Astronomy_-_June_2022

EXOPLANETS ASTRONOMERS DISCOVER OTHER WORLDS p.24 JUNE 2022 The world’s best-selling astronomy magazine ASSEMBLING SEE UNIVERSE THEHOW THE COSMOS CAME TOGETHER p.16 CHOOSING YOUR BEST FIRST SCOPE p.46 THE HISTORY OF MAPPING THE MOON p.40 PLUS The QHY 600 Bob Berman www.Astronomy.com Vol. 50 • Issue 6 camera on cosmic Explore road-tested p.54 amazement p.12 BONUS celestial gems ONLINE in Hercules p.52 CONTENT CODE p. 3

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Online Content Code: ASY2206 JUNE 2022 Enter this code at www.astronomy.com/code VOL. 50, NO. 6 to gain access to web-exclusive content FEATURES ON THE COVER 16 COVER STORY 34 46 Material from an accretion disk swirls around the young star The very hungry universe Star Dome and First scopes for adults FU Orionis in this artist’s concept. Paths of the Planets When it comes to If you’re new to observing, NASA/JPL-CALTECH understanding the formation RICHARD TALCOTT; you don’t need to buy the of galaxies, solar systems, ILLUSTRATIONS BY ROEN KELLY best telescope — just the COLUMNS or planets, accretion is one you’ll use the most. what brings it all together. 40 Strange Universe 12 PHIL HARRINGTON ARWEN RIMMER Mapping the Moon BOB BERMAN 52 24 While most of us will never Binocular Universe 14 set foot on the Moon, maps Zero in on a hero Exoplanets: How we can transport us there. PHIL HARRINGTON discovered other worlds Star clusters and galaxies RAYMOND SHUBINSKI will keep you looking at Observing Basics 15 The field of exoplanets has Hercules all night long. sprung up nearly overnight. GLENN CHAPLE What does the wealth of new MICHAEL E. BAKICH discoveries tell us about the Secret Sky 60 worlds circling our own Sun? 54 STEPHEN JAMES O’MEARA BRIAN MAY, PATRICK MOORE, The CMOS CHRIS LINTOTT, AND revolution is here 7 HANNAH WAKEFORD A new type of camera QUANTUM GRAVITY 32 may signal the future of astroimaging. TONY HALLAS Get the scoop on Sky This Month filaments at the center of 62 the Milky Way, Proxima A planetary extravaganza. Centauri’s third planet, Ask Astro SpaceX’s response to MARTIN RATCLIFFE potential collisions, and When black holes collide. other galactic news. AND ALISTER LING IN EVERY ISSUE ONLINE Picture of Trips and Sky This My Science FAVORITES the Day Tours Week Shop From the Editor 4 Gorgeous Astro Letters 6 Go to www.Astronomy.com photos from Travel the world A daily digest Perfect gifts for New Products 61 for info on the biggest news and our readers. with the staff of of celestial your favorite Advertiser Index 61 observing events, stunning photos, events. science geeks. Reader Gallery 64 informative videos, and more. Astronomy. Breakthrough 66 Astronomy (ISSN 0091-6358, USPS 531-350) is published monthly by Kalmbach Media Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Periodicals postage paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to Astronomy, PO Box 8520, Big Sandy, TX 75755. Canada Publication Mail Agreement #40010760. W W W.ASTRONOMY.COM 3

FROM THE EDITOR Exoplanet explosion Editor David J. Eicher Assistant Design Director Kelly Katlaps As we would expect One of the great aims of this from understanding magazine is to underscore that EDITORIAL how stars form, we are awash in a golden age of Senior Editor Mark Zastrow planets are very astronomy. The previous generation pro- Production Editor Elisa R. Neckar common in duced a firehose of discoveries and new Senior Associate Editor Alison Klesman the galaxy. understandings of many old questions Associate Editor Jake Parks about the cosmos. In terms of compre- Associate Editor Caitlyn Buongiorno ASTRONOMY: ROEN KELLY hending the universe and our place in it, Editorial Assistant Samantha Hill we’re living in the best time there ever was. No area of astrophysics, planetary sci- ART ence, or cosmology better represents that Illustrator Roen Kelly than astronomers discovering planets Production Specialist Jodi Jeranek orbiting stars around us in the Milky Way Galaxy. The first find came in 1992, and CONTRIBUTING EDITORS since then, scientists have detected nearly Michael E. Bakich, Bob Berman, Adam Block, 5,000 exoplanets orbiting 3,670 stars. And the search has just begun. Glenn F. Chaple Jr., Martin George, Tony Hallas, As technologies improve over time, we’ll be able to find smaller Phil Harrington, Korey Haynes, Jeff Hester, Alister Ling, and smaller planets at greater and greater distances. No doubt we’ll Stephen James O’Meara, Martin Ratcliffe, Raymond Shubinski, continue to witness what our understanding of how stars form Richard Talcott comfortably predicts: that planets are abundant in the cosmos. In “Exoplanets: How we discovered other worlds” (page 24), EDITORIAL ADVISORY BOARD Brian May, Patrick Moore, Chris Lintott, and Hannah Wakeford Buzz Aldrin, Marcia Bartusiak, Jim Bell, Timothy Ferris, describe what we know of planets outside our solar system. This Alex Filippenko, Adam Frank, John S. Gallagher lll, important story is an excerpt from a recently published book, the Daniel W. E. Green, William K. Hartmann, Paul Hodge, second edition of BANG!!, which you can order from our online Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern, store, MyScienceShop.com. James Trefil The update on exoplanets hints broadly at a question we don’t yet know the answer to: How common is life in the universe? Despite Kalmbach Media the facts we now have — that stars around us have lots of planets, our galaxy has several hundred billion stars, and at least 100 billion Chief Executive Officer Dan Hickey galaxies exist in the cosmos — we as yet know of only one place Chief Financial Officer Christine Metcalf with life, right here. Senior Vice President, Consumer Marketing Nicole McGuire But spectroscopy tells us that chemistry is consistent throughout Vice President, Content Stephen C. George the universe, and the stuff of life is out there in abundance. The Vice President, Operations Brian J. Schmidt only comet sample returned to Earth, for example, contains an Vice President, Human Resources Sarah A. Horner amino acid. Advertising Sales Director Scott Redmond We’re getting closer to answering that very big question. Exciting Circulation Director Liz Runyon times lie ahead. Director of Digital Strategy Angela Cotey Director of Design & Production Michael Soliday Yours truly, Retention Manager Kathy Steele Single Copy Specialist Kim Redmond Follow the David J. Eicher Dave’s Universe blog: Editor ADVERTISING DEPARTMENT www.Astronomy. Advertising Representative Kristi Rummel com/davesuniverse FOLLOW ASTRONOMY Phone (608) 435-6220 Email [email protected] Follow Dave Eicher on Twitter: RETAIL TRADE ORDERS AND INQUIRIES @deicherstar Selling Astronomy magazine or products in your store: Phone (800) 558-1544 Outside U.S. and Canada (262) 796-8776, ext. 818 Fax (262) 798-6592 Email [email protected] Website www.Retailers.Kalmbach.com CUSTOMER SALES AND SERVICE Phone (877) 246-4835 Outside U.S. and Canada (903) 636-1125 Customer Service [email protected] CONTACT US Ad Sales [email protected] Ask Astro [email protected] Books [email protected] Letters [email protected] Products [email protected] Reader Gallery [email protected] Editorial Phone (262) 796-8776 For reprints, licensing, and permissions: PARS International at www.parsintl.com Copyright © 2022 Kalmbach Media Co., all rights reserved. This publication 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. Single copy: $6.99 (U.S.). Print + digital subscription rate: U.S.: 1 year $58.95. Canadian: Add $12.00 postage. Canadian price includes GST, payable in U.S. funds. All other international: Add $22.00 postage, payable in U.S. funds, drawn on a U.S. bank. BN 12271 3209 RT. Not responsible for unsolicited materials. facebook.com/AstronomyMagazine twitter.com/AstronomyMag youtube.com/user/AstronomyMagazine instagram.com/astronomy.magazine 4 ASTRONOMY • JUNE 2022

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ASTRO LETTERS The winner? List misses While a wide range of astronomers were mentioned as deserving of being on the list, and some, like OUR FEBRUARY 2022 ISSUE featured an article by Michael E. Bakich Caroline Herschel and Vera Rubin, came up several times, one person’s name appeared in our inbox over called “Meet 20 Great Astronomers.” In it, Bakich wrote, “I love ranked lists and over (and over) again. Who was the scientist because they get me thinking. I hope this list does the same for you.” whose exclusion from Bakich’s rankings drew the most ire? Read on. Our readers clearly had many thoughts! We received more email about this story than anything else we’ve run in the last few years, so we’ve decided to turn I enjoyed the February his name. To omit Hubble the whole Astro Letters page over to your responses this month. Who should 2022 article on the 20 from your top 20 is like have been on the list? Who shouldn’t have? Here’s what your fellow readers think. greatest astronomers of listing the top inventors all time, but I would have without Thomas Edison. Caroline Herschel Moon guide included Edwin Hubble, — James Witker Henrietta Leavitt, and JOSEPH BROWN/ I would like to add an honorable mention to your list Vera Rubin. I was surprised that WIKIMEDIA COMMONS of great astronomers: Dr. Dinsmore Alter. Dr. Alter — Charles Ballard Edwin Hubble and was a longtime director of Griffith Observatory in Los Ejnar Hertzsprung and Edwin Hubble Angeles. He was the editor of the Lunar Atlas that was You include such Henry Norris Russell were prepared by the Space Sciences Laboratory of the Space noteworthy figures as not on the list, while JOHAN HAGEMEYER/ Division of North American Aviation, and used by the Clyde Tombaugh (one Claude Tombaugh was. I WIKIMEDIA COMMONS Apollo program. The Soviets, who photographed the far- major discovery), would claim that the H-R side of the Moon, honored Dr. Alter by naming a crater George Ellery Hale diagram and proving the Henrietta Leavitt after him. — Jim Baylor, Martinez, CA (primarily a financier), and existence of galaxies Maria Mitchell (one comet beyond our own and the WIKIMEDIA COMMONS High honors discovered), and yet make expansion of the universe no mention of either are more important to Vera Rubin According to my research, Maria Mitchell was not the Caroline Herschel (eight astronomy than the first woman to win an astronomy-related award: Caroline comets, dozens of double discovery of Pluto. ARCHIVES & SPECIAL Herschel was presented a gold medal on Feb. 8, 1828, by stars and nebulae and the — Eric Sieverling COLLECTIONS, the Astronomical Society of London. She was also the original creator/editor of VASSAR COLLEGE LIBRARY first woman to be salaried as an astronomer, and in 1832 the General Catalog) or I think it safe to say that was awarded a medal by the king of Denmark — before of Edwin Hubble, whose a weighty oversight was Mitchell received hers. In 1835, she received an honorary observations of Cepheid made by leaving Edwin membership in the Royal Astronomical Society. Caroline variables in the 1920s led Hubble off of the list. In started out her life as her mother’s scullery maid and directly to our modern fact, I would put Hubble ended up as a woman who was treated as an equal by men understanding of our at No. 2, right behind of science, who called her “my sister in astronomy” and place in the cosmos? Galileo as certainly one “priestess of the heavens.” — K. Lynn King, Wilmington, DE — Dan Young of the greatest. — Edward Rosenblatt Laying the groundwork I can’t quite wrap my head around Michael Bakich’s I enjoy your magazine I was wondering if your list of contributing physicists exclusion of Edwin Hubble and found Michael might expand to include Hans Bethe? It seems to me from his list of top 20 great Bakich’s list of 20 great that he laid the essential groundwork for the work by astronomers. Hubble’s astronomers compelling. Fred Hoyle that really opened up the science of nuclear work fundamentally However, I don’t synthesis. — Andy Werbeck, Sebastopol, CA changed the scientific understand how Edwin view of the universe and Hubble wasn’t included. Worthy of note cosmology. — Robert Jump — Ranny Heflin Whoa! What about Vera Rubin? She was denied a Nobel No Edwin Hubble? This Prize and now denied inclusion on your list. I’m not sure Edwin Hubble laid the author should be shunned which was the greater insult. — David Pippin, Dearborn, MO foundation for much of the by the astronomical astronomy of the past community and never Keys to success 100 years — that is why a be published again! certain telescope bears — Thomas Kehl I was sorry the article on 20 great astronomers through the ages did not mention Vera Rubin and Caroline which stars orbit around galactic centers provided evi- Herschel. Dr. Rubin’s measurements of the speeds at dence supporting the theories on dark matter, a game changer in the field of cosmology. Herschel was the first woman to discover a comet and cataloged 2,500 nebu- lae and many star clusters, adding to the work of John Flamsteed and her own brother. — Paul Warms, Niantic, CT Father of the Big Bang And where was Rev. Georges Lemaître, the originator of the Big Bang theory? How Michael Bakich could have overlooked one of the greatest minds in astronomy is completely beyond me! — Bill Hebenstreit, Montgomery, TX We welcome your comments at Astronomy Letters, P.O. Box 1612, Waukesha, WI 53187; or email to [email protected]. Please include your name, city, state, and country. Letters may be edited for space and clarity. 6 ASTRONOMY • JUNE 2022

QG QUANTUM GRAVITYEVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH SNAPSHOT I. HEYWOOD, SARAO. BOTTOM FROM LEFT: NASA/CXC/SAO/IXPE; UNIVERSITY OF WARWICK/MARK GARLICK; SOLAR ORBITER/EUI TEAM/ESA & NASA THE MILKY WAY’S HEARTSTRINGS Nearly a thousand filaments lie at the center of our galaxy. Mysterious threads glow black hole. But these high- and chaos at the Milky is a compact, powerful brightly in this view of the energy filaments lack a Way’s center could gener- source that astronomers Milky Way Galaxy, shown in direct source. Researchers ate the strands; another have not yet identified. radio waves. The composite is a say that the turbulence possibility for their origin mosaic of 20 images taken over — SAMANTHA HILL 200 hours by the South African Radio Astronomy Observatory’s HOT FIRST LIGHT LAST SUPPER FULL-BODY SHOT MeerKAT radio telescope array, BYTES A month after its Astronomers have ESA and NASA’s and was published Feb. 2 in The December launch, made the first direct Solar Orbiter spotted Astrophysical Journal Letters. NASA’s Imaging X-ray observation of a white the largest solar Polarimeter Explorer dwarf consuming prominence ever The strange strands, which (IXPE) returned its first planetary debris. imaged in the same were first discovered 35 years scientific image: the NASA’s Chandra X-ray frame as the Sun’s ago, are thought to be generated supernova remnant Observatory saw the full disk. The eruption by cosmic-ray electrons moving Cassiopeia A. rocky objects rain extended over 2 million at nearly the speed of light down on the stellar miles (3.5 million km) and interacting with magnetic remnant late last year. into space. fields. Most similar features elsewhere in the universe have a source of acceleration, such as a WWW.ASTRONOMY.COM 7

