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ON THE COVER Some 13.8 billion years ago, the Big Bang commenced a process that filled the universe with galaxies like M31. But we’re still CONTENTS 44 trying to determime how it all happened. TONY HALLAS

COLUMNS FEATURES Strange Universe 16 BOB BERMAN 20 38 56 For Your Consideration 18 Is the Big Bang in crisis? Star Dome and Target edge-on and JEFF HESTER Stubborn problems with Paths of the Planets face-on galaxies dark matter, dark energy, RICHARD TALCOTT; Hunting pins and needles in Observing Basics 64 and cosmic expansion have ILLUSTRATIONS BY ROEN KELLY the deep sky will give your GLENN CHAPLE some astronomers rethinking observing some pizzazz. Binocular Universe 66 what we know about the early 44 STEPHEN JAMES O’MEARA PHIL HARRINGTON universe. DAN HOOPER Cosmic clouds 3D A glimpse behind the dusty 62 30 veil of nebulae reveals the We test Canon’s new 9 V.M. Slipher’s chemistry of the universe. astrocamera QUANTUM GRAVITY expanding universe DAVID J. EICHER AND BRIAN MAY; With 30 megapixels of Everything you need to The Lowell Observatory STEREO IMAGES BY resolution, a full-frame sensor, know about the universe J.-P. METSÄVAINIO astronomer’s revolutionary and a mirrorless body, the EOS this month: an asteroid- findings include the expansion Ra camera can help you reveal strike crater found, a of the universe and the 52 the night sky in all its glory. second repeating FRB discovery of the interstellar Charting the TONY HALLAS tracked, new astronauts medium. DAVID J. EICHER 19th-century heavens introduced, and more. Schools and colleges 68 36 throughout America regarded Ask Astro Sky This Month The Geography of the Heavens Stellar collisions. IN EVERY ISSUE as a valuable tool for teaching Venus meets Mercury. From the Editor 6 astronomy. MICHAEL E. BAKICH MARTIN RATCLIFFE AND Astro Letters 8 ALISTER LING Advertiser Index 65 New Products 67 Reader Gallery 70 Breakthrough 74 ONLINE FAVORITES Astronomy Go to www.Astronomy.com Picture of Sky This My Science Trips and (ISSN 0091-6358, USPS 531-350) the Day Week Shop Tours is published monthly by Kalmbach Media for info on the biggest news and Co., 21027 Crossroads Circle, P. O. Box 1612, Gorgeous A daily digest Perfect gifts for Travel with Waukesha, WI 53187–1612. Periodicals postage observing events, stunning photos, photos from of celestial your favorite the staff of paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to informative videos, and more. our readers. events. science geeks. Astronomy. Astronomy, PO Box 8520, Big Sandy, TX 75755. Canada Publication Mail Agreement #40010760.

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WWW.ASTRONOMY.COM 5 FROM THE EDITOR

Editor David J. Eicher Design Director LuAnn Williams Belter EDITORIAL Galaxies, the Big Bang, Senior Editor Richard Talcott Production Editor Elisa R. Neckar Senior Associate Editor Alison Klesman Associate Editor Jake Parks Copy Editor McLean Bennett and existence Editorial Assistant Hailey McLaughlin ART Contributing Design Director Elizabeth Weber When I talked with my friend Dan Illustrator Roen Kelly Hooper at Fermilab a few months ago, Production Specialist Jodi Jeranek CONTRIBUTING EDITORS we decided that it was high time to do Michael E. Bakich, Bob Berman, Adam Block, a “state-of-the-art” story on where we stand with Glenn F. Chaple Jr., Martin George, Tony Hallas, Phil Harrington, Korey Haynes, Jeff Hester, Alister Ling, dark matter. When Dan started writing the story, Stephen James O’Meara, Martin Ratcliffe, Raymond Shubinski however, he evolved it into a summary of a much SCIENCE GROUP Executive Editor Becky Lang bigger dilemma: “Holes” in the Big Bang theory Design Director Dan Bishop of the origin of the universe are increasingly leav- EDITORIAL ADVISORY BOARD ing some astronomers unsettled. So his story, “Is Buzz Aldrin, Marcia Bartusiak, Jim Bell, Timothy Ferris, Alex Filippenko, Adam Frank, John S. Gallagher lll, the Big Bang in crisis?” describes the problems Daniel W. E. Green, William K. Hartmann, Paul Hodge, Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern, astronomers must yet overcome. James Trefil When the universe began to assemble matter, it preferred to lump it into galaxies — huge clouds Kalmbach Media The blue light in this Chief Executive Officer Dan Hickey and wheels of stars, gas, and dust. As I was grow- Senior Vice President, Finance Christine Metcalf image of MACS ing up — when we weren’t even sure that the Big Bang was the Senior Vice President, Consumer Marketing Nicole McGuire J0717.5+3745 shows Vice President, Content Stephen C. George the arrangement of correct model of the universe — one of my favorite books was Tim Vice President, Operations Brian J. Schmidt dark matter in this Ferris’ classic Galaxies. Since its publication in 1980, what we know Vice President, Human Resources Sarah A. Horner galaxy cluster. Despite Senior Director, Advertising Sales and Events David T. Sherman the ubiquity of dark about galaxies, the basic units of matter in the cosmos, has been Advertising Sales Director Scott Redmond matter in the universe, completely revolutionized. I’ve written my own book, Galaxies: Circulation Director Liz Runyon Director of Design & Production Michael Soliday astronomers still have Inside the Universe’s Star Cities, to explain exactly what we know Managing Design Director Lisa A. Bergman no good idea what it New Business Manager Cathy Daniels is made of. NASA/ESA/ about these majestic structures now. You can order copies of this Retention Manager Kathy Steele D. HARVEY (ÉCOLE POLYTECHNIQUE new book, just out, from MyScienceShop.com. Single Copy Specialist Kim Redmond FÉDÉRALE DE LAUSANNE)/ This issue features stories on galaxies, too. Veteran observer Steve ADVERTISING DEPARTMENT R. MASSEY (DURHAM UNIVERSITY)/ Phone (888) 558-1544 H. EBELING (UNIVERSITY OF O’Meara describes how you can observe face-on and edge-on galax- Ad Production [email protected] HAWAII)/J.-P. KNEIB (LAM) ies, and lists challenging objects in each category to target. We have Dina Johnston, [email protected] a historical story I’ve done on the great astronomer V.M. Slipher, RETAIL TRADE ORDERS AND INQUIRIES Selling Astronomy magazine or products in your store: who discovered in 1912 that the universe is expanding. Phone (800) 558-1544 Outside U.S. and Canada (262) 796-8776, ext. 818 And we have an excerpt from another brand-new book, Cosmic Fax (262) 798-6592 Clouds 3-D: Where Stars Are Born, which I wrote along with Brian Email [email protected] Website www.Retailers.Kalmbach.com May, my book-writing partner and founding member and guitarist CUSTOMER SALES AND SERVICE of the rock group Queen. This book features the incredible work Phone (877) 246-4835 Outside U.S. and Canada (903) 636-1125 of Finnish photographer J.-P. Metsävainio, who is a master at Customer Service [email protected] analyzing the data of distant nebulae and creating realistic 3D CONTACT US Ad Sales [email protected] images showing the relative distances of stars and gas clouds Ask Astro [email protected] surrounding them. You can also order this book from Books [email protected] Letters [email protected] MyScienceShop.com. Products [email protected] On a staffing note, please join me in congratulating Alison Reader Gallery [email protected] Editorial Phone (262) 796-8776 Klesman on her promotion to Senior Associate Editor. Since joining the magazine in 2016, Alison has taken on an increasingly larger For reprints, licensing, and permissions: PARS International at www.parsintl.com and more varied workload and has produced very nice stories that Copyright © 2020 Kalmbach Media Co., all rights reserved. This publication I know you have enjoyed. You’ll treasure her work for a long time may not be reproduced in any form without permission. Printed in the U.S.A. Allow 6 to 8 weeks for new subscriptions and address changes. Subscription to come. rate: single copy: $5.99; U.S.: 1 year $42.95; 2 years $79.95; 3 years $114.95. Canadian: Add $12.00 postage per year. Canadian price includes GST, payable in U.S. funds. All other international subscriptions: Add $16.00 postage per year, payable in U.S. funds, drawn on a U.S. bank. BN 12271 3209 RT. Not Follow the Yours truly, responsible for unsolicited materials. Dave’s Universe blog: www.Astronomy. com/davesuniverse FOLLOW ASTRONOMY Follow Dave Eicher on Twitter: David J. Eicher www.twitter.com/AstronomyMag @deicherstar Editor www.facebook.com/AstronomyMagazine

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WWW.ASTRONOMY.COM 7 ASTRO LETTERS

Remembering 2019 vapor has been identified on planet K2-18 b includes the Your January issue was spectacular. information: “The researchers were able to tease out the The “Top 10 space stories of 2019” undeniable fingerprint of water vapor in the atmo- shows what was accomplished this sphere.” This line was an opportunity to inform your past year. The overload of informa- readers that the “teasing out” was done by the research- tion is overwhelming, but the article ers’ use of spectroscopic analysis. Adding that informa- on black holes took my breath away. tion to the article would certainly benefit your readers. In his editor’s note, David Eicher — Frank Lock, Gainesville, GA

ESA/HUBBLE/M. KORNMESSER masterfully expresses the death and K2-18 b is a super-Earth birth of stars as the grandest recy- exoplanet, discovered in 2015. cling program. Little did I know what lurks behind the A job well done beautiful “like a diamond in the sky” stars at night. I appreciate Senior Associate Editor Alison Klesman. Not But the most exhilarating story was in Quantum only were her answers in January’s Ask Astro clear and Gravity. It covered the mighty super-Earth exoplanet, concise, I noticed she was the sole expert providing all of We welcome your comments K2-18 b, and its signs of habitability. I’m looking forward the answers. I hope Alison’s colleagues give her a well- at Astronomy Letters, to another astronomical year! — Shobha Kaicker, deserved pat on the back. — Jim McLeod, Charlotte, NC P.O. Box 1612, Mississauga, Ontario Waukesha, WI 53187; or email to letters@ Televised eclipse astronomy.com. Forever teaching Thank you for the fine article “Astronomy’s electronic Please include your name, city, state, and Each month I look forward to receiving Astronomy. I had revolution” in the February issue. I can relate to it as country. Letters may the wonderful experience of teaching high school astron- I used an RCA TK11 television camera, which had an be edited for space omy for the final six years of my 35-year career. image orthicon as the pickup device, to televise a lunar and clarity. The article in the January 2020 issue indicating water eclipse in 1960. — Bob Zuelsdorf, Grass Valley, CA Deep Sky Euphoria!

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8 ASTRONOMY • MAY 2020 QUANTUM GRAVITY QG EVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH

SNAPSHOT ANATOMY OF A COSMIC SWAN Infrared light reveals a famous object’s piecemeal past.

The Omega Nebula, also called the Swan Nebula, is a massive star-forming region about 5,000 light-years away. Hidden within its opaque, dusty clouds are more than 100 newly formed stars as well as clues to the region’s past, including how the nebula itself formed over time. Using the Stratospheric Observatory for Infrared Astronomy, or SOFIA, astronomers have peered deeper into the region than ever before to discover nine new massive protostars — collapsing sections of gas and dust that will soon ignite into suns. SOFIA’s observations also show that different areas of the nebula have different ages. Rather than forming all at once or sequentially from top to bottom, the central region of the nebula formed first, followed by the northern portion, while the southern part of the nebula is youngest. By studying the nebula NEW NAME TWIN SUNS BIG SOLO and how it is put together, HOT BYTES The Large Synoptic On January 6, In April 2019, LIGO astronomers hope to learn Survey Telescope, under researchers announced spotted the second- more about the conditions construction on Cerro that NASA’s TESS ever gravitational wave in which the galaxy’s most Pachón, Chile, is now planet-hunting signal generated by massive stars are born. called the National spacecraft had spotted a binary neutron star — ALISON KLESMAN Science Foundation Vera its first planet with merger. It is the first C. Rubin Observatory two suns. The world, confirmed event seen — the first national called TOI 1338 b, orbits with only one gravita- U.S. observatory named its binary stars every tional wave detector, A’S GODDARD SPACE FLIGHT CENTER; NATIONAL SCIENCE FOUNDATION/LIGO/SONOMA STATE UNIVERSITY/A. SIMONNETNASA/SOFIA/LIM, STATE SCIENCE FOUNDATION/LIGO/SONOMA DE BUIZER, FLIGHT CENTER; NATIONAL & RADOMSKI GODDARD ET SPACE NAS AL.,A’S BOTTOM ESA/HERSCHEL, FROM LEFT: RUBIN OBSERVATORY/AURA/NSF; NASA/JPL-CALTECH. for a woman. 93 to 95 days. LIGO Livingston.

WWW.ASTRONOMY.COM 9 QUANTUM GRAVITY FOUND: CRATER FROM 790,000-YEAR-OLD ASTEROID STRIKE The massive but elusive impact rained down ash over 10 percent of Earth’s surface, leaving a mark far beyond the site of the hit.

INCOMING. Large asteroids rarely end up on a collision course with Earth. But smaller impactors, like the one seen in this artist’s concept, can still wreak havoc around the world. URIKYO33 (PIXABAY)

The blinding flash of light identifying the potential impact site via just seconds. The meteorite’s speed came first, followed by a shock satellite imagery, researchers excavated and force would have been enough to wave and massive earthquake. Only the area and found the lava dated to send pillow-sized boulders careening later did the hailstorm of black, glassy around the same time as the impact, through the air at almost 1,500 feet debris begin, a rocky rain that fell on while the surrounding sediments were (460 meters) per second — faster than 10 percent of Earth’s surface. older. This evidence was bolstered by the speed of sound. “It would not That’s the scene that followed a mas- gravity measurements that hinted at have been a healthy thing to be on the sive asteroid impact 790,000 years ago. a crater hiding below. receiving end of that,” Sieh says. The rocky remains it scattered, called By finding the site of the asteroid Next, Sieh wants to focus on some tektites, have been found from Asia to strike, researchers have been able to of the ashy material surrounding the Antarctica. For decades, scientists have reconstruct some of the chaos that meteor’s debris. The impact would searched for the elusive resting place ensued after the impact, says study have incinerated all plant and animal of the impactor. And now, they think co-author Kerry Sieh, a geologist at life within 300 miles (480 km) of the they’ve found it. Nanyang Technological University impact site, and Sieh is curious how in Singapore. The finding could also that kind of settling dust would affect ELUSIVE CRATER illustrate some of what we could expect all of us today, if such an event were to A report published January 21 in the if a similarly large asteroid were to occur in modern times. Proceedings of the National Academy strike Earth again. The odds of such an impact in our of Sciences says that the meteorite lifetimes are extremely low, but the likely struck in the Bolaven Plateau in ANATOMY OF AN APOCALYPSE prospect still fascinates Sieh. “I’ve never southern Laos, carving a 10.5-by-8-mile Roughly 1.25 miles (2 km) wide, the worked on meteorites before,” he says, (17 by 13 kilometers) crater that’s now impacting rock would have gouged “but I got sucked into this with my covered by an ancient lava flow. After a hole larger than San Francisco in curiosity.” — LESLIE NEMO, JAKE PARKS

10 ASTRONOMY • MAY 2020 QUICK THE NEXT FAST FACT TAKES The three smallest ground-based GENERATION scopes shown here were the world’s best for nearly a century. HELLO, NEIGHBOR OF TELESCOPES NASA’S planet-hunting TESS telescope has discovered a habitable Earth-sized exoplanet candidate just Kepler Yerkes Observatory Hooker 100 light-years from Earth — close Earth-trailing California Hale solar orbit Wisconsin Bolshoi Azimuthal (1917) California Telescope Subaru enough that its atmosphere could (2009) (1897) (1949) Russia (1975) Telescope W.M. Keck be targeted by the upcoming Hawaii Observatory James Webb Space Telescope. Gaia (1999) Hawaii spacecraft (1990/1996) BLACK HOLE BULLIES Earth-Sun L2 Large Binocular (2013) Telescope Tidal Disruption Events (TDEs) — Arizona (2005) Gran Telescopio Canarias which occur when a black hole Hubble Space Canary Islands tears an unlucky star into a disk of Telescope Gemini (2007) North & South Magellan hot, glowing gas that is eventually Low Earth orbit Telescopes (1990) Hawaii/Chile Very Large consumed — may come in two (1999/2000) Chile (2000/2002) Telescope flavors: complete and partial. New Chile (1998) research suggests the light curves James Webb Simonyi of TDEs can help astronomers know Space Telescope Survey Telescope at which type they’re looking. Earth-Sun L2 Chile (planned 2021) (planned 2020) EARLY BIRD SPECIAL Thirty Meter Telescope Hawaii A distant, giant galaxy seen as it (planned 2027) existed 1.5 billion years after the Big 10m 30ft Bang appears to have finished forming stars at its center. The find Tennis court at same scale implies that other ancient and 0 Human massive galaxies might have also Key: Giant Magellan European Extremely completed star formation in their Northern Hemisphere (blue) Telescope Large Telescope cores early in the universe’s history. Southern Hemisphere (green) Chile Chile Space-based (orange) : RICKASTRONOMY JOHNSON, AFTER CMGLEE/WIKIMEDIA COMMONS (planned 2029) (planned 2025) SPACE TRIAGE OPTICAL EVOLUTION. An unnamed astronaut discovered Mount Wilson’s famous 100-inch (2.5 meters) Hooker Telescope they had a blood clot in their jugular reigned as the world’s largest from 1917 until Palomar Observatory’s 200-inch (5 m) Hale vein while carrying out a vascular Telescope was pressed into service in 1949. Although the primary mirrors of both Hooker study aboard the ISS. The clot was and Hale were modern marvels during their times, the telescopes of a century ago will look successfully managed with a treatment of blood thinners, and like toys in comparison to the goliath observatories now being built. When the European though it was still present 24 hours Extremely Large Telescope sees first light around 2025, its mirror will stretch a truly mind- after landing on Earth, it was gone 10 days later. boggling 129 feet (39.3 m) from edge to edge. — ERIC BETZ, J.P. REMIND ME LATER Astronomers expect a pair of stars known as V Sagittae, which are on a spiraling collision course with one another, to coalesce and go nova around 2083 — give or take about 10 years. The event is expected to briefly make V Sagittae the brightest star in the night sky. BAKER’S DOZEN

NASA/JPL-CALTECH Thirteen supermassive black holes were recently found within dwarf galaxies more than 100 times less Spitzer captures a stellar playground massive than the Milky Way. Half The Perseus Molecular Cloud, seen here, abounds with young stars. Located about 1,000 were in the center, as expected. But light-years from Earth, the expansive collection of dust and gas stretches some 500 light- half the black holes were located in years across and is home to a number of intriguing targets — including the young star the outskirts of their host galaxies, cluster IC 348 (the bright clump on the left) and the reflection nebula NGC 1333 (upper meaning researchers may need to right). This image, taken about 10 years ago with NASA’s now-retired Spitzer Space expand their hunt for supermassive black holes in dwarf galaxies beyond Telescope, captures the infrared radiation streaming from the cloud. — J.P. just their cores. — J.P.

