AstronomyWelcome to by Michael E. Bakich

A supplement to Astronomy magazine

618089 KPC ASY • 03/01/14 SH Sky Chart • 4C • 1 PG S Naked-eye astronomy RIE clear evening when the Sun sets, Starlight, TE the sky darkens and the stars come star bright S Eout. As our local piece of planet Earth As you look at the Y turns away from the Sun and daytime fades , you’ll e M into night, we look out toward the universe. notice that stars dif- th The simplest way to discover the stars is fer in brightness. k S! to begin as the earliest observers began, Astronomers rank c O using just your own two eyes. If this eve- stars on a scale that lo SM ning is clear, why not step outside and spot started with ancient n O a few star patterns? Greek skywatchers. U e C They used six “mag- Getting oriented nitudes.” Current h NEW RESULTS: Planck mission resets the universe’s age t Under the night sky, take a look around. astronomers add f p. 28 o Can you find the Big Dipper in the north? decimals to note OCTOBER 2013 It may be high in the sky and upside-down small steps in bright- The Milky Way glows above Te Waipounamu, the or near the horizon. It’s a bit longer than ness and even negative magnitudes for large southern island of New Zealand. To create Each monthly issue your hand at arm’s length with the fingers bright objects. Just remember that a larger this all-sky image, the photographer combined five 1-minute exposures. TUNÇ TEZEL of Astronomy magazine The world’s best-selling astronomy magazine spread. The Dipper’s stars form part of Ursa magnitude means a dimmer star. is packed with all the tools Major the Great Bear. The two outer stars Every star has a magnitude, but only a in the “bowl” point toward Polaris, the few hundred have names. Many star names apparent only after a few weeks. Typically, you need to get the most TOP 10 North Star. Polaris is part of a come from their place in the constellation they remain visible for months. often from exploring the universe. called Ursa Minor the Little Bear. as described by the ancients. For example, appears bright and red. Jupiter, colored Whether you’re a beginner If you don’t see bears, don’t worry. Con- , which is the Hunter’s left knee, white, is always bright. Saturn, dimmer EXOPLANETS stellations are invented patterns that began means “left leg of the giant” in Arabic. than Jupiter, looks yellow. The outermost or an experienced stargazer, Of nearly 1,000 distant planets found, as pictures in the sky to help early people Each hour, stars move westward about planets — Uranus and Neptune — glow we explore the most unusual remember important myths and legends. as far as your fist held at arm’s length with weakly and belong in binoculars territory. Astronomy can help you enjoy p. 22 Some constellations, such as spring’s the thumb extended. If you look north, fig- Far outshining any planet is the Moon, every minute under the stars! Leo the Lion, summer’s the Scor- ures like the Big Dipper creep around its face mottled with dark lava flows. The pion, and winter’s the Bull, are pre- Polaris like the hands of a giant clock run- Moon circles Earth, keeping one side See COMET ISON historic. They first appeared in records at ning backward. Besides this daily motion turned toward us. It first appears as a thin in October In the past 20 years, astronomers p. 50 have discovered planets unlike the dawn of history. Others were invented due to Earth’s rotation, the constellations crescent in the evening sky. Night by night, anything in our solar system. Capturing the Sun’s atoms more recently. Today, 88 constellations also slip westward as weeks pass. This sea- the lit portion grows. The half-lit point is Your subscription will include: p. 54 cover the sky with no gaps between them. sonal movement reflects Earth’s yearly called First Quarter because the Moon has AND MORE! travel in its orbit around the Sun. completed one-fourth of its monthly orbit. • Stunning images of the universe 10 GREAT Spice up images No one notices the sky changing from At Full Moon, it is completely lit and floods fall binocular Denkmeier’s with Hydrogen- binocular one night to the next. Yet any given star Earth with reflected sunlight. After Full sights p. 58 • The latest in astronomy and space news alpha p. 60 viewer tested p. 64 rises about four minutes earlier each eve- Moon, the lit portion shrinks. When Last • Monthly columns from the best writers ning due to Earth’s orbital motion. Four Quarter Moon arrives, we see it in daytime in the fi eld minutes difference per day means that after morning hours as well as after midnight. a month, stars rise two hours earlier and set After passing Last Quarter, the Moon • Tips for locating stars, planets, and Subscribers also get two hours sooner. Thus, constellations shrinks to a crescent visible shortly before deep-sky objects slowly drift westward throughout the year. sunrise. Then it reappears low in the west unlimited premium content after sunset, and the cycle begins anew. • All you need to know about the latest BONUS: on Astronomy.com! Wandering “stars” skywatching events Planets don’t reappear regularly each sea- Be prepared son the way stars do because planets con- Star-watching is easy, but a few basic prepa- Find us on Facebook Badge CMYK / .ai stantly orbit the Sun. Yet planets always lie rations make it comfortable. Depending on somewhere along a band of constellations the season, you may want a coat and a ski called the zodiac. cap — or insect repellent. Take a lawn chair Subscribe now and SAVE! Two planets, Mercury and Venus, orbit and a thermos filled with hot cocoa or tea. closer to the Sun than Earth. You will see If you have binoculars, bring them them only before sunrise or after sunset. along. But learning your way around the www.Astronomy.com/promo Mercury in particular is hard to spot, being sky goes better if you start with no optical often low in the twilight. (Binoculars help.) aid at all. Constellation patterns are easiest and enter code IK42A Imagine this photographer’s surprise when a bril- liant bolide (an exploding meteor) superimposed The outer planets (which lie farther to find with the wide-field view your eyes Mon.-Fri., 8:30 a.m.–4:30 p.m. CST. U.S. call 1-800-533-6644 itself on her image of an aurora. The bright dot to from the Sun than Earth) move slowly alone can provide. The next four pages will