QUANTUM GRAVITY BLACK HOLE’S CLOSE-UP ZOOMED IN. At the center of galaxy CONFIRMS THEORY M77 (which is shown at upper left in optical light) is a dusty disk hiding a supermassive black hole, whose light is reprocessed into infrared wavelengths and pictured at right. ESO/JAFFE, GÁMEZ-ROSAS ET AL. M77’s central black hole sports a ring of dust — as expected. All large galaxies host supermas- completely cloaked within a ring of gas spectrum (type 1) to those that glow sive black holes weighing millions and dust. The view is not just spectacu- softly only in low-energy light, such or billions of times the Sun’s mass. lar, but it also confirms a long-standing as infrared (type 2). Some are actively sucking in material, theory that explains why we see many releasing energy in the process. These types of AGN. The work was published The leading explanation for this are called active galactic nuclei, or AGN, Feb. 16 in Nature. variety is the unified model. This and astronomers have recently taken a theory holds that although we see close look at the one within the galaxy POINT OF VIEW different types of AGN across the M77, some 47 million light-years away. universe, there aren’t a variety of black Detailed imagery shows the AGN is AGN range from bright beacons scream- holes. Ultimately, all AGN are inher- ing at us across the electromagnetic ently the same, comprising a feeding Third planet found around Proxima Centauri JUST OVER 4 LIGHT-YEARS AWAY IS PROXIMA CENTAURI, the closest star to the Sun. In August 2016, researchers found a planet circling this star. Then, in January 2020, they spotted a second world. And now, Proxima’s family tree is growing again: A third terrestrial planet has been found. In a study published Feb. 10 in Astronomy & Astrophysics, astronomers announced the discovery of Proxima d. This tiny planet is just one-quarter the mass of Earth and orbits Proxima Centauri every five days at less than one-tenth THIRD ROCK. An artist’s impression shows the small Mercury’s distance from our Sun. Because Proxima Centauri is a red dwarf, this puts Proxima d in the star’s habitable zone, where conditions are right for liquid world Proxima d orbiting the Sun’s nearest neighbor, water to exist on its surface. Proxima Centauri. ESO/L. CALÇADA 8 ASTRONOMY • JUNE 2022

Jet QUICK TAKES Narrow line MOON BUGGY region Toyota is partnering with the Gas clouds Event Japan Aerospace Exploration Dusty torus horizon Agency to develop a pressurized, crew-carrying rover called the Broad Singularity Lunar Cruiser, slated for launch line region by the end of the decade. Corona Accretion PLANETARY of gas disk METAMORPHOSIS Supermassive Astronomers have spotted two black hole mini-Neptune exoplanets being CHANGING PERSPECTIVES. The unified model mid-Infrared SpectroScopic Experiment stripped of their puffy (MATISSE). They employed a technique atmospheres by radiation from of AGN states that all AGN are essentially the called interferometry, which dramati- their host stars. This process same, simply viewed at different angles. Every cally boosts the amount of detail visible. could ultimately transform the one contains a supermassive black hole, an When combined with radio data from the worlds into smaller super-Earths. accretion disk, a fast-moving gas region, an Atacama Large Millimeter/submillimeter obscuring torus of dust, and a slower-moving Array and the National Radio Astronomy PRIMEVAL MASHUP gas region. Some AGN also have powerful jets. Observatory’s Very Long Baseline Array, the team could finally map out M77’s cen- The Milky Way likely underwent a ASTRONOMY: ROEN KELLY tral dust. They found that the black hole sixth, previously unknown galaxy is completely embedded in the thicker, merger some 8 billion to 10 billion supermassive black hole surrounded by a ring-shaped center of a larger, edge-on years ago. Evidence comes from torus, or doughnut-shaped ring, of dust. disk of dust, confirming what is expected a group of stars that were once The different AGN classes are the result of from the unified model. part of the cannibalized satellite, the angle from which we see the system. Now the trick is to determine whether Pontus, and now reside in the M77 is a type 2 AGN that astronomers M77’s black hole is indeed typical and if outer halo of our galaxy. have long suspected is embedded in a the unified model accurately predicts what thick buffer of dust. Images have previ- we see in other galaxies. The team plans TWICE THE TROJANS ously spotted warm dust near the galaxy’s to observe other AGN with MATISSE to center. But recent observations suggest find whether they, too, match expecta- Our family of Trojans — asteroids that the ring of dust around the black tions. And confirming the unified model that lead or trail Earth in its orbit hole was too thin and not oriented at will also boost our understanding how — just doubled in size, from one the precise angle to hide the black hole black hole’s host galaxies form, grow, and to two. But astronomers predict as expected, challenging rather than ultimately die. — ALISON KLESMAN newly added asteroid 2020 XL5 supporting the unified model. will only be considered a Trojan for roughly another 4,000 years. A CLEARER PICTURE WRECKED WORLD Researchers needed a better picture of the dust to be sure. So, they zeroed in on the Sixty-five Moon-sized debris galaxy’s center with the Multi AperTure clouds have been found around WD1054-226, a white dwarf some Proxima d was found using the radial velocity method, where astronomers monitor a 115 light-years away. Because the star’s light for subtle changes in wavelength that occur as the gravity of an orbiting planet dusty, irregularly shaped clouds tugs on it. This is the same method used to detect Proxima Centauri’s other two planets, are evenly spaced, astronomers Proxima b and c. But Proxima d’s detection is impressive because, as it is so light, its think an intact planet in the star’s effect on its host star was small. By contrast, Proxima b and c are more massive and were thus easier to find — Proxima b is roughly the same mass as Earth and Proxima c is a habitable zone might be super-Earth about six times our planet’s mass. shepherding them. In fact, Proxima d is the lightest exoplanet discovered to date using the radial veloc- AMBITIOUS AGENDA ity method. The team found it with a new instrument called the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, or ESPRESSO, on the According to a white paper, China European Southern Observatory’s Very Large Telescope in Chile. aims to send a sample-collecting Now that ESPRESSO has shown its mettle at spotting small planets, astronomers are spacecraft to a near-Earth hoping it will uncover many more terrestrial worlds, perhaps much like our own, in more asteroid, build a space telescope distant systems. — A.K. that rivals Hubble, and launch two more Chang’e lunar missions to survey and sample the Moon’s south polar region. — JAKE PARKS WWW.ASTRONOMY.COM 9

QUANTUM GRAVITY ESA/HUBBLE & NASA, J. DALCANTON, DARK ENERGY SURVEY, DEPARTMENT OF ENERGY (DOE), CERRO TOLOLO INTER-AMERICAN OBSERVATORY/NOIRLAB/NATIONAL SCIENCE FOUNDATION/ It takes two to tango ASSOCIATION OF UNIVERSITIES FOR RESEARCH IN ASTRONOMY (AURA), SLOAN DIGITAL SKY SURVEY (SDSS); ACKNOWLEDGMENT: J. SCHMIDT Although galaxies seem to drift through the vast cosmic sea alone, astronomers now know that interactions between galaxies are quite common. Some 300 million light-years away, this galactic duo, known as Arp 282, is composed of NGC 169 (bottom) visibly interacting with IC 1559 (top). Wisps of gas and dust delicately link the two galaxies, a result of the immense tidal forces at play when gravitational goliaths stray too close. Such powerful encounters play a vital role in how galaxies evolve in size, shape, and structure over billions of years. And when galaxies interact, it can even stir up dormant material within them, kick- starting fresh bursts of star formation. So, although galactic collisions, at first blush, may seem like cosmic calamities, over the long run, they can actually breathe fresh life into otherwise dimming, dying island universes. — J.P. Astronomers find a unique neutron star ABOUT 4,000 LIGHT-YEARS Magnetars are the most magnetic objects in the universe, boasting from Earth, an astral entity is magnetic fields that are a thousand trillion times stronger than Earth’s. releasing a large, minute-long flash Like their less-magnetic cousins, pulsars, magnetars are known for of radiation three times an hour. emitting bursts of radiation. But where pulsars tend to send out About every 20 minutes, the object regular signals, magnetars are a bit more erratic. And in fact, some of becomes one of the brightest radio this behavior is why many astrono- mers believe magnetars are the sources in the sky. cause of fast radio bursts (FRBs), sudden and intense explosions of Its discovery, which was pub- radiation. lished Jan. 27, 2022, in Nature, took But how magnetars reach a stage where they produce FRBs is a researchers by surprise. mystery. The missing link could be ultra-long period magnetars. “This object was appearing and “[These are] a type of slowly disappearing over a few hours spinning neutron star that has been predicted to exist theoretically,” during our observations,” said lead said Hurley-Walker. “But nobody expected to directly detect one like author Natasha Hurley-Walker in a this because we didn’t expect them to be so bright. Somehow, it’s converting magnetic energy to press release. “That was completely radio waves much more effectively than anything we’ve seen before.” unexpected. It was kind of spooky Only more detections will tell astronomers whether they have stumbled upon a new breed of neutron star or if this for an astronomer because there’s object is one of a kind. — S.H. nothing known in the sky that STRANGE FLASHES. does that.” Radiation may be emitted Transients — objects that appear by a never-before-seen to turn on and off — are not new to kind of neutron star, researchers. However, they typically known as a long-period come in one of two speeds. Slow magnetar, shown in this artist’s concept. ICRAR transients, like supernovae, appear over a few days and disappear within months. Fast transients, on the other hand, appear for milliseconds or seconds at a time. Pulsars — neutron stars that release brief but reliable flashes of light — are one example of fast transients. This strange object did neither. Hurley-Walker now suspects it may be an ultra-long period magnetar. 10 ASTRONOMY • JUNE 202 2

“SUPERSONIC EXPANSION OF THE BIPOLAR H II REGION SH2-106: A 3500 YEAR OLD EXPLOSION?,” JOHN BALLY ET AL. 2022 APJ 924 50. DOI:10.3847/1538-4357/AC30DE THE UP AND AWAY. A Falcon 9 rocket AFTERMATH OF A launching from Cape Canaveral carries STELLAR 46 Starlink satellites to orbit Feb. 21. SPACEX TANTRUM SPACEX DEFENDS STARLINK Around 3,500 years ago, OVER COLLISION CONCERNS a spectacular explosion rocked the star-forming As SpaceX’s Starlink constellation of internet service satellites has grown — with region Sharpless 2–106. nearly 2,000 in orbit at the end of February — so has scrutiny of its potential to The culprit: a massive star, cause collisions. called S106 IR, at the heart of this nebula. S106 IR On Dec. 3 of last year, China submitted a complaint to the United Nations formed from the collapse of Committee on the Peaceful Uses of Outer Space, saying that the nation’s crewed its parent molecular cloud a space station was forced to maneuver to avoid a potential collision with a Starlink sat- mere 100,000 years ago. The ellite on two occasions, July 1 and Oct. 21, 2021. star then devoured nearby gas, ballooning from an esti- Then, on Feb. 7, NASA’s human spaceflight division submitted a letter to the Federal mated initial 10 times the Communications Commission raising concerns about SpaceX’s plans for its second- mass of the Sun to 15 solar generation constellation of 30,000 more satellites. NASA said a megaconstellation of masses. Around that time, that size would raise the risk of collisions in space that could threaten its satellites and scientists think, a compan- astronauts. ion star may have interacted with S106 IR, causing the On Feb. 22, SpaceX pushed back on those concerns, arguing that Starlink was explosion. — CAITLYN BUONGIORNO designed to be safe and sustainable. The company cited several design features, including that Starlink satellites are highly maneuverable and deorbit themselves after their service life; their onboard collision avoidance-system autonomously takes action to avoid collisions; and the satellites launch to very low orbits to perform initial system checks — just 130 miles (210 kilometers) high, where they quickly reenter the atmo- sphere if they fail to come online. SpaceX experienced one risk of the latter strategy Feb. 3, when it launched a batch of 49 Starlink satellites despite predictions of a geomagnetic storm. Flares from the Sun enhanced activity in Earth’s magnetic field, warming the atmosphere and caus- ing it to expand into space. SpaceX said the Starlink craft experienced 50 percent more drag than usual and, as a result, 38 of the 49 satellites fell out of orbit and were destroyed. “Despite such challenges, SpaceX firmly believes that a low insertion alti- tude is key for ensuring responsible space operations,” the company said. The statement also revealed details on how Starlink satellites autonomously avoid collisions. If public tracking data show a Starlink satellite has a 1-in-100,000 chance of a collision with another craft, it automatically “assumes maneuver responsibility” and takes avoiding action. If data indicate a “high-probability conjunction with another maneuverable satellite,” SpaceX says it coordinates any maneuvers with that satellite’s operator. “This is certainly the most detailed explanation SpaceX have given of their pro- cedures,” Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, told Astronomy. “It is welcome, although a couple years later than it could have been.” — MARK ZASTROW WWW.ASTRONOMY.COM 11

STRANGE UNIVERSE Levels of wasn’t moving? How can light live in a realm indepen- dent of everything else? amazement In the ’80s, my focus when writing for Discover was usually observational marvels like the fact that visible meteors are only the size of apple seeds. In the ’90s, it We’re into astronomy to be wowed. I’ll do my best. was quantum phenomena, such as how an entangled electron “knows” its twin is being observed and assumes characteristics like spin that are opposite to its partner. The underlying mind-blow is that this “communication” happens instantaneously. There is no light-speed limitation. Observe such a photon or electron in a Cleveland lab and its twin in the Whirlpool Galaxy changes its own physical form in real time. That’s tough to accept without abandoning the reality of space and time, which then makes it pretty darn hard to picture the cosmos. Not to mention the implication of an instantaneous connection between two distant things. And where do you go with that? Nowadays? Great minds from Isaac Newton to Werner Heisenberg to Roy Bishop have all been aware that we never see the external universe, but merely the inside of our brains, where visual images are created and perceived… And, well, I’m still getting used to that, too. It’s easy enough to get what Newton meant when he wrote, “The rays are not colored.” I can grasp that actual light, being solely an amalgam of magnetic and electri- This Hubble image Amazement may be the top reason people are cal fields, is devoid of any inherent color or brightness. of spiral galaxy into astronomy. This amazement takes differ- Since only our brains can generate the sensation of NGC 1300 is stunning ent forms. For example, telescopes open the brightness and color, observations are always mental — and all in your door to visions that are visceral — but also mysterious. creations. That part is easy: It’s in every physiology head. NASA, ESA, AND THE Why should a round, concentrated collection of white book. But it’s quite another thing to overcome a lifetime of bias and truly realize that the Dumbbell Nebula’s HUBBLE HERITAGE TEAM (STSCI/ AURA); ACKNOWLEDGMENT: P. KNEZEK (WIYN) dots against a dark background inspire gasps as globular visual existence happens entirely within the skull. To clusters do? Who can explain why Albireo never disap- me, it’s as if the brain’s interior, previously regarded as points, though its contrasting star hues are mere pastels black, mushy, and subjectively imperceptible, has actu- when compared to the saturated colors that ally been forever visible with every glance. nature provides in abundance elsewhere? It gets much worse when you conclude the Beauty certainly generates amazement. Beauty is cosmos is physically interconnected with us, But beauty is also difficult to quantify and, difficult to provided you trust the correlation between in our case, often telescopically obtainable quantify. observers and outcomes that physics only via dollar signs, with larger apertures experiments such as the famous double slit resolving globulars that cheaper models see have supported for decades. Beyond that, as mere blurry blobs. So instead, let’s focus according to ideas from Stephen Hawking, on mental amazement, arguably astronomy’s specialty. John Wheeler, and other theoretical physicists, a past I cannot know what you find most astounding in the that is set in stone can’t be entirely ruled out. Perhaps it astrophysics realm, so I’ll share what has most melted could even be as malleable as the future. Experiments my mind over the past several decades. have shown that it critically depends on our current A recently found box of yellowing astronomy col- observations and actions. Recent work even indicates BY BOB BERMAN umns and radio scripts published since 1974 shows that — hold on — that independently flowing time doesn’t Bob’s recent book, I’ve often repeated ideas and concepts I find astound- exist outside our perception. Earth-Shattering ing. I’ll bet we all shared many of these: In the ’70s it In the ongoing can-you-top-this amazement contest, (Little, Brown and was relativity, especially anything involving light- Company, 2019), speed. Even now, who among us can picture how each things have clearly gotten out of hand. explores the greatest photon in a light beam aimed at a fast-departing rocket cataclysms that have hits it at exactly the same speed as it did when the rocket BROWSE THE “STRANGE UNIVERSE” ARCHIVE shaken the universe. AT www.Astronomy.com/Berman 12 ASTRONOMY • JUNE 2022