WWW.ASTRONOMY.COM 11 QUANTUM GRAVITY

Giant wave of star-forming clouds lies near the Sun

DO THE WAVE. The Radcliffe Wave is a recently discovered 9,000-light-year-long structure composed of star-forming regions, colored red in this artist’s rendition, which also shows the Milky Way Galaxy and the Sun SHOCKING (yellow). Although astronomers aren’t sure what caused the ripple- SCENE

like structure, they do CHANDRA: NASA/CXC/SAO/E. XMM: ESA/XMM/E. OPTICAL: O'SULLIVAN. O'SULLIVAN. X-RAY: SDSS know it has interacted Galaxies rarely live alone. with the Sun in the past. ALYSSA GOODMAN/HARVARD Pulled together by gravity, UNIVERSITY they congregate into groups Our local arm of the Milky Way In particular, the wave’s discovery that, over time, can merge Galaxy is doing the wave. Harvard disproves the existence of a feature into larger clusters. That’s University astronomers recently uncovered known as “Gould’s Belt,” which astrono- what’s happening in NGC a strange, wave-shaped structure within mers believed was a ring-shaped structure 6338, where two galaxy 500 light-years of the Sun, made up of sev- of star-forming regions circling the Sun. groups are rushing toward eral interconnected stellar nurseries. Taken Many of the regions previously thought to each other at about 4 million as a whole, the wave is 400 light-years reside in parts of this belt are instead part mph (6.4 million km/h). wide and 9,000 light-years long, snaking of the Radcliffe Wave, the team found, This composite image shows 500 light-years above and below the plane while other regions associated with the of the galaxy. Findings regarding the wave belt now appear to be unrelated to either the scene of the impending — dubbed the Radcliffe Wave in honor of the wave or any ring structure. “For a smashup in X-rays and the Radcliffe Institute for Advanced Study long time, people have been trying to optical light. The hottest at Harvard, where the discovery was made figure out if these molecular clouds actu- gas, with temperatures over — were published January 7 in Nature. ally form a ring in 3D,” said lead author 36 million degrees Fahrenheit Researchers found the Radcliffe Wave João Alves of the University of Vienna. (20 million degrees Celsius) while analyzing data from the European “Instead, what we’ve observed is the is colored red. Cooler gas in Space Agency’s Gaia mission, which largest coherent gas structure we know is tasked with charting the location of in the galaxy, organized not in a ring the cores of the two groups and motion of stars within our galaxy. but in a massive, undulating filament. … appears blue, while stars and Combining that information with other It’s been right in front of our eyes all the galaxies shining in optical observations as well as simulations and time, but we couldn’t see it until now.” light are white. The thin strip data visualization, they discovered the Now, thanks to the team’s efforts, we of hot gas between the cores, undulating structure in the spiral arm of can see it, and the information will allow as well as the gas around the Milky Way closest to our solar system. astronomers to better understand the them, has been heated by According to the team, the wave looks properties of the star-forming clouds of shocks generated during the long and straight from above, but from gas and dust that are part of the wave. the side, it appears to bob up and down That’s because calculating the size and collision, similar to the sonic out of the plane of the galaxy. “The wave’s mass of such clouds relies on knowing booms made by supersonic very existence is forcing us to rethink our their distance, which until now has been aircraft. Although this understanding of the Milky Way’s 3D difficult to measure. Additionally, the pattern of shocked gas has structure,” said study co-author Alyssa data combination techniques used by been predicted by simulations Goodman, co-director of the Science the team can set the stage for even more, in the past, NGC 6338 is the Program at the Radcliffe Institute for perhaps also surprising, findings about first galaxy group merger that Advanced Study, in a press release. the structure of the Milky Way. — A.K. shows clearly this effect. — A.K.

12 ASTRONOMY • MAY 2020 HOW THE PLANETS LINE UP TILT-A-WHIRL. The planets orbit our Sun in a relatively flat plane. But the key word here is relatively — some planets lie closer to this plane than others. The amount a planet’s orbit is tilted, or inclined, away from the plane is called its inclination. As earthbound observers, we have defined the plane of the solar system, called the ecliptic, as the orbit of Earth around the Sun. Therefore, Earth has an inclination of 0.0°. Here’s how the other planets (and Pluto) stack up. — A.K. Pluto FAST FACT 17.2° The planets orbit in a plane because the solar system formed out of a relatively flat disk of gas and dust swirling around our infant Sun.

Jupiter Mars 1.3° Uranus Spin axis 1.9° 0.8°

Saturn Neptune Mercury Venus 7.0° Earth 2.5° 1.8° 3.4° 0.0° ASTRONOMY: ROEN KELLY

Our nearby gentle giant The spiral galaxy UGC 2885, also called Rubin’s Galaxy, is something of a local legend. At 232 million light-years away, it is the largest galaxy known in our nearby universe, spanning more than twice the width of the Milky Way and containing 10 times as many stars. But astronomers aren’t sure how it got so large. Galaxies typically grow by consuming or smash- ing into other galaxies. But UGC 2885 is alone in space, apparently having undergone neither process to gain its heft. Instead, researchers believe it may have grown by calmly siphoning gas from intergalac- tic space. One way to read the NASA, ESA, AND B. HOLWERDA (UNIVERSITY OF LOUISVILLE) galaxy’s past is to study the globular clusters of stars around it. These clusters often survive collisions and assimilations, The total, in USD, awarded revolving around the final result. Astronomers are now look- $58,000 by the Planetary Society, in ing to count up the globular clusters around UGC 2885 to see whether it has more than it should, which would hint varying amounts, to six amateur astronomers that it’s eaten other galaxies in the past. — A.K. focused on discovering and characterizing near-Earth asteroids.

WWW.ASTRONOMY.COM 13 QUANTUM GRAVITY

UP IN ARMS. FRB 180916 lies in a Milky Way- like spiral galaxy 500 million light- years away. The location of the FRB (circled) in one of the galaxy’s star-forming spiral arms challenges astronomers’ ideas about the origin of these mysterious bursts. GEMINI OBSERVATORY/NSF'S NATIONAL OPTICAL-INFRARED ASTRONOMY RESEARCH LABORATORY/AURA

Second repeating fast radio burst tracked, deepening mystery

Fast radio bursts (FRBs) are It is the closest FRB tracked to date the types of conditions that cause FRBs, short, powerful blasts of energy and lies within an outer arm of its host repeating and nonrepeating. that originate outside our galaxy. Only galaxy, where stars are rapidly forming. The current leading theory is that a few repeat, while most pop off only The spiral host is similar to our own FRBs are produced by neutron stars, the once. For more than a decade, astrono- Milky Way, however, making it unlike highly magnetized remnants of massive mers have sought to understand these any other galaxy in which an FRB has stars. While this could be the case for strange flashes and, in recent years, been found before. The only other some FRBs, it may not be the cause of have begun to trace some FRBs back repeating FRB that astronomers have all of them. The more FRBs astrono- to their origins. In a paper published tracked, FRB 121102, comes from a tiny, mers identify and track, the more January 6 in Nature, researchers distant dwarf galaxy 3 billion light- diverse the population becomes. “It may announced they have tracked yet years away — a dramatically different be that FRBs are produced in a large another FRB to its host galaxy. It is the environment than a spiral galaxy near zoo of locations across the universe and fifth time an FRB has been traced to our own. just require some specific conditions to its origin, and only the second time a “This object’s location is radically be visible,” Nimmo said. repeating FRB has been pinpointed. different from that of not only the previ- The team, along with many others, Combining observations from eight ously located repeating FRB, but also all aims to track an increasing number of separate telescopes, a team of astrono- previously studied FRBs,” said study co- FRBs to their hosts. They hope more mers tracked the burst, which is called author Kenzie Nimmo of the University information on where FRBs originate FRB 180916.J0158+65, to a spiral galaxy of Amsterdam in a press release. And will ultimately reveal what’s causing nearly half a billion light-years away. that has implications, the team says, for these strange flashes of energy. — A.K.

14 ASTRONOMY • MAY 2020 NASA astronauts graduate with eye toward Artemis The first class of NASA astronauts slated for the Artemis program graduated January 10. And after more than two years of basic training, the 11 NASA astronauts, in addition to two Canadian Space Agency (CSA) astronauts, are now eligi- ble for missions to the space station, the Moon, and eventually Mars. Selected from a record- setting pool of more than 18,000 applicants, this cosmic class includes some of the best and brightest our country has to offer. The next-gen astronauts are (top row, left to right) Matthew Dominick, Kayla Barron, Warren Hoburg, Joshua Kutryk (CSA); (middle row) Bob Hines, Frank Rubio, Jennifer Sidey-Gibbons (CSA), Jasmin Moghbeli, Jessica Watkins; (bottom row) Raja Chari, Jonny Kim, Zena Cardman, and Loral

O’Hara. Congratulations, graduates! — J.P. NASA

The temperature, in degrees Fahrenheit (4,300 degrees Celsius), 7,800 on the surface of the hottest-known exoplanet, KELT-9 b.

FAST FACT On February 1, asteroid 594 Mireille strayed 37° north of the ecliptic, the farthest AS in our sample. TER WL TAU O RO ID P LEO EC S O HE THE REST LI N T PTIC 291 PSC VIR AQR CET OPH

CAP LIB A THOUSAND POINTS OF LIGHT. SGR German astronomer Karl Reinmuth hit a milestone when he discovered the 1,000th aster- AQUARIUS SAGITTARIUS oid on August 12, 1923. Most 109 CAPRI- PISCES CORNUS 103 VIRGO of the first 1,000 objects lie in a 85 84 LIBRA 77 belt between the orbits of Mars OPHIUCHUS 67 TAURUS CETUS 56 LEO and Jupiter that aligns closely 45 40 43 with Earth’s orbital plane (the ecliptic). As such, they rarely : ROENASTRONOMY KELLY stray far from the zodiacal constellations where the major planets reside. The graph above shows the positions of these 1,000 asteroids on February 1, 2020. More than 70 percent of them resided in just 10 constellations. — RICHARD TALCOTT

WWW.ASTRONOMY.COM 15 STRANGE UNIVERSE

in the Albany, New York, metro area and Matt Francis’ Observatory Prescott Observatory south of that city in Arizona show, an imperfect sky is no reason to forgo such a project. True, this eliminates most deep-space objects. odds and ends However, the endless realm of double stars, as well as Moon and planet explorations, can keep you and your Don’t give up on your backyard astronomy dreams. visitors enthralled forever. Those crowd-pleasers are immune to light pollution. Of course, when galaxies and nebulae are important, you must have a dark site. If, like me, you already live far out in the boonies, your home environment might be perfect. Otherwise, if you can commute, buy some land in the middle of nowhere, where real estate is inexpen- sive. Solar panels and battery storage can preclude the need to spend a fortune erecting poles to connect to the grid. Don’t close until you’ve spent a night camping there. If one sky-direction must be blocked, sacrifice the north. Next decision: type and size. I built a big roll-off roof observatory in the mid-’80s. No one helped me, and I made major mistakes. I put the roof on swiveling casters. Don’t do that. I had to jack it up and replace everything. I also thought the roof’s wheels would roll on the wooden wall tops. Wrong again. When parked, the heavily loaded The author’s new casters created depressions and wouldn’t readily climb observatory in upstate New York, as In some alternate universes, astronomy is out of them. I jacked everything up again and topped the seen from his kitchen free. But around here, perusing these pages walls with thin steel plates. It was harder than it sounds. window. The rural filled with tempting gadgets and gleaming I also learned that everything needs to be periodically landscape is free of lights and houses. But telescopes, many of us have expensive dreams. greased. And that a reversible half-horsepower DC motor there’s no cell service I’m familiar with the drooling-craving syndrome. was best for moving the enormous weight. And to use or mail delivery, For me, it started with airplanes. During my three post- chains, not cables. Also, the 12-by-20-foot (3.7 by 6 meters) either. BOB BERMAN college years in Asia, some of my Peace Corps friends building was excessive. Do yourself a favor and go smaller. discovered cheap lessons at government- Then, last year, having moved to even run flight schools. Count me in! In 1985, darker skies and now significantly less I finished my training in the U.S., but A private poor, I gladly paid Explora-Dome to install what do you do after you’ve obtained a observatory may an 8-foot (2.4 m) motorized dome on their pilot’s license? Everyone’s biggest aspira- square building. Everything all together tion is to own a plane. seem utterly — the dome, building, and labor — totaled It seemed a pipe dream for this writer, unworkable for under $10K. Another few thousand cov- married to a kindergarten teacher. But, it urbanites. ered the masonry foundation and pier, and turned out, good used four-seaters are not Nonetheless, the end result was my big f/6 equatorial crazy expensive, and the next three many stubbornly reflector in one observatory (the roll-off) decades were peppered with fairy-tale and apochromatic refractor in the dome. aerial adventures. dream of Shuttling back and forth from a dome The parallels to our astronomy passion owning one. to a roll-off provides a great A/B compari- are obvious. A private observatory may son. Yes, a dome looks cool. But a roll-off seem impossibly opulent and utterly exposes the entire sky, letting occupants unworkable for urbanites. Nonetheless, many stub- stargaze or use binoculars while waiting their turn at the bornly harbor the dream of owning one. scope. You can’t do that in a dome. BY BOB BERMAN As someone who has traveled that road and managed The bottom line is: Don’t ever abandon your observa- Join me and Pulse to make every possible mistake in the process, let me tory dream. of the Planet’s share some hard-won lessons. I’ve skipped the part about how snakes like to nest Jim Metzner First is the issue of “where?” You might think a city in them. in my podcast, Astounding Universe, would be out of the question. But I watched a physician at www.astounding in light-polluted Kingston, New York, construct a dome BROWSE THE “STRANGE UNIVERSE” ARCHIVE universe.com on his Victorian rooftop. And, as Dudley Observatory AT www.Astronomy.com/Berman

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WWW.ASTRONOMY.COM 17 FOR YOUR CONSIDERATION

engineers, Apollo didn’t go to the Moon to beat the Rekindling dreams Soviets. Apollo went to the Moon for us. I was saddened by the disaster of space shuttle When will humankind leave the cradle? Columbia. I was livid when it became clear that space shuttle Challenger exploded because someone thought It is hard to say whether I political expediency was more important than physical truly remember Mercury reality. astronauts being bolted I never saw eye to eye with colleagues who bemoaned into tiny capsules and blasted into dollars spent on human spaceflight. While robotic explo- space, or whether I only remember ration of space is one of humanity’s grandest accomplish- remembering. Regardless, those ments, for many, including myself, robots aren’t enough. images are there in my mind. That is It matters that humans see, feel, experience, and push where my lifelong love affair with limits. It always has, and it always will. Had you told me science, engineering, and explora- at 12 years old that half a century would pass without a tion took root. return to the Moon, much less a trip to Mars, I probably Even as a young kid, I understood would have spit in your face. But here we are. that spaceflight was about pushing Personally, I can’t really complain. As a kid (and, to be the limits of human experience. honest, as an adult, too) I devoured books by the likes of Maybe I became aware of the danger Ray Bradbury, Isaac Asimov, and Arthur C. Clarke. when Gemini VIII tumbled out of Experiences like working in the Mission Operations When Gene Cernan control after the first-ever docking Center as STS-61 astronauts installed WFPC2, the snapped this photo of of two spacecraft in orbit. A quick-thinking Neil camera that saved Hubble, offered small tastes of what Jack Schmitt on the lunar surface, along Armstrong and David Scott narrowly averted tragedy that future might have been like. with the Apollo 17 by using the reentry system to wrestle the capsule back But do dreams from childhood ever really die? Call rover, no one yet under control. me a romantic, but apparently the answer is no. appreciated how long it would be until Or maybe it all became real with the Apollo 1 fire. When two reusable SpaceX Falcon Heavy boosters humans returned Along with much of the world, I was landed side by side, I felt hope and longing as to the Moon. NASA/JSC glued to the TV waiting for Apollo 8 to much as I did excitement. And, face it: It takes emerge from behind the Moon on Is all of the a certain je ne sais quoi to launch your cherry- Christmas Eve 1968. As a 10-year-old, I red electric sports car into Mars-crossing listened when Armstrong again demon- recent talk solar orbit with a spacesuit-clad mannequin strated his skill as a seat-of-the-pants pilot, about named Starman in the driver’s seat. landing on the Moon with only 15 seconds sending Those were teases; September’s rollout of of fuel to spare. humans to the shining, bullet-shaped Starship proto- By all accounts, Apollo 13 should have the Moon and type took my breath away. How could the ended in tragedy. I recall shocked amaze- cover artists for all of those 1940s and ’50s ment when I first saw a picture of the hole Mars a pipe science fiction magazines have known? blasted in the side of the Service Module dream? Robert Heinlein’s The Man Who Sold the when an oxygen tank exploded. Twenty-five Moon was pure fiction, but could Elon Musk years later, I was visiting Fermilab when a become The Man Who Sold Mars? While freshly minted particle physics graduate student scoffed SpaceX is careful not to say too much about schedules at the “preposterous” plot of the newly released Tom publicly, there is talk on the street of the possibility of a Hanks movie. I’m not sure that he believed me when I Mars landing within the next five years or so. One even told him it was a true story. hears that a base could be up and running within the I cried when I watched Apollo 17 lift off from the decade. If and when that happens, it seems clear that Moon, knowing that the last three planned missions Musk has no intention of walking away. had been canceled. I now understand why that decision This is a struggle. Is all of the recent talk about send- was inevitable. To the people calling the shots, Apollo ing humans to the Moon and Mars a pipe dream? Can was never really about exploration. We went to the Musk — or, for that matter, NASA or Blue Origin — Moon to one-up the Soviets in the eyes of the world. make it so? After a lifetime of resignation, should I again BY JEFF HESTER Having accomplished that end, each additional flight let myself dream of seeing humans on another world? Jeff is a keynote put that political victory at risk with little perceived Could I stop myself if I tried? speaker, coach, and astrophysicist. gain in status. Follow his thoughts But for a generation of young people who watched BROWSE THE “FOR YOUR CONSIDERATION” at jeff-hester.com that drama and went on to become scientists and ARCHIVE AT www.Astronomy.com/Hester

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For complete details and to book, go to: TravelQuestTours.com P36879 Spiral galaxy M101 harbors hundreds of Cepheid variables that scientists use to measure the universe’s expansion rate, though the value differs from that deduced from the cosmic microwave background. M101 also harbors vast amounts of mysterious dark matter. Enigmas such as these have cosmologists questioning their ideas on cosmic evolution. This composite image combines visible light (yellow), infrared radiation (red), and X-rays (blue). NASA/ESA/CXC/SSC/STSCI

20 ASTRONOMY • MAY 2020 Stubborn problems with dark matter, dark energy, and cosmic expansion have some astronomers rethinking what we know about the early universe. BY DAN HOOPER

WWW.ASTRONOMY.COM 21 With a diameter 2.5 times that of the Milky Way and containing 10 times as many stars, UGC 2885 ranks among the largest spiral galaxies in the local universe. But there’s more here than meets the eye: Invisible dark matter accounts for some 85 percent of UGC 2885’s mass. Vera Rubin discovered dark matter in this galaxy during her pioneering study of this mysterious material. NASA/ESA/B. HOLWERDA (UNIVERSITY OF LOUISVILLE)

series of powerful abundances of various chemical elements, and neutrons could have survived the observations has made and the distribution of galaxies and other aftereffects of the Big Bang. In fact, it clear that our uni- large-scale structures — we find stunning everything we know about the laws of verse has expanded for agreement. Each of these lines of evidence physics tells us that these particles should Abillions of years, supports the conclusion that our universe have been destroyed by antimatter long emerging from the expanded and evolved in just the way that ago. And in order to make sense of the hot, dense state we call the Big Bang. the Big Bang theory predicts. From this universe as we observe it, cosmologists Over the past several decades, new types perspective, our universe appears to be have been forced to conclude that space, of precise measurements have allowed remarkably comprehensible. during its earliest moments, must have scientists to scrutinize and refine this But cosmologists have struggled — undergone a brief and spectacular period account, letting them reconstruct the his- if not outright failed — to understand of hyperfast expansion — an event tory of our universe in ever greater detail. essential facets of the universe. We know known as cosmic inflation. Yet we know When we compare the results from dif- almost nothing about dark matter and next to nothing about this key era of ferent kinds of measurements — the dark energy, which together make up cosmic history. expansion rate of the universe, the tem- more than 95 percent of the total energy It’s possible that these puzzles are little perature patterns in the light released in existence today. We don’t understand more than loose ends, each of which will when the first atoms formed, the how the universe’s protons, electrons, be resolved as cosmologists continue to

22 ASTRONOMY • MAY 2020 TOP: This galaxy cluster, nicknamed El Gordo (Spanish for “The Fat One”), ranks as the largest known cluster in the distant universe. Composed of two individual clusters colliding at more than 1 million mph (1.6 million km/h), this structure holds a mass equivalent to 3 quadrillion Suns. ESA/HUBBLE & NASA/RELICS investigate our universe. But so far, these problems have proven to be remarkably ABOVE: The blue color added to this image maps the distribution of dark matter in the El Gordo galaxy cluster. Astronomers traced the presence of this shadowy substance by looking at how it distorts the stubborn and persistent. With the goal of appearance of more distant objects. NASA/ESA/J. JEE (UNIVERSITY OF CALIFORNIA, RIVERSIDE) identifying the individual particles that make up dark matter, scientists have designed and built a series of impressive the force that seems to be accelerating What we’ve learned by not experiments — yet no such particles the expansion of the cosmos. discovering dark matter have appeared. Even powerful particle It is from this perspective that some Dark matter is likely the most celebrated accelerators like the Large Hadron cosmologists have found themselves ask- problem facing modern cosmologists. Collider have revealed nothing that ing whether these cosmic mysteries Astronomers have determined that most moves us closer to resolving any of these might be symptoms of something more of the matter in our universe does not cosmic mysteries. And despite having significant than a few loose threads. consist of atoms or any other known measured the expansion history and Perhaps these puzzles are not as unre- substances, but of something else — large-scale structure of the universe in lated as they might seem, but are instead something that does not appreciably ever increasing detail, we have not collectively pointing us toward a very radiate, reflect, or absorb light. gained any substantively greater under- different picture of our universe and its Despite not knowing much about the standing of the nature of dark energy, earliest moments. nature of dark matter, cosmologists often

