Astronomy

MISSION UPDATE: CURIOSITY ROVER EXPLORES MARS p.24 SEPTEMBER 2022 The world’s best-selling astronomy magazine The SECRET LIVES of CELEBRITY STARS p. 16 See Saturn www.Astronomy.com at its best p.46 $6.99 PLUS: 09 Vol. 50 • Issue 9 The ABCs of observing p.52 The wild history of impacts on Earth p.56 0 74470 01096 8 Wide-angle sky wonders p.40

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SEPTEMBER 2022 VOL. 50, NO. 9 CONTENTS 24 ON THE COVER FEATURES 40 56 Massive, furiously burning stars like Eta Carinae are unpredictable, 16 COVER STORY Mine the sky’s Earth’s greatest hits and can reveal incredible secrets wide-angle wonders about the cosmos. X-RAY: NASA/CXC; The secret lives of We live in a cosmic shooting celebrity stars With the right equipment gallery, with our planet ULTRAVIOLET/OPTICAL: NASA/STSCI; COMBINED and planning, you can enjoy the inevitable target of IMAGE: NASA/ESA/N. SMITH (UNIVERSITY OF These high-wattage luminaries beautiful vistas all year round. incoming space rocks. ARIZONA), J. MORSE (BOLDLYGO INSTITUTE) AND can’t hide from astronomers. A. PAGAN KEVIN RITSCHEL RAYMOND SHUBINSKI RANDALL HYMAN COLUMNS 46 62 24 Strange Universe 12 Saturn’s rings Ask Astro Curiosity’s 10 years at their finest BOB BERMAN on Mars The full spectrum. The complex ring system Binocular Universe 14 This complex, car-sized rover is open wide during this Astronomy (ISSN 0091-6358, USPS 531-350) remains one of our best year’s opposition, making it is published monthly by Kalmbach Media PHIL HARRINGTON tools on the martian surface. a prime time to explore the Co., 21027 Crossroads Circle, P. O. Box 1612, beautifully adorned gas giant. Waukesha, WI 53187–1612. Periodicals postage Observing Basics 15 BEN EVANS paid at Waukesha, WI, and additional offices. STEPHEN JAMES O’MEARA POSTMASTER: Send address changes to GLENN CHAPLE 32 Astronomy, PO Box 8520, Big Sandy, TX 75755. 52 Canada Publication Mail Agreement #40010760. Secret Sky 60 Sky This Month The ABCs of stargazing STEPHEN JAMES O’MEARA Enjoy Jupiter at opposition. Take a seat at your scope 7 MARTIN RATCLIFFE AND and brush up on your ALISTER LING observing vocabulary. QUANTUM GRAVITY 34 MICHAEL E. BAKICH Everything you need to know about the universe Star Dome and this month: See the black Paths of the Planets hole at Milky Way’s center, watch Webb RICHARD TALCOTT; increase its focus, review ILLUSTRATIONS BY ROEN KELLY the results of the decadal survey, and more! ONLINE Sky This News My Science Ask Astro FAVORITES Week The latest Shop Archives IN EVERY ISSUE updates from Answers to all Go to www.Astronomy.com A daily digest the science Perfect gifts for your cosmic From the Editor 4 for info on the biggest news and of celestial and the hobby. your favorite questions. Astro Letters 6 observing events, stunning photos, events. science geeks. New Products 61 informative videos, and more. Advertiser Index 61 Reader Gallery 64 Breakthrough 66 W W W.ASTRONOMY.COM 3

FROM THE EDITOR Stars of the cosmos Editor David J. Eicher Assistant Design Director Kelly Katlaps The massive star Eta Our galaxy is filled Carinae is surrounded with tiny, dim stars. EDITORIAL by the Homunculus Astronomers believe Senior Editor Mark Zastrow Nebula, an enormous that about three-quarters of Production Editor Elisa R. Neckar gas cloud seen here the stars in the Milky Way are Senior Associate Editor Alison Klesman as the bright, double- M dwarfs — small, reddish Associate Editor Jake Parks lobed patch at left. embers that glow with a Associate Editor Caitlyn Buongiorno restrained light that will last Editorial Assistant Samantha Hill HUBBLE IMAGE: NASA, ESA, for hundreds of billions of years. Our Sun, the star we’re ART N. SMITH (UNIVERSITY OF used to, is a G-type yellowish- Illustrator Roen Kelly white orb; stars of its mass and Production Specialist Jodi Jeranek CALIFORNIA, BERKELEY), AND THE type represent perhaps 8 percent of the Milky Way’s suns. As we work toward more massive and energetic stars, however, the story CONTRIBUTING EDITORS HUBBLE HERITAGE TEAM (STSCI/ of the cosmos gets more compelling. The high-mass, “live fast and Michael E. Bakich, Bob Berman, Adam Block, die young” superstars of the cosmos represent a small number, but Glenn F. Chaple Jr., Martin George, Tony Hallas, AURA); CTIO IMAGE: N. SMITH their story tells us a great deal about the universe at large. Phil Harrington, Korey Haynes, Jeff Hester, Alister Ling, Science writer Randall Hyman describes some notable examples Stephen James O’Meara, Martin Ratcliffe, Raymond Shubinski, (UNIVERSITY OF CALIFORNIA, of these celestial behemoths in “The Secret Lives of Celebrity Stars” Richard Talcott on page 16. Among the glitterati covered in this story is one of BERKELEY) AND NOAO/AURA/NSF the most curious stars known, Eta Carinae. This peculiar object EDITORIAL ADVISORY BOARD has baffled astronomers for two centuries. The star, lodged in Buzz Aldrin, Marcia Bartusiak, Jim Bell, Timothy Ferris, the southern sky and associated with the famous Carina Nebula, Alex Filippenko, Adam Frank, John S. Gallagher lll, erupted onto the scene almost magically, nearly 200 years ago, Daniel W. E. Green, William K. Hartmann, Paul Hodge, mimicking a supernova, and became the second brightest star Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern, in the sky. It then faded in the mid-19th century, reappearing in James Trefil robust brightness just a generation ago. Astronomers believe the star is on track to become, over the coming decades, a “planetary Kalmbach Media nebula on steroids.” Some stars set new heights for weirdness. Magnetars are paired Chief Executive Officer Dan Hickey with supernova remnants and consist of neutron stars with mag- Chief Financial Officer Christine Metcalf netic fields 1,000 times more powerful than Earth’s. So-called S Senior Vice President, Consumer Marketing Nicole McGuire stars that orbit the center of our Milky Way are tugged in blistering Vice President, Content Stephen C. George orbits around the black hole in the galactic center. They can orbit Vice President, Operations Brian J. Schmidt the black hole in as little as 11 years. Vice President, Human Resources Sarah A. Horner Stellar oddities make for fantastic reading. Thankfully we can Circulation Director Liz Runyon do this reading from an ordinary armchair in a safe, sleepy corner Director of Digital Strategy Angela Cotey of the Milky Way. Director of Design & Production Michael Soliday Retention Manager Kathy Steele Yours truly, Single Copy Specialist Kim Redmond Follow the David J. Eicher ADVERTISING DEPARTMENT Dave’s Universe blog: Editor Advertising Representative Kristi Rummel www.Astronomy. 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ASTRO LETTERS Jupiter’s moon Europa Hidden life Planck mass may host simple life I’m a bit perplexed In “Imagining our infant universe” (April 2022), if the in its ocean. NASA/ by Cynthia Phillips’s Planck mass is measured in grams (10-5 g), it seems way response in the April out of scale with the other two constants in the Planck JPL-CALTECH 2022 Ask Astro. If the scale (length and time, 10-33 cm and 10-44 s, respectively). purpose of the Europa Smaller amounts are used regularly, for example micro- We welcome Clipper mission is to grams (10-6) as a vaccine dose and picograms (10-12 ) of your comments “assess the habitability a substance got a horse disqualified from the Kentucky at Astronomy Letters, of ... Europa,” yet the Derby. Why is it measured that way? — Fred Brunyate, P.O. Box 1612, moon spends all of its Waukesha, WI 53187; time inside Jupiter’s dangerous and powerful radiation Haslett, MI or email to letters@ belt, doesn’t that fact alone sort of answer the question? astronomy.com. Author Sten Odenwald responds: Using only the three natu- Please include your — Tom Sales, Somerset, NJ ral constants — the speed of light (c = 3x108 m/s), Newton’s name, city, state, and gravitational constant (G = 6.67x10-11 m3/kg s2), and country. Letters may Associate Editor Caitlyn Buongiorno responds: Great Planck’s constant (h = 6.6x10-34 m2 kg/s) — you can create be edited for space question, Tom! Europa is indeed blasted with radiation three “ fundamental scales”: length = (hG/c3)1/2, time = (hG/ and clarity. from Jupiter, so life probably doesn’t exist on the surface, c5)1/2, and mass = (hG/c)1/2. But these scales are experimen- but scientists think that simple life could exist in the tally inaccessible. Although the Planck mass looks reachable ocean beneath the surface. For any life there, the radia- (i.e., larger than other quantities, as you note), it actually tion would actually be one avenue for providing fuel represents an energy of 1019 gigaelectronvolts crammed into as it would split apart H2O molecules. The free oxygen a Planck-scale volume, which cannot be reproduced by could then provide chemical energy for microbial life. humans (yet). By comparison, the Large Hadron Collider Alternatively, as on Earth, hydrothermal vents could spew at CERN achieves only 104 GeV in a volume of space about out chemical nutrients necessary for simple life to survive. 1010 times larger than the Planck scale. EXCLUSIVELY FROM ALL-NEW 6-INCH ASTRONOMY MAGAZINE JUPITER GLOBE P40464 Marvel at the ever-changing surface of Jupiter with this 6 ASTRONOMY • SEPTEMBER 2022 gorgeous globe only available at MyScienceShop.com. • Beautifully detailed images from the Juno and Cassini missions. • 18 belts, bands, and major features identified and labeled. • Custom-produced, high quality injection-molded globe with single seam and clear acrylic base • Includes detailed fun facts booklet about the images and the globe’s production. Order your exclusive, limited-edition globe at MyScienceShop.com/JupiterGlobe Sales tax where applicable.

QG QUANTUM GRAVITYEVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH NASA, ESA, AND J. CHARLTON (PENNSYLVANIA STATE UNIVERSITY); IMAGE PROCESSING: G. KOBER (NASA GODDARD/CATHOLIC UNIVERSITY OF AMERICA). BOTTOM FROM LEFT: NASA/JPL-CALTECH/ASU/MSSS/SSI; ALMA (ESO/NAOJ/NRAO)/S. DAGNELLO (NRAO/AUI/NSF); NASA/C.THOMAS SNAPSHOT A GLIMMERING QUARTET OF GALAXIES Hubble HOT GROUNDED ALL THE INGREDIENTS MARTIAN ECLIPSE captures a BYTES Perseverance recently cascade of NASA and the German Scientists thought that spotted Mars’ moon star formation. Space Agency will cease following a collision, Phobos eclipsing the operating the airborne galaxies expelled their Sun. Watching such Hickson Compact Group 31, infrared telescope SOFIA gas and dust after events helps scientists composed of four interact- at the end of September. undergoing intense star predict how the moon ing dwarf galaxies located The last year’s formation. But recent will spiral into the Red 166 million light-years from astronomy decadal evidence shows they Planet within tens of Earth, shines with a brilliant survey concluded the might hold onto and millions of years. mix of powder-blue and observatory’s scientific condense it, raising the pearlescent streaks in this output did not justify question: Why aren’t WWW.ASTRONOMY.COM 7 photo made with NASA’s its cost. they still forming stars? Hubble Space Telescope. Originally captured in 2010 but recently reprocessed, the image shows a trio of galax- ies uniting at upper right. Two of the objects, which comprise NGC 1741, are tightly intertwined, while a cylindrical galaxy lies off to the side. A cerulean trail of young stars, shining brightly in visible light, leads the eye to the outlying galaxy of the group sitting at the lower left, while speckles of near-infrared objects litter the rest of the image. The vibrant blue colors within these galaxies are the result of massive quantities of hydrogen gas creating groups of new stars in clusters. The brightest of the young clusters are less than 10 million years old, and their emergence indicates these galaxies are in the final stages of assembly. — SAMANTHA HILL

QUANTUM GRAVITY BLACK HOLE AT MILKY WAY’S CENTER IMAGED FOR FIRST TIME The groundbreaking picture shows the gaping maw of our galaxy’s heart. In a triumph of observation and MEET SAGITTARIUS A*. The first direct image by the National Science Foundation data processing, the astronomers (NSF) at the National Press Club in of the Event Horizon Telescope (EHT) of the Milky Way’s supermassive black hole Washington, D.C. “But we prevailed.” Collaboration have captured the first- shows an glowing orange ring — gas heated ever picture of the supermassive black as it falls toward the singularity — with the A GLOBE-SPANNING TELESCOPE hole at the center of the Milky Way shadow of the black hole at the center. Galaxy. Black holes are accumulations of matter The black hole is named Sagittarius A* EHT COLLABORATION that are so dense, not even light can (Sgr A* for short, pronounced “sadge escape the grasp of their gravity. The A-star”). The reveal of its image received issue of The Astrophysical Journal “hole” itself — a singularity in space- an international rollout May 12 in Letters. time — remains invisible. But research- simultaneous press conferences on four ers have been able to study them in continents. The team also published The image represents 3.5 million part by observing their gravitational their results the same day in a special gigabytes of data taken at millimeter influence on stars around them. Since wavelengths by eight radio telescopes the 1990s, astronomers have observed around the world. “It took several stars at the center of our galaxy, roughly years to refine our image and confirm 27,000 light-years away, whipping what we had,” said Feryal Özel, an around an object that appears to have astronomer at the University of Arizona the gravitational pull of 4 million Suns. in Tucson, at a press conference held But obtaining a direct image of a black hole itself is a lot harder. Simulations show that the disk of gas around the singularity heats up and begins to glow before it falls into the black hole, crossing the event horizon, or point of no return. The black hole bends light rays around it and captures light that strays too close, casting a shadow against the disk. Until recently, however, such a shadow had never been seen. Then, in 2019, the EHT released the first-ever image of a black hole: M87* at the heart of the galaxy M87, about 53 million light-years from Earth. Using a technique called very-long-baseline interferometry, the EHT’s radio telescopes, scattered across the globe, worked together to achieve the effective resolution of a telescope the size of our planet. The resulting image is not exactly a traditional photograph, where light or radio waves are focused to form an image. Rather, scientists constructed the image through computational 8 ASTRONOMY • SEPTEMBER 2022

techniques to generate synthetic team to develop new processing QUICK images that fit the data collected techniques. TAKES by the telescopes. It was “a bit like trying to COSMIC MEGAMASER TALE OF TWO BLACK HOLES take a clear picture of a puppy quickly chasing its tail,” said The MeerKAT telescope in South Africa The data that went into making the Chi-kwan Chan, an astronomer spotted the most distant megamaser — M87* and Sgr A* images were taken at the University of Arizona, in a powerful source of radio-wave emission back in April 2017 during the EHT’s a statement. similar to an optical laser — ever observed, inaugural observing campaign. located some 5 billion light-years away. Such Despite its distance, M87’s central The results aren’t just a pretty concentrated beams are usually the result black hole appears roughly the same picture. The extent of the black size on the sky as that of our own gal- hole’s shadow also provides an of two galaxies violently colliding. axy’s. That’s because although M87* independent check of the mass is about 2,000 times more distant, it of Sgr A*. And at 4 million solar SAFE SKIES is also about 1,500 times larger. masses, it is “perfectly aligned” with the previous measurements based On April 18, the Biden administration In fact, M87* was easier to image: on the orbital motions of stars, said announced a moratorium on U.S. anti- Because it is so large, its overall Michael Johnson, an astrophysicist satellite tests. The move is meant to establish visual appearance is more stable. at the Harvard and Smithsonian an international norm against the practice As Sgr A* is smaller, the gas racing Center for Astrophysics, at the and rebuke Russia for its Nov. 15, 2021 test, around it causes the overall ring to NSF press conference. “This is an which produced over 1,500 pieces of wobble and glimmer more quickly extraordinary validation of general than M87*. This forced the EHT relativity.” — MARK ZASTROW trackable space debris. NASA/STSCI KEEP IT UP JWST comes into focus NASA has extended the missions of eight planetary science missions, including three The James Webb Space Telescope (JWST) took another step toward full operations with the April 28 announcement that the observatory is now martian orbiters; the Curiosity rover; the aligned and focused — and the images above prove it. They come from each Lunar Reconnaissance Orbiter; New of JWST’s instruments: NIRSpec, a near-infrared spectrometer; NIRCam, an imaging camera; NIRISS, a dual spectrometer and imaging camera; MIRI, a Horizons; and OSIRIS-REx, which will visit camera that observes at longer wavelengths; and the Fine Guidance Sensor, the near-Earth object Aphophis. The which helps the telescope precisely point at targets. The alignment process involved carefully adjusting each of the telescope’s 18 hexagonal mirror extensions range from two to nine years. segments, which make up a collecting area with a diameter of 6.5 meters. The JWST team says that the resolution of the fully aligned ensemble is even SLOW RIDE better than their predictions. — M.Z. Giant carbon-dioxide glaciers have been migrating across the south polar region of Mars for more than 600,000 years. If entirely turned into gas, the massive ice flows would double the atmospheric pressure of the Red Planet. SUPERNOVA SURVIVOR The Hubble Space Telescope observed a companion star that endured its partner going supernova. Due to a lack of hydrogen seen in the remnant, the find finally offers visual evidence for the theory that so-called stripped supernovae form in binary systems. MOON PLANTS In a first, scientists have sprouted seeds in real lunar soil, using samples from the Apollo missions. However, the resulting plants showed signs of stress and were smaller than those grown in control soil. NIGHT LIGHT Scientists have successfully tested a device that can convert infrared light (thermal radiation) into electricity. The researchers hope the technology may one day allow humans to harness solar energy absorbed by Earth and re-emitted as heat, even at night. — JAKE PARKS, M.Z. WWW.ASTRONOMY.COM 9