COVER IMAGES: MATTIAS MALMER/ IMAGING TEAM (SATURN); ADAM BLOCK/MOUNT LEMMON SKYCENTER (SPIRAL GALAXY); GALAXY); (SPIRAL SKYCENTER LEMMON BLOCK/MOUNT ADAM (SATURN); TEAM IMAGING MALMER/CASSINI MATTIAS IMAGES: COVER ASTRONOMERS) AMATEUR THREE WITH SCENE (HORIZON CLARO MIGUEL MOON); (FULL NASA/GSFC/ASU the far left of the meteor is Jupiter. SHANNON BILESKI among the stars, with changes becoming introduce you to each season’s sky. Outside U.S. and Canada, call 262-796-8776, Ext. 661 WWW.ASTRONOMY.COM 3 P21983 A41A1 Explore the spring sky

pring. Finally, it’s warm enough for and it marks the tip even thin-blooded observers to break of the Bear’s tail. Sout their binoculars and telescopes. If Unlike the Big Dip- you’re new to astronomy, however, you’ll per, however, most of want to become familiar with the constella- the other six stars of tions and bright stars that populate this the Little Dipper are season’s night sky before looking through faint. You’ll need a the eyepiece. Then, when you read that a dark location to see sky treat is in Boötes or near Regulus, you’ll them all. already have a frame of reference. Head back to the High in the northeast, the sky’s most Big Dipper, and The constellation Leo the Lion combines a huge recognizable star pattern — the Big Dipper locate its handle. sickle (right) that’s the Lion’s head and a triangle — is easy to spot after sunset. The Dipper is Follow beyond the curve of the handle to of stars (left) that forms its hindquarters and tail. part of the third-largest constellation, Ursa two brilliant stars: Arcturus and Spica. The brightest star is Regulus. BILL AND SALLY FLETCHER Major the Great Bear, but the other stars These two luminaries illustrate some of the are much fainter, so concentrating on the color differences between stars. Go back to the Big Dipper. To find our Big Dipper is the way to start. Arcturus appears copper-colored or next constellation, poke a hole in the Dip- Find the bend of the Dipper’s handle. orange, while Spica is bright blue. Stars have per’s bowl, let all the water run out, and Sharp-eyed observers can see two stars in different colors because nuclear reactions in wait for a loud roar. Mythologically, that’s this space. Arabian astronomers 10 centu- their cores heat their surfaces to different what you’ll hear because the water fell on ries ago called them the Horse and Rider. temperatures. Arcturus is a giant star with a the back of Leo the Lion. The brighter of the two is Mizar, shining relatively cool surface temperature of 7300° Leo’s figure has two parts: A back- five times brighter than Alcor, which sits a Fahrenheit (4040° Celsius). ward question mark and a triangle. The bit to the east-northeast. This pair is an Spica also is a giant, but it ranks among question mark, or sickle-shaped figure, rep- optical double, as in optical illusion. Mizar the hottest of stars. Its surface burns at resents the front of the Lion. Dotting the lies 78.2 light-years away while Alcor sits 35,500° F (19,700° C). For comparison, the question mark with a distinctive blue-white 81.2 light-years distant. Sun lies in the middle of the temperature color is Regulus. Regulus lies 77 light-years Because the Big Dipper is so easy to range. On its surface, a thermometer would from Earth. find, amateur astronomers use it to help read 10,300° F (5700° C). East of the sickle, a right triangle marks them locate lots of constellations and stars Arcturus lies in the constellation Boötes the Lion’s back and tail. The star farthest in the spring sky. For example, use the Big the Herdsman some 37 light-years away. east of Regulus is Denebola. It lies 36 light- Dipper’s Pointer Stars, Dubhe and Merak, The star’s name comes from a combination years away, about the same as Arcturus. A to find the most famous star in the sky: of terms that means “the Bear’s guard,” slightly brighter star than Denebola, Polaris, the North Star. Draw a line from which signifies its position near Ursa Major Algieba, lies to the upper left of Regulus. Merak to Dubhe, and extend that line five the Great Bear. The main part of Boötes Algieba is a spectacular orange and yellow times the distance between those two stars. looks like a thin kite or an ice-cream cone. double star 126 light-years distant. You’ll Polaris, which lies roughly 430 light- Spica sits 260 light-years away in the have no difficulty seeing both components years from Earth, marks the end of the Lit- southern reaches of Virgo the Maiden. This through a 3-inch telescope. tle Dipper’s handle. Alternatively, it’s the sprawling star group ranks second in size Some 20° (the width of two fists at arm’s brightest star in Ursa Minor the Little Bear, among the 88 constellations. length) west of Leo’s sickle lies one of the sky’s faintest constellations, Cancer the Crab. At its center you’ll find M44, the fab- ulous Beehive Cluster. Through 10x50 bin- oculars, most observers can count three dozen stars. The Beehive Cluster lies at a distance of about 580 light-years. Below Virgo sits the small constellation Corvus the Crow. Its four moderately bright main stars and “crooked box” shape make it easy to find. There’s another way to be sure you’re looking at Corvus: See if its top two stars point upward to Spica. Spring is an ideal time to start learning the sky. Many of the constellations are The Big Dipper (left) and the Little Dipper (right) The Beehive Cluster, also known as M44, is an easy are famous star patterns. Note how the Pointer target through binoculars. This object is a star large, and helpful indicators like the Big Stars in the Big Dipper point toward Polaris, the cluster, a group of stars that formed together out Dipper lead you to the brightest stars. North Star in the Little Dipper. BILL AND SALLY FLETCHER of a large cloud of gas and dust. RICHARD MCCOY Before you know it, summer will dawn.