WWW.ASTRONOMY.COM 23 The supercluster Abell 901/902 holds hundreds of galaxies and massive amounts of dark matter. The magenta-tinted clumps show the dark matter’s distribution, derived from Hubble Space Telescope The Coma Cluster packs thousands of galaxies into a sphere measuring more than 20 million light-years observations, overlaid on a ground-based image of across. Fritz Zwicky discovered dark matter in this cluster in the 1930s when he deduced that the galaxies the supercluster. HUBBLE DATA: NASA/ESA/C. HEYMANS (UNIVERSITY OF are moving too fast to stay together unless the cluster contains nearly 10 times as much matter as what BRITISH COLUMBIA) ET AL./THE STAGES COLLABORATION. GROUND-BASED IMAGE: can be seen. NASA/ESA/THE HUBBLE HERITAGE TEAM (STSCI/AURA) ESO/C. WOLF (OXFORD UNIVERSITY) ET AL./THE COMBO-17 COLLABORATION speculate about the kinds of particles scientists were optimistic that these Helen Quinn in 1977. Although that might make up this substance. experiments would bear fruit. But dark scientists are searching for axions in In particular, researchers have long matter has turned out to be very differ- experiments that use powerful magnetic recognized that if dark matter particles ent, and far more elusive, than we had fields to convert them into photons, interact through a force that is approxi- once imagined. these investigations have yet to place mately as powerful as the weak nuclear Although it’s still possible that dark very strict constraints on the properties force (which governs radioactive decay), matter could consist of some form of of these particles. then the number of these particles that difficult-to-detect WIMPs, the lack of any Another possibility that could explain should have emerged from the Big Bang signal from underground experiments has why dark matter has been so difficult to would roughly match the measured led many physicists to shift their focus detect is that the first moments of the abundance of dark matter found in toward other dark matter candidates. One universe may have played out much dif- the universe today. With this in mind, such contender is a hypothetical ultralight ferently than cosmologists have long weakly interacting massive particles — particle known as an axion. Axions are imagined. Take the case of the conven- WIMPs — became the best guess for predicted according to a theory proposed tional WIMP. Calculations show that the dark matter’s nature. by particle physicists Roberto Peccei and fledgling universe should have produced One initially appealing aspect of vast quantities of these particles during WIMPs was that scientists thought they the first millionth of a second or so after knew how to detect the particles and the Big Bang, when they reached a state study their properties. Motivated by this of equilibrium with the surrounding goal, physicists engaged in an ambitious plasma of quarks, gluons, and other sub- experimental program to identify these atomic particles. The number of WIMPs WIMPs and learn how they were forged that could have survived these conditions in the Big Bang. Over the past couple of — and ultimately contributed to the dark decades, researchers have deployed a suc- matter found throughout today’s uni- cession of increasingly sensitive dark verse — depends on how, and how often, matter detectors in deep-underground they interacted. But when carrying out laboratories that are capable of detecting calculations such as these, scientists individual collisions between a dark mat- generally assume that space expanded ter particle and the atoms that make up steadily during the first fraction of a sec- the target. ond, without any unexpected events or The blue light in this image of MACS J0416.1–2403 These sophisticated experiments per- shows the arrangement of dark matter in this galaxy transitions. It is entirely plausible that formed beautifully — as well as or better cluster. Despite the ubiquity of dark matter in the this simply was not the case. than designed. Yet no such collisions universe, astronomers still have no good idea what Although cosmologists know a great it is made of. NASA/ESA/D. HARVEY (ÉCOLE POLYTECHNIQUE FÉDÉRALE DE have been observed. A decade ago, many LAUSANNE)/R. MASSEY (DURHAM UNIVERSITY)/HST FRONTIER FIELDS deal about how our universe expanded

24 ASTRONOMY • MAY 2020 Although dark matter in galaxy clusters typically traces the ordinary matter that radiates light, ZwCl 0024+1652 goes its own way. This massive cluster sports a dark matter ring (in blue) spanning 2.6 million light- years that appears largely divorced from the visible galaxies and gas. NASA/ESA/ M.J. JEE (JOHNS HOPKINS UNIVERSITY)

and evolved over most of its history, they Our understanding of this period of illuminate. Matter likely interacted in know relatively little about the first sec- cosmic history is, in many respects, little ways that it no longer does, and space onds that followed the Big Bang — and more than an informed guess based on and time themselves may have behaved next to nothing about the first trillionth inference and extrapolation. Look far differently than they do in the world of a second. When it comes to how our enough back in time, and almost every- we know. universe may have evolved, or to the thing we know about our universe could With this in mind, many cosmologists events that may have taken place during have been different. Matter and energy have begun to consider the possibility these earliest moments, we have essen- existed in different forms than they do that our failure to detect the particles tially no direct observations on which to today, and they may have experienced that make up dark matter might be tell- rely. This era is hidden from view, buried forces that have not yet been discovered. ing us not only about the nature of dark beneath impenetrable layers of energy, Key events and transitions may have matter itself, but also about the era in distance, and time. taken place that science has yet to which it was created. By studying dark

WWW.ASTRONOMY.COM 25 Earthbound experiments on the hunt for dark matter

COUNTERCLOCKWISE FROM TOP LEFT: The The Large Underground Xenon experiment (LUX) The Axion Dark Matter Experiment looks for IceCube Neutrino Observatory sits under South Pole attempted to detect interactions between weakly hypothetical axions when they decay into ice, hunting for cosmic neutrinos. Some of these interacting massive particles and 816 pounds microwaves in the presence of a strong magnetic subatomic particles could come from the decay (370 kg) of liquid xenon inside this tank. The field. Here, technicians install the superconducting of weakly interacting massive particles — a prime experiment, which operated from 2013 to 2016 in magnet in a lab at the University of Washington. candidate for dark matter — though none has been an old mine in the Black Hills of South Dakota, LAMESTLAMER/WIKIMEDIA COMMONS detected yet. MARTIN WOLF (ICECUBE/NSF) turned up none of these dark matter particles. A successor, the 7-ton LUX-ZEPLIN, should begin taking data in 2020. CARLOS FAHAM/WIKIMEDIA COMMONS

matter, scientists are learning about the plagued with systematic errors that led One way to determine the Hubble first moments after the Big Bang. him to overestimate the expansion rate constant is to directly measure how fast by a factor of 7. As recently as the 1990s, objects are moving away from us, just as How fast is space textbooks often quoted values ranging Hubble did in 1929. For his measurements, expanding? from as low as 50 to as high as 100 kilo- Hubble used a special class of pulsating In 1929, Edwin Hubble discovered that meters per second for every million stars known as Cepheid variables, whose galaxies are moving away from us at parsecs separating two points in space intrinsic luminosities track nicely with the speeds proportional to their distances. — usually written as 50 to 100 km/s/Mpc. periods over which they brighten and fade. This provided the first clear evidence (One megaparsec [Mpc] equals 3.26 mil- Modern cosmologists continue to use that our universe is expanding. Ever lion light-years.) Although the precision Cepheids for this purpose, but they also since, the current rate of this expansion of these measurements has improved employ other classes of objects, including — the Hubble constant — has been one considerably over the past two decades, type Ia supernovae — exploding white of the key properties of our universe no consensus yet exists regarding the cor- dwarfs that all have the same approximate that cosmologists study. rect value for this quantity. In fact, as luminosity. When researchers combine It’s fair to say that the Hubble constant these measurements have improved, the the latest data, they find that the universe has long been difficult to measure. results from different methods seem to is currently expanding at a rate of about Hubble’s original determination was disagree with one another even more. 72 to 76 km/s/Mpc.

26 ASTRONOMY • MAY 2020 expands depends on the density of density on the depends expands space at rate which the of relativity, BigBang. the following years thousand few hundred first the during universe the in energy and of forms matter the expanded and evolved, or to reconsider cosmos the how weto change think forced be would astronomers consistent, mutually results To discrepant these make model. cosmological standard ofthe text con- the within —at least incompatible to be appear Hubble constant the ing of ways determin- two these observations, the in inherent uncertainties tematic sys- the for accounted all have correctly studies these that Assuming universe? our measurements. more direct through have found cosmologists than value smaller —asignificantly 67 km/s/Mpc tells us that the Hubble constant is about It also expanding. was how space fast as well were as present, of energy forms other how and much matter including universe, young about our details many time. that at universe the throughout distributed shows how was amapthat as matter serve — background microwave cosmic the as —known light of this patterns temperature detailed The BigBang. the after years atoms 380,000 some formed first the when released light primordial the by studying Hubble constant of the value the infer can also Cosmologists GALAXIES INGALAXIES MOTION AFTER EDWIN HUBBLE/ EDWIN AFTER the basic relationship right. right. relationship basic the were a of factor nearly 10 too small, he got the distances his data.) Although estimated to fit best the gives line (The distances. their to relative galaxies of individual velocities the plotted first he when 1929, in universe Edwin Hubble discovered the expanding 1,000

According to Einstein’s general theory theory toEinstein’s general According What does this mismatch mean for mapreveals this scrutinized, When story. end ofBut the that’s not the Velocity (km/s) 500 0 12 01 Distance (megaparsecs) PNAS (MARCH 1929) 15, : ROEN KELLY,ASTRONOMY: ROEN down the Hubble constant. constant. Hubble the down remote galaxies. Scientists need both markers to pin more to distances finding to link avital as serves that hosted a type Ia supernova, an exploding white dwarf and in 2011 galaxies, nearby to relatively distances Cepheid variables, which use astronomers to gauge dozens contains ladder. of distance The galaxy cosmic the in link akey forms 3972 NGC galaxy Spiral two. the between alink forge thus and candles standard of types both possess that systems from Earth. Host to many Cepheid variable stars as well as a type Ia supernova, light-years million the 65 located pair spirals interacting is are two 4039) and NGC one 4038 (NGC of a handful Galaxies Antennae The of NASA/ESA/A. RIESS (STS RIESS NASA/ESA/A. C I/JHU) ESA/HUBBLE &NASA ESA/HUBBLE values refine astronomers for the Hubble constant. helps thus and distance galaxy’s the measure way to The microwave emission provides an independent center. its at hole black supermassive the — orbiting microwaveamplified emission from water molecules — megamaser awater harbors pair) galaxy this of member lower (the MCG+01-38-005 galaxy Spiral WWW.ASTRONOMY.COM ESA/HUBBLE &NASA ESA/HUBBLE 27 TENSION IN THE CMB LOCAL UNIVERSE COSMOS Planck (2018) SH0ES (2018)

Carnegie (2018, H band)

Carnegie (2018, B band)

H0LiCOW (2020)

60 65 70 75 80 Hubble constant (km/s/Mpc)

A type Ia supernova exploded in the grand design spiral M100 in early Astronomers have been trying to determine the expansion rate of the February 2006. (The supernova is the brighter of the two stars to the lower cosmos for nearly a century. Although measurements of this so-called right of the galaxy’s center.) Supernovae of this type, which arise when a Hubble constant have grown more precise over the years, different white dwarf accumulates too much mass from a binary companion, all methods yield different results. Direct observations of relatively nearby have the same intrinsic brightness and thus make excellent distance galaxies give significantly higher values than those deduced from indicators. ESO/IDA/DANISH 1.5 M/R. GENDLER, J.-E. OVALDSEN, C.C. THÖNE, AND C. FÉRON observations of the cosmic microwave background. ASTRONOMY: ROEN KELLY

matter and other forms of energy it con- matter remains unknown, and the prob- It is from this perspective that I some- tains. When cosmologists infer the value lem of dark energy seems nearly intrac- times find myself considering whether of the Hubble constant from the cosmic table. We do not know how the particles these mysteries might represent some- microwave background, they have to that make up the atoms in our universe thing greater than a few open and unre- make assumptions about the amounts managed to survive the first moments lated questions. Perhaps they are telling of dark matter, neutrinos, and other of the Big Bang, and we still know us that the earliest moments of our uni- substances that were present. little about cosmic inflation, how it verse were far different from what we Perhaps the simplest way to explain played out, or how it came to an end — long imagined them to be. Perhaps these the tension between the different mea- assuming that something like inflation problems represent the beginning of a surements of the Hubble constant would happened at all. revolution for the science of cosmology. be to hypothesize that the cosmos con- Sometimes I wonder whether we tained more energy than expected during might be on a significant precipice of the first hundred thousand years or so WHAT IS THE UNIVERSE scientific history, similar to what we following the Big Bang. This energy MADE OF? experienced in 1904. At that time, phys- might have taken the form of an exotic ics had never before seemed to be on Normal matter species of light and feebly interacting Dark matter 4.9% such solid footing. For more than two particles, or of some kind of dark energy 26.8% centuries, the principles of Newtonian associated with the vacuum of space physics had been applied successfully to itself that has long since disappeared problem after problem. And although from the universe. Or perhaps there is physicists expanded their knowledge into something else we don’t understand areas such as electricity, magnetism, and about this era of cosmic history. We heat, these aspects of the world were simply do not yet know how to resolve really not so different from those Newton this intriguing mystery. had described hundreds of years earlier. To the physicists of 1904, the world Is a revolution coming? seemed well understood. There was little Dark As I said earlier, it’s possible that the energy reason to expect a revolution. various puzzles cosmologists face today 68.3% Similar to the situation cosmologists are little more than a few trivial threads confront today, however, the physicists of that scientists will tie up nicely in the The atoms that make up stars, planets, and 1904 had not yet been able to address a people add up to less than 5 percent of the years ahead with the help of new experi- universe’s constituents. Invisible dark matter few challenges. The medium through ments and observations. But lately, it contributes more than five times as much, which they believed light traveled — while the dark energy that powers the seems the more we study the universe, accelerating cosmos accounts for more the luminiferous ether — should have the less we understand it. Despite than two-thirds of the total. ASTRONOMY: ROEN KELLY induced variations in the speed of light, decades of effort, the nature of dark and yet light always moves through space

28 ASTRONOMY • MAY 2020 The gravitationally lensed quasar HE 0435–1223 offers an independent method for determining cosmic distances. The close-up view reveals the foreground galaxy that creates the four nearly identical images of a more distant quasar. The galaxy lies about 4.8 billion light-years from Earth, while the quasar resides twice as far away. NASA/ESA/HUBBLE/S. SUYU (MPIA) ET AL. at the same rate. Astronomers observed the orbit of Mercury to be slightly differ- ent from what Newtonian physics pre- dicted, leading some to suggest that an unknown planet, dubbed Vulcan, might be perturbing Mercury’s trajectory. Physicists in 1904 had no idea what powered the Sun — no known chemical or mechanical process could possibly generate so much energy over such a long time. Lastly, scientists knew various chemical elements emitted and absorbed light with specific patterns, none of which physicists had the slightest idea The European Space Agency’s Planck satellite has captured the best data on the cosmic microwave how to explain. In other words, the inner background radiation. Combining these results with the standard model describing the universe produces workings of the atom remained a total a Hubble constant that is slightly but unequivocally smaller than that gleaned from nearby galaxies. and utter mystery. ESA/PLANCK COLLABORATION Although few saw it coming, in hind- sight, it’s clear that these problems were the inner workings of atoms. These new There is no question that we have heralds of a revolution in physics. And theories even opened doors to new and made incredible progress in understand- in 1905, the revolution arrived, ushered previously unimagined lines of inquiry, ing our universe, its history, and its ori- in by a young Albert Einstein and his including that of cosmology itself. gin. But it is also undeniable that we are new theory of relativity. We now know Scientific revolutions can profoundly profoundly puzzled, especially when it that the luminiferous ether does not transform how we see and understand comes to the earliest moments of cosmic exist and that there is no planet Vulcan. our world. But radical change is never history. I have no doubt that these Instead, these fictions were symptoms easy to see coming. There is probably no moments hold incredible secrets, and of the underlying failure of Newtonian way to tell whether the mysteries faced perhaps the keys to a new scientific revo- physics. Relativity beautifully solved by cosmologists today are the signs of an lution. But our universe holds its secrets and explained each of these mysteries imminent scientific revolution or merely closely. It is up to us to coax those secrets without any need for new substances the last few loose ends of an incredibly from its grip, transforming them from or planets. successful scientific endeavor. mystery into discovery. Furthermore, when scientists combined relativity with the new theory Dan Hooper is a senior scientist at the Fermi National Accelerator Laboratory in Illinois of quantum physics, it became possible and a professor of astronomy and astrophysics at the University of Chicago. He is author to explain the Sun’s longevity, as well as of At the Edge of Time: Exploring the Mysteries of Our Universe’s First Seconds.

WWW.ASTRONOMY.COM 29 30 ASTRONOMY • MAY 2020 V.M. Slipher’s expanding universe

The Lowell Observatory astronomer’s revolutionary findings include the expansion of the universe and the discovery of the interstellar medium. BY DAVID J. EICHER

EDWIN HUBBLE REVOLUTIONIZED ASTRONOMY IN 1923 Slipher’s interests toward the heavens and when he discovered that the “Andromeda Nebula” was actually a distant island galaxy Cogshall who introduced him to the idea full of stars, gas, and dust. That breakthrough helped set the cosmic distance scale of moving west to work at an observatory. and the overall nature of the cosmos. But fewer astronomy enthusiasts know that a decade before Hubble’s discovery, a little-known astronomer at Lowell Observatory Called to the West in Flagstaff, Arizona, discovered the expanding universe. At the time, Lowell Observatory was a fledgling institution less than a decade Indiana youth those who were much younger. Slipher old, overseen by its founder, the wealthy Vesto Melvin Slipher was born on a farm had a brother, eight years his junior, Earl Boston adventurer-scientist Percival in Mulberry, Indiana, on November 11, C. Slipher, who would also grow up to Lowell. 1875. Invariably known as “V.M. Slipher,” be an astronomer and work at Lowell At first, Lowell was reluctant to seek he had an unspectacular childhood in Observatory. Slipher’s help, but Cogshall persuaded the American Midwest, with few details But during Slipher’s youth, this was all him to bring on the young astronomer. of his youth ever recorded. Certainly a distant future dream. Slipher graduated The year was 1901, and as far as Lowell growing up on a farm kept Slipher in from high school, taught briefly at a coun- was concerned, the association would be robust shape. Many years later, astrono- try school, and then enrolled at Indiana temporary. In the end, however, Slipher mers remarked on his ability to climb University in Bloomington. One of his would stay at the observatory for 53 mountain peaks, staying well ahead of professors was Wilbur Cogshall, who had years. In 1915, he became assistant direc- worked as an astronomer at Lowell in tor, and when Lowell died the following This iconic image of V.M. Slipher shows the 1896 and 1897. Another professor was year, Slipher became acting director and astronomer with his famous spectrograph on the John Miller, an astronomer who later then director by 1926. He served as the 24-inch Clark telescope, with which he discovered the expanding universe and the interstellar medium. became director of Sproul Observatory in observatory’s chief until retiring in 1954 ALL PHOTOS: LOWELL OBSERVATORY Pennsylvania. It was Miller who turned at age 79.

WWW.ASTRONOMY.COM 31 Revolutionary astronomer V.M. Slipher (third from left) sits inside the 24-inch Clark refractor dome at Lowell Observatory in 1905 with Harry Hussey, The Lowell staff poses Wrexie Leonard, Percival Lowell, Carl Lampland, and on the steps of the John Duncan. 24-inch Clark dome in 1905, with V.M. Slipher in back, along with Harry Hussey (back Slipher’s astronomical studies went in left). In the middle are John Duncan and several simultaneous directions. Shortly Wrexie Leonard. Out after his arrival in 1901, the observatory front are Percival Lowell received a state-of-the-art spectrograph and Carl Lampland. made for the 24-inch Clark refractor, the institution’s main instrument. By 1902, Slipher had worked out the bugs with this tricky piece of equipment and made some spectrograms of Mars, Jupiter, and Saturn worthy of sharing with the astronomical community. His own work focused on radial velocities of stars and the discovery of binary stars by measuring shifts in the spectra of the visible component. Slipher began to use this spectrograph exhaustively. He studied planetary atmo- spheres, such as that of Mars, and exam- ined the rotation period of Venus. He also studied the spectra of the giant outer planets Uranus and Neptune. Attempting to determine the rotation periods and detection of various substances — such as chlorophyll on Mars — took up much of his research.

32 ASTRONOMY • MAY 2020 The discovery of matter among the stars of the Pleiades was a big one. This put Slipher on the map, with a legitimate claim to a major discovery in astrophysics.