QUANTUM GRAVITY ESA/HUBBLE & NASA, W. KEEL ACKNOWLEDGEMENT: J. SCHMIDT EXPLOSIVE CONSEQUENCES. A white dwarf in a binary system siphons material from a companion in this HUBBLE’S artist’s concept. The stolen material is funneled to the poles, triggering a micronova. ESO/M. KORNMESSER, L. CALÇADA ANGEL Astronomers find a WING new type of stellar blast These intertwined, merg- When a white dwarf orbits however: Micronovae are several weeks, micronovae ing galaxies, cataloged as a full-sized companion star, still extremely powerful. shine for just a few hours. VV689, are nicknamed sometimes it will siphon Even at just one-millionth It took the watchful eye of the Angel Wing. The pair gas from its larger neigh- the strength of a classical NASA’s Transiting Exoplanet features long, swooping bor. The accreted hydrogen nova, micronovae release Survey Telescope (TESS), swirls of dust, gas, and and helium build up on the about 40 million trillion which images a patch of sky stars that have been tugged surface of the white dwarf pounds (20 million trillion every 30 minutes, for the to and fro by strong until it reaches a critical kilograms) of material. A team to be able to spot them gravitational forces as the temperature and pres- paper detailing the obser- in the first place. Looking galaxies crash together. sure. Then, thermonuclear vation was published in further, the team found more Researchers targeted the fusion ignites, combining Nature on April 20, the same signals, observing them on system with the Hubble the hydrogen into heavier day as a follow-up paper in three white dwarfs in total. Space Telescope after the elements and releasing a Monthly Notices of the Royal Angel Wing was discov- burst of energy and material Astronomical Society. Because the discovery ered by citizen scientists from the surface of the white is so recent, astrono- participating in the Galaxy dwarf. This is called a nova So why haven’t astrono- mers aren’t sure whether Zoo project. It is among a or classical nova. mers caught a micronova micronovae are related to number of oddball objects before? classical novae — especially uncovered by the project, But astronomers have because at least one of the which catalogs galax- recently spotted a differ- “These events may actu- observed white dwarfs has ies to explore how they ent way that white dwarfs ally be quite common, but experienced both novae and evolve over time. Mergers can rapidly burn off some because they are so fast, micronovae in its past. The such as this are common of their stolen gains: a they are difficult to catch team is hopeful that large- throughout a galaxy’s micronova. in action,” said Simone scale surveys partnered with lifetime, and often begin Scaringi, who led the study quick follow-up observations the process of turning Micronovae are small published in Nature, in a by telescopes like the Very young, star-forming spiral compared to novae (hence press release. “It just goes Large Telescope in Chile galaxies into old, quiescent their name) and are con- to show how dynamic the will unlock the mysteries ellipticals. — ALISON KLESMAN tained near the magnetic universe is.” of these new explosions. poles of a white dwarf. Don’t let the name fool you, While classical novae — CAITLYN BUONGIORNO light up a white dwarf for 10 ASTRONOMY • SEPTEMBER 202 2

SCIENTISTS PLAN THE FUTURE OF SOLAR SYSTEM EXPLORATION Uranus, Enceladus, and Mars are would descend to the moon’s surface all winners in the planetary science and spend two years hunting for signs community’s new decadal survey, the of life. blueprint for how U.S. policymakers should invest the limited resources COSMIC ROAD MAP available for space exploration. Getting Mars rocks to Earth is another The once-a-decade report, released priority in the decadal. NASA’s April 19, is the product of a committee Perseverance rover is already collecting convened by the National Academies and caching samples to be picked up of Science that sought and received by a future sample-return mission. recommendations from the planetary Retrieving and launching these science community. It guides the deci- samples from Mars back to Earth is sions of funding agencies like NASA estimated to cost around $5.3 billion. and the National Science Foundation. The decadal also outlined possibili- And because U.S.-led missions often ties for two smaller missions, includ- include international ing proposed flights to collaborators, Triton, Titan, Venus, the decadal also has Mars, and asteroids. global resonance. Planetary defense Topping the list is a also received atten- proposed $4.2-billion- tion, particularly the dollar flagship mission Near-Earth Object to Uranus, which Surveyor, an infrared would be the first craft space telescope meant to return to the ice to scan for potentially giant since Voyager 2 hazardous space rocks. flew by it in January The decadal’s 1986. The orbiter TOP PRIORITY. Uranus’ only visit portfolio is “exciting would launch during and ambitious,” says the 2030s and arrive at from a spacecraft came in 1986, Jim Bell, a planetary when Voyager 2 flew past it and took this photograph. NASA/JPL-CALTECH the planet sometime scientist at Arizona around 2044. “Uranus and Neptune are State University. But, he adds, “securing still poorly understood, and there are the funding for the recommended many key open fundamental questions program over the next decade is likely about them,” says Ravit Helled, a to be the biggest challenge.” planetary scientist at the University of The planetary science decadal Zurich. Answering those questions also follows the Nov. 4, 2021, release of the teaches us about exoplanetary systems equivalent report for observational that feature ice giants, says Helled. astronomy and astrophysics. That Saturn’s 310-mile-wide (500 kilome- survey endorsed a series of proposed ters) moon Enceladus also received star and upcoming observatories, including treatment in the report. That’s largely a versatile 6-meter space telescope because in 2005, the Cassini mission that could observe in the infrared, discovered water geysers erupting optical, and ultraviolet; the ground- from cracks in the moon’s icy surface. based Giant Magellan Telescope and The plumes contain unusual amounts Thirty Meter Telescope projects; the of possible biosignatures, such as Cosmic Microwave Background-Stage methane. The proposed $4.9-billion- 4 ground-based observatory, which dollar Orbilander mission would would survey the universe’s earliest arrive at Enceladus in the 2050s and detectable radiation; and the Next orbit the moon for 18 months, flying Generation Very Large Array radio through the plumes. Then the craft observatory. — CHRISTOPHER COKINOS WWW.ASTRONOMY.COM 11

STRANGE UNIVERSE Reasonable teems with life. We can’t even catalog all the species here; they’re too numerous. No place could be more fecund. questions What do you wonder More importantly, no current observation could por- about the cosmos? tray any exoplanet as most (or even more) ideal for life. Sure, it might orbit at the right distance from its parent star to allow liquid water. But does it also have a nearby moon that stabilizes its axial tilt to keep conditions friendly over long periods, as we do? Or, on the flipside, might it have lethal surface radiation? Overactive volca- noes? We can’t know such things. Conjectures about “ideal conditions” ignore such critical holes in our data. To reach firm conclusions, we’d need to detect atmo- spheric gases specifically produced by life. Those are some common questions. Among the more unique is: “Might a person be contentedly weightless in a cavern at the Earth’s center?” That’s a cool question. But the comfort level 4,000 miles (6,400 kilometers) below your shoes might be degraded by the pressure from the overlying layers. You’d be pressed upon by 55 million pounds per square inch (3,900 metric tons per square centimeter). That’s 3,900,000 bars, or around 4 million times the air pressure you’re currently experiencing. Another subsurface query: “How hot is it under- ground?” Here on Earth’s surface, the daily air tempera- ture cycle disappears at a depth of 6 inches (15 cm). Below 30 feet (9 meters), like in large caves, a thermometer would remain unchanging and read the same as your region’s With 40 years of For the past 40 years, I’ve driven to a radio average annual air temperature. answering the studio in Albany, New York, to answer on-air Another caller asked: “At what altitude would time pass public’s questions on astronomy questions. For an hour each month, astronomy under my the eight stations of the WAMC Northeast Public Radio at the same rate for an orbiting astronaut as someone on belt, I’ve learned that Network broadcast this in five states. Earth’s surface?” Remember that both higher speed and people have some stronger gravity slow time, so an astronaut on the Moon, interesting queries experiencing only 1/6 Earth’s gravity and partaking of about our universe. IEVGENII TRYFONOV/DREAMSTIME After so many years, I’ve noticed common our satellite’s leisurely 0.6-mile-per-second themes — and questions — pop up. One trend (1 km/second) orbital speed, would age faster that’s emerged is that a lot of folks don’t trust I’ve noticed than in his Chicago bedroom. Conversely, an our government. The recent Netflix movie common astronaut on the International Space Station Don’t Look Up, which depicted the feds themes — zooming at 4.76 miles per second impounding astronomers’ orbit calculations and (7.66 km/second) while bathed in 90 percent of and calling it “classified information,” plays Earth’s surface gravity ages more slowly than into this paranoia. If a world-destroying questions when she took her SATs on the ground. So, comet was en route, many think the govern- — pop up. where would gravity and speed combine to ment would keep it a secret. exactly match the time-passage at your local The reality? If a new comet or asteroid was mall? Answer: In a space station orbiting about to create an extinction-level event, the discoverers 2,000 miles (3,220 km) above Earth’s surface. Lower would first quickly share it with other observatories to down, you’d have to move too quickly to stay in orbit. confirm everything. Experienced astronomers have Another: “Could an astronaut consciously survive a favorite journalists and media outlets, and by the end of brief helmetless transfer through space from one space- BY BOB BERMAN the first day, word of the danger would have reached the craft to another, as in 2001: A Space Odyssey?” Yes! (See Bob’s recent book, entire world. The government would have no chance of my February 2018 column to learn why — and how.) Earth-Shattering keeping it under wraps. Aren’t we forever nourished by such scientific mor- (Little, Brown and Company, 2019), Last year, several callers asked about articles from 2020 sels? Keep the calls coming! explores the greatest saying that astronomers had found exoplanets with better cataclysms that have conditions for life than Earth. This may have been histo- BROWSE THE “STRANGE UNIVERSE” ARCHIVE shaken the universe. ry’s most unsupportable supposition. First off, our planet AT www.Astronomy.com/Berman 12 ASTRONOMY • SEPTEMBER 2022

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BINOCULAR UNIVERSE Off the beaten path between them below the Little Dipper’s bowl for about twice their span. There, just east of a small right triangle of 7th- and 8th-magnitude stars, lies our quarry: There are challenges η NGC 6946, the Fireworks Galaxy. A spectacular spiral galore in Cepheus. galaxy, it gets its nickname from its preponderance of observed supernovae — 10 in the past century. (By com- parison, the Milky Way averages about one or two per century.) β Little NGC 6939 NGC 6946 is a tough challenge through common- Big Dipper sized binoculars. But that’s the fun of it! I spotted it ο recently through my 10x50s, but only after I secured CEPHEUS NGC 6946 them to a tripod and viewed from a comfortable seated position. Using the Little Big Dipper and that right tri- ι angle as guides, I spotted NGC 6946 using averted vision. ξ So if you don’t see it right away, persevere, as you may NGC 6939 need to pull out all your best tricks for this one. NGC 7160 α η Without shifting the aim of the binoculars, glance ν across the field for our next challenge, open cluster NGC NGC 6946 6939. The cluster is just north of the star at the right angle λ μ of that triangle. I saw it as a delicate, starless glow. If you δ are using 70mm and larger binoculars, some of the clus- NGC 7235 ζ 5° ter’s 80 faint stars may be resolvable. Something to con- ε sider: While NGC 6939 is some 5,500 light-years away, I have heard from several readers who, while its galactic “neighbor,” NGC 6946, lies something like 22 These targets can be they enjoy looking at showpiece targets, also million light-years distant! demanding, but are worth the trouble. Too difficult? Here’s an easier option that doesn’t even STEVE BELLAVIA like it when we go off the beaten path. So this require binoculars, just a dark sky. Trace the Milky Way month, let’s turn our eyes to the faint and the formidable by eye from Cygnus northward toward Cepheus. About hiding within the constellation Cepheus the King. 10° northeast of Deneb, you should notice that the Milky Spotting Cepheus may itself be a bit tricky, since its Way branches, with a portion heading off into southern brightest star, Alderamin (Alpha [α] Cephei), shines at Cepheus. This “spur” measures about 10° long by 5° wide magnitude 2.5. The rest of its major stars, which form and looks perfectly straight. Formed in part by the the image of a house with a steeply pitched Cepheus OB2 stellar association, this region roof, all shine between 3rd and 4th magni- resolves into myriad stars through binoculars. tudes. To locate Alderamin, look not quite This month, It is also home to star clusters NGC 7160 and halfway between Deneb (Alpha Cygni) and let’s turn NGC 7235. Polaris (Alpha Ursae Majoris). our eyes NGC 7160 is easiest to find by scanning 4° Once you’ve found the dim twinkle of east from Eta Cephei back to Alderamin, and Alderamin through your binoculars, shift 4° to the faint then continuing another 4° farther east. Look west-southwest to Eta (η) Cephei. Here comes and the for a round, misty patch of gray light. Examine your first real challenge. Just over a degree to formidable. it carefully and you may just spot one, two, or Eta’s southwest is a grouping of 7th-magnitude three faint stars within the glow. All three and fainter stars that reminded Rhode Island form a sharply pointed isosceles triangle. amateur Jim Hendrickson of a tiny version of Our last target is NGC 7235, which lies just the Big Dipper. Jim’s Little Big Dipper, as he christened half a degree from 4th-magnitude Epsilon (ε) Cephei. it in 2010, is a flip-flopped mirror image of its famous Like NGC 7160, this cluster also looks like a small, hazy counterpart. The two “pointer stars” are the brightest, smudge at first glance — at least, that’s how it appears in while several fainter stars form the rest of the bowl and my 10x50s. Larger binoculars may be able to resolve one handle extending to the northwest. The full pattern or two 9th-magnitude stars, the cluster’s brightest. BY PHIL spans about 1.6°. Although it is a challenge through I hope you enjoyed these challenges. If you have sug- HARRINGTON binoculars, I have spotted it with my 10x50s from my gestions for others, drop me a line through my website, Phil received the light-polluted suburban backyard, so it’s possible. Give philharrington.net. Until next time, remember that two Walter Scott Houston it a try and let me know if you succeed. eyes are better than one. Award at Stellafane 2018 for his lifelong Just as we use the Big Dipper’s Pointer Stars to find BROWSE THE “BINOCULAR UNIVERSE” ARCHIVE AT work promoting and other stars in the sky, we can use the Little Big Dipper’s www.Astronomy.com/Harrington teaching astronomy. two pointers to find our next challenge. Extend the line 14 ASTRONOMY • SEPTEMBER 2022

