Astronomy August 2022

2 ASTRONOMY • AUGUST 2022

Online Content Code: ASY2208 AUGUST 2022 Enter this code at www.astronomy.com/code VOL. 50, NO. 8 to gain access to web-exclusive content FEATURES 32 48 ON THE COVER 16 COVER STORY Sky This Month Capturing the Cloud belts swirl around Jupiter’s Moon in high res southern hemisphere in this image How Juno Giant planet time. captured by Juno Dec. 16, 2017. unmasked Jupiter The digital revolution has MARTIN RATCLIFFE AND enabled amateur astronomers ENHANCED IMAGE BY KEVIN M. GILL (CC-BY) NASA’s plucky probe has ALISTER LING to take crisp, clear images BASED ON IMAGES PROVIDED COURTESY OF NASA/ brought us unprecedented that would have been views of the solar system’s 34 the envy of professionals JPL- CALTECH/SWRI/MSSS . biggest planet, from its just a few decades ago. enigmatic aurorae to its Star Dome and COLUMNS dramatic storms. BEN EVANS Paths of the Planets LEO AERTS AND KLAUS BRASCH Strange Universe 12 25 RICHARD TALCOTT; 54 ILLUSTRATIONS BY ROEN KELLY BOB BERMAN Catch Pluto this summer The star that 40 changed the cosmos Binocular Universe 13 Planet or not, Pluto is a worthy target. MICHAEL E. BAKICH The strange case An astroimager follows in PHIL HARRINGTON of the eyeball planets Edwin Hubble’s footsteps to 28 prove the utter vastness of our Secret Sky 14 These tidally locked worlds universe using a single star. Scopes for city dwellers could be the key to finding life STEPHEN JAMES O’MEARA in the universe — if they exist. ROD POMMIER Don’t let bright lights prevent Observing Basics 15 you from exploring cosmic MICHAEL CARROLL 62 sights. PHIL HARRINGTON GLENN CHAPLE Ask Astro 7 Skydiving onto Venus. QUANTUM GRAVITY ONLINE Picture of Trips and Sky This Dave’s FAVORITES the Day Tours Week Universe What you need to know Gorgeous The inside about the universe this Go to www.Astronomy.com photos from Travel the world A daily digest scoop from month: Hubble spots our readers. with the staff of of celestial the editor. the farthest found star, for info on the biggest news and events. a stellar remnant leaks Astronomy. antimatter, a black hole observing events, stunning photos, goes rogue, and more. informative videos, and more. IN EVERY ISSUE From the Editor 4 Astro Letters 6 New Products 61 Advertiser Index 61 Reader Gallery 64 Breakthrough 66 Astronomy (ISSN 0091-6358, USPS 531-350) is published monthly by Kalmbach Media Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Periodicals postage paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to Astronomy, PO Box 8520, Big Sandy, TX 75755. Canada Publication Mail Agreement #40010760. W W W.ASTRONOMY.COM 3

FROM THE EDITOR A very special star Editor David J. Eicher Assistant Design Director Kelly Katlaps Edwin Hubble poses Edwin Hubble was neither the most with a model of the accomplished astronomer on Earth EDITORIAL telescope he used nor the most well-liked by his col- Senior Editor Mark Zastrow to unlock the nature leagues. Yet, in the fall of 1923, he discovered Production Editor Elisa R. Neckar of galaxies. a special star that turned our understanding Senior Associate Editor Alison Klesman of the cosmos on its head. On the night of Associate Editor Jake Parks HUB 1033 (11), EDWIN POWELL October 5/6, using the 100-inch Hooker Associate Editor Caitlyn Buongiorno Telescope at Mount Wilson Observatory out- Editorial Assistant Samantha Hill HUBBLE PAPERS, THE HUNTINGTON side Los Angeles, Hubble recorded a deep exposure of what was then called the ART LIBRARY, SAN MARINO, CALIFORNIA Andromeda Nebula. He was intensely curious Illustrator Roen Kelly about so-called spiral nebulae: Were they Production Specialist Jodi Jeranek clouds of gas and stars within our galaxy, or very distant, mysterious objects? CONTRIBUTING EDITORS Hubble was elated with his glass-plate Michael E. Bakich, Bob Berman, Adam Block, negative. He believed he had found a nova, Glenn F. Chaple Jr., Martin George, Tony Hallas, an exploding star, within the nebula, and he Phil Harrington, Korey Haynes, Jeff Hester, Alister Ling, marked it with an N. Subsequent checking Stephen James O’Meara, Martin Ratcliffe, Raymond Shubinski, back at his office, however, nearly made him fall out of his chair. The Richard Talcott star demonstrated a regular and well-known pattern of dimming and brightening: It was a Cepheid variable. He changed the marking to EDITORIAL ADVISORY BOARD “VAR!” The star’s incredibly faint nature, at around 19th magnitude, Buzz Aldrin, Marcia Bartusiak, Jim Bell, Timothy