4 WELCOME TO ASTRONOMY Explore the summer sky

f you want to begin observing the sky, unique among start when it’s warm. High in the north- humans, but most Iwest in the evening, seven stars form the observers see these Big Dipper. This well-known group daily stars as and circles the North Star, Polaris. The two sapphire-blue. stars at the end of the Dipper’s bowl — the Try finding the Pointer Stars — point to Polaris. The Big Coathanger aster- Dipper, however, is not a constellation. It’s ism through your part of Ursa Major the Great Bear. binoculars. About Use the curve of the Big Dipper’s handle halfway between to lead you to Arcturus, the brightest Albireo and Altair, Boötes This picture captures two constellations. Cygnus star in the constellation the Herds- the Coathanger is a the Swan dominates most of the image while Lyra man. Arcturus glows orange, indicating it’s line of six stars with a curve of four stars the Harp lies at the lower right. Lyra’s main star, a cool star. It ranks as the fourth-brightest (the hook) protruding from its center. blue-white Vega, shines brightly. BILL AND SALLY FLETCHER nighttime star and the brightest in the A bit west of the lies northern half of the sky. Hercules, the legendary hero. This constel- through the small telescopes of Messier’s Overhead, three bright stars form sum- lation contains one of amateur astronomy’s day, such objects resembled comets. He mer’s second-easiest star picture (next to main tourist sights — the Hercules Cluster wanted other observers to realize they the Big Dipper) — the Summer Triangle. (M13), the finest globular star cluster in the weren’t comets. Through today’s scopes, Each is the brightest star in its constella- northern sky. M13 lies along one side of the however, Messier’s list contains many of the tion. The brightest is Vega in Lyra the Keystone, a crooked box of four medium- finest celestial targets. Harp; next brightest is Altair in Aquila the bright stars that mark the Hero’s body. Now head far to the south from Hercu- Eagle; and the third is Deneb, the star You’ll find the Keystone about two- les to Scorpius the Scorpion. Because Scor- marking the tail of Cygnus the Swan. thirds of the way from Arcturus to Vega. pius and neighboring Sagittarius lie in the Cygnus contains the (a recog- You can glimpse M13 with your unaided southern part of the sky, thick air layers nizable star group that’s not a constellation) eyes under a dark sky, but it looks better dim their glory from northern latitudes. of the Northern Cross. Albireo lies at the through binoculars, where it will appear Everyone should be able to find Antares, base of the cross. This object is one of the half the width of the Full Moon. the bright star marking the Scorpion’s top 10 showpieces for small telescopes. The “M” before the number 13 stands heart. Antares is a red supergiant 400 times Albireo is a colorful double star, wide for “Messier object.” French comet-hunter larger than the Sun. enough that even 10x50 binoculars will Charles Messier (1730–1817) compiled a list Next to the Scorpion’s stinger lie two separate the pair. Color perception is of 109 such objects. When observers looked glorious open star clusters, M6 and M7. M6, popularly known as the Butterfly Cluster because of its shape, appears slightly ellipti- cal, and its brightest star is an orange giant that varies in brightness. M7 is easy to spot with your naked eyes as a bright knot in the southern Milky Way. Through binoculars, M7 appears more than twice as wide as the Full Moon. M7’s central stars are arranged in an X while the outliers form a triangle. East of Scorpius lies Sagittarius the Archer, whose central part resembles a tea- pot. When we look at this star pattern, we’re looking toward the center of our gal- axy. Many more stars lie in this region than anywhere else in the sky. The area also has a large amount of gas and dust, however, which dims the stars’ light. That’s why the area isn’t overwhelmingly bright. Once you learn the main constellations and bright stars in the summer sky, you’ll find lots of excuses to be out at night during this season. In fact, you’ll probably have so The constellation Scorpius the Scorpion is one of the few star patterns that looks like its namesake. It lies much fun that you won’t even notice fall’s in the direction of the center of the Milky Way, so we see a lot more stars in this area. BILL AND SALLY FLETCHER chillier air all that much.

WWW.ASTRONOMY.COM 5 Explore the fall sky

all is a great time for stargazing. Eve- Just north of nings arrive more quickly than in the Andromeda, look for Fsummer, and all the stress from trav- the bright constella- eling or getting the kids ready for school tion Cassiopeia the lies in the past. And although the fall sky Queen. Depending may not contain the most brilliant stars, on the time of night, great targets abound. The Milky Way the five luminaries arches from the northeast to the southwest, of this star group and it contains countless wonders. Set up a will appear either as reclining chair at a dark site, and scan our the letter W or M. galaxy’s spiral arms with just your eyes or Cassiopeia lies Cassiopeia the Queen is a fall constellation with an through binoculars. You’ll be glad you did. smack-dab in the easily identified shape. It looks like the letter W. Let’s start our tour high overhead. As Milky Way, so it’s full of tightly packed star Or, if you see it on the other side of the sky, it looks the glow of sunset wanes, you’ll spot the clusters you can spot through binoculars. like the letter M. BILL AND SALLY FLETCHER three bright stars that form the Summer The W of Cassiopeia opens toward the Triangle: Vega in Lyra the Harp, Altair in north and the constellation the fall, M45 doesn’t rise until several hours Aquila the Eagle, and Deneb in Cygnus the King. Search for five stars that look like a after sunset, but it’s worth the wait. With Swan. Deneb marks the tail of the Swan, pencil sketch of a house. your naked eyes, you can see six Pleiads in and Albireo is its head. Albireo makes a Cepheus lies midway between Cassio- the form of a tiny dipper. It’s not the Little terrific small-telescope target: a double star peia’s W and Polaris, the North Star. Dipper, however, which is in the north. that glows gold and blue. Polaris ranks as the sky’s 47th-brightest Through binoculars, three dozen stars But the Summer Triangle isn’t the only star, which is still pretty bright. will dazzle you. For M45, a magnification geometric figure you’ll find in the fall sky. Next, return to Cassiopeia’s W figure. between 10 and 15 times works best. If pos- Look east of the Summer Triangle for four Use binoculars to search two binocular sible, mount your binoculars on a tripod stars that form the main part of the constel- fields of view east of Cassiopeia for the because high-power units tend to weigh lation Pegasus the Winged Horse. Astron- Double Cluster (NGC 869 and NGC 884), more, and your arms will fatigue long omers call this stellar quartet the Great which lies just above the head of the con- before you get tired of the view. Square, and it’s the easiest way to find the stellation Perseus the Hero. Although you Once you learn the bright stars and con- legendary horse. Pegasus is a huge constel- can spot both clusters as fuzzy objects with stellations in the fall sky, it will be easy for lation that spreads out toward the west your eyes, binoculars bring out their best. you to transition to the other three seasons. from the Great Square. Just beyond Perseus’ other end lies the In a short time, you’ll be locating lots of From a dark site, point binoculars or a fall sky’s best naked-eye/binocular deep- great celestial objects to enjoy alone or to telescope about four binocular fields of sky object: the (M45). Early in the share with others. view west of the star at the Great Square’s southwest corner. There, you’ll find a glob- ular cluster (a spherical grouping of tens of thousands of stars) named M15. The northeast star of the Great Square doesn’t belong to Pegasus. It’s Alpheratz, the brightest star in Andromeda the Prin- cess, which appears as two lines of stars that start at Alpheratz and curve northeast. Follow the northern curve for two stars and then go right one star. Look about half a binocular field northwest, and you’ll spot the Andromeda Galaxy (M31), the north- ern sky’s greatest galaxy. You can see it without optical aid from a dark site, where it will appear as a faint piece of the Milky Way that broke off. But it’s not part of our galaxy. Rather, it’s a separate system that numbers nearly half a trillion stars. That many stars give off an incredible amount of light, but M31 still appears faint because of its distance. Although M31 is one of the nearest galaxies to us, it lies some 2.5 mil- The Pleiades, also known as M45, is the brightest of all star clusters. You’ll see six or seven stars with just lion light-years away. your eyes, three dozen through binoculars, and more than 100 through a telescope. ANTHONY AYIOMAMITIS

