the eclipse later. Those fleeting moments of totality, of actually seeing the Sun’s corona with your own eyes, are priceless. Make the most of them. Just sit back and watch. Trust me — you’ll thank yourself later.

A ST R O N O M Y • AUG UST 2017

DAVID BUCHLA; TOP FROM LEFT: EUROPEAN SPACE AGENCY; NASA/JPL; THE HUBBLE HERITAGE TEAM (AURA/STSCI/NASA)

An old maxim in astronomy: “Every eclipse lasts 8 seconds.”

A total solar eclipse is a rare event: Wherever you are, as totality approaches, remember to just sit back and watch. Soak it in. It will go by quickly.

I hope you’ll share whatever experiences you have of the eclipse with us at the magazine, whether it be a written memory, observations or sketches, or, yes, photos. We’ll be

listening. We will take pleasure in providing the best and most complete follow-up coverage of this exciting event we can. Enjoy! — David J. Eicher

ASTROLETTERS A word of eclipse caution After reading Michael Bakich’s story on choosing an eclipse camera in the April issue, I was surprised the author devoted not a single word of caution to filtration to prevent eye and camera damage. He speaks of cameras and lenses, but depending on the focal length of the unfiltered lens, the effect of heat and light when the camera is trained on the Sun at any phase — other than a handful of seconds on either side of totality, along with totality itself — can be devastating and swift. Experienced eclipse shooters know this, but Bakich should have added a sentence or two in the interest of safety for the novice and first-time shutterbugs he addresses in his article. — Jim Keenan, Vista, CA

A stellar mirage I am a skywatcher from Norfolk, England, and a regular reader of Astronomy. I’ve been reading the March issue and was drawn to Stephen O’Meara’s article “Twice-setting stars.” I regret that, despite living all my life on the coast and scanning sea and sky for many years, I’ve never seen any comparable astronomical event. However, your photos of mirages recalled a singular event that occurred a few years ago, the memory of which has stayed with me ever since. Sunday, May 23, 2010, was the hottest day so far of that year, but the North Sea had not yet warmed up. Imagine my surprise when I took my customary walk along the shore and observed six “ghost ships” raised a little above the horizon. These showed the classic features of cargo ships. Some “real” ships were still quite prominent out to sea. But more remarkable was the sight of a lake, or harbor, floating just above the horizon, in which two or three ghostly yachts appeared to be at rest. Beyond this scene was a line of what seemed to be squat buildings and then a hilly landscape. Oddly, there is no land until you We welcome your comments at Astronomy Letters, P. O. Box 1612, Waukesha, WI 53187; or email to letters@ astronomy.com. Please include your name, city, state, and country. Letters may be edited for space and clarity.

get to Holland! I realized I was seeing a “fata morgana.” There is a description of this phenomenon in The Nature of Light and Colour in the Open Air by Marcel Minnaert. Strangely, while observing this apparition I, too, was aware of a feeling of happiness and longing. I did not have my camera with me. Yet, I believe that even if I had it, I would’ve forgotten to use it, being absorbed in the rare moment. I have observed mirages out to sea before and since, but never anything like this. Clearly, the conditions were just right, and I was extraordinarily lucky and privileged to be there at the perfect time. I was not aware of anyone else looking at this rare event. What wonderful things there are in the sky and, regrettably, how so few people watch it day or night. — Michael Bean, Gorleston, Great Yarmouth, Norfolk, England

A cactus and the universe I want to applaud Jeff Hester for his article “A Saguaro’s universe” in the April 2017 issue. What a refreshing change. Jeff’s linking of the cactus to weather patterns and the universe was superb. The 4.6 billion-year history of Earth is fascinating, with climate changes, tectonic plate shifts forming supercontinents, and snowball Earths, not to mention the progression of life-forms. This is a prime example of how all the sciences are linked together in Earth’s history. Thank you, Jeff, and keep up the good work. — Tom Rusek, Aberdeen, MD

The cosmic coincidence Has anyone noticed the coincidence of August 20, 2017 — the 40th anniversary of the launch of Voyager 2 — and August 21, 2017, the total eclipse of the Sun? It’s an amazing coincidence separated by only one day! Voyager 1 was launched on September 5, 1977, and is now in interstellar space. — Mark Gordon, Los Angeles

W W W.ASTR ONOMY.CO M

STRANGEUNIVERSE BY BOB BERMAN

Eclipse chasing Are you a newcomer or a totality hunter?

Down the road Let’s play the eclipse prediction game. We’ll add another 18 years and 11 days and look 120 degrees west, and voila! — a six-and-a-half minute totality over Egypt’s Nile River on August 2, 2027. With likely clear skies! Now we’re greedy for our own six-plus minute totality. Another one-third of an Earth spin should bring that Saros to our neck of the woods. Indeed, three Saroses — an interval called an exeligmos, a period of 54 years and one month — bring the same sort of eclipse back to roughly the original region. Bingo! After Egypt in 2027, the next superlong totality is August 12, 2045, in the southern United States — the longest in U.S. history. It’s one exeligmos after Baja. After this month’s totality, there’s none next year. The

HAN-CHANG WANG

et’s talk about future total solar eclipses. It’s for newbies as well as the fanatics. After this month’s coast-to-coast event, the addicted group may well number in the millions. Some eclipse chasers — those who seek out the thrill of an eclipse over and over, including literally following the Sun on its path during a single event — are so hooked, they rarely miss a totality and crisscross the globe. When planning such trips, cost and convenience figure prominently. But weather may top the list of basic concerns: A friend went to seven eclipses, but was clouded out of four. Choices are limited. There’s only a single total solar eclipse each year, and every three to four years, there are none. Upcoming zero years are 2018, 2022, 2025, and 2029. An eclipse happens only during “eclipse seasons” six months apart, which drift 11 days earlier each year. Thus, after the long Baja eclipse on July 11, 1991, the next was June 30, 1992. A second pattern, the Saros, is more famous. The ancient Babylonians and Greeks noted that exact eclipse conditions repeat after 18 years, 11 ⅓ days, give or take a day. That “⅓ day” business means our planet rotates one-third of a spin, pushing the location of the next event westward by 120 degrees longitude. Considering that wonderfully long Baja totality of July 10, 1991, we’d expect another long-period eclipse later in July, but 18 years later. Sure enough, China saw a six-and-a-half minute totality on July 22, 2009.

The view from the March 2016 total eclipse in Asia hints at this summer’s big event.

Beat the odds My eclipse story started March 7, 1970, at Virginia Beach, Virginia. Later, George Schy, a tour operator for Special Interest Tours, asked me to be an eclipse lecturer. We planned and took thousands to one totality after another. We never got clouded out. Why? We cheated! We never wanted disappointed clients, so we skipped totalities with dismal weather prospects. We “sat out” the short 2013 Africa event and the 2015 North Atlantic totality and were glad we did. Very few people managed to see those.

There’s only a single total solar eclipse each year, and every three to four years, there are none. 2019 totality sweeps across southern Chile and Argentina. In 2020, those countries get hit again. Then times get hard. In 2021, the Moon’s shadow strikes only Antarctica. Then 2022 has none anywhere. And in 2023, totality lasts just 1 minute, in a cloudy region of Mexico. But April 8, 2024, brings a totality whose path runs from Texas northeastward over many cities, including Cleveland; Buffalo, Rochester, and Syracuse, New York; and Burlington, Vermont. Wow!

Sometimes it’s a no-brainer. In 1999, totality stretched from England through France, Germany, Eastern Europe, and Turkey. Logic dictated avoiding cloudy Western Europe and we did, and we enjoyed cloudless skies over the Black Sea. Some go anyway and luck out. Famously, after World War I, several universities wanted to launch eclipse expeditions since the next events were in the United States. They could afford only one trip. The choice was between an upcoming San Diego totality on September 10, 1923,

BROWSE THE “STRANGE UNIVERSE” ARCHIVE AT www.Astronomy.com/Berman.

A ST R O N O M Y • AUG UST 2017

and New York City on January 24, 1925. Which was more likely to be clear? Everyone picked Southern California, of course. Yet on eclipse day, the La La Land area was overcast, while New York enjoyed a cloudless winter day. So climate probabilities don’t always pan out. Some go to gloomy-seeming events and beat the odds. Good for them! Me? I’m a coward. Sun elevation can be a factor, too. With half-cloudy conditions, the overhead sky offers big holes, while puffy clouds nearer the horizon “fill in” and merge together. So if you have a choice of location, go where the Sun is higher — though a low Sun makes for better photographs. Yet another factor is time of day. Midmornings are often clearer than midafternoons. There are many other considerations. Should you choose a tour, which takes care of lodging, transport, and so on, and where you’ll meet fellow eclipse addicts? Or go it alone? I used to prefer the latter, but a tour is certainly hassle-free, especially in esoteric locales. Now let’s see if this month’s eclipse makes you an addict. Contact me about my strange universe by visiting http://skymanbob.com.

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VENUS TWIN. NASA’s Kepler space telescope discovered a planet around an M-dwarf star 219 light-years away that could be a Venus analog. Its size and the amount of stellar radiation absorbed are much like those of Venus.

PROSPECTS FOR LIFE ON ENCELADUS NASA/JPL-CALTECH/SPACE SCIENCE INSTITUTE

ents on Earth’s seafloor provide one of the most extreme environments where life manages to thrive despite high temperatures. Now it seems that Saturn’s moon Enceladus may have similar hydrothermal vents. In a paper published April 13 in Science, NASA researchers said they found traces of hydrogen associated with such vents spewing out of Enceladus’ geysers. “Enceladus is too small to have retained the hydrogen from when it formed, so the hydrogen we see today is coming from inside Enceladus,” Linda Spilker, project scientist on the Cassini mission, said in a press conference. Cassini researchers were taken by surprise when they discovered geysers of water erupting from Enceladus’ south pole in 2005. Subsequent investigations built a picture of their origin: liquid water under the surface of the tiny moon, which led to the hypothesis that an entire ocean lay beneath its icy crust. Cassini’s Ion Neutral Mass Spectrometer observed molecular hydrogen in the ejecta from these geysers. According to principal investigator Hunter Waite of the Southwest Research Institute and his co-investigators, the

Cassini shows Earth and Moon from Saturn

SPRINKLER SYSTEM. Enceladus’ jets eject water 100 miles or more into interplanetary space in this illustration. NASA/JPL/SSI

FOND FAREWELL. On April 12, Cassini took one last glance toward Earth and the Moon through Saturn’s rings, capturing this image. The Cassini probe has been exploring Saturn’s system of 62 moons since 2004, taking a few shots of Earth along the way. The mission will end in September when the probe plummets into Saturn’s atmosphere. — Nicole Kiefert

source almost certainly has to be hydrothermal vents on Enceladus’ seafloor. This means there’s plenty of geological activity, increasing the chances for life. Indeed, research published in July 2016 in Nature Microbiology suggests that hydrothermal vents were the source of life on Earth, where chemical reactions fed early microbes. “The hydrogen could be a potential source of chemical energy for any microbes living in Enceladus’ ocean,” Spilker says. — John Wenz

The number of intriguing radio signals the massive SETI project Breakthrough Listen is following up on after its initial listening campaign.

BRIEFCASE LANDSLIDE BRINGS CERES DOWN A study published in Nature Geoscience identified three different types of landslides on Ceres. Type I landslides are round, large, and occur at higher latitudes, which is where researchers believe most of Ceres’ ice is located. Type II are most common and occur at middle latitudes. These landslides look like deposits from avalanches on Earth and are thinner and longer than Type I landslides. The last type of landslide the team discovered is Type III, which forms at low latitudes when ice melts during impact events that create large craters.

SO WHAT’S IN AN EARTH-LIKE PLANET, ANYWAY? WEIGHING IN. When a new planet is discovered, the phrase “Earth-like” frequently comes up. But it’s a bit of a misnomer. We don’t know if it’s Earth-like at all! Our current instruments fall just short of the ability to direct image or resolve such a small planet, much less tell what’s in its atmosphere. Here’s a guide to how terms should be used. — J. W.

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TITAN’S SEAS FIZZ

A ST R O N O M Y • AUG UST 2017

So what is Earth-like? A planet not only has to be the same size and the same mass as Earth, but it must have liquid water oceans and a substantial atmosphere. Otherwise, you may have a planet that is more like Venus, Mars, or Mercury, even if it’s seemingly in the “right” place. Thus we have found Earth-mass and Earth-size planets but are still searching for something that is actually Earth-like.

Several known exoplanets have masses similar to Earth, but radii several times bigger, suggesting they are miniature ice giants — mini-Neptunes.

FAST FACT

•

NOT TOO HOT?

ASTRONOMY: KELLIE JAEGER

A planet is considered Earth-mass when its mass is similar to our own world. That’s 1.31660063 × 1025 pounds (5.972 × 1024 kg). Planets between 1 and 5 Earth masses are likely rocky. Those 5 to 10 Earth masses may resemble Neptune. Planets more massive than Earth are often called super-Earths. Mass is measured by watching the tug a planet has on its star.

A planet is considered Earth-size when it is one and a quarter times the radius of Earth or below. Super-Earths are one and a quarter to two times the radius of Earth. Planets called mini-Neptunes, which are likely gaseous instead of rocky, are between two and six times Earth’s radius. Neptune is six times the radius of Earth.

Researchers at NASA’s Jet Propulsion Laboratory simulated the conditions in Titan’s lakes. They found that changes in temperature can cause nitrogen to dissolve into a freezing methane rain that then pools into bodies of liquid hydrocarbons. Changing temperatures (both hot and cold) and differences in air pressure can all play a role in separating nitrogen out of the hydrocarbon liquids in a process called exsolution, which, in turn, causes bubbles.

Research published in The Astronomical Journal suggests that planets around M-dwarf stars can retain atmospheres even after their turbulent early years. GJ1132b, which is about 39 light-years away, is a scorching hot planet whose upper atmosphere reaches 500° F (260° C). However, as an older planet around an M-dwarf star, it shows that red dwarf planets can survive the first few billion years with atmospheres intact, improving the chances for life on much balmier planets than GJ1132b. — N. K., J. W.

ASTRONEWS

TEMPORARY AIR. Solar activity could cause a transient atmosphere on Ceres. Particles from the Sun turn surface ice into water vapor, which forms an atmosphere around the dwarf planet that may last up to a week.

Coming soon: Our first picture of a black hole On April 5, astronomers brought an Earth-sized telescope online. Dubbed the Event Horizon Telescope, for a week and a half it observed both the center of our galaxy and the elliptical galaxy Messier 87 in the Virgo Cluster. Its goal: Image the space around a supermassive black hole all the way down to its event horizon. The Event Horizon Telescope uses a technique called Very Long Baseline Interferometry (VLBI) that requires several telescopes observing the same object from different locations to image small sections of the sky. The farther apart the telescopes are located, the greater the detail they can achieve. The Event Horizon Telescope links eight radio telescope facilities around the world — including the Atacama Large Millimeter/submillimeter Array in Chile, the Caltech Submillimeter Observatory in Hawaii, the Large Millimeter Telescope Alfonso Serrano in Mexico, and the South Pole Telescope in Antarctica — to obtain the longest baselines possible. When astronomers “see” black holes, they are actually seeing light from a disk of material around the black hole, sitting outside the event horizon. (Anything within the event horizon itself is truly invisible.) Currently, individual telescopes don’t have the resolution to see the disk closely or image its structure. This is why every “image” of a black hole in a news article or textbook is an artist’s rendering rather than an actual picture. But that’s about to change. Highresolution images will enable astronomers not only to study the structure

NAP TIME X-ray close-up

New Horizons, now halfway to its next target in the Kuiper Belt, has entered a 157-day hibernation to save power during the flight. It will reawaken September 11.

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HYDROGEN MAP 1/2 light-year

The Wisconsin H-Alpha Mapper project released the most comprehensive survey of the Milky Way’s ionized hydrogen component to date. Rotating with the galaxy, the massive structure is 75,000 light-years across and 6,000 light-years thick.

•

FLICKERING LIGHTS

ZOOMING IN. Sagittarius A* is the supermassive black hole lurking in the heart of the Milky Way. Although the area around the black hole can be seen here in infrared and X-ray light, there is little detail at the scale of the black hole’s central regions. The Event Horizon Telescope aims to change that. X-RAY: NASA/UMASS/D. WANG ET AL.; IR: NASA/STSCI

of the disk around the black hole, but also to test general relativity, get a better look at how the black hole feeds on material, and better determine how the black hole creates outflows and jets. One of the telescope’s targets was Sagittarius A*, the Milky Way’s central supermassive black hole, with a mass of about 4 million Suns. At a distance of 25,600 light-years from Earth, its apparent size makes it the largest massive black hole visible in our sky. But large is a relative term; current estimates place the size of the black hole at roughly 50 million miles across (80 million

kilometers), which at that great distance is equivalent to about the size of an orange sitting on the surface of the Moon. Between April 5 and 14, the telescope gathered an amount of information too immense to transfer digitally. Instead, the data were stored physically and taken to the Max Planck Institute in Germany and the Haystack Observatory in Massachusetts for processing. That processing will take time. But in a few months, we may finally have our first picture of the region immediately around a supermassive black hole. — Alison Klesman

History of Mars’ craters contains a lull

ESA/DLR/FU BERLIN (G. NEUKUM)

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QUIET TIME. Southwest Research Institute scientists studying the bombardment history of Mars discovered a 400 million-year “lull” in its impact record, starting 4.5 billion years ago. This agrees with cratering histories on Mercury, the Moon, and main belt asteroids. A period known as the Late Heavy Bombardment is theorized to follow 4.1 to 3.8 billion years ago, creating Mars’ younger features. — A. K.

Twenty-three new stars in Kepler’s catalog have been flagged for unusual periodic dips in brightness. Researchers at the Spitzer Science Center at Caltech are studying these changes, which occur each time the stars rotate, to determine their origin.

•

SIMULATED GALAXIES Cosmologists at Durham University have created simulations of galaxy formation in the presence of dark matter. The results produce galaxy sizes and rotation rates that match astronomers’ observations of galaxies throughout the universe, bolstering the validity of standard dark matter-based cosmological models.

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WATER WORLDS A study authored by Fergus Simpson of the Institute of Cosmos Sciences in Barcelona suggests that most habitable exoplanets may be largely ocean worlds with little or no dry land.

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BREAK THE ICE NASA researchers are developing robotic prototypes that can explore and sample icy worlds like Europa and Enceladus in preparation for future missions to these moons.

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LOOKING FOR PLANET 9 Australian National University astronomers are investigating four objects as potential “Planet 9” candidates. They were identified through a citizen science project hosted by Zooniverse.org.

•

STORM WARNING When material from solar eruptions reaches Earth, it can strip areas of the upper atmosphere of electrons. This process, along with the addition of electrons in other areas of the atmosphere, can disrupt communications in affected areas. — A. K.

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ASTRONEWS Stellar survivor

TOTAL ECLIPSE APP. The free Totality app by Big Kid Science contains everything you need to know about the upcoming August eclipse, including the percentage of totality and the local start and end times from any location.

AND THEN THERE WAS ONE. The remains of SNR 0509–68.7 (near the top of the image) have revealed a Sun-like main sequence star that appears to be associated with the gauzy remnant. Astronomers believe the supernova was a type Ia, which may occur when a white dwarf pulls gas off a binary companion until it reaches a critical mass and explodes. If this were the case, the companion should survive, which explains the star left behind. — J. W.

New planet could be a good case study for life A newly discovered nearby exoplanet could be just the boilerplate needed to find out if life could exist in untold numbers of star systems. The planet, LHS 1140b, lies 39 light-years away. It orbits a small M-dwarf star every 24 days. The planet itself is 1.4 times larger and 6.6 times more massive than Earth, and the principal investigators of the study, published April 19 in Nature, believe it to be rocky. M dwarfs (often called red dwarfs) like LHS 1140 are the most abundant stars in the galaxy and are some of the easier stars to capture transit signals from. A planet is considered habitable when it’s in an area where liquid water might exist (instead of existing as vapor or ice). But planets around M dwarfs can have complicated lives because red dwarfs start out as furious flare machines that can violently strip away primordial atmospheres around recently formed planets. We’ve never spotted an atmosphere around an M-dwarf planet in the habitable zone. LHS 1140b could

A ST R O N O M Y • AUG UST 2017

provide an opportunity for some of the first observations, as LHS 1140 is a relatively calm, older star, unlike other planetary hosts like Proxima Centauri or TRAPPIST-1. If a planetary atmosphere managed to form, it could still survive. The star’s relative inaction also makes studying atmospheric signals from its planets easier than around more active M dwarfs. Modern telescopes, like the Giant Magellan Telescope and Hubble Space Telescope, might even be able to spot oxygen in the atmosphere of LHS 1140b. It may also make an ideal target for the upcoming James Webb Space Telescope. “I think that even during the star’s active early lifetime that water can possibly survive to the present day on these planets,” principal investigator Jason Dittman of the HarvardSmithsonian Center for Astrophysics told Astronomy. “We don’t know how much water they start with, so it’s perfectly feasible that these planets lost lots of water early on, but still managed to hold on to a little bit of water today.” — J. W.

This pulsar stays young The 1 million-year-old pulsar XB091D looks good for its age. Pulsars, which are the neutron star remnants left behind by a massive star’s death, rotate quickly on their axes, often several times a millisecond. But as pulsars age, their rotation rate slows — unless they can find a nearby star to spin them back up again. That’s exactly what XB091D is doing. As it pulls matter from a companion star, the pulsar accelerates, mimicking a much younger object. Astronomers at Lomonosov Moscow State University speculate that in about 50,000 years, the pulsar will increase its rotation from once every 1.2 seconds to once every millisecond. — A. K.

BENEATH THE RINGED PLANET POLE STAR. If you could stand on the cloud tops at the south pole of Saturn and look straight overhead, these are the stars you would see. The gas giant’s axis points toward a nondescript region near the border between Octans and Apus, less than 1° from magnitude 4.3 Delta (δ) Octantis. The sky’s third-brightest star, magnitude 0.0 Alpha (α) Centauri, lies less than 25° away. — Richard Talcott

CENTAURUS CRUX TRIANGULUM AUSTRALE

APUS CARINA PAVO

South Celestial Pole

5°

δ OCTANS

HYDRUS

Because Saturn’s major moons orbit in the planet’s equatorial plane and their axes are perpendicular to their orbits, observers at their south poles would have similar views.

ASTRONOMY: ROEN KELLY

NASA, ESA AND Y.-H. CHU (ACADEMIA SINICA, TAIPEI)

FOUNTAIN OF YOUTH. The pulsar XB091D is pulling gas off a companion star. As the gas forms an accretion disk and falls onto the pulsar, it increases the pulsar’s spin for a period of about 100,000 years. NASA/GSFC

FAST FACT

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This March, the Chandra X-ray Observatory caught an explosion 10 billion light-years away in an image called the Chandra Deep Field-South. The image is the “deepest X-ray image ever obtained,” according the Chandra team. Chandra has stared at this region of sky repeatedly for 17 years, with a total exposure time of two and half months. X-ray images show energetic events that don’t appear in visible light. This particular event, called CDF-S XT1, brightened quickly by 1,000 times, but within a day, it was gone. No X-rays were seen from CDF-S XT1 prior to October 2014. The destructive event could be a neutron star merger, a massive star collapsing into a compact object, or an intermediate-mass black hole (100 to 1 million times the mass of the Sun) consuming a white dwarf. No host galaxy has been pinned down yet. — J. W.