Ferris, meant the “nebula” was immensely far away. In his landmark observa- Alex Filippenko, Adam Frank, John S. Gallagher lll, tion, Hubble had discovered the nature of galaxies and the first clues Daniel W. E. Green, William K. Hartmann, Paul Hodge, to the huge cosmic distance scale. Hubble thought what could then be Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern, renamed the Andromeda Galaxy was a million light-years off, three James Trefil times larger than the previously imagined size of the whole universe. (We now know it lies 2.5 million light-years away.) Kalmbach Media This legendary star has received scant attention since the days of Hubble, but astronomy enthusiast Rod Pommier, a frequent contribu- Chief Executive Officer Dan Hickey tor to Astronomy, set out to hunt for the star, succeeding in imaging it Chief Financial Officer Christine Metcalf with his 14-inch scope. I know that a few others, notably Tony Hallas, Senior Vice President, Consumer Marketing Nicole McGuire have also imaged this star, which has come to be known as M31-V1. Vice President, Content Stephen C. George Rod’s story of cosmic discovery (page 54), retracing the steps of Vice President, Operations Brian J. Schmidt Hubble’s great discovery, will open your eyes to the amazing capabili- Vice President, Human Resources Sarah A. Horner ties amateur astronomers now have with their telescopes and digital Circulation Director Liz Runyon equipment, ready to be unlimbered on any given dark night. Director of Digital Strategy Angela Cotey Director of Design & Production Michael Soliday Yours truly, Retention Manager Kathy Steele Single Copy Specialist Kim Redmond Follow the David J. Eicher Dave’s Universe blog: Editor ADVERTISING DEPARTMENT www.Astronomy. 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ASTRO LETTERS A rainbow appears Rain and shine bests for beginners: The Edmund Sky Guide by Terence on clouds above the Dickinson and Sam Brown, and the Edmund Mag 5 Gemini South telescope I’ve just read Stephen O’Meara’s Star Atlas. As a youngster many years ago, I found these in Chile. INTERNATIONAL GEMINI April 2022 column, “The impropri- two 36-page books both engaging and comprehensive. ety of rainbows.” I was intrigued OBSERVATORY/NOIRLAB/NSF/AURA/ by the fact that many cultures refer — Vance Purdy, Rancho Palos Verdes, CA MANUEL PAREDES to rain while the Sun is in the sky as a monkey’s wedding (or some Errata We welcome animal’s wedding). In Portuguese, your comments there are also two popular say- In the map titled “A Warped View,” on page 59 of at Astronomy Letters, ings about rain and Sun relative to someone’s wed- the February issue, the scale is given as +/-600,000 P.O. Box 1612, ding. When it’s raining and the Sun comes back, we light-years. It is actually +/-60,000 light-years. Waukesha, WI 53187; say: Chuva com sol, casamento de espanhol, meaning or email to letters@ “Raining with Sun, Spanish wedding.” When it’s sunny In the Paths of the Planets section of our March issue, astronomy.com. and it starts raining, we say: Sol com chuva, casamento the path of the Moon was depicted incorrectly, with the Please include your de viúva, meaning “Sun with rain, widow’s wedding.” Moon going to the south of the sky’s June solstice point name, city, state, and and north of the December solstice point. The reverse is country. Letters may — Lucca Vanoni Ruggiero, São Paulo, Brazil true: The Moon is currently south of the ecliptic around be edited for space the December solstice point and north of it at the June and clarity. Reading the sky solstice point. Raymond Shubinski brought back some fond memo- The Ask Astro section of the March issue incorrectly ries with his “Check out these classic sky guides” piece stated that a Type Ia supernova results in the birth of (April 2022). My copies of Norton’s and Olcott’s hard- a new stellar remnant. Instead, this type of supernova cover books are somewhat beyond well-worn. However, normally obliterates the white dwarf completely. I would like to add two I personally consider all-time ECLIPSE ESSENTIALS Get everything you need to learn about eclipses past, present, and future! Shop Today at: MyScienceShop.com/EclipseShop Sales tax where applicable. While supplies last. P40395 6 ASTRONOMY • AUGUST 2022