During his time spent on planetary separated regions of space, producing that the dust near the star Merope in this research, Slipher also managed to keep what he called “selective absorption of cluster was shining only by reflected light investigating spectroscopic binary stars. light in space.” Some astronomers con- demonstrated the existence of stuff His work here led to a major break- gratulated Slipher for this conclusion, but between the stars; that stuff came to be through, hailed by astronomers as a many others ignored the findings for a called the interstellar medium. milestone. He found that certain spectral long time. Observations in the 1920s lines in the otherwise blurred spectra of would finally prove Slipher correct. The breakthrough some stars were sharp and stationary, Moreover, in December 1912, Slipher The discovery of matter among the stars and noted this phenomenon in a variety used the spectrograph to discover the of the Pleiades was a big one. This put of stars in Scorpius, Perseus, and Orion. presence of dust — or “pulverulent mat- Slipher on the map, with a legitimate From this he concluded in 1909 that ter,” as he termed it — between the stars claim to a major discovery in astrophys- interstellar gas must exist in widely of the famous Pleiades Cluster. Proving ics. He then turned toward solving the biggest mystery of the age, the nature of so-called spiral nebulae. These numer- ous, faint, diffuse objects had remained mysterious for a century and a half. The German natural philosopher Immanuel Kant had suggested they were separate, large “island universes” of matter as early as 1755. But the evidence of their nature

LEFT: The Slipher and Lampland families roll out in the Lowell Stevens-Duryea car, with Verna Lampland, Emma Slipher, and Marcia Slipher in the back seat, and V.M. Slipher (driving), David Slipher, and Carl Lampland in the front seat.

BELOW: V.M. Slipher made this image of a solar eclipse expedition at Syracuse, Kansas, in 1918.

WWW.ASTRONOMY.COM 33 announce results for 15 spirals. Nearly all were receding at high velocities. Three years later, Dutch astronomer Willem de Sitter theorized that the universe is expanding. It was Slipher’s observations of the so-called spiral nebulae that estab- lished this fact.

Slipher’s varied work In addition to discovering that the spiral nebulae were receding at great velocities, Slipher found that radial motions existed within the spiral nebulae themselves. That is, they were rotating. These first discoveries again included what we now know as the Andromeda and Sombrero galaxies. This finding contradicted what astronomer Adriaan van Maanen of Mount Wilson Observatory had reported earlier, that the spiral arms of these objects were unwinding. This would suggest they were close and not at great distances, or such a detection would be V.M. Slipher (bottom) accompanies Carl Lampland impossible. at the business end of the 24-inch Clark refractor, in an undated image. on the nights of December 29, 30, and 31, As with many aspects of astronomy, and into the predawn hours of New debates ensued, and most astronomers Year’s Day 1913. He measured the plates took the side of van Maanen rather than was slow in coming. Some thought they over the first half of January, finding that Slipher. Another decade passed before were within the Milky Way, embryonic the nebula was moving three times faster the realization came that Slipher was planetary systems in their early stages of than any previously known object in the right and van Maanen wrong. By the end formation. universe. of World War I, other astronomers rein- In 1909, Slipher began recording spec- Confusion ensued, and Slipher spent forced Slipher’s work on spiral nebulae tra of spiral nebulae, urged on by Lowell, more time measuring the plates. On with their own observations, and the tide who thought they might show spectral February 3, 1913, he wrote to Lowell that of belief began to turn. And then in 1923 similarities to our solar system. This task the Andromeda Nebula was approaching came Hubble’s discovery of the nature of was difficult, however, because these Earth at the unheard-of velocity of galaxies. By 1929, Hubble derived his objects were faint. Nonetheless, Slipher 186 miles per second (300 kilometers per crucial velocity-distance relationship for Although Slipher was a cautious thinker, he adopted some of the more aggressive and controversial ideas of his employer, Percival Lowell, throughout the early part of his career.

consulted with astronomers at other second), still an accurate value. “It looks galaxies, using, as Hubble wrote Slipher, observatories and experimented with as if you had made a great discovery,” “your velocities and my distances.” equipment, including faster lenses and wrote Lowell. “Try some other spiral Slipher and Hubble had together uncov- observing techniques that might mini- nebulae for confirmation.” ered the expanding universe, the nature mize the difficulty. Slipher next went after what we now of galaxies, and a way to measure extra- In the fall of 1912, Slipher recorded a call the Sombrero Galaxy (M104) in galactic distances. plate of the “Andromeda Nebula” that he Virgo. He found its spectral lines shifted Slipher also conducted critical work felt was sufficiently good to obtain its far toward the red, indicating that it is on aurorae and on the phenomenon radial velocity. No radial velocities of receding from Earth at 620 miles per sec- known as sky glow, the brightness of the nebulae were known at that time. He ond (1,000 km per second). By the 1914 night sky. He turned to these areas in recorded better plates in November and American Astronomical Society meeting part because he had mostly exhausted December 1912, and still a better result in Evanston, Illinois, Slipher was able to the research capability of the 24-inch

34 ASTRONOMY • MAY 2020 ABOVE: In 1947, V.M. TOP RIGHT: In 1955, RIGHT: V.M. Slipher Slipher (left) poses during the centennial (right) and Al Wilson with Carl Lampland celebration of Percival pose in Lowell in front of the Lowell Lowell’s birth, V.M. Observatory’s reading Observatory Slipher (left) and Stanley room about 1955. administration Sykes lay a wreath on building. Lowell’s tomb.

Clark telescope for further studies of a new outer solar system planet, bringing he laid the foundation of the great struc- nebulae. Before World War I was fin- on board Clyde Tombaugh, a young ture of the expanding universe. ... If cos- ished, he studied spectral lines in aurorae Kansas farm boy, who would in 1930 mogonists today have to deal with a and found a “permanent aurora.” By this, find Pluto. universe that is expanding in fact as well he meant that the night sky was not Although Slipher was a cautious as in fancy, at a rate which offers them absolutely dark. He discovered many thinker, he adopted some of the more special difficulties, a great part of the new features in the spectrum of the sky, aggressive and controversial ideas of his blame must be borne by our medalist.” revealing ionized elements in Earth’s employer, Percival Lowell, throughout When it comes to the expanding uni- upper atmosphere. Later, in the mid-’30s, the early part of his career. He did not verse, the rotation of galaxies, the discov- Slipher extended his analyses of the sky question the possibility of life on Mars, ery of the interstellar medium, important to the zodiacal light, studying that glow and believed that the cosmos contained studies of aurorae and sky glow, and from dust particles in the plane of the millions of planets that could support other areas, we should not forget the solar system. some sort of life. name V.M. Slipher. Edwin Hubble helped In addition, Slipher led two eclipse But Slipher will be remembered for us define galaxies. His associate Slipher expeditions, in 1918 to Syracuse, Kansas, his discoveries relating to spiral nebulae gave us universal expansion, a concept and in 1923, to Ensenada, Mexico. He and the expanding universe. When he that governs the mighty cosmos. also made spectral studies of unusual received the Royal Astronomical objects like the Crab Nebula, Hubble’s Society’s Gold Medal in 1933, the presi- David J. Eicher is editor of Astronomy Variable Nebula, and the unusual nebula dent said: “In a series of studies of the and the author of 23 books on science and NGC 6729. He supervised the search for radial velocities of these island galaxies history.

WWW.ASTRONOMY.COM 35 Visible to the naked eye SKY THIS MONTH Visible with binoculars Visible with a telescope THE SOLAR SYSTEM’S CHANGING LANDSCAPE AS IT APPEARS IN EARTH’S SKY. BY MARTIN RATCLIFFE AND ALISTER LING

A brilliant Venus shines to the right of an overexposed crescent Moon during twilight at Lake Wendouree in southern Australia. A barely perceptible Mercury hovers below and slightly to the MAY 2020 right of Venus. BLACHSWAN/FLICKR Venus meets Mercury

Whether you prefer 24-percent-lit crescent disk month presses on, Venus rapidly reaches conjunction with Venus evening or morning spans 39" when viewed through descends deeper into twilight on May 21/22. Their closest observing — or both — May a telescope. The world main- and its altitude falls as it nears approach occurs during the has you covered. Venus and tains a reasonable altitude June’s inferior conjunction. early morning of May 22, so the Mercury appear in the night through the middle of May However, there’s one more best time for U.S. observers to sky this month, offering fine as its separation from the Sun event that observers may want target the pair is on the previ- views during evening twilight. diminishes. And on May 16, it to catch: a conjunction with ous evening, May 21, when they Meanwhile, the morning sky stands 11° high an hour after Mercury, which is moving on stand slightly more than 1° holds the magnificent trio of sunset. By then, the disk of the far side of the Sun in the apart one hour after sunset. Jupiter, Saturn, and Mars. All Venus has grown to 50" wide, opposite direction of Venus. At this point, Mercury shines three planets are improving as but it’s even more slender, just Mercury passes through supe- at magnitude –0.6 and Venus they approach their respective a 10-percent-lit crescent. As the rior conjunction May 4 and at magnitude –4.4. oppositions later this year, Telescopic views of Mercury which results in larger disks reveal a tiny 6"-wide disk that’s The innermost planets share the evening sky when viewed with a telescope. 69 percent lit. This vividly con- But first, let’s begin with the trasts with the Venusian cres- inner planets in the evening sky. cent, which spans 53" as a Venus is the brilliant beacon 6-percent-lit crescent. Within hanging in the western sky soon GEMINI days, Venus descends out of after sunset. Shining at magni- Capella view. But at the same time, tude –4.7, it dazzles near the AURIGA Mercury climbs higher along northern horn of Taurus the the ecliptic, making it relatively Bull. During the first week of easy to spot the rest of the May, the Hyades and Pleiades Venus month. Look to the west- sit low near the horizon before Betelgeuse Mercury northwest in a clear sky May 31 disappearing in twilight. Look TAURUS PERSEUS to find the innermost planet west an hour after sunset to ORION hovering 8° high an hour after catch these open clusters before the Sun goes down, shining at low altitude fades them. 10° magnitude 0.1. Venus sits 37° east of the Sun May 21, 30 minutes after sunset Jupiter rises close to 2 a.m. Looking west-northwest on May 1, and stands 23° above across mid-northern latitudes the western horizon an hour The innermost planets stand only about 1° apart above the west-northwestern May 1, and by May 31, it is up after sunset. Its beautiful, horizon shortly after sunset May 21. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY by midnight. Look for the gas

36 ASTRONOMY • MAY 2020 RISING MOON I Cracks, craters, and domes

TODAY’S SEA OF TRANQUILLITY was once Crater Cauchy and its companions quite untranquil. It began 4 billion years ago, when a giant impact excavated a large basin. Millions of years later, lava erupted through fis- Rima Cauchy OBSERVING sures in the basin floor. The cracks tended to Crater Cauchy HIGHLIGHT be oriented along stress lines that were created by other large impacts. During a second round VENUS MERCURY and cross of upwelling lava, the terrain unevenly heaved paths this month, and they stand just 1° apart an hour from below, causing the formation of a scarp or Rupes after sunset May 21. fracture. In other places, lava tubes collapsed into Cauchy rilles. Nearby, some volcanoes made it to the sur- Omega Cauchy N face, but the failed ones created domes. Mini- Tau asteroids that slammed into the surface mil- Cauchy lennia later added the final touch of texture. E On May 26, roughly four days after New Details abound in and around Cauchy Moon, the Sun rises on the fascinating giant rising above the southeast- Crater, a 7.5-mile-wide impact site region of crater Cauchy, just north of the ter- located in eastern Mare Tranquillitatis. ern horizon as Altair in the minator’s midpoint. The terminator is the line CONSOLIDATED LUNAR ATLAS/UA/LPL. INSET: NASA/GSFC/ASU Summer Triangle reaches an that divides lunar day and night, but at such a altitude of 20°. Saturn rises 20 young age, the dark face of our sister Luna might Cauchy, which lies parallel to the rille. Well minutes later, standing less than be modestly lit by the gray glow of earthshine, known to lunar aficionados, the fault is second 5° from Jupiter. which is sunlight reflected from Earth’s dayside. only to the famous Straight Wall. When the Sun Jupiter begins the month at Crater Cauchy itself is a modestly small, rises over the region, the scarp casts a sharp magnitude –2.3 and brightens 7.5-mile-wide, simple impact feature with nice, shadow westward, but the dark line disappears to –2.6 by May 31. Saturn glows sharp edges that reveal its relative youth. a couple of Earth evenings later. at magnitude 0.6 in early May Immediately to Cauchy’s north is a prominent As an added bonus for this region, a pair of rille named Rima Cauchy, where years of tiny before brightening by 0.2 mag- lava domes sit at the edge of Mare Tranquillitatis. impacts have softened its edges. Within a couple Look for the small, light-dark pairing caused by nitude by May 31. Both planets of Earth days, the higher angle of the Sun shines these hills protruding up in the sunlight. The east- slow their eastern track against light directly into the rille, wiping out the shad- ern dome, cataloged as Omega, is likely a shield the background stars as the ows and making it all but invisible. South of volcano, while the western one, Tau, appears to month goes on, with Saturn Cauchy is a prominent fault scarp called Rupes have been formed by uplifting from below. reaching its stationary point May 11 and Jupiter May 14. The beautiful pair remain less than 5° apart all month, METEOR WATCH I Comet Halley returns to Earth’s sky straddling the border of Sagittarius and Capricornus. Eta Aquariid meteor shower MAY’S MAIN METEOR SHOWER Check out the field of view with is heavily affected by a nearly Full binoculars — can you spot the Moon that remains visible most of dim (magnitude 9.5) globular the night. The Eta Aquariids is one of cluster M75 forming an isosce- two showers associated with Halley’s les triangle with the planetary Comet, which has spent eons litter- duo? It lies less than 2° south of Enif ing its path with debris that results a line between the two planets. in the yearly shower (the Orionids in A waning gibbous Moon stands October is the other). PEGASUS The Aquariids sport a maximum 3° south of Jupiter on the morn- CAPRICORNUS Radiant observable rate of about 10 meteors ing of May 12. per hour under perfectly dark skies. Thanks to Jupiter’s southerly d Mars AQUARIUS However, with a bright Moon present, declination, it remains at a rela- you’ll be lucky to spot five streaks per tively low altitude for the rest of 10° hour in most urban locations. The first the year. It reaches its highest few days of May after the Moon sets May 5, 4 A.M. elevation of about 30° above the .M. Looking east (4 A on May 2) is a good time to southern horizon (depend- catch the few early shower members ing on your latitude) dur- ETA AQUARIID METEORS streaking through the sky. A New ing morning twilight, Partly due to the low altitude of the Eta Active dates: April 19–May 28 Moon on May 22 offers dark skies for when it’s located in eastern Aquariids’ radiant when viewed from Peak: May 5 northern latitudes, the shower is not viewing sporadic meteors, as well as Sagittarius. Jupiter is just Moon at peak: Waxing gibbous considered one of the year’s best. But with the occasional straggler of the Eta two months away from Maximum rate at peak: Mars hovering in the nearby sky this year, Aquariid shower. — Continued on page 42 10 meteors/hour it’s worth taking the time to view it.

WWW.ASTRONOMY.COM 37

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S BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. MAY 2020

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SEXTANS 13 Venus is stationary, 6 A.M. EDT 14 Last Quarter Moon occurs at 10:03 A.M. EDT Jupiter is stationary, 2 P.M. EDT b i CRATER The Moon passes 3° south of Mars, 10 P.M. EDT 16 The Moon passes 4° south of Neptune, 11 A.M. EDT 17 Mercury passes 7° north of Aldebaran, 5 A.M. EDT HYDRA 18 The Moon is at apogee (252,018 miles from Earth), 3:45 A.M. EDT _ 20 The Moon passes 4° south of Uranus, noon EDT j ANTLIA 22 Mercury passes 0.9° south of Venus, 4 A.M. EDT SW New Moon occurs at 1:39 P.M. EDT 23 The Moon passes 4° south of Venus, 11 P.M. EDT 24 The Moon passes 3° south of Mercury, 7 A.M. EDT The Moon passes 0.6° north of asteroid Vesta, 11 A.M. EDT 27 Asteroid Juno is stationary, 10 A.M. EDT 29 First Quarter Moon occurs at 11:30 P.M. EDT

WWW.ASTRONOMY.COM 39 PATHS OF THE PLANETS

AND LAC LYR HER CVn PER CYG BOÖ TRI CrB ARI PSC VUL COM Sun PEG Pallas Uranus SGE EQU SER TAU PSC Pa th AQL SER of OPH the Celestial equator Mo on Neptune VIR ERI AQR CET LIB Mars SCT CAP Herculina CRV Ceres Saturn Iris Jupiter FOR SCL Pluto SGR The Moon passes 2° south CrA of Jupiter on May 12 LUP SCO

Moon phases Dawn Midnight

23 22 21 20 19 18 17 1516 14 13 12 11 10 9 8 7 6 5

To locate the Moon in the sky, draw a line from the phase shown for the day straight up to the curved blue line.

THE PLANETS IN THEIR ORBITS Uranus Arrows show the inner planets’ monthly motions Venus and dots depict the outer planets’ positions Jupiter Neptune at midmonth from high Mercury above their orbits. Saturn

Pluto Mercury Superior conjunction is May 4

PLANETS MERCURY VENUS Date May 31 May 15

Venus Magnitude 0.0 –4.6 Angular size 7.4" 48.5" Mars Earth Ceres Illumination 47% 12% Distance (AU) from Earth 0.910 0.344 Distance (AU) from Sun 0.397 0.723 Right ascension (2000.0) 6h11.7m 5h21.9m Jupiter Declination (2000.0) 25°28' 27°14'

40 ASTRONOMY • MAY 2020 This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows MAY 2020 and colored dots show motions and locations of solar system objects during the month.

1

UMa Callisto 2 LYN PER 3 Io LMi AUR GEM Europa Venus 4 Ganymede M CNC ercury ) cliptic Io un (e 5 LEO he S Sun of t ath P Mercury passes just south of TAU Venus the evening of May 21 6 Ganymede 7 Callisto SEX MON 8 Jupiter CRT CMa JUPITER’S MOONS 9 LEP Dots display HYA ERI FOR positions of ANT PYX Galilean satellites 10 Europa COL at 5 A.M. EDT on PUP CAE the date shown. 11 Early evening South is at the top to match the 12 view through a 4 3 2 1 telescope. 13

14 31 30 29 28 27 26 25 24 23 22 21 15

16 THE PLANETS IN THE SKY S 17 Jupiter These illustrations show the size, phase, and orientation of each planet and the two WE brightest dwarf planets at 0h UT for the dates 18

N in the data table at bottom. South is at the top to match the view through a telescope. 19

Saturn 10" 20

21

22 Mars Ceres Uranus Neptune Pluto 23

24

MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO 25 May 15 May 15 May 15 May 15 May 15 May 15 May 15 26 0.2 9.1 –2.4 0.5 5.9 7.9 14.7 8.3" 0.4" 42.5" 17.3" 3.4" 2.2" 0.1" 27 85% 97% 99% 100% 100% 100% 100% 28 1.127 2.992 4.635 9.586 20.766 30.359 33.527 1.425 2.970 5.178 10.019 19.802 29.931 34.039 29

22h14.9m 22h42.4m 19h56.1m 20h15.8m 2h20.7m 23h25.9m 19h46.9m 30 –12°57' –17°34' –20°56' –19°55' 13°33' –4°49' –22°04' 31 WHEN TO SKY THIS MONTH — Continued from page 37 VIEW THE PLANETS Morning planets the southern equatorial belt. As Jupiter rises, Callisto’s shadow is EVENING SKY Altair already on the jovian disk while Mercury (northwest) Callisto itself lies to the east of Venus (northwest) PEGASUS Enif AQUILA the planet. Ganymede lies west MORNING SKY of Jupiter, and during a couple Mars (southeast) of hours, Callisto’s shadow Jupiter (south) nears the western limb of Saturn (south) Uranus (east) Saturn Jupiter Jupiter while Ganymede AQUARIUS Neptune (east) CAPRICORNUS approaches. Both events occur SAGITTARIUS Mars almost simultaneously at 4:49 a.m. CDT (in the eastern time zone, it’s already twilight, trifecta of events occurs the Fomalhaut though the event is still observ- morning of May 21, when able). Ganymede’s disappear- Ganymede itself and Europa’s 10° Late May, 3:30 A.M. ance takes just seven minutes, shadow are both visible soon Looking southeast while Callisto’s shadow ambles after 2 a.m. CDT before being off the disk over the course of joined by a transiting Europa A trio of planets — Mars, Jupiter, and Saturn — will grace the southeastern sky 20 minutes. This is because at 3:23 a.m. CDT. a few hours before sunrise this month. Callisto is in a wider, slower- Before moving on to Saturn, moving orbit — illustrating the it’s worth pointing out that opposition, and a telescope will shadow onto Jupiter’s northern laws of planetary motion. Pluto sits just 2.1° west of reveal its growing apparent temperate cloud tops as On May 6 and May 22, Io Jupiter throughout May. But at size. During May, it expands Ganymede begins to disappear and its shadow traverse the magnitude 14.7, you’ll need a from 41" to 45", just 5 percent behind the same limb, south of jovian disk. And a notable large scope and ideal viewing shy of its opposition peak. The dramatic display of atmospheric belts and zones are Jupiter’s main attraction. Most COMET SEARCH I Peaking near a cigar obviously, a pair of dark equa- torial belts straddle Jupiter’s HIGHLIGHT OF THE YEAR: Comet PanSTARRS (C/2017 T2) equator. Other features are Comet PanSTARRS (C/2017 T2) more delicate, however, and the shares a low-power field with the Cigar Galaxy (M82)! As ideal as N dazzle of the planet can drown modest-telescope comets get, them out for casual observers. PanSTARRS hits a peak bright- May 1 Let your eye become accus- ness of 8th or 9th magnitude tomed to its brilliance for a while sailing high in the northern 6 minute before seeking out finer sky. The comet makes its closest DRACO Path of 11 details. The view of Jupiter is approach to the Sun, or reaches E Comet exquisite when our turbulent perihelion, May 4, at a distance PanSTARRS 21 16 URSA earthly atmosphere calms for a of 149 million miles. On the plus h MAJOR second or two and enables a side, PanSTARRS crests near M82 beautiful spacelike view of the Polaris, making it accessible to 26 M81 l solar system’s giant planet. northern observers all night. 2° In addition to the appeal of New Moon occurs May 22, 31 which is perfect timing because the cloud belts, Jupiter’s four _ o Galilean moons offer an ever- PanSTARRS lies only ¾° from 23 k M82 the following weekend. varying display, including PanSTARRS is just barely visible occultations, eclipses, and tran- It takes roughly 15 minutes for light from the comet to reach us, but about with binoculars; it will show up 12 million years for light from the Cigar Galaxy to get here. sits. Individual events occur better in a 4-inch scope, and will throughout May, and occasion- likely sport some green when viewed through a 12-inch scope. ally dual events occur within From May 24 to May 26, make sure to look for a double-spike. The comet’s short, fan-shaped tail flat- minutes of each other. One tens to edge-on when Earth passes through the orbital plane, so as long as our visitor from the Oort Cloud such back-to-back display produces a decent amount of both gas and dust, we can expect to see a green or blue streak on the lead- occurs the morning of May 3, ing edge and an “anti-tail” knife blade of white on the other. If you can, take a peek every other night to when Callisto casts its large catch the whole transformation. For the rest of the apparition we get more and more of a top-side view.