6 WELCOME TO ASTRONOMY Explore the winter sky

he winter sky offers the brightest will see the area as stars of any season. This makes find- slightly fuzzy. This is Ting the constellations that contain the Orion Nebula them easy. At this time of year, the Milky (M42) — a huge star- Way arches from north to south. Along that forming region. Bin- path, deep-sky treasures visible through oculars improve the binoculars abound. All you need is this view, but the view article and a way to stay warm. through a small tele- Toward the south, look for the magnifi- scope with an eye- cent constellation Orion the Hunter. Orion piece that gives a looks like a giant butterfly, with the three magnification of stars of his Belt marking the butterfly’s about 100x is best. body and wings to either side. Because Orion is Orion’s brightest star is Rigel. It marks so easy to find, you his left knee (the one to the bottom right, as can use it as a start- we see it in the sky). ing point to locate To Rigel’s upper left, past Orion’s Belt, many other stars and lies . Although modern descrip- constellations. For tions list Betelgeuse as one of Orion’s shoul- example, if you draw ders, the original Arabic name more closely a line down to the means “the armpit of the mighty one.” southeast from Ori- As you view Rigel and Betelgeuse in the on’s Belt, you’ll sky, you’ll notice they have quite different arrive at , the colors: Rigel is bright blue, and Betelgeuse night sky’s brightest shines with a coppery tone. Stars shine with star. Because of its different colors because their surfaces radi- Canis The constellation Orion the Hunter dominates the position in winter sky. Notice how the copper hue of the star ate at different temperatures. Blue stars typ- Major the Big Dog, the ancient Greeks Betelgeuse makes it stand out among the mostly ically have surface temperatures above referred to Sirius as the Dog Star. blue suns in this group. BILL AND SALLY FLETCHER 20,000° F (11,000° C). The surface of a red Point your binoculars at Sirius, and star like Betelgeuse heats the thermometer move the star so it sits at the top of the field appears best through 10x to 15x binoculars. to only 3000° F (1650° C). of view. Near the center, you’ll see a faint, Telescopes tend to magnify the cluster too In the region of Orion’s Sword, which fuzzy patch of light that looks like a cotton much, spreading out the stars and reducing hangs below his Belt, sharp-eyed observers ball. That’s open star cluster M41. Open the number of them that you’ll see at once. clusters are loose collections of dozens to If you extend a line straight up through hundreds of stars that formed at the same Orion’s body and head, you’ll find the con- time. Few open clusters are old because stellation the Charioteer. The their stars disperse due to gravitational brightest star in this pattern is yellow interactions within the clusters. . Capella is a word that means isn’t Orion’s only canine “mother goat,” and early observers called companion — there’s also the the triangle of faint stars just to the south- Little Dog. To find it, make an equilateral west of Capella the “Kids.” triangle using Betelgeuse, Sirius, and Canis Return to Orion one last time. Draw a Minor’s brightest star, . These line from Rigel to Betelgeuse. Continue the three stars form an asterism (a recognizable line about 11⁄2 times that distance to find star pattern that’s not a constellation) called the Twins. The two stars marking the Winter Triangle. Once you find Pro- the Twins’ heads are Castor and Pollux. An cyon, draw a line northwest to the star easy way to tell which is which is to remem- Gomeisa, and you’ve outlined the little dog ber a bright star first-letter match: Castor — just two stars! lies closer to Capella, and Pollux is on the Now draw a line from Orion’s Belt in the same side as Procyon. opposite direction. You’ll soon come to a Learning the major constellations and V-shaped group of stars called the , bright stars in the winter sky is easy, even which marks the head of Taurus the Bull. from a brightly lit backyard. And if you Taurus’ eye is the ruddy star . chill quickly, just five or 10 minutes a night The Orion Nebula, also known as M42, is a vast cloud of dust and gas where stars are forming. Continue the line upward, and you’ll hit will do it. In a short time, you’ll be the The cloud glows because radiation from stars the Pleiades (M45). This naked-eye star astronomy expert in your group of friends. energizes the atoms within it. TONY HALLAS cluster (sometimes called the Seven Sisters) And you won’t even need a star map.

WWW.ASTRONOMY.COM 7 To create this moonrise sequence near Valley, Arizona, the photographer took shots of the Full Moon every four 10 tips for Moon watchers minutes and then stacked them into one image. BURLEY PACKWOOD

