Travel through the whole universe in 30 pages! EXTRA! DECEMBER 2015 THE COSMOS TO SCALE The world’s best-selling astronomy magazine SPECIAL ISSUE THE IMMENSITY OF THE COSMOS p. 20 • Gas, ice, and rocks in the solar system p. 24 • The Milky Way’s barred spiral p. 30 • Gravitational supremacy in the Local Group p. 44 • The Virgo Supercluster of galaxies p. 50 • To the limits of the universe! p. 56 www.Astronomy.com BONUS Vol. 43 PLUS! 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Specifications subject to change without notice. 20-15026. Thanksgiving is coming up and we here at Sky-Watcher USA HQ have been thinking about making one of those deep fried turkeys, ex aperture and speed. YOU’D THINK WE’RE SANTA CLAUS! With the holidays just around the corner, the coolest thing we could do is make it even easier to own an award-winning Sky-Watcher scope or mount. So, from Nov. 15th to Dec. 31st save up to $500 on some pretty frosty deals! For complete details and specifications, go to skywatcherusa.com Save up to $50 Save up to $300 Save up to $500 on our traditional on an ultra-portable and get light bucket Dobsonians. An Sky-Watcher collapsible value with GoTo excellent mix of classic Dobsonian. Lots of light convenience with our styling and easy to use gathering in an line of GoTo collapsible functionality. easy-to-move package. Dobsonians. Save $100 on the ProED 80/AllView mount combo. The ideal night and day, grab and go kit! Or save up to $150 on one of our ProED Apo doublet OTAs that deliver an elegant balance of value and performance. Save 10% on the versatile Virtuoso mount. Create easy time lapse and panoramic videos and pics. Only $225! For information on all of our products and services, or to find an authorized Sky-Watcher USA dealer near you, just visit www.skywatcherusa.com. Don’t forget to follow us on Facebook and Twitter for exclusive offers! Online Content Code: ASY1512 Enter this code at: www.astronomy.com/code DECEMBER 2015 to gain access to web-exclusive content VOL. 43, NO. 12 TONY HALLAS TONY ON THE COVER The universe, at least 93 billion light-years across, is awash in some 100 billion galaxies like NGC 6946, a beautiful face-on spiral. CONTENTS 20 COLUMNS FEATURES Strange Universe 10 20 36 50 BOB BERMAN How immense is the The Sky this Month The Virgo Supercluster: For Your Consideration 14 JEFF HESTER universe? A gemlike shower. Our 100,000 closest Unfettered by tales of science MARTIN RATCLIFFE AND galaxies Observing Basics 64 fiction, the cosmos is almost ALISTER LING Small groups combine with larger GLENN CHAPLE incomprehensibly large. clusters to form a vast network Secret Sky 66 DAVID J. EICHER 38 of interconnected galaxies that STEPHEN JAMES O’MEARA StarDome and spans 110 million light-years. 68 24 SARAH SCOLES Cosmic Imaging Path of the Planets ADAM BLOCK Our solar system: RICHARD TALCOTT; Realms of fire and ice ILLUSTRATIONS BY ROEN KELLY 56 We start your tour of the cosmos Limits of the cosmos: QUANTUM GRAVITY with gas and ice giants, a lot of 44 The far reaches of space Snapshot 9 rocks, and the only known abode The Local Group: Everything astronomers have Astro News 12 for life. FRANCIS REDDY Our galactic learned points to a universe neighborhood populated by superclusters of gal- IN EVERY ISSUE 30 axies, incredibly long filaments, The Milky Way’s family of galax- The Milky Way: and colossal voids. LIZ KRUESI From the Editor 6 ies is locked in a multi-billion- Earth’s home galaxy year battle for gravitational Letters 10, 14, 64 Giant clouds of gas and dust supremacy. KATHERINE KORNEI 62 Web Talk 65 sprinkled with splashy star clus- Ask Astro New Products 67 ters adorn the Milky Way’s spiral Gathering the dark. arms, while the galaxy’s vast halo Advertiser Index 70 teems with darker matter. Reader Gallery 72 FRANCIS REDDY Breakthrough 74 Visit Astronomy.com/toc for bonus material — it’s ONLINE exclusive to Astronomy FAVORITES magazine subscribers. Astronomy (ISSN 0091-6358, USPS 531-350) is pub- Go to www.Astronomy.com Blogs from The Sky Reader Photo 50 Weirdest lished monthly by Kalmbach Publishing Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI for info on the biggest news and the Local this Week Gallery Objects 53187–1612. Periodicals postage paid at Waukesha, observing events, stunning photos, Group A daily digest Share your Explore the WI, and additional offices. POSTMASTER: Send Insight from of celestial astroimaging most curious address changes to Astronomy, 21027 Crossroads informative videos, and more. Circle, P. O. Box 1612, Waukesha, WI 53187–1612. the editors events efforts cosmic oddities Canada Publication Mail Agreement #40010760. 4 ASTRONOMY • DECEMBER 2015 LARGE APERTURE VIEWS ROCK SOLID DESIGN NO COMPROMISE CPC COMPUTERIZED TELESCOPES Instantly recognizable by their dual fork arm mounts, the Celestron CPC has become a favorite at star parties worldwide for its comfortable yet bright, wide views and is currently in use by astronauts on board the International Space Station for Earth-based observation from space. Bring home the iconic CPC and experience these acclaimed views for yourself. WITH CPC, YOU GET THE BEST OF CELESTRON’S 55 YEARS OF INNOVATION: + Rock-solid dual fork arm mount with precision drive base and mechanics + Quick-release clutch and large drive gears + Celestron’s signature Schmidt-Cassegrain optics in sizes 8, 9.25, and 11 inches + StarBright XLT optical coatings + SkyAlign technology so you are aligned and ready to observe in minutes without having to know the name or location of any star + NexStar+ hand control with 40,000+ object database + Internal GPS + Compatible with Celestron’s latest accessories: StarSense AutoAlign for quick, self-guided alignment or SkyQ Link 2 WiFi Module for wireless control with your smartphone or tablet + Heavy-duty steel tripod with accessory tray and spring-loaded mounting screws CPC 800 CPC 925 CPC 1100 OPT Telescopes – 800.483.6287 – opttelescopes.com High Point Scientific – 800.266.9590 – highpointscientific.com B&H Photo – 800.947.9970 – bhphotovideo.com Optics Planet – 800.504.5897 – opticsplanet.com Hands On Optics – 866.726.7371 –handsonoptics.com Focus Camera – 800.221.0828 – focuscamera.com Astronomics – 800.422.7876 – astronomics.com Woodland Hills – 888.427.8766 – telescopes.net Adorama – 800.223.2500 – adorama.com FROM THE EDITOR BY DAVID J. EICHER Editor David J. Eicher Art Director LuAnn Williams Belter EDITORIAL Senior Editors Michael E. Bakich, Richard Talcott Production Editor Karri Ferron Associate Editors Eric Betz, Korey Haynes The end of Editorial Associate Valerie Penton ART Senior Graphic Designer Chuck Braasch Illustrator Roen Kelly Production Coordinator Jodi Jeranek everything CONTRIBUTING