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GOING BLACK. When you hear people say, “It’s all about totality,” or “Nothing compares to totality,” here’s why that’s true. The Sun’s disk is 1 million times as bright as its corona. That means 50 percent of the Sun’s face is 500,000 times as bright, and so on. If you know the obscuration (the percentage of the Sun’s disk covered by the Moon) at any location or time, you can figure out how much brighter the partially eclipsed Sun is than totality. Just subtract the obscuration from 100, and multiply by 10,000. So, if the Moon is covering 90 percent of the Sun at your location: 100 – 90 = 10; 10 x 10,000 = 100,000. At that moment, the Sun is still 100,000 times as bright as totality. — Michael E. Bakich

The solar corona is equal in brightness to the Full Moon.

A ST R O N O M Y • AUG UST 2017

FAST FACT

ASTRONOMY: ROEN KELLY

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LIVE FAST, DIE YOUNG. A galaxy spotted just 1.65 billion years after the Big Bang is unusually large and inactive at a time when most galaxies were actively forming stars. Astronomers believe the galaxy formed all its stars rapidly in one massive starburst, leading to its premature death.

Milky Way satellite distribution explained In the current “standard model” of cosmology (known as the Lambda-Cold Dark Matter model, or ΛCDM for short), “normal” matter makes up only a small percentage of the universe when compared with dark matter. But because dark matter is difficult to detect directly, its existence, abundance, and properties remain hotly debated. In a study published in February’s Monthly Notices of the Royal Astronomical Society, Andrew Lipnicky and Sukanya Chakrabarti of the Rochester Institute of Technology explore whether the current orientation of satellite galaxies around the Milky Way upholds or challenges the ΛCDM model. Satellite galaxies are small galaxies that have been pulled in by the gravity of more massive galaxy, such as the Milky Way or Andromeda galaxies. Many of the Milky Way’s satellite galaxies currently lie in a plane near the galaxy’s poles known as the vast polar structure (VPOS). Some of Andromeda’s satellites appear similarly oriented. But the VPOS challenges the current cosmological model, which predicts no preferred plane or orientation of dark matter subhalos around galaxies. Dark matter subhalos are clouds of dark matter inside which galaxies and their satellites reside. They are distributed evenly around a galaxy, which should be reflected in an isotropic distribution of satellite

galaxies, not any type of observed preferred plane or other structure. Lipnicky and Chakrabarti sought to determine whether the VPOS is a permanent or transient structure. If permanent, the VPOS would pose serious problems for the ΛCDM model as a stable structure that disagrees with dark matter simulation results. But if transient, the VPOS isn’t a problem. They used Hubble Space Telescope observations of the positions and motions of several of the Milky Way’s satellite galaxies to essentially “rewind” the system and determine whether the VPOS is stable over long periods of time, cosmologically speaking. But the VPOS dissipates as the clock is turned back, making it transient, rather than a permanent structure. The plane is not very old and likely formed later in the evolution of the Milky Way and its satellites, rather than early on, as would have happened if it was associated with the dark matter halos that shape such systems. Because it developed recently, it is not associated with the original formation of the galaxy and its subhalo. In a press release announcing the results, Chakrabarti explained: “If the planar structure lasted for a long time, it would be a different story. The fact that it disperses so quickly indicates that the structure is not dynamically

TAGALONG. The Large Magellanic Cloud is one of the Milky Way’s many satellite galaxies. This object, which has been trapped by our galaxy’s gravity, sits nearly 200,000 light-years away, but is still inside the Milky Way’s massive dark matter halo. ESO/S. BRUNIER

stable. There is really no inconsistency between the planar structure of dwarf galaxies and the current cosmological paradigm.” These results agree with a 2016 study led by Nuwanthika Fernando, which also found the planes of satellite galaxies unstable. — A. K.

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ASTRONEWS

LOST: MARS’ ARGON. NASA’s MAVEN spacecraft has determined that 65 percent of the argon in Mars’ atmosphere was lost to space over the planet’s history. Atmospheric loss transformed Mars from an Earth-like planet into its present state.

Cassini weaves through Saturn’s rings It’s the beginning of the end for NASA’s Cassini spacecraft. On April 21, Cassini made its final close approach to Saturn’s moon Titan and sent images and additional data back to Earth so scientists could study the hydrocarbon seas and lakes on its north polar region. After the Titan flyby, during which Cassini captured its last image of Earth (see p. 12), the spacecraft began its Grand Finale, which will include making 22 dives through Saturn’s rings. The first dive on April 26 was successful, and Cassini reconnected with Earth the next day to send back data that surprised scientists. The team expected and prepared the craft for incredibly dusty conditions, but the data revealed little to no dust between the planet and its rings. Researchers are now calling the area “the big empty.” Cassini underwent a successful second dive through the rings on May 2 and sent back even more stunning images of Saturn’s rings than the set returned from the first dive. With 20 ring dives to go, the team is updating observation plans and camera settings to obtain even better results. The spacecraft is scheduled to make its death plunge into Saturn’s atmosphere on September 15. — N. K.

50,000

JUMPING THROUGH HOOPS. Cassini has taken several dives through Saturn’s rings on its slow descent toward death. This image was sent back May 2, 2017. NASA/JPL-CALTECH/SPACE SCIENCE INSTITUTE

The number of orbits completed by the Mars Reconnaissance Orbiter over the course of 12 years, as of March 29.

A CLOSER LOOK AT A SUPERMASSIVE BLACK HOLE

ASTRONOMY: ROEN KELLY

WHAT’S IN THERE? The majority of galaxies contain supermassive black holes (over 1 million solar masses) in their centers. Sometimes, these black holes accrete matter at a high rate, bringJet ing them to the attention of astronomers. These are called active galactic nuclei (AGN). There are several different classifications of AGN; the current unified picture of AGN concludes that many of these classifications arise not from intrinsic differences in the objects, but in their orientation and the amount of obscuring material around them. When viewed from a specific angle, an AGN may Gas clouds show different properties than when viewed a different way. Black holes themselves are spherical, and Dusty torus matter can fall in from any direction. But Event horizon most infalling matter forms an accretion Singularity disk, which heats up and shines brightly — this is frequently what astronomers spot when they “see” a black hole. A corona of high-energy particles around the accretion disk emits X-rays that astronomers may also observe. Black holes also often produce jets — material that is pulled off the accretion disk Accretion and flung outward before it can fall past disk the event horizon. A dusty “torus” is thought to surround SUPERMASSIVE the entire system. While it’s often drawn as BLACK HOLE a solid ring or doughnut, its actual shape is still in question. Additional clouds of material can also Although relatively quiet today, the Milky Way’s supermassive become caught in the black hole’s gravity, moving black hole shows evidence of a much more active past. Its last faster or slower depending on their proximity to burst of activity was likely 6 million to 9 million years ago. the central black hole. — A. K.

FAST FACT

A ST R O N O M Y • AUG UST 2017

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The actions you take before the celestial lineup can help everything run smoothly August 21. by Michael E. Bakich

Delicate coronal streamers flow from the Sun’s hidden surface during the precious moments of totality. SABERS, ROYER, DRUCKMÜLLER, AND PADILLA

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If you’re reading this story shortly after the issue arrived in your mailbox or first appeared on the newsstands, roughly one and a half months remain until the big event. But you may not have gotten to it right away, and thus don’t have even that much time left. In your case, what do I suggest? Panic? Not exactly. What’s the word that means “almost panic”? I’m going to give you several brief pieces of advice. You should take them. Why? Because I’ve been an astronomer my whole life, I work for the world’s most popular astronomy publication, and I’ve been to many more eclipses than you likely will ever see. For those of you who are still skeptical, I’ll follow each suggestion with a brief explanation. Let me begin, however, with an exhortation: You must see this event. Nearly 95 percent of the continental United States will experience only a partial eclipse on August 21. Do you know the difference between a partial and a total eclipse? It’s the difference between a lightning bug and lightning. Between testing negative and positive with a pregnancy test. Between a paper cut and stepping on a land mine. In other words, there’s no comparison. However you choose to approach it — with a fully formed plan or as a spur-of-themoment decision — I cannot stress enough that you really should observe totality. I think of it as “awesome” in the truest sense of that word: able to inspire or generate awe. Especially in the United States, people throw “awesome” around like it’s nothing. “Your shoes are awesome!” “This crème brûlée is awesome!” “Little Julie’s new crayon drawing is awesome!” Really? Do these things actually generate awe? But the August 21 eclipse will be nothing short of awe-inspiring. I guarantee that if you stand in the Moon’s shadow under a clear sky, you’ll never forget it. Furthermore, it will stand out as one of the greatest — if not the greatest — sights you 22

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Pat

f to

tali

Get in line! For solar eclipses, it’s all about totality. If at all possible, abandon any location within the 95 percent of the United States that will see only a partial eclipse and head for the path of totality. ASTRONOMY: ROEN KELLY

WHAT DO YOU REALLY NEED TO KNOW? All the information in this issue — as well as most of what you’ll find in books and on the Internet — is great, but let’s boil it down to the basics. What do you really have to know about the August 21 eclipse? If you’re a parent, a teacher, or just someone who wants to understand the basics without all the frills, here are 10 simple facts about the event.

eclipse. In other words, it’s all about totality.

A solar eclipse occurs when the Sun, the Moon, and Earth line up, in that order, and the Moon’s shadow falls on Earth.

Every location in the continental United States will see at least a partial eclipse.

The best spots to view the eclipse (outside of weather concerns) lie on the center line.

To see a total eclipse, you must be under the darkest part of the Moon’s shadow.

The total part of the eclipse is the only time you’ll see the Sun’s outer atmosphere. It’s called the corona, the Latin word for “crown.”

A partial eclipse doesn’t compare to the spectacular total phase of the

Except for a solar filter, you don’t need any equipment to watch the eclipse.

ever have or ever will behold. I’m smiling as I write this because I know some of you are thinking, “Wow, this guy should have worked for P. T. Barnum!” Remember, however, that I’ve traveled to observe 13 total solar eclipses, and for 11 of those, I had groups accompanying me. I made passionate presentations to thousands of people before those events. And afterward, how many people thought I’d gone overboard? That I’d overhyped the eclipse? That I’d set their expectations so high they could never be reached? Zero.

You must use an approved solar filter or eclipse glasses to view the partial phases of the eclipse.

Do not use any filter when viewing the total phase of the eclipse.

The next total solar eclipse visible from the United States after August 21 will occur April 8, 2024. It’s a good one, too, with a maximum length of totality of more than 4 minutes.

Advice from the sage My first suggestion should be treated more as a commandment: Pay attention to weather, not climate. If you’re planning on traveling to a certain location, you probably already have checked into the climate, at least in a general sense. This far ahead of time, nobody can tell you with certainty what the weather will be at a specific location on eclipse day. As the event approaches, don’t get tied up in predictions of cloud cover for August 21. Many forecasters don’t distinguish between days with a few clouds and those that are overcast.

North American climate

THINGS TO BRING TO THE ECLIPSE

I drew up this list for people who will be traveling to see the eclipse but won’t be part of an organized travel group. You might be planning to observe the eclipse alone, with friends or family, or at a public event. I wanted to provide a checklist of both common and unusual items that I’ll be bringing along and that I think you should bring to the eclipse as well. Such an inventory could get out of hand quickly, so I limited it to 25 entries. They’re not ordered in any special way except for items #1 and #2, which I consider the most important of all.

North American weather

1. SUNSCREEN When someone says, “solar safety,” this is what I think of. So should you. And here’s something to note: If your bottle of sunscreen is more than two years old, replace it. That’s the standard shelf life for this product. If you see someone who has forgotten sunscreen, please be a peach and share. You also might want to bring an umbrella for some welcome shade. 2. WATER August 21 will be warm everywhere in the United States and hot in many places. Even large events may run out of this vital fluid. Don’t leave home without it. If you’re driving, bring at least a case of bottled water with you. For just a couple of bucks, you’ll be guaranteed not to dehydrate.

Pay attention to weather, not climate. Climate maps like the one at top show general trends around August 21. But as eclipse day draws near, weather maps, like the one created from August 21, 2016, data shown above, will show actual cloud cover, possible storms, and all the clear regions along the path of totality. CLIMATE: JAY ANDERSON; WEATHER: SPACE SCIENCE AND ENGINEERING CENTER (UNIVERSITY OF WISCONSIN-MADISON) AND NASA/GSFC

These descriptions never give the thickness of the clouds. Another thing to be aware of is that all the predictive websites now use satellite data, including that gathered by infraredsensitive equipment. This type of instrumentation detects much more cloudiness than human observers do. So the “broken clouds” a satellite-based site predicts may not be visible to you at all. But starting August 16, give your utmost attention to weather predictions for your chosen site. Watch all the local broadcasts as well as CNN’s weather predictions, the Weather Channel, weather.com, and whatever other sources you can find. Try to make your final decision by the 19th. Sunday the 20th is a bit late to change your location, especially if you don’t have an alternate site already picked out. And eclipse day? Forget about moving at all.

Next, schedule a vacation day for August 21 now, if you can. That’s a big “if.” It may be that so many of your co-workers already have taken the day off that you are unable to. When we look back on this event months from now, August 21 may turn out to be the most popular vacation-day request in American history. My third piece of advice is to consider the eclipse only one element in a terrific long weekend. The eclipse falls on a Monday, and many locations touched by the Moon’s inner shadow will offer related activities on Saturday and Sunday. Depending on your destination, you’ll find talks, workshops, special exhibits, concerts, public evening star parties, and more. Find out what they are and where they’re being held. Then decide which ones you want to attend, and make a minivacation out of the eclipse.

3. APPROVED SOLAR FILTER Whether you use eclipse glasses, a homemade filter using solar Mylar, or a #14 welder’s glass, you will need this to view the partial phases. Also, if you plan to view the partial phases through any equipment (binoculars, telescope, etc.), you will need approved solar filters — not eclipse glasses — for each of them. 4. CAMERA You’ll want to document the day and the activities surrounding the event. My advice remains firm, though: Do not photograph the eclipse! For those of you ignoring this sage wisdom, also pack a tripod. 5. TRANSISTOR RADIO Some events (like the one in St. Joseph, Missouri) will be broadcasting as the eclipse happens. Others will be reporting eclipse-related news, including important items like traffic and weather. The nice thing about a radio is that the broadcast will come in no matter how many people are listening. That won’t be true if you’re relying on Wi-Fi or cell service. Make sure your radio’s batteries are fresh. 6. BINOCULARS This is a great way to get close-up views of the corona during the total phase of the eclipse. And during the half-hour or so prior to totality, you can scan the sky away from the Sun to try to locate Venus (and Jupiter from locations east of Idaho). 7. AN ECLIPSE GUIDE Several are available as books or e-books. You might, for example, check the selections at Astronomy’s online store, www.myscienceshop.com. W W W.ASTR ONOMY.CO M

THINGS TO BRING TO THE ECLIPSE

When worlds align

8. FOOD OR SNACKS Certainly this isn’t as critical as water; I mean, you’re not going to starve. You probably will get hungry waiting for the eclipse to start, however. Don’t assume your location will have food. We expect millions of people to flock to events along the center line. It’s quite possible that even well-stocked stores and supply stands will sell out even before you arrive. Consider having some healthy snacks or premade sandwiches. Such items can help you avoid fast food and give you options in more culinary-challenged communities.

To experience the August 21 total eclipse, be within the path of the Moon’s umbra (its dark inner shadow). If you’re anywhere under the penumbra, you’ll see only a partial eclipse. ASTRONOMY: ROEN KELLY

9. MEDICINE Be sure you have any prescriptions you need to take with you. And some pain medication also is a good idea. Sometimes too much Sun gives certain people headaches, and too much standing for older folks can be painful. Which leads to . . . 10. CHAIRS Bring at least one chair (fold-up varieties pack best) for each person in your party. Even if you attend an organized event, don’t assume anyone will provide seats. Do assume that if there are seats, they will already have been taken. You’re not going to want to stand for (a minimum of) three hours, and if you’re like me, you don’t do well lying on the ground. The best chairs you can bring let you sit upright or recline. Actually, if I weren’t hosting an event, I’d bring the nice air mattress we keep for those occasions when several guests visit. 11. TOILET PAPER Let’s see, millions of people on the road, rest stops few and far between . . . you fill in the details. 12. HAND SANITIZER See #11. 13. EXTRA EYEGLASSES You won’t forget the ones on your face, but something may happen to that pair. 14. KIDS’ STUFF I have no children, so I can’t specify items. I can, however, advise you to bring whatever you will need to keep your offspring happy, comfortable, and occupied. Be aware that, in many locations, cellphone and Wi-Fi access may be limited or nonexistent. Bring along something that doesn’t rely on wireless access to entertain your kids. You may discover, much to your chagrin, that your young children do not share your appreciation or awe for the eclipse. Obviously, you’re a terrible parent. But don’t worry; they’ll be seven years older when the 2024 eclipse rolls around. 15. BROAD-BRIMMED HAT This will keep the Sun off your head and face, and also your neck if the hat’s brim is wide enough. You’ll probably sweat, but that’s a reasonable tradeoff. Keep drinking water. 16. POWER INVERTER You can’t plug most laptops or video players directly into a car. A small DC-to-AC power inverter will let your passengers play games or movies for the whole length of the trip without having to worry about draining the batteries in their devices. Another similar device is a car-lighter-plug-to-USB socket. Such adapters can operate or charge items that don’t require much power, like cellphones.

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Path of totality Greatest eclipse

Umbra Penumbra

Moon

Earth

AUGUST 18TH-21ST

Are you ready to rock ’n’ roll? The Moonstock Music Festival is a four-day musical celebration at Walker’s Bluff Vineyard in Carterville, Illinois. At the exact moment totality begins there, Ozzy Osbourne (known to his fans as “The Prince of Darkness”) will open his concert with his classic song, “Bark at the Moon.” WALKER’S BLUFF WINERY

Think about attending an event. You’ll enjoy the eclipse more if you spend time with like-minded people. Of course, you’ll want to view the two-plus minutes of totality in peace, but afterward you’re going to need someone with whom to share what you saw. By now, astronomy clubs, planetaria, and science centers will know about organized eclipse activities in their regions. If you’re heading to the zone of totality but don’t know what’s going on at your intended destination, look up one of these organizations and give them a call. One advantage to most organized activities is that you’ll have access to one or more solar telescopes. You really don’t need a scope to view the eclipse, but a telescopic view of the partial phases will help you identify sunspots and prominences (if it’s a Hydrogen-alpha scope). Remember this, however: The telescope’s owner will not be sharing views during totality. There just isn’t enough time. Next — and this one comes with as much respect as I can muster — don’t wait until 10 minutes before totality to search

for a bathroom. Too much is happening. Make a preemptive strike 45 minutes beforehand. Now, if you liked that tip, you’ll flip at my follow-up. If you bring young children to the event — and I hope you do — and they tell you they need to use the bathroom a couple of minutes before totality, you need to be mentally prepared to tell them to just hold it. I can’t say this enough: Avoid distractions around totality. My penultimate suggestion is to be sure to record your memories of eclipse day. I don’t suggest you photograph the eclipse, but I do suggest you take lots of pictures and/or videos before and after totality. When you look at your photo album or scrapbook in the coming months and years, I guarantee it will help you relive this fantastic event. Finally, stay flexible on eclipse day. Well, as flexible as possible. Can you imagine what traffic might be like on eclipse day? I can. Gridlock. If you decide you need to change locations, you can be certain that thousands of

THINGS TO BRING TO THE ECLIPSE 17. PILLOW Actually, bring a pillow for every reclining chair you take along. Your passengers also might like to use these in the car if the ride is long. 18. SUNGLASSES Remember, despite their name, sunglasses are not for viewing the Sun through. They are for providing eye comfort when you look at everything else. 19. CASH If you meet me at the event I’m hosting in St. Joseph, Missouri, you can thank me with this. Seriously, some vendors at eclipse events may not take credit or debit cards, and, even for those who do, with the huge numbers of people in transit, paying with cash may save you some serious time. 20. INSECT REPELLENT The farther along the shadow’s path toward the southeastern United States you set up, the more important this item will become. 21. PHONE I list this mainly for completeness. Does anyone ever forget to bring a phone anymore? Certainly nobody under 35. Now, permit me one further note about this item. It’s probable that at large events (especially in smaller towns), the number of people accessing their cellphones will overwhelm nearby cell towers. Be sure to tell anyone tracking your movements that you may be out of touch for a significant amount of time. If you need definite access to communication, consider renting a satellite phone for the weekend. I hope you don’t need it, but a small investment will yield peace of mind. ST. JOSEPH CONVENTION & VISITORS BUREAU

22. TELESCOPE But reduce the hassle by bringing along only the minimum number of items to go with it. I won’t detail them here because everyone’s scope “kit” is different. Before you pack it, set up your scope either outside in the daytime or indoors, and verify that you have a complete system.

One of the best things you can do during the weekend before the eclipse is find a location hosting a large event or series of events. By luck, St. Joseph, Missouri, already had scheduled its Trails West celebration for eclipse weekend — many years before they knew about the eclipse.

Most young children will not be interested in the spectacle going on above them. At least during the two and a half minutes of totality, be sure they are in a safe area with items that will hold their interest. That way, you won’t be distracted during the best part of the sky show. DYLAN MCDONNELL

other people are making that same call. That’s why I made watching the weather my first suggestion. If it’s cloudy six hours, three hours, or even one hour before the eclipse starts, you’re going to want to move to a different location, but probably won’t be able to. So, the earlier you make the decision to move, the better. And here I’m talking days, not hours. I’ll wrap up by offering a suggestion for what you should do after totality ends. Relax. Traffic will be horrendous. And the sooner you try to leave, the worse it will be. So, let the nearly 90 minutes of the eclipse

between third and fourth contacts play out. Lots of people will view this as “what we saw before totality, but in reverse,” and hit the road. But it’s really the best time to experience the effects you can see during the partial phases — only now without the emotional anticipation of totality. It’s a great way to unwind as you contemplate your next encounter with totality. Michael E. Bakich is a senior editor of Astronomy who will be hosting the world’s largest eclipse gathering at Rosecrans Memorial Airport in St. Joseph, Missouri.

23. ASTROPHOTO GEAR If you’re going to photograph the eclipse, you’ll need more than a camera. Make sure you have whatever essentials you need. Keep these items together, preferably in the same bag or container as your camera. Check them twice, then have someone else check them while you watch. 24. ODD PARTS AND TOOLS If you have a telescope, you’ll understand what I mean. As an example, some of the things my kit contains are extra knurled knobs, an Allen wrench set, half a dozen small ziplock plastic bags, at least two each of three types of small clamps, a microscrewdriver set (also useful for fixing eyeglasses), lens-cleaning paper, at least a dozen each of two sizes of plastic zip ties, extra hardware for any tripod-mounted setups I may attempt, extra solar filters, and, you guessed it, duct tape. 25. PERSONAL ITEMS You won’t be hiking the Himalayas or venturing into the deep ocean aboard a submarine to experience this event. You’ll have room for a few extras, especially if you’re driving. If there’s something that’s especially meaningful to you and you want to bring it along, no harm done.