OBSERVING BASICS Join the club previously touted the perks of astronomy clubs in my Nov. 2014 column; one of the underrated ones I men- Don’t underestimate the power of banding together. tioned is the social aspect of an astronomy club, which provides members the opportunity to “talk shop” with other astronomy enthusiasts. Prior to joining ATMoB, I would bore friends, relatives, and neighbors with tales of my adventures exploring the universe with binoculars and telescope. What a relief it was for everyone when I instead could share these tales with kindred souls who were truly inter- ested in what I had to say! Even better, in return I would be treated to cosmic-related narratives of their own. Club observing sessions are another perk, too. Like many backyard astronomers, I sometimes prefer to be alone outside with my telescope, taking in nature’s back- ground music (chirping crickets, nocturnal birds) as I gaze into the eyepiece. However, it’s fun to occasionally opt for the nearby chatter of fellow telescopists, swapping views of different cosmic sights. This gives me the oppor- tunity to see celestial objects I’ve never seen before, as well as test drive astronomical equipment like eyepieces, Roughly 600 people What is the best beginner telescope? What do filters, or telescopes before deciding to purchase them. attended a public star the numbers 7x50 on my binoculars mean? How However, the best things in life aren’t always free, and party July 27, 2019, at Rothney Astrophysical that goes for membership to an astronomy club. Observatory, just much magnifying power do I need to see the Fortunately, the annual fees are usually quite reasonable southwest of Calgary in Alberta, Canada. Andromeda Galaxy? These are just a few of the questions — typically less than about $50. An entire family can This composite image of the event shows readers of this column have sent me over the years. I often be enrolled for a small additional fee. And students members of the RASC Calgary astronomy could have answered them and many others by simply and senior citizens can usually expect discounts. club pointing out the star Polaris with green replying: “Join your local astronomy club to find out.” Membership in an astronomy club can actually be a lasers. ALAN DYER Admittedly, that would be a rather brusque money-saving venture, too. You’ll often get response. But it’s true. One of the best sources first dibs on bargain-priced used astronomi- of astronomical know-how, particularly as it I didn’t cal equipment. Over the years, I’ve acquired pertains to backyard astronomy, is your local have all the a number of astro goodies for a fraction of astronomy club. Not only will members be their original cost, culminating in the pur- able to answer the majority of questions you answers chase of what I consider the “ideal” telescope: might have, but in many cases, you’ll learn to your a bare-bones 6-inch f/8 Dobsonian reflector. even more valuable info than you bargained questions. If I’ve piqued your interest in joining an for. And that can lead you down a new path astronomy club, you can search for one in of exploration altogether! your area by visiting www.astronomy.com/ Because my stint as writer of this column community/groups. (Any astronomy club is in its final months, I’ll also make a confession: I didn’t officers reading this column should check to be sure your have all the answers to your questions. Whenever I was organization is listed, and if not, click “Add Your Group” stumped by a reader’s query, I would turn to my astron- at the top of the page.) And remem- omy club, the Amateur Telescope Makers of Boston ber, most astronomy club members (ATMoB). I could rest assured that an ATMoB member are down to Earth and welcoming would know the answer, or at least point me in the right to newbies. After all, they probably direction. That same pool of communal knowledge exists joined as novices themselves. in almost any astronomy club, big or small. Questions, comments, or sug- BY GLENN CHAPLE What if you need to know about something physical, gestions? Email me at gchaple@ Scan the QR Glenn has been an like repairing out-of-alignment binoculars or collimat- hotmail.com. Next month: Phil code to search avid observer since ing a reflecting telescope? An astronomy club can help Kane’s 35 time-tested doubles. for astronomy a friend showed you with that too. Put out an SOS to the membership, Clear skies! clubs near you. him Saturn through and somebody will come to the rescue. a small backyard BROWSE THE “OBSERVING BASICS” ARCHIVE scope in 1963. Finding solutions to astronomy-related issues is just AT www.Astronomy.com/Chaple one of the benefits of joining an astronomy club. I WWW.ASTRONOMY.COM 15

The secret lives of CELEBRITY These high-wattage luminaries can’t hide from astronomers. BY RANDALL HYMAN 16 ASTRONOMY • SEPTEMBER 2022

CLOCKWISE FROM TOP LEFT: Eta Carinae Eta Carinae and the surrounding Homunculus Nebula show off a range of false colors in this composite image of optical light (white), ultraviolet (cyan), and X-rays (purple). X-RAY: NASA/CXC; ULTRAVIOLET/OPTICAL: NASA/STSCI; COMBINED IMAGE: NASA/ESA/N. SMITH (UNIVERSITY OF ARIZONA), J. MORSE (BOLDLYGO INSTITUTE) AND A. PAGAN V2487 Ophiuchi Recurrent novae are caused by a white dwarf (left) siphoning matter away from its aging companion star (right), as seen in this artist’s concept. Periodically, this material builds up and ignites in a thermonuclear explosion. While this usually takes years or decades, in the extraordinary case of V2487 Oph, it happens every day. DAVID A. HARDY & PPARC GLEAM-X J1627 GLEAM-X J162759.5–523504.3 is thought to be magnetar — a neutron star with an extremely powerful magnetic field. But unlike previously- known magnetars, which rotate once every few seconds, J1627 appears to rotate only once every 18 minutes. ICRAR 4FGL J1120.0–2204 The white dwarf 4FGL J1120.0–2204 (left, foreground) orbits a millisecond pulsar (right, background) in this artist’s concept. The system is still in its early days: The white dwarf has yet to shed its outer layers and the pulsar is still spinning relatively lazily. NOIRLAB/NSF/AURA/J. DA SILVA/SPACEENGINE; ACKNOWLEDGMENT: M. ZAMANI (NSF’S NOIRLAB) STARS WWW.ASTRONOMY.COM 17

Among the Milky Way’s 100 clues as to their whereabouts SOAR billion stellar denizens, there for scientists to decipher. is no shortage of showoffs. Sam Swihart of the U.S. The 4.1-meter Southern Astrophysical Research Telescope (SOAR; Naval Research Laboratory left) sits atop Cerro Pachón in Chile. The Gemini South telescope Some of these heavenly in Washington, D.C., is an is in the background (right). B. C. QUINT/SOAR/CTIO/NOIRLAB/NSF/AURA bodies have long been in expert at spotting them. the limelight, like planetary Recently, he pored over 12 15-hour orbit and, after it spin by sucking material from nebulae, featuring beguiling years of data from the Fermi burns up the 2 billion years’ its companion. billows of expanding gases. Gamma-ray Space Telescope, worth of hydrogen left in its Others, such as luminous blue focusing on one such reclu- tank, will eventually become When your dance partner variables, are new to the scene sive object: the source of one a white dwarf just one-fifth is a neutron star packing the and already flaming out, of the brightest unidentified its current mass. weight of an entire mountain wildly unstable and burning gamma-ray signals on record, into a single teaspoon, inti- with the intensity of millions called 4FGL J1120.0–2204 But what is it orbiting? macy can be dangerous of Suns as they expand and (J1120 for short). Given the star’s ultra-fast business. “These are some of contract. Many of these stars orbit, the only object with the the most extreme objects in will end their lives in explo- Gamma rays pack the most mass to occupy center stage of the universe,” Swihart says. sive supernovae — living fast powerful punch in the elec- the J1120 system yet remain “You’re talking about some- and dying young, briefly tromagnetic spectrum and invisible to us is a neutron thing that’s twice the mass igniting our skies with the cannot be focused or reflected star. (A black hole would far of the Sun and the size of brilliance of entire galaxies by mirrors. As a result, exceed the measured mass.) Washington, D.C., and it’s before disappearing forever. gamma-ray detectors cannot This neutron star is likely a spinning hundreds of times produce crisp images, and millisecond pulsar (MSP) every second with extremely For decades, astronomers objects emitting gamma rays whirling in place so fast that high magnetic fields that thought they understood the appear to occupy patches of it beams hundreds of radio would just wreck you.” galaxy’s stars fairly well, and sky sometimes as large as the pulses toward Earth per sec- could trace their dramatic Full Moon. Zeroing in on ond, and turbocharging its J1120 is the first suspected story arcs with charts and their sources requires obser- MSP system to be discovered models. Based on observa- vations at other wavelengths. tions and calculations, it Using X-ray and optical data, mobilism.org seemed that stars cycled Swihart’s team was able to through life phases as predict- pinpoint a hot blue star at ably as a three-act screenplay. J1120’s coordinates last year. But a single blue star could But in recent years, new not produce the level of methods and instruments gamma rays that were barrel- have revealed stars that ing across 2,600 light-years to exhibit shockingly unconven- Earth. Therefore, this star had tional behavior. These are to have a secret companion. true standouts, modern celeb- rity superstars that tantalize To solve the mystery, us with their secret lives and Swihart employed the exotic physics. Young stars Southern Astrophysical whirling around our galaxy’s Research Telescope (SOAR), supermassive black hole at a 4.1-meter telescope with a fantastic speeds; pulsars spin- sophisticated spectrograph, ning like madcap lighthouses sitting atop Cerro Pachón in with the precision of atomic Chile. Through analysis of its clocks; stars that don’t bow optical and near-infrared out with a single bang, but light, Swihart’s team discov- keep coming back to relive ered that J1120’s detectable their former glory. star is much hotter and denser than the Sun. After deter- These extraordinary orbs mining its temperature and have stories worth telling, and surface gravity, thereby astronomers are scrambling deducing its mass, they mea- to bring them to light. sured the Doppler shifts in the star’s light as it swung A hidden co-star toward and away from Earth. This showed the star has a Some stellar celebrities dodge publicity and live in the shadows, leaving anonymous by Scorbione 18 ASTRONOMY • SEPTEMBER 2022

before it has evolved to its the University of Minnesota times the mass of our own it is taking much longer: final stage: Its white dwarf at a June 2021 press confer- star — typical of all such Nearly 200 years after its is still puffed up, its layers ence hosted by the American impostors — it expelled the initial outburst, Eta Car has bloated. Catching the white Astronomical Society. “This is equivalent of 15 to 20 Suns recovered only to about mag- dwarf at this early stage the only supernova impostor, before fading in the late 1850s. nitude 4, with erratic periods makes J1120 a relative teen- or giant-eruption survivor, of minor brightening. ager, Swihart says — and also where we can see details.” The event had seemed like a missing link in our under- a normal supernova, with a Still, astronomers have standing of how MSPs form. closely monitored it for signs WHEN YOUR DANCE PARTNER IS A NEUTRON of impending eruptions. One Stealing the show STAR PACKING THE WEIGHT OF AN ENTIRE potential telltale is Eta Car’s Then there are the stunt MOUNTAIN INTO A SINGLE TEASPOON, spectral signature, which doubles. Called supernova INTIMACY CAN BE DANGEROUS BUSINESS. shifts every 5.5 years when impostors, these stars mimic its much smaller companion their peers with an explosive In 1837, Eta Car suddenly blinding grand finale of self- star swings by. As the stars’ curtain call, only to make leapt from relative obscurity immolation. But in 1892 it stellar winds collide during a comeback decades later. to become the second bright- faintly reappeared as a 6th- these flybys, the system emits However, they’re hard to est star in the sky. Davidson magnitude star, only to fade less radiation at ultraviolet study: Most of the dozen or so estimates that it lost 10 to again a few years later. Some wavelengths. However, during known supernova impostors 20 percent of its mass before astronomers predicted it the last several close passes, are found in distant galaxies its brightness peaked in 1843. would return to its peak this has not happened. millions of light-years away. Originally more than 100 brightness by 1900. In fact, Davidson thinks that Eta Car’s outflow has become “The one exception is “almost a normal stellar Eta (η) Carinae, which, freak- wind,” and that may presage ishly, is only 7,500 light-years a major eruption. away,” said Kris Davidson of “In the next 20 or 30 years, WWW.ASTRONOMY.COM 19

Eta Carinae There are only 10 known Sun’s most devastating solar recurrent novae in our galaxy. flares in modern times — Even in the bustling starscape of the Carina Nebula, a celebrity One, V2487 Ophiuchi, some which set fires in telegraph like Eta Carinae (far left) stands out — surrounded by its 21,000 light-years distant, offices across the U.S. in 1859 entourage, the bright, double-lobed Homunculus Nebula. HUBBLE made headlines in January and fried power grids in when a team led by Bradley Canada in 1989 — were tens IMAGE: NASA, ESA, N. SMITH (UNIVERSITY OF CALIFORNIA, BERKELEY), AND THE HUBBLE HERITAGE TEAM Schaefer of Louisiana State of millions of times weaker. University announced the (STSCI/AURA); CTIO IMAGE: N. SMITH (UNIVERSITY OF CALIFORNIA, BERKELEY) AND NOAO/AURA/NSF system was producing stellar “V2487 Oph is extraordi- flares about 1 billion times nary,” says Schaefer. An order it’s going to change its appear- Giant superflares more powerful than the Sun’s. of magnitude stronger than ance,” predicts Davidson. The from a dwarf all other known superflares, star is already brighter than Stars like Eta Car are not the Using data from the Kepler “it’s also fast, pounding every the Homunculus Nebula sur- only celebrity lookalikes in space telescope, his team single day. How do you get rounding it, and he thinks it our galaxy. Supernova impos- found that these extreme that much energy?” could brighten by another ters are a category of recurrent superflares occur once a day, magnitude. “When it does, it novae, systems that repeatedly lasting an hour each episode. Schaefer says the answer will ionize the Homunculus surge on and off. Most consist The work was published lies in V2487’s twisted mag- Nebula, making it look like of a white dwarf gulping gas March 2 in Monthly Notices netic fields, which are yanked a planetary nebula, but 100 from its companion until it of the Royal Astronomical round and round between the times brighter and with a overindulges, triggering peri- Society. By comparison, the white dwarf and its rapidly central star,” or, as he also odic surface explosions up orbiting companion. These puts it, “A planetary nebula to a million times the white on steroids.” dwarf’s normal luminosity. 20 ASTRONOMY • SEPTEMBER 2022

Gamma Ray Burst fields are anchored in the roil- Jan. 6, the same day they ing plasma and photons jet- reported their find in The Gamma Ray Visible and UV ting between the two stellar Astrophysical Journal. “For the surfaces. When the over- first time, we watched a red Because gamma rays cannot be focused or reflected by lenses stretched magnetic fields supergiant star explode!” The or mirrors, images produced by gamma-ray detectors show snap, they release potentially outbursts they saw leading up objects as extended over a much wider area than they actually devastating bursts of electro- to the final explosion suggest occupy on the sky. This can be seen in this comparison of an magnetic energy. these stars experience a exploding star, GRB 080913B, imaged in gamma rays (left) greater deal of inner turmoil and the visible and ultraviolet (right). NASA/SWIFT/STEFAN IMMLER, ET AL. According to Schaefer, this than previously thought, their relentless radiation rules out internal structures shifting chances of any exoplanet life before they collapse. in the V2487 Oph system. But he adds that its actual nova To boldly go eruptions, which occur about Not every astronomer every 18 years, are even more dreamed of being a member severe — on the order of a of the celestial paparazzi. billion times more powerful than the daily flares. A nova As Natasha Hurley-Walker eruption is now overdue by tells it, she always wanted to six years, and Schaefer says pilot a starship. When she he expects to see it very soon. grew up and realized how impossibly vast space is, she Despite the fresh attention settled for being an astrono- on recurrent novae, superno- mer, learning to navigate the vae still hold plenty of stories cosmos using radio telescopes. for astronomers to unearth. She launched her journey Stars eight times the mass of aboard the Murchison the Sun or larger end their Widefield Array (MWA), a lives as Type II supernovae. sprawling, knee-high network As hydrogen fuel runs dry of dipole antennas stretched and they lose mass, they puff across the parched red sands outward to become red super- of Western Australia, giants. When the outward 400 miles (640 kilometers) force from their waning north of Perth. It’s one of nuclear fusion grows weaker the few radio arrays in the than the inward force of grav- Southern Hemisphere doing ity, the star collapses onto widefield surveys, scanning itself, becoming a super dense huge swathes of sky at a time. neutron star or black hole. Since 2018, Hurley-Walker In late 2020, using spectral has helmed MWA’s analysis from two telescopes GLEAM-X all-sky survey in Hawaii, a team of scientists across the Southern led by Wynn Jacobson-Galán Hemisphere, logging some of the University of California, 300,000 galaxies. One of the Berkeley, made an unprec- most startling discoveries edented observation of such a came early in the project, dying star in a galaxy 120 mil- when she assigned Tyrone lion light-years away. They O’Doherty, an undergrad at tracked the target for four Curtin University in Perth, months as it grew increasingly to pore over MWA’s copious unstable and finally exploded, data. She had him look for with enormous jets of gas something slowly changing punching outward. over a matter of months. She wasn’t expecting him to find “This is a breakthrough something periodic and fast. in our understanding of what massive stars do moments “When you find a signal before they die,” said repeating a cadence in the Jacobson-Galán, the study’s radio band that nobody’s ever lead author, in a press release WWW.ASTRONOMY.COM 21