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BINOCULAR UNIVERSE Scotty’s Triangle Vulpecula. M27 is the second-brightest planetary nebula in the sky at magnitude 7.5. But finding M27 can be Take a journey with me to 1946. tricky. I get to it by using the constellation Sagitta the Arrow. M27 is due north from the arrow’s tip, orangish magnitude 3.5 Gamma (γ) Sagittae. In one of his col- umns, Scotty suggested to first find an M-shaped aster- ism 5° north of Gamma formed by 12, 13, 14, 16, and 17 Vulpeculae — all of which are around 5th magnitude. Our target is just ½° south of 14, the M’s middle star. M27’s two-lobed shape — which led to its popular nicknames of the Dumbbell, Hourglass, and Apple Core Nebula — does not readily show itself at 7x to 10x. For me, it takes my 16x70s to reveal the cloud’s tapered waist, while my 25x100s begin to reveal some of the subtle irregularities in its structure. Scotty’s second featured object was another planetary nebula, M57, the Ring Nebula in Lyra. At magnitude 8.8, M57 is bright enough to be seen through most binocu- lars. Confirming it, however, is difficult because of its small apparent size. While M27 measures about 8' by 6', M57 spans less than 2'. That reduces it to a starlike point at low magnifications. To find it, center your aim along the bottom of Lyra Walter Scott Houston was born in Milwaukee, the Lyre’s rectangular frame, between the stars Sulafat Wisconsin, on May 30, 1912. He developed a (Gamma Lyrae) and Sheliak (Beta [β] Lyrae). M57 sits love for physics, optics, and astronomy at an almost exactly halfway between them. To confirm that early age. By 12, he had observed all the Messier objects you are looking in the right place, M57 marks the vertex and his love of astronomy had grown into one that of an isosceles triangle with two 8th-magnitude stars just would last a lifetime. to its north. If you can identify that triangle, then you’ve After college, Scotty — as his countless friends knew hit M57. If not, try again! It’s the thrill of the hunt that him — moved around, teaching in Alabama, Ohio, makes it fun to spot tough targets through binoculars. I officially met Scotty Kansas, Missouri, and Connecticut. During It’s the Lastly, we come to Scotty’s third target, the at the 1991 Stellafane those years, he landed a contributor role at Sky thrill of the Wild Duck Cluster (M11) in Scutum. M11 is convention. Prior to & Telescope magazine, taking over a column hunt that the easiest of the three to see through binocu- our introduction, I and called Deep-Sky Wonders from Leland makes it fun lars. Find it by tracing Aquila the Eagle’s others at Stellafane Copeland in 1946. He would spend the next to spot tough diamond-shaped body from Altair to the 1975 joined him in a 48 years educating and enthralling readers, curve of its tail-feather stars, Lambda (λ) and game of frisbee. including myself, on the magic of deep-sky targets. 12 Aquilae. Together with Eta (η) Scuti, observing. I’ve affectionately dubbed us Lambda and 12 form a three-star arc that TOP: RICHARD SANDERSON. “Scotty disciples.” hooks right toward M11. BOTTOM: PHIL HARRINGTON I met Scotty several times at Stellafane M11 is one of my favorite summer objects. conventions. He was quite the character. It looks like a ball of celestial cotton, resem- And, through the years, he was very kind to bling an unresolved globular cluster more me. He mentioned my first book, Touring the Universe than an open cluster. That’s because, save for a single Through Binoculars, in his February 1991 column, 8th-magnitude star buried within, none of its suns saying, “Unlike other guides intended for binocular shine brighter than 11th magnitude. What also users, ... the author works hard at addressing the special impresses me are the star-studded surroundings. I like problems encountered when observing with binocu- to just sit back in a comfortable chair and drink it all in. BY PHIL lars.” You can imagine my despair when Scotty passed Next time you observe, think of people in your life HARRINGTON away just three years later, in December 1993. who have influenced your enjoyment of the night sky, Phil received the as Walter Scott Houston did for so many. And until next Walter Scott Houston In honor of Scotty’s 110th birthday, I’d like to feature month, remember that two eyes are better than one. Award at Stellafane the three objects he profiled in his first column. All are 2018 for his lifelong visible in this month’s sky, laid out in a pattern that I BROWSE THE “BINOCULAR UNIVERSE” ARCHIVE AT work promoting and call Scotty’s Triangle. www.Astronomy.com/Harrington teaching astronomy. The first target is the Dumbbell Nebula (M27) in 14 ASTRONOMY • JUNE 2022

OBSERVING BASICS Appreciating out of the grayish Sea of Rains is the bright peak Mons Piton. When near the terminator, Piton casts a long, the Moon pointed shadow, giving the impression that this mountain is a tall, needle-shaped structure. In reality, Piton rises just 1.4 miles (2.2 km) above its 16-mile-wide (25 km) Our natural satellite has many treasures to observe. base. The lofty spire is actually a gently rolling hill! By the evening following First Quarter, the lunar terminator (the boundary between day and night on the Mario Motta Moon) has drifted westward to reveal a dark oval patch really hates encircled by a bright rim. This is the 63-mile-wide the Moon. In (101 km) crater Plato, which appears dark because its fact, he would nuke it floor is covered by low-reflectivity lava rocks. A popular into oblivion if he had observing challenge for lunar observers is to search for the means. You see, the tiny craterlets that dot the crater’s floor. If seeing Mario is an accom- conditions are favorable, a 6-inch scope and a magni- plished astroimager fication of 175x or more should reveal a few. How many whose work appears in can you spot? the second edition of Directly south of Plato and rising out of the Sea of Stephen O’Meara’s Rains is the 8,000-foot-high (2,400 m) Mons Pico. Like Deep-Sky Companions: Piton, Pico casts a sharp and lengthy shadow when near The Messier Catalog. the terminator, belying its relatively flattened shape. And as anyone who Another evening will reveal more mountains that images clusters, nebu- emerge from the Sea of Rains. Northwest of Pico is a lae, and galaxies knows, 70-mile-long (113 km) jumble of peaks known as the a bright Moon obscures Montes Teneriffe (Teneriffe Mountains), whose tallest The lunar disk is these cosmic delights. members reach a height of 8,000 feet (2,400 m). Further shown in crisp detail But even the most west is a mountain chain that’s shorter (56 miles in this mosaic of an [90 km]) and less lofty (average height 6,000 feet 11-day-old-gibbous vocal Moon-hater has to acknowledge the jaw-dropping [1,800 m]) but far more eye-catching. Appearing more Moon imaged on visual impact of the Moon when viewed through a like a massive, artificially created wall than a natural March 17, 2019. ALAN DYER telescope. Nothing in the evening sky packs a “Wow!” lunar feature, this line of mountains is appropriately punch like the sight of its rugged, cratered surface. No cluster. No nebula. No galaxy. Saturn, with named the Montes Recti (Straight Range). its fabled rings, is a distant second. Three nights after First Quarter, the ter- The Moon is resplendent with lofty moun- Nothing in minator has moved westward enough to tain ranges, sinuous ridges and rilles, and the evening reveal the entire north shore of the Sea of hundreds of craters. And, to sample a variety sky packs a Rains and our pièce de résistance, the mag- of lunar features, you can do no better than to nificent Sinus Iridum (Bay of Rainbows). explore the expanse that runs along the north- “Wow!” The “bay” is actually the remnant of a crater ern border of Mare Imbrium (Sea of Rains) punch like 160 miles (258 km) across. Its northern rim from the Montes Alpes (Lunar Alps) west- the sight of forms the craggy Jura Mountains. The ward to the Montes Jura (Jura Mountains). its rugged, remaining rim was erased by the lava flow cratered that created the Sea of Rains. The Bay of The Lunar Alps come into view around Rainbows is flanked by the two mountain- First Quarter. Located at the northeast edge surface. ous capes of Promontorium Laplace and of the Sea of Rains, this range is about 155 miles (250 kilometers) long. Most of its Promontorium Heraclides. peaks reach elevations between 6,000 and So, my deep-sky-imaging friends, stop 8,000 feet (1,800 to 2,400 meters). They arose from the cursing the Moon. Set up a small telescope in the back- impact that created the Sea of Rains some 4 billion years yard and spend some time exploring this amazing BY GLENN CHAPLE ago. Bisecting the Lunar Alps is the Vallis Alpes (Alpine world. Glenn has been an Valley), a gash a little over 100 miles (160 km) long and Questions, comments, or suggestions? Email me at avid observer since 5 to 6 miles (8 to 9.6 km) wide. Once thought to be the a friend showed result of an oblique strike by an object thrown out by the [email protected]. Next time: Here comes the Sun! him Saturn through Sea of Rains impact, it’s now thought to be a graben — a Clear skies! a small backyard segment of the lunar crust thrust downward by the event. scope in 1963. BROWSE THE “OBSERVING BASICS” ARCHIVE Near the southern end of the Montes Alps and jutting AT www.Astronomy.com/Chaple WWW.ASTRONOMY.COM 15

The Taurus ACCRETION IS ONE of the Molecular Cloud is a vast star-forming region most fundamental processes in the threaded by a network of cosmos. It is a universal phenom- filaments. It was captured enon triggered by gravity, and the here by the European process by which bits of matter Space Agency’s Herschel accumulate and coalesce with more Space Observatory, bits of matter. It works inexorably which operated from on all scales to attract and affix 2009 to 2013. ESA/HERSCHEL/ smaller things to bigger things, from the tiniest dust grains to NASA/JPL-CALTECH, CC BY-SA 3.0 IGO; supermassive black holes. ACKNOWLEDGEMENT: R. HURT (JPL-CALTECH)

TUHNHEIUVNVEGERRRSYYEuonfdgpearllasatnxabeinetrsdsi,n,iWnasgcogshclBiaetrtYhnerateAsiilRoytlfWosntcEtoroeNmigmsmReaIwteMsths,iMhoeotEarnorRt. Accretion creates everything For instance: Why do some definitive answers to any of these Material from there is: galaxies, stars, planets, stellar nurseries form a few mas- questions yet, but there are some an accretion and eventually, us. It is the reason sive stars instead of lots of smaller theories gaining traction — and disk swirls around the the universe is filled with a whole ones? What causes so much evidence. young star FU Orionis bunch of somethings instead of a accreting material to ultimately in this artist’s concept. whole lot of nothing. fall inward onto its central object, All objects instead of just circling it forever? great and small NASA/JPL-CALTECH The fact that matter tends to And how do space rocks ulti- glom together may seem intuitive. mately stick together to form Accretion is the inevitable result But to scientists, accretion planets instead of just bouncing of gravitational forces operating remains a mysterious topic, filled off each other? No one knows the on all scales, and on all types of with unanswered questions. material — gas, dust, plasma,

even dark matter. Gravity makes But the true renaissance began arrangements of objects have matter accrete. And when matter a decade ago, when the Atacama been interpreted as evidence of accretes, it forms objects. Thus, Large Millimeter/submillimeter such superstructures. They are accretion and formation are very Array (ALMA), an array of 66 given various names according closely related in astronomy: radio telescopes in Chile, came to their observed shapes, such The former can be considered online. With the ability to study as arcs, rings, or walls. an aspect of the latter. distant, cool objects in detail came the data necessary to The observable portions of The Soviet scientist Otto understand the process of accre- superstructures consist mostly of Schmidt devised the first accre- tion in a variety of circumstances. molecular clouds of gas millions tion model of planetary formation Seeing accretion in action prom- of light-years across. Over the ised to be a game-changer. eons, these diffuse regions are TLCMSILHUGOOEPHSUEOTTDR-BLSSYYSTEOEOARRFFRUVGSCMAATBAOSULCLREMREEOCPSIULSOLCLSRIOA.OTNRNIOSSINSOSTFOF perturbed by a variety of effects: Today, ALMA and other the chaotic motions of the galax- in 1944, and his countryman advanced telescopes are observ- ies within them, the winds Viktor Safronov fleshed out the ing numerous objects of different thrown by quasar jets, the passing mathematics of accretion in 1969. sizes and stages of evolution: wakes of rotating black holes, and The underlying principles of galaxy groups, molecular clouds, blasts from supernovae. Here and gravitational attraction have since stellar nurseries, protostars, there, a confluence of gas and been applied to the formation of planetary disks, black holes, and dust will become dense enough stars and even galaxies. The dis- many more. We now know that that gravity takes over and a covery of quasars and compact whether on scales of kilometers domino effect begins, as more X-ray sources in the 1960s, using or light-years, accretion operates and more mass is drawn into a optical, radio, and X-ray observa- on the same broad principles. conglomeration, where a star- tions, set the field in motion. The particular mechanisms forming region is born. remain mysterious, but the veil is beginning to lift. The mechanics of these stellar nurseries, from which hundreds Stellar nurseries or thousands of stars are created, at the crossroads are not completely understood. Sometimes a region containing The largest structures in the a few hundred solar masses of universe are groups of galaxies dense gas and dust will form 100 that are gravitationally bound Sun-like stars. Other times a few to each other. We are not yet massive stars will also appear. able to see them, but peculiar This difference is of particular PLASMA IN THE WIND Collapsing Magnetic molecular cloud field lines Magnetic Protostar field lines Plasma Accretion disk

large, very cold objects that were The Giant difficult to detect and resolve GRB Ring until recently. The first observa- is a suspected tions were made with the Infrared superstructure — a Space Observatory in 1996. It was collection of nine a serendipitous find, made during gamma-ray bursts the first detailed survey of stellar (immensely powerful populations in the galactic plane. stellar explosions) Nowadays these regions are stud- arranged in a loose ring ied in detail with ALMA and the that spans 5.6 billion Submillimeter Array in Hawaii, light-years, as shown in which are more sensitive and have this artist’s concept. higher resolution at submillimeter wavelengths where cold molecular PABLO CARLOS BUDASSI/WIKIMEDIA gas is easiest to detect. COMMONS/CC BY-SA 4.0 These facilities have allowed interest to astronomers because starting to see evidence of these astronomers to map the gas flows massive stars can alter the evolu- filaments. “They fragment and they believe provide the necessary tion of a galaxy. What guides the intersect at certain places, espe- supply for the growth of massive seemingly random accretion pro- cially in the center of clusters,” stars. One survey, published in cess on these vast scales? says Hunter. “And where they The Astrophysical Journal in 2019, meet is where protostars have identified hundreds of protostel- One theory posits that there are access to a lot of gas on a short lar and prestellar core candidates “filaments of flowing gas, which timescale” — which feeds the for- in a particular region and studied thread through these clusters,” mation of massive stars. how they affect each other. The says Todd Hunter, an astronomer researchers suggest a kind of at the National Radio Astronomy These objects are called infra- “competitive accretion” process Observatory. Astronomers are red dark clouds, and they are very takes place, alongside what they call “global hierarchical collapse” — where chaotic gravitational forces cause a series of collapses within collapses, with small-scale events happening later and faster than large-scale events. This Escaping plasma THE REASON THAT the gas in a molecular cloud can (MHD wind) accrete into a star may be due to magnetohydrodynamics ASTRONOMY: ROEN KELLY (MHD), the physics of how magnetic fields interact with hot ionized gas. Interstellar space and everything in it is permeated by a weak magnetic field. Normally, this background magnetic field has no effect on a cold, dense cloud of gas and dust. But this changes when a collapsing cloud heats up and begins to generate plasma. Because plasma is electrically charged, it is linked to the magnetic field: As it moves, it drags the magnetic field lines with it. As the cloud collapses further and begins to form an accretion disk, the magnetic field becomes wound up by the disk’s rotation. The magnetic field also becomes stronger as the field lines bunch together. All of these magnetic field lines then act as highways for plasma to escape the strong magnetic field: Following the field lines, the charged particles zip away from the accretion disk into space. This MHD wind carries angular momentum away from the disk — and this, astronomers suspect, helps the cloud collapse into a star. WWW.ASTRONOMY.COM 19