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A step-by-step guide to the

Great American Eclipse Don’t miss a thing as you watch the magnificent sky drama unfold. by Richard Talcott

you’ve planned everything just right, August 21 will dawn with clear skies from horizon to horizon. As the brilliant Sun climbs higher in the east, the invisible New Moon will silently creep toward it. The immutable laws of celestial mechanics dictate what happens next: The Moon will pass directly in front of the Sun, delivering the first total solar eclipse to grace the continental United States since 1979. The dark inner part of our satellite’s shadow, called the umbra, first hits land on the Oregon coast. The shadow then crosses the country on a southeasterly 26

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course before exiting the mainland in South Carolina. (Find detailed maps of the path in “Astronomy’s Atlas of Totality” on p. 54.) The umbra extends at least 30 miles (48 kilometers) on both sides of the center line, where totality lasts longest. Anyone within this broader path of totality will witness darkness at midday and glorious views of the Sun’s ghostly corona.

Protect your eyes Although totality lasts up to 2 minutes, 40 seconds, the partial phases of the eclipse extend the show to nearly three hours. Those fleeting moments of totality — when

the Moon completely blocks the solar surface from view — are the only time you can safely view the eclipsed Sun without eye protection. Even during the partial phases, the Sun’s brilliant disk can damage your eyes quickly and painlessly. To view the Sun directly, use only an approved solar filter or a #14 welder’s glass. A #12 welder’s glass also is safe, but the Sun’s image appears too bright to some people through this option. Each blocks dangerous ultraviolet and infrared radiation while letting through just enough visible light to guard your eyes. (The organizers of most eclipse expeditions will

The totally eclipsed Sun hangs just above the horizon from Svalbard, Norway, on March 20, 2015. The Sun promises to be higher — and temperatures warmer — on August 21. TUNÇ TEZEL

supply everyone with eclipse glasses, but it doesn’t hurt to confirm this before you go.) If you want to view the eclipse through binoculars or a telescope, place the filter over the front of your optical system. And be sure to keep the lens cap on the finder scope, or remove the finder altogether. Curious people, especially children, are apt to look through the finder without realizing the danger. You also can view the partial phases indirectly by projecting the Sun’s image. To make a simple pinhole camera, you’ll need two pieces of stiff white cardboard and a small sheet of aluminum foil. Cut a

square hole in one of the cardboard pieces, then tape the foil over the hole. Next, take a straight pin and poke a small hole in the center of the foil. To view the eclipse, let the Sun’s light pass through the pinhole and onto the second piece of cardboard, which serves as a screen. You can focus the image of the Sun by changing the distance between the two pieces of cardboard. This method works well with children because they will stand with their backs to the Sun and aren’t tempted to stare at it. From start to finish, the August 21 eclipse will last close to three hours. This might sound long enough to view

everything at a leisurely pace, but you’ll soon find out that eclipse time seems strangely compressed. To compound the problem, most of the excitement takes place in the moments around totality. If you keep alert to the changing scene, you’ll be able to soak in the entire experience.

The Moon’s first bite The eclipse officially gets underway at first contact, when the Moon’s limb (edge) first touches the solar disk. It takes a minute or two before our satellite intrudes far enough to appear as a tiny nick at the Sun’s edge. This occurs in midmorning on the W W W.ASTR ONOMY.CO M

The phases of the March 29, 2006, total solar eclipse play out from shortly after first contact (top left) through totality (bottom right). JAMIE COOPER

West Coast, and the notch appears near the top of the Sun. (Although both objects are ascending in the eastern sky, the Sun climbs a bit faster.) On the East Coast, first contact takes place in early afternoon, and the Moon’s initial bite appears near the 2 o’clock position on the Sun’s face. For the next 30 minutes, most observers won’t notice much change to their surroundings. If you don’t check the Sun occasionally to see that the Moon is making steady progress, you might not realize that an eclipse is taking place. Although the sky grows darker, it happens slowly, and your pupils dilate to compensate for the reduced lighting. Once the Moon blocks half of our star, however, the signs of change grow more obvious. At about 80 percent coverage, shadows become sharper as the Moon covers most of our source of illumination. For a brief while, colors become more saturated, or intense. And if you bring a thermometer to your eclipse site, you should see a leisurely but significant drop in temperature. Be sure to place your thermometer out of direct sunlight. The Moon’s advance soon reduces the Sun to a crescent. This is a good time to explore your surroundings closely. The sky grows noticeably darker at this stage, but don’t spend all your time looking up. Study sunlight filtering through the leaves of nearby trees or bushes. Each of the tiny openings between the leaves serves as a pinhole that projects an image of the eclipsed Sun. If you find the right spot, you can see hundreds of solar crescents cast on the ground. 28

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The final few minutes In the minute or two before totality, you might see shadow bands — a mysterious, subtle pattern of light and dark waves that undulate across the ground or on the sides of buildings shortly before and after totality. They look similar to the pattern of ripples seen at the bottom of a swimming pool on a sunny day. The best place to spot them is on a large, smooth, lightcolored surface. As testimony to the subtlety of shadow bands, many veteran eclipse chasers have never seen them. And many don’t even try, feeling that the moments before totality are better spent viewing the wealth of

other exciting phenomena. On the other hand, some viewers consider shadow bands an eclipse highlight. Bottom line: If this is your first experience with totality, don’t go out of your way to look for them. If you can’t resist, consider trying to record them on video with a tripod-mounted camcorder pointed at a blanket, building side, or screen. About 30 seconds before totality, steal another few seconds from viewing the Sun and look toward the western horizon. There you might see the Moon’s shadow descending on you like a wall of darkness, particularly if you’re at an elevated site with an expansive view to the west. Traveling at supersonic speed, the looming shadow impresses all who see it. Now turn your full attention back to the Sun. As the solar crescent dwindles to a tiny sliver, it eventually begins to break up. Sunlight no longer forms a complete arc around the Moon’s edge. Instead, lunar mountains poke through the Sun’s disappearing limb. As the Moon continues its march, more mountains cut off the Sun, and the only places sunlight passes through are valleys along the lunar limb. The string of sunlit pearls arrayed along the Moon’s advancing edge is a phenomenon called Baily’s beads, named after the 19th-century English astronomer Francis Baily, who first described them in detail. Just a few seconds before totality, the jewel-like Baily’s beads shrink to a final solitaire, which, when combined with the suddenly visible corona, is known as the diamond ring. If you’re viewing through

The branches of a nearby tree project images of a crescent Sun onto a rock’s surface near the peak of the May 20, 2012, annular solar eclipse. KEVIN CRELLIN

A brilliant diamond ring marks both the beginning and end of totality. In this view of the July 11, 2010, solar eclipse, cirrus clouds slightly interfere with the scene. MIKE REYNOLDS

Baily’s beads appear as a string of pearls when sunlight passes through a series of lunar valleys shortly before totality on March 9, 2016. JACQUES GUERTIN

eclipse glasses, put them aside and marvel at this last bit of sunlight streaming through the deepest valley along the Moon’s edge.

Totality! When the Moon extinguishes the diamond ring, totality has arrived. Remove solar filters from your telescopes and binoculars. You don’t have to worry about protecting your eyes or equipment during totality because the Moon completely hides the Sun’s blinding surface, the photosphere. The next feature you’ll see pops into view along the Moon’s advancing limb within five seconds. This is the chromosphere, the thin layer of the Sun’s atmosphere just above the photosphere. This region glows a vivid red because the hydrogen atoms there emit radiation at a specific wavelength in the red part of the spectrum. But look quickly — the chromosphere is approximately 1,200 miles (2,000 kilometers) thick, and the Moon quickly conceals it. Once the chromosphere disappears, you’ll be immersed in the full glory of totality. The Sun’s magnificent corona blossoms into view. The highly ionized gases in our star’s outer atmosphere appear as a delicate, pearly white glow that typically stretches a few times the Sun’s diameter. The corona appears surprisingly bright — about the same as the Full Moon. Except for these moments when it is blocked, the photosphere always shines with such intensity that it drowns out this extended glow. Coronal details emerge as your eyes adjust to the onset of darkness. After taking in the scene with your naked eye, point your binoculars at the Sun and

A deep exposure of the March 9, 2016, eclipse captures a fading diamond ring (at 11 o’clock), a large prominence (at 9 o’clock), and the inner corona. HAN-CHANG WENG

Several fiery-red prominences rise above the Moon’s black limb just as totality begins on March 20, 2015. TUNÇ TEZEL

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The deep-red color of the Sun’s chromosphere comes into view just after totality begins during the March 9, 2016, eclipse. JACQUES GUERTIN

The Sun’s corona reveals delicate brushstrokes during the July 11, 2010, total eclipse, when solar activity was near a minimum. MIKE REYNOLDS

look for any loops, swirls, or streamers. The corona’s size and shape vary from one eclipse to another. During periods of high solar activity — when many sunspots and other magnetic features crop up — the corona tends to be round and symmetric. When the Sun is quieter, the corona typically appears asymmetric with many streamers. Because the current solar cycle is winding down, astronomers expect an uneven corona showing many fine details. Still, scientists can’t predict with any certainty what the corona will look like August 21. Also look for any reddish prominences that might be hugging the Moon’s black silhouette. Anchored in the photosphere and extending into the corona, these fiery tongues of glowing hydrogen stand out when the Moon completely hides the Sun’s bright surface. If you can tear your eyes away from the Sun for a few seconds, be sure to explore your surroundings. The sky will display the colors of twilight as Earth’s atmosphere bends the longer wavelengths of sunlight into the path of totality. You can also expect to see a few bright stars and planets come out in the darkened sky. Venus shines like a beacon, so bright that you should be able to spot it at least 10 minutes before totality. It lies 34° west of the Sun and will be conspicuous from everywhere in the eclipse track. Also look for Sirius — the sky’s brightest star with the Sun hidden from view — and Jupiter, which will appear low in the east-southeast by the time the Moon’s shadow reaches Wyoming. The maps on p. 31 show where to look for these and some fainter objects.

The Sun’s corona shows several long streamers during the November 14, 2012, total eclipse, when solar activity was approaching a maximum. ROBERT B. SLOBINS

Twilight colors ring the horizon at the peak of the August 1, 2008, solar eclipse. Venus stands to the eclipsed Sun’s upper left, while fainter Mercury appears closer in. TUNÇ TEZEL

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The sky above Oregon

The sky above South Carolina

Vega

Capella

Arcturus

Betelgeuse Capella

E Regulus Sun

Mars Venus

Regulus

Betelgeuse Spica

Procyon

Venus

Arcturus

Jupiter

Mars Sun

Procyon Sirius

Rigel Sirius

Spend a few seconds to take in your surroundings during totality. Although Venus will dominate the darkened sky, several other bright planets and stars may pop into view. The objects’ positions will depend on your location. ASTRONOMY: ROEN KELLY

All good things must come to an end It likely took you as long to read the previous section as totality will last on August 21. Before you know it, the diamond ring that signifies the end of the total eclipse will arrive — far too soon. This second ring occurs on the opposite side of the Moon from the first and appears brighter because your eyes have started to grow accustomed to a dark sky. You can look at the diamond ring with your naked eye for about five seconds before you need to use eye protection again. For those observing through binoculars or a telescope, replace the solar filters at the first hint of the diamond ring. The sequence of partial phases now plays out in reverse. Although many people will pay little attention — they’ve seen the show they came for — don’t squander the opportunity to view some of the highlights you might have missed in the excitement leading up to totality. Check out Baily’s beads and perhaps look for shadow bands. Sharp shadows and projected solar crescents will stick around for a half-hour or so. And as the Moon’s shadow races off to the southeast, take a minute to imagine the lucky people out there no doubt waiting for their view of totality. Senior Editor Richard Talcott plans to view the August 21 eclipse from western Wyoming.

This six-frame all-sky panorama taken March 9, 2016, from eastern Indonesia during the first minute of totality shows the eclipsed Sun behind a sky full of clouds. It also shows the 360° sunset all around the horizon (except where blocked by trees). The photographer shot all six 1/15-second exposures within a 27-second timeframe. TUNÇ TEZEL

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What

“The 28th, clouds were in the sky; solar eclipse, when I watched [I did not see it].” — BABYLONIAN SCRIBE, 193 B.C. clipses have always happened at the mercy of the weather. The anonymous Mesopotamian who inscribed those impassive words on a clay tablet must have been disappointed, unaware that the eclipse was over Antarctica and too far south to see, even if the weather had cooperated. Nevertheless, his comments have echoed through the ensuing millennia for those unlucky enough to be caught under the “heavenly garment” and unable to escape. History is replete with stories of astronomical expeditions caught up in

clouds, sometimes after great effort and hazardous travel. August 21 — the big upcoming eclipse day — comes at a favorable time of year, when summer’s thunderstorms are gradually fading away and winter storms have yet to form. Even so, it would be an exceptional day on the 21st if the whole of the eclipse track across America were cloudless, so we must rely first on climatology and then on forecasts if we are to find the

This city has one of the sunniest climates along the eclipse track. As you look southwest toward the center line in this image, notice the wide-open spaces with plenty of room for those searching for the best weather prospects.

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right spots to be when the Moon places its shadowy kiss on the continent. Multiyear satellite observations of cloudiness favor areas west of the Missouri River over those to the east. The difference of cloud cover from morning to afternoon and between east and west is striking, with the average morning (10:30 A.M.) and early afternoon (1:30 p.M.) cloud cover across the United States shifting. Nevertheless, both regions have microclimates where cloud cover statistics depart from the average and where the avid eclipse traveler can find a favorable site.

should you expect? Make your best guess more than a roll of the dice come the big day. Text and images by Jay Anderson

The park will experience totality first come eclipse day, although the weather prospects for that location are poor. It is near a popular whale watching site.

The graph of cloud cover (p. 35) along the central line of the eclipse, derived from the cloud maps, exposes the finer details in the climatology. In the western states, low cloud cover comes with low elevations, and high cloudiness is associated with mountain peaks. Five places with exceptionally low cloud cover stand out on the graph: Oregon’s Columbia Basin, two locations in Idaho’s Snake River Plain,

central Wyoming, and the western parts of Nebraska. The first four lie at low elevations within the western mountains, protected from prevailing winds and Pacific moisture by the high terrain to their windward side. Western Nebraska derives its good fortune from the Rocky Mountain bulwark that lies to its west, and from a relatively high elevation that discourages the influx of moisture from the Gulf of Mexico. East of the Missouri River, where moisture is more readily available, the link between topography and cloudiness is much less distinct.

Western states When Pacific air first arrives at the Oregon coast, it is compelled to pause and rise over the 3,200-foot-high Coast Range, which lies just inland along the eclipse path. The air cools as it rises, causing its relative humidity to increase, and, if enough moisture is present, clouds and precipitation to form. The influence of these oceanfront mountains gives Oregon’s coast an average cloudiness of around 60 percent, along

The unincorporated town may present a challenge on eclipse day. This site veers between sunny days like the one shown and hazy, salt-laden air with cold onshore winds.

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This region intercepts the eclipse track in two places, and both have excellent prospects for sunny weather. Air descending into the valley warms and dries, leaving the clouds behind on the higher terrain, as seen in this panorama taken from the Craters of the Moon National Monument.

with a propensity for fog and mist. In sunny weather with light winds, it’s a fine place to view the eclipse, but climatology promises much better viewing inland. Across the Coast Range, the Willamette Valley brings a sunnier climate, where the prevailing westerly winds must descend the mountain slopes to Salem and Corvallis. In contrast to rising airflows, winds that flow downhill are warmed, dried, evaporating clouds. The Coast Range is not high, but the average August cloudiness is a useful 15 to 20 percent less than that on the coast, making Salem and the valley a good Plan B site if the coastal weather is touchy. Even sunnier weather can be found farther east across the next mountain chain, the 6,600-foot-high Cascade Range, where the eclipse track drops sharply into the

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Columbia Basin. So much moisture is wrung from the Pacific air in the transit across the Cascades that the Basin is rewarded with some of the best viewing statistics along the track. Madras, Oregon, lies just south of the central axis of the shadow track, and the surrounding landscape offers a wide-open view of the August Sun — well suited to the crowds expected to view from there. Beyond the Columbia Basin, cloud cover increases modestly toward the Idaho border as the terrain rises over the Columbia Highlands. There are attractive eclipse sites in this terrain, and the cloud penalty is relatively modest — from an 8 percent rise to around 30 percent east of Mitchell, Oregon. At the Idaho border, the elevation on the path drops 6,000 feet into the west branch of the Snake River Plain, a deep rift valley that arcs across southern Idaho in the form of a large topographic “smile.” The lunar shadow’s sojourn in the western valley is short-lived, for 50 miles later it ascends the

This view, taken west of Casper, shows the terrain in one of the best eclipse viewing sites in the Wind River Basin near Riverton. This site is protected by the bulk of the Rocky Mountains to the west, and it is too high for eastern moisture to reach.

13,000-foot peaks of the Sawtooth Range. After a short stay on the mountains, the eclipse track descends once more into the Snake River bottomland near Idaho Falls. As in Oregon, the lower elevations of the Snake River Plain bring a pronounced drop in average cloudiness, to about 20 percent near Ontario, Oregon, and Weiser, Idaho, and 25 percent in the east near Idaho City, Idaho. While satellites offer a marvelous overview of the cloud cover, the data are difficult to translate into the actual probability of seeing the eclipse. The question of probability is better revealed by measurements from sunshine recorders, which are sparsely distributed along the eclipse track. There are two that are well situated in Idaho, however, at Boise and at Pocatello. Both reveal that the number of hours of sunshine in August is more than 80 percent of the maximum possible, a sign of very good eclipse-weather prospects for the state. The Grand Teton mountain range along the Idaho-Wyoming border brings impressive scenery, but may be cloudy. What is left of the Pacific moisture must first cross the Tetons and then the even higher Wind River Range. Average cloud amounts begin

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to rise just past Idaho Falls where the winds begin to “feel” the Tetons, eventually culminating at 45 to 50 percent over the Wind River Range, the highest measurements west of Missouri. The only valley of note is Jackson Hole, where the reduction in cloud cover is barely visible in the satellite record as air descends from the Tetons. In actuality, Jackson Hole is probably better than that, but the valley is too narrow to be resolved in satellite measurements. Jackson Airport observations show an average of 33 percent cloud cover in August, a value that seems more acceptable in view of the terrain. Riverton, in central Wyoming, will be much like Madras, with little cloudiness for the eclipse. Satellite records show 20 percent cloudiness on average around

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Scenic Jackson Hole and the Grand Teton mountains lie astride the eclipse track and create one of the most attractive vistas for eclipse watchers. Clouds tend to hang on the mountains and not in the valley, but eclipse chasers should have a good Plan B in case the weather doesn’t cooperate.

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Longitude The average August cloud cover along the eclipse track, derived from 15 to 17 years of observations by the Terra and Aqua satellites, is a good indicator for visibility. NASA

that time. In some respects, Wyoming may be the best location anywhere along the eclipse track, as it not only has climatology on its side, but a highway system that allows movement from Jackson, Wyoming, to Scottsbluff, Nebraska, and then to Alliance, Nebraska, without leaving the umbral path. The lunar shadow reaches central Nebraska at about noon local time, when afternoon clouds, if there are to be any, are beginning to form. The cloud cover here can increase as much as 20 percent from 10:30 a.m. to 1:30 p.m. over the eastern half

of the state, mostly due to the development of cumulus buildups in the rising heat of the day. Fortunately, the gradual masking of the Sun by the Moon will drop the temperature, and smaller convective clouds should dissipate about midway between first and second contact. If it’s an unstable day, any rain clouds are unlikely to disappear, though they may erode somewhat as their energy is cut off. Watchers at viewing sites near North Platte and Grand Island will have to keep an eye on cloud development, but the time of the eclipse is typically a bit early for serious cloud buildups.

Eastern states You can watch the eclipse from this whimsical re-creation of Stonehenge, called Carhenge, just north of Alliance. Eclipse prospects are good for the region, owing to a dry climate.

Beyond the Missouri River, average August cloud cover rises steadily along the track

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Cloud atlas The rolling sandhills of western Nebraska provide a dry climate with abundant sunshine. The state also offers conveniently located highways that allow a shift in position without leaving the path of totality.

of the eclipse, with afternoon values climbing from around 45 percent near St. Joseph, Missouri, to around 70 percent at the height of the Appalachians near Athens, Georgia. There are small ups and downs in the cloud cover across Missouri, Kentucky, and Tennessee, but little to suggest that one site is better than another, other than just heading west to sample a drier climatology. Across the Blue Ridge Mountains and into South Carolina, the satellite record shows no decline in cloudiness, but here the data lead us a bit astray. The cloud statistics are correct, but examination of the cloud images from day to day shows that most of the clouds consist of small convective buildups â&#x20AC;&#x201D; almost all of which will dissipate when the lunar shadow The upper map displays average fractional August cloud cover for a nominal Moon crossing time of 10:30 A.M. local time, while the lower map displays the same conditions for 1:30 P.M. This shows the striking difference between the two. Want to experience the longest duration of totality? Maximum eclipse, in which the Moon most surpasses the size of the Sun in the sky, will happen in this city in southwestern Kentucky.

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approaches. If normal weather patterns are active on eclipse day, South Carolina could be very good for viewing. Locations near the water will see less cloud cover, partly because the temperature difference between land near water and land away from water moves clouds away. This gives locations near Lake Marion and Lake Moultrie and along the Atlantic coast a big advantage: Winds blowing off of the water will bring cooler air that suppresses the buildup of convective clouds. Santee, South Carolina, seems particularly suited as an eclipse base, as it is close to the shadow axis, provides access to two interstate highways, and lies on the west shore of Lake Marion.

What to do on eclipse day Climatology can give you the long-range view, but it loses its value as August 21 approaches and weather forecasts begin to suggest what the real weather will look like. There will be many specialized forecasts on television and the internet, but the question will always be, “How accurate is this prediction?” For an unbiased opinion, I go to the numerical models themselves before they

become embellished by local and national meteorologists. As eclipse day approaches, the forecasts should become more reliable, but farther out — three to five days or more — I like to form my own opinion. There are two signs that the computer models are “locking in” on a solution to a particular day’s forecast: First, the prognosis doesn’t change as the model updates from day to day, and second, other models offer a similar solution. Models usually won’t begin to converge until three or four days out, so don’t get too upset if they seem to go back and forth before then. At least four medium- to long-range operational computer models are available online as well as a number of other shortrange (one day or so) models that are familiar to storm chasers. One site you may find handy is spotwx.com, where you can type in a location or click on a map to reveal an assortment of machine-based forecasts of weather elements (including clouds) presented as a graph. The site

This town — dubbed America’s “eclipse crossroad” — is an ideal location not just for this eclipse, but for the April 8, 2024, total solar eclipse as well.

makes it simple to compare the models with each other and each with its previous predictions. If you’d like to get a map display of cloud and weather patterns, try weather.cod.edu. This College of DuPage site is geared toward storm chasers, and offers convenient access to numerical models and satellite images. Time is short. Now is the time to pick a spot. When you get in place in August, watch and compare the forecasts, but don’t change locations until as late as you can. With the models in hand, pick a site that’s “safe,” not one that has a small opening in a large area of cloud. Anyone who really wants to see this eclipse and who has two or three days to spare is almost guaranteed to be successful. Jay Anderson is a retired Canadian meteorologist who has been publishing eclipse climatology studies since 1978. Read his blog at eclipsophile.com.