S STARS IN MOTION S62 S55 Sgr A* S29 S300 March 30, 2021 S55 ABOVE: Painstaking observations over decades have revealed the orbital motions of S stars S62 around Sagittarius A*, the supermassive black hole at the center of the Milky Way, as depicted in this simulation. ESO/L. CALÇADA/SPACEENGINE.ORG Sgr A* S29 S300 May 29, 2021 S STARS: AT THE HEART OF IT ALL S55 S62 NEAR THE CENTER OF OUR GALAXY live figure out what’s going on,” says Andrea Sgr A* Ghez, an astrophysicist at the University of stars in a class all their own, called S stars. California, Los Angeles, who used this tech- S29 Many times the mass of the Sun, they orbit nique to study the center of our galaxy. “All the galactic center in as little as a dozen we could tell is that there was an object and S300 years, reaching speeds that can exceed you could trace it.” But when adaptive optics 1.5 percent the speed of light. The dense gas came online in the early 2000s, “we saw that June 24, 2021 and dust of the Milky Way’s central bulge the objects we’d been tracking for almost a long hid S stars from prying eyes, but their decade were young, hot stars.” S55 existence and secrets began to emerge in S29 Sgr A* S62 the 1990s with improvements in infrared These S stars are among the most enig- telescopes, adaptive optics (AO), and tech- matic stellar inhabitants of the Milky Way: S300 niques such as speckle imaging. young stars living where old stars should be, thriving in a mysterious, overcrowded Speckle imaging takes rapid short- region of gravity-warped time and space. exposure images to capture the effects of But their orbits provide overwhelming evi- atmospheric turbulence, allowing astrono- dence of the supermassive black hole at the mers to remove those effects from their galactic center. They have also provided images. AO uses minutely adjustable tele- powerful confirmation of the theory of scope mirrors to continuously correct for general relativity, looping around a deep atmospheric distortion by monitoring laser gravitational well that is perfect for testing beams bounced off Earth’s high-altitude Einstein’s concepts under the most severe sodium layer of vaporized meteors. conditions — the crux of research that gar- nered Ghez a share of the 2020 Nobel Prize “I often call [speckle imaging] ‘poor man’s in physics. — R.H. adaptive optics’ because it takes quick snapshots and, in post processing, you July 26, 2021 LEFT: Stars can be seen whipping around the Milky Way’s central black hole in a matter of months in these images from the Very Large Telescope Interferometer at the European Southern Observatory in Chile. Even before Sagittarius A* and its accretion disk had been directly imaged, these images allowed researchers to pinpoint its mass and distance: 4.30 million times the mass of the Sun and 27,000 light-years away. ESO/GRAVITY COLLABORATION

seen, you think you’ve made a repeating transient ever seen, GLEAM-X J1627 mistake,” Hurley-Walker says. from pulsars to variable stars “I thought, OK, it’s an air- to recurrent novae. J1627 was discovered by the Murchison Widefield Array, a radio plane or it’s a satellite, because nothing changes that quickly, J1627 suddenly stopped in array telescope in the outback of Western Australia. PETE WHEELER, ICRAR nothing is there one minute April 2018. But it left one last and then gone the next.” clue. The signals were highly continents, a team reported infrared with unprecedented polarized, the fingerprint of Jan. 13 in The Astrophysical speed, resolution, and depth. Then, some time later, she strong magnetic emissions, Journal Letters. found the signal again at the kind that come from pul- Instruments like these are 154 megahertz. “That was sars. Or, at the extreme end, Meanwhile, the James taking astronomers into new terrifying because, of course, magnetars — neutron stars Webb Space Telescope, the frontiers. Who knows what the SETI Institute is looking with intense magnetic fields most powerful infrared tele- wild and unbridled celebrity for periodic repeating radio 1,000 times stronger than scope ever deployed in space, superstars may have graced signals from space,” she says. those of typical neutron stars. promises to peer back in time the early universe? “But when I found it at to the most distant and earli- another frequency band, But there’s a catch: est galaxies in the universe. Randall Hyman is a journalist we knew it wasn’t aliens.” Magnetars repeat far more Within five years, the Vera C. and photographer whose work rapidly than J1627, once every Rubin Observatory and the has been featured in numerous Searching frequencies on few seconds. Given its Nancy Grace Roman Space publications, including either side of the first detec- 18-minute period, Hurley- Telescope will begin all-sky Smithsonian, Science, and tion, Hurley-Walker realized Walker believes J1627 may be surveys in optical and near- The Atlantic. that the transmission wasn’t an entirely new class of object, just in one single narrow and she hopes it will inspire band. She found it across a more widefield low-frequency large 30-MHz band in each surveys around the world. observation. Parsing five transmissions by frequency, “The MWA was the first amplitude, and time, her team telescope to be observing this concluded that the signals part of the galaxy at these low came from something much frequencies in 40 years,” says farther away than a satellite, Hurley-Walker. “Putting it all and something that was together, we can’t find a smaller than the Sun. “Since model that would generate we don’t know how it would anything like this beautiful produce flares this bright, we polarization and these think it’s more likely that it’s repeated pulses that always smaller still, and that would look the same. If it is an ultra- mean it’s a compact object long period magnetar, there like a white dwarf or neutron should be a huge population star,” says Hurley-Walker. waiting to be discovered.” But this object, dubbed Stars of the past GLEAM-X J162759.5–523504.3 With MWA and SOAR (J1627 for short) and reported already online and a fleet of in Nature Jan. 26, didn’t look revolutionary ground- and like any ordinary white dwarf space-based telescopes in the or neutron star. Analysis of wings, astronomers are slowly signal lags — how much peeling back the aura of mys- slower lower frequencies tery from objects like mag- travel through interstellar netars. NASA’s Neutron star space than higher frequencies Interior Composition Explorer — pegged it at around (NICER), installed in 2017 4,000 light-years from Earth. aboard the International Space It was beaming radiation Station, has resolved features across our planet every on the surface of a magnetar 18 minutes for an entire min- some 13,000 light-years distant ute, and during each burst, it in the constellation Scutum, became one of the brightest seeing three hotspots merg- radio sources in the southern ing. These could be analogues sky. It was unlike any to sunspots or even tectonic WWW.ASTRONOMY.COM 23

10Myeaonarrss This complex, MARS IS A WORLD ENTIRELY POPULATED BY ROBOTS: car-sized rover remains one of our Orbiters and landers from a half-dozen space agencies scout its wafer- best tools on the thin atmosphere and stark surface to unveil a surprisingly active past. martian surface. On the ground, a hardy six-wheeled rover named Curiosity observed its 10th anniversary on the Red Planet this summer. Dust-streaked BY BEN EVANS and running on punctured wheels, it long exerted an irresistible pull, from the 24 ASTRONOMY • SEPTEMBER 2022 continues to explore a desiccated land- canals imagined by Percival Lowell to the scape of wind-chiseled mesas, isolated monstrous otherworldly tripods of H.G. buttes, and swirling sands for relics of a Wells to the classic lyrics of David Bowie. warmer, wetter, perhaps habitable Mars. But while life-forms would find it diffi- cult to thrive on this radiation-drenched The idea of life on the Red Planet has

Curiosity snapped this stunning selfie in front of the from earthbound telescopes, but with But costs spiraled. The initial 20-foot-tall (6 m) rock feature Mont Mercou, which on-the-ground reconnaissance from an $1.63-billion price tag swelled to more appears behind the rover. The final image is a ever-growing lineage of robotic explorers. than $2 billion. To save money, spare parts combination of 60 photos taken by the MAHLI were deleted, tests modified, and software instrument at the end of the rover’s arm and A rover is born redesigned. Engineers removed a zoom 11 images taken with the Mastcam on its mast, function on the rover’s Mastcam camera or “head.” NASA/JPL-CALTECH/MSSS The car-sized Curiosity’s story truly and replaced a rock-grinding device with began in 2003, when the Mars Science a motorized wire-bristle brush. wasteland, the infant Mars 3.5 billion Laboratory (MSL) — a mission to deliver years ago was unlike today’s grizzled, a new rover to the Red Planet — earned It was not enough. Testing and hard- middle-aged world. Girdled by a thick hearty endorsement from the National ware complexities made a 2009 launch carbon dioxide atmosphere and with free- Research Council. NASA chose 11 sci- unattainable. MSL was delayed to the next flowing water on its surface, conditions entific instruments from seven nations, Mars launch window in late 2011. then may have permitted life to take root. aiming to launch MSL in October 2009. The same complexities that Today, our quest to find hints of that life continues — not with observations mobilism.org by Scorbione WWW.ASTRONOMY.COM 25

Mastcam ChemCam UHF antenna Navcams SAM (inside) ROBOTIC ARM REMS CheMin (inside) INSTRUMENTS DAN RAD MAHLI APXS Drill and DRT CHIMRA Rear hazcams MARDI Front hazcams Excluding its hazcams and navcams (but including the Mastcam), Curiosity carries 10 instruments to explore In partnership with Walt Disney’s 2008 the martian environment. The rover’s robotic arm also sports a drill and a scoop. NASA Pixar movie WALL-E, NASA asked U.S. students aged 5 to 18 to find one. slowed the launch and gave NASA From orbit, Mars Reconnaissance Orbiter spotted headaches in 2009 are today part of Curiosity’s discarded parachute and aeroshell. This More than 9,000 names were submit- Curiosity’s success. The rover’s 7-foot-tall photo is one of seven taken between Aug. 12, 2012, ted. The winner, selected in May 2009, (2.1 meters), multi-jointed robot arm is and Jan. 13, 2013. In successive images, the was suggested by 12-year-old Clara Ma of strong, yet sufficiently agile enough to parachute appears to flap in the mild martian Lenexa, Kansas, who won a trip to the Jet drop an aspirin into a thimble. A cross- breeze, changing position, shape, and even Propulsion Laboratory (JPL) in Pasadena, shaped turret houses five instruments, reflectivity from shot to shot, as dust blows onto California, to sign her name on the rover. among them a percussive drill (the Rock or off the material. NASA/JPL-CALTECH/UNIV. OF ARIZONA “Without curiosity,” Ma wrote in her Abrasion Tool or RAT), the motorized essay, “we wouldn’t be who we are today.” brush (called the Dust Removal Tool or Albedo of Neutrons (DAN) looks for sub- DRT), and a scoop called the Collection surface water at depths up to 2 feet Picking a landing site came next. and Handling for In-situ Martian Rock (0.6 m). The Chemical and Mineralogy Scientists mulled over dozens of locations, Analysis (CHIMRA) to gather, sieve, and (CheMin) instrument uses X-ray diffrac- all exhibiting traces of Mars’ watery past, portion soil specimens. tion to measure mineral abundances. And potentially housing biomarkers that the Chemistry and Camera complex ancient organisms might once have left Also atop the turret, the Alpha Particle (ChemCam) employs infrared laser pulses behind. Curiosity’s robustness made X-ray Spectrometer (APXS) irradiates to zap rocks from up to 23 feet (7 m) away previously hard-to-reach places now samples and maps X-ray emissions to and observe their emitted spectra. reachable. The right site, NASA noted in measure chemical constituents. And the September 2008, “will combine a deep Mars Hand Lens Imager (MAHLI), with a Name and address love of adventure with due respect for focus range from 0.8 inch (2 centimeters) safety.” Safe, in this case, meant “flat and to infinity, snaps high-resolution pictures. Engineers placed the names of 1.2 million fairly free of rocks,” while adventure “gen- It has acquired multiple self-portraits of people (including the author’s) onto the erally involves streambeds, rugged terrain, the rover on Mars, winning awards for the rover, inscribed on two microchips as and rocks exposed in steep cliff walls.” best “space selfies.” part of the Send Your Name to Mars campaign. But MSL needed its own name. In July 2011, NASA chose Gale Crater. The Rover Environment Monitoring Station (REMS) on the mast measures Destination: Gale Crater local humidity, temperature, pressure, and wind. One of its two anemometers Ninety-six miles (154 km) wide and cov- was hit by a rock during landing, but the ering an area equal to Connecticut and other works just fine. REMS also ana- Rhode Island combined, Gale Crater lyzes ultraviolet radiation at the surface today is a dry, desolate locale south of to better inform future human missions. the martian equator. Its current state has more in common with the Badlands of The Sample Analysis at Mars (SAM) southern Utah than the Garden of Eden. collects, heats, and analyzes soil and Named for the Australian astronomer atmospheric specimens. The Dynamic Walter Gale (1865-1945) — who, like Lowell, was a proponent of canals and oases on Mars — the crater formed from an asteroid strike between 3.8 billion and 3.5 billion years ago. Over time, this gaping wound filled with sediment, first deposited by water, 26 ASTRONOMY • SEPTEMBER 202 2

This 2017 image shows four distinct layers of Mount rocket speared into a cloud-dappled ABOVE: 12-year-old Clara Ma, who proposed the Sharp. The band that separates the redder Florida sky at 10:02 A.M. EST on the 26th, name Curiosity for NASA’s rover, stands in JPL’s foreground rocks from the pale gray rocks in the “seeking clues to a planetary puzzle about Mars Yard with a full-scale model of Curiosity in middle distance was nicknamed Vera Rubin Ridge life on Mars,” the launch commentator 2009. NASA/JPL-CALTECH by mission engineers. NASA/JPL-CALTECH gushed. And thus, Curiosity began its 352-million-mile (567 million km) voyage BELOW: NASA’s Mars Reconnaissance Orbiter then by wind. Eons of erosion then to the Red Planet. captured this shot as Curiosity descended through scoured out the sediments to leave an iso- Mars’ thin atmosphere on Aug. 6, 2012, slowed by lated peak: the 18,000-foot-high (5,500 m) During the 36-week cruise, four mid- its large parachute. The inset shows the same Aeolis Mons, nicknamed Mount Sharp for course correction maneuvers helped shift image, stretched for visual clarity to avoid U.S. geologist Robert Sharp (1911-2004). Curiosity’s landing point 4 miles (7 km) saturation. NASA/JPL-CALTECH/UNIV. OF ARIZONA Rising taller than Mount Rainier stands nearer to Mount Sharp. This correspond- over Washington state and nearly three ingly shaved months of drive time off the times higher than the Grand Canyon is rover’s journey to reach selected sam- deep, Mount Sharp’s layer-cake stratigra- pling locations sooner. phy promised to lay bare some 3 billion years of the martian landscape’s evolution, Also during the cruise, the Radiation and maybe even reveal how the planet Assessment Detector (RAD) measured morphed from an Earth-like paradise into radiation levels inside a Marsbound space- an arid, rusty desert. craft for the first time. Researchers hoped the readings would reveal the environ- “Mount Sharp is the only place we can ment that humans might experience currently access on Mars where we can during a similar trip — and they did. investigate this transition in one strati- Results published in 2013 highlighted the graphic sequence,” said John Grotzinger biggest solar particle event in a decade, of Caltech, then chief scientist for the finding that radiation levels surpassed mission, in a 2012 NASA press release. “The hope of this mission is to find evi- dence of a habitable environment; the promise is to get the story of an impor- tant environmental breakpoint in the deep history of the planet.” Yet accessing Gale would be tough. Its potential to unlock a crucial chapter in Mars’ past had seen it considered for the earlier Spirit and Opportunity rovers; their limited capabilities and the chal- lenging terrain ultimately ruled it out. But Curiosity, with a unique landing sys- tem and long-duration nuclear battery, would be a more capable beast. Seven minutes of terror Curiosity’s three-week launch window opened Nov. 25, 2011. That first day was missed, as engineers replaced a flight termination battery. But the Atlas V WWW.ASTRONOMY.COM 27