At just 450 light- process works over a couple of stop. But how can this happen — started to show promise. years away, the million years, eventually trans- when the closer it gets, the faster “What if the angular momentum Taurus Molecular forming a diffuse cloud of starless it moves? Why doesn’t it just swirl is not redistributed in the disk, Cloud is an ideal place cores into a flattened disk of around forever? What dissipates but extracted through winds?” to search for accretion protostars. the angular momentum, allowing Pascucci says. disks. Two examples gravity to win the tug-of-war? are the young stars A widening gyre Star-forming regions have HL Tauri (bright blue, There are two prevailing theo- magnetic fields running through at upper center left) Where there is gravity and mat- ries. “The old idea is that disks them. While they do not affect and V1213 Tauri ter, there will also be accretion. are turbulent, and this turbulence neutral gas, particles that have (lower right). The Infalling matter forms a swirling generates a kind of viscosity,” been heated and ionized have an latter is hidden by an accretion disk. This gravitational or friction within a fluid, says electric charge and will tend to accretion disk, though gyre forms because the infall- Ilaria Pascucci, an astrophysicist follow these magnetic field lines. the star partly ing material — like everything and planetary scientist at the As the large-scale clouds collapse illuminates the disk else in the universe — had some University of Arizona in Tucson. under their own gravity, these above and below it. motion and angular momentum In this scenario, the disk is full of magnetic field lines also become The visible disk and before becoming caught up by an eddies, which means the gas par- twisted and tangled. And if mag- the jets comprise the object’s gravity. The laws of phys- ticles don’t orbit smoothly. As netic field lines are somehow bent object HH 30. ESA/HUBBLE ics state that angular momentum inner material accelerates, it drags outward, anchored to plasma that must be conserved — so, to fall the material outside of it along for remains outside the collapsing AND NASA; ACKNOWLEDGEMENT: into a star, black hole, or other the ride, like a jar of molasses cloud, plasma that is zipping object, material must lose its being stirred. “The viscosity along the magnetic field might JUDY SCHMIDT angular momentum first. It can- redistributes angular momentum be able to overcome gravity and not be simply sucked toward the outward, enabling disk gas close accelerate away from the disk. core along a straight line. Instead, in to accrete,” says Pascucci. Astronomers call these outflows it forms a flattened structure magnetohydrodynamic (MHD) called an accretion disk. This turbulence-viscosity winds, and they could carry away model of disk accretion was first angular momentum. This would The closer the material is car- suggested around 40 years ago. enable the leftover disk material ried to the center, the faster it But astronomers have never really to fall onto the forming protostar. spins. (Physicists often use the been able to make the numbers metaphor of a figure skater to add up. The models required Both observations and demonstrate this effect; when the disks to be stickier and more simulations seem to point toward skater pulls their arms in, they viscous than turbulence could spin faster.) There’s just a small probably account for. problem: For material to actually fall onto the core, it must slow Then, in the last decade, an down and eventually come to a overlooked characteristic of accretion disks — magnetic fields

The accretion disk that surrounds the elliptical galaxy M87 feeds its central supermassive black hole (SMBH) and relativistic jet in this artist’s concept. ESO/M. KORNMESSER The ghostly halo we see in the groundbreaking image of an SMBH from the Event Horizon Telescope is the hot, glowing plasma in the accretion disk surrounding it. EVENT HORIZON TELESCOPE COLLABORATION the MHD wind hypothesis. The factors. Turbulence, magnetic University. “This causes clumps best evidence so far for an MHD fields, and the play of viscosity to form, which over time can pro- wind is a 2021 study in The between gas and dust may cause a duce larger and larger objects.” Astrophysical Journal of an active kind of traffic jam that eventually young star, where astronomers congeals to form protoplanets. So far, this protoplanetary have measured how high the Closer in, most of the gas gets evolution mechanism, called wind appears to sustain itself consumed by the star, leaving streaming instability, seems to be as it flows away from the disk. rocky material and heavy metals, a promising way to grow things Measuring how powerful these which form terrestrial planets. from centimeter to kilometer winds are — and therefore how sizes. The most intriguing part much angular momentum they But there is a long-standing of the theory is that the gas is the carry away — will be the next question about how rocky bodies crucial component: Without it, major task in testing the theory. accrete, involving a concept dust in the disk couldn’t coalesce called the bouncing barrier. to form planetesimals. But there Disk worlds Electrostatic forces cause small is not yet direct evidence. grains to stick together and larger At the same time a star is form- planetesimals are attracted to ing, so are the planets that will each other by gravity. But how orbit it. Both star formation and does a particle become a planet? planet formation happen within Models show that objects in that disks via accretion. As gas and middle range between tiny and dust swirls around the star, delin- massive just tend to bounce off eations begin to appear in the each other. So how do amassing disk. Astronomers saw this for objects overcome this barrier to the first time in 2014 in a young growth? star called HL Tauri. This obser- vation, made using ALMA, was a One theory is that the particles major advancement in our under- experience a drag force as they standing of how planets form. move through gas in the disk. “There’s a strong interaction In a nascent planetary system, between solid particles and the the congregation of matter gas in the disk,” says James Stone, depends on lots of different an astrophysicist at Princeton WWW.ASTRONOMY.COM 21

The hope is that within a planetary systems form, because centers of galaxies, they draw decade or two, we will have seen the star is only about 2.5 million material from the vast roaming lots of planets at different stages years old. stars, clouds, and nebulae within of formation. This will stand in as the galaxy itself. a kind of time-lapse and we can Gathering dust judge how well predictions of pre- As material from the disk falls vailing hypotheses, like streaming Every star grows up on its own into the central object — whether instability, match up to actual schedule. The protostar stage is a star, planet, or singularity — it exoplanets. This ambitious ven- like a star’s volatile teen years. releases energy in the form of ture received a kickstart in 2021 When its accretion disk stabi- radiation. The disk itself also lizes and material stops falling radiates as it swirls around the TSAGUHTCRNCEEOIVRRLWELEERATTISRESHE-EINM’SSNOAOLCSWUAUSGRRAHGRBYEELMFNAAOACTTRKTAETAHGRHOESIEA.LINELGTTLOOE into the core, it becomes a main gravity well and heats up, with with the discovery of the youngest sequence star. There may still different factors like viscosity, planet ever observed: 2M0437b. be a debris disk and the planets friction, and speed making some The discovery image, taken by the around might still be figuring out parts hotter than others. The Subaru Telescope on Mauna Kea where they orbit, but accretion stronger the draw of the central in Hawaii, shows a world still has largely stopped. That doesn’t object, the more powerful the glowing hot from energy released mean there won’t be any more radiation emitted, as gas can be during its formation, meaning accretion in the star’s future, transformed into plasma. The it just recently (astronomically though. Depending on its mass, groundbreaking 2019 image of speaking) finished accreting. The when fusion ceases, it will then the supermassive black hole at the study, led by Eric Gaidos of the transition into either a white center of the galaxy M87 is not of University of Hawai’i, also fills dwarf, a neutron star, or a black the hole itself, but of the black in our picture of how quickly hole, all of which can form accre- hole’s shadow on the charged tion disks of their own. plasma swirling around it. In 2014, the ALMA radio The supply for this new disk A black hole gains mass from telescope revealed can come from a variety of everything it accretes over time. distinctive gaps in sources. Compact objects, like But while we understand how HL Tauri’s accretion white dwarfs and black holes, Sun-sized black holes form, we disk. They mark may siphon gas from a compan- don’t know how SMBHs got as regions where planets ion star. A white dwarf may also big as they are. For example, are accreting and pull in material that it puffed off the SMBH at the center of the sweeping up material. in the earlier red giant phase. Whirlpool Galaxy (M51) in And when black holes grow and Canes Venatici has a mass equiv- ALMA (ESO/NAOJ/NRAO) merge to become the supermas- alent to 1 million Suns. There is sive black holes (SMBHs) at the no way for a single small, stellar- mass black hole to accrete enough material to grow this large at the universe’s current age. “It’s one of the biggest myster- ies of black hole research,” says Joanna Piotrowska, a graduate student at Cambridge University. The laws of physics limit how quickly an object can accrete matter, called the Eddington limit. Above that limit, the radia- tion from the accretion disk is so intense, it blows material away — preventing more accretion from happening. “The mass of [SMBHs] exceeds what is expected from continuous accre- tion at the Eddington limit over the lifetime of our universe,” says Piotrowska. One proposed solution is that SMBHs were big to start with. Perhaps in the early universe, 22 ASTRONOMY • JUNE 2022

even before the first stars, there And that’s not all ... actually preclude the process else- Supercomputer were molecular clouds with just where. There is a rare kind of simulations the right conditions to collapse It’s tempting to picture accretion supernova, called Type 1ax, where reveal the turbulent straight away into singularities. as a peaceful, gradual, and the accretion disk around a white and hierarchical The James Webb Space Telescope constructive process, like erosion dwarf explodes. The accretion dynamics of might be able to shed some light in reverse. It can certainly disks around quasars have power- collapsing infrared on this dark topic when it comes take time to get going. But the ful magnetic forces which shoot dark clouds (IRDCs), online this year. It was designed methods by which an accretor material out in supersonic jets. forming filaments especially to see the first galaxies gains mass can be quite quick And there is evidence that winds within filaments. In and stars, and those primordial and chaotic. Recently, observers from the jets of actively feeding the densest regions formations could help us to have seen what they call accretion SMBHs can actually quench, or of this simulation, understand the initial distribution bursts around protostars — turn off, star formation in their shown in red, of potential collapsible matter. instances of extreme instability host galaxies. molecular clouds are in a disk, where large amounts forming cores that of material suddenly plunge into These are exciting times for will become massive the star. Hunter recently observed those who study accretion. stars. RICHARD KLEIN, this on NGC 6334 I, a protostar Astronomers finally have the cluster in the Cat’s Paw Nebula capability to compare their math- LAWRENCE LIVERMORE NATIONAL (NGC 6334) in the constellation ematical predictions to actual Scorpius, using the Stratospheric astrophysical objects at key stages LABORATORY; PAK SHING LI, Observatory for Infrared of their lives. Whether their theo- Astronomy (or SOFIA). He ries ultimately measure up to UNIVERSITY OF CALIFORNIA, theorizes that a high proportion reality, or whether new ones will of the total accretion of some need to be invented to account for BERKELEY; TIM SANDSTROM, NASA stars — up to 50 percent — may observations, only time — and a actually happen in this way. lot more data — will tell. AMES RESEARCH CENTER Furthermore, accretion is not Arwen Rimmer is a writer and IRDCs appear always a constructive process — musician in Cambridge, England. as shadows accretion in one place might splayed across the bright mid-infrared background of the Milky Way, as seen in this false-color image from NASA’s Spitzer Space Telescope. Though they are some of the darkest objects in the sky, these ultracold and dense clouds give birth to the brightest, most massive stars in the galaxy. NASA/ JPL-CALTECH WWW.ASTRONOMY.COM 23

The field of exoplanets has sprung up nearly overnight. What does the wealth of new discoveries tell us about the worlds circling our own Sun? BY BRIAN MAY, PATRICK MOORE, CHRIS LINTOTT, AND HANNAH WAKEFORD How we discover

ed other worlds Astronomers have found thousands of worlds circling other stars — and many look very unlike own solar system’s familiar planets. ASTRONOMY: ROEN KELLY

WHILE ASTRONOMERS HAVE BEEN EXPLAINING the known exoplanets. This overstates their origin and composition of our Sun’s family of planets for hundreds actual abundance — it is easier to find a of years, this story has only come together in the last 30 years or so. large planet close to its star, where it will Before then, astronomers assumed that planets were born in the induce significant wobbles, than to pick out the signal of a puny Earth-sized world. location and configuration in which we see them today. The idea of Correcting for these biases, hot Jupiters planets moving about while they are forming was only seriously seem to account for about 1 percent of all considered once planets in other systems — exoplanets — worlds. That doesn’t sound like much, but it could easily had actually been found. mean there are a billion “Hot Jupiters” hot Jupiters in the The hot Jupiters times closer to its like the planet Milky Way alone! In 1995, astronomers studying the nearby star than Mercury perturbing 51 Peg were The method used star 51 Pegasi found that it appeared to is to the Sun. To found to be common. to find the planet be wobbling back and forth, movement find a giant planet More than 400 are around 51 Pegasi, that revealed itself through a regular pat- so close to its star known as the radial tern of Doppler shifts in its spectrum. that its year was known to date, and they velocity method, The observations suggest that the star is measured in just a account for around 10 requires enough in orbit around a position just slightly few days was com- telescope time to pay percent of known offset from its center. By measuring the pletely unexpected, exoplanets. close attention to a size of the wobble, it was possible to get calling into question star of interest over an estimate of the mass of the perturbing everything we’d assumed many nights. Most exoplan- object, which turned out to be less than about planetary systems. ets known today have been half the mass of Jupiter, too small to be One such planet might have been found instead by searching for transits, a a star. They had found an exoplanet! an exception, the result of some gloriously method which allows us to survey many The discovery was puzzling. The new unlikely freak accident of planet forma- stars at once. This technique relies on the planet completed an orbit every 4.23 days. tion. But “hot Jupiters” like the planet fact that, if a planet’s orbit happens to be That placed this giant world, which we perturbing 51 Peg were found to be com- aligned such that — as seen from Earth would have expected to find in the icy mon. More than 400 are known to date, — it passes in front of the star, the star reaches of its outer solar system, seven and they account for around 10 percent of will appear to fade just slightly. A similar effect is seen from Earth when Mercury or Venus transit in front of the Sun. Thanks to the complexities of planetary geometry, such events are rare, but throughout the galaxy there must be worlds which happen to be positioned such that the planets of our solar system cross in front of the Sun with every orbit, causing a regular series of blinks. Indeed, the nearby dwarf Teegarden’s Star seems to have just such a system. If there are astronomers on these planets, what could they learn about our solar system? They could measure the radius of each planet relative to the size of the Sun; the amount of light blocked by the planet corresponds to the ratio of the two areas. By timing the period between successive transits, they would get the orbital period and — thanks to Kepler’s laws — the dis- tance of the planet from the star. (You can see why large, close-in planets would be easier to detect via this method than smaller planets which are further from their stars.) Applying these techniques to ALMA made the first large-scale survey of protoplanetary disks around nearby stars. This image shows 20 the known hot Jupiters tells us that they nearby systems where dust and gas are forming new planets. It is possible to make out gaps in the disks, span a range in size that starts from which seem to demarcate their inner and outer portions. ALMA (ESO/NAOJ/NRAO), S. ANDREWS ET AL. 100 Earth masses (about a third of the 26 ASTRONOMY • JUNE 202 2