This site, about 30 miles north of Charleston, has a view toward the center line of the eclipse, which will be just 2 miles (3.2 kilometers) away. Sea breezes might keep the clouds away from the coast.

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THE TOTAL SOLAR ECLIPSE THAT WILL HAPPEN AUGUST 21, 2017, will dazzle every-

HOT SPOTS to view the eclipse People will view the spectacle from thousands of locations. Here are some you should consider. by Michael E. Bakich

one who views it. Potential observers may have some questions, however. Where in the United States does totality happen? That’s easy to answer with a detailed map. Where are the best spots to view the event? That isn’t as straightforward. Except for knowing that you want to be on, or at least near, the eclipse’s center line — where totality will last the longest — what makes for a good viewing location? Here are 20 sites you should consider, starting in the Northwest and working to the Southeast. I do offer one suggestion when choosing a site: Carefully consider the population. All things being equal, a town of 10,000 is much more likely to have event-related problems than a city of 75,000. Traffic will be one of the primary issues. Small communities with one main road may suffer hours of gridlock. If you choose to head to such a location, get there early, perhaps even a day or two ahead of the eclipse. Remember: August 21, 2017, is a Monday. So the whole weekend beforehand will be free for most people.

1Madras, Oregon

This town of some 6,500 residents lies 120 miles southeast of Portland, which itself sees a 99 percent partial eclipse. Close, but no cigar. Madras probably boasts the best weather prospects of any location within the path of totality. In August, the average precipitation is less than half an inch. I’m cautious about saying something like, “If you can get there, do it” because I’m not certain how many tourists the place can accommodate. Traffic

on eclipse day, and even the weekend prior, may be brutal. Take a weeklong vacation there, however, and you’ll roll out of bed under the Moon’s shadow without a care in the world. ECLIPSE STARTS: 9:06:47 A.M. PDT ECLIPSE ENDS: 11:41:04 A.M. PDT MAXIMUM ECLIPSE: 10:20:38 A.M. PDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 41.6° DURATION OF TOTALITY: 2 minutes, 3 seconds WIDTH OF THE MOON’S SHADOW: 62.6 miles (100.8km)

2 Lime, Oregon

This location may be my most outlandish suggestion, but hear me out. Lime is an unincorporated community that once had a thriving manufacturing plant that produced lime. Big surprise, huh? These days, not many people stop by the abandoned town. For the eclipse, however, Lime has two advantages: stunningly good weather and easy access, right off Interstate 84.

ECLIPSE STARTS: 9:10:04 A.M. PDT ECLIPSE ENDS: 11:47:55 A.M. PDT MAXIMUM ECLIPSE: 10:25:54 A.M. PDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 44.9° DURATION OF TOTALITY: 2 minutes, 10 seconds WIDTH OF THE MOON’S SHADOW: 64 miles (102.9km)

Smiths Ferry, Idaho

According to the 2010 census, this burg had a population of 75, so traffic problems could occur. Still, if you’re in western Idaho, this looks to be a great viewing site with easy access. Smiths Ferry

stands at an elevation of 4,554 feet (1,388m) and lies along Idaho State Highway 55 north of Boise. ECLIPSE STARTS: 10:11:14 A.M. MDT ECLIPSE ENDS: 12:50:11 P.M. MDT MAXIMUM ECLIPSE: 11:27:42 A.M. MDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 45.9° DURATION OF TOTALITY: 2 minutes, 11 seconds WIDTH OF THE MOON’S SHADOW: 64.4 miles (103.6km)

1. The World War II Erickson Aircraft Collection in Madras, Oregon, flies the largest U.S. flag in the state. Mount Jefferson stands in the background. JOE KRENOWICZ 2. Lime, Oregon, used to have a thriving cement plant. For the eclipse, it could host a throng of people under a predictably clear sky. PHOTO BY LYZADANGER (OWN WORK) [CC BY-SA 3.0 (HTTP://

Terreton, Idaho

This unincorporated community of 1,100 people lies at an elevation of 4,790 feet (1,460m). Terreton is 35 miles northwest of Idaho Falls and is a two-hour drive to either West Yellowstone, Montana, or Jackson Hole, Wyoming. It boasts great access from Interstate 15.

CREATIVECOMMONS.ORG/LICENSES/ BY-SA/3.0)], VIA WIKIMEDIA COMMONS

3. Smiths Ferry, about 60 miles (100km) north of Boise, is an unincorporated township in Idaho that could welcome many times its population on eclipse day. MAP: XAVIER M. JUBIER; DATA: GOOGLE IMAGERY/TERRAMETRICS

ECLIPSE STARTS: 10:14:57 A.M. MDT ECLIPSE ENDS: 12:57:08 P.M. MDT MAXIMUM ECLIPSE: 11:33:20 A.M. MDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 49.0° DURATION OF TOTALITY: 2 minutes, 17 seconds WIDTH OF THE MOON’S SHADOW: 65.6 miles (105.5km)

4. Terreton is a small agricultural community in Idaho whose population will be staring upward August 21, 2017. MAP: XAVIER

5. Looking west from Jackson Hole valley, the John Moulton Barn stands at the base of the Grand Teton Mountains. WIKIPEDIA

Jackson, Wyoming

Although this seems like an ideal spot, lots of tour groups and individuals are heading here. This town of 9,577 inhabitants sits at an elevation of 6,311 feet (1,924m) and has a total area under 3 square miles. Jackson lies slightly south of the eclipse’s center line, so if you drive north a few miles along U.S. Route 26, you’ll experience an extra 4 seconds of totality.

M. JUBIER; DATA: GOOGLE IMAGERY/ TERRAMETRICS

CREATIVE COMMONS

6. The skyline of Casper, Wyoming, is impressive. This city will host tens of thousands of eclipse watchers. WIKIPEDIA CREATIVE COMMONS

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7. The Carhenge monument lies 3 miles (4.8km) north of Alliance, Nebraska, along state Highway 87. JACOB KAMHOLZ (OWN WORK) [CC BY-SA 4.0 (HTTP:// CREATIVECOMMONS.ORG/LICENSES/ BY-SA/4.0)], VIA WIKIMEDIA COMMONS

8. A view of the east side of Main Street in Stapleton, Nebraska, looking northeast from about Fifth Street. WIKIMEDIA COMMONS

9. The Stuhr Museum in Grand Island, Nebraska, preserves the legacy of the pioneers who settled the central Nebraska plains in the late 19th century. WIKIMEDIA COMMONS 10. The Missouri River flows through sleepy St. Joseph, though it won’t be so sleepy on eclipse day! TIM KISER (W:USER:MALEPHEASANT) (OWN WORK (SELF-MADE PHOTOGRAPH)) [CC BY-SA 2.5 (HTTP://CREATIVECOMMONS.ORG/ LICENSES/BY-SA/2.5)], VIA WIKIMEDIA

ECLIPSE STARTS: 10:16:43 A.M. MDT ECLIPSE ENDS: 1:00:29 P.M. MDT MAXIMUM ECLIPSE: 11:36:03 A.M. MDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 50.5° DURATION OF TOTALITY: 2 minutes, 15 seconds WIDTH OF THE MOON’S SHADOW: 66.1 miles (106.3km)

6 Casper, Wyoming

Wyoming’s second-largest city had a population of 55,316 in 2010, and it has increased by some 5,000 since. Its elevation is 5,200 feet (1,585m). Because Casper offers more amenities than most places along the center line to its northwest, it will be the destination for vast numbers of visitors. Let’s hope its 27 square miles and 100 restaurants can handle them. ECLIPSE STARTS: 10:22:17 A.M. MDT ECLIPSE ENDS: 1:09:26 P.M. MDT MAXIMUM ECLIPSE: 11:43:52 A.M. MDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 54° DURATION OF TOTALITY: 2 minutes, 26 seconds WIDTH OF THE MOON’S SHADOW: 67.4 miles (108.5km)

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7 Alliance, Nebraska

I’ve been asked where I’d view the eclipse if I were not hosting a huge event in St. Joseph, Missouri. My answer: Alliance. OK, not exactly in Alliance, but rather at Carhenge, a replica of Stonehenge built using 39 automobiles, just 3 miles north of the town along Nebraska Route 87. This attraction boasts great weather prospects, lots of open ground, and a modern (1987) construction that honors an ancient monument that marked the

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Sun’s position. My friends, for those of us interested in astronomy, it doesn’t get much better. ECLIPSE STARTS: 10:27:09 A.M. MDT ECLIPSE ENDS: 1:16:42 P.M. MDT MAXIMUM ECLIPSE: 11:50:28 A.M. MDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 56.7° DURATION OF TOTALITY: 2 minutes, 29 seconds WIDTH OF THE MOON’S SHADOW: 68.4 miles (110km)

8 Stapleton, Nebraska

If you’re looking for small-town charm, this burg with a population of 305 might just be for you. It lies at an elevation of 2,904 feet (885m), 29 miles north of Interstate 80 along U.S. Route 83, directly on the center line. Your best bet may be to stay in nearby North Platte, then drive north to Stapleton for the extra 50 seconds of totality. ECLIPSE STARTS: 11:30:46 A.M. CDT ECLIPSE ENDS: 2:21:54 P.M. CDT MAXIMUM ECLIPSE: 12:55:18 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 58.5° DURATION OF TOTALITY: 2 minutes, 33 seconds WIDTH OF THE MOON’S SHADOW: 68.9 miles (110.9km)

9 Grand Island, Nebraska

With a population of some 50,000, this city can handle quite an influx of eclipse watchers. Grand Island’s elevation is a bit lower than more westerly locations — 1,860 feet (567m) — but still high enough to offer a particulate-free sky. Just note that the south and southwestern edges of the city (where the center line intersects U.S. Route 34

or U.S. Route 30, respectively) offer ever-so-slightly longer totalities. ECLIPSE STARTS: 11:34:19 A.M. CDT ECLIPSE ENDS: 2:26:35 P.M. CDT MAXIMUM ECLIPSE: 12:59:50 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 59.9° DURATION OF TOTALITY: 2 minutes, 34 seconds WIDTH OF THE MOON’S SHADOW: 69.4 miles (111.8km)

Joseph, Missouri 10 St.(Rosecrans Memorial Airport)

This facility has a capacity of 75,982. She’s also setting up ancillary sites to accommodate the expected quarter-million visitors that day all around the city.

UPLOADED TO FLICKR BY USER KOMUNEWS

ECLIPSE STARTS: 11:45:41 A.M. CDT ECLIPSE ENDS: 2:40:15 P.M. CDT MAXIMUM ECLIPSE: 1:13:41 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 62.9° DURATION OF TOTALITY: 2 minutes, 37 seconds WIDTH OF THE MOON’S SHADOW: 70.6 miles (113.6km)

(HTTP://WWW.FLICKR.COM/PHOTOS/ KOMUNEWS/7298225366/) [CC BY 2.0 (HTTP://CREATIVECOMMONS.ORG/LICENSES/BY/2.0)], VIA WIKIMEDIA COMMONS

12. These water towers outside St. Clair, Missouri, have the labels “Hot” and “Cold” painted on them. JAMES HAYES FROM USA ([1] UPLOADED BY LONGLIVEROCK) [CC BY 2.0 (HTTP://CRE-

Perhaps the largest single astronomy observing event ever will occur on eclipse day at Rosecrans Memorial Airport, which has space for more than 100,000 visitors. Although St. Joe is the fifthlargest city to fall under the Moon’s shadow, facilities will be strained. Luckily, Kansas City lies a scant 40 miles south. If you’re in the area, come join me. Do get there early.

ECLIPSE STARTS: 11:40:34 A.M. CDT ECLIPSE ENDS: 2:34:28 P.M. CDT MAXIMUM ECLIPSE: 1:07:39 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 61.9° DURATION OF TOTALITY: 2 minutes, 38 seconds WIDTH OF THE MOON’S SHADOW: 70.1 miles (112.9km)

ECLIPSE STARTS: 11:48:33 A.M. CDT ECLIPSE ENDS: 2:43:29 P.M. CDT MAXIMUM ECLIPSE: 1:17:04 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 63.4° DURATION OF TOTALITY: 2 minutes, 40 seconds WIDTH OF THE MOON’S SHADOW: 70.8 miles (114km)

Missouri 11Columbia, (UM Stadium)

13 Carbondale, Illinois

Another huge event will occur in the Show Me State when astronomer Angela Speck hosts the public at Faurot Field at Memorial Stadium, where the University of Missouri football team plays.

11. The University of Missouri will host some 75,000 eclipse watchers at Faurot Field at Memorial Stadium. CLARE MURPHY/KOMU;

St. Clair, Missouri

St. Louis lies on the northeastern edge of the eclipse path, so it won’t offer much in the way of length of totality. Instead, head southwest roughly 50 miles via Interstate 44 to the center line in St. Clair, a town of some 5,000 residents. If you can book a room there, great. If not, St. Louis offers thousands.

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13. This statue in downtown Carbondale, Illinois, salutes its railroaders. The city was a thriving train gateway, with the first train passing through July 4, 1854. EXPLORECDALE/ WIKIMEDIA COMMONS

Although this city of nearly 30,000 lies slightly off the center line, I offer it as a choice because it’s much larger than the burgs around it that are on the center line. Positioned near the eclipse’s greatest duration, Southern Illinois W W W.ASTR ONOMY.CO M

Greetings from

14. Technically, the longest duration of the August 21, 2017, total solar eclipse will occur at Giant City State Park in Illinois. ALAN SCOTT WALKER/ WIKIMEDIA COMMONS

15. Cerulean is an unincorporated community in Trigg County, Kentucky. MAP: XAVIER

University will host events headed by physics department staff member Bob Baer.

offers the longest duration of totality, surely will flock there. Repeat after me: “Gridlock!”

ECLIPSE STARTS: 11:52:27 A.M. CDT ECLIPSE ENDS: 2:47:30 P.M. CDT MAXIMUM ECLIPSE: 1:21:26 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 63.7° DURATION OF TOTALITY: 2 minutes, 38 seconds WIDTH OF THE MOON’S SHADOW: 71.1 miles (114.4km)

ECLIPSE STARTS: 11:52:33 A.M. CDT ECLIPSE ENDS: 2:47:43 P.M. CDT MAXIMUM ECLIPSE: 1:21:37 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 63.8° DURATION OF TOTALITY: 2 minutes, 40 seconds WIDTH OF THE MOON’S SHADOW: 71 miles (114.3km)

M. JUBIER; DATA: GOOGLE IMAGERY/ TERRAMETRICS

16. The First Presbyterian Church of Hopkinsville stands on land purchased for it in 1822. People on eclipse day will be praying for clear skies. WIKIMEDIA

Makanda, Illinois (Giant City State Park)

I like bearing good news and don’t much care to announce bad news. This attraction has the longest duration of totality anywhere. That’s the good news. The bad news is that Makanda has a population of 561, and thousands of unknowing eclipse watchers, hoping to be in the spot that

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This unincorporated community has a population of about 400. It’s easy to reach, it has essentially the longest duration of totality, and, most importantly, many people may overlook it as a prime site. Oh, and be sure to note this: If you plan to observe totality anywhere in Kentucky, you’ll be in the Central Time Zone. Although most of the state observes Eastern Time, those locations will see only a partial eclipse. ECLIPSE STARTS: 11:56:01 A.M. CDT ECLIPSE ENDS: 2:51:12 P.M. CDT MAXIMUM ECLIPSE: 1:25:27 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 63.9° DURATION OF TOTALITY: 2 minutes, 40 seconds WIDTH OF THE MOON’S SHADOW: 71.2 miles (114.6km)

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15 Cerulean, Kentucky

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16 Hopkinsville, Kentucky

An aggressive ad campaign by astronomy enthusiasts, paired with one of the longest totality times, means this city of nearly 35,000 residents better prepare itself. It does boast easy access: Just take U.S. Route 68 roughly 17 miles east from where it meets Interstate 24.

ECLIPSE STARTS: 11:56:33 A.M. CDT ECLIPSE ENDS: 2:51:43 P.M. CDT MAXIMUM ECLIPSE: 1:26:02 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 63.9° DURATION OF TOTALITY: 2 minutes, 40 seconds WIDTH OF THE MOON’S SHADOW: 71.2 miles (114.6km)

17 Gallatin, Tennessee

Although Nashville is the single largest city that lies within the path of totality, I recommend you take U.S. Route 31E northeast 29 miles to Gallatin. Why? Because depending on where you start in Nashville, you’ll gain up to nearly 1 minute of totality. For an extra minute of totality, I would walk the 29 miles. So would just about everyone I know who has experienced a total solar eclipse. So worth it! ECLIPSE STARTS: 11:59:04 A.M. CDT ECLIPSE ENDS: 2:54:11 P.M. CDT MAXIMUM ECLIPSE: 1:28:47 P.M. CDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 63.9° DURATION OF TOTALITY: 2 minutes, 40 seconds WIDTH OF THE MOON’S SHADOW: 71.3 miles (114.7km)

Sparta, Tennessee

This town of 5,100 people should prove a relatively quiet setting from which to observe the eclipse. If you like regional history and gorgeous buildings, this might just be your spot. ECLIPSE STARTS: 12:01:31 P.M. CDT ECLIPSE ENDS: 2:56:29 P.M. CDT MAXIMUM ECLIPSE: 1:31:24 P.M. CDT

SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 63.7° DURATION OF TOTALITY: 2 minutes, 39 seconds WIDTH OF THE MOON’S SHADOW: 71.4 miles (114.8km)

17. Downtown Gallatin in Tennessee is a quaint space. On eclipse day, however, expect it to be bustling with activity. ICHABOD/WIKIMEDIA COMMONS

19 Greenville, South Carolina

Although this city of more than 62,000 residents lies within the path of the Moon’s shadow, if you head 28 miles southwest to anywhere near the intersection of state Route 81 and Interstate 85, you’ll gain nearly half a minute of totality.

ECLIPSE STARTS: 1:08:59 P.M. EDT ECLIPSE ENDS: 4:03:01 P.M. EDT MAXIMUM ECLIPSE: 2:39:03 P.M. EDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 62.8° DURATION OF TOTALITY: 2 minutes, 37 seconds WIDTH OF THE MOON’S SHADOW: 71.5 miles (115km)

Columbia, South Carolina

This city of some 135,000 is sure to be the destination of tens to hundreds of thousands of hopeful eclipse chasers from locations up and down the Eastern Seaboard. And it might be one of the few spots able to handle such numbers. It also has the least favorable weather prospects, so start paying careful attention to forecasts up to a week before the event. ECLIPSE STARTS: 1:13:08 P.M. EDT ECLIPSE ENDS: 4:06:21 P.M. EDT MAXIMUM ECLIPSE: 2:43:07 P.M. EDT SUN’S ALTITUDE AT MAXIMUM ECLIPSE: 61.9° DURATION OF TOTALITY: 2 minutes, 30 seconds WIDTH OF THE MOON’S SHADOW: 71.5 miles (115km)

18. The Rock House in Sparta, Tennessee, was built in the late 1830s and served as a stagecoach inn. The guardrail of U.S. 70 spans the embankment in the background. BRIAN STANSBERRY/WIKIMEDIA COMMONS

19. The Falls in downtown Greenville, South Carolina, are often visited by locals and tourists alike. They’ll be much more difficult to see when the Moon’s shadow envelops them. YOUSEF ABDUL-HUSAIN/WIKIMEDIA COMMONS

20. Columbia is the thirdlargest city covered by the Moon’s umbra. Officials are bracing for the influx of several hundred thousand people. AKHENATON06/WIKIMEDIA COMMONS

Michael E. Bakich is a senior editor of Astronomy. This story is an excerpt from his book Your Guide to the 2017 Total Solar Eclipse (Springer, 2016). To order the guide, visit MyScienceShop.com.

W W W.ASTR ONOMY.CO M

SKYTHIS MONTH

Visible to the naked eye

MARTIN RATCLIFFE and ALISTER LING describe the

Visible with binoculars Visible with a telescope

solar system’s changing landscape as it appears in Earth’s sky.

August 2017: Totality comes to America

The Sun’s glorious corona will blossom into view for observers in the United States who make it into the path of August 21’s total solar eclipse. ANTHONY AYIOMAMITIS

he long-anticipated Great American Eclipse is finally here. To witness nature’s grandest spectacle — a total eclipse of the Sun — you need to be within the narrow path of totality that spans the United States from sea to shining sea (from Oregon to South Carolina) on August 21. This is the first time the Moon’s dark umbral shadow has touched the continental United States since 1979. Everyone in North America with a clear sky can experience at least a partial solar eclipse, with the Moon covering a larger fraction of the Sun’s disk the closer you get to the path of totality. But the difference between a total and a partial eclipse is, well, like night and day. Totality is the main event, the partial eclipse a mere sideshow. At least 90 percent of the dramatic sights take place during or just outside the brief moments of totality.

A ST R O N O M Y • AUG UST 2017

Nearly every page of this issue brings you helpful information about the eclipse and how best to experience it. But if you are a first-time eclipse chaser, pay particular attention to “Astronomy’s Atlas of Totality” on p. 54, so you can find a good viewing location, and to “A step-by-step guide to the Great American Eclipse” on p. 26, so you know what to watch for during this priceless event. August 21 is but a single day, however. Don’t forget that August also boasts 31 nights of worthy celestial treats. Jupiter and Saturn lead the way on late-summer evenings, shining brightly and showing fine detail when viewed through a telescope. Farther out in the solar system, Uranus and Neptune show their more subtle charms best after midnight. And by the time morning twilight commences, Venus dominates the eastern sky.

But the first stop on our night-sky tour lurks low in the west shortly after sunset. Mercury appears as an inconspicuous dot against the twilight during August’s first few days. On the 1st, the innermost planet shines at magnitude 0.4 and stands 6° high a half-hour after sundown. You should be

able to spot it with your naked eye, though binoculars can help you locate it initially. Mercury becomes harder to see with each passing day as it dims and dips closer to the horizon. By August 8, it glows at magnitude 0.9 and appears just 3° high 30 minutes after sunset. That’s about as long as observers at mid-northern latitudes will be able to track it. If you swing a scope toward Mercury, you’ll see a relatively large, crescent-shaped disk. On the 1st, the planet appears 8.1" across and 42 percent lit. By the 8th, the disk spans 9.2" and the Sun illuminates 30 percent of its Earth-facing hemisphere. Look to the upper left of Mercury and you can’t help but see Jupiter. The solar system’s largest planet shines at magnitude –1.9 in early August. It stands out in the deepening twilight and doesn’t set until 11 p.m. local daylight time. Jupiter resides in Virgo, some 8° northwest of that constellation’s brightest star, 1st-magnitude Spica.