1 2 CURIOSITY FOR ALL Atmospheric 2 entry begins Public outreach goes hand in glove with science on what NASA has called a “mission for everyone.” Altitude: about MAHLI’s calibration target, which provides a refer- ence for color and brightness in the rover’s images, 78 miles (125 km) includes a 1909 Lincoln penny — a tip of the hat to geologists’ practice of using coins to provide con- Velocity: about 13,200 text. The choice has a public outreach function, too. mph (21,250 km/h) “Everyone in the United States can recognize the Time since entry: penny and immediately know how big it is, and can 0 seconds compare that with the rover hardware and Mars materials in the same image,” said MAHLI principal MAHLI’s calibration target is located Atmospheric deceleration 3 investigator Ken Edgett in a press release. “The near one of the robotic arm’s shoulder public can watch for changes in the penny over the joints. The target includes color chips, Friction with the atmosphere long term on Mars. Will it change color? Will it cor- a bar graphic, and a 1909 Lincoln slows the spacecraft by more than rode? Will it get pitted by windblown sand?” — B.E. penny. NASA/JPL-CALTECH 90 percent; the heat shield’s temperature climbs to a maximum of about 3,800 F (2,000 C). Parachute deploys Altitude: about 7 miles (11 km) Velocity: about 900 mph (1,450 km/h) Time since entry: about 255 seconds Aeolis Palus Yellowknife LEFT: The Curiosity rover first Map Bradbury Bay touched down at a spot now area Landing called Bradbury Landing Aug. 6, 2012. Since then, Curiosity has Aeolis Darwin trekked parallel to the Bagnold Mons Dunes and made its way through the Marias Pass, past Ogunquit Gale Crater Beach, over Vera Rubin Ridge, Cooperstown and up the slopes of Greenheugh Curiosity’s Pediment. As of early June 2022, landing Kimberley Dunes Curiosity had traveled a total distance of 17.48 miles (28.13 km). the thin atmosphere at 13,200 mph Marias Pass Pahrump Hills Bagnold (21,250 km/h). The heat shield guarded its ASTRONOMY: ROEN KELLY, AFTER NASA/JPL-CALTECH/ cargo from temperatures of 3,800 degrees Bridger 0 0.5 1 mile UNIV. OF ARIZONA Fahrenheit (2,000 degrees Celsius), as fric- Basin tion slowed its meteoric descent. Once carry it safely to the ground. Curiosity was plummeting at 900 mph Gobabeb 0 1 2 km Instead, Curiosity used an (1,450 km/h), or 1.7 times the speed of innovative new piece of tech- sound, it jettisoned several tungsten bal- Naukluft nology: a rocket-powered sky last weights and its supersonic parachute opened, unfurling a canopy 165 feet Plateau (50 m) long and nearly 52 feet (16 m) wide. Murray Vera Rubin Ridge crane that lowered the rover, Next, the craft discarded its aeroshell. Buttes wheels-down, to the surface The Mars Descent Imager (MARDI) on on 25-foot (7.6 m) tethers. Curiosity’s chassis started recording video Ogunquit of the landing site. From orbit, MRO pho- Beach Because of the immense tographed Curiosity descending beneath its parachute. “You could consider us the distance between Earth and closest thing to paparazzi on Mars,” joked MRO team member Sarah Milkovich P Greeendhimeeungth Mars, there is no way for when the photo was released. “We caught earthbound controllers to NASA’s newest celebrity in the act.” Aeolis Mons land a rover in real time. (Mount Sharp) Instead, an entirely autono- At an altitude of 1.1 miles (1.8 km), the backshell containing the parachute mous procedure enabled detached. Still moving at 220 mph (350 km/h), the sky crane’s eight retro- Curiosity to land itself with rocket engines, perched on extendible arms, roared to life, their exhaust almost pre-loaded software. NASA’s invisible in the martian air. After it Mars Odyssey and Mars NASA’s current astronaut career limit. Reconnaissance Orbiter (MRO) watched One scientist opined that an astronaut’s from orbit, relaying their data back home. accumulated radiation dose on the way Seven minutes elapsed between when to Mars would be like undergoing a full- Curiosity reached the top of Mars’ atmo- body CT scan every week of the flight. sphere (called entry interface) and landed Curiosity reached the Red Planet after on the surface — and all the while, the just over eight months of travel. Its rover’s status remained unknown. NASA approach for landing on Mars differed called these the “seven minutes of terror.” from earlier missions. At 1,982 pounds The craft discarded its cruise stage just (899 kilograms), it was too heavy for just before entry interface and the rover, still parachutes, landing legs, or airbags to cocooned in its protective aeroshell, hit 28 ASTRONOMY • SEPTEMBER 202 2

4589 5 6 8 10 Radar collects data Back shell separates Rover separates Flyaway A radar system on the Pyrotechnic cutters descent stage measures the Altitude: about Altitude: about on the rover sever spacecraft’s exact velocity 1.1 miles (1.8 km) 66 feet (20 m) the connecting and altitude; meanwhile, the Velocity: about cords, and the Mars Descent Imager Velocity: 220 mph 1.7 mph (2.7 km/h) descent stage photographs the surface. (350 km/h) Time since entry: 9 flies 2,100 feet 4 Time since entry: about 390 seconds (650 m) away. about 350 seconds Heat shield separates Touchdown Altitude: about 5 miles (8 km) 7 Altitude: 0 feet Velocity: about 280 mph (450 km/h) Velocity: about Time since entry: about 279 seconds Powered descent 1.7 mph ( 2.7 km/h) Retro-rockets fire to slow Time since entry: the spacecraft further. about 403 seconds ASTRONOMY: ROEN KELLY slowed to 1.7 mph (2.7 km/h), the rover’s distance. (Curiosity serendipitously “T D” for a safe touchdown — followed wheels snapped into position as the crane recorded the sky crane’s demise when by verification that Curiosity was on firm began to lower Curiosity via tethers. At one of its rear-mounted hazcams came ground, then confirmation of a strong 1:32 A.M. EDT on Aug. 6, 2012, Curiosity online 40 seconds after landing and cap- ultra-high frequency (UHF) signal. plonked down onto alien soil. The sky tured a plume of dust on the horizon.) Finally, the words “touchdown con- crane paused a couple seconds for a firmed” visited a sheer pandemonium “weight on wheels” signal, then cut the On Earth, flight controllers waited of cheering and joyous applause on the tethers and flew away to crash at a safe anxiously. First came the call of “Tango control room. Delta nominal” — phonetically denoting More than 3 million people watched Rocknest is the ripple of sand located to the right of the online as Curiosity landed that morning. grouping of dark boulders in the image above. It was here A thousand others gathered in New that Curiosity first used the scoop at the end of its robotic York’s Times Square for a live broadcast. arm to study the surface material and its properties. The JPL engineer Bobak Ferdowsi became an inset at right shows two of several trenches left behind in unexpected Twitter sensation with his the sandy sediment by the scoop. NASA/JPL-CALTECH/MSSS yellow-starred Mohawk haircut. In the following days, Curiosity transmitted back to Earth words from NASA Administrator Charlie Bolden and played will.i.am’s “Reach for the Stars,” the first time recorded human voices had been broadcast to Earth from another planet. Looking for signs of life A laboratory like no other was ready to get to work. The rover’s touchdown spot was named Bradbury Landing after science fiction writer Ray WWW.ASTRONOMY.COM 29

Bradbury, who had died earlier in The rover’s touchdown spot LEFT: DIMOSBARBOS/DREAMSTIME 2012. Curiosity’s first port of call was named Bradbury Landing was Glenelg, a patch of terrain after science fiction writer Ray Bradbury, 1,300 feet (400 m) from the landing site. who had died earlier in 2012. Along the way, ChemCam zapped its first target (the fist-sized Coronation Rock) Yellowknife had pointed to habitable con- Gale Crater region that contained carbon with 30 laser pulses over 10 seconds, ditions for tens of millions of years, as and hydrogen in sedimentary rocks delivering more than a million watts of lakes rhythmically emerged, dried, then within 2 inches (5 cm) of the surface. power per shot. re-emerged. Even when the soil was dry, Analysis of a football-sized rock the subsurface remained wet, as shown by Curiosity also found nitric oxides and (named Jake Matijevic for MSL’s late mineral veins deposited into fractures in organic salts, whetting many astrobiolo- surface operations chief engineer) drew the rocks by underground water. gists’ appetites. Nitrates can be processed parallels with volcanic materials on Earth, by biological systems; their discovery thus revealing high levels of feldspar and traces The planet’s past came even more alive provided another line of evidence in favor of magnesium and iron. Curiosity saw at Cumberland, a patch of bedrock at least of Mars once having had suitable condi- evidence of long-vanished streambeds 3.9 billion years old, whose surface bumps tions for microbial life. None of these with rounded gravel — ranging in size were possibly forged by flowing water. finds conclusively proved that life does or from grains of sand to golf balls — SAM revealed organic molecules, though did once thrive in this now-blasted land- prompting excited suggestions that per- whether these could have formed on Mars scape; indeed, most compounds can arise haps water had once flowed through the or been transported by meteorites remains through non-biological processes. But area at a comfortable human walking pace unclear. The rover also discovered these underscored a growing realization of 3 feet (90 cm) per second, rising to smectite clays, which can absorb and that Mars’ past was far more hospitable ankle or even waist height. retain water, potentially providing an than its present. A wind-deposited ripple of sand called environment for life to thrive. Rocknest gave Curiosity a chance to scoop Up the mountain up some soil. This revealed uncanny simi- Data from Hidden Valley on Mount larities with the weathered basalts of Sharp’s lower flank, which Curiosity In July 2013, the rover began to head Hawaii. At a shallow depression called entered in 2014, suggested long-lived for the slopes of Mount Sharp to the Yellowknife Bay, which might be the end lakes existed there some 3.8 billion to southwest. To progress across difficult, of an ancient river system or intermit- 3.3 billion years ago. And in 2018, rugged terrain, the engineers tested tently wet lakebed, the rover first used its researchers announced that over the pre- Curiosity’s autonomous navigation, with DRT to prepare a rock dubbed Ekwir-1 vious three years, Curiosity had observed the Mastcam cameras identifying hazards for inspection and mineralogical analysis. ancient organic molecules within the in advance. This enabled Curiosity to In February 2013, Curiosity drilled into its first rock, nicknamed John Klein for the mission’s late deputy project man- ager. The 2.5-inch (6.4 cm) hole uncovered traces of sulfur, nitrogen, hydrogen, oxy- gen, phosphorus, and carbon, all key ingredients for life. Such findings — again showing Mars may have had flowing sur- face water just as the first signs of life appeared on Earth — kindled speculation that life on Earth and Mars might have arisen around the same time. Certainly, ABOVE: Curiosity captured this view of Yellowknife Bay Dec. 24, 2012. To the upper left are the foothills of Mount Sharp, while two of Curiosity’s future drill sites, John Klein and Cumberland, appear in the foreground of the image, just right of center. NASA/JPL-CALTECH/MSSS LEFT: NASA chose 96-mile-wide (154 km) Gale Crater as Curiosity’s target. This view of the crater, including its 3.4-mile-high (5.5 km) peak, Mount Sharp, was generated using data from ESA’s Mars Express and NASA’s Mars Reconnaissance Orbiter and Viking missions. The rover touched down to the lower right of Mount Sharp from this viewpoint, which looks southeast. NASA/JPL-CALTECH/ESA/ DLR/FU BERLIN/MSSS

ABOVE: Curiosity left these tracks while crossing a martian dune in early February 2014. This particular image has been white balanced, which better shows what the surface of Mars would look like under an Earth-like sky. NASA/JPL-CALTECH/MSSS RIGHT: Over time, the tough martian terrain has damaged Curiosity’s wheels. The result of such wear and tear is visible in this image, snapped by the MAHLI instrument Jan. 27, 2022. NASA/JPL-CALTECH/MSSS compute its own route without requiring material called hematite. Later sampling in its arm, and trouble opening and clos- constant attention from its human han- halts revealed jarosite, which forms in ing CHIMRA’s scoop. Its percussion drill dlers back home. acidic conditions, and the silica mineral suffered a motor malfunction that sus- cristobalite. Since these minerals are pended operations from December 2016 The journey from Bradbury Landing known to be formed or altered in wet to May 2018. And in mid-2018, it survived to the foothills of Mount Sharp took two environmental conditions, their discov- the planet-circling dust storm that ended years. Curiosity crested Panorama Point, ery furnished important clues about the life of the solar-powered Opportunity photographed a pale-toned outcrop multiple episodes of fluid motion in rover, leaving Curiosity as the only func- named Darwin, and observed the striated Mars’ far-off past. At higher levels, the tioning rover on Mars for a time. region called the Kimberley, including a rover found polygonal sand ripples, rock- 16-foot-high (5 m) isolated butte called ier terrain, and extraordinary sandstone Ten years after arriving in Gale Crater, Mount Remarkable. Rocks here were plateaus carved by eons of wind erosion the rover has covered more than 17 miles darker than the mudstone slabs of into isolated ridges and knoblike buttes. (27 km), and Curiosity’s future remains to Yellowknife, revealing more magnetite be seen. Little trace of the rover now sur- and the presence of orthoclase, a But after a decade on Mars, Curiosity vives at Bradbury Landing, as the martian potassium-rich feldspar. All this implied is clearly aging. By late 2014, the rover’s wind and dust have long since begun to that Gale Crater underwent complex geo- wheels were already showing signs of cover its earliest tracks. For now, though, logical processing in the distant past, wear. Engineers began selecting routes to Curiosity continues to live up to its name. including multiple episodes of melting avoid sharp rocks and deployed driving and possibly even volcanism. techniques to alleviate pressure. By 2016, As Clara Ma wrote in her prize- punctures had begun to perforate the winning essay, “Curiosity is an everlasting Passing through a gap in a band of wheels’ outer skins; the wheels are now flame that burns in everyone’s mind.” dunes and entering a rockier landscape, monitored via imaging every 3,280 feet And it surely guides the teams who Curiosity’s exploration of Mount Sharp (1 km). Since 2017, software algorithms tenderly watch over Curiosity as it greets finally began in earnest in September 2014 have been implemented to adjust the each martian morning, prepared for at Pahrump Hills. wheels’ speed while climbing to prevent whatever the day ahead may hold. slipping that can cause further damage. Since then, Curiosity has gingerly Ben Evans is a frequent Astronomy threaded its way up the slopes of Mount Curiosity has also weathered multiple contributor who writes about the history Sharp, surveying its lower levels and computer reboots, a transient short circuit of crewed and robotic spaceflight. revealing the presence of an iron-oxide mobilism.org by Scorbione 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 SEPTEMBER 2022 Jupiter dominates the sky above is tilted with respect to Earth’s Dinosaur Provincial Park in Alberta, by 2.5°. Enjoy Jupiter Canada. This month, the gas giant at opposition reaches opposition, offering Saturn’s disk remains near amazing views of its disk and its peak diameter of 18\" across Jupiter is at its best all Mercury. By Sept. 5, Mercury’s Galilean moons. ALAN DYER the equator, with a polar diam- month, reaching brightness dims to 0.6 and it eter of 16.5\". The rings span 42\" opposition in late September. drops to 3° altitude within 20 system, visible even in the across the major axis and only Saturn puts on a great evening minutes of sunset. Southern smallest scope. The apparent 10\" across the minor axis. By show, along with a brief view of Hemisphere observers have a tilt of the rings increases to 15° 2025, they will appear edge-on. elusive Mercury soon after better time following the planet by Sept. 30, slightly better than sunset. For early risers, the this time around. the 12° tilt over the summer. Titan, Saturn’s largest morning sky carries a growing Overall, this angle is declining moon, is magnitude 8.5, an Mars as its main planetary The early evening is domi- as Saturn moves along its easy target for small telescopes. focus, while early in the month nated by Saturn’s appearance orbit; such variations are the You’ll find it north of Saturn you can catch Venus in the in the southeastern sky as result of the way Saturn’s orbit early on Sept. 6 and 22, and bright morning twilight. darkness falls. It’s now a month due south Sept. 14 and 30. It Mercury hugs the western past opposition. On Sept. 7 and lies due east of the planet on horizon during the first two 8, a gibbous Moon stands near Sept. 25. Inside Titan’s orbit are weeks of September, poorly the ringed planet. Saturn is 20° many more moons, all fainter. placed for Northern Hemisphere high by 9 P.M. local time in Tethys, Dione, and Rhea shine observers. It is also fading, shin- early September. It glows at at 10th magnitude and orbit ing at magnitude 0.4 on Sept. 1 magnitude 0.3 in western every two to five days. and setting 50 minutes after the Capricornus the Sea Goat, Sun. Try to spot the planet 3° outshining 1st-magnitude Iapetus passed superior con- high at 8 P.M. local time. If your Fomalhaut 24° to its southeast. junction in late August and now sky is clear and transparent heads to a Sept. 15 eastern elon- enough to see Arcturus shining Follow Saturn all evening as gation, when it appears faintest through twilight 40° above the it climbs higher; it shows off — about 12th magnitude — horizon, drop straight down to best when it is 35° high in the nearly 9' due east of Saturn. find the approximate location of southern sky, around local midnight. Telescopic views Neptune reaches opposition reveal the magnificent ring Sept. 16 and is consequently visible all night. Shining at magnitude 7.7 in northeastern Aquarius, it’s within easy reach Late-night views PISCES Sadalmelik Jupiter Neptune AQUARIUS CETUS Saturn Diphda Skat Deneb CAPRICORNUS Fomalhaut Algedi PISCIS AUSTRINUS SCULPTOR 10° Sept. 26, 11 P.M. Looking south Jupiter, Saturn, and Neptune (shown here but requires binoculars to see) are visible all night this month. The best views come in the few hours around midnight. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY 32 ASTRONOMY • SEPTEMBER 2022