he Moon offers something for every- The termina- one. It’s visible most nights, its ever- tor is great Tchanging face has features one night During the two prime- not seen the previous night, and it doesn’t time periods, aim your take an expensive setup to enjoy it. To help scope along the line you get the most out of viewing the Moon, that divides the Moon’s follow these 10 tips, and you’ll be on your light and dark parts. way to a lifetime of lunar observing. Astronomers call this line the terminator. It’s To start, don’t use optics where sunrise (or sun- The best way to begin your journey as a set) is happening. lunar observer is to learn the Moon’s major You’ll see the tops features. Head out with a simple Moon of mountains protrud- map, and use just your eyes to identify our ing just high enough to catch the Sun’s light Work from a list only natural satellite’s top attributes. Once while surrounded by lower terrain that A great way to learn the Moon is to under- you know a few, you can add binoculars. remains in shadow. Features along the ter- take an observing project. In the United minator change in real time, and during a States, the Astronomical League offers one The Full Moon is bright night’s observing, the differences you’ll see such project, the Lunar Observing Club. Contrary to what you might think, Full through your telescope are striking. You’ll learn a lot about our satellite as you Moon is not the best time to observe our work through a list of 100 lunar features. natural satellite. When the Moon is Full, The best Moon scope? To receive a certificate, you must be a the Sun lies behind Earth (as we face the Nearly any telescope will do to observe member of the league, either individually Moon), shining directly down on the lunar lunar details. Observers with several or through an astronomy club. For details surface. Shadows are at their minimum options (but not a permanent observatory) about the club, see www.astroleague.org/al/ lengths, so you can’t see much detail. usually pick a scope they can set up many obsclubs/lunar/lunar1.html. nights in a row. Observing on successive View at “prime time” nights makes it easier to follow the termi- Dig for the details Two intervals during the lunar “month” nator’s progress. Of the 1,940 named lunar features, 1,545 (from one New Moon to the next) are best are craters. Challenge yourself to see either for observers. The first begins shortly after Cut down the moonlight how small a crater you can detect or how New Moon and continues until two days Many observers use either neutral density many you can observe in a given area. past First Quarter. On these days, the Moon filters or variable polarizing filters to You’ll need a Moon map for this project. lies in the evening sky. reduce the Moon’s light. The latter lets you For the second challenge, you can An equally good observing period starts change how much light the filter transmits. choose a lunar sea, but usually a large, flat- about two days before Last Quarter and Two other methods to reduce the bottomed crater works best. For example, if ends when the Moon lies so close to the Sun Moon’s brightness are high magnification you search the large crater Plato, you’ll find that it’s lost in morning twilight. During and an aperture mask. High powers restrict four small craters on its floor. Lunar both intervals, shadows are longer and fea- the field of view, thereby reducing light observers consider seeing these craters a tures stand out in sharp relief. throughput. An aperture mask causes your test for a 6-inch telescope. telescope to act like a much smaller instru- First ment, but at the same focal length. Shoot the Moon Quarter Lunar orbit Not to scale How can a celestial object that’s so easy to Turn on your best vision photograph be so difficult to photograph Waxing Waxing gibbous crescent Some years ago, an observer found a better well? The Moon is large and bright, and you way of observing the Moon: Turn on a can use any camera connected to any size Sunlight white light behind you when you observe telescope to image it. That’s the easy part. Full New between Quarter and Full phases. The light But the Moon also contains vast areas of Moon Moon should be moderately bright (in the 60-watt low contrast that have little color differen- range), but neither your eyes nor the eye- tial. Recording those regions so they look piece should be in direct view of the fixture. like what your eyes see is the hard part. Waning Waning The addition of white light suppresses Luckily, we live in the digital age. It costs gibbous crescent the eyes’ tendency to dark adapt at night. nothing extra to take 200 images instead of Last Not dark adapting causes the eye to use just one. Examine them, delete what you Quarter normal daytime vision, which is of higher don’t like, change one or more parameters This graphic shows the phases of the Moon as we see them from Earth (outer circle of Moons) and quality than dark-adapted night vision. So, (including the techniques you used to pro- also how the Sun illuminates our satellite (inner you’ll see more detail because you’re view- cess the images) each time, and shoot some circle). ASTRONOMY: ROEN KELLY ing with a better part of your eye. more as you perfect your techniques.

8 WELCOME TO ASTRONOMY Plotted here are the locations of eight easy-to-observe lunar features. Just point your telescope at the spot shown on the Moon map, and you’re on your way to Explore 8 lunar targets observing our satellite. North is up in all images. FULL MOON IMAGE BY LICK OBSERVATORY

Sinus Iridum, the Bay of Rainbows, on the Moon’s Plato Crater lies at the Moon’s top center. It Archimedes Crater lies at 30° north latitude northwestern edge spans a whopping 162 miles spans 63 miles (101 kilometers) and has one of centered between the eastern and western limbs. (260 kilometers). Numerous tiny craters dot Sinus the darkest crater floors on the Moon. Polish This 52-mile-wide (83 kilometers) Iridum’s remarkably flat surface. The Jura Moun- astronomer Johannes Hevelius called Plato the lies just northwest of the Moon’s largest moun- tains form its curved edge. ALAN FRIEDMAN Greater Black Lake. ALAN FRIEDMAN tain range, the Montes Apenninus. ALAN FRIEDMAN

Gassendi Crater, whose long axis mea- Copernicus Crater marks the center sures 68 miles (110 kilometers) across, is of a system of bright rays. Copernicus a spot that will hold your attention. To the measures 58 miles (93 kilometers) wide. north, the crater Gassendi A has broken its Because of its great depth — 12,300 feet wall. Together, both craters give the appear- (3,750 meters) — shadows here create dra- ance of a diamond ring. ALAN FRIEDMAN matic relief. PAOLO LAZZAROTTI

Pitatus Crater (upper right), which spans 60 Clavius Crater ranks as the third-largest crater Messier and Messier A are two small but well- miles (100 kilometers), contains features strewn on the Moon’s nearside. It spans 140 miles (225 known craters that sit on the Moon’s eastern about its floor. A low central peak sits just to the kilometers). But it’s what’s in Clavius that’s cool. side only 2° south of its equator. Messier is an northwest of the crater’s center. With a medium- Look for the curving of decreasing oblong crater measuring 5.6 by 6.8 miles (9 by 11 sized telescope and a magnification of about 100x, size that begins at Clavius’ eastern (right) wall. The kilometers). Messier A spans 8.1 by 6.8 miles (13 you’ll spot a system of clefts across the lava-filled largest is Rutherford Crater, then Clavius D, Clavius by 11 km). Two linear rays (splashes of material floor. The feature with double walls to the left of C, Clavius N, and Clavius J. Crater breaks from impacts) extend westward from Messier A for Pitatus is Hesiodus Crater. ALAN FRIEDMAN Clavius’ wall to the upper right. DAVID TYLER more than 60 miles (100km). ANTHONY AYIOMAMITIS