The Moon meets Venus ORION

Betelgeuse GEMINI

Castor Pollux LYNX

Venus Moon Procyon

10°

August 19, 1 hour before sunrise Looking east A slender crescent Moon poses with brilliant Venus and the background stars of Gemini before dawn August 19. ALL ILLUSTRATIONS: ASTRONOMY: KELLIE JAEGER

RISINGMOON Mountain-making in a lunar ocean What a sight the Moon must have been a few billion years ago, when lava surged from the lunar interior and spread across its huge basins. As the surface cooled and solidified, local hot spots continued to ooze magma. These upwellings gradually built modest hills that appear starkly different from the mountain ranges and crater rims that formed around impact sites. The most extensive complex of these lunar hills comes into view on the August 4 waxing gibbous Moon. Early that evening, Mons Rümker lies on the terminator — the dividing line between lunar day and night. As the night wears on, sunlight reveals the mountain’s full

The planet’s brilliance drowns out the light of a more immediate neighbor. On August 1, Jupiter sits in front of the 11th-magnitude spiral galaxy NGC 4941. Although visual observers have no hope of seeing the two in the same telescopic field, astroimagers looking for a challenge might be able to capture both. You’ll need to take multiple exposures to record the bright planet, its fainter moons, and the dim galaxy. Practice your technique the previous evening, when Jupiter lies 9' west of NGC 4941. You might consider capturing a sequence of images over several nights to show the planet’s passage by the diminutive spiral. Jupiter’s eastward motion against the stellar backdrop continues all month. By the 31st, it has pulled within 4° of Spica, though the pair lies lower and sets around the time twilight ends. August will bring your last good looks at Jupiter through a telescope during

extent. The jumbled complex of hills spans about 45 miles and doesn’t look anything like the rim of a large crater. Instead, Mons Rümker gives an impression as if the Moon has hives. To locate Mons Rümker, start at the Moon’s brightest feature: Aristarchus Crater. Then slide north along the terminator through Oceanus Procellarum (Ocean of Storms) until you reach the hills. Under the rising Sun, these gentle hills cast long shadows. Just 24 hours later, however, the shadows have all but disappeared. We then see the flat central part of the complex, which some lunar scientists suspect is a caldera formed when the peak collapsed.

METEORWATCH The Hero’s dubious reign of glory Nearly everyone considers the Perseid meteor shower to be the finest of the year. Not only does it deliver a consistently high rate of “shooting stars,” but it also occurs during the warm summer nights that are conducive to extended observing sessions. Unfortunately, a bright waning gibbous Moon interferes with the Perseids’ August 12 peak this year. Typically, this shower can produce up to 150 meteors per hour under a dark sky. In 2017, the Moon will wipe out the fainter ones, reducing the overall rate by 80 to 90

this apparition. On the 1st, the giant spans 34" and stands high enough an hour after sunset to deliver sharp views of cloud features. But the planet’s

OBSERVING HIGHLIGHT

Mons Rümker

Oceanus Procellarum

N E This complex of volcanic hills rises from the floor of Oceanus Procellarum the night of August 4/5. CONSOLIDATED LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU

Perseid meteors Perseid meteor shower

Active dates: July 17–Aug. 24 Peak: August 12 Moon at peak: Waning gibbous Maximum rate at peak: 150 meteors/hour

A gibbous Moon shares the sky with this year’s Perseid shower, but bright meteors and fireballs still make it a worthwhile event. LUO CHENG

percent. Still, 15 to 30 meteors in an average hour is nothing to sneeze at, so keep your eyes to

lower altitude late in the month means you have to look through more of Earth’s atmosphere, making fine detail hard to see.

the sky for bright Perseids radiating from Perseus the Hero before dawn on the 12th.

Saturn stands about 30° above the southern horizon as twilight comes to a close. The magnitude 0.3 planet — Continued on page 50

The Moon totally eclipses the Sun on August 21 for observers along a path that stretches from Oregon to South Carolina. W W W.ASTR ONOMY.CO M

N CA

STAR DOME LO

γ NG

M81

M82 CA

β DR

M3 1

β LA

η α

Planets are shown at midmonth

11 P.M. August 1 10 P.M. August 15 9 P.M. August 31

URSA MINO

Polaris

N O M A

M3 3

The all-sky map shows how the sky looks at:

NCP

How to use this map: This map portrays the sky as seen near 35° north latitude. Located inside the border are the cardinal directions and their intermediate points. To find stars, hold the map overhead and orient it so one of the labels matches NE the direction you’re facing. The stars above the map’s horizon now match what’s in the sky.

C ER

ν S

M13

ζ β

α κ

T TA R

α β

μ M22 λ

ζ IUS

S at

M20

C O RO NA AU S T R A L I S

A ST R O N O M Y • AUG UST 2017

κ ι

TELESCOPIUM

urn

6231 NGC θ η

α ARA

U SAGI

ν M16 M17

π ξ

γ IC

γ VU

SCUTU

M11

β PR

Fainter stars can’t excite our eyes’ color receptors, so they appear white unless you use optical aid to gather more light

The coolest stars glow red

β O

α C

SERPENS C AU DA

η θ AQ

IS IN SC TR PI US A

Lower-temperature stars appear orange

Intermediate stars (like the Sun) glow yellow

Slightly cooler stars appear white

STAR COLORS

The hottest stars shine blue

α Veg a

η χ M27

α β

cli

3.0 4.0 5.0

A star’s color depends on its surface temperature.

• • • • • •

0.0 1.0 2.0

α EUS M15 UL QU ε E β

Enif

Sirius

γ ε

PEGASUS

PISCES

th Pa

STAR MAGNITUDES

Al ta

δ C

U RC

η μ

De n

Note: Moon phases in the calendar vary in size due to the distance from Earth and are shown at 0h Universal Time.

AUGUST 2017

SUN.

MON.

TUES.

WED.

THURS.

FRI.

SAT.

MAP SYMBOLS Open cluster Globular cluster UR

Diffuse nebula 6

Planetary nebula

ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY

Galaxy

ÖT BO

P M64

ζ GO VIR

Uranus is stationary, 6 A.M. EDT 7

25 The Moon passes 3° north of Jupiter, 9 A.M. EDT

SPECIAL OBSERVING DATE 7 Observers across most of Europe, Africa, Asia, and Australia will witness a partial lunar eclipse.

Saturn is stationary, 11 A.M. EDT 26 Asteroid Juno is stationary, 6 A.M. EDT Mercury is in inferior conjunction, 5 P.M. EDT 29

12 Mercury is stationary, 2 A.M. EDT

Venus passes 7° south of Pollux, 3 P.M. EDT

Full Moon occurs at 2:11 P.M. EDT

9 The Moon passes 0.9° south of Neptune, 7 P.M. EDT

Perseid meteor shower peaks

First Quarter Moon occurs at 4:13 A.M. EDT

30 The Moon is at apogee (251,226 miles from Earth), 7:25 A.M. EDT The Moon passes 4° north of Saturn, 10 A.M. EDT

13 The Moon passes 4° south of Uranus, 1 A.M. EDT

New Moon occurs at 2:30 P.M. EDT; total solar eclipse

Arcturus

3 The Moon passes 3° north of Saturn, 3 A.M. EDT

δ C O RO NA BOREALIS

SE R CA PEN S PU T β

2 The Moon is at apogee (251,671 miles from Earth), 1:55 P.M. EDT

MA ES CO ENIC R E B

I N C A N AT E V

iza

Calendar of events

P OR

σ es tar α 4 An M τ

U UP

Last Quarter Moon occurs at 9:15 P.M. EDT

16 The Moon passes 0.4° north of Aldebaran, 3 A.M. EDT 18 The Moon is at perigee (227,497 miles from Earth), 9:18 A.M. EDT 19 The Moon passes 2° south of Venus, 1 A.M. EDT

BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. W W W.ASTR ONOMY.CO M

PATH OF THE PLANETS

The planets in August 2017 Objects visible before dawn

UM a

AND

PE R

AUR

LYN

CYG GEM

LMI

Comet PANSTARRS ARI (C/2015 ER61)

Ceres Venus

LEO

The Moon passes 2° south of Venus on August 19

C NC

TRI

PE G

Iris Path Path o of t h f the e S un ( Moo eclip n tic) PSC TAU Uranus

Mars

Sun

L AC

CMi

VUL DE L

E QU

Julia

S GE AQL

Celestial equator Neptune

ORI

SEX

Pallas

MON HYA

AQR C ET

ERI

CAP

CM a

Pluto

LEP F OR

PYX

ANT

A partial lunar eclipse occurs August 7 across partsPsA of Europe, SCL Africa, Asia, and Australia

C OL

PUP

CAE

M IC

PH E

V EL HOR Dawn

Moon phases

Midnight

To locate the Moon in the sky, draw a line from the phase shown for the day straight up to the curved blue line. Note: Moons vary in size due to the distance from Earth and are shown at 0h Universal Time.

The planets in the sky

These illustrations show the size, phase, and orientation of each planet and the two brightest dwarf planets at 0h UT for the dates in the data table at bottom. South is at the top to match the view through a telescope.

Uranus

Mercury

Mars

S W

Pluto

10"

Saturn

Ceres

Venus

Neptune

Jupiter

Planets

MERCURY

VENUS

MARS

CERES

JUPITER

SATURN

URANUS

NEPTUNE

PLUTO

Date

Aug. 1

Aug. 15

Magnitude

0.4

–4.0

1.8

8.9

–1.8

0.3

5.8

7.8

14.2

Angular size

8.0"

13.5"

3.5"

0.4"

33.2"

17.4"

3.6"

2.4"

0.1"

Illumination

44%

79%

100%

99%

100%

Distance (AU) from Earth

0.845

1.240

2.655

3.385

5.939

9.532

19.485

29.000

32.553

Distance (AU) from Sun

0.466

0.722

1.652

2.658

5.449

10.061

19.917

29.947

33.387

Right ascension (2000.0)

10h27.9m

7h11.2m

9h15.8m

7h03.2m

13h11.2m

17h21.3m

1h45.7m

22h59.4m

19h13.6m

Declination (2000.0)

7°52'

21°35'

17°05'

24°12'

–6°19'

–21°56'

10°17'

–7°29'

–21°39'

A ST R O N O M Y • AUG UST 2017

This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows and colored dots show motions and locations of solar system objects during the month.

Jupiter’s moons

Objects visible in the evening CVn

H ER LYR

BOÖ

CrB

C OM

LYN

UM a

A total solar eclipse occurs August 21 on a narrow track that runs from Oregon to South Carolina LEO

Sun

SE R SE R

OPH

Mercury VI R

Io Europa

Ganymede Callisto

SE X

Jupiter

LI B

Hebe

Dots display positions of Galilean satellites at 11 P.M. EDT on the date shown. South is at the top to match S the view E through a W N telescope.

SC T

C RV C RT

HYA 4

Saturn

PYX

ANT

SGR

LUP

CrA

SCO

CEN

TEL

Callisto

V EL

ARA

8 Early evening

Jupiter

9 10

11 28

Europa

13 14 15

Ceres

16 17

Venus Mars

Earth

Mercury Inferior conjunction is August 26

Ganymede

20 21

Jupiter

22 23

24 25

The planets in their orbits Arrows show the inner planets’ monthly motions and dots depict the outer planets’ positions at midmonth from high above their orbits.

Jupiter Uranus

ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY

27 28

Neptune Saturn

29 30

Pluto

W W W.ASTR ONOMY.CO M

— Continued from page 45

WHEN TO VIEW THE PLANETS

The ringed planet’s magnificent seven S Mimas

EVENING SKY

MIDNIGHT

Mercury (west) Jupiter (west) Saturn (south) Neptune (east)

Saturn (southwest) Uranus (east) Neptune (southeast)

appears against the backdrop of Ophiuchus. No star in this region appears nearly as bright; its closest competitor is 1st-magnitude Antares in Scorpius, which lies 13° to the west-southwest. Closer in, 3rdmagnitude Theta (θ) Ophiuchi resides 3° due south of Saturn. The planet remains nearly stationary relative to these background stars all month. Your best views through a telescope come when the world lies high in the south as darkness falls. Even the smallest scope shows that Saturn’s disk is not a perfect circle. The planet’s rapid spin and gaseous nature gives it an equatorial bulge. On August 15, the giant spans 17.4" across the equator and 16.1" through the poles.

Enceladus Dione

MORNING SKY Tethys

Venus (east) Uranus (south) Neptune (southwest)

Titan Rhea

Saturn W

But the disk is a mere afterthought to most observers, who spend their time focused on Saturn’s stunning rings. The system appears 40" in diameter and tips 27° to our line of sight at midmonth. This wide tilt affords dramatic views of ring structure. Notice in particular the Cassini Division — a dark gap between the outer A ring and the brighter, broader B ring. Small scopes also reveal Saturn’s family of moons. The brightest, 8th-magnitude Titan, shows up through any instrument. You can find it north of Saturn on August 10 and 26 and south of the ringed world on the 2nd and 18th. Closer in lies a trio of 10thmagnitude satellites — Tethys,

COMETSEARCH Sliding south of the Seven Sisters

Iapetus

August 14, 12:30 A.M. EDT

Saturn’s bright moons all appear near the planet the night of August 13/14. Look carefully for Mimas and Enceladus just outside the edge of the rings.

Dione, and Rhea — visible through 4–inch scopes. Mimas and Enceladus glow more faintly and seem to hug the outer edge of the rings. You’ll need an 8-inch instrument to spy them when their orbits carry them farthest from the planet. Perhaps the best opportunity this month comes the night of August 13/14, when Enceladus reaches greatest eastern elongation less than two hours after Mimas reaches greatest western elongation.

The chart above should help you to identify them relative to the brighter moons. That same night, look for outer Iapetus 2' north of Saturn. This two-faced moon — highly reflective ice covers one hemisphere, nearly black dirt the other — then glows at 11th magnitude. It appears slightly brighter early in the month when it lies west of the planet and its icy side faces Earth, and dims as it heads east after mid-August.

Comet PANSTARRS (C/2015 ER61) N

Although astronomers expect Comet PANSTARRS (C/2015 ER61) to glow at an unimpressive 9th magnitude in August, it should be fairly easy to find. This deepspace visitor remains within a few degrees of the Seven Sisters — the Pleiades star cluster (M45) — all month. The comet passes less than 1° south of the cluster from August 14 to 21. For the best views, hunt for PANSTARRS in August’s first few nights or after the midmonth, when the Moon is out of the predawn sky. When astronomers discovered this object in March 2015, they classified it as an asteroid on a highly eccentric orbit. But within a few months, this “space rock” started showing signs of

A ST R O N O M Y • AUG UST 2017

cometary activity. PANSTARRS’ path through the solar system carried it nearly tangent to Earth’s orbit in May, but we were then one-quarter of a year behind it. If our planet had been three months farther along in its orbit, we would have had a naked-eye comet all night. Two other comets are not as well placed. Comet Johnson (C/2015 V2) should glow at 8th magnitude as it heads south from Centaurus into Lupus. Unless you live far enough south that you can easily see the bottom of Scorpius, Johnson won’t be worth the effort. Meanwhile, Comet 71P/Clark glows at 10th magnitude as it slides through southern Scorpius, passing less

TAURUS

Pleiades 7 E

ARIES

26 9

66 6

Aug 1 Path of Comet PANSTARRS

1° This 9th-magnitude visitor sweeps less than 1° south of the Pleiades star cluster (M45) during August’s third week.

than 1° from magnitude 1.6 Shaula and the 7th-magnitude

globular cluster NGC 6441 in August’s final two weeks.

The Moon’s brush with Earth’s umbra

LOCATINGASTEROIDS Julia rides the back of Pegasus

August 7/8 brings a partial lunar eclipse to most of the Eastern Hemisphere. At maximum, 25 percent of the Full Moon will be in shadow. ALISTER LING

Distant Neptune will reach opposition and peak visibility in early September, but the view in August is nearly as good. The planet rises in midevening and climbs some 30° high in the southeast by midnight. You can find the magnitude 7.8 object through binoculars or a telescope against the backdrop of Aquarius. On August 1, it lies 2° east of 4th-magnitude Lambda (λ) Aquarii and in a direct line with the 6thmagnitude stars 81 and 82 Aqr. Neptune moves slowly westward during August and ends the month 1.3° east of Lambda. Although binoculars gather enough light to show you the planet, identifying it from nearby stars can be a challenge. A telescope should remove all doubt. At magnifications of 60x or more under good viewing conditions, Neptune shows a 2.4"-diameter disk with an obvious blue-gray color. Uranus rises nearly two hours after Neptune along with the stars of Pisces the Fish. The closer planet glows at magnitude 5.8 and shows up easily through binoculars. (It’s even bright enough to see with the naked eye under a dark sky.) The best time to look for Uranus is an hour or two before morning twilight begins, when it lies more than halfway to the zenith in the southeastern sky. Uranus remains 1° north of 4th-magnitude Omicron (ο)

Piscium all month. If you center the star in your binoculars’ field of view, the planet will be the bright object just above it. A telescope can confirm a sighting by showing Uranus’ distinct blue-green color on a disk that spans 3.6". While it takes some effort to track down the faint murmurs of Uranus and Neptune, Venus shouts its presence. The brilliant “morning star” rises in darkness more than 2½ hours before the Sun and climbs some 20° above the eastern horizon an hour before sunup all month. Shining at magnitude –4.0, Venus is impossible to miss on any clear morning. The inner planet begins August in western Gemini and moves eastward quickly. Look for a waning crescent Moon a few degrees below Venus on August 19. Two mornings later, the planet passes 7° south of Gemini’s brightest star, magnitude 1.2 Pollux. Venus crosses the border into Cancer during the daylight hours of August 25, and ends the month barely 1° from the fabulous Beehive star cluster (M44). When viewed through a telescope, Venus shows a relatively small, gibbous disk. On August 1, it appears 15" across and 74 percent illuminated. By the 31st, its apparent diameter has shrunk to 12" while

nearly equal stars you find in the Milky Way star fields of Sagittarius, for example, where it’s easy to get lost in the forest. Use the chart below to target Julia’s position, then make a sketch of four or five stars and label the one you think is the asteroid. Come back a night or two later to see that the dot has moved. On the mornings of August 17, 24, 29, and 30, Julia passes close enough to field stars that you should notice its displacement after three hours. French astronomer Édouard Stephan discovered Julia in 1866, but he is better known for detecting Stephan’s Quintet, a tight group of five galaxies.

Although few high-numbered asteroids ever get brighter than 10th magnitude, 89 Julia reaches magnitude 9.0 in late August. Your signpost for finding this solar system wanderer is a squashed box of four 5thmagnitude stars: 55, 57, 58, and 59 Pegasi. The box lies 6° south of magnitude 2.5 Markab (Alpha [α] Pegasi), the star at the southwestern corner of the Great Square, and fits beautifully in a finder scope’s field of view. When hunting asteroids, patterns are your friend. At first, the background stars here seem to be a hodgepodge of brightnesses. But this is an advantage compared with the hordes of

The Winged Horse hosts a main belt asteroid N

57 59

Path of Julia

ρ 16 PEGASUS

11 6

1°

Aug 1 Keep an eye out for 9th-magnitude Julia as it treks northwest against the background stars just south of the Great Square of Pegasus.

its phase has waxed to 83 percent lit. Mars was in conjunction with the Sun in late July, and it remains lost in our star’s glare throughout August. It will return to view before dawn next month. Most of the world outside the Americas can view a partial lunar eclipse the night of August 7/8. The Moon’s southern edge enters Earth’s dark

shadow at 17h22m UT on the 7th and exits at 19h19m UT. Greatest eclipse occurs at 18h20m UT, when 25 percent of the Moon’s diameter resides in Earth’s shadow. Martin Ratcliffe provides planetarium development for Sky-Skan, Inc., from his home in Wichita, Kansas. Meteorologist Alister Ling works for Environment Canada in Edmonton, Alberta.