QG QUANTUM GRAVITYEVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH SCIENCE: NASA, ESA, BRIAN WELCH (JHU), DAN COE (STSCI); IMAGE PROCESSING: NASA, ESA, ALYSSA PAGAN (STSCI). BOTTOM FROM LEFT: NASA/JPL-CALTECH; NASA/KIM SHIFLETT; HARIKANE ET AL. SNAPSHOT HOT MAD DASH HELIOPHYSICIST MOST DISTANT GALAXY BYTES More than a year after PASSES At 13.5 billion light-years, HUBBLE its arrival, NASA’s Solar science pioneer HD1 is the farthest SPIES THE Perseverance rover Eugene Parker died known galaxy. Strangely, FARTHEST made a 31-martian- March 15. In 2018, it has a surplus of light, STAR day-long beeline to Parker became the suggesting it is home an ancient river delta first living person to to either the earliest A cosmic on the edge of Jezero witness the launch of a supermassive black magnifying glass Crater that scientists spacecraft bearing his hole or hypothetical made it possible. hope once housed name — NASA’s Parker Population III stars — microbial life. Solar Probe. the universe’s first stars. At the risk of sounding like a broken record, NASA’s Hubble Space Telescope has broken another record. With the help of a phenomenon called gravitational lensing, the aging observatory recently captured this image of the most distant star ever seen, nicknamed Earendel. “When the light that we see from Earendel was emitted, the universe was less than a billion years old,” said Victoria Strait, a postdoc at the Cosmic Dawn Center in Copenhagen, in a press release. “At that time, it was 4 billion light-years away from the proto-Milky Way, but during the almost 13 billion years it took the light to reach us, the universe has expanded so that it is now a staggering 28 billion light-years away.” Earendel shines millions of times as brightly as the Sun and might have weighed as much as 500 times the mass of the Sun, though researchers think it was more likely between 50 and 100 solar masses. Either way, astronomers say Earendel lived fast and died young, blowing itself apart long, long ago. — JAKE PARKS WWW.ASTRONOMY.COM 7

QUANTUM GRAVITY UP IN THE AIR. Russia RUSSIA’S WAR IN UKRAINE has cast doubt on its REORDERS SPACE ALLIANCES future participation in the International Space Fallout from international sanctions leaves Station, pictured here Russia’s space program isolated. Nov. 8, 2021, from the SpaceX Crew Dragon Endeavour. NASA The repercussions of Russia’s In one of the highest-profile breaks, ruling council March 17, adding that invasion of Ukraine — the largest the European Space Agency (ESA) it is “fully aligned with the sanctions land war in Europe since World War II, announced March 17 it would suspend imposed on Russia by its Member still ongoing as of this writing — have work on the ExoMars rover, which it States.” extended not just beyond Ukraine’s bor- built in a joint mission with Roscosmos. ders but also above Earth’s atmosphere. The rover had been scheduled to ESA officials are now exploring When Russia invaded Ukraine launch aboard a Russian Proton rocket options to team up with other nations Feb. 24, much of the world responded from the Baikonur Cosmodrome later and agencies to finish the mission. by levying economic sanctions on in 2022. Russia had also been set to The rover, named Rosalind Franklin, Russia and rushing aid and weapons provide the landing vehicle that would is “technically ready for launch,” says to Ukraine. In response, the Russian carry the rover to the martian surface. ESA. But in May 3 comments reported space agency Roscosmos cut ties and by SpaceNews at a conference in Denver, canceled agreements with a string “As an intergovernmental ExoMars ESA project scientist Jorge of spacefaring nations. The war has organization mandated to develop Vago said that realistically, the rover also forced the international scientific and implement space programs in would not launch before 2028. community to weigh the moral cost full respect with European values, we of collaborations with Russia, pushing deeply deplore the human casualties FRAYING TIES relationships forged after the Cold War and tragic consequences of the aggres- beyond the breaking point. sion towards Ukraine,” the agency said ExoMars isn’t the only collaboration in a statement after a meeting of its that has fallen by the wayside. In the days immediately after the invasion, 8 ASTRONOMY • AUGUST 2022