42 ASTRONOMY • MAY 2020 LOCATING ASTEROIDS I Double feature

WHEN IT COMES TO ASTEROIDS, luck works both ways. Jupiter’s moons Rather than one bright asteroid all by itself, May brings two fainter ones almost side by side. During midevening from the Northern Hemisphere, the blue-white luminary Spica shines in the south- S Io east. If you then look about 15° east (1 hour of right ascension), you’ll spot 4th-magnitude Iota (ι) Virginis — the anchor star for Ganymede Jupiter this month’s pair of space rocks. Both 23 Thalia and 40 Harmonia sport a diameter of about 67 miles and lie beyond the orbit of W 30" Mars in the inner asteroid belt. Correctly identifying both asteroids will take a bit more care Europa Callisto’s shadow and patience than usual, as they stand in front of many back- May 3, 4:30 A.M. EDT Callisto ground stars glowing at 10th magnitude. Despite being far from the Milky Way’s bulge, the lack of dust clouds here lets light from many distant stars shine through. If you want to risk the weather, On May 3, Callisto’s shadow traverses Jupiter’s northern cloud tops as you can sketch the star field May 15 or 16 with 40 Harmonia on Ganymede begins to disappear behind the gas giant. the southern edge of the field, then return May 29 through 31 to pinpoint the extra dot on the northern edge that is 23 Thalia. conditions to spot it without and reaches the middle of this During the month, the two asteroids are never closer than photographic equipment. range May 11 when it’s at infe- about 2°, but that is actually an easier shift than you might think. Saturn sits just 5° east of rior conjunction (48" due south If your telescope uses a diagonal, take a picture of the chart and Jupiter every evening in May. of Saturn). Iapetus is brightest flip it left to right to match the orientation in the eyepiece. The planet’s disk spans 18" and at western elongations, like the its expansive rings stretch 40" one it reaches May 31, when it 23 Thalia shares the sky with 40 Harmonia wide by the end of May. Any shines at about magnitude 10.5 telescope will reveal Saturn’s and stands about 9' due west of N rings. The minor axis of the the planet. 90 rings is just 14", narrower than Mars is best viewed in the p the planet itself, so you’ll notice hour before dawn during May. Path of VIRGO the northern pole of Saturn arcs On the 1st, it stands 15° above Thalia May 1 6 11 above the far ring edge. the southeastern horizon by 16 21 26 It’s also worth observing 4:45 a.m. local daylight time, 31 Saturn’s moons, including its and it climbs to 26° high at the E 21 31 largest and brightest, Titan. same time May 31. Still far from 11 16 26 This intriguing world orbits its October opposition, Mars’ 6 Path of f May 1 Harmonia Saturn once every 16 days, and apparent size continues to grow stands due south of the planet during May, expanding from 8" May 5 and 21, and due north to 9". This is still too tiny for May 13 and 29. At magnitude small scopes to resolve much 1° 8.6, it will remain the brightest detail, but the better resolution object near Saturn unless a of 10-inch scopes and larger will The two 10th-magnitude asteroids will take some effort to pick out from rare field star joins in. Shining reveal fine details. This is a good a backdrop of similarly bright stars. between magnitude 10 and 11, time to begin practicing video the moons Tethys, Dione, and imaging, as it will enhance Rhea orbit closer to Saturn and details not visible to the eye. the end of May, the planet Meanwhile, Uranus rises with shorter periods. Their Mars continues to climb shines at magnitude 0.0 and with the onset of twilight and relatively quickly changing to higher declinations as it is at a declination of –9°, put- remains difficult to spot positions are easy to follow crosses into Aquarius. It ting it 2° south-southeast of throughout May. So your best with modest telescopes. begins the month at 15° south Lambda (λ) Aquarii. bet is to hold off until next May is also a great month in northeastern Capricornus, Neptune returns to the night month before trying to pick out to spot Iapetus. This odd satur- which puts it 2.7° from 3rd- sky by late May. On May 31, it its blue-green glow from the nian moon changes brilliance magnitude Deneb Algiedi. The sits 8.6° east-northeast of Mars starry background. between eastern and western Red Planet then shines at mag- and 3° east of 4th-magnitude elongations depending on nitude 0.4. It crosses into Phi (ϕ) Aquarii. To spot Neptune Martin Ratcliffe provides whether its bright or dark hemi- Aquarius on May 9, passing with binoculars, use Mars as a planetarium development for sphere faces us. Iapetus shifts less than a Moon’s-width from guide. Neptune shines at magni- Sky-Skan, Inc., from his home between magnitude 10 and 12 Iota (ι) Aquarii May 11/12. By tude 7.9, but at just 15° high an in Wichita, Kansas. Alister hour before twilight, its low alti- Ling, who lives in Edmonton, GET DAILY UPDATES ON YOUR NIGHT SKY AT tude makes it more difficult to Alberta, has watched the skies www.Astronomy.com/skythisweek. spot than later in the year. since 1975.

WWW.ASTRONOMY.COM 43 The most observed emission nebula in the Northern Hemisphere is the famed Orion Nebula (M42), lying some 1,300 light-years away. Visible to the naked eye as a misty spot of stars, this cloud of gas is forming an infant star cluster, the four brightest of which are called the Trapezium. This wide-field view shows the Orion Nebula at left with bluish reflection nebulae around it, the brightest of which is NGC 1973–5–7, at right. TONY HALLAS

44 ASTRONOMY • MAY 2020 A glimpse behind the dusty veil of nebulae reveals the chemistry of the universe. BY DAVID J. EICHER AND BRIAN MAY; STEREO IMAGES BY J.-P. METSÄVAINIO

he universe is a magical place. Many people don’t know this; they are born, go through their lives, and perish without ever realizing it. I’m not talking about magic the way you might think. The universe is not a supernatural place. It’s not full of tricks. There are no violations of the natural order of the cosmos, no validity in amu- lets, curses, spells, miracles, or occultism. Rather, the universe is a place domi- nated by natural magic — by nature’s own laws that make it an amazing won- der in itself. The truth about the universe is far stranger and more incredible than the petty imaginary stories we concoct every day on our little blue planet Earth.

The universe’s building blocks Consider the very stuff you’re made from, for example. The average human has 7 octillion atoms in their body. That’s 7 times 10 to the 27th power. Put another way, it’s 7 billion billion billion atoms. Suffice to say, it’s a lot. These very same atoms were created in the early stages of the universe or in the bellies of exploding

WWW.ASTRONOMY.COM 45 The story of elements in nature, of why we are here, of our cosmic roots, is strongly tied to the story of stars in our galaxy and universe.

philosopher Joseph Priestley and French chemist Antoine Lavoisier also discovered oxygen at about the same time.) So, where did the elements that make up our stars, our planets, and even us, The Eagle Nebula (M16) in Serpens resembles the widespread wings of a majestic bird. It contains bright come from? The creation of the first emission nebulosity, a young star cluster, and towering pillars of dust that gravity is compressing into stars. The dust features in this nebula gave rise to the name “Pillars of Creation” in images made with the Hubble atomic nuclei took place immediately Space Telescope. This big nebula lies some 7,000 light-years away. ADAM BLOCK following the Big Bang itself, the origin of the universe some 13.8 billion years ago. That process, called Big Bang stars long ago. As the great astronomer The first known elements were met- nucleosynthesis, created mostly hydro- Carl Sagan said, “The nitrogen in our als, dating back to the last part of the gen, deuterium (an isotope of hydrogen), DNA, the calcium in our teeth, the iron Stone Age, when copper was discovered and helium, with trace amounts of other in our blood, the carbon in our apple pies around 9000 b.c. in the Middle East. elements like lithium. were made in the interiors of collapsing However, beads found in Çatalhöyük, Long after Big Bang nucleosynthesis, stars. We are made of starstuff.” Anatolia, in what is modern Turkey, more complex elements formed through Right now, you have at least traces suggest clear manufacturing of copper a variety of processes. Stars are nuclear of 60 chemical elements within you. By goods dating to 6000 b.c. This is highly fusion reactors — engines that fuse mass, oxygen is the most abundant; car- interesting, as Çatalhöyük is one of lighter elements together into heavier bon follows second, and then hydrogen the first and most important proto- and nitrogen. But you also have heavier city settlements on Earth. Clear evi- elements such as calcium, phosphorus, dence of copper smelting dates to at least potassium, sulfur, sodium, chlorine, and 5000 b.c., from Belovode in the Rudnik magnesium. And, yes, you even have nat- Mountains of what is now Serbia. urally occurring radioactive elements By 6000 b.c., humans were also smelt- within you — again, all natural. ing and using lead and gold. Silver and The elements, of course, are the basic iron came next, before 5000 b.c. By the atomic building blocks of the cosmos, time of the Egyptians, alchemists had from which all normal matter is com- discovered carbon. The smelting of tin by posed. Consider, just for a moment, our 3500 b.c. led to the Bronze Age, combin- discovery and understanding of them. ing tin with copper to fashion the hardy Organized by their properties in the alloy that gave the epoch its name. periodic table, the 118 known elements Important elements have been found display a wide range of characteristics. in modern times, too. Hydrogen, the most The Russian chemist Dmitri Mendeleev abundant element, was discovered by the The spectacular Helix Nebula (NGC 7293) in created the first detailed periodic table English natural philosopher Henry Aquarius is one of the closest planetary nebulae, in 1869 to understand and organize the Cavendish in 1766. The Swedish-German lying nearly 700 light-years away. The curling form of the gas is reminiscent of the DNA double helix, elements. The first 94 elements occur chemist Carl Wilhelm Scheele uncovered leading to its distinctive name. The central star that naturally, and the last 24 have been syn- a variety of elements during the 1770s, gave rise to the nebula is plainly visible in backyard telescopes, and astronomers believe the nebula thesized in labs or nuclear reactors but including oxygen, chlorine, manganese, formed about 10,000 years ago. ADAM BLOCK/MOUNT LEMMON are not yet observed in nature. and tungsten. (The English natural SKYCENTER/UNIVERSITY OF ARIZONA

46 ASTRONOMY • MAY 2020 A stereo view of the Crescent Nebula (NGC 6888) shows an oblate bubble of gas encapsulating its hot central star, with blebs of multicolored nebulosity aligning here and there to form the three-dimensional cloud.

ones. The process of fusion itself creates number of elements are created, or at all know it, but we are part of the biggest many more elements on the periodic least can be created, by exploding white recycling program that exists: the birth, table, up to iron and nickel. Exploding dwarf stars, the final, decayed ultra- life, and death of stars. stars — supernovae — are the dying car- dense remnants of stars like the Sun. Stars are born in great clouds of gas casses of massive stars far heavier than the These include titanium, vanadium, chro- called nebulae. The word nebula comes Sun. Their bombastic blasts create heavier mium, manganese, iron, and nickel. from Latin and means “cloud” or “fog.” elements still, and the blasts send them far These are incredible facts to ponder These clouds exist between the stars and out into the surrounding galaxy. These as you walk out under a starry sky on a consist of mostly hydrogen and helium, processes, over vast amounts of time, have clear, moonless night. Look deep toward along with some other gases. They are created and spread the variety of elements, the shimmering glow of the Milky Way, typically ionized, meaning they are most far heavier than hydrogen and and you’ll see many twinkling stars and excited — energized — by hot stars helium, that we know of today, including the unresolved light from millions more inside and nearby them, which causes the stuff that makes up our bodies. that make up the hazy band running these clouds to glow. Thankfully, because The cosmic origins of the elements, across our sky. That oldest of all human of this process, we can see nebulae from then, are varied. About two dozen ele- questions — “Why am I here?” — very large distances, across our galaxy ments originate from dying low-mass actually has an answer. You’re here and even in other nearby galaxies. stars. These include carbon, nitrogen, because atoms created in the Big Bang Interstellar clouds also contain various strontium, and tin. Another two dozen or and in the bellies of stars have recom- amounts of dust. Astronomers believe so elements come mostly from superno- bined in a way to make you, billions of these veils of dust in the universe were vae. These include oxygen, potassium, years after their creation — with a big formed in supernova explosions. sodium, arsenic, and aluminum. Two thank you to your parents as well. Observations of the universe have elements arise from cosmic ray fission shown that not only is the cosmos — when energetic particles from space The story of the stars expanding, as we have known for more impact Earth’s atmosphere and surface. The story of elements in nature, of why than a century, but that the universal This process creates boron and beryllium. we are here, of our cosmic roots, is expansion also is accelerating over time. About another two dozen elements strongly tied to the story of stars in our On large scales, everything is moving are created largely from merging neutron galaxy and universe. And that means away from everything else, and the uni- stars — the clashes of super-dense, dying exploring the lives of stars, how stars verse is getting bigger. But various forces stellar remnants made mostly of packed come to be, what happens during their are at work in the universe. One of the neutrons. These include iodine, xenon, lifetimes, and how they, too — like most important, the very force that keeps cesium, platinum, and gold. And a small humans — eventually die. We may not us on Earth’s surface, is gravity. The

WWW.ASTRONOMY.COM 47 In stereo, a close-up view of the Elephant’s Trunk Nebula within IC 1396 The Bubble Nebula (NGC 7635) is an object seemingly custom-made for a reveals a complex multilayering of the many regions of dust and gas within stereo view. An incredible curtain of nebulosity wisps throughout the entire field this giant star-forming region. of view, as the bubble itself takes on an eerie, cocoonlike quality, the hot star forming it nestled within. Foreground stars pepper the field. attraction of gravity means that even vital to spread this knowledge for the composed of dusty, black grains, and though the universe is expanding, things unborn billions to come. obstruct the light from stars beyond that are near each other are drawn The majority of nebulae in our sky them. Thus, we see them in outline as together because of their mass. Galaxies are stellar nurseries. But not all of them. ghostly clouds of darkness, floating in close to each other can merge together as Some are simply blobs of gas that are not the immense void of space. And some one. It also means that new stars can be energized and glowing of their own glowing nebulae are the remnants, the born, as gravity causes the gas and dust accord, but are rather reflecting the torn-away insides, of massive stars that in nebulae to condense into smaller vol- light from nearby bright stars toward have violently exploded as a cosmic umes. As this process occurs, enough our line of sight. Others are truly dark, bomb. These leavings glow for a short hydrogen, helium, and other elements cosmic time before dissipating into are compressed so that a critical mass invisibility. Still other types of nebulae is reached, and a new nuclear fusion are the endpoints of ordinary stars like reactor — a star — is born. the Sun, shells of softly glowing gas that So, the majority of nebulae we see cocoon outward, belched away by the scattered across our sky, almost all dying remains of their progenitor stars belonging to our Milky Way Galaxy, are within. Each of these types of nebulae cauldrons that make possible the births offers numerous varieties and you can of new stars. They are stellar nurseries, see many examples on these pages, in and that’s why they are frequently inter- both stereo and mono imagery, for your mingled with clusters of young stars. By visual pleasure. observing nebulae, we are peering into Exploring the world of nebulae offers the world of infant suns, seeing a process an eye-opening understanding of the that for our own Sun took place some cosmos at large. We’re able to understand 4.6 billion years ago. a great deal about the universe because of This is an important story to under- chemistry. Specifically, spectroscopy is a One of the sky’s best-known dark nebulae is stand and appreciate, because it truly the Horsehead Nebula (B33), so named for its vital and powerful tool for astrophysi- allows us to see where we came from and distinctive equine shape. Dark nebulae are cists. By carefully analyzing the spectra, composed of dust grains, making them visible only why we’re here on a planet orbiting one when backlit by brighter objects. The Horsehead or patterns of light, from various objects, rather ordinary star in the Milky Way. lies in the constellation Orion, at a distance of about astronomers can understand the chemis- To understand the universe is paramount 1,400 light-years, and is a difficult object to spot try of the target they’re looking at. visually in backyard telescopes. ADAM BLOCK/MOUNT LEMMON for the billions alive now, but it’s also SKYCENTER/UNIVERSITY OF ARIZONA Countless millions of spectral

48 ASTRONOMY • MAY 2020 When one views the distinctive Dumbbell Nebula (M27) in stereo, the two-dimensional dumbbell shape transforms into the object’s true shape: a three- dimensional bloated sphere. Such planetary nebulae form from low-velocity gas belched away from the parent star, which is followed by higher-velocity ejections. The collision between the gas clouds helps to light them up, giving us such a majestic view. observations of stars, planets, galaxies, to create a crystal. The more solution of what spectroscopy tells us. From that and so on have demonstrated that chem- that’s available, the larger the crystal can technique, as stated, we know that istry is uniform throughout the cosmos. grow. The same is true of the whole spec- chemistry and physics are consistent That is, it works the same way in a galaxy trum of about 5,400 known minerals, throughout the universe. Temperatures, 10 billion light-years away as it does in including emeralds, diamonds, quartz, pressures, and many other local your backyard. And that’s a crucially garnets, wulfenite, rhodochrosite, and conditions could be wildly variable, but important fact that astronomers use to many others. countless other worlds throughout our understand how the universe works. Holding a mineral specimen in your galaxy and the universe might contain hand can be a special experience because minerals very much like the ones we Chemistry all around us Chemistry is everywhere in the cosmos. All matter that exists in the universe is made of chemicals. The only thing we HOW TO VIEW OUR 3D IMAGES experience every day that’s not made of There are two ways to view the images printed chemicals is thought — but our thoughts in 3D. To free view the images with no mechan- are themselves byproducts of chemical ical assistance, let your eyes relax as you view interactions within the brain. the photos as though focusing on a point Let’s step away from ourselves for a behind them. At first, you will see the two moment to consider how matter goes images split into four; as your eyes focus at the correct distance, the middle two images will together. Again, there’s no magic combine to create a single, crisp 3D image. The involved in the way the universe assem- outer two images will remain on either side of bles things. Consider some of the most the 3D image and become blurry. abundant objects on our planet: rocks Alternatively, you can use a 3D viewer, such and minerals. There’s no randomness as the Lite OWL viewer designed by Brian May and included with the Cosmic Clouds 3-D book, here, nor any magical behind-the-scenes to view images in 3D. Only 5.3 by 2.5 inches (134 thought or preordained control. A simple by 64 millimeters) and 0.1 inch (3 mm) thick, the pyrite crystal builds itself when iron and Lite OWL viewer is designed for easily viewing sulfur atoms are in solution in the right 3D images in books, magazines, modern and vin- abundances. The atoms are electrochem- tage stereocards, and even video or other VR content on your smartphone. You can purchase individual Lite OWL viewers ically attracted to each other, and they separately at www.MyScienceShop.com assemble in a lattice in just the right way