GET DAILY UPDATES ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek. W W W.ASTR ONOMY.CO M

Navigating the sky There’s so much more in the sky during the eclipse than the Sun and Moon. Here’s how to make sure you’ll see it all. by Michael E. Bakich

So, August 21 has finally arrived.

about 10 minutes or so before totality. Don’t spend minutes huntYou can’t believe how excited you are. You’re probably a bit nering for it, though, because there’s a lot more to see, and Jupiter will vous, too. Everything has led up to your trip to the shadow, to this surely pop out during totality. You can take a few seconds to day, to the 1½-hour buildup to totality, and especially to the 2-plus glance at it then. minutes of totality itself. Still, I’m sure that some of you would like to increase your Before the mid-eclipse spectacle, however, other sights will chances of pinpointing Jupiter and perhaps other celestial objects. draw your eyes. Around the three-quarter mark, which will be Sirius, the night sky’s brightest star, is a real possibility. Arcturus, roughly 20 minutes before totality, you’ll start to notice that shadthe fourth-brightest star, is possible from probably Wyoming eastows are getting sharper because the Sun’s disk is shrinking — litward. In Oregon and Idaho, that star will be really low and hard to erally approaching a point — and a smaller light source produces see. How low? At mid-totality in Salem, Oregon, Arcturus will sit a better-defined shadows. Be scant 2° above the horizon. To find these numbers sure to check your own from your location, you’ll need shadow occasionally. A few what’s often referred to as minutes before totality, it will planetarium software. One be razor-sharp. such program is called During that most awesome TheSKY by Software Bisque. time called totality, you’ll want In “Location,” enter your latito concentrate on the Sun’s tude and longitude (or your corona. It’s safe to look at the city/town name, if that’s one of corona without any filter, so the choices). Then set the you’ll probably switch between “Date” for August 21 and the looking with just your eyes (for “Time” for the middle of the the widest view) to checking it eclipse from your planned out through binoculars. viewing location. But step back a bit. At about Clicking on “Venus,” 85 percent coverage, either you “Sirius,” and other objects will or someone you’re with will give you their altitudes and see Venus 34° west-northwest of the Sun. Venus pops out azimuths. I’ll say more about first because, after the Sun and these later. To find each the Moon, it’s the brightest object’s distance from the Sun This is the author’s intended setup on August 21. Nine interlocking foam tiles object we ever see in the sky. If it’s an early using the displayed chart, first click on the form the platform for arrows pointing sighting, or if the person first saw Venus Sun, then click on the object. (Make sure to the positions (azimuths) of Venus (V), through binoculars, the sky will still be you set your chart size to show both Sirius (S), Jupiter (J), and Arcturus (A) at pretty bright, so you’ll probably also need objects.) The software will then tell you the mid-eclipse from St. Joseph, Missouri; a fifth arrow orients the base to north binoculars to locate it. Once you find it distance — either in degrees, minutes, and (N). Each arrow is 12 inches (30.5 centiwith your naked eyes, you’ll see it consisseconds or in decimal degrees — between meters) long with a 2-inch-wide (5.1cm) tently until well after totality ends. the points you’ve chosen. shaft and a head base 3 inches (7.6cm) wide. The altitude of each object will be Jupiter may be a different story. It lies Here’s my plan, which you can see in added to its corresponding arrow prior 51° east-southeast of the Sun and blazes at this story’s main image. I have marked a set to the event. During assembly on eclipse magnitude –1.8. Rather than trying to figof floor mats with the cardinal points day, the author will carefully drive two ure out that distance and direction from (north, south, east, and west) and then thin, 6-inch-long nails through the head and tail of each arrow so they don’t blow the Sun, note that, from where I’ll be in added arrows to show the locations of away or become accidentally misaligned. St. Joseph, Missouri, Jupiter will stand 23° objects I want to target during totality. I Other nails will hold the base tiles in above the east-southeastern horizon at midchose interlocking “anti-fatigue” mats that place on the ground. ASTRONOMY: WILLIAM ZUBACK; COMPASS, TOP LEFT: © DMSTUDIO | DREAMSTIME.COM eclipse. Start looking for the giant planet can cover an area however large you choose. 52

A ST R O N O M Y • AUG UST 2017

N I’ve seen them used for yoga, but my arrow is perpendicular to the edge of the wife and I use them in our workshop tile. Then just label this arrow with a for foot relief. Each tile measures capital letter N — north — in white Vega 2 feet (61 centimeters) square. paint or with a white stick-on letter. I bought nine of them. Now let me detail the Jupiter I chose yellow tiles arrow. You’ll also use this procebecause I want the markers dure for any other objects you Capella to really stand out. For choose to label. By this point those, I’ve chosen to make you’ve used your chosen softthem from ⅛-inch-thick ware to calculate the azimuth Betelgeuse black poster board because of each object at mid-totality. E W Arcturus I didn’t think paint would Azimuth is the number of Mars Venus adhere well to the tiles. degrees, from 0 to 360, it Rigel And as for coloring in takes to reach the object startProcyon Regulus Sun Jupiter appropriate-size arrows ing at north and heading Sirius Spica with markers . . . yeah, I don’t through east. So, due east has an think so. Instead, I cut arrows azimuth of 90°; south is 180°; west is 270°, and so on. Using out and attached them with TheSKY, I find that, at mid-totality, nuts and bolts. the azimuth of Jupiter at Rosecrans At this point, you may be thinkMemorial Airport in St. Joseph, Missouri ing, why do you need the tiles? Can’t S (and only there), is 122°. you just figure out a way to stick the So, you’ll need to cut out an arrow and arrows in the ground? Sure. But I want my label it “Jupiter,” or “J,” or whatever. To posi“map” premade so I don’t have to fool At the moment of greatest eclipse, the Sun will share the sky with several bright tion it, find the center of the center tile, and around aligning every arrow on eclipse day. celestial objects. Stars that may become mark it with a dot — this is why I’m includTime then will be intensely valuable, and visible include Regulus (magnitude 1.3) ing the center tile for now. Once you conmore so because I’m hosting the event. I 1.3° east of the eclipsed Sun (certainly nect all the tiles, you’re defining the line want to pull this setup out of my trunk, through binoculars), Sirius (magnitude from the central point through the tip of plop it on the ground, connect the pieces, –1.5) 57° west-southwest of the Sun, and Arcturus (magnitude 0) 61° west of your northern arrow as due north, or azimake a single alignment, and that’s it. the Sun. Note that from northwestern muth 0°. This will be your starting point. The alignment I’ve chosen is, as you states, Arcturus will be too low to spot. Carefully use a protractor to help you may have guessed, north. And I can do that The same will be true for Sirius from draw a line along the angle of Jupiter’s aziwith any number of smartphone apps that southeastern states. Visible planets muth from your location. Try to be as accuemulate a compass. Some of them offer an include Venus (magnitude –4.0) 34° west-northwest of the Sun and Jupiter rate as possible as you position the middle incredible number of features. All I need, (magnitude –1.8) 51° east-southeast of of the Jupiter arrow along the line. Oh, and however, is an accurate rendering of north. the Sun. Mercury (magnitude 3.3) and if an arrow crosses one of the connecting My tile layout is as follows: Tile #1 is top Mars (magnitude 1.8) will be too faint edges, it’s your call on which tile you posirow middle. Each row will have three panto spot by eye. ASTRONOMY: RICHARD TALCOTT AND ROEN KELLY tion it. Lay it out and see what works best els. Tile #2 is top row right; Tile #3 is center for you. Then repeat this procedure for any row right; #4 is bottom row right; and so other objects whose positions you want to on clockwise around to Tile #8, which is identify during the eclipse. top row left. I do have a ninth tile, but I haven’t decided whether Don’t get too carried away. My tiles have only five arrows: to use it or not. Leaving the center slot empty means that anyone Jupiter, Sirius, Arcturus, Venus, and north. I’m including Venus standing there won’t be shifting the mat’s position each time they not because it’ll be hard to see as the light fades, but because I move their feet. want to try to spot it as far before totality as I can. For that reason, The tiles can sit atop grass, dirt, or gravel. Hopefully, I’ll be I plotted its position a half-hour before totality. able to find a nice flat spot that doesn’t have much in the way of TheSKY also gives the altitude (degrees above the horizon) of tall grass. I’ll secure the tiles with as many spikes (large nails) as each object. I will write that in large print on the corresponding necessary, but at least one per tile. arrows to help me find them more easily. Now here’s how I worked out the positions. I assembled all This project has one main purpose: to help you best utilize nine of the tiles on the floor of my shop. You’ll understand why your time on eclipse day. It takes little effort to complete, doesn’t I’m using the center one in a minute. The first thing I do is place one poster board arrow at the exact cost an arm and a leg, and will ensure you don’t miss any of the celestial objects you want to spot during the eclipse. top center of Tile #1, pointing outward. Use whatever arrow size appeals to you. Mine are 12 inches (30.5cm) long with a head base Michael E. Bakich is a senior editor of Astronomy. 3 inches (7.6cm) wide. Do make sure, however, that this initial W W W.ASTR ONOMY.CO M

Astronomy’s

Viewing the upcoming eclipse is all about totality. Here’s how to position yourself under the Moon’s inner shadow. text by Michael E. Bakich; maps by Michael Zeiler

The next 12 pages show — in minute detail — many of the locations within and near the zone of totality. For this eclipse, that path averages 67 miles (108 kilometers) wide. Within it are one large city (Nashville), several medium-sized cities, and many small towns. Our goal is to help you decide which destination is best for you, and determine whether your chosen location even offers a view of totality. If you’re a first-time eclipse chaser, consider a spot near the center line, the track where totality will last the longest. As you move closer to the northern or southern limit of the Moon’s shadow, the length of time the Sun remains covered shrinks to zero. We realize many people will not be able to view totality — which falls on a Monday — because of work, school, or other commitments. But if you can travel to where darkness in the daytime will occur, you owe it to yourself to experience it at least once in your life. Truly, where solar eclipses are concerned, it’s all about totality.

A trip along the center line You might wonder where in the United States totality begins. The Moon’s umbra, after sweeping eastward across part of the Pacific Ocean, makes its initial landfall in Oregon. If you want to be the first person to experience totality in the continental U.S., be on the waterfront at Yaquina Head, Oregon (just north of Newport), at 10:15:51 a.m. PDT. There, the total phase lasts 1 minute, 59 seconds. The umbra remains in the state a bit more than 11 minutes. For those in Salem, totality will begin at 10:17:21 a.m. and will last for 1 minute, 54 seconds. 54

A ST R O N O M Y • AUG UST 2017

Next, the center line takes roughly 12 minutes to cross Idaho, entering the state just before 11:25 a.m. MDT and leaving just before 11:37 a.m. Idaho Falls gets 1 minute, 50 seconds of totality. But if you drive north on U.S. Highway 20 to the center line just south of Rexburg, your time under the umbra will increase to 2 minutes, 18 seconds. An extra 28 seconds may not

MEET THE MAPMAKER Michael Zeiler is a technical writer at the Environmental Systems Research Institute. He helped develop the popular ArcGIS geographic information system for MICHAEL ZEILER creating maps and compiling, analyzing, and sharing geographic information in database format. He has written seven books on geographic data modeling. He began making eclipse maps in 2009, when he wanted one for an eclipse cruise. At the time, no existing eclipse maps had lines of latitude and longitude, so he made his own and brought it aboard ship. It proved to be a big hit, and he’s been making eclipse maps ever since. Zeiler runs GreatAmericanEclipse.com with his wife, Polly White. As he says, “She’s the business brains, and I develop the maps and animations.” He has seen eight total solar eclipses since 1991. His favorite? “Like your children, you love them all,” he says. “But I’d say the one in Svalbard on March 20, 2015, was the best.”

sound like it’s worth the effort. It is. No matter how long totality lasts for you during the 2017 eclipse, it won’t be long enough. Next up is Wyoming, where the umbra dwells until just past 11:49 a.m. MDT. Grand Teton National Park is sure to be popular. With the Sun 50° high at totality, you can bet photographers will capture it above some gorgeous earthly terrain. Locals might head to Riverton because the center line passes between it and Boysen State Park. Take state Route 789 north out of town, find a nice place off the road, and enjoy 2 minutes, 24 seconds of totality. The largest Wyoming city to be rocked by totality is Casper. People headed there will experience 2 minutes, 27 seconds of totality. If you’re not into crowds, head east to Glendo, Glendo State Park, or Glendo Reservoir right along Interstate 25. At 11:46:55 a.m. MDT, the center line of the eclipse reaches the Nebraska border. When the Moon’s shadow enters Nebraska, it’s Mountain Daylight Time. One-third of the way through the state, however, it changes to Central Daylight Time. Please remember this if you’re headed to Nebraska. Totality along the center line ends in Nebraska at 1:07:19 p.m. CDT. The center line hits the northeastern corner of Kansas at 1:04 p.m. CDT and enters Missouri a scant two minutes later. Small towns near the Kansas center line will enjoy nearly the longest possible duration of totality; in Hiawatha, it will last 2 minutes, 38 seconds. The tiny burgs of Troy, Wathena, and Elwood will get an extra second over that. I’ve already heard a few humorous remarks related to people being trapped in a town south of the center

line for the eclipse: Leavenworth, the site of the United States Penitentiary, gets 1 minute, 41 seconds of darkness. Insert joke here. Finally, at 1:06:16 p.m. CDT, the Moon’s dark inner shadow arrives at eclipse central: Missouri. Two huge metropolitan areas — Kansas City and St. Louis — lie along the path’s limits, so millions of people will experience darkness in the daytime by virtue of their hometown. Although half of each city lies in the path, no part of either is on the center line. But lots of towns lie in the umbra’s path through Missouri, as well as two other sizable cities: St. Joseph and Columbia.

Missouri and the Southeast To avoid crowds, head southeast from St. Joseph along the 20-mile stretch of U.S. Route 169 to Gower. You’ll experience 2 minutes, 39 seconds of totality all the way. Plattsburg, Lathrop, and Lawson all enjoy the same duration. If you head east from St. Joseph along U.S. Route 36, you’ll have a bit more than 2½ minutes of totality at the intersection with state Route 33. Marshall and Boonville, which sit a bit closer to the center line, each get 2 minutes, 40 seconds of totality. Then it’s Columbia’s turn. While the city just skirts the center line, students and instructors at the University of Missouri can gaze safely at the eclipsed Sun for 2 minutes, 36 seconds. For three more seconds of darkness, head south to Rock Bridge Memorial State Park. And you’ll enjoy 2 minutes, 40 seconds of totality at Columbia Regional Airport. Other towns in eastern Missouri that receive about 2 minutes, 40 seconds of darkness are New Bloomfield, Chamois, St. Clair, Lonedell, De Soto, Olympian Village, and Ste. Genevieve. At 1:19 p.m. CDT, the shadow’s midpoint is fully in the Land of Lincoln, and only about a minute passes before totality begins above the point on Earth that will enjoy the longest duration of totality: 2 minutes, 41.6 seconds in and around Giant City State Park near Makanda, Illinois. The center line leaves Illinois at its Ohio River border with Kentucky at 1:24:43 p.m. CDT. Totality for that state starts two minutes earlier and lasts until nearly 1:29 p.m. Kentucky’s highlight town is Hopkinsville, with 2 minutes, 41 seconds of totality as the eclipse’s midpoint passes to the northwest. Roads into town are good. Interstate 24 passes 5 miles south of town, and an extension from it leads into Hopkinsville. Other tiny but terrific spots in Kentucky west of Hopkinsville include Hampton,

Tiline, Fredonia, Kuttawa, Princeton, and Cerulean. Favored towns south and east include Pembroke, Trenton, Elkton, Guthrie, and Adairville. Fort Campbell, near the Tennessee border, enjoys 2½ minutes of totality even though it’s well off the center line, and Franklin sees 2 minutes, 25 seconds of darkness. The center line crosses the Tennessee border around 1:26 p.m. CDT. Nashville, which is home to 601,000 people and has a metro area of nearly 1.6 million, is the largest city fully in the shadow’s path. That said, it is not on the center line. From downtown, viewers will enjoy a second or two under 2 minutes of totality. Die-hard shadow-chasers should head northwest to Springfield, north to White House, or northeast to Gallatin, where they’ll be rewarded with 41, 42, and 42 extra seconds of totality, respectively.

The entire city of Greenville lies on the path, although residents might think about heading south on Interstate 85 to net an extra 20 to 25 seconds of totality. Some options include Walhalla, Clemson, Central, Pendleton, Liberty, Northlake, Centerville, Anderson, Williamston, Belton, and Honea Path. Then it’s Columbia’s turn — the other Columbia. The whole city of 129,000 lies in the shadow’s path. So does its metro area, which claims 794,000, according to the 2010 U.S. Census. If you’re downtown, you’ll revel in 2 minutes, 30 seconds of totality. Those at the city’s north end will lose four seconds, and people who position themselves at the southern tip will gain five seconds. Red Bank, Gaston, and St. Matthews each receive 2 minutes, 36 seconds of darkness. If you’re in McClellanville, one of the last inhabited

MAGNITUDE VS. OBSCURATION Just about every eclipse map you’ll see lists the partial percentages in terms of magnitude. That’s the percentage of the Sun’s diameter the Moon covers at maximum eclipse. We, instead, are using obscuration. It is the percentage of the Sun’s total surface area covered at maximum. An example will help illustrate the difference. Let’s say we observe a partial eclipse where the Moon covers half the Sun’s diameter. In this case, the magnitude of the eclipse equals 50 percent. However, the amount of obscuration is only 39.1 percent. For a total solar eclipse, the maximum obscuration always equals 100 percent. You really can’t cover more than 100 HOLLEY Y. BAKICH/NASA percent of the Sun’s surface. The magnitude, however, can range anywhere from 100 percent, which astronomers designate as 1.0000, to a bit more than 108 percent, or 1.0805 (the magnitude of the total solar eclipse that will occur July 16, 2186). For the August 21 eclipse, the magnitude will be 1.0306.

Other great destinations include Castalian Springs, Hartsville, Lebanon, Carthage, Sparta, Spring City, Evensville, Ten-Mile, Athens, Sweetwater, and Englewood. And please remember: Just past the midpoint of the Volunteer State, the time zone changes to Eastern. The center line crosses the western tip of North Carolina from just past 2:35 p.m. EDT until not quite 2:39 p.m. And although there are only small towns near the center line, all of them will enjoy more than 2½ minutes of totality. Next, the umbral center line just grazes Georgia. The best location will be Clayton, with 2 minutes, 37 seconds of totality. Hiawassee and Lakemont see just nine fewer seconds of darkness. Finally, it’s South Carolina’s moment in the shadow. Totality starts at 2:36 p.m. EDT.

spots on land for the eclipse, you’ll relish 2 minutes, 32 seconds of totality. Another large city, Charleston, also lies under the Moon’s dark shadow. Residents in its northern regions will experience about 2 minutes of totality while those at the city’s southern limits will have 1 minute, 30 seconds to watch the Sun’s corona. The last land contact of the center line happens at 2:49:08 p.m. EDT at Cape Island. Totality here lasts 2 minutes, 34 seconds. After that, the center line moves into the Atlantic for another 1 hour, 13 minutes, 30 seconds. Then the total solar eclipse of August 21, 2017, passes into the history books. Michael E. Bakich is a senior editor of Astronomy. He’s also the author of Your Guide to the 2017 Total Solar Eclipse. W W W.ASTR ONOMY.CO M

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WHAT DO THE SYMBOLS MEAN?

Mt Rainer National Park 101

Rather than taking up room on every map and covering up locations of potential interest, here is a single key, applicable to all maps.

Northern limit of totality Center line

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Ketchum

Caldwell

11:30 A.M . MDT 1,970 m Hailey ph

Boise Nampa

20 20

Rigby

Idaho Falls

20 26

Craters of the Moon National Monument and Preserve

Shelley

11:33 A .M. M 1,901 m DT ph

Blackfoot

Mountain Home 26 91 26

Chubbuck

Pocatello Jerome 93

Rupert

Twin Falls

Burley

84 91 36

City of Rocks National Reserve

N E VA D A

191 15

U TA H

Logan Golden Spike National Historic Site

Brigham City

Ogden 0

60 Miles 15 80

Bountiful Elko

Salt Lake City

Spring Creek 80

Park City

191 3

Billings 90

Bozeman 87

Laurel

Livingston

212

Bighorn Canyon National Recreation Area

310

191 212

Yellowstone National Park

Powell

Sheridan

310

Cody

20 14

16 20

89 287

Worland 89

Felt Alta

Grand Teton Moran National Park

2m21s

Thermopolis

2m22s

Jackson

2m23s

26 26

2m24s

Hoback 26

Lysite

Crowheart

Bondurant

2m25s

Alpine 287

11:36 A .M. M 1,861 m DT ph

Kinnear 26

Riverton Arapahoe Boulder Flats

Arminto

2m26s

Hiland

189

11:39 A.M. 1,805 MDT mph

Antelope Hills

Powder River

Fort Washakie

Homa Hills

2m27s 26

Casper

Lander

2m28s

Bessemer Bend

789

Alcova 287

W YO M I N G

191 89

11:42 A.M 1,740 . MDT mph

11:45 A.M 1,697 . MDT mph Fossil Butte National Monument

287 30

Rawlins 80 30

Rock Springs 189

Green River 80

Laramie Evanston

191

Flaming Gorge National Recreation Area

CO LO R A D O Dinosaur National Monument

Rapid City

Mount Rushmore National Memorial

Newcastle 85

Jewel Cave National Monument

Wind Cave National Park

W YO M I N G

Badlands National Park

Hot Springs

S O U T H D A K O TA

385 18

Antelope Hills

Powder River Homa Hills

Lacreek National Wildlife Refuge

2m27s 20

Casper 2m28s

Chadron 25

Douglas

Bessemer Bend

Shawnee 18 20

2m29s Alcova

2m30s

Agate Fossil Beds National Monument 2m31s

Esterbrook

Marsland

385

11:45 A.M 1,697 . MDT mph

2m32s Wheatland

385 26

2m33s

Huntley

ScottsbluďŹ&#x20AC;

11:4 8 A.M 1,65 . MDT 9 mp h

Rawlins

Whitman

Ashby

Veteran 30

Alliance

Torrington

Scotts BluďŹ&#x20AC; National Monument 26

287

2m34s 85

Lisco 11:5 1A 1,62 .M. MDT 6 mp h

Lemoyne

Laramie

Kimball

Cheyenne

385

80 80

Sidney

287

138

CO LO R A D O

Fort Collins

Sterling 6

Rocky Mountain National Park

Steamboat Springs

Greeley Estes Park

Loveland

385 34

Ogallala

287

Fort Morgan

Longmont

Yuma

Brighton

Boulder 40

Denver

Golden

Vail Edwards

385 285

Carbondale

Castle Rock

25 70

Goodland

Burlington

Aspen 24

60 Miles

Colorado Springs

285 287

Gunnison

Salida

Madison 81

MINN.