RISING MOON I Big and small, younger and older OBSERVING THE MOON’S APPEARANCE is always chang- Hipparchus and Albategnius HIGHLIGHT ing. The play of shadows and light morphs as the hours pass. A prominent crater boasting Hipparchus JUPITER reaches opposition fantastic shadows might almost be invisible the next evening under a higher Sun angle. Albategnius Sept. 26, 10 days after When you come back a lunar month later (about 29.5 days), that crater has changed again, as the Klein N NEPTUNE reaches opposition angle and shadows will be a half-day different. E Sept. 16. Two large craters stand out prominently along the light-dark terminator on Sept. 2nd. Early in the month, the terminator falls of binoculars. Find it 5° due The southern and more rugged of the two is across two prominent craters. CONSOLIDATED south of Lambda (λ) Piscium, Albategnius, named after the 9th-century the southeasternmost star in Arabian prince al-Battani. A smaller impactor LUNAR ATLAS/UA/LPL. INSET: NASA/GSFC/ASU the Circlet of Pisces asterism. created the earringlike crater Klein on its west- With Jupiter coming to opposi- ern edge. Note the fairly smooth lava plain in its Edmond Halley, centuries later, to demonstrate tion 10 days later, it is not far interior. The long shadows cast by its tall rim and that the stars move relative to one another. away, 11° east of Neptune. central peak retreat fast enough that in 20 or 30 minutes, you’ll notice the change. Return 30 days later (Oct. 2) to see Albategnius Wait until late evening, once fully lit, while the subtle mottling inside Neptune has reached a decent The highly battered rim of Hipparchus Hipparchus is practically gone. Meanwhile, a trio of altitude, then scan the region lies just north, a mute testament to the outstanding craters has shown up just to the west. with binoculars. Look for a relationship on the lunar surface zigzagging line of four stars 5° between more cratering and greater south of Lambda, each slightly age. Even the lava-flooded floor is fainter than its western older, with many more features com- neighbor (magnitudes 6.3 to pared to Albategnius to the south. In a 7.2). The group looks like a couple of nights, Hipparchus will almost miniature Cassiopeia, with one disappear from sight, its lower and rounder star missing in the northwest. slopes unable to cast shadows under a higher Follow that line east to a bright Sun angle. magnitude 5.5 star — Neptune is roughly midway between this You might recognize the name Hipparchus, and the zigzag’s easternmost whose 2nd-century-B.C. star catalog was a signifi- star. A telescope will reveal the cant first in the history of science, enabling distant planet’s dim bluish disk, spanning a mere 2\". METEOR WATCH I Predawn glow Jupiter reaches opposition Scattered sunlight SEPTEMBER METEOR RATES on the 26th in southern Pisces. It rises soon after 8:30 P.M. local The zodiacal light appears as a soft, cone-shaped glow thrusting drop significantly after the August time on Sept. 1 and by sunset at upward from the horizon. EDDIE YIP peak, with only small background the end of the month. It shines rates visible. The occasional fireball all month at magnitude –2.9, can occur anytime — so regular the brightest object in the night observers, keep watch for those. sky after the Moon. The planet Early-morning viewers well before is best viewed when it’s highest dawn could be treated to the zodia- above the southern horizon, cal light if your eastern horizon is which occurs in the few hours clear of streetlights and your skies on either side of local midnight. are transparent. This ethereal glow comes from sunlight scattering off Jupiter’s apparent diameter fine meteoritic dust filling the solar reaches a stunning 50\" by late system. Favorable conditions occur September, and any telescope when the ecliptic is angled high will reveal magnificent features relative to the eastern horizon. The in its turbulent and dynamic broad base of the cone-shaped glow is in Leo and narrows higher in the — Continued on page 38 sky through Cancer and Gemini. Catch it on moonless nights (the first and last week of September). WWW.ASTRONOMY.COM 33

N STAR DOME HOW TO USE THIS MAP C A M E L O PA R DA L I S M82 M81 This map portrays the sky as seen near 35° north latitude. Located NE IA CNAGS SCI8O6P9E inside the border are the cardinal NGC directions and their intermediate R E 884 points. To find stars, hold the map P overhead and orient it so one of U E S URSA the labels matches the direction MINOR you’re facing. The stars above S the map’s horizon now match NCP Polafis what’s in the sky. T ANDROMEDA CEPHEUS The all-sky map shows how the sky looks at: R 10 P.M. September 1 I 9 P.M. September 15 8 P.M. September 30 A Planets are shown N at midmonth G DRACO U L U M33 M31 M PISCES L A C E RTA CYGNUS Deneb PEGASUS M57 MAP SYMBOLS E LY R A Vega Open cluster Path Globular cluster Diffuse nebula of M27 V U L P E C U L A Planetary nebula SAGIT TA Galaxy the Altaif STAR Sun (ecliptic) DE MAGNITUDES Jupitef M15 Sirius Enif 0.0 3.0 1.0 4.0 L 2.0 5.0 CETUS PHINUS EQUU L EU S AQUARIUS AQUILA M11 M16 SCUTUM M17 Satufn Fomalhaut AUPSI CA P R I M22 M20 SCU STCRIISN U S M8 C O R STAR COLORS N U S A star’s color depends L on its surface temperature. SE P The hottest stars shine blue TO •• Slightly cooler stars appear white • Intermediate stars (like the Sun) glow yellow R • Lower-temperature stars appear orange • The coolest stars glow red MICROSCOPIUM SAGIT TARIUS • Fainter stars can’t excite our eyes’ color INDUS CORO NA I S receptors, so they appear white unless you AUST RAL use optical aid to gather more light GRUS TELESCOPIUM BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. S

URSA MAJOR SEPTEMBER 2022 M 51 C AVNE ENSAT I C I SUN. MON. TUES. WED. THURS. FRI. SAT. ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY izar NW 1 23 M 4 5 6 7 8 9 10 CBOEMRAE N I C E S 11 12 13 14 15 16 17 BOÖTES Arcturus 18 19 20 21 22 23 24 S 25 26 27 28 29 30 Note: Moon phases in the calendar vary in size due to the distance M13 A from Earth and are shown at 0h Universal Time. HERCULES LI CALENDAR OF EVENTS N A 3 First Quarter Moon occurs at 2:08 P.M. EDT 4 Venus passes 0.8° north of Regulus, 9 P.M. EDT CORO 7 Asteroid Juno is at opposition, 1 P.M. EDT BORE The Moon is at perigee (226,485 miles from Earth), 2:19 P.M. EDT SERPENS VIRGO 8 The Moon passes 4° south of Saturn, 7 A.M. EDT CAPUT W Mars passes 4° north of Aldebaran, 9 P.M. EDT 9 Mercury is stationary, 4 P.M. EDT M5 10 Full Moon occurs at 5:59 A.M. EDT OPHIUCHUS The Moon passes 3° south of Neptune, 3 P.M. EDT 11 The Moon passes 1.8° south of Jupiter, 11 A.M. EDT LIBRA 14 The Moon passes 0.8° north of Uranus, 7 P.M. EDT 16 Neptune is at opposition, 6 P.M. EDT S ECRAPUEDNAS The Moon passes 4° north of Mars, 10 P.M. EDT Antares 4 17 Last Quarter Moon occurs at 5:52 P.M. EDT M 19 The Moon is at apogee (251,379 miles from Earth), 10:43 A.M. EDT M6 SW 22 Autumnal equinox occurs at 9:04 P.M. EDT LUPUS 23 Mercury is in inferior conjunction, 3 A.M. EDT M7 25 New Moon occurs at 5:55 P.M. EDT 26 Jupiter is at opposition, 4 P.M. EDT O R P IUS N6G2C31 WWW.ASTRONOMY.COM 35 S C

PATHS OF THE PLANETS CV UMa LYN AUR PER AND LAC COM LM GEM Mars Bamberga TRI DEL CNC CM ORI ARI EQU Asteroid Juno reaches Ceres Path PEG opposition September 7 Uranus LEO of the Moon PSC CAP Saturn Venus TAU Vesta Sun PsA SEX Celestial equator Mercury H YA MIC CRV CRT MON Pallas Jupiter appears at its best for the year in late September CM LEP ERI Neptune appears at its best for the year in September ANT PYX COL SCL PHE VEL PUP CAE Moon phases Dawn Midnight HOR 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 To locate the Moon in the sky, draw a line from the phase shown for the day straight up to the curved blue line. THE PLANETS Uranus Neptune THE PLANETS IN THE SKY IN THEIR ORBITS Opposition is Jupiter September 16 These illustrations show the size, phase, Arrows show the inner Saturn and orientation of each planet and the planets’ monthly motions two brightest dwarf planets at 0h UT for and dots depict the the dates in the data table at bottom. outer planets’ positions South is at the top to match the view at midmonth from high through a telescope. above their orbits. Pluto Venus Mars Mercury Mercury Ceres Inferior conjunction Ceres is September 22/23 PLANETS MERCURY VENUS Venus Mars Date Sept. 30 Sept. 1 Jupiter Magnitude 1.7 –3.9 Earth Opposition is Angular size 9.1\" 10.1\" Autumnal equinox September 26 Illumination 12% 97% is September 22 Distance (AU) from Earth 1.658 Distance (AU) from Sun 0.736 0.718 Right ascension (2000.0) 0.322 9h48.9m Declination (2000.0) 11h38.3m 14°23' 1°36' 36 ASTRONOMY • SEPTEMBER 202 2

This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows SEPTEMBER 2022 JULY 2021and colored dots show motions and locations of solar system objects during the month. DRA Callisto CYG HER UM Callisto 1 Ganymede LM 2 Jupiter VUL CV Io SGE LYR BOÖ COM LEO Europa AQL CB Sun SEX Europa 3 Pluto SER Io 4 Ganymede 5 SER OPH 6 VIR LIB SCT C RV CRT HYA JUPITER’S 7 Path of the Sun (ecliptic) MOONS 8 9 SGR Comet C/2017 K2 ANT Dots display 10 CA LUP positions of 11 Galilean satellites 12 SCO CEN at 11 P.M. EDT on 13 the date shown. TEL South is at the ARA top to match the view through a Early evening telescope. 7 6 5 4 3 21 Jupiter 30 29 28 27 26 25 24 14 Saturn 15 S 16 WE 17 18 N 19 10\" 20 Uranus Neptune Pluto 21 22 23 MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO 24 25 Sept. 15 Sept. 15 Sept. 15 Sept. 15 Sept. 15 Sept. 15 Sept. 15 26 –0.4 8.8 –2.9 0.4 5.7 7.7 15.1 27 10.7\" 0.4\" 49.6\" 18.5\" 3.7\" 2.4\" 0.1\" 28 86% 99% 100% 100% 100% 29 0.878 3.971 100% 100% 30 1.430 3.394 4.956 8.998 19.114 28.910 34.032 2.561 9.862 19.686 29.915 34.605 4h48.0m 9h51.9m 0h20.7m 21h29.1m 3h04.3m 23h39.0m 19h53.5m 21°21' 19°41' 0°29' –16°15' 16°57' –3°36' –23°07'

WHEN TO SKY THIS MONTH — Continued from page 33 VIEW THE PLANETS Catching up transit Sept. 6. You can spy the shadow starting at 9:46 P.M. EVENING SKY S S EDT, followed by the moon just Mercury (west) over an hour later. Catch Jupiter (east) Jupiter Io’s Jupiter Io’s Ganymede and its large shadow shadow shadow transiting the evening of Saturn (southeast) Neptune (east) W Io W Io Sept. 20 — the event is again MIDNIGHT underway for Midwestern Mars (east) observers as Jupiter rises. The Jupiter (southeast) shadow leaves the disk over a Saturn (south) Sept. 16, Sept. 23, 30\" period of about 10 minutes Uranus (east) 9 P.M. EST 30\" 11 P.M. EST starting around 10:55 P.M. EDT. Neptune (south) Ganymede itself leaves the disk MORNING SKY This close to opposition, the relative positions of Jupiter’s moons and their about 30 minutes later. Venus (east) shadows are changing noticeably. These two transits of Io provide the perfect The four moons typically Mars (south) example. The other visible Galilean moons lie outside this field of view. Jupiter (west) reside east or west of Jupiter in Uranus (southwest) atmosphere. Try observing the the event starts just before a line. But the tilt of its orbital Neptune (west) plane is such that Callisto, the brown-tinted equatorial belts 10 P.M. EDT, with the shadow moon farthest from Jupiter, and the salmony-red hue of the leading the way and Io follow- misses a transit when at infe- Great Red Spot. Colors can be ing, now only five minutes later. rior conjunction. Instead, spot opposition in November. This is enhanced by using quality eye- The moon and shadow almost Callisto due south of Jupiter a good time to spot the distant pieces and modest magnifica- overlap — we are three days overnight on Sept. 4/5. planet, which is a fine challenge tion. High magnification tends from opposition. Can you sepa- Uranus resides in Aries the for binoculars, since it lies in a to blur features because you rate them visually? Ram all month and shines at sparse region of the sky. Second- also magnify Earth’s atmo- Europa and its shadow magnitude 5.7. It is approaching magnitude Menkar in Cetus is a spheric turbulence. It’s the best time to capture high-speed video frames as Iwell — you will need long focal COMET SEARCH Sailing the Scorpion lengths. Adding a 2x Barlow helps. Check your collimation JUGGERNAUT C/2017 K2 Comet C/2017 K2 (PanSTARRS) each night for the best results. (PANSTARRS) dominates the Jupiter’s atmospheric fea- comet ranks at 7th magnitude N tures move quickly with its while passing the eyes of Scorpius M80 δ Sept. 1 roughly 10-hour rotation this month. Enjoy the easy treat of ο 5 period. Also keep watching the a comet in binoculars from dark σ ever-changing positions of its skies or through a small scope Antares NGC 6144 π 10 LIBRA four Galilean moons. They from the suburbs. Just avoid the Path of orbit with periods ranging 2nd, when the First Quarter Moon M4 from two to 16 days. lies nearby. E 15 Comet PanSTARRS As opposition nears, transits Start looking 15 minutes after of moons and their shadows nautical twilight, because once it τ SCORPIUS ρ 20 υ occur almost at the same time. Prior to opposition, the shadow τ comes first, while after opposi- tion, the shadow trails the gets truly dark, PanSTARRS sinks 25 moon. You can see this effect particularly with Io, which tran- quickly into the murky horizon. LUPUS sits Sept. 16 and 23. On the 16th, the transit is underway when Spend some time comparing it 30 χ Jupiter rises in the Midwest; with globular cluster M80, which ψ2 ψ1 note the separation between Io lies just off our line of sight. Their ξ 2° brightness and size should be Comet PanSTARRS sails through a rich region of the sky this month as it close, but their shape and con- curves past Scorpius the Scorpion. centration noticeably different. The comet appears out of round, very sharp on the south flank, where the solar wind pushes against the dust, and flowing into an ill-defined stubby fan off to the north. Go for medium to high power on this very compact object. and its shadow. They leave the Discovered May 21, 2017, by the Panoramic Survey Telescope and Rapid Response System (PanSTARRS), disk 15 minutes apart, starting K2 is an estimated four times larger than Halley’s Comet. Sadly, this huge snowball never comes inside at 10:13 P.M. EDT. On the 23rd, Mars’ orbit, so it’s unlikely to sport a green halo or blue tail. The Sun’s rays are too weak at that distance. 38 ASTRONOMY