WWW.ASTRONOMY.COM 49 Exploring the world of nebulae offers an eye- opening understanding of the cosmos at large.

systems. Astrophysicists believe that stars form as cosmic clouds — nebular stellar nurseries — collapse and stars wink on inside them. The leftover detritus from the collapse, swirling slowly around the infant suns, make a cadre of planets and A stereo view of the Lagoon Nebula (M8) shows it as bright nebulosity buried within a cave that encloses smaller bodies surrounding the new star. a shell of fainter gas and appliqués of dark nebulosity stretching into the foreground. And we are only in the pioneering days of being able to see farther out into the galactic neighborhood that surrounds have on Earth. So, mineral specimens Only in recent times have astrono- us. Understanding that stars are so give us a window into faraway worlds mers had the power to discover planets numerous and that planetary systems are that we will never see up close. orbiting stars other than the Sun. plentiful is exciting. After all, the most That’s intriguing, because the more Technological advances in telescopes and basic driving question everyone would we look around our area of the Milky observing methods brought the first like to answer is at the foundation of it Way Galaxy, the more we have discov- confirmed discovery of an exoplanet — all: “Are we alone? Is there other life in ered that many other planetary systems shorthand for extrasolar planet — in exist around nearby stars. Our galaxy 1992. As of January 2020, we now know consists of several major parts, but the of about 4,100 exoplanets in more than most recognizable and distinctive is the 3,000 systems, and astronomers have Milky Way’s disk — the brightest portion only reached out to relatively nearby where most of the stars, gas, and dust space in our galaxy. reside. The Milky Way contains some Because of the difficulty of detecting 400 billion stars spread across this flat- planets orbiting stars from enormous tened disk, some 100,000 light-years distances, many of these planets are across. Our Sun is just one of the roughly massive, so-called “hot Jupiters” that are 400 billion stars. relatively close to their suns. The most We’ve known about our own plan- productive planet-hunting instrument etary system since ancient times, of was the Kepler Space Telescope, which course, when ancient skywatchers named trailed Earth in its orbit around the Sun the naked-eye planets after gods because and cataloged exoplanets from 2009 they had the power to move night to through 2018. This magnificent tele- night relative to the fixed stars. We’ve scope studied a relatively small area of been all the way through the discovery sky and found more than 2,600 of the of Pluto in 1930 and its demotion to roughly 4,100 known exoplanets. A dwarf planet in 2006, and understand newer telescope, TESS, was launched in Rarely do cosmic clouds create letters suspended the huge population of smaller bodies in 2018 and has begun another epoch of in the sky, but such is the case with a pair of dark nebulae, B142 and B143 in Aquila, which seem to our solar system: dwarf planets, Kuiper exoplanet detection. form a capital letter E. It is nicknamed Barnard’s E Belt objects, comets, and asteroids. They As we look out into the galaxy because the nebulae were discovered by astronomer E.E. Barnard. Set off by a particularly are almost countless, and many thou- surrounding our solar system, it’s not rich Milky Way star field, this nebula can be sands are cataloged and named. surprising to see lots of nearby planetary glimpsed in small telescopes on a dark night. BERNHARD HUBL

50 ASTRONOMY • MAY 2020 EXPLORE FROM HOME

Cosmic Clouds 3-D: Where Stars Are Born by David J. Eicher, Creative Director Brian May, and 3D images by J.-P. Metsävainio, presents a new and unique story of the life cycles of stars and nebular clouds, where they are born, and how they die. This visually amazing volume, with text and 3D images, takes readers inside the birthplaces of stars — the cosmic clouds called nebulae. Seen in the night sky, they glow, energized by the new stars within and around them. Cosmic Clouds 3-D offers hundreds of magnificent images of nebulae captured by ground- based and space telescopes. Along with the high-resolution views of nebulae are unique stereo views that show the nebulae in three dimensions. The story of elements in nature, of why we are here, and of our cosmic roots, is strongly tied to the story of stars in our galaxy and universe. And that means exploring the lives of stars, how stars come to be, what happens during their lifetimes, and how they, too — like humans — eventually die. We may not all know it, but we are part of the biggest recycling program that exists — the birth, life, and death of stars. This is a detailed story, and we aim to share it with you in this unique book. NGC 6960 is the westernmost portion of the great Veil Nebula in Cygnus, one of You’ll learn about many aspects of the sky’s best supernova remnants. Appearing to slice right through the bright star the universe as you travel 52 Cygni, the nebula actually lies far behind the star. Sometimes called the Witch’s Broom, this nebula sits some 1,470 light-years away and is expanding into the through the tale of cosmic surrounding medium, causing the ionized shock front that we see. DON GOLDMAN clouds. Our tale involves detours of science, history, and maybe even a bit of philosophy. the solar system? In the Milky Way? In astronomy has com- A 3D viewer, designed other galaxies?” menced with Earth by astrophysicist (and lead We just don’t yet know. The numbers being at the center of guitarist with the rock group are staggering. By taking very deep expo- everything, the most Queen) Brian May, is included with the book. sures of small areas of sky with the special place there is, Hubble Space Telescope, astronomers and finding out how have estimated that something like 100 disastrously wrong COSMIC CLOUDS 3-D billion galaxies must exist in the uni- that idea is. Now we IS AVAILABLE ONLINE AT verse. And that’s in the visible universe, know that chemistry is uniform www.MyScienceShop.com which may not represent the whole uni- throughout the cosmos, and that complex verse that exists. But for simplicity’s sake, organics, the stuff of life, exist in all let’s say that it does. Let’s say that an manner of places out in space. average galaxy contains 100 billion stars, And yet we know, thus far, of just one Astronomy Editor David J. Eicher is the as many dwarfs are smaller than our gal- planet in the cosmos that hosts life: ours. author of 25 books on science and history. axy. Multiplying that out gives us the The story of nebulae, these cosmic clouds, Brian May is an astronomer and founding approximate number of stars in the uni- can lead us on an exciting exploration of member and guitarist of the legendary rock verse as something like 10,000 billion all these questions, of why we’re here on a band Queen. billion. That’s an awful lot of stars. watery little world, how we got to be where Is it possible that our little blue planet we are, and what the universe holds at This story is adapted from Cosmic Clouds Earth is the only place in the entire uni- large. After all, the very atoms that make 3-D: Where Stars Are Born, by David J. Eicher, verse with life? Or with a civilization? It up our bodies were born in the Big Bang Creative Director Brian May, and 3D images would seem almost completely unbeliev- and in the explosions of massive stars. We by J.-P. Metsävainio, © 2020 by London able. Our whole heritage of discovery in are indeed children of the cosmos. Stereoscopic Co. and MIT Press, Boston.

WWW.ASTRONOMY.COM 51 CHARTING THE 19TH-CENTURY HEAVENS Schools and colleges throughout America regarded The Geography of the Heavens as a valuable tool for teaching astronomy. BY MICHAEL E. BAKICH

The Geography of the Heavens, along with the atlas designed for it, appeared in 1833 and single-handedly changed the landscape of astronomy edu- cation. Its author, Elijah Hinsdale Burritt, wrote in a more understandable style than was common in the textbooks of the day. More importantly, he stressed observation over theory. Burritt created this combination textbook and set of maps specifically to get students out under the stars.

ABOVE: The stars and constellations of winter (left, Map III) and fall (Map II) are the first pair a student would encounter in Burritt’s Atlas. As in the sky, Orion the Hunter stands out on the winter map. Note that some regions of the figures, which should share the central borders of the maps, are missing. ALL IMAGES: LIBRARY OF CONGRESS

LEFT: The summer (far left, Map V) and spring (Map IV) star figures join better than the previous pair. The “shadow” drawing of Libra the Scales forms the main connecting point.

52 ASTRONOMY • MAY 2020 Despite being relatively easy it the most popular star atlas he suffered an accident. That, Burritt reads, the two publications of the 19th century. In fact, it along with motivation from carried impressive titles: wasn’t surpassed in sales until his friends, caused him to created this The Geography of the Heavens, the mid-20th century, after enroll in Williams College in or Familiar Instructions for numerous editions of Arthur Williamstown, Massachusetts, combination Finding the Visible Stars and Philip Norton’s Star Atlas and where he studied astronomy, a Constellations; Accompanied Reference Handbook, first pub- subject he’d read a lot about textbook and by a Celestial Atlas, with a lished in 1910, had appeared. during his recovery. View of the Solar System, After a year, his finances set of maps Illustrated by Engravings and Who was Burritt? forced him to take up a teach- Atlas Designed to Illustrate Elijah Hinsdale Burritt ing job in 1817 to earn money specifically Burritt’s Geography of the (his middle name was his to continue his studies. He to get Heavens. Each cost $1.25 in mother’s maiden name) was then went back to college, but 1833, a bit pricey for the text- born April 20, 1794, in New in 1819, he left to teach school students out book, but a steal for the atlas. Britain, Connecticut. He was (among other pursuits, The set was a smash hit. In the first of 10 children. including editing a weekly under the the 16th edition, published in When he was 18, Burritt newspaper) in Milledgeville, 1876, the preface stated that ventured to a nearby town to Georgia. He remained there stars. more than 300,000 copies had study for two years to become for 10 years before moving been sold. That number makes a blacksmith. Unfortunately, back to New Britain. While in

ASTRONOMY.COM 53 Geography of the Heavens. He wanted to call it Uranography, but his publisher (probably wisely) insisted on Geography. Apparently buying into this notion, Burritt writes in the preface that he wants the book to be to the heavens what geog- raphy is to Earth. Burritt devotes the main part of the book to the constellations. He describes each star figure, recounts its mythology and his- tory, and lists the brightest stars it contains, giving their magni- tudes and other facts. The next section deals with the solar system, followed by a number of problems for readers (mainly students) to solve, and then an appendix with 13 astro- nomical tables. The Atlas contains seven maps. Four of them show con- stellations in the equatorial regions by season, two illustrate the star figures in the polar regions, and one is an all-sky chart that shows the Sun’s posi- tion on the ecliptic throughout the year. Burritt drew all the maps and supervised their engravings. But although he drew them, he didn’t create them — he copied all the con- stellation figures from English Map VI in the Atlas astronomer Francis Wollaston’s displays the stars and constellations around Georgia, he married Ann He followed it with a section A portraiture of the heavens, as the North Celestial Williams Watson, with whom on astronomy, and devoted the they appear to the naked eye: Pole. Note the presence he had five children. final 40 pages to a table of loga- constructed for the use of stu- of the defunct constellation Quadrans Upon returning to rithms from 1 to 10,000, each dents in astronomy, which Muralis (“Mural Connecticut, he converted some calculated to seven decimal appeared in 1811. Later editions Quadrant” on the map). In its boundaries property he owned, called the places. Burritt also included a of the Atlas included an addi- was the radiant of the Stone Store, into a school. As method for students to calculate tional spread showing the rela- Quadrantid meteor part of the conversion, Burritt the logarithms of numbers up tive sizes and distances of the shower (thus the name). That point installed an observatory, to 10 million. Sun, Moon, and planets, along now lies in Boötes. featuring a telescope he had In 1821, Burritt wrote a with many other solar system Another now-defunct constellation is also purchased, on the top floor. 28-page pamphlet: Astronomia, facts. present: Gloria or directions for the ready find- Burritt also added material Frederica. Geography ing of all the principal stars in to the second (1835) and third Once back in Connecticut, the heavens which are named on (1836) editions of the textbook, Burritt began writing The Carey’s Celestial Globe. He fol- but he died before further edi- Geography of the Heavens. He lowed this work in 1830 with tions were printed. The next had one major book under his another pamphlet that showed four editions (1841, 1844, 1846, belt already, having authored how to compute interest, both and 1849) were reissues of the Logarithmick Arithmetick in simple and compound. third edition. In 1852, American 1818. The first half of this work The book that made Burritt astronomer Hiram Mattison was a textbook on arithmetic. famous, however, was The revised the Geography, and

54 ASTRONOMY • MAY 2020 added two pages containing 80 drawings of double stars, com- ets, clusters, and nebulae to the Atlas. Mattison produced nine editions, the last one in 1876.

Gone too soon Burritt died January 3, 1838, in Galveston, Texas. Late in the previous year, he had orga- nized and led a group of 30 colonists, which included one of his sisters and a brother, to Houston, Texas, to settle there. In 1836, Texas seceded from Mexico and became an inde- pendent republic. It wouldn’t become part of the U.S. until 1845. Burritt was drawn to Texas because the government had passed laws that granted colonists generous plots of land. Burritt’s group chartered a ship and, after a 28-day voy- age, landed at Galveston — well, sort of. A storm caused the ship to wreck on a sandbar, which delayed the actual land- ing by several days. The jour- ney to Houston took just a few more days, but once they arrived, the party had to live in tents because nobody was expecting them. Within a week, yellow fever broke out and wiped out nearly the entire The final map (Map VII) in the Atlas displays the group, including Burritt, who the stars after purchasing a which he inherited from his stars and constellations died in Houston just a few copy of Burritt’s Geography grandmother: “Her copy of around the South weeks later. at an auction in 1862 in New Burritt’s Geography of the Celestial Pole. Several defunct constellations Orleans, where Burnham was Heavens is today the most are visible, including Testimonials a shorthand reporter in Maj. prized volume in my library.” Robur Caroli and I have owned a copy of the Gen. Benjamin Butler’s Union For the simplicity of the Solarium. original 1833 edition of The Army headquarters. After text, the beauty of the illustra- Geography of the Heavens for studying the constellations tions, and the sheer number many years, as well as a set shown in the Atlas, Burnham of sales, The Geography of the of Burritt’s 1835 constellation began to identify them in the Heavens is rightly hailed as a maps, which I had framed sky. He held positions at sev- terrific teaching tool. Likewise, in the 1980s. When I began eral observatories and finished Elijah Hinsdale Burritt collecting 19th-century first- his career as an astronomer at deserves his place as one of edition astronomy books, this Yerkes Observatory. the great popularizers in the set was one of the top 10 items Praise also came from out- history of astronomy. I set out to acquire. But I wasn’t side the field of astronomy. the only one who thought In a letter dated January 1, Michael E. Bakich is a highly of Burritt’s work. 1915, to Maurice Winter Moe, contributing editor of Astronomy The famous double-star American horror author H.P. whose library once contained discoverer Sherburne Wesley Lovecraft cited his admiration 475 first-edition 19th-century Burnham became interested in for Burritt’s work, a copy of astronomy books.

ASTRONOMY.COM 55 EDGE-ON AND FACE-ON GALAXIES Hunting pins and needles in the deep sky will give your observing some pizzazz. BY STEPHEN JAMES O’MEARA

his month, we’ll visually thread our way through the extragalactic haystack that’s nowno prominent along the meridian. We’ll focus on three types of spiral galaxies: grand-design (those(th with striking spiral arms), flocculent (those that appear “fluffy”), and edge-on or near-edge-on (those whose orientation doesn’t allow us to see their disks). I call the first two types “pins” and the third “needles.” The galaxies in this hunt run the gamut from strik- ing to elusive. To approach this galactic scavenger hunt in a systematic way, I’ve divided the sky into four sec- tions. In each section, we’ll follow a one-to-one extra- galactic stitch pattern — first a needle, followed by a pin — looping our way from one region of sky to the next. (And in an effort to introduce you to some lesser- known beauties, none of the objects discussed below is on Messier’s famous list.) Let the needlework begin!

56 ASTRONOMY • MAY 2020 NGC 2683, also known as the UFO Galaxy, is one of the sky’s best “needles,” running three times as long as it is wide. It lies in Lynx. ADAM BLOCK/MOUNT LEMMON SKYCENTER/ UNIVERSITY OF ARIZONA NGC 3079

KEN CRAWFORD

NGC 3184 NGC 3310

DAN SMITH/ADAM BLOCK/NOAO/AURA/NSF ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA

SECTION 1

The first section of sky we’ll examine lies in the constellations Lynx and Ursa Major.

e begin with our first needle, NGC 2683, located Next, turn your attention 2° northeast of Phi (ϕ) UMa to the Wwithin the borders of Lynx, but about 1° northwest spectacular edge-on gem NGC 3079. This galaxy tilts only 2° of magnitude 5.4 Sigma2 (σ2) Cancri. This luscious from edge-on. It is one of the nearest and brightest Seyfert gal- magnitude 9.7 spiral, which tilts just 11° from edge-on, car- axies, which have both glowing, active cores and clearly visible ries the moniker “UFO Galaxy.” Through all instruments, disks. Visible in a 4-inch scope at 100x, this 8'-by-1.5' streak of it appears as a silver needle (9' by 3') elongated northeast light looks like a phantom Frisbee (oriented roughly north to to southwest. It also has a distinct sheen — like moonlight south) near a triangle of stars. glinting off the blade of a sword. Heading northward, we encounter the peculiar grand- Now thread your way to Tania Australis (Mu [μ] Ursae design spiral NGC 3310. We see this face-on, 10.8-magnitude Majoris) and look only 45' west for the Little Pinwheel Galaxy starburst galaxy less than 3.5° southwest of 44 UMa. Through (NGC 3184). Seen nearly face-on, this magnitude 9.5 circular a 4-inch telescope at 150x, it resembles a swollen planetary neb- glow sports a 7'-wide disk hugging a stellar core. At a magnifi- ula 3.5' across. It is one of the bluest spirals known, and it’s also cation of 100x, its disk breaks down into delicate waves of the brightest disturbed galaxy in the late Halton Arp’s Atlas of impure light. Note that the northern flank is punctured by Peculiar Galaxies. To see its arms well, however, will require at an 11th-magnitude field star. least a 12-inch instrument.

58 ASTRONOMY • MAY 2020 NGC 3448

SLOAN DIGITAL SKY SURVEY

NGC 3631

ESA/HUBBLE/NASA/LUCA LIMATOLA

NGC 4026

SLOAN DIGITAL SKY SURVEY

SECTION 2 NGC 3893

BOB UMINSKI/CINDI KRISTOPEIT/ADAM BLOCK/NOAO/AURA/NSF

Our second section lies entirely within Ursa Major.

ere, we come to our dwarf 3.8' to the west. magnifications of 150x to Next, turn your gaze about Hfirst challenge: mag- Also in this section, nearly reveal this hefty appendage. 1° north-northeast of Chi (χ) nitude 11.5 NGC 5° west of Phecda (Gamma [γ] Visible in a 4-inch scope, UMa for the last target in this 3448. I call this object the UMa), we find the 10th- NGC 4026 is a high-surface- section: the magnitude 10.5 Cigarillo Galaxy because it’s magnitude grand-design spi- brightness magnitude 10.8 grand-design spiral NGC an edge-on amorphous galaxy ral NGC 3631. While only edge-on lenticular galaxy in 3893. Through a 5-inch tele- like the Cigar Galaxy (M82), 4.5' in extent, this nearly face- Ursa Major. Look for a star- scope, it’s an elegant sight. The only smaller. This smooth, on galaxy sports a visual like core punctuating its 4'-by-2' spindle has a soft oval 5'-by-1.5' sheet of light hugs enigma — namely, one “heavy 4.5'-by-1' needle-thin disk core, as well as fainter arclike 44 UMa only 20' to the south- arm,” as Arp described it. (oriented north to south), extensions. Magnifications of east. Among the galaxies with This peculiar feature origi- which swells with averted 100x and greater will reveal the highest known rate of nates just north of the galaxy’s vision. You’ll find it about 3° a tiny nucleus and two high- star formation per unit mass, nucleus and points east. south-southeast of Phecda. surface-brightness arms NGC 3448 is interacting with Those viewing through 8-inch Larger scopes will also reveal wrapping tightly around UGC 6016, a 14th-magnitude or larger apertures should use its faint elliptical halo. the galaxy’s core.