Mitchell

Luverne

281

183

Sioux Falls Rock Rapids Winner

Canton 18

18 83

I O WA

Yankton

183

Valentine

Vermillion Cherokee 281

Sioux City

O'Neill

South Sioux City Sergeant Bluï¬&#x20AC;

20 75

Wayne

NEBRASKA

29 Onawa

275

Norfolk

281

Missouri Valley

Tryon

De Soto National Wildlife Refuge

2m35s Broken Bow

Fremont

Columbus

275

Omaha

2m36s

Archer Central City St Libory

North Platte Howard City

12:5 4P 1,59 .M. CDT 7m ph

183

Gothenburg

Grand Island

2m37s

Cozad

Lexington

12:5 7 1,57 P.M. CDT 0m ph

Seward

York

Aurora

Lincoln

81 30

Kearney

281

Inland

2m38s

Hastings

Minden

Nebraska City

Martell

Crete

Lorton

Auburn

Holdrege 136

1:00 1,54 P.M. CDT 5m ph

McCook

Beatrice 81

136

Fairbury

281

2m39s

283 83

1:03 1,52 P.M. CD 5m T ph

183

Norton Phillipsburg

KANSAS

Falls City

136

Bremen Marysville

Baileyville

Hiawatha

81 281 77

Concordia 24

1:06 1,50 P.M. CD 3m T ph

Beloit

Colby

Clay Center

Manhattan

281

Junction City

183

Topeka Hays

Salina

135 156 281

NEBRASKA Seward

Ottumwa

80 34

I O WA

Mount Pleasant

63 218

Lincoln 6

169

275

Martell

Crete

Lorton 136

Maryville

Beatrice 136

136

Auburn

136

Fairbury

Kirksville

Falls City 159 169

Savannah

Bremen

1:03 1,52 P.M. CD 5m T ph

Marysville

Quincy

Hiawatha

Baileyville

24 63

Chillicothe

St. Joseph 73

Cameron 73

169 24

Carrollton

Platte City

Leavenworth 73

Lawrence

Kansas City

1:0 9 1,4 P.M. CD 94 mp T h

Topeka

Overland Park

Independence

Marshall Boonville

Columbia

Lee's Summit

Sedalia

1:1 2 1,4 P.M. CD 80 mp T h

335 169

Emporia

Fulton Steedman Hermann

Lake Mykee Town

California

Florence

JeďŹ&#x20AC;erson City 54

Clinton

Williamsburg

50 50

Warrensburg

Tallgrass Prairie National Preserve

Centralia Mexico

Fayette

Moberly

De Witt

Excelsior Springs

Liberty

Hannibal

Dawn

Faucett

Atchison

159

1:06 1,50 P.M. CD 3m T ph Manhattan

Etterville

1:1 5 1,4 P.M. CD 69 mp T h

MISSOURI 35 54 56

Vichy 63

Rolla

KANSAS

Fort Scott

44 Lebanon

400

Bolivar

Fort Leonard Wood 63

65 77

Pittsburg

160

SpringďŹ eld 59 166

Joplin 166

59 60

Bartlesville

Ponca City

44 60

OKLAHOMA

160

169

75 62 177

Claremore

Tulsa

412

Stillwater

Rogers

Mountain Home

Springdale 412

412

Broken Arrow

167

Fayetteville 69

ARKANSAS

44 62

Muskogee 40

Van Buren

60 Miles

Fort Smith

Cuba

Kankakee 31

Monmouth Galesburg

Huntington

39 24

Burlington 24

Logansport

Peoria

Marion

Kokomo

Macomb

Chautauqua National Wildlife Refuge

136 136

Bloomington

155

Lafayette

Frankfort

136

Lincoln

Danville

Champaign

Anderson

Urbana 45

Carmel 69

41 150

Decatur

Springﬁeld

Jacksonville

Indianapolis

Plainﬁeld 51

Greenwood

Mattoon

Charleston

Terre Haute

ILLINOIS 55

Shelbyville

Franklin

Bloomington Columbus

150

Jerseyville Eﬃngham

INDIANA Seymour

70 231

Warrenton

St. Peters

Olney

O'Fallon

Chesterﬁeld

St. Louis

270

Washington 50 Vincennes

Washington

Belleville

44 Beaufort

Centralia

Oakville

St. Clair House Springs Lonedell

Pinckneyville Du Quoin

Ste. Genevieve Chester

Potosi

Benton West Frankfort

Knob Lick

Fort Knox Henderson

60 31

Murphysboro

Perryville

164

Evansville

Oraville

Park Hills Farmington

64 Sparta

Harrisburg Carrier Mills

Marion

Carbondale

Owensboro

Jackson

Burna

24 Villa Ridge

Metropolis

Hickory

Poplar Bluﬀ

160

55 67

Gilbertsville

Dunmor

Gracey

Paragould

Woodlawn Cunningham

Moss Bethpage Springﬁeld

Gallatin

24 Paris

1:2 7 1,4 P.M. C 47 D mp T h

155

Hendersonville

Nashville Antioch

Dickson

Brentwood

Dyersburg 63 51

Jonesboro

Humboldt

Milan 31

Jackson

Brownsville Covington

Columbia 412

Memphis

43 64

Lancaster

231

Smyrna

Smithville

Murfreesboro 70 1:3 0 P. 1,4 M. C 47 mp DT h

Elmwood 40

Shelbyville

Scottsville Adolphus

Clarksville

TENNESSEE 412

Russellville 31 231 Franklin

Martin 49

Glasgow

Rockﬁeld

Union City

Bowling Green

Land Between the Hopkinsville 68 Lakes National Herndon Recreation Area Fort Campbell North Murray

Mammoth Cave National Park

231

Browder

Graham

Cerulean

Benton

1:2 4 1,4 P.M. C 49 D mp T h

Madisonville Dawson 69 Springs Princeton

641

Lovelaceville

Sikeston

Marion Crayne

Bandana Paducah

Cairo

Eleven Point National Wild and Scenic River

431 62

1:2 1 1,4 P.M. C D 54 mp T h

KENTUCKY

Sullivan Tolu

Grantsburg

Cape Girardeau

Ozark National Scenic Riverways

Tunnel Hill

Wolf Lake Anna

Patton

Uniontown

Louisville

Mount Vernon Red Bud

De Soto

1:1 8 1,4 P.M. C D 60 mp T h

Jasper

Waterloo

Festus

Sullivan

150

Mount Carmel

Tullahoma 65

McMinnville

Bowling Green Russellville

421

KENTUCKY

Scottsville

Adolphus

Springﬁeld

Carthage

Hendersonville

Nashville

Cookeville Monterey

321

40 Smithville

Smyrna

321

Grandview

2m40s

McMinnville

Farragut

Loudon 321 Maryville

127

Sweetwater

321

Asheville

Great Smoky Mountains National Park

Madisonville

Athens

Englewood 75 Etowah Cokercreek Soddy-Daisy 2:3 Hopewell 3 1,4 P.M. E Cleveland Delano

Tullahoma 41

Chattanooga

D mp T h

441

Lake Santeetlah

2m39s

Epworth 76 72

2:3 6 1,4 P.M. E 51 D mp T h

Toccoa Cornelia

Newberry

2:3 9 1,4 P.M. 58 EDT mp h

411

2m37s

Mount Carmel

Saluda Johnston 1

25 2:4 2 1,4 P.M. 67 ED mp T h

Carrollton

Birmingham

Augusta

Talladega Peachtree City Griﬃn Alabaster

431

ALABAMA

Aiken

Hoover

Lake Murray of Richland

Athens

Atlanta

Jenkinsville

Greenwood

Center Point

Blair

Mountville 25

Sandy Springs

Marietta

Laurens 176 Clinton

2m38s

85 441

Roswell Gadsden

Union Enoree 385

Honea Path

Hartwell

985

575

411

Fair Play Anderson

Gainesville

Cullman

Moore

Williamston

Spartanburg

Gantt

441

Rome

Easley Clemson

Westminster

Albertville

Sautee

Marietta Wellford

Greenville

178

411

176

Sunset

Mountain Rest

Gastonia

Rabun Gap Lakemont

Dalton

431

276

Whittier

23 Topton Andrews Franklin 64 Marble 19 Otto Cashiers

Huntsville

Cherokee

Dunlap

231

129

Tallassee Dayton

Shelbyville 41

Knoxville

40 Rockwood 70

1:3 Bradyville 0 1,4 P.M. C 47 D mp T h

NORTH CAROLINA

Oak Ridge

Crossville

Sparta

Murfreesboro

221

Johnson City

Morristown

Clarkrange

421

Brentwood

Wheeler National DecaturWildlife Refuge

Kingsport

TENNESSEE

Rickman

Buﬀalo Valley

Antioch

Athens

Bristol

Monroe

Gallatin

Cumberland Gap National Historical Park

Moss

Lafayette

Columbia

Middlesborough

2m41s

119

231

Franklin

Allensville

Mammoth Cave National Park

231

LaGrange

GEORGIA

Piedmont National Wildlife Refuge

Milledgeville

41 25

Alexander City

Macon

31 280 80

301

185

Auburn

280

Dublin

Warner Robins Selma

Columbus

Prattville

Montgomery

Statesboro

221

65 23 25

280

Americus

280 280

Fort Stewart 75

Hinesville

23 1

17 95

Albany

60 Miles

Dothan

Moultrie

Waycross

Fort Frederica National Monument

Roanoke

Petersburg 77

VIRGINIA

Fishermans

Hampton Island National Wildlife Refuge

Newport News

Norfolk

460

221 220

Portsmouth Martinsville

Chesapeake

Danville

1 15

Great Dismal Swamp National Wildlife Refuge

Roanoke Rapids

220

158 21

158

17 158

Henderson

311

95 158

301 421

Virginia Beach

Winston-Salem

Greensboro

401

High Point 77

Burlington Chapel Hill

Durham

Rocky Mount

85 73

421 70

264

Wilson

Raleigh

Wright Brothers National Memorial

Greenville

220

Sanford 70

Concord

Cape Hatteras National Seashore

401

Goldsboro

Charlotte

Kinston

117

220

Fort Bragg 1

421

Fayetteville

40 17

Havelock

301

Rock Hill

264

601 52 301 95

Jacksonville

SOUTH CAROLINA

Lumberton

Cape Lookout National Seashore

421 301

Winnsboro

74 76

LugoďŹ&#x20AC;

Florence

Wilmington

701

Columbia Hopkins

421

Oswego 301

Sumter Congaree National Park

378

New Zion Manning

Cades

321

701

Orangeburg

Atlantic Ocean

Myrtle Beach

Kingstree

2m36s

Andrews

Pineville

Bamberg

Georgetown

176

2:4 5 1,4 P.M. 76 ED mp T h

Dorchester Moncks Corner

2m35s

Summerville Awendaw

Johns Island

Mount Pleasant

2m34s

Charleston 278

2:4 8 1,4 P.M. 89 ED mp T h

2m33s

Hilton Head Island

Savannah

2m32s

Wilmington Island

Wassaw National Wildlife Refuge

2:5 1 1,5 P.M. 03 ED mp T h

Maps by Michael Zeiler, GreatAmericanEclipse.com Predictions by Fred Espenak, eclipsewise.com Computations by Xavier Jubier, xjubier.free.fr Umbral ďŹ gures by Ernie Wright, svs.gsfc.nasa.gov Maps built with ArcGIS software by Esri.com

2m31s

2:5 4 1,5 P.M. 18 ED mp T h

2m30s

Taking video of your eclipse experience is easy. All you need is a digital camera and an adequate memory card. You can add a tripod to achieve the viewpoint you want and ensure stability. PIXABAY: WWW.PIXABAY.COM

S E I G E T A R T S O E VID Y A D E S P FOR ECLI

s I’ve counseled probably a million times: Don’t photograph the eclipse. This tip — specifically directed at first-time eclipse viewers — may sound strange because I’m the photo editor of the bestselling astronomy publication on Earth. But no picture will capture what your eyes will reveal during the eclipse. Trust me, I’ve seen them all. Only the top 1 percent of the top 1 percent of photographers have ever come close. And you — with your point-and-shoot pocket camera, off-theshelf digital SLR, or (ugh!) cellphone — are not one of them. (No offense meant.) And remember, this eclipse will last, at most, 161 seconds. That’s it, my friends. If

A ST R O N O M Y • AUG UST 2017

Forget the point-and-shoot option — video mode is your camera’s most valuable feature on August 21. by Michael E. Bakich

your camera isn’t acting as expected, you’re going to lose valuable time adjusting it. So just watch. You won’t be disappointed. What I’m going to say next might sound like the exact opposite advice: Why not capture your eclipse experience on video? Here’s the difference. Snapping photographs takes constant monitoring from one shot to the next. But recording the memory of you and your loved ones experiencing an

eclipse takes just starting the camera recording before totality and stopping when you feel like it afterward. For any video projects during eclipses, I use common point-and-shoot cameras, all of which seem to do a good job recording video.

Dark, camera, action! The simplest video project you can perform is to record the darkening during the lead-up to totality. It requires just your camera (one that records video) and a tripod. And, honestly, you could get by even without a tripod. I have used this setup for the past half-dozen or so total solar eclipses I’ve experienced, and always felt glad afterward.

When I say “simplest video project,” I mean just three easy steps. First, determine your “spot” for viewing the eclipse. It may be with your spouse, family, friends, or alone with your telescope, but you’ll need to stake out an area well before the eclipse begins. Second, move your camera on its tripod far enough away from where you’re set up so that it just frames you or your group completely. From this point onward, the camera will be facing directly away from the Sun’s position at mid-eclipse. Third, begin recording video at a time you’ve decided on in advance. I have used either 15 or 10 minutes prior to totality. Let the camera run an equal amount of time after totality, then stop recording. You will have a video record of the darkening (and subsequent brightening) that occurred during the most dramatic part of the eclipse. If your camera also records sound when in video mode, you’ll have captured your reactions, and probably those of people around you, to watch or share with others whenever the mood strikes you. I have three important notes to add to these instructions. First, make sure your camera isn’t set to compensate for decreasing light levels. You want the scene to darken; check the camera’s instruction manual to learn how to change the setting. Second, make sure your camera has enough memory to record 20 to 30 minutes of video. Some cameras will display how many minutes are left on the memory card, or some such message, when you begin video recording. Others provide this information in the instruction manual, which will say something like, “If you use a 16GB memory card, you can record X minutes of video.” If your camera does neither, then do this: At least a month before the eclipse, charge the battery, start recording, and see how long it will go before your memory card fills up. If it’s still going after half an hour, you can stop. That’s long enough. Finally, make absolutely sure the battery you’re using is fully charged before you begin — and the spare battery, too. This detail is easy to overlook.

Is it getting cooler? OK, that project was easy enough. Want another? Here’s how to record the temperature drop at your location during the eclipse. You’ll need a digital thermometer and a digital watch or clock. An analog mercury thermometer also will work, but the temperature readings won’t be as precise. Likewise, an analog watch or clock will work, but discerning the time won’t be as quick. If you go with a digital thermometer, make sure its display doesn’t shut off after a certain amount of time; 10 minutes is the usual amount. One benefit of this project is that you don’t need a tripod. You can set the three components on a table, a

Total solar eclipses cause temperature variations as the Sun disappears and reappears from behind the Moon. One of the simplest video projects you can undertake involves pointing your camera at a thermometer and a timekeeping device and hitting record. HOLLEY Y. BAKICH

board, or, in a pinch, directly on the ground. If you can shade the thermometer from direct sunlight, the temperature reading will be more accurate. This last tip will apply only to some of you. If your camera has an intervalometer — an internal timer that trips the shutter at preset intervals — use it for this project. You really don’t need a continuous reading of temperature because it won’t change that fast. But if you can set your camera to record a frame every 1, 2, or 5 seconds, the movie you create will be 1/30, 1/60, or 1/150

times the size of a continuous one at 30 frames per second, and it will play back that much faster.

Let the bands play Shadow bands are undulating parallel lines sometimes seen in the few seconds before or after totality. The ultra-thin crescent of the Sun’s disk that forms as the Moon just starts to blot out its light, or as our lone natural satellite begins to move away from the Sun, creates a refractive phenomenon of alternating light and dark lines. Movement of Earth’s atmosphere (in other words, wind) causes them to ripple. Knowing this, and that observing shadow bands occurs infrequently, you might want to see them or, better yet, to photograph them. Here’s a simple way to do that. Mount a video camera on a tripod and point the camera at the ground. Start recording roughly five minutes prior to totality and stop five minutes afterward. It’s as simple as that. All you have to remember is when to start recording. If, in all the excitement, you forget to turn the camera off, ah, so what? You can improve your chances of capturing shadow bands by aiming your camera at a light region of ground. An even better approach: Some observers have stretched out a white sheet or blanket on the ground and pointed the camera at it. If shadow bands appear, this technique will reveal them. Be prepared in case the day is windy, or you’ll likely be chasing your sheet rather than the Moon’s shadow. Have some rocks or other small heavy items to weigh down the edges of the sheet. I suggest a minimum of four weights along each edge — not just on the corners. Later, you can use a simple video editor to cut out the excess before and after the shadow bands appear, if they do.

Go for it! You can dream up a bunch of other aspects of the eclipse to record that I haven’t mentioned. Pick the one that sounds best to you, and try it. Hey, you only need to press start and stop. And doing that won’t, in any way, impact your enjoyment of totality. Michael E. Bakich is a senior editor of Astronomy. W W W.ASTR ONOMY.CO M

Mike Reynolds offers tried-andtrue techniques for photographing a total solar eclipse, from cameras to smartphones. by Mike Reynolds

At the moment of totality, the Sun’s “crown,” or corona, appears, and the Sun can be viewed or imaged safely without a filter. This image is a combination of five separate photos taken during the total solar eclipse on March 29, 2006, from the Aegean Sea. ALL PHOTOS BY MIKE REYNOLDS UNLESS NOTED

IMAGINE

the Super Bowl of astronomy: a total solar eclipse. Now imagine all the cameras, smartphones, and camcorders clicking away on August 21, 2017. Finally, imagine how you will take the photo that you will want to share with family and friends: your keepsake of the 2017 Great American Eclipse. The answer will depend on the equipment you use. Thanks to digital imaging, you are likely to capture something on any device you choose, even your smartphone.

Protection first As you will hear over and over again, you need to protect your eyes from the Sun during the partial phases of the eclipse. The same holds true for your imaging 70

A ST R O N O M Y • AUG UST 2017

devices. Make certain your setup includes a proper solar filter that you can remove for totality. You need to strike a balance here: Choose a filter that attaches snugly to the front of your photographic system so it won’t be easily blown off or removed by little hands, yet is simple to remove at totality. This is easier to achieve with smartphones, point-and-shoot cameras, and digital single-lens reflex cameras (DSLRs) with a telephoto lens. For my telescopeDSLR setup, I use Velcro; a strip at the top and bottom of the filter with the reciprocating side on the telescope keeps the solar filter in place, yet easily releases when it’s time for the main event.

Imaging the eclipse begins with understanding safety. Well in advance of the event, choose an appropriate solar filter for your equipment, such as this full-aperture glass filter from Orion Telescopes & Binoculars.

Your equipment options Smartphones and tablets are everywhere. It seems nearly everyone carries a smartphone with an integrated camera, and many models include decent lenses. If you don’t try to push your smartphone’s capabilities too much by zooming in

Imaging your surroundings, including those gathered to observe the eclipse with you, is a great way to record your experience. Your smartphone camera, camcorder, or point-and-shoot camera can capture such a scene easily, or you can pair a wide-angle or normal lens with your DSLR. This series of images was captured during the total solar eclipse on November 13, 2012, from a cruise ship north of New Zealand.

closely on the eclipsed Sun, you can get some reasonable photos of totality with colors around the horizon and people in the foreground. Avoid using your phone’s electronic zoom function at all — it will diminish the photo quality. You might want to turn off your smartphone’s flash to avoid bothering others during totality as well. In addition to serving as still cameras, smartphones are easy-to-use video and audio devices, too — perhaps this is the best use of your smartphone during totality. External auxiliary lenses can add telephoto or wide-angle capabilities to a smartphone camera. Also available are mounts that attach your smartphone to a telescope’s eyepiece. I have seen good success when using this method for imaging the Moon. Easy-to-use point-and-shoot cameras give you the flexibility of a reasonably good optical system and more imaging options. A couple of features separate this type of camera from the DSLR, such as a viewfinder that is separate from the camera’s actual imaging system. However, point-and-shoot cameras do allow you to adjust the camera’s sensitivity and other features; some point-and-shoot cameras include interchangeable lenses. A point-and-shoot camera can image several different eclipse aspects: the horizon and the Moon’s shadow as it approaches, people watching the eclipse, and even the partial phases. But don’t expect those magazine-quality partial and totality photos unless you have a high-end optical system. You will probably want to use the camera’s image stabilization feature and mount the camera on a tripod. When imaging the partial phases, do not forget to put a solar filter over the viewfinder in addition to protecting the camera’s lens. By adjusting your point-and-shoot camera’s sensitivity (ISO), aperture (f/stop), and

exposure length, you can take a variety of exposures showing the Sun’s corona. The DSLR or interchangeable lens camera (ILC) will provide you with the highest-quality images of the eclipse, whether you photograph the changing landscape, the horizon colors, the partial eclipse, or totality. One major benefit of these cameras is the ability to change lenses, from wide-angle to telephoto, and even to use a telescope directly as a lens. Like many cameras, not all DSLRs are created equal; some have basic functions, whereas others will support a variety of options, such as mirror lock-up, automatic exposure bracketing, computer control, and direct image download to a computer or other device. Choose a lens based on what you want to photograph. The 14mm to 50mm wideangle and normal lenses will let you capture the overall scene, from the changing

amount of light as the eclipse progresses to the incoming lunar shadow and horizon colors — the sunset-sunrise effect. The normal lens is also useful for imaging people. Note that these lenses are not effective for capturing the Baily’s beads, diamond ring, chromosphere, corona, or prominences at totality. For those, you will need a telephoto lens or a telescope. Specifically for eclipses, I use a highquality apochromatic (APO) refractor coupled to my Canon EOS 5D Mark II with a T-mount. I use an 80mm APO when traveling overseas, but I will use a 102mm APO this August. Camcorders offer another option for capturing the eclipse. Many people will record time-lapse video of changes in the environment, of the people, of the partial phases, and even of totality. Video also allows you to capture audio around totality, which is often a keepsake of its own.

Eclipse image size 200mm 135mm*

400mm 270mm*

500mm 330mm*

1,000mm 670mm*

1,500mm 1,000mm*

2,000mm 1,500mm*

*Approximate focal length for most crop sensor DSLR cameras.

The right focal length will help you capture the Sun in as much or as little detail as you’d like. This simple figure shows the image size of the eclipsed Sun for various focal lengths, as photographed with both a full-frame and crop sensor DSLR. ASTRONOMY: ROEN KELLY

W W W.ASTR ONOMY.CO M

WHAT CAMERA SETTINGS SHOULD I USE? There are some important camera settings to consider when photographing an eclipse. First, image at the camera’s highest quality: RAW or large JPEG. The higher quality will use up more memory, but it is well worth it. Make certain that your memory card has enough space to hold all of the images you hope to take. I usually set my camera’s ISO to 100 to avoid noise, which appears as graininess on digital images. If you do not have a stable motorized mount, you will need to shoot at a higher ISO.

In addition to imaging the Sun directly during the partial phases of the eclipse, you can opt to photograph a projected image. Pinholes can be artificially created in many ways, such as with a simple straw hat. Sunspotter telescopes also provide a clear, easy-to-photograph projection.

Mounting your equipment There are a number of ways to support your equipment. The simplest is a handheld approach; this works OK for smartphones, tablets, and wide-angle imaging. Remember that as totality approaches, the environment will darken as sunlight decreases dramatically. This makes for longer exposures, thus introducing vibration. Image-stabilized cameras and lenses can take some vibration out of your images. Many will go with an alt-azimuth mount. This type of mount runs the gamut from simple camera tripods to sturdy astronomical mounts. Like most equipment, tripods are available with different features. One such feature is the amount of weight the tripod and tripod head will support. If you want more stability, I suggest stringing a gallon water jug to the middle of your tripod. Astronomical alt-azimuth mounts have become commonplace. They usually feature a dovetail fitting and are heavier than 72

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I manually adjust the length of exposures during totality, since the telescope is at a fixed f/ratio. When shooting an eclipse from a ship, I usually start around 1/8000 second and increase exposures to about 1/30 second. I then

reverse the process, decreasing the exposure length. On land, such as during the 2017 eclipse, you should be able to shoot at much slower speeds with a tracking telescope. I’ll probably shoot as slow as 1 second in August.

FOCUS One of the most important settings is the focus. Poor or soft focus cannot be cleaned up with image-processing software. If you use a telephoto lens, do not use the autofocus setting — if it’s on, the lens will search for the focus point throughout totality, and you will get few pictures, if any. You need to focus in advance, and continue to check the focus as the day warms and then cools in the Moon’s shadow. Achieving good focus is time well spent. — M. R.

most camera tripods. These are easy to use and provide good stability as long as you don’t overweigh the mount. Features may include slow-motion controls or a dual telescope capability that allows you to place two telescopes (or a telescope and a camera, camcorder, etc.) on a single mount. This eclipse offers the opportunity to use an equatorial mount. Although transporting a heavy, large equatorial mount by plane can be challenging to the point of infeasibility, driving with an equatorial mount to your August viewing location should not be an issue. The advantages are obvious: continued tracking during the partial phases and totality. Just make certain you have time to polar align the mount the night before the eclipse, at the latest.