LOCATING ASTEROIDS I Suburban sightings Riding high I LOVE 4 VESTA! Walk outside (or even stand on the balcony) without dark adapting your eyes, point your binoculars 10° to Mars Pleiades Saturn’s lower left, and tag an asteroid in under five minutes. If Aldebaran ARIES you’re new to tracking asteroids and star-hopping, you might need 30 minutes to get oriented at first. But return a few times Betelgeuse TAURUS Uranus and it’s obvious that one starlike dot has moved since the last ORION time. Menkar Even from the suburbs, Vesta’s 6th-magnitude glow is such CETUS that only three field stars are brighter, and you can use them as signposts in a single field of view. Start at Saturn, drop down to a Sirius Diphda parallelogram on the east (left) side of Capricornus, and slide one CANIS MAJOR more field to the lower left. 10° Vesta was the fourth asteroid discovered and at 330 miles across, ranks second in size among the main-belt population. Its Sept. 8, 1 hour before sunrise pummeled surface reflects some 40 percent of the light that hits Looking south it, making Vesta the brightest of the lot, even visible to the unaided eye in a dark sky. The world rides higher in the sky for Mars spends early September near Aldebaran in Taurus. Uranus, in Aries, observers in the southern U.S.; those farther north will need a is at the edge of naked-eye visibility and will likely require binoculars. departing rain to clear away any horizon haze or smoke. South and east of Saturn N Deneb Algedi Saturn γ good guide. Uranus stands 13° 10 P.M. local time at the end E κ due north of this star, slightly of the month. Throughout A Q UA R I U S ε less than two fields of view in September, Mars moves east 7x50 binoculars. Find three through Taurus. Late in the Sept. 1 Path of Vesta CAPRIC ORNUS 6th-magnitude stars forming month, Mars, Aldebaran, and 5 a triangle (one is 53 Arietis); Betelgeuse form a lovely triangle ζ Uranus, somewhat brighter, of brilliant red-hued objects. 10 15 20 25 30 1° is in the middle. M30 The best time to view Mars The next three months are a through a telescope is the hour Vesta’s 6th-magnitude glow has little competition from background great time to check out Uranus or two before dawn, when it stars this month. Saturn’s position is shown here on Sept. 1. with a telescope. Its tiny, aqua- stands more than 60° high. It’s hued 4\"-wide disk is a sight to been a long time since the Red Cimmerium with Syrtis Major Sept. 4 to 5. A lovely crescent behold, more than 1.7 billion Planet was this high in the sky rotating on, Sept. 30: Mare Moon stands 9° above Venus miles from Earth. Use higher for Northern Hemisphere Sirenum. Enjoy becoming the morning of Sept. 24. Look magnifications on nights of observers. Mars is now a fine familiar with these features for them about 25 minutes good seeing for the best views. object spanning 10\", growing to as Mars approaches its early before sunrise. Venus shows off 12\" through the month. Its dis- December opposition. Practice a full disk (99 percent lit) in a Mars joins Aldebaran in tinctive phase of 85 percent imaging now so your workflow telescope. Taurus the Bull, changing the also grows, ending September is well developed by then. appearance of this familiar at 88 percent. This offers The autumnal equinox constellation. At magnitude observers great opportunities Venus shines as a brilliant occurs Sept. 22 at 9:04 P.M. –0.2, the Red Planet outshines to spot its polar cap and many morning star at magnitude –3.9 EDT. the 1st-magnitude star; Mars dark features. in the predawn twilight in early brightens to magnitude –0.6 by to mid-September. Its elongation Martin Ratcliffe is a Sept. 30. Watch the pair rise In the hours soon after mid- from the Sun is diminishing planetarium professional with together in the east in early night, the following features lie and the planet is only 9° from Evans & Sutherland and enjoys September just before local on the Earth-facing hemisphere: our star on the 18th. Venus observing from Wichita, Kansas. midnight, separated by about Sept. 1: Tharsis ridge, Sept. 8: spends most of the month in Alister Ling, who lives in 5°. Mars passes 4° due north Valles Marineris, Sept. 14: Leo the Lion, sliding north of Edmonton, Alberta, is a longtime of Aldebaran Sept. 8. Hellas basin with Syrtis Major 1st-magnitude Regulus from watcher of the skies. rotating off, Sept. 22: Mare The Red Planet rises around GET DAILY UPDATES ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek. WWW.ASTRONOMY.COM 39

Mine With the right equipment and planning, you can enjoy beautiful vistas all year round. BY KEVIN RITSCHEL the sky’s wide-angle wonders EARS AGO, I heard with a particularly wide-angle combina- equipment the market has to offer. But reports of amateur astrono- tion, I achieved my first direct view of with the right equipment (and a little mers glimpsing a huge emis- IC 1396: a big, round, splotchy glow in bit of patience) you can easily take an sion nebula in our galaxy, the sky. ultrawide-angle tour of the night sky. cataloged as IC 1396. Deep astroimages showed an expansive, So how was IC 1396 hidden in plain Consider some of these tips to make complex nebula in Cepheus, about sight? My error was observing with a the most of your observing experience. 3° in diameter on the northern side scope that had too much focal length of the brightest visual band of the and eyepieces with too-narrow apparent You may wonder if binoculars Milky Way, above Cygnus. Being fields of view (AFOV). The telescopes can be used to observe wide- a huge fanboy of all things that shine and eyepieces I initially employed angle targets. Binoculars are with the dim glow of ionized hydrogen showed me only a portion of the nebula, wonderful, and in many cases, and oxygen ions, I had to see it! rendering it unrecognizable. Essentially, a good pair will allow you to Based on years of success observing I was trying to discern the subject of a locate these objects under a faint, challenging galaxies, I confidently painting using a microscope. dark sky. However, I recommend aimed my telescope towards Cepheus, eagerly anticipating visions of a grand The magic combination of telescope a wide-angle telescope if nebulosity. But the best I could manage and eyepiece that finally revealed IC 1396 possible, as it is far more was the faint impression that something was a modest 3.1-inch f/6 achromatic flexible and usually has better was there. I was sorely disappointed. refractor (500mm focal length), com- optical quality and performance. Frustrated, I dismissed other observers’ bined with a 35mm eyepiece with an written reports as wishful thinking. apparent field of view of 68°. The magni- As it turned out, the fault was my fication of this rig was 14x, providing own. I was using the wrong eyepieces me a huge 4.8-degree true field of view. and my telescope was too big for the I finally had a wide enough field to see challenge. the entire object at one time! It wasn’t until the fall of 2020 that I routinely started using small, short-focal- Secrets to ultrawide-angle length telescopes with some massive, 2\" observing wide-angle eyepieces. Upon my first try My mistake is a common one for first- 40 ASTRONOMY • SEPTEMBER 2022 time and experienced observers alike, since it’s easy to be drawn to the best

FALL TARGET: Pacman Nebula CHUCK AYOUB TIP 1: Configure an ultrawide- spotting your target but in making its astronomical trip, consider someplace in angle telescope kit colors shine. For gaseous nebulae, you’ll the mountains of the western U.S. or want a Hydrogen-beta (Hβ) filter. Most Canada — portions of Yellowstone, the If you want to track down wide-angle emission and planetary nebulae are best wonders, you’ll want a fairly short-focal- paired with an Oxygen-III (OIII) filter. — continued on page 44 length telescope. Why? As evident in my struggle to view IC 1396, these kinds of TIP 2: A dark sky is paramount Targets expansive targets require a low power, By far the most important thing you can or wide-angle, view of the sky. To find do to assure success in chasing down These wide-angle the power of your setup, divide the focal wide-angle targets is to observe from a wonders (on the next four length of your scope by the focal length dark-sky location — the darker the bet- pages) provide stunning of the eyepiece. As a rule of thumb, to get ter. I’ve seen numerous objects in my 3.1- views through any a low enough power, you will likely need inch refractor from a dark-sky location telescope-and-eyepiece a telescope with less than 1,000mm of that were invisible when viewing from an combination that offers focal length. urban or suburban location. at least a 3° field of view. (I used a 3.1-inch refractor Your kit also will need a few 2\" eye- If you have a choice, pick an observ- to observe each of them.) pieces with long focal lengths and large ing location at a higher altitude. This gets apparent fields of view. you above the dense lower atmosphere, which noticeably dims the light of all the A light pollution filter — which, as its objects in the sky. If you are planning an name suggests, weeds out unwanted light sources — can be an asset in not only WWW.ASTRONOMY.COM 41

Pleiades DREW EVANS M31/M32/M110 Double Cluster CHUCK AYOUB JARED BOWENS OBJECT CONSTELLATION FALL TARGETS Andromeda Andromeda Galaxy NOTES and satellites You can get three galaxies for the price of one target with this one: M31, M110, and M32. M110 might be hard to see at low power. To challenge yourself, see how far out you can track Andromeda’s spiral arms. NGC 253 & Sculptor The Silver Dollar Galaxy or Sculptor Galaxy (NGC 253) is large and bright. You can also NGC 288 see NGC 288, a fainter globular star cluster, which lies at the other side of the field. Pacman Nebula Cassiopeia NGC 281 is an emission nebula that resembles Pac-Man with a foreground (NGC 281) dust cloud that appears to take a bite out of the circular emission patch. Can you see the dark nebula several degrees to the east and northwest? Triangulum Galaxy Triangulum (M33) Hint: An Oxygen-III (OIII) filter really helps. The Triangulum Galaxy is the third largest galaxy in the Local Group. Even in an 80mm refractor under really dark skies, there are hints of its spiral structure. Double Cluster Perseus When viewing this target, can you spy hints of a third galaxy nearby, (NGC 869 & Taurus the Hamburger Galaxy (NGC 3628)? NGC 884) Perseus The Pleiades is a wonderful visual treat for any binoculars or small telescope. Pleiades (M45) With a wide-angle scope, can you see the reflection nebula? Also try to spot the large, faint emission patches IC 353 and IC 1995, located about 1.5° northeast of M45. California Nebula (NGC 1499) This one can be a challenge if you’re not prepared. Go armed with an 80mm refractor, a low-power 2\" eyepiece, and a Hβ filter, and this object should reveal itself from any dark-sky site. 42 ASTRONOMY • SEPTEMBER 2022

WINTER TARGETS OBJECT CONSTELLATION NOTES M36 to M38 Auriga The entire expanse between M36 on the east and M38 on the west is a grand vista. A wide-angle telescope with about 4° of true field should get you a wonderful view of the two open star clusters, which form a triangle with emission nebula NGC 1931. The Flaming Star Nebula (IC 405) is about 3° west of NGC 1931 but difficult to see visually. Sword of Orion Orion This is one of the best vistas in the night sky, presenting seven NGC objects: 1973, Orion 1975, 1977, 1982, 1976 (also known as M42, the Orion Nebula), 1988 and 1999. Flame Nebula (NGC 2024) and Orion With an 80mm wide-angle telescope you can easily see Orion’s entire belt, including Gemini, Orion the Flame Nebula (NGC 2024) east of the star Alnitak. The Horsehead Nebula (Barnard Orion’s Belt 33) is a dark nebula to the south of Alnitak embedded in the emission nebula IC 434. Barnard’s Loop There are small emission patches north of both the eastern and western stars in the belt, but you will likely need a larger scope to see them. M35 to the Monkey Head Nebula To see this target, you’ll need a wide field, a very dark and transparent sky, and an OIII (NGC 2174) or Hβ filter. If you’re having trouble, move slowly east from M78 and watch for the background to grow slightly brighter. M35 is a fantastic, rich, symmetrical cluster with a smaller cluster, NGC 2158, tagging along on its southwest side. At the far edge of an approximately 5° field is NGC 2174, a fairly bright, round emission nebula. Rosette Nebula Monoceros This nebula is wonderful to view through a wide-angle telescope equipped Puppis with an OIII filter. Can you spot the dark center? What about the pretty M46 & M47 Puppis bright star cluster there? NGC 2477 & With this target you’ll observe two contrasting open star clusters — one with big, NGC 2451 bright stars (M47) and the other with much finer, fainter stars (M46). If you boost the power, you should see the planetary nebula NGC 2438 hiding among M46’s stars. This target includes two fine open star clusters in southern Puppis at about –40° declination. At 2.8-magnitude, NGC 2451 can even be viewed with the naked eye. Barnard’s Loop VINCE AND MAGGIE FARNSWORTH Flame Nebula ANDREW ALVEY ANDREI PLESKATSEVICH Rosette Nebula

M81 & M82 Markarian’s Chain DREW EVANS DAVID BARNETT SPRING TARGETS OBJECT CONSTELLATION NOTES M44 Cancer M44 is a bright star cluster that stands out in a relatively empty sky. M81 & M82 Ursa Major These are two of the finest galaxies in the night sky. The pair lies northwest of the Big Dipper’s bowl. M81 is a grand spiral and M82 is an active irregular. Even in an 80mm refractor, their shapes are noticeably different. Owl Nebula Ursa Major The Owl Nebula is a big planetary nebula, larger than the Ring Nebula but with (NGC 3587) & M108 a lower surface brightness. If you need help catching it, try using an OIII filter. M108, meanwhile, is a nice, nearly edge-on spiral galaxy. Markarian’s Chain Virgo Spring can be slim pickings for low-power, wide-angle telescopes, but Virgo does contain one worthwhile vista. Try seeking out M84, M86, or M87, then switch to a higher power to better see the details of these and other galaxies. — continued from page 41 close to overhead as it will get during To do this, draw a circle correspond- your observing session. This makes some ing to your telescope’s field of view on a Grand Canyon, Canyonlands, and of the trickiest objects easier to spot. If piece of clear plastic, or cut out a circle in Yosemite are all relatively free of light you do try to locate an object close to the a piece of paper that matches your tele- pollution and give you altitude. horizon and are unsuccessful, just wait scope’s widest field of view. Slide the until it is higher in the sky and try again! overlay over your star charts, especially TIP 3: Plan, plan, plan along any portion of the Milky Way that Plan your viewing sessions ahead of And for those of you keen to make the will be visible: You will encounter other time. Consult your star charts (such as most of your nights, you can prospect for groupings of several objects that define Astronomy’s The Complete Star Atlas vistas (groupings) beyond the ones I’ve new vistas. Doing this ahead of an available at MyScienceShop.com) for listed here by making an overlay for your observing session will ensure you get the best season and time to tackle these charts. the most out of it! targets. For an added treat, check out If this sampling gets you hooked on One easy way to ensure a night well the Milky Way. Wonderful star wide-angle wonders, then I suggest join- spent is to target objects when they’re ing your local astronomy club. And if high in the sky. The distance from clusters, emission nebulae, you take any pictures of these objects, an object to the horizon measured in and crowded star clouds can share your new vistas with Astronomy! degrees is called the altitude of an object be spotted in the fall, winter, (0° at the horizon, 90° when straight Kevin Ritschel previously worked at overhead), which changes as the and summer months. major telescope companies and has loved night passes. watching the night sky since the third grade. Try to observe an object when it is as 44 ASTRONOMY • SEPTEMBER 2022