WWW.ASTRONOMY.COM 9 Beyond the Moon

ll the planets are fair game for back- Polar caps grow and yard telescopes — even distant shrink as seasons pass. APluto. But the most popular are Mars is a challeng- Jupiter, Saturn, and Mars because they ing world to observe show the most features. from Earth because of Jupiter spins in less than 10 hours, so its small size and vary- the vista changes all the time. What looks ing distance — it’s like a cloud-striped surface on Jupiter is the close to Earth for only top of a deep hydrogen atmosphere two months out of 26. churned by heat from below. Spots and Yet, in many ways, markings appear, last for months or years, Mars is our most then merge and disappear. The Great Red Earth-like neighbor. Spot, twice the size of Earth, has lingered This exerts an irresist- The region around the star Rho Ophiuchi is one for more than 350 years. Jupiter-watchers ible pull on every back- of the most colorful in the sky. And because it’s monitor the planet for changes and alert yard telescope owner. near the center of our galaxy, this area also is one scientists when they occur. packed with billions of stars. TONY HALLAS Around Jupiter, a family of moons The Sun swirls like a miniature solar system. Gali- Before leaving the solar system, take a look leo discovered the biggest four, which you at its central star — the Sun. Solar viewing can easily follow in any size telescope. (See requires a special solar filter that fits over the monthly illustration in Astronomy.) the front of the telescope — never use an Saturn is a smaller, lighter, cooler Jupi- eyepiece solar filter. A front-mounted solar ter, so its cloud bands are less pronounced filter lets you safely view features such as — but the prominent ring system makes a sunspots, which are relatively cool and world of difference. Saturn never fails to dark regions far bigger than Earth. They elicit a gasp when people see it for the first occur where the Sun’s magnetic field time. You’ll want to look at its jewel-like becomes knotted and hinders the flow of beauty all night long. internal heat. For reasons no one yet understands, sunspot numbers wax and The Red Planet wane over an 11-year cycle. No one has yet stood on the sands of Mars, but you can peer into a backyard telescope The starry sky and sometimes see hazy clouds over its Scanning the sky — and particularly the These dark streaks on Mars may be the result of large volcanoes. Occasionally, dust storms Milky Way — with a telescope, you find flowing — but quickly evaporating — water. The gather to veil parts of Mars — or all of it. stars in pairs and triplets. Some are chance streaks only appear during the martian spring and groupings, but most are real multi-star sys- summer. HIRISE/MRO/LPL (UNIV. OF ARIZONA)/NASA tems, locked together by gravity. While they orbit at high speeds, their distances globular through a telescope, you see a are so great that decades or centuries will bright center sprinkled with stars that run pass before changes become apparent. outward until the blackness of space takes Stars also gather in clusters — tight, over. A globular cluster looks like a tiny pile rich groups that stand out from the of sugar dropped on black velvet. background. Open clusters contain a The best place to look for open clusters few dozen to a few thousand mem- is along the Milky Way, but globulars are bers. The Pleiades (M45) in Taurus is usually found flanking it. The region of sky a beautiful open cluster, more popu- richest in globular clusters lies in Scorpius lous and less scattered than its and Sagittarius, best seen in summer. But a neighbor, the Hyades. superb globular, M13, lies in spring’s Her- Stars also group together as glob- cules, where it shines bright enough to see ular clusters. If open clusters are like by eye from a dark observing site. small towns, globulars are cities, con- Star clusters are born from vast clouds taining tens of thousands to upward of of dust and gas that occur throughout the a million stars each. When you look at a Milky Way. Astronomers call such clouds nebulae, and they make favorite targets for Jupiter is the largest planet in our solar system. If it were hollow, it could hold some 1,300 Earths. The telescope users. A nebula looks like a soft large red spot is a storm twice as large as our planet that haze through the eyepiece. Irregular in has lasted at least 350 years. NASA/JPL/UNIV. OF ARIZONA shape, many nebulae contain an open star

10 WELCOME TO ASTRONOMY Our Sun is a star like the stars we see in the night sky. The biggest difference between it and them is that the Sun lies much closer to Earth. Note the International Space Station crossing at the upper right. ALAN FRIEDMAN

realm of galaxies you can spend the rest of your life discovering. Backyard astronomers who prowl for galaxies are the deepest of the deep-sky The Fireworks Galaxy, also known as NGC 6946, got its name after eight supernovae exploded there explorers. As they peer into the in the past century. It lies in the constellation Ce- telescope, they look back in time, pheus. ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA deciphering light that took millions of years to arrive. cluster, born from the nebula perhaps in the Quirks of geometry present some galax- last few million years. A famous example is ies edge-on, like pencil beams of light. the Orion Nebula (M42). Some have ragged edges. Others, tipped Another kind of nebula is the planetary face-on, tantalize us with spiral arms that nebula, so called because through small hover on the edge of invisibility. A few gal- telescopes many resemble Neptune. A plan- axies show dark smudges like black eyes, etary nebula represents the end of a star’s where dust lies thick and the star-making life. As Sun-like stars age, they blow off factories are running day and night. shells of gas around their hot cores. The The Milky Way and Andromeda galax- shells expand and fade, and the cores cool. ies both belong to the Local Group, a clus- Not all stars die quietly, however. The ter of some 50 galaxies. Nearby in Virgo Crab Nebula (M1) in Taurus marks where a lies a much larger galaxy cluster, one of star exploded about 1,000 years ago. The many millions that shape the framework of remnant is expanding, shooting gaseous the universe. Backyard astronomers can debris back into space, where much of it explore this realm in part — but even the will wind up in a new generation of stars. pros haven’t sounded its depths. 47 Tucanae is a grouping of hundreds of thousands of stars called a globular cluster because of its round Realms of infinity Of space and time shape. This one is visible to the naked eye from a You can take your first step beyond the When we turn from the realm of the galax- dark site at latitudes south of the U.S. FRED HERRMANN Milky Way just by using your naked eyes. A ies and look homeward, distances shrink, dark autumn night shows the Andromeda and the light our telescopes receive grows hours away from the Sun, while Earth zips Galaxy (M31) as a pale smudge of light near younger. Globular clusters appear as they around just 8 light-minutes from the Sun. the Great Square of Pegasus. M31 lies 2.5 were perhaps 20,000 to 50,000 years ago. And what about moonlight? It’s million light-years away. And the Androm- And star clusters like the Pleiades shine as reflected sunlight that left the Moon’s dusty eda Galaxy is just the start; beyond lies a they were hundreds to thousands of years surface just 1.3 seconds ago. When you Crater on Mars was the site of a meteorite ago. Light from the nearest star — Alpha look through a telescope, you get more impact years ago. It measures 30 feet (9.1 meters) Centauri — takes 4.3 years to crawl from than a spaceship of the imagination — you in diameter. KENNETH KREMER/NASA/JPL/CORNELL/SPACEFLIGHT NOW there to here. Pluto orbits some 5 light- get a time machine, too.