Number of planets per star (orbital period < 100 days) SIZING UP EXOPLANETS 0.12 0.10 Neptune Uranus Saturn Jupiter 0.08 Earth 0.06 0.04 0.02 Planets from our solar system Exoplanets discovered by Kepler 0 1 1.3 1.8 2.4 3.5 4.5 6 8 12 20 Planet radius (REarth) The Kepler spacecraft’s mission was designed to look at a region Planets’ sizes of the Milky Way and determine the fraction of the hundreds of relative to each billions of stars in our galaxy that might host exoplanets. Kepler other are shown discovered thousands of transiting exoplanets, getting a measure to scale of their radius relative to their stars. This diagram charts the number of planets it discovered with orbits of less than 100 days, showing there are a large number of worlds quite unlike those in our solar system. ASTRONOMY: ROEN KELLY, AFTER WAKEFORD & DALBA, 2020 mass of Jupiter) and which goes all the THE TRANSIT METHOD way up to 13 times Jupiter’s mass. This higher figure is most likely a funda- Star mental limit; any more massive than this, and the pressure and temperature Planet at the core will be high enough to enable deuterium fusion, at which point Occultation Stadra+yspidlaenet the body is at least a brown dwarf and Stanrig+hptslaidneet perhaps a full-blown star. Flux Time Star alone Building giants Transit This range of masses makes it clear Star–planet shadow we’re not dealing with planets like our own Mercury, the only world that lies ABOVE: When a planet crosses the face of a star, close enough to the Sun to complete an there is a slight dimming in the brightness of that orbit in less than 100 days — a range star measured from Earth. This principle is used that includes three-quarters of known to identify exoplanets orbiting other stars. exoplanets. How did these strange worlds come to be? ASTRONOMY: ROEN KELLY One part of the answer is that it is RIGHT: Brian May observes the transit of Venus sometimes easier to form planets effi- in 2004 by projecting the Sun’s image onto a ciently. Perhaps unsurprisingly, there’s white card. KATE SHEMILT a correlation between the metallicity of the star — how much material there is in forms other than hydrogen and helium — and the likelihood that giant planets would exist. The more material there is from which to form planets, the more planets form! But, though this relation sounds like nothing more than

BRING THE Bang!!: COSMOS The Complete HOME History of the Universe is now Our universe is a available online at vast, strange place www.MyScience where stunningly Shop.com powerful phenomena abound. Bang!!: The Complete History of the Universe will take you all the way from the Big Bang that birthed our cosmos through its cold, dark demise in the unimagin- ably distant future. Written for everyone with a curiosity about how we got here and where we’re going, this highly anticipated update to a beloved and bestselling common sense, it doesn’t seem to hold The answer is that most of the time, book includes more than 20 percent for planets smaller than Neptune. This you probably don’t. In many systems, new content. Each chapter dives into a suggests that there is a fundamental planets will form, migrate through the different part of our universal story, threshold that needs to be reached before disk, and disappear into fiery oblivion. But exploring the cosmos in depth in an in some cases, tidal interactions between the migrating planet and its star force the understandable, approachable, and a giant planet can form. newly hot Jupiter to settle into the circular compelling way. This new volume is The necessary conditions must be — stable — orbits we see today. expanded and retooled to cover the very latest advances in our understand- reached more often in the outer proto- Tackling the gaps ing of every aspect of astronomy, from a planetary disk, where planet formation clearer picture of the dark matter and can proceed rapidly. To reconcile these What of the 99 percent of planets which are not hot Jupiters? The most pro- dark energy that rule our ultimate fate hot Jupiters with a theory of planet for- lific planet hunter was the Kepler Space to the plethora of extrasolar worlds now mation that says that such large worlds Telescope, designed specifically to detect teaching us in detail how our own solar must form out beyond the ice line where transits. Following launch in 2009, it system — and the life within it — water and other volatiles exist as ice, the spent three years staring at a single patch formed. idea of planets migrating through the of the night sky, chosen because it is rich in stars and yet devoid of any particularly Penned by rock star and astronomer bright examples, on the border between the constellations of Cygnus and Lyra in Brian May, University of Oxford astro- disk as they form becomes essential. To the northern part of the sky. Kepler mea- physicist Chris Lintott, planetary scientist get to be a hot Jupiter, these worlds must sured the brightness of each of 150,000 Hannah Wakeford, and the beloved late have traveled a significant distance, stars every 30 minutes, and that of a Sir Patrick Moore, this updated edition is plowing through the inner disk, gather- smaller number of selected systems every sure to become your go-to reference for ing up and expelling material through minute. Its intended quarry was planets all things cosmic. where life like our own might, perhaps, their gravitational pull as they did so. This is probably bad news for any small rocky planets with ambitions to remain in a nice sedate, stable orbit, but it also raises a fundamental question — how do you stop such a planet from falling into the star? 28 ASTRONOMY • JUNE 202 2

The planet 51 Pegasi b, imagined in this artist’s rendition, was the first extrasolar planet discovered circling a Sun-like star. It is a hot Jupiter that orbits its star once every four days, from a distance some seven times closer than Mercury orbits the Sun. ESO/M. KORNMESSER/NICK RISINGER (SKYSURVEY.ORG) Beta Pictoris is a well-known example of a star with a surrounding debris disk. This star was the first to have an exoplanet imaged directly. Infrared observations made from the European Southern Observatory in Chile revealed a planet orbiting the star (whose bright presence has been artificially removed by the large disk to increase the contrast needed to reveal the planet). ESO/A.-M. LAGRANGE ET AL. exist — terrestrial worlds around Sun- type of planet in the Milky Way is one super-Earths, if their density suggests that like stars, preferably at the right distance that does not exist in our own solar sys- they are rocky, or mini-Neptunes, if a from the star that the temperature would tem, with a radius between that of Earth lower density indicates a gaseous nature. allow for liquid water. What it found was and that of a planet like Neptune, four Ideally, we’d know not only the radius, much more interesting. times larger than Earth. Members of which can be determined by the transit this new class of planets are known as method, but also the mass, for which we It turns out that the most common need a detection via radial velocity. Unfortunately, most of the stars stud- ied by Kepler are too far away or too faint to enable useful radial velocity measure- ments to be made. A new NASA satellite, TESS (short for Transiting Exoplanet Survey Satellite), is searching for planets KEPLER-22 b KEPLER-69 c KEPLER-62 e KEPLER-62 f EARTH Rocky planets larger than Earth, dubbed super-Earths, are becoming increasingly common among exoplanet finds. No such planet exists in our solar system, of course. These super-Earths — all artist’s renditions, except for Earth at the far right for comparison — all sit within their stars’ habitable zones, meaning they could potentially support life. NASA AMES/JPL-CALTECH WWW.ASTRONOMY.COM 29

RADIAL VELOCITY METHOD Star Planet Star Center Center of mass of mass Planet Redshift Blueshift Astronomers have several ways to find planets 100 circling other stars. One is the radial velocity Blueshift method, which measures the way a star “wobbles” to and fro on the sky as an orbiting 50 planet tugs on its sun. This wobble affects the wavelength, or color, of light we receive from 0 the star, making it appear redder or bluer, depending on the direction of motion. -50 The star’s back-and-forth motion stretches -100 (redshifts) and squeezes (blueshifts) its light. Time Star’s velocity Redshift toward Earth ASTRONOMY: ROEN KELLY around nearby stars, partly to correct their atmospheres. If the forming planet BELOW: Mini-Neptunes are gaseous planets smaller this problem. So far, what we know is is not massive enough, its atmosphere is than Neptune but larger than Earth. Our solar that mini-Neptunes and super-Earths are lost and it will end up as a super-Earth, system is also conspicuously missing this type of both so common that it is odd that nei- while the more massive worlds can hang planet, which astronomers are discovering are ther exists in our own planetary family. onto the gas and remain mini-Neptunes. common throughout the cosmos. Here, artist’s If we take all the planets found by Kepler illustrations of two such mini-Neptunes (TOI-421 b on orbits less than 100 days and adjust The details of these processes, and and GJ 1214 b) are shown to scale with photos of for the fact that larger, close-in planets how they might have influenced our own Earth and Neptune. NASA, ESA, CSA, DANI PLAYER (STSCI) are easier to see, over half of the detected world’s formation, are still being worked planets still fall into this category. out, but the existence of this fundamen- EARTH tal division between planetary types Actually, this exercise reveals another which we were completely oblivious to new truth about the planetary popula- until a few years ago gives you an idea as tion. There’s a distinct absence of planets to how fast things are changing. Careful with sizes right in the middle of the gap observations of planets on both sides of between Earth and Neptune; at 1.7 Earth the radius valley, along with their stars, radii, in particular, there are few planets, will be a big part of astrophysics in the a feature that has become known as the next decade or so. radius valley. It seems that planets really are either a super-Earth or a mini- On the move Neptune, lying on one side of the valley or the other. The explanation comes A third big surprise from our exoplanet from the time when planets are still discoveries is that one-third of known forming. As the star heats the disk, only worlds have orbits which are distinctly the most massive planets can hang onto eccentric. It’s true that Earth’s orbit isn’t precisely a circle, but it’s pretty 30 ASTRONOMY • JUNE 202 2

close — its eccentricity is 0.016, so the of the Milky Way — can be found by the star, and direct imaging has been used difference in length between the longest and shortest axes is not much more than this technique, specifically via a form to find worlds tens or even hundreds of 1 percent. A third of exoplanets have eccentricities greater than 0.1, an order known as microlensing, because the astronomical units from their star. of magnitude larger. This fact is a clue that life in a forming solar system may changes are small. What’s more, the (One astronomical unit is the average be even more complicated than we had suspected until now. amount the star brightens tells us about Earth-Sun distance.) There are only 50 We know that planets can move the mass of the planet and several of or so planets which have been directly through the protoplanetary disk, usually by interacting with the material in the those detected have masses imaged, each of them extremely disk itself. These large eccentricities were caused by more dramatic interactions comparable to Earth. precious. They tend to be between planets — so the fact that the planets of our solar system have largely Picture perfect It turns out young, and massive — circular orbits tells us it must have been many are nearly large an unusually calm place when they were forming. It’s clear we can that the most enough to be stars. Even more extreme interactions are learn a lot from common type of planet Comparing each possible. When two large bodies come close together, their spheres of gravita- these indirect in the Milky Way is one of these exoplanet tional influence overlap. Anything methods of planet that does not exist in our systems to our own caught between them will become detection. Indeed, own solar system, with a raises many ques- dynamically excited — in other words, for most systems tions. Why are the once-stable orbits will be disrupted, and we have no choice radius between that worlds of the solar material can be expelled from the system. but to rely on these of Earth and system on nearly cir- It’s even possible for one of the planets to be expelled, spinning off into space. techniques, where we Neptune. cular orbits? Why don’t Some interstellar wanderers have even learn about the plan- we have a super-Earth? been detected, thanks to a technique called gravitational lensing, originally ets by studying stars. It Why did Jupiter remain developed for looking at distant galaxies. If a planet passes between us and a dis- is, though, undoubtedly true where it was, rather than plow- tant star, it acts as an otherwise unde- tected lens, bending and amplifying the that direct imaging — seeing the planets ing through the inner solar system and star’s light and revealing its presence. Distant planets — even on the other side themselves — can tell us much more. The becoming a hot Jupiter? Today, scientists problem isn’t so much that the planets look at the origins of our own solar sys- are intrinsically faint — especially after tem in the light of these new discoveries, formation, when they are still being heat- learning more about our own home now ed by their gravitational contraction, they that we’ve looked outward at the stars. will shine brightly — but that the glare of light from the star makes them very dif- Brian May is best known as the lead ficult to detect. guitarist for Queen and holds a Ph.D. The solution is to use an instrument in astrophysics. Patrick Moore was a called a coronagraph to block the light beloved astronomer and presenter of the from the star. By placing an obstruction BBC’s The Sky at Night. Chris Lintott is in the field of view, and through some an astrophysicist, author, and broadcaster very careful use of image processing algo- at the University of Oxford. Hannah rithms, planets can be revealed. It is easier Wakeford is a lecturer in astrophysics to see companions which are further from at the University of Bristol. TOI-421 b GJ 1214 b NEPTUNE WWW.ASTRONOMY.COM 31