PLAN A. The ExoMars rover Rosalind Franklin came after Rogozin demanded March 2 QUICK that OneWeb guarantee its satel- TAKES explores the martian surface in this artist’s lites would only be used for civilian concept. In the background at left lies the purposes and that the U.K. divest its SLS SLIPS AGAIN now-cancelled Russian-built lander. ESA/ATG partial ownership of the company. Both demands were rebuffed. Later NASA called off a wet dress rehearsal MEDIALAB that month, OneWeb announced it had for its new Moon rocket, the Space reached a deal with SpaceX to conduct Roscosmos responded to international future launches of its satellites. Launch System (SLS), due to a series of sanctions by severing a series of ties issues including a leaking hydrogen with the U.S., U.K., and Europe. One project that has remained supply line and a faulty valve. The outwardly unaffected by the war in On Feb. 26, Roscosmos Director Ukraine is the International Space rocket’s first uncrewed flight, Artemis 1, General Dmitry Rogozin said Russia Station (ISS), in which Russia is a key is now expected to launch no earlier would halt Soyuz rocket launches from partner — for now. However, Rogozin than August. Europe’s spaceport in French Guiana. has threatened to pull Russia out of Previously scheduled Soyuz launches the ISS and undock Russian modules NOT-SO-STANDARD MODEL of European payloads included Galileo and spacecraft. Russia contributed satellites for Europe’s global navigation the station’s service module, which Scientists at Fermilab pinned the mass system and ESA’s Euclid infrared space is responsible for keeping the ISS of the W boson, a fundamental force- telescope. ESA hopes to launch the aloft, periodically boosting its orbit carrying particle, to about 80 times the craft on different rockets — perhaps to counteract drag from Earth’s upper mass of a proton (with an unparalleled the agency’s own upcoming Ariane 6 atmosphere. precision of 0.01 percent). This puts the or Vega-C launchers. In a Feb. 28 media teleconference, measurement in tension with the Also on Feb. 26, Rogozin declared NASA’s head of human spaceflight, Standard Model of physics. NASA could no longer participate in Kathryn Lueders, said SpaceX and Russia’s Venera-D mission, a Venus Northrop Grumman could potentially STEP ASIDE STARLINK orbiter and lander planned for 2029. provide reboost capabilities. But, she (This was largely ceremonial, as no added, it would still be difficult to oper- On April 5, Amazon announced it formal role for NASA had yet been ate the station without some Russian had inked deals with three rocket agreed on.) cooperation. companies for up to 83 launches over the next five years, which will deliver And on March 4, Rogozin canceled Russia’s collapse in relations with the more than 3,200 satellites into low- a contract for a series of launches with U.S. and Europe comes as it ramps up the London-based internet provider cooperation with China on plans for a Earth orbit to provide internet OneWeb, even as 36 of the company’s lunar space station and base. If China connectivity around the globe. craft sat loaded in a Soyuz rocket on a remains willing to work with what is Baikonur launchpad. The cancellation now a pariah state, the future of space ALIEN ETHER exploration may look less like the global cooperative model of the ISS and more For the first time, astronomers have like a Cold War, with blocs of spacefar- detected dimethyl ether — a precursor ing nations. — MARK ZASTROW to larger organic molecules that can spur life — within the planet-forming Pulsar leaks antimatter X-RAY: NASA/CXC/STANFORD UNIV./M. DE VRIES; OPTICAL: NSF/AURA/GEMINI CONSORTIUM disk around another star. With nine The pulsar J2030+4415 (J2030 for atoms, the compound is the largest yet short) — a dense stellar remnant with a strong magnetic field and fast spin — found in such a disk. is traveling through our galaxy at about 500,000 mph (800,000 km/h). This LUNAR SENTRY causes its winds, which contain both matter and antimatter, to trail behind it, The Earth-Moon system could serve while a bow shock of gas leads in front. as an enormous gravitational-wave But somehow, about 20 to 30 years ago, the bow shock slowed down and J2030 detector capable of picking up smashed into it, causing a particle leak. microhertz signals from the ancient The result: a beam of matter and antimatter 40 trillion miles (64 trillion kilometers) long. universe. These waves would create This image, from research published March 25 in The Astrophysical Journal, suggests that tiny changes in the distance between pulsars could be partially responsible for the large swaths of positrons — the antimatter counterpart of the electron — that mysteriously dot the universe. — CAITLYN BUONGIORNO the two bodies, which scientists currently track to within 0.04 inch (1 millimeter). OLDER DRYAS A new analysis of the 19-mile-wide (31 kilometers) Hiawatha Crater beneath Greenland’s ice shows the impact scar is some 58 million years old. That means the impact responsible was not related to Younger Dryas — a period of global cooling some 12,000 years ago — as previously speculated. — J.P. WWW.ASTRONOMY.COM 9