WWW.ASTRONOMY.COM 11 30 cosmic questions

Who invented the Why does 1 telescope? 7 the Moon Historians attribute this invention to Dutch rise later each spectacle maker Hans Lipperhey in 1608. night? Italian astronomer Galileo Galilei made The Moon orbits telescopes and used them to observe the Earth once every heavens beginning the following year. 27.3 days. It moves from west to east How does the Sun produce through the sky, so 2 energy? its position on any 14 Within its core, extreme pressure causes night is about 12° Comets are small ice balls that glow and form tails protons (the nuclei of hydrogen atoms) to east of where it stood the previous night. as they approach the Sun. GERALD RHEMANN collide with other protons. The process On average, therefore, it rises 50 minutes continues until four protons fuse together, later from one night to the next. orbited the planet. The gravity of Saturn’s creating a helium nucleus. Nuclear “fusion” moons then divided the system into rings. releases enough energy for the Sun to shine. How are planets different 8 from stars? What causes a meteor Planets do not generate their own light, 12 shower? although large planets like Jupiter may As a comet approaches the Sun, solar radia- radiate some infrared and radio energy. tion boils away the comet’s ice, releasing Planets also are much smaller and less mas- dust particles trapped within. If Earth’s sive than stars. orbit intersects that of the comet, the par- ticles enter our atmosphere at high speeds, Why is Mars called the creating a meteor shower. 9 Red Planet? 3 The color comes from the large amount of Where do comets iron oxide (Fe O ) — known commonly on come from? Sunspots in active region 11164 appear dark in 2 3 13 contrast to the rest of the Sun’s surface. DAVE GRADWELL Earth as hematite (or rust) — on the plan- Short-period comets (those that orbit in less et’s surface. than 200 years) originate in our solar sys- Why are sunspots dark? tem’s Belt or in the scattered disk, 3 Actually, they’re not. They just appear Who discovered Jupiter’s both of which lie outside Neptune’s orbit. dark by contrast. Sunspot regions measure 10 four large moons? Long-period comets come from the Oort between about 2000° and 4500° Fahrenheit Italian astronomer Galileo Galilei found Cloud, a sphere of icy bodies that stretches (1100° and 2500° Celsius) cooler than the three of them (Io, Europa, and Callisto) nearly 1 light-year from the Sun. surrounding surface. January 7, 1610. On January 13, he observed the fourth one, Ganymede. Initially, he Why do comet tails point How much of the Sun’s thought they were stars, but their motions 14 away from the Sun? 4 energy does Earth receive? during the next several weeks convinced The reason is that radiation and the solar Approximately two-billionths. him that they orbited the planet. wind literally push the tail outward. Com- ets have two types of tail: ion (made of What is Universal Time? What process created gases) and dust. The solar wind makes the 5 It is a measure of mean solar (clock) 11 Saturn’s rings? ion tail straight in the direction opposite time at 0° longitude. Astronomers use Uni- Long ago, the orbit of one of the ringed the Sun. Radiation pressure pushes the dust versal Time — usually abbreviated UT — planet’s moons decayed until it reached a tail out, but it curves because its more mas- to standardize the times of celestial events distance where tidal forces from Saturn tore sive particles fall behind the comet, moving and observations made by observers it into trillions of separate particles that still into slower orbits. around the world. If the Moon rotates, why do 9 6 we always see the same side? The long-term effect of tides between Earth and the Moon has locked our satellite’s spin. That is, the Moon now rotates on its axis in the same time that it takes to revolve around Earth. Enough irregularities in the Moon’s rotation exist, however, that we see 59 percent of its surface. Despite its odd reddish coloring, Mars is the planet in our solar system most like Earth. DAMIAN PEACH