SKY THIS MONTH Visible to the naked eye Visible with binoculars THE SOLAR SYSTEM’S CHANGING LANDSCAPE AS IT APPEARS IN EARTH’S SKY. Visible with a telescope BY MARTIN RATCLIFFE AND ALISTER LING Noctilucent clouds (left) float in the dawn sky in this summer 2020 panorama. Visible from left to right are Venus, Mars, Saturn, Jupiter, and the Moon. This year, the remaining three planets will join in. ALAN DYER JUNE 2022 A planetary Uranus and Neptune are Pisces, and Venus, in Taurus. also in the mix. Both can be On the morning before or after observed in binoculars or with a this date, the Moon is closer to Mars or Venus, respectively. extravaganza small telescope before the onset of twilight. Uranus stands 6° The magnitude of each east of the Moon that morning, naked-eye planet on June 24th shining at magnitude 5.9 in is as follows: Mercury –0.1, Venus –3.9, Mars 0.5, Jupiter Aries the Ram. Neptune is in –2.4, and Saturn 0.5. western Pisces, 11.5° west of June 7 is the earliest date you might catch Mercury, as it All seven major plan- of Jupiter and Saturn, the fact Jupiter and magnitude 7.8. shines at magnitude 1.5 and rises shortly before 5 A.M. local ets congregate in the that the other planets gather The planets are spread along time. That morning, the span from Mercury through Saturn morning sky — yes, all seven! near them is not that unusual. a 106° swath of the ecliptic. is 91° — their closest for the month. The span from Mercury The five naked-eye planets line On June 24, the five classical Mercury is last to rise, shortly to Jupiter is only 52°. Later dates in June are more favorable for up in order of distance from the planets and a crescent Moon before 4:30 A.M. local time, catching Mercury, though, as it brightens considerably through Sun, stretched along the eclip- span the eastern sky in order of allowing for at least half an the month. tic. The Moon joins in later this distance from the Sun: Mercury, hour of good viewing before No planets are visible in the evening this month, so let’s fol- month. The morning spectacu- Venus, the Moon, Mars, Jupiter, twilight starts to interfere. The low the Moon instead. On June 1, a 2-day-old Moon is lar is perfectly situated for and Saturn. All are visible to the Moon on the 24th is roughly nearly 20° high in the west 30 minutes after sunset. You’ll find hours of remarkable telescopic naked eye. midway between Mars, in the slender crescent 13° below Gemini’s pair of 1st-magnitude views, beginning when Saturn stars, Castor and Pollux. rises soon before midnight in View across the solar system Two days later, the fattening late June. Within a span of just Moon stands 5° northwest of the Beehive star cluster (M44) over 90°, you can spy the rings Mirfak PEGASUS Saturn in Cancer the Crab. On June 5, of Saturn, the atmospheric belts PERSEUS Alpheratz the waxing crescent floats less and the Galilean moons of than 5° north of Regulus, the Jupiter, the rusty surface of A Q UA R I U S brightest star in Leo the Lion, Mars, the phase of Venus — and a fleeting glimpse of Hamal PISCES Neptune Mercury. ARIES Jupiter Fomalhaut Instead of our usual start in Mars Uranus Moon the evening sky, we’ll jump TAURUS Venus CETUS right into the main event and Mercury later discuss each planet as it 10° Aldebaran rises throughout the night. June 24, 50 minute before sunrise The presence of all seven Looking east planets in the morning sky is a relatively rare sight. Of course, This month, all seven planets line up, joined by the Moon. Pull out binoculars following last year’s conjunction or a small scope to spot Uranus and Neptune. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY 32 ASTRONOMY • JUNE 2022

RISING MOON I Lunar standstill OBSERVING IF THE JUNE FULL MOON on the 14th looks Honey Moon HIGHLIGHT really yellow, there’s a good reason. The closer an object is to the horizon, the longer the The Full June Moon often looks honey-colored, as in Observers in Canada and slanted path its light rays take through our this photo taken June 22, 2013. STEPHEN RAHN the northeastern U.S. atmosphere. Blue is preferentially scattered away, leaving the golden hue responsible for pegged the extreme rise points with their amazing will see THE MOON occult one of its common names: the Honey Moon. stone megalithic structures and circles. the star Dschubba in You might think our satellite will turn its usual Observers south of the equator can also note Scorpius on June 12. white when it climbs higher in the sky, but it the standstill, but the yellow color will be there remains unusually low the entire night. We know only when the Moon rises or sets. and remains visible at least an the lowest declination at which the planets on hour after local midnight. the ecliptic cross Sagittarius is –23.5°, yet Luna is almost another 5° farther south. An extremely The First Quarter Moon late-rising June Full Moon, after midnight in some occurs June 7, as our satellite places, still amazes the experienced skywatcher. has just crossed into Virgo. The lunar low lines up with the ecliptic low (and Spica is less than 6° southeast the high with the high) in an 18.6-year cycle. of the gibbous Moon June 9. But there’s more: The Moon will also stand Check the Moon as it rises still. At First Quarter on the 7th, the Moon rises on June 12 among the stars of the north side of due east. Every day thereafter, Scorpius, only 7° northwest moonrise shifts southward until it hits an extreme of Antares. In twilight for southeast rise point on the 14th, followed by a Midwestern observers and in retreat back north. This echoes the Sun’s annual dark skies farther east, watch swing south to the December solstice and back with binoculars as the Moon north again. So, it’s really the moonrise point that glides past 2nd-magnitude stands still on the horizon. Technically, the major Dschubba (Delta [δ] Scorpii). standstill happens in March 2025, but for the Full Skywatchers in the northeastern Moon, the next five Junes will all be near that U.S. will see the star disappear extreme southeast rise point. behind the Moon: In Hartford, Massachusetts, this occurs at Hipparchus, in the 2nd century B.C., was the first 10:19 P.M. EDT., with the star to write about the 18.6-year cycle. Yet long before reappearing 52 minutes later. him, skygazers in both Europe and the Americas Since Dschubba disappears near the southern limb of the Moon, METEOR WATCH I High-flying clouds timing can vary significantly depending on your location. For Flowing noctilucent clouds THERE AREN’T ANY major mete- example, in Washington, D.C., it or showers in June, so most meteors begins five minutes later. If you spot noctilucent clouds, try setting up a camera to capture a time you’ll see this month are part of lapse of their gentle flows. MARTIN KOITMÄE/WIKIMEDIA COMMONS the so-called sporadic background Full Moon occurs June 14; it rate. They appear at random, up is visible all night in Sagittarius. to seven per hour, and are likely This date is a good time to turn related to old debris streams from our attention to the morning long-dead comets. sky and the panorama of plan- ets stretching along the ecliptic. One feature of the summer sky, The Moon will join in during noticeable from Canada and some the latter half of the month to northern U.S. states, is the appear- follow this line of planets. ance of noctilucent (night-glowing) clouds. These are preferentially seen The first naked-eye planet to from latitudes of 55° to 70° north rise in the southeast is Saturn, and generally appear toward the soon after 1 A.M. local time early northern horizon. Located at more in the month and shortly after than 10 times the height of cirrus midnight by mid-June. It’s clouds, these iridescent pearly clouds remain in sunlight long after — Continued on page 38 the Sun has set. They’re produced by ice crystals that form on high- flying dust particles. WWW.ASTRONOMY.COM 33

STAR DOME b C A M E L OPA R DA L I S ` A ¡ _ _ ` d PE S S A C N a O I I HOW TO USE THIS MAP k af This map portrays the sky as seen NE near 35° north latitude. Located inside the border are the cardinal L A C E RTA ` c CEPHEUS NCP directions and their intermediate b _ points. To find stars, hold the map _ 81 overhead and orient it so one of Polaris M82 the labels matches the direction you’re facing. The stars above `+ the map’s horizon now match what’s in the sky. MINOR _ The all-sky map shows URSA d how the sky looks at: Deneb DRACO _ midnight June 1 _ 11 P.M. June 15 PEGASUS b a 10 P.M. June 30 ` Planets are shown c c at midmonth ¡ b b_ a Mizar Vega ` ¡ ¡ a i cf CYGNUS d ` M51 d dr EQUULEUS M15 DE M27 a ` _ LYRA d SAGIT TA a ` _ _ _ V b COMA a M57 a` L d BERENICES _ MAP SYMBOLS P UL /b Open cluster H _ HERCULES M13 Globular cluster Diffuse nebula I P BOÖTES Planetary nebula Galaxy N E E U C c CBOORROENAAL I S ` S U + L A _ ¡ ` A Q U I L A M11 c bh e CAPRICORNUS d Altair SE _ _g ` Arcturus _ _` C ` SERPENS A Q UA R I U S R CAPUT A _ PUEDNAS M5 STAR d OPHIUCHUS ` MAGNITUDES 20 i b a LIBRA _ Sirius M16 c ¡ 0.0 3.0 _ 1.0 4.0 Path of the Sun (ecliptic) 2.0 5.0 SCUTUM M17 d / ` + M20 STAR COLORS mc M22 e Antares m b m o  h M8 M6 / A star’s color depends b o _ M4 g / on its surface temperature. ` e S A G a ¡ SCORPIUS The hottest stars shine blue M7 C SE I T TA ¡ •• Slightly cooler stars appear white c • Intermediate stars (like the Sun) glow yellow RI U S d hp + LUPUS • Lower-temperature stars appear orange g c NGC 6231 • The coolest stars glow red f d a • Fainter stars can’t excite our eyes’ color e ¡ d receptors, so they appear white unless you d _ use optical aid to gather more light NORMA c a S BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart.

JUNE 2022 SAT. SUN. MON. TUES. WED. THURS. FRI. k NW 1 234 LYNX 5 6 7 8 9 10 11 f 12 13 14 15 16 17 18 ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY MAJOR e 19 20 21 22 23 24 25 URSA ` _ 26 27 28 29 30 R Note: Moon phases in the calendar vary in size due to the distance from Earth and are shown at 0h Universal Time. +h O ` CALENDAR OF EVENTS EO MIN 1 The Moon passes 0.1° north of dwarf planet Ceres, 5 P.M. EDT The Moon is at apogee (252,396 miles from Earth), 9:13 P.M. EDT L 2 Mercury is stationary, 8 P.M. EDT I s a 5 Saturn is stationary, 10 A.M. EDT ¡ 7 First Quarter Moon occurs at 10:48 A.M. EDT C 11 Venus passes 1.6° south of Uranus, 9 A.M. EDT 14 Full Moon occurs at 7:52 A.M. EDT I The Moon is at perigee (222,098 miles from Earth), 7:23 P.M. EDT AT 16 Mercury is at greatest western elongation (23°), 11 A.M. EDT 18 The Moon passes 4° south of Saturn, 8 A.M. EDT N i c 19 The Moon passes 0.7° south of asteroid Vesta, 4 A.M. EDT 20 The Moon passes 4° south of Neptune, 1 P.M. EDT E LEO _ Regulus Last Quarter Moon occurs at 11:11 P.M. EDT ` d 21 Summer solstice occurs at 5:14 A.M. EDT V Mars is at perihelion (128 million miles from the Sun), 9 A.M. EDT The Moon passes 3° south of Jupiter, 10 A.M. EDT CANES 22 The Moon passes 0.9° south of Mars, 2 P.M. EDT 23 Mercury passes 3° north of Aldebaran, 10 A.M. EDT _ ` Denebola M66 e b W 24 The Moon passes 0.05° south of Uranus, 6 P.M. EDT M64 NGP M65 26 The Moon passes 3° north of Venus, 4 A.M. EDT SEXTANS _ 27 The Moon passes 4° north of Mercury, 4 A.M. EDT VIRGO b ¡ ` 28 Neptune is stationary, 7 P.M. EDT a New Moon occurs at 10:52 P.M. EDT 29 The Moon is at apogee (252,637 miles from Earth), 2:08 A.M. EDT c WWW.ASTRONOMY.COM 35 CRATER i _ Spica M104 S b U RV a ¡ b O C a ` _ M83 SW HYDR Aj TA U R US E N f C i NGC 5128 + c NGC 5139

PATHS OF THE PLANETS LYN CAS DRA U AUR AND LAC HER Sun PER LYR Mercury CYG SER CC/2o0m17etK2 ORI The Moon passes 3° nortThRI CrB BOÖ OPH MofoVone-nVeunsuson June 26ARI SCT callout Venus Uranus PEG VUL SGE PSC TAU Mars Jupiter EQU SER AQL Neptune Juno LIB Celestial equator Path of the Moon ERI CET AQR LUP FOR LEP Vesta Saturn Pluto SCL CAP SGR PsA MIC COL CAE PHE CrA SCO GRU Moon phases Dawn Midnight 21 To locate the Moon in the sky, draw a line from the phase shown for the day straight up to the curved blue line. 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 1 THE PLANETS Uranus THE PLANETS IN THE SKY IN THEIR ORBITS Jupiter Neptune These illustrations show the size, phase, Arrows show the inner Saturn and orientation of each planet and the two planets’ monthly motions brightest dwarf planets at 0h UT for the dates and dots depict the in the data table at bottom. South is at the top outer planets’ positions to match the view through a telescope. at midmonth from high above their orbits. Venus Ceres Pluto Mercury Mars Ceres Venus Mars Jupiter PLANETS MERCURY VENUS Perihelion is June 21 Date June 15 June 15 Magnitude 0.6 –3.9 Earth Mercury Angular size 8.5\" 12.7\" Summer solstice Greatest western Illumination 33% 82% elongation is June 16 Distance (AU) from Earth 1.310 is June 21 Distance (AU) from Sun 0.794 0.727 Right ascension (2000.0) 0.423 Declination (2000.0) 3h57.7m 3h12.9m 16°42' 16°01' 36 ASTRONOMY • JUNE 202 2

This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows JUNE 2022 JULYand colored dots show motions and locations of solar system objects during the month. UMa 1 Jupiter 2 Europa CVn LYN Callisto 3 Callisto Ganymede AUR 4 Io Europa 5 LMi 6 Io 7 COM GEM 8 Ganymede 9 CNC Ceres 10 Sun JUPITER’S 11 MOONS 12 Path of the Sun (ecliptic) ORI 13 Dots display 14 VIR CMi positions of 15 CRV Galilean satellites 16 SEX MON at 4 A.M. EDT on 17 HYA the date shown. 18 CRT South is at the 19 top to match the 20 CMa view through a 21 telescope. 22 ANT LEP ERI 23 COL 24 PYX 25 CAE 26 CEN VEL PUP 27 Early evening 28 29 30 29 28 27 30 11 10 9 8 7 6 5 4 3 2 1 Jupiter S WE Saturn N 10\" Uranus Neptune Pluto MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO June 15 June 15 June 15 June 15 June 15 June 15 June 15 0.5 8.8 –2.3 0.5 5.9 7.8 15.1 6.8\" 0.4\" 38.9\" 17.8\" 3.5\" 2.3\" 0.1\" 86% 100% 99% 100% 100% 100% 1.382 3.537 5.073 100% 1.382 2.601 4.965 9.355 20.502 29.926 33.700 9.884 19.699 29.917 34.544 0h58.8m 6h56.6m 0h21.9m 21h50.2m 2h57.4m 23h43.8m 20h01.4m 4°19' 26°43' 1°02' –14°20' 16°29' –3°02' –22°37'