WWW.ASTRONOMY.COM 59 NGC 4111

ESA/HUBBLE/NASA/JUDY SCHMIDT NGC 5033

BERNARD MILLER

NGC 4244 NGC 4414

JOE NAUGHTON/STEVE STAFFORD/ADAM BLOCK/NOAO/AURA/NSF HUBBLE HERITAGE TEAM (AURA/STSCI/NASA/ESA)

SECTION 3

Our third section lies in two small northern constellations, Canes Venatici and Coma Berenices.

he first target, NGC 4111, lies near 10x50 binoculars, this 10th-magnitude at 75x, is a compelling ghostly ellipse Tthe border between Canes Venatici marvel is the visual twin of NGC 5005, with an uncanny sharpness to the gal- and Ursa Major. This small but which lies 0.5° to the northwest. This axy’s slender shape. fascinating edge-on lenticular galaxy lies 5'-long lens-shaped object becomes Last but not least in this section, NGC about 1° due east of 67 UMa. It cuts a fine increasingly more compressed toward its 4414 is another superb flocculent spiral line against the night sky. A dark dust lane highly condensed core, a result of the about 3° north of Gamma Comae runs perpendicular to the galaxy’s plane, galaxy swallowing a companion some- Berenices. The 10th-magnitude galaxy’s causing a dramatic decrease in brightness time in the distant past. 4.5'-by-3' disk has a relatively high sur- between the edge of the bulge and the Our third target in the third section is face brightness and makes a good target beginning of the disk. Use at least 100x the Silver Needle Galaxy (NGC 4244), for small-telescope users, even under to see its bright starlike core, eye-shaped which glows at magnitude 10.5 about 4½° suburban skies. A 5-inch instrument at bulge, and hyperfine needlelike disk, ori- southwest of Chara (Beta [β] CVn). This a magnification of 100x will reveal the ented west-northwest to east-southeast. galaxy’s exactly edge-on disk (15.5' by inner lens. This feature appears mottled Next, thread your way about 1.5° 1.5') is devoid of a strong central bulge, along the major axis, and the outer lens northeast of 14 Canum Venaticorum for but it does display a small central con- has hints of knotty enhancements along the amazing flocculent galaxy NGC centration. The galaxy orients northeast what appears to be a spiral pattern, 5033. Visible with averted vision in to southwest and, through a 4-inch scope although nothing is connected.

60 ASTRONOMY • MAY 2020 NGC 4631 NGC 4725

ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA BOB FERA

NGC 4565 NGC 4535 NGC 4762

R. JAY GABANY ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA ESA/NASA/HUBBLE

SECTION 4

Our final section encompasses parts of Canes Venatici, Coma Berenices, and Virgo.

or a whale of a view, slide about 3.5° east-northeast of The last object is the Lost Galaxy (NGC 4535). While rela- FNGC 4414 to NGC 4631. Popularly known as the Whale tively bright (magnitude 10.5), this barred spiral is of low sur- Galaxy, this 9th-magnitude tapered monolith (oriented face brightness, so it’s a challenge to small-scope observers. The roughly east to west) is replete with dark vapors in a delicate 7'-long glow lies 2¼° northwest of 31 Vir and, in a 4-inch scope, embrace. Star clumps pepper the 15'-long disk like snowballs shines as a circular patch of ill-defined light. Views through on the side of a house. For a triple treat, check out NGC 4627, 12-inch and larger scopes bring out the spiral’s main, S-shaped a magnitude 12.5 dwarf elliptical galaxy 3' to the north, and its arms within what I describe as “extragalactic ectoplasm.” equally slender partner, the Hockey Stick (NGC 4656/7), a magnitude 10.5 edge-on barred spiral 30' to the southeast. BONUS: A FINISHING STITCH Next is a different sort of pinwheel. NGC 4725 is a peculiar We’ll end our needlework with magnitude 10 NGC 4762, an one-armed spiral — a transition system between a normal spi- edge-on system 2° west and slightly north of Vindemiatrix ral and a barred spiral that forms one of the most complete (Epsilon [ε] Virginis). A 5-inch scope shows it as a 9'-by-2' wisp rings of any galaxy known. To find this magnitude 9.5 gem, sporting a nuclear bead within an inner lens. Bright dots flank look 2° south and slightly west of 31 Com, which lies near the the core, beyond which threads give way to hyperfine exten- North Galactic Pole. Through a 4-inch scope, the galaxy’s inner sions. In larger scopes, the thin disk tapers to sharp points. region displays a bar that connects a bright, broken inner ring And with that, our galactic stitchwork is done. But there’s an surrounded by a fainter lens of light. entire universe at your disposal, and I encourage you to sew To find our next treat, travel westward to a point 2° due east your own wonders together. As the late hand-knitting expert of 17 Com. There, you’ll find the Needle Galaxy (NGC 4565). Elizabeth Zimmermann said, “Properly practiced, knitting This magnitude 9.5 wafer of light has two 8'-long threads of soothes the troubled spirit, and it doesn’t hurt the untroubled light extending from the galaxy’s slightly swollen belly — like spirit either.” Enjoy. silk from a spider’s abdomen. A 4-inch telescope at high power will resolve NGC 4565’s classic dark lane, which cleanly divides Stephen James O’Meara is a contributing editor and columnist the galaxy’s bright hub into two distinct ovals. for Astronomy who enjoys frequent trips into the deep sky.

WWW.ASTRONOMY.COM 61 WE TEST Canon’s new astro With 30 megapixels of resolution, a full-frame sensor, and a mirrorless body, the EOS Ra camera can help you reveal the night sky in all its glory. TEXT AND IMAGES BY TONY HALLAS

With all the noise about Sony and Nikon designed filter that lets the emission line good balance between resolution and cameras over recent years, I was under of Hydrogen-alpha (Hα) at 656.3 nano- light sensitivity, as each of the Ra’s pixels the impression that Canon had gone dor- meters really shine through. This leads absorbs more photons than the smaller mant. I could not have been more wrong. to a roughly fourfold increase in the pixels found in many other camera sen- Not only has Canon been quietly creating transmission sensitivity of Hα light — sors. The Ra’s electronics incorporate the new innovations in camera lenses and enabling you to capture deeper, more latest DIGIC 8 image processor, which design, but they also have been working vivid reds — for the Ra compared to pre- has powerful noise-suppression capabili- to improve the overall quality of their vious models, yet the window is so pre- ties. Images taken in extremely low-light products. This is clearly evident with the cise that the camera can still be used in situations and then stretched to look nor- release of their new EOS Ra camera. daylight. Though Canon officials “do not mal show very low noise — on par with The camera is based on the company’s recommend” using the Ra for daytime the best cameras currently available. mirrorless R model, with two significant applications, after two months of day- The Ra is a thoroughly modern cam- modifications. Instead of the usual 10x time use, I have yet to see a bad picture. era, with most of its main controls acces- magnification, the latest Ra model can go The Canon Ra, like the R, has a full- sible via touch screen. This makes to 30x, allowing you to obtain an frame, 30.3-megapixel CMOS sensor with adjustments at 2 a.m., when you are half- extremely precise focus on stars, espe- an individual pixel size of 5.36 microns. asleep, a breeze. The rear screen also cially when using a wide-angle lens. The large pixel size articulates into any position, unlike Additionally, the Ra model sports a newly helps it strike a many other screens that have limited or One of the most no movement. When you’re not using striking features of the the camera, the screen can be folded Canon Ra is its vari-angle so its glass face is on the inside, pro- LCD screen, which makes it a breeze to view your target no tecting it from damage. And, matter where the camera unique to the Canon R series, when points. In this case, the target is the Orion Nebula seen the camera is turned off, the shutter through a 200mm lens. closes, protecting the delicate sensor inside from dust and other contami- nants. This also means that changing lenses while the camera is off does not expose the sensor to the environment. Canon optical engineers also enlarged the Ra’s front opening to 52mm. The larger opening facilitates lenses that are sharper to the edge and have less vignett- ing, helping keep images crisp all the way to the periphery. Lenses that are dedi- cated to the R series bear the “RF” desig- nation; the RF 70–200mm f/2.8 is a prime example. You can, however, still use older EF lenses with a short adapter, and you can order the adapter with a built-in filter housing. Canon also offers polarizing and variable neutral density filters that you can insert into the adapter

62 ASTRONOMY • MAY 2020 Canon’s EOS Ra sports a DIGIC 8 processor and a full- frame CMOS chip. Its shutter also closes when the camera is off, camera protecting the sensor.

— a really neat idea. You’ll likewise be able to insert astronomy-related filters as they become available. As an added bonus, you can assign custom functions to most of the Ra’s buttons and its multi-function bar. There’s also a ring with click stops for the RF lenses and some EF adapters, which allows you to make additional adjustments. Being a nuts-and-bolts kind of person, I chose to turn the multi- handle being five-minute exposures at an ISO of 800 function bar off. Because the ring can attached to a tripod to 1600 (depending on the target) and an only be activated when another button is or mount, I would not recommend going f-ratio of f/3.5 to f/4. Shooting wide open held down, this negates the chance of any on a hike with them. For daytime use, records the worst the lens can perform accidental movement. my favorite lenses are the 24–70mm and usually leads to heavy vignetting While I was at the Advanced Imaging f/4 EF with macro and the 70–200mm that must be dealt with after the fact. Conference in 2019, I had the opportu- f/4 IS EF. Both of these are used with an I always shoot RAW images, taking nity to see more of the latest RF lenses adapter to allow for internal filtering, as anywhere from five to nine exposures, made specifically for Canon’s R-series mentioned earlier. dithering between each. I then convert cameras. These lenses are wider than a The Ra does not come with a built-in them to Digital Negative Image (DNG) normal lens. And if they are fast, they are intervalometer, so to automatically shoot files and import them into Adobe also quite heavy. Although they can continuous images, you’ll need to buy an Camera Raw (ACR) for processing. external one that plugs into the camera. Once I’ve processed the images in ACR, But if you are shooting three-minute, I save them as 16-bit TIFF files and PRODUCT INFORMATION dithered exposures (by slightly shifting import those into RegiStar, where the the camera between exposures), the files are aligned and combined — or Canon EOS Ra exposure time in bulb mode can be set stacked — to create a master TIFF file. Type: Digital single-lens non-reflex all the way to 60 minutes. No external Finally, I import the master file into Sensor: 30.3-megapixel CMOS timer needed. Photoshop for final adjustments and Format: Full frame (36 by 24 millimeters) I should also say something about enhancements. Resolution: 6,720 by 4,480 pixels how I prefer to image with the Ra. As Processor: DIGIC 8 previously noted, the Ra has very little Better than a small step ISO range: 100 to 40000 noise. This means you can get by shoot- The Canon EOS Ra is a giant leap for- Shutter speed: 1/8,000 to 30 seconds ing just a single frame. But to get the ward in astronomical imaging. Its com- Continuous shooting: 8 frames/second most detail out of the sky, nothing beats bination of high sensitivity, low noise, Wi-Fi: Built in shooting multiple frames. Through and good resolution in a modern archi- Display: 3.15-inch vari-angle touchscreen experimentation I’ve found that longer, tecture is a true winner. Plus, the touch- LCD low-ISO exposures are better than screen menus alone are worth the price Dimensions: 5.35 by 3.87 by 3.32 inches shorter, high-ISO shots. However, this of admission. All in all, the camera is a (135.8 by 98.3 by 84.4 mm) means you’ll need some form of tracking real joy to work with. Weight: 1.28 pounds (580 grams) with a small equatorial mount, for Price: $2,499.00 (body only) instance, or a star tracker like the Vixen Tony Hallas is one of the world’s top Polarie. I typically shoot three- to astroimagers.

WWW.ASTRONOMY.COM 63 OBSERVING BASICS

elliptical galaxy M87, whose giant black hole was Explore recently targeted by the Event Horizon Telescope. If we continue the M58-to-M87 route another 1½°, we arrive at the side-by-side ellipticals M84 and M86. They mark Markarian’s Chain the western edge of Markarian’s Chain. Once you have M84 (magnitude 9.2; 6.5' by 5.6') and Tour a tightly packed group of gorgeous galaxies. M86 (magnitude 8.9; 8.9' by 5.8') centered in the eye- piece field, gently nudge your scope slightly less than ½° eastward. Here you’ll find the close pair NGC 4435 (magnitude 10.8; 3.0' by 2.2') and NGC 4438 (magni- ¡ l tude 10.0; 8.5' by 3.0'). Because of their visual appear- VIRGO ance, they’re nicknamed the Eyes Galaxies. Switch to a NGC 4458 higher magnification if you have trouble seeing them. COMA NGC 4477 Less than ½° east and slightly north of the Eyes is a BERENICES NGC 4435 NGC 4473 fainter galactic duo. It’s comprised of the elliptical galaxy VIRGO NGC 4461 NGC 4438 NGC 4458 (magnitude 11.8; 1.6' by 1.5') and its lenticular M86 M84 M87 neighbor NGC 4461 (magnitude 11.1; 3.4' by 1.4'). M58 The final members of Markarian’s Chain, NGC 4473 M59 (magnitude 10.2; 4.5' by 2.5') and NGC 4477 (magni- ¡ M60 tude 10.4; 3.7' by 3.3'), lie across the border in Coma Berenices. The former is yet another elliptical galaxy, Rho (l) while the latter is a barred lenticular galaxy. Although M84 and M86 are visible in an ordinary 60mm refractor, spotting the rest of the chain will 2° require larger instruments. All can be glimpsed with an 8-inch scope under dark-sky conditions, while an Markarian’s Chain observer with a keen eye might be able to see them with (yellow), located about To the passionate deep-sky observer, spring a 6-inch or smaller scope. 50 million to 55 million light-years away, means one thing — galaxies! And nowhere is Markarian’s Chain is named after the Armenian might not look that the number of galaxies greater than in the astrophysicist Benjamin Markarian (1913–1985). impressive through a backyard scope. But Virgo Cluster. I featured this galactic swarm in my April However, he didn’t discover these galaxies. That honor targeting this many 2013 column, but this month, we return to the goes to Charles Messier, who cataloged M84 galaxies contained Virgo Cluster to explore a remarkable group and M86 in 1781, and William Herschel, in such a tiny section of the sky is worth of galaxies within it: Markarian’s Chain. A nearly who found the rest of the chain’s members a the challenge. If your scope has go-to capability, you can straight row few years later. Markarian discovered their ASTRONOMY: ROEN KELLY arrive at the group by entering the coordi- of bright common motion in the early 1960s. nates R.A. 12h27m45.6s, Dec. 13°00'31". This Visually speaking, Markarian’s Chain is will take you directly to NGC 4438, which Messier hardly a cosmic masterpiece. Its member lies near the center of Markarian’s Chain. galaxies runs galaxies are too far away (an estimated However, if you opt for this direct route, from just 50 million to 55 million light-years) to you’ll miss some of the surrounding scenery. north of Rho appear as much more than fuzzy blobs in I instead suggest you star-hop from the Virginis all most backyard scopes. Still, it’s intriguing nearby 5th-magnitude star Rho (ρ) Virginis. to see so many galaxies packed in such a Rho serves as an ideal “base camp” because the way to small area of sky. The “wow” factor comes it teams up with three surrounding field Markarian’s from the realization that the photons stimu- stars to form a northwest-pointing arrow- Chain. lating your retinal cells as you gaze into the head that quickly establishes field and size eyepiece started their journey during the orientation. Use an eyepiece that yields a 1° early part of Earth’s Eocene Epoch, just or 2° field of view for the scenic journey. 10 million years after the extinction of the dinosaurs. BY GLENN CHAPLE A nearly straight row of bright Messier galaxies runs Questions, comments, or suggestions? Email me at Glenn has been an from just north of Rho all the way to Markarian’s Chain. [email protected]. Next month: We explore the avid observer since a friend showed From Rho, move 1½° northward to the elliptical galaxies “Fadeaway Star.” Clear skies! him Saturn through M60 and M59. A slight shift westward will bring the a small backyard barred spiral M58 into view. A sweep from M60 to M58 BROWSE THE “OBSERVING BASICS” ARCHIVE scope in 1963. and extended an equal distance beyond takes us to the AT www.Astronomy.com/Chaple

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...... 65 of ...... 17 ...... 65 ...... 7 ...... 19 ...... 65 ...... 5 ...... 65 ...... 2 ...... 65 ...... 5 ...... 67 ...... 7 ...... 5 INDEX INDEX ...... 5 ...... 7 ...... 65 ...... 65 ...... 65 ...... 17 ...... 65 ADVERTISERS ...... 8 ...... 76 ...... 3 ...... 7 iOptron iOptron Knightware Forum Northeast Astronomy Gleg Photography Buzz Aldrin Puzzle Explore ...... Scientific 8 Bob Berman Tours Bob Berman Knobs Bob's Celestron Astronomy Astronomy Astro-Physics Astro Haven...... 65 Astro ADM Accessories ...... 65 ADM Accessories Optic Wave Laboratories Optic Wave Omegon Oberwerk The Advertiser Index is provided as a service to Astronomy The The magazine is not responsible for magazine readers. omissions or for typographical errors in names or page numbers. Revolution Imager Revolution Rocky Mountain Star Stare Rainbow Symphony Rainbow Symphony Optical Structures ...... 75 QHYCCD Princeton University Press Press University Princeton Precise Parts Precise Technical Innovations Technical ScopeStuff Scope Buggy Inc. Optics, Vue Tele TravelQuest International TravelQuest True Astronomy and Sciences Astronomy True Woodland Hills Cameras & Telescope Hills & Cameras Woodland BINOCULAR UNIVERSE

and continuing southward for 3½°, you will come to Curve to Corvus 5th-magnitude HD 109799 in neighboring Hydra. Can you also see a smudge of faint light just to its northeast? That will be M68, a rogue globular cluster lying in the and beyond Milky Way’s outer halo, about 33,600 light-years from us. Owing to its southern position in the sky from The region of the crow hides some pretty cool celestial stuff. midnorthern latitudes, M68’s gentle glow can be quickly extinguished by horizon-hugging light pollu- tion and haze. But if you wait for a moonless night, it will reveal itself with just about any binocular. As you strain to see M68, consider that that feeble glow is actu- ally the combined effort of more than 100,000 stars that have been in existence for an estimated 11 billion years. The long-period variable star R Corvi lies within the trapezoid, about 2½° southeast of Gienah (Gamma [γ] Corvi). Like most long-period variables, R Corvi is a red giant that varies dramatically from maximum to mini- mum. At peak brightness, it reaches magnitude 6.7, while at minimum it drops to magnitude 14.4. A full cycle, from one max to the next, takes approximately 317 days. The magnificent And, guess what? It’s on the rise. Max light is predicted Sombrero Galaxy (M104) is a great One of the first catchphrases we probably all to occur in mid-June, so now is a great time to check it edge-on spiral, and heard when learning our way around the out. It forms a tiny right triangle with two faint stars that makes a fine target spring sky was that from the handle of the Big it will easily outshine as it ascends. Use the customizable for any pair of binoculars. R. JAY GABANY Dipper, you “arc to Arcturus, then speed to Spica, and, Variable Star Plotter on the American Association of finally, curve to Corvus.” Arcturus and Spica are bril- Variable Star Observers’ website, www.aavso.org, to liant stellar beacons, far outshining the handle stars create your own finder chart. that guide us their way. The four primary stars that Just north of Gamma Corvi, there is an arrow-shaped make up the trapezoidal body of Corvus the Crow, asterism of eight 6th- and 7th-magnitude stars that however, shine at an insipid 3rd magnitude. Despite points right at our next target, the Sombrero Galaxy their modest numbers, those four stars stand out sur- (M104). What could be more convenient than that? The prisingly well, even under the veil of subur- galaxy is just 2° northeast beyond the arrow’s ban light pollution. tip, barely across the invisible boundary in Let’s begin our exploration at Zeta (ζ) I always Virgo. Although M104 shines at only 9th Corvi, a wide double star within the southern magnitude, my old 7x35s still reveal its oval confines of the trapezoid. Shining at 5th enjoy disk. Increasing to my 10x50s, that disk magnitude, Zeta shows a subtle hint of blue, hearing grows more prominent, surrounding a stellar while its 6th-magnitude companion, of your core. It takes my 16x70s to reveal why M104 HD 107295, 6' to the west, is yellowish. binocular is nicknamed the Sombrero; they reveal a Whether they form an actual binary star exploits and protruding core and broad, flattened disk system or just a chance optical double is open cleaved by a “brim” of opaque dust. to debate. Zeta is projected to be 415 light- successes. Finally, look about halfway between the years away, while HD 107295 is calculated at tip of the arrow and M104. Can you see a tiny 386 light-years distant. Some ambiguity in triangle of faint stars? If you are viewing the data, however, may mean that they are actually through 14x or higher giant binoculars, you might much closer to one another. notice that there are six stars here, forming a triangle Corvus also holds a second widely spaced double within a triangle. Nicknamed the Stargate, this little star about 2° south of the midway point between Beta object is one of my favorite springtime asterisms. (β) and Epsilon (ε) Corvi. The brighter of the pair is I always enjoy hearing of your binocular exploits and 6th-magnitude 6 Corvi, while 5' to its west is successes. You can contact me through my website, BY PHIL HD 107756, one magnitude fainter. Both are orange philharrington.net. Until next time, remember that two HARRINGTON Phil is a longtime giant stars. Slightly defocus your binoculars to eyes are better than one. contributor to enhance their delicate colors. δ Astronomy and the By extending an imaginary line from Delta ( ) BROWSE THE “BINOCULAR UNIVERSE” ARCHIVE AT author of many books. through Beta Corvi along the trapezoid’s western side, www.Astronomy.com/Harrington

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WWW.ASTRONOMY.COM 67 ASK ASTRO Astronomy’s experts from around the globe answer your cosmic questions.