12 WELCOME TO ASTRONOMY When were the Do eclipses occur in a 15 current constellations 19 regular series? established? Yes. Astronomers call it the Saros cycle, and In 1928. Prior to that date, celestial map- it’s approximately 18 years and 11⅓ days makers were free to populate star charts long. One cycle after any eclipse, the Sun, with as many or as few constellations as the Moon, and Earth will have the same they desired. Today, 88 stellar figures cover geometry and a similar eclipse will occur. the sky. No gaps exist between them, none overlap, and only one — Serpens — has two What causes the Moon’s parts. This formal list arose out of a com- 20 colors during total lunar 25 mission established by the International eclipses? The Witch Head Nebula reflects and scatters light Astronomical Union in 1922. Earth’s blanket of air scatters some sunlight from the nearby star Rigel. ROGELIO BERNAL ANDREO onto its surface. A totally eclipsed Moon Why do stars twinkle? may appear yellow-white, orange, copper, so, however, it also scatters the light, creat- 16 They don’t. Stars appear to twinkle rust, reddish-brown, brick red, gray, or ing a characteristic blue color. because they are points of light (not disks nearly black. The color depends on the like planets) and because their light passes amount of dust and clouds in our atmo- What is a planetary through our atmosphere. Layers of air act sphere at the time. 26 nebula? like moving lenses, which bend the light It is a phase at the end of the life of every rapidly in alternating directions. The air What is light pollution? Sun-like star during which the outer atmo- layers also may act like a prism, causing a 21 It is excess — unneeded — artifi- sphere of the star expands into space. The star’s light to change color as it twinkles. cial nighttime lighting that interferes with core of the original star emits enough radi- observing. The worst examples occur in ation to keep the nebula glowing for 10,000 What creates the glow of large metropolitan areas. In the United years, on average. 17 the Milky Way? States, 1.8 percent of energy generated goes This subtle nighttime radiance visible from to public outdoor lighting. Light pollution What objects form from a dark sites represents the combined light of wastes $2.2 billion per year. 27 star’s death? billions of stars along our galaxy’s plane. A Sun-like star will shed its outer layers as a Unfortunately, they’re too distant for our How many stars are visible planetary nebula. Its core will contract and eyes to resolve as points, so their light com- 22 from a dark site? become a white dwarf. It still contains most bines to create a glow. Most people could spot approximately of the star’s mass but will be only as big as 5,000 stars between the end of evening twi- Earth. More-massive stars will explode, light and the beginning of morning twi- producing supernova remnants rushing out light. Those with exceptional eyesight into space. The cores of such stars will might boost the count to 8,000. become either neutron stars (dense suns only a few miles across) or black holes. What is a Messier object? 23 It is one of 109 deep-sky objects What is a galaxy? (star cluster, nebula, or galaxy) cataloged by 28 Each of these building blocks of 18 French comet-hunter Charles Messier, who our universe contains massive collections The spectrum gives researchers lots of information compiled the list so other observers would of stars, gas, dust, and associated unseen about celestial objects. ASTRONOMY: ROEN KELLY not mistake these objects for comets. For matter bound by gravity. observers, Messier’s list contains some of How do astronomers the sky’s true wonders. How many stars does the 18 analyze light from 29 Milky Way contain? celestial objects? What percentage of stars Astronomers think between 250 billion and They disperse the light into a spectrum, an 24 are double or multiple? 400 billion stars populate our galaxy and electronic plot that shows the relative Approximately 60 percent. that its total mass is somewhat less than 1 strengths of each of the colors, which trillion Suns. astronomers call wavelengths. By compar- What makes the gas in a ing a star’s spectrum to one created in a 25 nebula glow? What’s the universe laboratory, astronomers can deduce the Nebulae can glow by emitting or reflecting 30 made of? percentages of all the elements the star con- light. Atoms of gases like hydrogen can Current estimates by cosmologists divide tains. A star’s spectrum also can tell scien- absorb energy from nearby stars and re- the universe into: dark energy, 68 percent; tists how hot the star is, how fast it is emit it as light of various colors. If the star dark matter, 27 percent; free hydrogen and moving toward or away from us, whether it is too far away to energize the atoms, the helium, 4 percent; stars, 0.5 percent; neutri- has a strong magnetic field, and more. nebula can still reflect its light. As it does nos and everything else, 0.5 percent.

WWW.ASTRONOMY.COM 13 Be an observer in 10 steps

stronomy remains a vibrant science generally clear the sky because something’s always making is and how steady the Anews. In essence, the sky is calling. air above you is. But how do you start observing the sky? What do you need to know? Double your 5 observing Learn sky basics time with 1 Earth rotates once a day, so sky objects the Sun rise in the east and set in the west. It orbits The Sun beckons the Sun once each year, making different beginning observers constellations appear in each season. because it’s big, bright, You don’t need a telescope when you begin look- The sky is a celestial sphere. It has a and full of features ing at sky objects. That said, you may soon want north pole, an equator, a south pole, and that change daily. Put safety first by using a one because most of our fascinating universe lies two sky coordinates: Right ascension is like filter, and even a small scope will deliver beyond what our eyes can detect. NEIL KOPICKI longitude, and declination mimics latitude. high-quality views. The Moon first becomes visible as a thin Be sure to get a filter that fits correctly crescent low in the western evening sky. over the front end of your telescope. A good Each night thereafter, it appears to grow solar filter will not transmit harmful ultra- and move eastward until Full Moon, after violet or infrared radiation. It also will drop which its lit part shrinks to invisibility. the Sun’s brightness to a viewable level. Dive into the subject Comfort is everything 2 Check out Astronomy magazine. It 6 Comfort means a lot more than staying features a combination of science and warm in the winter. So, sit. When you are hobby stories. “The Sky this Month” is an comfortable at the eyepiece, you’ll see a up-to-date guide to the current sky. And great deal more. Many amateurs use adjust- more is out there. Your public library and able chairs sold specifically for observing. bookshops offer many observing guides. Photography: rewarding but Try before you buy 7 time-consuming Interact with others and try out new telescopes 3 Don’t purchase a telescope without Here’s the good news: You can take pic- and accessories by attending a star party. PHIL first viewing through it. One way to test- tures of sky objects. Here’s the other side: It drive a scope is to attend an observing ses- takes practice, and there is a learning Get social sion or a star party hosted by an astronomy curve. Producing a high-quality picture 9 Visit a planetarium. Attend a star club. Take your time, ask lots of questions, involves two stages. First you acquire the party. Observe with other amateur astrono- and you’ll soon enjoy a lifetime of data, and then you process it with appro- mers. Get on the Internet and chat in one of viewing pleasure through your priate software. Astronomy.com’s forums. very own scope. Without question, the best step you can Keep a log take is to join a local astronomy club. This Pick your site 8 A simple log contains the date will place you with a group of like-minded 4 carefully and time of your observation, individuals who can answer your questions. If you’ll be content with the name or names of the bright stuff, pretty much any objects you looked at, and Observe everything! location will do. To see faint, a brief description, like, 10 You may hear, “I’m a lunar diffuse objects like nebulae “Saw spiral arms!” or observer,” or “I only observe galaxies.” and galaxies, however, you’ll “Really blue, but no Really? Are these observers saying they’d need a dark site. details visible.” pass up watching a total solar eclipse, a Some things to consider Once you get the hang bright comet, or a rich meteor shower? are how light-polluted the of it, more detailed log The Moon has hundreds of targets on its observing location is, the entries might contain ever-changing face, and even a small driving distance, how portable information about the tele- instrument will show most of them. The your telescope is, safety (do you scope, eyepiece(s), sky con- planets spend lots of time in the early eve- get cellphone service?), and ditions, and the faintest star ning sky. A trip now and then to a dark site weather factors, including how you could see with your may yield dozens of galaxies. While you You can spend a lot on a telescope, so naked eye. Observers call take them all in, you’ll surely marvel at the make sure you’re getting a high-quality that quantity the sky’s magnificent universe above and the rich- product. Try it out first. CELESTRON “limiting magnitude.” ness of the hobby you have chosen.

14 WELCOME TO ASTRONOMY