WHEN TO SKY THIS MONTH — Continued from page 33 VIEW THE Skimming the top east of Jupiter. The Moon stands PLANETS some 5° south-southwest of the MIDNIGHT Io S 30\" gas giant. The following morn- Saturn (east) Jupiter Ganymede ing, June 22, the Moon has Europa drifted east and is 5° from Mars. MORNING SKY W Mercury (east) Callisto Jupiter is up shortly before Venus (east) 1 A.M. local time by the end of Mars (east) June 5, 4:30 A.M. EDT June and stands some 40° high Jupiter (east) an hour before dawn. It’s the Saturn (south) planet with the most to offer Uranus (east) telescopic observers: four bright moons that move in front of and Neptune (southeast) Early on June 5, Callisto skims the northern limb of Jupiter, just barely dipping behind its disk, plus a wealth of behind the disk. atmospheric details that change quickly, carried by its less-than- located at the eastern end of Jupiter and Mars rise 10-hour rotation period. this year, Callisto began under- Capricornus and ends the together in the eastern sky Jupiter’s diameter grows from going occultations, but that month 1.6° due north of Deneb June 1, soon after 2:30 A.M. local 37\" to 41\" during June. Its path ends again this month. An Algedi, with the planet glowing time. The stunning pair stands carries it into the northwest intriguing event occurs early on at magnitude 0.5. Saturn only 1.8° apart. Jupiter is corner of Cetus the Whale for June 5, when Callisto is partially reaches a stationary point brighter at magnitude –2.2, the last six days of the month. hidden behind Jupiter’s north- June 5 and begins its retrograde while Mars shines a rusty Frequent observers of Jupiter ern limb. Observe between loop as it approaches opposition magnitude 0.6. They’re both are aware that in recent years, 4 A.M. and 5 A.M. EDT to watch in two months’ time. in Pisces as well. the tilt of Callisto’s orbit relative Callisto skim the planet. Saturn is best viewed in When the Last Quarter to our line of sight takes the Following last month’s con- the hour before dawn, when it Moon enters the vicinity on moon north and south of the junction, the distance between stands more than 30° high in June 21, Mars is more than 13.5° planet, avoiding the disk. Earlier Mars and Jupiter grows by more the south. Its disk spans 17\" in early June and grows barely COMET SEARCH I K2 is summer’s king perceptibly to 18\" by the end of the month. The stunning rings are tilted 12° to our line of sight, IT’S NICE to have a dependable Comet C/2017 K2 (PanSTARRS) Rasalhague the narrowest for the year. 7th-magnitude comet on stage during summer star parties. That’s N Neptune is in western bright enough to follow from the Pisces, shining at magnitude 7.8. suburbs with a 4- to 6-inch scope. June 1 f It rises after 2 A.M. local time With binoculars under a country 5 g in early June and soon after sky, you can compare the fuzz- midnight in late June. The easi- ball to a whole bunch of Messier NGC 6633 10 OPHIUCHUS est way to find its approximate globular star clusters. location is to first find Jupiter E IC 4665 and look to the gas giant’s west Comet C/2017 K2 (PanSTARRS) 15 Path of Comet PanSTARRS to find 4th-magnitude Phi (ϕ) was discovered May 21, 2017, at a Aquarii. Neptune is roughly then-record-breaking distance 20 ` m midway between the two early beyond Saturn. Astronomers a 25 in June. But Jupiter is drifting estimate the nucleus is 25 miles 30 eastward, so the gap between across, some four times wider than SERPENS M14 2° the two planets increases later in Halley’s Comet! But PanSTARRS is CAUDA the month. Neptune, too, is not destined to be great because d moving eastward against the the closest it gets to the Sun will background stars; it comes to a halt June 28 as it turns for its be outside Mars’ orbit. Comet PanSTARRS flies on a straight path through Ophiuchus this month, retrograde loop. This occurs near a 7th-magnitude field star PanSTARRS starts off in binoc- passing near the picturesque star cluster IC 4665. 0.25° away — the pair will appear as a close double ular heaven between Aquila and through binoculars. Ophiuchus during New Moon. The rich Milky Way, split by the Great Rift, is fabulous under a dark sky. Three nights after the Moon hits Full, jump back into action to watch the fan-shaped tail night by night. It swings through its edge-on perspective on the 19th, only to next tilt to the other side. Look for a short green spike peeking out on the south flank, while the sharp white dust tail extends northward. The comet’s proximity to the sprawling star cluster IC 4665 near Beta (β) Ophiuchi during this transition is a real bonus. 38 ASTRONOMY • JUNE 2022

LOCATING ASTEROIDS I Taking turns Disappearing star Zubenesch Spica THE BLAZING LUMINARY SPICA soars due south, its blue- VIRGO white starbeam leading the way to minor planet 10 Hygiea. From OPHIUCHUS the suburbs, you’ll need a 4-inch scope to pull the 10th-magnitude Zubenelgenubi space rock out of the veiled sky. LIBRA A single 1° field of view holds Hygiea all month as it completes b a tight retrograde arc. Draw a rendition using the nine field stars that are brighter; each night you return, add another dot to sketch Antares Menket out Hygiea’s movement. From the 20th to the 25th, it slides C E N TAU R U S between two background stars (8th and 9th magnitude). If you SCORPIUS LUPUS are imaging with a telephoto lens, note that you will also pick up 88 Thisbe only 2° west and 13 Egeria about 4° southeast. Both are 10° performing similar curves, but at magnitude 11. June 12, 1 hour after sunset Star-hoppers will need to carefully slide 8° southeast of Spica Looking south to reach our quarry. Avoid the 9th through the 11th, when the waxing gibbous Moon spreads its light across the area. This Midwestern view shows the Moon passing by Delta Scorpii, or Dschubba, June 12. Canada and the northeastern U.S. will see the star disappear. Named for the Greek goddess of health, the 10th “missing planet” between Mars and Jupiter was first noted by Annibale de Gasparis in 1849. Hygiea is a borderline dwarf planet, spanning a broad 270 miles and sporting a relatively round shape. Although 29 Amphitrite is brighter this month, it plows the dense fields near the core of the Milky Way, making it a tougher target. South and east of Spica N Spica than 0.5° each morning. By a 78-percent-lit disk spanning VIRGO June 3, Mars crosses into the 14\" on June 1 to 86 percent lit E northwest corner of Cetus, trek- and 12\" wide on June 30. Its king through the Whale’s magnitude stays a constant –3.9. 30 2520 domain until June 9. The Red Planet continues eastward Mercury joins Venus in June 1 15 Path of 1° toward Omicron (ο) Piscium, mid-June. The pair provide 10 Hygiea ending the month 1.5° from dramatic photo opportunities. 5 the 4th-magnitude star. Mercury stands 8° due south of the Pleiades (M45) on June 13, Tenth-magnitude Hygiea makes a tight turnaround this month in Virgo. Mars brightens from magni- glowing at magnitude 0.8. Also nearby, though not shown, are 11th-magnitude Thisbe and Egeria. tude 0.6 to 0.4 during June. It Venus is 11.5° farther west. remains challenging through a above the eastern horizon an on the morning of June 27, with telescope. Its disk spans 7\" and By the time Mercury reaches hour before sunrise. The Moon Mercury less than 4° to its lower is 86 percent lit. The small disk its greatest elongation west of and M45 have been up since right (southwest). Mercury con- will be strongly affected by local the Sun (23°) on June 16, it about 3 A.M. local time, followed tinues dipping back toward the atmospheric turbulence, so the forms an equilateral triangle by Venus around 3:40 A.M. By Sun and glows at magnitude best views will come in random with Venus and M45. The two 4:30 A.M., the Hyades and –0.7 on June 30. That morning, occasional moments of good planets continue their eastward Mercury are on view. Venus sits 1.2° north of Epsilon seeing. Telescopes larger than drift and on June 22, Mercury (ε) Tauri. 10 inches will do best. We are stands at one tip of the Hyades, On June 26, Venus and the only half a year away from the 3° northwest of Aldebaran. The Moon stand less than 3° apart, Martin Ratcliffe is a Red Planet’s opposition, so this planet has now brightened to with M45 6° above them. planetarium professional with will improve soon. magnitude 0.1. The faint stars of Directly below the Moon you’ll Evans & Sutherland and enjoys the Hyades will be hard to catch find Aldebaran, with Mercury observing from Wichita, Kansas. Venus starts June in Aries, in the growing twilight. Venus 5.5° to the star’s left (northeast). Alister Ling, who lives in rising before 4 A.M. local time stands 6° due south of the Mercury is 2° high a full hour Edmonton, Alberta, is a longtime all month. It crosses southern brighter Pleiades this morning. before sunrise. watcher of the skies. Aries before entering the brighter constellation Taurus On June 25 and 26, a waning Look for the waning Moon midway through June. Through crescent Moon joins in. The a telescope, Venus changes from Hyades, Pleiades, Venus, Mercury, and the Moon sit GET DAILY UPDATES ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek. WWW.ASTRONOMY.COM 39

Mapping Moonthe While most of us will never set foot on the Moon, maps can transport us there. BY RAYMOND SHUBINSKI W hen the Apollo 11 Lunar Module was running low on fuel and getting too close to the lunar surface to abort, alarms began to light up in Mission Control. The site for the July 20, 1969, landing had been carefully chosen, informed by years of careful observation and mapping of the Moon’s surface. Neil Armstrong was forced to take manual control to dodge boulders that could not have been detected by prior observations. But the familiarity with the terrain he had acquired from training — including simulations using maps of the landing site — paid off. When Armstrong radioed, “The Eagle has landed,” pandemonium broke out in Mission Control. Those years of planning and cartography had resulted in a fantastic achievement. Not since the early age of global exploration had maps been so impor- tant to the success and survival of adventurers. This was a culmination of work begun nearly 400 years earlier, when Thomas Harriot, Galileo Galilei, and others first turned their telescopes on the Moon, revealing a world of wonder and surprise. The first lunar maps The rising of a bright Full Moon has inspired poets, songwriters, and 40 ASTRONOMY • JUNE 2022

NASA’s Lunar Reconnaissance Orbiter has mapped both the nearside (left) and farside (below) of the Moon in exquisite detail. NASA/GSFC/ARIZONA STATE UNIVERSITY. BACKGROUND PAPER: FLAS100/DREAMSTIME

Thomas Harriot’s lunar maps from 1609, produced by telescopic observations, are the oldest known efforts of their kind. WIKIMEDIA COMMONS storytellers. What they imag- Galileo burst onto the topography. Harriot was representation of the Moon ined they saw on its surface scene in March 1610 with the interested in the spatial rela- that showed how its features had a great deal to do with publication of his Sidereus tionships of lunar features, in varied in height. cultural context. The most Nuncius, or Starry Messenger. part to understand the wob- obvious features visible with- He realized that the interplay ble, or libration, of the Moon. Just 37 years after Galileo out optical aid are the vast of light and shadow across the This phenomenon means that published his drawings of the dark areas known as maria, Moon indicated a rugged sur- over the course of one libra- Moon, Polish astronomer or seas, which are bordered face, which he captured in his tion cycle, roughly 18 percent Johannes Hevelius released by lighter areas. Europeans drawings. This upended the of the lunar farside can be his book Selenographia would refer to these features wisdom of Aristotle from seen creeping around the (Pictures of the Moon). Unlike as the man in the Moon, 2,000 years before, which held Moon’s limb. Thus, Harriot’s Galileo’s topographic artistry, the Cowichan First Nation the Moon was in the realm of maps are two-dimensional Selenographia was a first peoples in Canada’s Pacific perfection and that there and tried to capture the physi- attempt at organized lunar Northwest see a toad, and would be nothing to map! cal and spatial relationships of cartography. Hevelius made the image of a rabbit is pre- lunar features. Galileo’s his money by brewing beer, ferred in Asia — to name a It’s important here to sketches were topographic, but became fascinated with few examples. However, these understand the difference creating a three-dimensional astronomy. He built an obser- depictions of the Moon’s sur- between cartography and vatory and many of his own face are not the same as maps. In 1608, news spread quickly through Europe of a new instrument that made distant objects appear closer. The telescope was first sold for military and mercantile purposes, but people soon turned it skyward. In England, Thomas Harriot was one of the first to seriously observe the Moon with such an instrument. He produced the earliest datable map of the Moon on July 26, 1609, though he never published it. Within a few years, Harriot had drawn maps with more details, including the dark seas and prominent craters displayed in correct propor- tion to each other. Galileo took advantage of the light and shadows at the terminator to understand the three- dimensionality of the lunar landscape, and captured it in his sketches. WIKIMEDIA COMMONS 42 ASTRONOMY • JUNE 2022

telescopes, including a tube- 18th century, the president The man who UNIVERSITY OF ARIZONA/LUNAR AND PLANETARY LABORATORY less instrument 150 feet of the Royal Society, Joseph named (46 meters) long. Banks, said features of the Moon could “only be rendered Moonthe But why go to the trouble of adequately by an artist.” One mapping the Moon — a place of the most prominent por- For centuries, astronomers around the world no one would ever visit? The trait artists of the day, John pinned names to lunar features as they saw answer lies in trade and world Russell, took up the challenge. fit, resulting in variations, duplication, and power. As ships improved and Russell was obsessed with confusion. By the 1960s, lunar nomenclature trade increased, knowing your observing the Moon and was needed to be standardized. The English-born location at sea became of on close terms with astrono- Ewen Whitaker, then an amateur astronomer, paramount importance. The mers William Herschel, Nevil took it upon himself to begin updating the problem of finding where you Maskelyne, and others. official 1935 International Astronomical were on Earth was one of Union (IAU) Moon map for the Space Age. keeping accurate time. If you Russell was unimpressed by could determine your local the lunar maps produced by Whitaker’s expertise was recognized by time and compare it to the the Italian-French astronomer planetary scientist Gerard Kuiper, who time at a reference location, Giovanni Domenico Cassini at recruited him to work at Yerkes Observatory such as London or Paris, you the Paris Observatory, and in Wisconsin and, later, the University of could find your longitude thought he could do better. Arizona. Whitaker’s own renown as the based on the time difference. Russell spent every clear night world’s foremost selenographer grew as he But clocks in the 17th century observing the Moon with worked on the Orthographic Atlas of the were not reliable enough to high-quality telescopes. As a Moon (1960–61) and the Rectified Lunar Atlas keep an accurate reference portrait artist, he knew the (1963), which were critical to NASA’s selec- time over months at sea. importance of accuracy. He tion of landing sites for Moon missions, both was careful to represent lunar robotic and Apollo. In the mid-1960s, the IAU Galileo had suggested features in their correct pro- adopted the set of crater names and lettered using his newly discovered portions and relationships, naming system that he and his collaborator four moons of Jupiter and using triangulation and David Arthur proposed. —R.S. their regular, repeated motion micrometers. As a result, the as a kind of clock in the sky. maps he produced are nearly In 1969, when NASA wanted to demonstrate the Others thought the same photographic. His masterpiece ability to make an accurate, pinpoint landing on could be done with lunar was the Selenographia, a globe Apollo 12, Whitaker was able to identify where eclipses: By observing when of the Moon that could dem- Surveyor 3 had landed two years earlier. Thanks the edge of Earth’s shadow onstrate the effect of libration to his work, Apollo 12 touched down just 600 feet crossed a given feature on and the extent of the farside it (180 m) from the craft. NASA the Moon, you could use an reveals. almanac to compare that time to when this happened back at Actual lunar photographs your reference location, thus would arrive courtesy of John giving the difference in time William Draper, a chemist and the longitude. Hevelius at what is now New York hoped his lunar maps might University. From a university be a suitable reference for this rooftop in Greenwich Village, method. Unfortunately, the Draper captured the first observations were too diffi- detailed daguerreotype of cult to make from the deck of the Full Moon in 1840. The a ship. And in any case, since moment was a milestone in lunar eclipses are not that fre- how astronomers observe and quent, the method would have map the Moon’s surface. been of limited use. Early photographs also had The solution to the longi- detractors, including William tude problem had to wait for a Pickering, director of Harvard sea-going clock. Nonetheless, College Observatory. “[T]he Hevelius’ maps continued to best lunar photograph ever set the standard of lunar car- taken will not show what can tography for a century. be seen with a six-inch telescope under favorable Picture perfect atmospheric conditions,” he said, as reported by In the second half of the