WHEN STARS COLLIDE happen when a star runs into the cen- tral black hole in our galaxy. The star won’t survive, of course, but it goes out in a blaze of glory called a tidal disruption event. Some of the star’s material gets thrown away, but the rest High-speed stellar collision falls into the black hole and forms a Stellar collision hot disk of gas before it is consumed. Star/black hole collision Alison Sills Professor, Department of Physics & Astronomy, McMaster University, Hamilton, Ontario Blue straggler star Stellar material SINCE SURFACE Accretion disk (hot gas) QI ATMOSPHERIC PRESSURE ON MARS IS ROUGHLY EQUIVALENT TO WHAT EXISTS WELL Hydrogen gas INTO THE STRATOSPHERE ON EARTH, HOW WOULD Stars rarely collide, A HELICOPTER BE ABLE but when they do, the result depends on TO GENERATE SUFFICIENT LIFT TO GET factors like mass and OFF THE GROUND? speed. When two Stellar John A. Ferko stars merge slowly, Colorado Springs, Colorado they can create a new, brighter star called a blue straggler. If two collisions Flying a helicopter on Mars, such as the Mars stars traveling at a I Helicopter that will be traveling to the Red fast pace hit, they’ll EVERY TIME I READ ABOUT THE A likely leave behind I Planet with the Mars 2020 mission, is a bit of a trade-off. only hydrogen gas. Q ANDROMEDA GALAXY COLLIDING The air pressure at the martian surface is equivalent to Stars that collide with a black hole are WITH THE MILKY WAY, SOMEONE POINTS the air pressure at about 100,000 feet (30,500 meters) ultimately consumed. OUT HOW UNLIKELY IT IS FOR TWO on Earth, but the current height record for helicopters ASTRONOMY: ROEN KELLY STARS TO COLLIDE BECAUSE OF IT. BUT on Earth is roughly 40,000 feet (12,200 m). According WHAT WOULD HAPPEN IF TWO STARS to staff at NASA’s Jet Propulsion Laboratory (JPL), the DID COLLIDE? softball-sized, 4-pound (1.8 kilograms) Mars Helicopter Jeremy Strzynski will compensate for the lower atmospheric density on Aurora, Indiana Mars by using more power and rotating its blades at a higher speed than would be required to lift the craft It’s rare, but stars do collide in the densest parts AI of our galaxy: near the center and in massive globular star clusters. The outcome of the collision depends on how fast the stars are moving relative to each other, rather like a car accident. In star clusters, the stars are moving relatively slowly, and so the “fender bender” results in the two stars merging into one new, more massive star that we call a blue straggler. We can identify these stars fairly easily, since they are hotter and brighter than the other stars in the cluster. The center of the galaxy is more like the interstate, and the stars are moving very quickly. A collision there is much more destructive, and often the aftermath is The Mars Helicopter’s small size and fast rotor rotation will allow it to fly on Mars. This photo shows the helicopter’s flight model, just “star bits” (that is, mostly hydrogen gas) spread out as well as the base, crossbeam, and side posts that will protect all over interstellar space. The most exciting collisions its delicate legs and attach it to the Mars 2020 rover. NASA/JPL-CALTECH

68 ASTRONOMY • MAY 2020 off the ground on Earth. It will spin its two counter- rotating blades at nearly 3,000 revolutions per minute, or about 10 times as fast as a helicopter on Earth, to stay aloft. The trade-off, JPL says, is that Mars’ gravity is about 40 percent the strength of Earth’s gravity — so the Mars Helicopter will require less lift to stay airborne. Over the course of 30 days, mission engineers plan to fly the helicopter up to five times, aiming for incrementally longer distances and hoping to reach a distance of a few Sirius A (left) and B, hundred yards with a maximum flight time of about separation, but still much smaller than the separation shown in this artist’s concept, are 90 seconds. Its first flight, however, aims to have the between Sirius A and B. AGB stars blow away a lot of separated by about helicopter rise about 10 feet (3 m) straight up and hover their mass — perhaps 75 percent — in the form of a 25 times the Earth- for about 30 seconds. dusty, slow-moving wind, and this can be partially Sun distance and circle each other Although the Mars Helicopter project is an exciting captured by the white dwarf. once every 50 years. one that engineers expect to succeed, there is still a In order to explode as a supernova, the white dwarf Although it is possible chance that some aspect of this project won’t go as must increase its mass to close to 1.4 times the mass of the white dwarf Sirius B might gather planned. But because the helicopter is simply a proof- the Sun, known as the Chandrasekhar limit. It seems enough material of-concept test for future helicopters on Mars, even if unlikely that it will be able to do this unless the wind from its companion to explode as a this helicopter fails, it will not impact the overall Mars from the AGB star is even slower than expected, espe- supernova, it is 2020 mission. cially as the orbit of the two stars will widen as mass not likely. NASA, ESA, Alison Klesman escapes from the system as a whole. Even if the white AND G. BACON (STSCI) Senior Associate Editor dwarf were to capture this much mass, it may not neces- sarily stick! The hydrogen-rich material from the giant star can periodically ignite on the white dwarf’s surface, WHEN SIRIUS A EXPANDS INTO A causing a more modest explosion, called a nova, which QI RED GIANT, COULD WHITE DWARF would blow the material back into space and might even SIRIUS B GO SUPERNOVA BY PULLING reduce the mass of the white dwarf. GAS FROM SIRIUS A’S OUTER LAYERS So, in summary, in about 500 million years Sirius A AND PRODUCE HEAVY ELEMENTS VIA will expand dramatically and lose nearly three-quarters THE R-PROCESS? of its mass in the form of a slow, dusty wind. A fraction John Holmes of this will be captured by the white dwarf, but in order McLean, Virginia to explode as a supernova, it must first accrete enough mass to get close to the Chandrasekhar limit, and, sec- The answer is perhaps, but unlikely. The key ond, must avoid explosively igniting the accreted mate- AI uncertainties are the speed at which mass is lost rial prematurely. Based on our current understanding, from the giant Sirius A, whether the material that lands neither of those two conditions looks likely. on the white dwarf explodes on contact, and whether The final part of your question asks about r-process enough mass can be collected by the white dwarf to get elements. These are elements that are built up by a series close to the Chandrasekhar limit. of “rapid” neutron captures followed by radioactive Sirius A and B are quite widely separated, by about decay. Examples of these are precious metals like gold SEND US YOUR 25 times the distance between Earth and the Sun. The and platinum. There are two probable sites in the uni- QUESTIONS larger Sirius A is about twice the mass of the Sun and verse where r-process elements are made: colliding Send your its white dwarf companion is about the same mass as neutron stars and core-collapse supernovae of massive astronomy questions the Sun. As stellar winds blow material off the surface stars. The supernova caused by the detonation of a via email to askastro@ of Sirius A, some mass can be gravitationally captured white dwarf is quite different. It consists of the explosive astronomy.com, or by the white dwarf. ignition of carbon and oxygen, and there is no rich write to Ask Astro, The effectiveness of this capture is strongly related source of neutrons to make r-process elements. So, the P.O. Box 1612, to the wind speed. As a main sequence star, Sirius A elements produced in a white dwarf supernova (known Waukesha, WI 53187. currently loses little mass, which escapes at high speeds, as a type Ia supernova) are mostly the products of oxygen Be sure to tell us your full name and so Sirius B cannot easily capture it. However, when and carbon fusion, like silicon, sulfur, iron, and nickel. where you live. Sirius A draws toward the end of its life, it will swell to Rob Jeffries Unfortunately, we become an asymptotic giant branch (AGB) star. These Professor of Astrophysics and Head of Physics & Astrophysics, cannot answer all huge red giants have radii as big as the Earth-Sun Keele University, Staffordshire, U.K. questions submitted.

WWW.ASTRONOMY.COM 69 READER GALLERY Cosmic portraits

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1. NOT THE MILKY WAY The gegenschein (German for “counterglow”) is a faint, diffuse patch of light sometimes seen directly opposite the Sun. This view is from Yaha Pass, some 14,800 feet (4,500 meters) above sea level. The mountains include Mount Gongga, the highest peak in Sichuan Province, China. Yellow and green airglow is also visible in the image. • Jeff Dai

2. NOT IDENTICAL TWINS Open clusters M46 (left) and M47 lie in the constellation Puppis the Stern. M47 is the brighter of the two, but M46 offers a bonus — planetary nebula NGC 2438 lies in the same line of sight. The cluster’s stars are 5,400 light-years away, while NGC 2438 is a bit less than 3,000 light- years distant. • Dean Salman 2

70 ASTRONOMY • MAY 2020 3. KNIGHT SKY The star trails in this image were made by combining 106 exposures of 25 seconds each. They circle above the Castle of Noudar, a medieval castle in Barrancos, Portugal. The smallest trail, that of Polaris, is to the upper right. • Sérgio Conceição

4. FERRERO 6 This faint planetary nebula in Cassiopeia wasn’t identified until French amateur astronomer Laurent Ferrero found it in 2013. Its thin, bright outer rim indicates it is strongly interacting with the interstellar medium. • Peter Goodhew 3 5. DARK HORSE The Seahorse Nebula (Barnard 150) is a cloud of dust and cold gas in the constellation Cepheus the King. We see it only because of the dense star field behind it. B150 stretches across 1° in apparent length and lies some 1,200 light-years away. • Jeffrey Weiss

6. CHECKING IT TWICE Sharpless 2–115 is an emission nebula in Cygnus, here imaged in the Hubble palette. Abell 71 (Sh 2–116), the small round object at lower right, is an emission nebula. • Chuck Ayoub 4 5

SEND YOUR IMAGES TO: Astronomy Reader Gallery, P.O. Box 1612, Waukesha, WI 53187. Please include the date and location of the image and complete photo data: telescope, camera, filters, and exposures. Submit images by email to 6 readergallery@ astronomy.com.

WWW.ASTRONOMY.COM 71 READER GALLERY

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7. JUST PASSING BY Mars (the bright spot to the left) passed through the region of the Lagoon Nebula (M8) and the Trifid Nebula (M20), both of which are in the constellation Sagittarius the Archer, on February 21, 2020. • Damian Peach

8. CHILLED TO THE BONE The Full Moon of December 11, 2019, shines through the Whale Bone Arch in Barrow, Alaska. Barrow is the northernmost city in the U.S. • Mark Morris

9. DON’T GET PINCHED The Lobster Claw Nebula (Sharpless 2–157) is an emission nebula in the constellation Cassiopeia the Queen. The photographer captured 668 two-minute exposures through Hydrogen-alpha and Oxygen-III filters to produce this image. The small open cluster near the top is NGC 7510. • Douglas J. Struble

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72 ASTRONOMY • MAY 2020 9

WWW.ASTRONOMY.COM 73 BREAKTHROUGH

DIVING DEEP INTO THE MILKY WAY’S HEART On the next clear summer evening, gaze through binoculars toward the center of our galaxy. Under a dark sky, you’ll see countless stars interspersed with dark dust lanes. But what would the scene look like without the obscuring dust? The answer appears above. Astronomers at the European Southern Observatory (ESO) lifted the veil by viewing the Milky Way at near-infrared wavelengths, which penetrate all but the thickest dust clouds. The researchers captured more than 3 million stars in their survey of the galactic nucleus using the HAWK-I instrument on ESO’s Very Large Telescope. The image achieves a resolution of 0.2 arcsecond, equivalent to seeing a quarter from 16 miles (25 kilometers) away! ESO/NOGUERAS-LARA ET AL.

74 ASTRONOMY • MAY 2020

B&H Photo – 800.947.9970 – bhphotovideo.com Astronomics – 800.422.7876 – astronomics.com Adorama – 800.223.2500 – adorama.com High Point Scientifi c – 800.266.9590 – highpointscientifi c.com OPT Telescopes – 800.483.6287 – optcorp.com Focus Camera – 800.221.0828 – focuscamera.com Optics Planet – 800.504.5897 – opticsplanet.com Woodland Hills – 888.427.8766 – telescopes.net Agena AstroProducts – 562.215.4473 – agenaastro.com SOUTHERN SKY BY MARTIN GEORGE July 2020 Jupiter and Saturn at their best

The solar system’s two nights in western Capricornus horizon. The brilliant planet share a border, but they do largest planets make a before crossing into Sagittarius. rises before twilight starts and not. Tucked between the two spectacular pair this month. Glowing at magnitude 0.1 at climbs high in the northeast as is the tiny constellation Jupiter and Saturn appear low opposition, it pales in compari- the sky brightens. Venus shines Circinus the Compasses. in the east soon after darkness son with Jupiter but easily out- at magnitude –4.7, its brightest Don’t confuse Circinus with falls in early July. And not only shines the background stars in for this morning apparition, another constellation having a do they climb higher hour by these constellations. against the backdrop of Taurus. similar common name: Pyxis hour, they also rise earlier as Few sights can match the It spends the first two weeks of the Compass. The two repre- the month progresses. beauty of Saturn through a July passing in front of the sent entirely different instru- Jupiter shines at magnitude telescope. As with Jupiter, plan V-shaped Hyades star cluster. ments. The compass Circinus –2.7 and stands out more than to wait until the ringed world It’s worth getting up early refers to is the type we all used its neighbor. The giant planet climbs high in the sky. The to view Venus’ lovely crescent in school to draw circles. Pyxis, reaches opposition and peak planet spans 18" while the stun- through a telescope. On July 1, on the other hand, represents a visibility July 14, when it rises at ning ring system measures 42" the inner planet shows a mariner’s compass that seafar- sunset and climbs highest in the across and tips 22° to our line 43"-diameter disk that is just ers use to tell directions. north around midnight local of sight. This large tilt affords a 19 percent illuminated. By Circinus covers an area of time. You can find it among the nice view of the dark Cassini month’s end, the world appears 93.35 square degrees, making it background stars of eastern Division that separates the 28" across and 42 percent lit. the fourth-smallest constella- Sagittarius, though truth be outer A ring from the brighter The second half of July also tion. (With an area of 68.45 told, it’s easier to locate the con- B ring. Saturn’s brightest features a brief appearance by square degrees, Crux the Cross stellation using the planet as a moons, led by 8th-magnitude Mercury. For about a week on is the tiniest.) guide than vice versa. Titan, are also a treat. either side of its July 22 greatest French astronomer Nicolas July is the best time this By late evening, a third western elongation, the small Louis de Lacaille introduced year to observe Jupiter through bright planet graces the sky. planet lies low in the east- Circinus in the 1750s. On his a telescope. At opposition, its Mars rises in the east before northeast during morning twi- star chart, he clearly marked disk spans 48" across the equa- midnight local time and climbs light. At its peak on the 22nd, the constellation as le Compas tor and 45" through the poles, highest in the north shortly the magnitude 0.2 world lies and described the device as the a difference that’s surprisingly before twilight starts to paint 6° high 45 minutes before one used in geometry class- easy to see. Look for an alter- the sky. The Red Planet begins sunrise. A telescope reveals rooms. In the wonderful vol- nating series of bright zones and ends July among the back- Mercury’s 8"-diameter disk ume Histoire de l’Académie and darker belts that run paral- ground stars of Pisces the Fish, and 38-percent-lit phase. royale des sciences, Lacaille lel to the giant planet’s equator, but it spends the middle of the described it as le Compas du as well as fine details that show month in Cetus the Whale. The starry sky Géomètre, not to be confused up during moments of good Mars continues to brighten Our view to the south early on with La Boussole ou le Compas seeing. Also watch for Jupiter’s rapidly. As July begins, it shines these winter evenings features de mer, which was the mariner’s four bright Galilean moons as at magnitude –0.5; it appears the spectacular Southern compass we know as Pyxis. they dance around the planet. 75 percent brighter (magnitude Cross and two bright stars Circinus holds a few objects The best views come when the –1.1) by month’s end. Mars’ nearby: Alpha (α) and Beta (β) worth observing through a tele- planet lies high in the sky and telescopic appearance improves Centauri. Just southeast of scope, though most of them are its light passes through less of noticeably as well. Its disk Alpha Cen, the night sky’s best viewed with large aper- Earth’s atmosphere. swells from 11.5" to 14.5" third-brightest star, resides tures. One of the nicest subjects Saturn follows Jupiter across across, big enough to show the distinctive constellation for small instruments is the the sky, reaching opposition just some dusky surface markings. Triangulum Australe the double star Alpha Circini. Its six days after its companion, As Jupiter and Saturn dip Southern Triangle. It seems at two stars glow at magnitudes on July 20. The ringed planet low in the west before dawn, first glance that Triangulum 3.2 and 8.6 and are easy to split spends the month’s first few Venus pokes above the eastern Australe and Centaurus must thanks to their 15" separation.

STAR DOME S

NGC 2070 NGC LMC

SMC

HYDRUS

VOLANS

CARINA

NGC 2516 NGC

HOW TO USE THIS MAP MENSA

This map portrays the sky as seen 104 NGC

near 30° south latitude. Located SW inside the border are the cardinal OCTANS

directions and their intermediate SCP points. To find stars, hold the map overhead and orient it so one of

the labels matches the direction VELA CHAMAELEON

you’re facing. The stars above PYXIS

the map’s horizon now match 3372

PAVO NGC NGC

what’s in the sky. AUSTRALE

TRIANGULUM

_

NGC 4755 NGC ANTLIA

The all-sky map shows CRUX

how the sky looks at: b `

P.M. a

9 July 1 ` _ 5139

OPIUM

P.M. NGC SC 8 July 15 CIRCINUS

P.M. 6397 NGC

7 July 31 Alphard CENTAURUS

ARA

HYDRA

NORMA Planets are shown 5128 NGC

at midmonth

6231

NGC

CORVUS M83

MAP SYMBOLS SEXTANS LUPUS

CRATER

W

SCORPIUS M6

Open cluster _

M4 Globular cluster Antares

Diffuse nebula M104 Spica

Planetary nebula _ Galaxy ) VIRGO LIBRA un (ecliptic Path of the S STAR M5 MAGNITUDES M66 OPHIUCH M65

Sirius Denebola LEO SERPENS 0.0 3.0 ` Arcturus CAPUT 1.0 4.0 M64 2.0 5.0 _

COMA NGP BERENICES STAR COLORS A star’s color depends NW CORONA on its surface temperature. BOÖTES BOREALIS • The hottest stars shine blue M13 • Slightly cooler stars appear white CANES • Intermediate stars (like the Sun) glow yellow VENATICI Lower-temperature stars appear orange HERCULE • M51 • The coolest stars glow red • Fainter stars can’t excite our eyes’ color receptors, so they appear white unless you use optical aid to gather more light

N BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. JULY 2020

SUN. MON. TUES. WED. THURS. FRI. SAT.

1234 TUCANA

567891011 SE GRUS

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: ROEN KELLY ROEN : INDUS 19 20 21 22 23 24 25 ASTRONOMY

26 27 28 29 30 31 ILLUSTRATIONS BY BY ILLUSTRATIONS

MICROSCOPIUM Note: Moon phases in the calendar vary in size due to the distance

from Earth and are shown at 0h Universal Time.

AUSTRALIS

CORONA TELESC

CALENDAR OF EVENTS

CAPRICORNUS SAGITTARIUS

Saturn 1 Mercury is in inferior conjunction, 3h UT M7 2 Asteroid Herculina is at opposition, 14h UT 4 Earth is at aphelion (152.1 million kilometers from the Sun), 12h UT

M8 E

Jupiter 5 Full Moon occurs at 4h44m UT; penumbral lunar eclipse

M22 Asteroid Vesta is in conjunction with the Sun, 6h UT M20

M17 The Moon passes 1.9° south of Jupiter, 22h UT SCUTUM M11 6 M16 The Moon passes 2° south of Saturn, 9h UT 10 AQUILA The Moon passes 4° south of Neptune, 7h UT Venus is at greatest brilliancy (magnitude –4.7), 8h UT US H 11 The Moon passes 2° south of Mars, 20h UT _

Altair 12 Venus passes 1.0° north of Aldebaran, 7h UT SERPENS DELPHINUS CAUDA The Moon is at apogee (404,199 kilometers from Earth), 19h27m UT Last Quarter Moon occurs at 23h29m UT SAGITTA 13 Dwarf planet Ceres is stationary, 2h UT Asteroid Pallas is at opposition, 2h UT 14 Jupiter is at opposition, 8h UT The Moon passes 4° south of Uranus, 12h UT

VULPECULA 15 Pluto is at opposition, 19h UT 17 NE The Moon passes 3° north of Venus, 7h UT LYRA 19 The Moon passes 4° north of Mercury, 4h UT _ 20 New Moon occurs at 17h33m UT ES Vega Saturn is at opposition, 22h UT 22 Mercury is at greatest western elongation (20°), 15h UT 25 The Moon is at perigee (368,361 kilometers from Earth), 5h02m UT 27 First Quarter Moon occurs at 12h33m UT 29 Southern Delta Aquariid meteor shower peaks