QUANTUM GRAVITY A strange FRB in a strange place Fast radio bursts, or FRBs, are in a dense grouping of old stars called PLANETBIRTH. The hot, glowing mass at the brief, intense flashes of radio a globular cluster. Finding a magnetar — waves believed to arise on extremely the product of short-lived stars — in this bottom of this image is a nascent planet. The magnetic neutron stars called magnet- environment is unexpected, the team central star, AB Aurigae, has been masked by ars. One-off bursts are difficult to trace, said. All other FRBs with known posi- the instrument that snapped the image at the but a few repeat, allowing researchers tions lie in regions of distant galaxies Subaru Telescope in Hawaii. T. CURRIE/SUBARU TELESCOPE to more easily determine their origin. that house young, massive stars. That’s exactly what a team studying one PROTOPLANET repeater, called FRB 20200120E, accom- So, how did the magnetar power- plished — with unexpected results. Their ing FRB 20200120E form in such an SHAKES UP work was published Feb. 23 in Nature unexpected place? There are two and Nature Astronomy. possibilities: first, a long-predicted FORMATION Bursts from FRB 20200120E are as but never-before-seen phenomenon short as 60 billionths of a second. That called accretion-induced collapse. THEORY indicates they are coming from “a tiny This is when a white dwarf pulls mass volume in space, smaller than a soc- from a companion and tips over a Astronomers have spotted a spectacular cer pitch,” said team co-leader Kenzie cosmic weight limit, collapsing into a stellar maelstrom birthing a planet Nimmo of the Netherlands Institute for denser neutron star. Although posited roughly nine times the mass of Jupiter. Radio Astronomy (ASTRON) and the to be rare in globular clusters, it’s the University of Amsterdam in a press simplest and likeliest explanation, the The star is AB Aurigae, about release. The fact that the signal origi- team says. Alternatively, perhaps FRB 530 light-years away. Just a couple of nates from such a small area supports 20200120E is the result of a merger million years old, it is still surrounded by the idea that FRBs come from magne- between two white dwarfs, two neutron a disk of leftover gas and debris — and a tars, as neutron stars themselves are stars, or one of each. Such mergers are prominent hot clump at its outer fringes small: roughly the size of Manhattan. more common in globular clusters and that appears to be a protoplanet. Using several radio telescopes, could create a neutron star. the team tracked FRB 20200120E to The team verified this with observa- its origin. It lies in M81, just 12 million For now, the mystery remains. And tions from the 8.2-meter Subaru Telescope light-years away. That makes it the clos- regardless of the answer, it indicates atop Mauna Kea in Hawaii and the est FRB to date. Even odder, the FRB is there are likely many ways to create the Hubble Space Telescope, including data magnetars that power these strange from Hubble’s archives taken 13 years signals. — ALISON KLESMAN earlier. Their results were published April 4 in Nature Astronomy. MYSTERIOUS ORIGINS. Researchers have traced a fast radio burst to a globular cluster full of Especially unusual is the protoplanet’s old stars in a nearby galaxy. But the magnetars believed responsible for FRBs are young, raising great distance from its star — roughly questions of how it could have gotten there. ASTRON/DANIËLLE FUTSELAAR, ARTSOURCE.NL 8.6 billion miles (14 billion kilometers), or more than twice the distance of Pluto from 10 ASTRONOMY • AUGUST 202 2 our Sun. This is hard to square with the most popular model of planet formation, called core accretion, in which planetary cores begin forming when dust grains and pebble-sized bits of debris glom on to each other. The planet, named AB Aurigae b, is so far out from its star that there’s likely not enough debris to form a large core. This makes it powerful evidence for an alternate method of planet formation called disk instability, where large clumps of gas in the protoplanetary disk become unstable and collapse under their own gravity. This would form planets directly, similar to how stars are born. — M.Z.