Moon ,While two astronauts descended to the one remained in orbit, taking images and collecting data. The simulated lunar landscapes that James Nasmyth and James Carpenter turbulence blurred the result- mountain ranges, which produced for their book The Moon Considered as a Planet, a World, and a ing image. “The eye can seize seemed to have been taken by Satellite were products of careful visual observations, meticulous plaster model the instant of exquisite defini- spectators on the surface of work, and inventive photography. INTERNET ARCHIVE tion; the camera must take the Moon! The photographs what comes,” Clark wrote. were ingenious special astronomer George Clark in and more delicate features … effects: To create them, the a 1901 paper in The British — the photograph does not In an effort that illustrated pair combined observations Journal of Photography. When hint at their existence.” the value of both visual acuity made by eye and using pho- photographing the Moon, and photographic accuracy, in tography, plus some informed continued Clark, “what is Part of the issue was that 1874, engineer James Nasmyth speculation, to create highly really most interesting upon the long exposures that pho- and astronomer James detailed plaster models. the moon — the finer detail tographs of the era required Carpenter of Greenwich Then, they set the models meant that any atmospheric Observatory published The against a black background Moon Considered as a Planet, and photographed them with a World, and a Satellite. The strong, raking light to simu- book drew on 30 years of late the sunlit lunar surface. Nasmyth’s personal observa- tions and addressed topics The imagined craggy ranging from the Moon’s rug- lunar landscape so impressed ged topography — which the astronomers and readers authors claimed was due to alike that both men have cra- volcanism — to the possibility ters named for them. Their of a lunar atmosphere. vision of the Moon had tre- mendous staying power, But what astounded read- influencing artists such as ers most were the incredibly Lucien Rudaux, Chesley detailed photographs of lunar Bonestell, and even Walt features like craters and Disney. But this imagery would change dramatically by the middle of the 20th century, when robotic probes began an intensive study of the lunar surface. Nasmyth and Carpenter’s Visiting the Moon landscapes achieved a vividness of detail — both real and imagined — In the early hours of a cool that would not be equaled by October morning in 1957, actual photographs until Americans learned that Earth spacecraft visited the Moon. At left had an additional satellite: is their simulation of the Apennine Russia had successfully placed Mountains; above is the same view Sputnik I in orbit. This event from the Lunar Reconnaissance launched the most expensive Orbiter. INTERNET ARCHIVE; NASA technology race in history, with the goal of putting humans on the Moon. There were many parts to this complex puzzle, includ- ing the need for highly detailed maps of potential landing sites. To obtain them, 44 ASTRONOMY • JUNE 2022

Russia began by launching 1961 to study the lunar sur- Luna 3 captured the first pictures of Charted territory Luna 1 in 1959, with the face — with mixed success. the lunar farside. Like other probes of intent to impact the lunar Five Lunar Orbiter missions its era, it was equipped with cameras, Our understanding of the surface. It missed the Moon followed between 1966 and automated film-developing Moon has come a long way. In and was followed by Luna 2, 1967. These were incredibly equipment, and a photomultiplier tube the 19th century, curious visi- which transmitted pictures successful. Their principal that scanned the processed film tors in Bonn, Germany, could until it slammed into the mission was to map areas of negative and transmitted the result as visit an exhibition by Thomas Moon’s surface. Luna 3 flew the Moon for potential Apollo a television signal, line by line, back to Dickert: a 19-foot-wide (6 m) around the farside of the landing sites, but after that Earth. ROSCOMOS plaster model of the Moon. It Moon and sent back pictures was accomplished by the first was a matte yellow with exag- of terrain never before seen by three missions, the remaining pockmarked with impact cra- gerated three-dimensional human eyes. The blurry two mapped essentially the ters, and lacking the familiar relief, based on lunar maps images showed a few large entire surface. dark seas of the nearside. The by astronomers Wilhelm dark areas and heavily cra- Apollo missions also added Beer and Johann Madler and tered landscape. The mission’s high- more information about the Russell’s drawings. If one resolution camera systems hidden side of the Moon. walked around the back side, The U.S. responded with revealed the Moon’s farside to While two astronauts it would have been blank. the Ranger program — a be very different than the side descended to the Moon, one series of missions starting in we always see — rugged, remained in orbit, taking This remained the case images and collecting data. with Moon globes well into the 1960s. Not so today. We While crewed lunar mis- have made incredible strides sions ended nearly 50 years in understanding our neigh- ago, the work of mapping the bor. We have filled in its far- Moon continues. In 2009, the side and gleaned cartographic Lunar Reconnaissance information undreamed of Orbiter reached the Moon just a few decades ago. From and is still imaging the sur- simple maps drawn while face and collecting data. gazing though low-power tele- Efforts have now gone beyond scopes to images from orbit- cartography and topography ing spacecraft peering deep to include mapping out lunar into the Moon’s cratered sur- resources such as minerals face, we now know our celes- and even water, in anticipa- tial partner in breathtaking tion of a long-term human detail. presence on the Moon. Raymond Shubinski is a longtime contributing editor to Astronomy. He has been moonstruck ever since his first view of the lunar surface through an old 6-inch refractor. To understand what the Moon would look like from orbit, Whitaker, William To acclimate Apollo astronauts to the visuals they would experience at the Hartmann (pictured), and others produced a lunar atlas of “rectified” images. Moon, NASA’s Langley Research Center in Virginia created the Lunar Orbit and Since no craft had yet orbited the Moon, photographs of the Moon from Earth Landing Approach simulator. In it, TV cameras “flown” by the pilot tracked along were projected onto a globe, which was then photographed from different painted giant murals of the surface of the Moon, projecting a simulated view to angles. This technique eliminated the effects of foreshortening, and craters that the pilot’s cockpit. NASA appeared distorted and elliptical near the Moon’s limb were rendered circular on the resulting maps. UNIVERSITY OF ARIZONA/LUNAR AND PLANETARY LABORATORY WWW.ASTRONOMY.COM 45



If you’re new to observing, you don’t check that it will safely fit into your need to buy the best telescope — car before purchasing. just the one you’ll use the most. Where will you store it? This is BY PHIL HARRINGTON an issue that many amateurs don’t consider. Ideally, your telescope MAYBE YOU HAVE HAD a casual interest in astronomy should be easily accessible and stored for years, looking up at the night sky every chance you get. in an unheated but clean location. Or maybe you’ve just recently become interested in the Keeping it at the ambient outdoor wonders hanging high above our heads. Either way, you’ve temperature will speed the optics’ decided to take the next step and get your first telescope. acclimation to the night air. By con- Thumbing through Astronomy’s pages, you see many that trast, bringing a scope into the cool are intriguing. But at the same time, you’re baffled. What night air from a heated home will kind should you get? How much do you really have to cause images to blur due to heat spend? Which is best for you? currents in the tube before the com- ponents stabilize. FRAMESTOCK FOOTAGES/DREAMSTIME These are all important questions can purchase a well-appointed that you need to answer before instrument for $1,000 to $1,500. But Storage will also play a major role purchasing a telescope, whether avoid the urge to go straight to a in the size of the telescope you it’s your first scope or 10th. This high-tech telescope immediately. choose. For instance, if you must overview will help shed some light. While they are tempting, many carry it down a flight of stairs, it newbies find them daunting to set should be compact and light enough Some hard questions up and use. not to create a fall hazard. Before you decide which type of tele- Where will you use it? This might Types of telescopes scope to get, you need to take a hard not be the first thing you think of, look at your situation. Ask yourself but it’s critical in deciding what kind Today’s astronomers use one of three the following questions and be hon- of telescope to get. Will you be using basic telescope designs: the refrac- est with your answers. your telescope from home, where you tor, the reflector, and a hybrid design set it up in your yard for a night called the catadioptric. What is your budget? While you under the stars? Or do you need to may feel some sticker shock when drive a good distance to view the sky Refractors are recognizable by you look at telescope prices, the good properly? their long, slender tubes. A large news is that you do not need to spend objective lens sits in the front, while a small fortune purchasing your first If your location of choice is hours the observer looks through an eye- telescope. You can get a very nice away, then look for telescopes that are piece at the back. Changing the eye- instrument for under $300. quick and easy to set up. And, for piece will change the telescope’s those driving to a location, double magnification. If your budget is a bit higher, you Reflectors, on the other hand, don’t have a lens up front. Instead, they use a large, concave primary mirror located near the bottom of the tube to gather light from a target and bring it into focus. The most popular type of reflector WWW.ASTRONOMY.COM 47

among amateurs is the apertures run between 3 and 16 REFRACTORS Newtonian. Light reflects from inches (7.6 and 41 cm). the primary to a small, flat sec- CELESTRON ondary mirror tilted at 45°. The Mounting concerns light then bounces off the sec- $349.95 ondary and out through a hole in Just as important as the the side of the front of the tube kind of telescope is the Celestron AstroMaster 102AZ and into an eyepiece. type of mount used to support it. A good This 4-inch (10.2 cm) refractor pairs a well-designed tele- Finally, catadioptric tele- mount must be strong scope on a simple altitude-azimuth mount. It comes with scopes combine both lenses and enough to carry the two eyepieces, a finder scope, and an erect image diagonal mirrors. Light first passes telescope’s weight while for both astronomical and terrestrial viewing. through a large front lens, called minimizing vibrations. the corrector plate, and on SPECIFICATIONS Focal ratio: f/6.5 toward the primary mirror at the Altitude-azimuth mounts Eyepieces: 20mm (33x) back of the tube. The corrector move both in azimuth, or left to Price: $349.95 and 10mm (66x) plate reduces or eliminates aber- right, and in altitude, up and Mount: altitude-azimuth Weight: 12.2 pounds ration caused by the mirrors. down. Many are simply aimed Aperture: 4 inches (10.2 cm) (5.53 kg) After bouncing off the primary, by hand, while more elaborate Focal length: 660mm the light reflects toward a sec- models feature computerized ondary mirror at the front, then aiming and tracking systems. Explore Scientific FirstLight AR127 back through a small hole in the middle of the primary and into A popular variation of the Equipped with the Twilight I Mount, the AR127 features a 5-inch an eyepiece. altitude-azimuth mount turns a (12.7 cm) objective. Accessories include a 25mm eyepiece, a star Newtonian telescope into what diagonal, a red-dot finder, and a smartphone camera adapter. So, which telescope is right is called a Dobsonian telescope. for you? That depends on your Dobsonians are simply SPECIFICATIONS Focal length: 826mm answer to the earlier questions as Newtonian reflectors situated Focal ratio: f/6.5 well as where your interests lie. on a mount that moves up and Price: $749.99 Eyepieces: not included down in elevation and pivots in Mount: altitude-azimuth Weight: 15.6 pounds (7.1 kg) If you crave sharp, highly azimuth, like a lazy Susan. Most or equatorial detailed views of bright sky are aimed by hand, although Aperture: 5 inches (12.7 cm) objects, such as the Moon, plan- some are tricked out with com- ets, double stars, and sparkling puterized drive systems. star clusters, then a refractor is ideal. They come in apertures Alternatively, many tele- ranging from 2 to 6 inches (5 to scopes come on equatorial 15 centimeters). Smaller models mounts. These mounts compen- are perfect for anyone who pre- sate for Earth’s rotation by fers extreme portability — think keeping on the rotational axis scopes you might bring on a parallel to Earth’s axis of rota- family camping adventure — or tion. Because of this, the mount is looking for a quick grab-and- can stay fixed on a celestial go instrument to run outside object just by moving one axis with on a given clear night. at a constant speed. The two most popular designs among If, however, you prefer hunt- amateur astronomers are the ing for faint fuzzies such as neb- German equatorial mount and ulae and galaxies, then a the fork mount. Both are widely reflector is a better choice. Dollar available with computerized for dollar, reflectors offer the aiming and tracking systems. largest aperture for the invest- Many amateurs prefer equato- ment. These instruments range rial mounts, but bear in mind from 3 to 25 inches (7.6 to 64 that some mounts — especially cm) in size and, if you want to the German equatorial style — spend the money, you can even can be much heavier than get a larger custom-made scope. alt-azimuth mounts. Finally, if you want a reason- Some possibilities ably large aperture but at the same time need portability to Here are a few suggested models travel to dark skies, then a cata- that would make a great first dioptric is a great choice. Their telescope. 48 ASTRONOMY • JUNE 2022

EXPLORE SCIENTIFIC $2,195 CHRIS COOK Stellarvue SVX102D Featuring an advanced 4-inch (102mm) objective lens, the SVX102D delivers incredibly sharp images. Be aware that you will need to purchase a mount and other accessories separately. SPECIFICATIONS Focal length: 714mm TELE VUE Focal ratio: f/7 Price: $2,195.00 Eyepieces: not included Mount: altitude-azimuth Weight: 9 pounds (4.1 kg) or equatorial Aperture: 4 inches (10.2 cm) $749.99 $2,167 Tele Vue-85 For those looking for a grab-and-go telescope, the 3.35-inch (8.5 cm) TV85 is a great choice. Couple it to a sturdy mount (sold separately) and you have a wonderful scope for both astronomical and terrestrial viewing. SPECIFICATIONS Focal length: 600mm Focal ratio: f/7 Price: $2,167.00 Eyepieces: not included Mount: altitude-azimuth Weight: 6.1 pounds (2.8 kg) or equatorial Aperture: 3.35 inches (8.5 cm) EXPLORE SCIENTIFIC WWW.ASTRONOMY.COM 49

REFLECTORS CATADIOPTRICS $479.95 CELESTRON EXPLORE SCIENTIFIC Celestron StarSense Explorer $399.99 DX 130AZ This 5.1-inch (13 cm) Newtonian comes on an innovative altitude-azimuth mount. After installing the free StarSense app on your smartphone and mounting the phone in the included cradle, you use the app to help while manually aiming the tele- scope. It also includes two eyepieces and a red-dot finder. SPECIFICATIONS Focal ratio: f/5 Eyepieces: 25mm (26x) and Price: $479.95 10mm (65x) Mount: altitude-azimuth Weight: 18 pounds (8.2 kg) Aperture: 5.1 inches (13 cm) Focal length: 650mm Orion SkyView $849.99 Sky-Watcher Classic 200P Pro 8 This basic Dobsonian delivers a lot at an affordable This 8-inch (20.3 cm) price. The 8-inch (20 cm) primary mirror gathers reflector mates a enough starlight to reveal faint galaxies, well-appointed clusters, and nebulae. The mount may Newtonian to a be no-frills, but it is built to last for substantial German years. Two eyepieces, dust equatorial mount and caps, and a finder scope are tripod. Standard also included. accessories include ORION two eyepieces and an SKY-WATCHER 8x40 finder scope. SPECIFICATIONS $655 SPECIFICATIONS Price: $655.00 Mount: Dobsonian Price: $849.99 Aperture: 8 inches Mount: equatorial mount (20 cm) Aperture: 8 inches (20.3 cm) Focal length: Focal length: 1000mm 1200mm Focal ratio: f/4.9 Focal ratio: f/5.9 Eyepieces: 25mm (40x) and Eyepieces: 25mm 10mm (100x) (48x) and 10mm (120x) Weight: 56.5 pounds (25.6 kg) Weight: 45 pounds (20.4 kg) 50 ASTRONOMY