Other useful accessories I always carry with me a number of other accessories and must-have items; I have used every one of these during one eclipse or another, or lent them to others if I didn’t use them myself. I find a remote timer useful. These devices attach directly to a DSLR or connect via Bluetooth. The remote allows you to take photographs without touching the camera — and thus avoid introducing vibrations into the system. Backup camera batteries and additional memory media are essential. I cannot tell you how many times I have seen people stare at their dead camera or run out of space on their memory card right before totality. You do not want to struggle with replacing your camera’s battery or

memory card at second contact when totality commences, so change out these necessities well before this time. You might also want to consider using a battery pack or external power source. I keep a red flashlight handy during the eclipse. As second contact approaches, it will get dark enough that you will need some extra light. If I want to check something — say, a cable connection — the red flashlight gives me that opportunity. Think nighttime observing here. Some like to use a digital audio recorder to document comments, observations, and even photo notes. Others use it to record reminders or a checklist, such as looking for Venus or checking the camera’s available memory. An audio recorder can also capture the excitement that occurs around totality. No matter where I go for an eclipse, I carry a tool bag. I include slotted and Phillips screwdrivers, a jeweler’s screwdriver set, a hex set, pliers, and an adjustable wrench. I also carry a roll of duct tape. I rarely need any of these tools or supplies, but someone else always needs something. I also bring a cover for my equipment, in case of inclement weather. You can go as fancy as a tarp, but a heavy-duty garbage bag will work just as well. Be certain you can attach the cover so it doesn’t blow away. Let’s hope we will not find any use for this item on August 21. How do I keep all this straight? I learned long ago to create a checklist. You don’t want to travel 700 miles from home and realize you left your camera sitting on the sofa.

What to photograph Your first reaction might be to photograph everything! That will probably set you up for failure and frustration, especially if this is your first (or second) total solar eclipse. Even those of us who have observed and photographed a number of total solar eclipses limit the amount we try to accomplish. The partial eclipse can be imaged through your telescope, telephoto lens, or as a projection. Beyond the partial eclipse itself, you can image pinhole projections of the Sun’s shrinking (or growing) disk. Pinholes are created by the interactions of tree leaves or via human-made projectors. The diminishing light, as well as people and your surroundings, all make great subjects. You might also want to image the partial phases with a Hydrogen-alpha or other narrowband solar filter. Right before totality, the mood will become exciting, electric, and frantic. This is a great time to record people and your surroundings; video works best here. You can also image the approaching lunar shadow and the sunset-sunrise effect. Some will also try to image planets and stars, and even those elusive shadow bands that sometimes appear just before totality. As the last solar vestiges disappear, the brilliant second contact diamond ring will appear. There is much debate as to when you should remove your solar filter; some say you should remove it just before the diamond ring, and some say right afterward. I take mine off about 20 to 30

Varying your exposure times during totality allows you to capture the Sun’s inner and outer corona, as well as solar prominences. These two images of the 2012 total solar eclipse illustrate this concept and its effectiveness: The left image clearly shows the Sun’s corona with an exposure time of 1/80 second; the right image shows prominences seen with an exposure time of 1/8,000 second.

seconds before the diamond ring appears. You’ll begin to see Baily’s beads dancing along the Sun’s edge just before the Moon completely covers the Sun. Now the Sun is totally eclipsed! The Sun’s crown — its corona — extends outward. By varying your exposure length, you can image the Sun’s inner and outer corona. Both are magnificent. You may also see solar prominences. Shorter exposures work well for photographing these. You might image the eclipsed Sun, stars, and planets, especially Venus. For those in a location where the Sun’s altitude during totality will not be very high, imaging people in the foreground and the eclipsed Sun in the background can make for a spectacular photo. All too soon, you will see the second diamond ring appear and witness the return of Baily’s beads. Keep imaging; just be prepared to put the solar filter back on your equipment.

Practice makes perfect

The author prepares to photograph the March 29, 2006, total solar eclipse from a ship on the Aegean Sea. HOLLEY Y. BAKICH

Those of us who have successfully imaged eclipses know the importance of checking all of your equipment and planned techniques prior to eclipse day. I check my entire setup and procedures by practicing on the Full Moon. During a Full Moon, it is somewhat dark outside, and it will help you appreciate those nighttime imaging challenges. I also perform several solar imaging sessions for practice. Some eclipse watchers opt to use computer-control software specifically designed for total solar eclipses. This software allows you to input your equipment

specifics, such as lens/telescope and DSLR. It will then control your camera during totality, taking the guesswork out of exposures and eliminating manual operation. Personally, I still prefer the old-fashioned option to manually control my system — maybe I am just too leery of letting go of my eclipse photography. If you opt to let computer software handle your imaging needs, it’s still important to perform at least one practice imaging session prior to the big event. The minutes leading up to totality are not the time to discover that you don’t know as much about your software as you thought you did.

Ready for the eclipse? As we prepare for that exciting day and event, ask yourself one more question: Do I really want to photograph the eclipse? If this is your first total solar eclipse, I would say the answer should be no. Or, at most, plan to take a minimum number of photographs or a limited amount of video. Even those of us who are intensely focused on imaging take time to enjoy the eclipse. Look around before totality and note environmental changes, sky darkening, colors, and the visibility of planets and stars. During totality, take time away from the camera and soak in the event. Catching a great photo is exciting, but taking in one of nature’s most incredible spectacles is even more so. Mike Reynolds is an experienced eclipse photographer who has observed and photographed 18 total solar eclipses. W W W.ASTR ONOMY.CO M

LE T T H E CO U N T D OW N TO

B EG I N Let’s do this all over again in seven years — with two more minutes of totality! by Michael E. Bakich

hat just happened? It’s August 22, 2017. Citizens of and visitors to the United States are abuzz about yesterday’s celestial event. Videos, photos, and social media reports abound, and traffic still isn’t back to normal. But you missed it. Why doesn’t matter. Whether you were serving on a submarine at the bottom of the Pacific Ocean, just awoke in a hospital after a zombie apocalypse, or were hampered by the thickest (and darkest!) clouds anyone ever saw, you failed to experience the awesome wonder of the 2017 total solar eclipse. Now what? Well, you can check various sources to see when Earth will again experience totality. Perhaps you’ll want to plan a trip to South America or Antarctica. I urge you, however, to look carefully at April 8, 2024. That’s when the next total solar eclipse will cross the United States. And although six years and seven months (plus 19 days) sounds like a long time from August 21, 2017, it’s much shorter than the average time between eclipses in a specific 74

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location (330 years in the Northern Hemisphere and 550 years for locations south of the equator).

A few details The length of totality varies from one eclipse to the next. The reason stems from the fact that Earth is not always at the same distance from the Sun, and the Moon is not always the same distance from Earth. The Earth-Sun distance varies by 3 percent and the Moon-Earth distance by 12 percent. The result is that the maximum duration of totality from 2000 b.c. to a.d. 3000 is 7 minutes, 29 seconds. (That eclipse will occur July 16, 2186, so don’t get too excited for it.) While the maximum length of totality during the April 8, 2024, eclipse won’t be that long, it’s still a worthy chunk of time: 4 minutes, 28 seconds. And as with the 2017 total eclipse, everyone in the contiguous U.S. will see at least a partial eclipse. In fact, as long as you have clear skies on eclipse day, the Moon will cover at least 16.15 percent of the Sun’s brilliant surface — that minimum comes at Tatoosh Island, a tiny speck of land west of Neah Bay,

Washington. Although our satellite covering any part of the Sun’s disk sounds cool, you need to aim higher. Likening a partial eclipse to a total eclipse is like comparing almost dying to dying. If you are outside during a solar eclipse with 16 percent coverage, you won’t even notice it getting dark. And it doesn’t matter whether the partial eclipse above your location is 16, 56, or 96 percent. Only totality reveals the true celestial spectacles: the two diamond rings, the Sun’s glorious corona, 360° of sunset colors, and stars in the daytime. To see any of this, you must be in the path of totality. That said, your next goal is to be as close to the center line as possible. The fact that the Moon’s shadow is round means that the longest eclipse occurs at its center line because that’s where you’ll experience the lunar shadow’s full width.

The big day The Moon’s shadow first touches Earth just north of Penrhyn Island, one of the Cook Islands in the South Pacific. That location will experience a 98-percent partial eclipse.

Border crossing Totality first occurs in the United States as the shadow crosses the Rio Grande River at the wonderfully named Radar Base, Texas, which lies in Maverick County. There, totality lasts 4 minutes, 27 seconds. As the eclipse progresses through the Lone Star State, a huge number of people won’t have to travel anywhere to see it. That said, just a few miles’ journey to the center line can increase their duration of totality. San Antonio, Austin, Waco (Baylor University will enjoy 4 minutes, 10 seconds of darkness), Dallas, and Fort Worth all lie under the shadow, although none is on the center line. Still, that’s more than 11 million people who can experience the eclipse with little to no effort. And we’re not even out of Texas yet. The center line then passes through Oklahoma, Arkansas, Missouri, Illinois, Indiana, Ohio, New York, Vermont, and Maine. Those wishing to observe the eclipse from the same location the center line crossed during the August 21, 2017,

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Burlington Syracuse Rochester Cleveland Dayton ASTRONOMY: ROEN KELLY AFTER MICHAEL ZEILER

Seventy-three minutes later, totality first strikes land at Socorro Island, a possession of Mexico. If, for some reason, you choose that location to view the eclipse, be sure to position yourself at the island’s far southeastern tip — you’ll enjoy an extra 34 seconds of totality there. (The span is 3 minutes, 36 seconds.) The shadow’s path covers a few more tiny islands before it encounters North America just southeast of Mazatlán, Mexico. Hey! That city was my base of operations for the 1991 total solar eclipse. Viewers from that location will enjoy 4 minutes, 27 seconds of totality. And if you wish to stay in Mazatlán, you’ll lose only 10 seconds off that span. The greatest duration of totality — 4 minutes, 28.1 seconds — occurs when the shadow reaches San Martín, north of Torreón and roughly half the distance from the coast to the Mexican border with Texas. In fact, the duration of totality along the center line is never more than 1 second less than this maximum during the shadow’s more than 550-mile (885 kilometers) voyage through Mexico.

W Aust aco San in Anto nio

Torr eón Dur ang o

eclipse should head to a location near Makanda, Illinois, which lies just south of Carbondale. A word of warning, if I may: The weather in Illinois in April — and here I’m specifically talking about cloud cover — is a far cry from what it is in August. Your chances of actually seeing the 2024 eclipse increase dramatically as you head to the southwest. Not to mention that you’ll pick up an extra 15 seconds of totality from center line locations near San Antonio. Other cities in the path include Little Rock, Arkansas; Indianapolis; Dayton and Cleveland, Ohio (with northwestern parts of Cincinnati and Columbus under the shadow); Buffalo, Rochester, and Syracuse, New York; and about half of Montréal, Québec, Canada.

Beyond 2024 For those wanting to view a total solar eclipse in the contiguous United States after the 2024 event, it’s a 20-year wait until August 23, 2044, for the next one. That eclipse is visible only in northeastern Montana and a tiny segment of North Dakota. Its greatest duration of totality, 2 minutes, 4 seconds, happens over Canada’s Northwest Territories. At the intersection of the center line and the United States–Canada border, totality is 20 seconds shorter: 1 minute, 44 seconds. The small towns near that point, namely

Longest duration Greatest eclipse

Hogeland and Turner, Montana, experience totalities just a few tenths of a second less. And Chinook, Zurich, Harlem, Dodson, and Malta lose only another second. Three more total solar eclipses track through the contiguous United States in the 21st century. And if 2044’s eclipse disappoints you, you’ll be thrilled by the one that happens less than one year later. The event August 12, 2045, is a truly spectacular cross-country eclipse with totalities lasting 4 minutes, 23 seconds on the Northern California coast to an amazing maximum of 6 minutes, 6 seconds at Port St. Lucie, Florida. The center line of the total solar eclipse on March 30, 2052, lands only on Florida and Georgia, but totality in that small path lasts between 3 minutes, 30 seconds in Savannah, Georgia, and 3 minutes, 44 seconds near Laguna Beach, Florida. The final total solar eclipse whose path intersects the contiguous United States this century occurs May 11, 2078. Like the one in 2052, it also tracks through the southeastern United States. Totality lasts 5 minutes, 17 seconds for those in Nags Head, North Carolina. For those of you who stand beneath the Moon’s umbra this month, no convincing will be necessary to get you to darkness in 2024. It’s a sight you’ll never rate as anything other than awesome. Just be sure to check the weather first. Michael E. Bakich is a senior editor of Astronomy. W W W.ASTR ONOMY.CO M

DIAMOND RING | the effect just prior to or just after totality of a solar eclipse when a small portion of the Sun’s disk plus its corona produce an effect similar to the real-world object it’s named after.

Totality, arcminutes, chromosphere . . . it’s easy to get lost in technical terms. We’re here to help. by Michael E. Bakich

DO YOU SPEAK

MANY TERMS WILL BE batted around during the

APOGEE | the position of the

eclipse — some specific to the event, others astronomical terms that first-time stargazers may not know. This simple dictionary will help you understand the terms people use the most. And to help you visualize the meanings further, we’ve included explanatory illustrations for some of the words and phrases.

Moon or other object in Earth orbit when it lies its farthest from our planet.

ARCMINUTE | also called a minute of arc, an angular measurement that equals 1/60 of 1°.

AZIMUTH | the angular distance from north (0°) to an object measured eastward along the horizon. The azimuth of an object due north is 0°; east is 90°; south is 180°; and a due west azimuth equals 270°. CENTER LINE | the

ALTITUDE | the height, in

APHELION | the position

degrees, of an object above the horizon. The horizon’s altitude equals 0°, and that of the zenith (the straight-overhead point if you crane your head back) is 90°.

of an object in solar orbit when it lies its farthest from the Sun.

ANGULAR DIAMETER

the apparent size of a celestial object measured in degrees, minutes, and/or seconds of arc.

ANGULAR DISTANCE

the apparent distance between two celestial bodies expressed in degrees, minutes, and/or seconds of arc. 76

A ST R O N O M Y • AUG UST 2017

a second of arc, an angular measurement that equals 1/60 of 1 arcminute. So, 1° contains 3,600 arcseconds.

Taking umbrage PENUMBRA | the less dark, outer region of the Moon’s shadow; an observer under the penumbra sees a partial solar eclipse. UMBRA | the dark inner region of the Moon’s shadow; anyone under the Moon’s umbra will experience a total solar eclipse.

midpoint of the width of the Moon’s shadow on Earth; the location for the maximum duration of totality along that width.

Umbra (total eclipse)

Moon Earth Penumbra (partial eclipse)

ASTRONOMY: ROEN KELLY

ARCSECOND | also called

CHROMOSPHERE | the region of the Sun’s atmosphere between its visible surface and its corona sometimes briefly visible just before or after totality as an intense red glow at the Moon’s edge.

CORONA | the shell of thin gas that extends out some distance from the Sun’s surface, normally visible only during totality; corona is the Latin word for “crown.”

FIRST CONTACT

SECOND CONTACT

During a solar eclipse, the moment the Moon makes contact with the Sun; this marks the beginning of the eclipse.

During a total solar eclipse, the moment the Moon covers 100 percent of the Sun’s disk; the instant totality begins.

MIKE REYNOLDS

TAKESHI KUBOKI

DISK | the visible surface of any heavenly body.

FLARE | a sudden burst of particles and energy from the Sun’s photosphere often appearing brighter than the surrounding area.

BAILY’S BEADS | the effect often seen just before and just after totality when only a few points of sunlight are visible at the edge of the Moon, caused by the irregularity of the lunar surface; named after English astronomer Francis Baily, who first explained it in 1836.

HYDROGEN-ALPHA FILTER | a filter that passes only light with a wavelength of 656.28 nanometers (or 6,562.8 angstroms). Such a filter allows you to observe the Sun’s chromosphere, flares, prominences, and more; abbreviated H-alpha filters, these accessories are expensive but impressive.

MAGNITUDE | the amount of the Sun’s diameter the Moon covers during an eclipse; this is not the same as “obscuration.” Michael Bakich is a senior editor of Astronomy.

During a total solar eclipse, the instant totality ends.

During a solar eclipse, the moment that the disk of the Moon breaks contact with the Sun; this moment marks the end of the eclipse.

amount of the Sun’s area the Moon covers during an eclipse; this is not the same as the eclipse “magnitude.”

measurement that equals 1/360 of a circle.

apparent annual path through the stars; the plane of Earth’s orbit around the Sun.

FOURTH CONTACT

OBSCURATION | the

DEGREE | an angular

ECLIPTIC | the Sun’s

THIRD CONTACT

TOTALITY During a total solar eclipse, the length of time between second and third contacts; any instant the Moon covers 100 percent of the Sun’s disk.

ORBIT | the path of one celestial body around another. PERIGEE | the position of the Moon or other object in Earth orbit when it lies its closest to our planet.

PERIHELION | the position of an object in solar orbit when it lies its closest to the Sun.

where the Moon lies between Earth and the Sun and seems completely unlit from our perspective; solar eclipses occur only at New Moon.

NODES | with regard to solar eclipses, the two points at which the Moon’s orbital plane intersects the ecliptic plane; in other words, the two places the plane of the Moon’s orbit crosses the plane of Earth’s orbit; eclipses can occur only near nodes.

SAROS CYCLE | a time period equal to 6,585.3 days between which similar eclipses occur. Each Saros cycle lasts a period of around 18 years, so the 2035 eclipse will have a similar overall path across the sky, though that eclipse will fall over parts of East Asia instead of the United States. SHADOW BANDS | faint ripples of light occasionally seen on flat, light–colored surfaces (like cement) just before and just after totality.

SOLAR TELESCOPE | a PHOTOSPHERE

| the

visible surface of the Sun; where our star emits visible light; the Sun’s disk.

PROMINENCE | a largeNEW MOON | the phase

ASTRONOMY: ROEN KELLY

CONJUNCTION | a point on the sky where two celestial bodies appear to line up; the lineup may be an exact one, like a total eclipse, or it may be a near one, as in the case of New Moon (when our satellite is “in line” with the Sun).

Phases of the eclipse

scale, gaseous formation above the surface of the Sun, usually occurring over regions of solar activity such as sunspot groups; during totality, observers often see prominences seeming to erupt from the dark edge of the Moon.

telescope whose design lets you safely observe the Sun.

SUNSPOT | a temporarily cooler (and therefore darker) region on the Sun’s visible disk caused by variations in its magnetic field.

SYZYGY | the lineup of three celestial bodies; for a solar eclipse, the lineup is the Sun, the Moon, and Earth. UNIVERSAL TIME (UT) |

REVOLUTION | in astronomy, the orbiting of one body around another.

ROTATION | the spinning of a celestial body on its axis; Earth rotates once a day.

also known as Greenwich Mean Time; standard time kept on the Greenwich meridian (0° longitude); astronomers use UT to coordinate the observation of celestial events across the globe. W W W.ASTR ONOMY.CO M

BINOCULARUNIVERSE BY P H I L H A R R I N G TO N

Eclipse time! Get your binocs ready for the biggest event of the year.

t’s finally here — the first total solar eclipse to cross the continental United States in 38 years! Many of us will be traveling to points along the center line to witness the dramatic beauty of totality, hopefully with binoculars in tow. If you ask me, low-power binoculars are the most versatile instruments you can use to take in the full beauty of the Sun’s far-reaching corona during the fleeting moments of totality. Higher-power giants will also show details in prominences whisking away from the solar limb. But binoculars can also be used on any sunny day to monitor solar activity, including the coming and going of sunspots. That’s why I’d like to devote this month’s column to our star, the Sun. Before we begin our journey, however, I must emphasize the critical importance of exercising extreme care. Without proper precautions, an observer may suffer permanent eye damage and even blindness. The Sun’s ultraviolet rays, the same rays that cause sunburn, will burn’s your eyes’ retinas in less than a second. Fortunately, there are two safe ways of looking at the Sun. If you wish to view the Sun directly through binoculars, special solar filters are required. DO NOT use welder’s glass, smoked glass, or overexposed film. They can all lead tragically to blindness. The proper filters are commonly made of specially coated film or glass, and must be securely mounted in front of both objective lenses

A ST R O N O M Y • AUG UST 2017

beforehand. In this way, the dangerously intense solar rays are reduced to a safe level prior to entering the binoculars and your eyes. Never place the filters between the eyepieces and your eyes. Some people prefer to project the Sun through their binoculars onto a screen. I recommend that binoculars be mounted on a tripod or other rigid support. Keep a dust cap over one of the objective lenses to prevent two overlapping images. And never look through the binoculars at any time, not even to aim them. You can align the glasses by adjusting the shadows they cast

A large sunspot group, caused by magnetic disturbances on the Sun, can stand out nicely as viewed with properly filtered binoculars. DAVID HANON

until they are at their shortest. With precautions in place, let’s do some Sun-watching. It’s fun to monitor the constantly changing face of our star. For most, the principal attraction is watching the fluctuating number of sunspots across the photosphere. Sunspots are transient features that result from disruptions in the Sun’s magnetic field. These disruptions block some of the radiation pouring from the Sun’s core. The resulting

A total eclipse, like the one that will happen across the United States this month, is one of nature’s grandest spectacles. JAMIE COOPER

Sunspots often cluster together in groups, making them relatively easy to see with filtered binoculars.

temperature of the affected region is over 2,000 K (3,000° F) cooler than the surrounding photosphere, causing the sunspot to appear darker by contrast. Each sunspot consists of a black central portion, the umbra, and an encircling grayish ring called the penumbra. Sunspots usually range in size from hundreds to thousands of miles in diameter. They typically form in groups, with the largest dwarfing our planet. Just how many sunspots are visible at any moment depends on several factors. It naturally stands to reason that higher magnifications will resolve smaller spots. The number seen, however, also depends on where the Sun is in its current sunspot cycle. Astronomers in the 19th century determined that sunspot numbers regularly oscillate over approximately an 11-year period. Toward the maximum phase of the cycle, which last occurred in 2012, there might be a hundred or so visible; at minimum, the solar disk may appear blank. Observers using high-power binoculars may also be able to detect faculae, brighter areas set close to major sunspots. Faculae give the false impression of being brighter than the surrounding photosphere only because they actually lie a couple of hundred miles above the visible surface. This increased altitude means that they are less affected by the solar atmosphere’s “limb darkening” effect than the photosphere itself.

Faculae are most easily seen near the Sun’s limb, where the contrast between faculae and the photosphere is greatest. Try sketching the solar disk every second or third day over a span of a month. The projection method lends itself very nicely to this. Depending on the size of binoculars used, draw a 3- to 4-inch diameter circle in the center of a piece of paper and attach it to the projection screen. Adjust the binocularscreen distance so that the projected Sun exactly fills the circle. Then, simply trace the exact positions and sizes of the visible sunspots. Be sure to note the four cardinal directions on your observation sheet. Over a period of days, you can watch as the sunspots march across the Sun. With each successive sketch, sunspots will appear to form and change in size and shape as the solar disk spins. From this exercise, you can directly estimate the Sun’s period of rotation in much the same way as Galileo did over 400 years ago. By paying special attention to the exact location of the visible spots relative to each other, it will soon become clear that different latitudes on the Sun rotate at different speeds. Next month, we return to the night, but until then, enjoy the eclipse. And remember that two eyes are better than one.

JOHN CHUMACK

Phil Harrington is a longtime contributor to Astronomy and the author of many books.

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