22,000 miles (36,000 km) In geostationary orbit, satellites are ACTION barely impacted by Earth’s atmosphere Move 200 miles (320 km) and could stay in orbit indefinitely. up to a graveyard orbit GPS satellite INVISIBLE WANDERER. Astronomers may have HUNDREDS OF MILLIONS OF YEARS AGO detected a lone, or rogue, black hole by watching Dinosaurs’ era and before how its gravity bends the light of a background star. UTE KRAUS (BACKGROUND MILKY WAY PANORAMA: AXEL MELLINGER), 750 miles (1,200 km) INSTITUTE OF PHYSICS, UNIVERSITÄT HILDESHEIM If the Roman Empire had Jason-2 satellite launched a satellite to this Found: A rogue height, it would just now ACTION black hole be falling back to Earth. De-orbit to quickly burn up in the atmosphere Stellar-mass black holes are formed 2,000 YEARS AGO The Roman Empire when a massive star dies. To date, astron- omers have only indirectly detected black 500 miles (800 km) holes by watching them devour material from a companion star. Satellites at this Iridium satellite height take between But now, researchers think they’ve found 100 to 150 years to ACTION an isolated stellar-mass black hole some return to Earth. De-orbit to quickly burn 5,200 light-years away. The find has been up in the atmosphere submitted to The Astrophysical Journal. 100-150 YEARS AGO Era of Charles Darwin The team combined two techniques to spot the black hole. The first, microlensing, 310 miles (500 km) is a form of gravitational lensing that occurs when a small celestial object crosses in This is where Tiangong and the ISS, the International ASTRONOMY: ROEN KELLY, AFTER ESA/UNOOSA front of a distant star. That object’s grav- Hubble Space Telescope, and Starlink Space Station ity bends and magnifies the starlight as satellites orbit. The satellites at and below this it travels past. Astronomers can estimate orbit fall back to Earth in less than 25 years. ACTION the nearer object’s mass by how long the De-orbit to quickly burn event lasts. A long lensing event caused by up in the atmosphere something invisible could be a black hole. SATELLITE FALL TIME FASTFACT But a faint star moving slowly could An impact from a create the same effect. So, the team also Return trip. In February, a solar storm hit 49 of SpaceX’s debris fragment less than applied astrometry, the precise measure- ment of objects’ positions on the sky. By Starlink satellites, destabilizing their orbits enough to half an inch (1.3 centimeters) seeing how much the background star’s position appeared to shift during the send them careening back to Earth. Thankfully, they were wide can generate as lensing event, astronomers could better determine the nearer object’s mass: just small and burned up in Earth’s atmosphere, but not every much energy as a small over seven times the mass of the Sun. object circling above our heads will simply disappear on its car crashing at 25 mph Such an object would be shining brightly if it was a star. That would mean it must way down. While thus far no one has died from space debris (40 km/h). be a black hole. (that we know of), space agencies do have contingency plans. However, there’s another possibility: A separate team’s analysis of the same event Above we take a look at how long — in comparison to Earth timelines — it would puts the object between about 1.5 and 4 solar masses, which means it could be take a satellite at various heights to fall naturally, and the actual plans space a neutron star instead. Astronomers have never detected an isolated neutron star agencies have in place, should satellites at specific heights start to fall. —C.B. either, so it would still be a remarkable discovery. — ASHLEY BALZER WWW.ASTRONOMY.COM 11

STRANGE UNIVERSE Black as night that’s pitch black under all conditions, as long as you observe it from the outside — an excellent safety pre- How do we find true darkness? caution. But inside these dead suns there’d be plenty of light, since once you pass the event horizon, you’d still see by the light of all the infalling photons around you. We care so much about blackness that some of us own sky-quality meters, which quantify celestial brightness in magnitudes per square arcsecond. These units also measure surface brightness, whose impor- tance we saw early this year as we struggled to glimpse Comet Leonard. When 5th magnitude, the comet might have seemed to match the Little Dipper’s faintest star, visible with the naked eye. But as we know, a star’s brightness is concentrated in a point, while a comet has it smeared over a large area, which changes everything. For you to really see any celestial object, it must be brighter than its background. The glow of a cigarette at the Moon’s distance would be a 30th-magnitude dot, technically detectable by the Giant Magellan Telescope. But since the sky is always brighter than that, the job of enforcing lunar no-smoking ordinances would be challenging for Earth-based police, provided they’re observing visually. Even at night, Earth is It may seem cruel and unusual that days get Human vision has more than a mere darkness-cutoff