SUMMER TARGETS OBJECT CONSTELLATION NOTES False Comet Scorpius Looking through your scope, you’ll immediately understand where this target gets Pipe Nebula Ophiuchus its name. While looking at the bright and faint star clusters combined with emission Scorpius patches, make sure to turn your eye to star clusters NGC 6231, Tr 24, and NGC 6242. Ptolemy’s Cluster Part of the Dark Horse Nebula, the Pipe Nebula is a dark nebula. Try targeting it with binoculars first — it’s really big! Now that you’ve found it, can you make it out with the unaided eye? With an 80mm wide-angle telescope you can catch M7, also known as Ptolemy’s Cluster, a spectacular open star cluster. About 2° to the south is NGC 6441, a small globular cluster just east of the Scorpion’s stinger. M24 Star Cloud Sagittarius M24 is the Small Sagittarius Star Cloud, a strongly enriched portion of the Milky Way. Sagittarius It is closely guarded by three open star clusters: M18 to the north, M25 to the east, Lagoon Nebula Serpens Cauda, and M23 to the west. To the south and slightly west is M21 and the M8/M20 vista. Sagittarius M16 & M17 & M18 Scutum After the Orion Nebula, this is probably one of the most imaged areas of the sky. This vista runs from the open cluster M21 to the Trifid Nebula (M20) M11 & Aquila and the Grand Lagoon Nebula (M8). Scutum Star Cloud Cygnus This is another vista consisting of three Messier objects: the open cluster M18; the Barnard’s E Cepheus, Cygnus Omega Nebula (M17); and the Eagle Nebula (M16), home to the Pillars of Creation. IC 1318b & M16 appears a reddish violet in large telescopes. What colors do you see? Gamma Cygnus Tucked away at the southeast edge of the bright Scutum Star Cloud is a delightfully NGC 6946 & bright and compact cluster of uniformly bright stars. The Wild Duck Cluster (M11) is NGC 6939 surrounded by an exceedingly rich section of the Milky Way. With very wide-angle Veil Nebula telescopes, you might also see the globular cluster NGC 6712 nearly due south, or the North America & open cluster M26 slightly more west and south of M11. Pelican Nebulae Elephant’s Trunk Barnard’s E was included in Astronomy’s “101 cosmic objects you must see” (see the January 2022 issue). This cosmic letter is formed by a pair of dark nebulae, Barnard 142 and 143. IC 1318b is a patch of nebulosity northwest of the star Sadr (Gamma [γ] Cygni). It is not obvious, but IC 1318b can be detected on clear nights when Cygnus is high in the sky. Moving the field towards the area south of Sadr, you will also find the open cluster M29 and a supernova remnant, the Crescent Nebula (NGC 6888). M29 is easy, but the Crescent is difficult at low power, so use an OIII filter to see the emission nebulosity in the area. This vista is an interesting study in contrast. NGC 6946 is a galaxy, while NGC 6939 is an open cluster. The pair sits on the border of the constellations Cygnus and Cepheus. Cygnus Once thought difficult or impossible for visual detection by small telescopes, Cygnus a wide-angle 80mm scope with an OIII filter makes the Veil Nebula an easy target. Cepheus The delicate wisps of this supernova remnant are small, but the entire nebula is visible in one vista with the 80mm. The key to finding these objects is to pair a 80mm wide-angle scope and an OIII filter. While the North America Nebula is a direct-vision object, the Pelican Nebula is much harder — but it is there, so keep trying! You’ll want to pair the lowest power you have and an OIII filter to see this pachyderm’s appendage. In addition to the Elephant’s Trunk Nebula, some dark nebulae are hidden within this region for observers to enjoy. However, don’t expect to see this vista unless you have a very dark site and excellent atmospheric transparency! Veil Nebula False Comet Elephant’s Trunk MIKE BRADY MICHAEL STECKER PATRICK COSGROVE

SATURN’S AT THEIR FINEST The complex ring system is open Saturn, the ringed wonder, achieves opposition this wide during this year’s opposition, year on Aug. 14 at 17h02m Universal Time (UT), when making it a prime time to explore its rings are 14° open. And this event is not one you’ll the beautifully adorned gas giant. want to miss! It will be another five years before Saturn’s rings are again open enough (13°) to fully reveal all their BY STEPHEN JAMES O’MEARA components. 46 ASTRONOMY • SEPTEMBER 2022 Next year’s opposition (Aug. 27 at 8h20m UT) is also favorable, but the rings will open only 9° to our line of sight. That’s just narrow enough to limit the clarity of visual details, especially in the outermost ring, Ring A.

RINGS LEFT: Saturn displayed itself in all its glory This year’s opposition, then, during the gas giant’s marks the denouement of the opposition in 1998, northern face of Saturn’s rings. captured here by After this apparition, Saturn’s the Hubble Space rings will gradually narrow until Telescope (background they turn edgewise in 2025; we stars added). NASA, ESA, AMY will not see them open substan- tially again until 2027. SIMON (NASA-GSFC), MICHAEL H. At opposition, Earth will WONG (UC BERKELEY); IMAGE move between Saturn and the Sun. With the ringed world PROCESSING: ALYSSA PAGAN (STSCI) rising as the Sun sets, this event marks when the planet is at its BELOW: Saturn’s rings closest and brightest for the year. are currently closing, If you can’t make the actual date a consequence of the planet’s 27° tilt and how our view of the world changes as it orbits the Sun. During every orbit, Saturn first presents one side of its rings to us, then, after a ring-plane crossing, the other. The 2022 opposition (similar to top right) will provide observers with fantastic views of the rings’ northern face before they start closing again over the next few years (bottom left). NASA

of opposition, don’t worry. For Saturn only climbs to half that brightness, followed by Ring several nights leading up to and altitude, making observations A, and Ring C is the dimmest following that event, observers of it more susceptible to atmo- and most difficult of the trio to will still be able to view and spheric turbulence. detect. Each of these sections image the finest details, not contain subtle details, includ- only in Saturn’s rings, but on Survey the rings ing ring divisions, variations in the planet as well. intensity and color, and many Saturn’s rings, as splendid as other curious aspects worthy While Saturn virtually turns they appear in whole, require of investigation. into “Super-Saturn” at opposi- a careful eye to pick out fine tion, the great gulf between it details within. The illustration Let’s look at each ring section and Earth (nearly 824 million below shows its three main ring individually, and I’ll describe miles [1.33 billion kilometers], sections: Ring A (outermost), some historical features that or 8.86 times the average Earth- Ring B (middle), and Ring C were regularly seen and imaged Sun distance) causes it to shine (inner). Ring B is superior in during last year’s opposition. modestly. At magnitude 0.3, RIGHT: Saturn’s three Saturn will be about as bright as Ring A major rings (A, B, and the star Procyon in Canis C), as well as two of the Minor. The world’s angular Cassini Ring C most sought-after ring diameter is also demure at 18.8\", Division divisions (the Encke which is less than half the Gap and the Cassini diameter of Jupiter’s disk during Encke Gap Ring B Division), are popular its opposition. targets for amateur observers. NASA With a declination of –15.5° (in far eastern Capricornus, BELOW: During its near the western border of 29-year journey around Aquarius), this opposition the Sun, Saturn and its favors the Southern majestic ring system Hemisphere, where observers put on quite a show. will see the planet loom 60° These Hubble Space above the horizon at its highest. Telescope images, From mid-northern latitudes, captured from 1996 to 2000 (bottom left to top right), reveal Saturn’s rings opening from just past edge-on to almost fully open. NASA AND THE HUBBLE HERITAGE TEAM (STSCI/AURA) Many of these features will likely be accessible again dur- ing this year’s apparition, with perhaps a few added bonuses. Note that as a general rule, viewing the features described in this article (unless other- wise noted) requires a quality telescope, eyepieces with mag- nifications of 250x or higher, and impeccable atmospheric seeing. Wonders in the rings At a glance, Ring A, the out- ermost of Saturn’s three main ring sections, appears like an ashen cap to brilliant Ring B. But a careful look with a mag- nifying power of roughly 100x or more will show the Cassini Division, a prominent dark gap (about 0.7\" wide) separat- ing rings A and B. And this 48 ASTRONOMY • SEPTEMBER 2022

year marks the penultimate observers to perceive plenty of watch. As of early May, no The summer Milky Way chance to glimpse two other detail. First impressions reveal spokes have been seen or joins the planets Jupiter popular features before the ring- that the ring gradually dims imaged. But they could appear (brightest point of light) plane crossing occurs: the Encke from a sandy white color in its in time for opposition. It’s hard and Saturn (second Minima and Encke Gap. outer portion, fading to a dusty to say, as so little is known brightest point of light) in beige color in its darker inner about these strange radial fea- the sky over the Badlands The Encke Minima are not portion. Furthermore, as tures. Note that if they do formations at the Trail of a true ring division, but instead American astronomer Charles appear, they should be most the Fossil Hunters site at a low-contrast feature (a dim- Wesley Tuttle described Oct. 20, prominent along the morning Dinosaur Provincial Park, ming) caused by longitudinal 1851, the view through Harvard ansa (protruding “handle”) of Alberta. The ground is variations in the ring’s density Observatory’s 15-inch Great Ring B. illuminated thanks to a or transparency. They appear as Refractor at high power showed rising Last Quarter Moon broad fuzzy lanes in the middle that Ring B was “minutely sub- A faint inner ring, or Ring C, off frame to the left. ALAN DYER of Saturn’s A ring. German divided into a great number of has a milky transparency astronomer Franz Encke made narrow rings … not unlike a against the blackness of space. This year’s the first definitive records of series of waves.” However, it appears as a dusky them beginning April 25, 1837. veil when seen against the globe opposition On that night, using a 9.6-inch This year’s opposition may of the planet, which is why it refractor, he noted that the also have a major surprise in was known originally as the may also “outer ring is divided by a line store for us: Saturn’s spokes, Crepe Ring. Astronomer George parallel to the edges into two which are mysterious streaks Phillips Bond of Harvard first have a very close equal parts from both that cut across the rings. suspected its “feebly illumi- sides.” Today, they are the most Astronomers think these spokes nated” form Oct. 10, 1850. But major viewed and imaged feature in are made of micrometer-sized he saw it “with full certainty” Ring A through 4-inch and dust electrostatically held in Nov. 11, not only as “a dark surprise in larger telescopes. place above the rings. They band in front of the planet,” but may be a seasonal phenomenon, as the “filling up of light inside store for The Encke Gap, on the other appearing only during the low- of the inner edge of the inner hand, is one of Ring A’s most angle lighting that occurs near ring [B].” us: Saturn’s elusive visual challenges. This equinox, namely when the rings hyperfine thread of darkness (a are less than or equal to about Today, amateurs using spokes, true gap) in the extreme outer 17° open. But no one knows for quality telescopes as small as portion of Ring A lies less than sure. Spokes have appeared and 3 inches have spied the feature which are one-fifth of the ring from its disappeared before, so the only in its entirety. It remains the outer edge. Saturn’s walnut- way to catch them is to keep least surveyed of Saturn’s mysterious shaped moon Pan is responsible main rings, though it could for keeping the 200-mile-wide streaks that (320 km) gap open. In January 1888, on a night of exceptional cut across seeing, American astronomer James Keeler discovered the gap the rings. through the Lick Observatory 36-inch refractor at high power. Other observers had likely spied the Encke Minima and Encke Gap on earlier dates, but Encke and Keeler’s observations were the most definitive. Today, the Encke Gap is commonly seen and imaged through 10-inch and larger telescopes, though it has been viewed through smaller quality instru- ments at high power, as shown in the sketch on page 50 by David Graham of England. Ring B, the brightest, dens- est, and most pronounced of Saturn’s rings, also displays the most texture, generally allowing WWW.ASTRONOMY.COM 49

potentially be one of the most illusions, they are nonetheless it can be appreciated through fascinating for study. Historical worthy of further scrutiny. the smallest of telescopes, per- observations of Ring C have haps even with the unaided eye. shown it to vary in color and Seeliger effect Generally, Saturn’s rings appear intensity over time, as well as to and Ring A about as bright as the planet’s display asymmetries, brightness globe. In the days leading up to anomalies, and spurious dark In the days leading up to and opposition, however, the rings features. While some, or all, around opposition, the rings of suddenly outshine Saturn before of these curiosities may be Saturn surge in brightness. It is dimming back to their normal the result of optical effects or one of the most visually allur- appearance. German astrono- ing planetary phenomena, and mer Hugo von Seeliger first noticed this change in 1887 and LEFT: Franz Encke’s the phenomenon was named in April 25, 1837, drawing his honor. shows brightness minima in the middle of Two factors come into play to Ring A on each ansa, create the Seeliger effect. First, the protruding parts of when we see Saturn directly the planet’s rings. illuminated by the Sun (as it is during opposition), the planet’s ABHANDLUNGEN DER KÖNIGLICHEN shadow “hides” behind the disk, placing more ring surface into AKADEMIE DER WISSENSCHAFTEN ZU view. As a result, the rings appear brighter. The same direct BERLIN (1838) lighting angle also causes the shadows of individual particles RIGHT: This drawing by David Graham of in the rings to temporarily van- Richmond, North Yorkshire, England, shows ish, enhancing the effect. details he spied while observing Saturn at 286x through a 6-inch refractor owned by Ohio Second, Cassini spacecraft amateur Tom Dobbins. Note the Encke Minima observations of the opposition and Encke Gap in Ring A. DAVID GRAHAM effect in Saturn’s rings reveal that “coherent backscattering” BELOW: The record-groove effect seen in also significantly contributes to Saturn’s rings is most prominent in the brighter the phenomenon. This occurs Ring B when seen through a telescope, as when sunlight interacts with the shown in the drawing by Charles Wesley Tuttle particles in the planet’s rings. at left. The color differences in the rings are Individual reflections off the brought into stunning focus in the Cassini many irregular bits of rock and image at right. LEFT: CHARLES WESLEY TUTTLE/HARVARD; RIGHT: dust combine to produce more coherent, intense light. This light NASA/JPL/SPACE SCIENCE INSTITUTE scatters back to our eyes and makes the rings seem brighter. ABOVE: NASA’s Cassini spacecraft captured the mysterious spokes in Saturn’s Ring B on Oct. 19, 2008, shown at left. Meanwhile, one of the author’s pre-spacecraft sketches of the observed spokes in Saturn’s Ring B is shown Saturn’s Ring A also displays at right. The spokes appeared on the morning ansa and were viewed through a 9-inch refractor at Harvard alternating bright and dark College Observatory Nov. 24, 1976. LEFT: NASA/JPL/SPACE SCIENCE INSTITUTE; RIGHT: STEPHEN JAMES O’MEARA quadrants, known as an asym- metrical azimuthal brightness variations. These features change in intensity depending on the ring elevation angle (between 26° and about 10°), reaching a peak amplitude near 10°. So, the effect may be particularly pronounced during this apparition; expect brightness differences of about 20 to 30 percent between the light and dark quadrants. It’s important to note that around opposition, the azimuthal effect appears to diminish. So, start