enveloped in the soft shorter the moment summer begins. But this point. We’re equipped with two radically different light- light of airglow, visible expansion of night is ideal for exploring the detection systems. Backyard astronomers often use from the International shadowy topic of darkness. their scotopic mechanism, consisting of some Space Station as an 120 million rod-shaped retinal cells. These are sensitive orange-green aura. to low light levels, letting some of us see the Andromeda NASA Actually, the only convenient way to experience full Galaxy or even the Hercules Globular Cluster from darkness is to lock yourself in a closet. The night cer- dark backyards without optical aid. But these cells need tainly isn’t black; even in the most rural a few minutes of stimulation to work and are regions, the heavens aren’t truly dark. The best when dark adapted. They also suffer source of this illumination is the sky itself. What’s dark from colorblindness, unable to observe deep The name for the sky’s natural fluores- in one reds. Worst of all, rods deliver only 20/200 resolution. Thus, as pointed out on this page cence is airglow. It was discovered by Swedish situation long ago, a galaxy’s blurriness comes not physicist Anders Ångström in 1868, and it’s caused by incoming solar particles exciting can be light from your telescope but your eyesight. our atmosphere’s gases to produce an effect in another. Nobody has ever visually seen intricate galac- like constant miniature, widespread aurorae. tic detail, not even when allowed to peek This background glow varies greatly, but can through the world’s largest telescopes. be up to three times brighter than the com- When a celestial object’s brightness bined light of all the stars. That’s part of why you can exceeds a certain level that varies with wavelength, our still see where you’re going even at night on the darkest eyes switch to their 6 million cone-shaped cells, giving country road — as long as you’re under the sky, rather us photopic vision. Now we see in full color and get than a forest canopy. instant results with 20/20 sharpness. Knowing this So if night is not truly dark, what is? Coal and asphalt explains why stars too dim to show color when viewed BY BOB BERMAN only seem black compared with more reflective objects with the naked eye, like the Pleiades, burst into their Bob’s recent book, viewed in identical conditions. A light meter — true blue when binoculars ramp up their brightness. Earth-Shattering remember those? — can confirm that a black cat in Meanwhile, if you really want to see what black is like (Little, Brown and sunlight is still 2,000 times whiter and brighter than a Company, 2019), white cat under a Full Moon. What’s dark in one situa- — I’ll meet you in the closet. explores the greatest tion can be light in another. cataclysms that have BROWSE THE “STRANGE UNIVERSE” ARCHIVE shaken the universe. What about a black hole? Here finally is something AT www.Astronomy.com/Berman 12 ASTRONOMY • AUGUST 2022

BINOCULAR UNIVERSE Poniatowski’s Bull is marked by 68 Ophiuchi, while 66 Ophiuchi is the western eye. Fourth-magnitude 72 Ophiuchi marks the end of the eastern horn, while the western horn extends Hunt the skies for summer’s Taurus. toward 6th-magnitude HD 163641 and beyond. Poczobut drew the bull’s body among the faint stars northeast of the V, but he lost me there. Three of the stars that form the triangular head of Taurus Poniatovii — 67, 68, and 70 Ophiuchi — along with a scattering of about a dozen others belong to a sparse open cluster cataloged as Melotte 186 72 53 (Collinder 359). The group is centered on 67 Ophiuchi and spans 4°. But ironically, its size also makes it difficult HD IC to confirm. Which stars in this densely populated area 162641 4665 belong to the cluster and which do not is a chore best left to the professionals. A study published in Astronomy and 66 Astrophysics in 2006 suggested this may not be a cluster 73 at all, but rather a “moving group” of stars following a 67 similar path through the Milky Way. 70 That same study mentioned that Melotte 186 might 68 be linked to our next target, IC 4665, as both troupes exhibit similar proper motion through the galaxy. Located some 1,100 light-years away, there is no mis- taking the identity of open cluster IC 4665 through binoculars. It can be found just 1° north-northeast of This annotated version As most readers know, there are 88 constella- Cebalrai. On dark, clear nights, a faint hint of this cluster of chart IX within tions adorning the sky. These were codified is visible to the eye alone. Swing your binoculars its way Johann Bode’s in 1930 by the International Astronomical and IC 4665 resolves into a fine collection of about ten Uranographia shows Union through international agreement. Before this, 7th- to 9th-magnitude stars, along with many fainter the position of IC 4665. points. Although its stars are not tightly packed, IC 4665 Unlike Messier or the stands out in binoculars. Depending on how faint you Herschels, Bode plotted this object — astronomers could create and publicize their You’re can see, you might see the brighter stars as although he failed to own constellations, hoping they would catch forming a triangle, a diamond, a short-tailed label it. IMAGE COURTESY: on with the masses. kite, or even a distorted H. HISTORY OF SCIENCE COLLECTIONS, UNIVERSITY OF OKLAHOMA Although many of these obsolete constel- probably Our last stop this month is the binary star LIBRARIES lations have faded away as footnotes in familiar with 53 Ophiuchi. You’ll find it 3° south of astronomical history books, there is one lost Rasalhague (Alpha [α] Ophiuchi) at the top of pattern in the summer sky that is fun to spot winter’s the constellation’s pentagonal form. The through binoculars. You’re probably familiar Taurus the binary’s 6th-magnitude primary star is with winter’s Taurus the Bull. But what about Bull. But accompanied by an 8th-magnitude compan- Taurus Poniatovii? what about ion, separately cataloged as SAO 122525, about 42\" to its south. Both are spectral type A white Taurus Poniatovii, or Poniatowski’s Bull, Taurus stars located around 370 light-years away. was a small constellation created in 1777 by Poniatovii? They are just on the edge of resolution through Marcin Poczobut, a Polish-Lithuanian astronomer and the director of Vilnius my 10x binoculars, but should be relatively Observatory. Poczobut devised the constella- easy at 12x and up. To resolve the companion, tion to honor Stanislaus Poniatowski, the king of Poland you need to reduce shaking, however. If you don’t have and Lithuania at the time. image-stabilized binoculars, brace them against some- Like its namesake constellation in the winter, Taurus thing. Better yet, mount them on a tripod. BY PHIL Poniatovii is drawn from a V-shaped pattern of stars that I welcome observations, suggestions, and comments. HARRINGTON fills the field of my 10x50 binoculars. The stars range Contact me through my website, philharrington.net. Phil received the from 4th to 6th magnitude and can be found just east of Until next month, remember that two eyes are better Walter Scott Houston Cebalrai (Beta [β] Ophiuchi), the eastern shoulder of than one. Award at Stellafane Ophiuchus. If you compare the formation to winter’s 2018 for his lifelong Taurus, then the role of bright-eyed Aldebaran is played BROWSE THE “BINOCULAR UNIVERSE” ARCHIVE AT work promoting and by 6th-magnitude 73 Ophiuchi. The tip of the bull’s nose www.Astronomy.com/Harrington teaching astronomy. WWW.ASTRONOMY.COM 13

SECRET SKY Volcanic twilights lunaraureole—formedby the diffraction of light by water droplets in clouds — The Tonga eruption early this year yielded an array has a radius ranging from of atmospheric phenomena. 0.4° to several degrees, depending on droplet size. The radius of Bishop’s Ring, however, usually consists of a roughly 20° silvery blue interior surrounded by a diffuse, smoky orange outer ring (adding an additional 10° to 20° or more to the Ring’s radius, depending on particle size). Sereno Edwards Bishop of Honolulu first recorded ABOVE: Glowing The powerful Jan. 15, 2022, eruption of the the phenomenon in the volcanic aerosols and Hunga Tonga-Hunga Ha‘apai volcano in the aftermath of the 1883 eruption of Indonesia’s Krakatau crepuscular rays volcano. More than a century later, following the 1991 formed this display Feb. 8, 2022, over South Pacific archipelago nation of Tonga eruption of Mount Pinatubo in the Philippines, lidar Maun, Botswana. produced plumes that reached an altitude of 36 miles studies of Bishop’s Ring found that this diffraction STEPHEN JAMES O’MEARA (58 kilometers). The plume contained 400,000 tons of phenomenon was caused by frozen sulfuric acid TOP RIGHT: Jupiter shines through sulfur dioxide, which drifted west with the strato- particles with a radius of about 0.8 microns. volcanic twilight clouds Jan. 23 (top). spheric winds — and soon began to produce remarkable The Tongan volcanic clouds vanished after Jan. 25, The sky evokes Edvard Munch’s The sunsets in the Southern Hemisphere. — only to return 10 days later, creating Scream (bottom), which has been Stunning images appeared in the news as further stunning displays (although the linked to volcanic twilights from 1883’s the cloud swept west over Australia. The rippled rippling effect was diminished). February’s Krakatau eruption. Five days later, the cloud passed over sky put on waxing Moon also allowed me to measure STEPHEN JAMES O’MEARA; southern Africa, including my home in phenomenal Bishop’s Ring visually and photographically. Maun, Botswana. It arrived as a high- shows of light, Interestingly, the radius of the ring near First NATIONAL GALLERY OF NORWAY altitude haze blanketing the Sun, which color, texture, Quarter Moon was only about half the shone as if seen through frosted glass. Closer radius near Full Moon, a 10° inner aureole BOTTOM RIGHT: inspection of the haze revealed it was com- and tone. versus a 20° inner aureole. In both cases, the Bishop’s Ring as seen shortly before night posed of irregularly spaced ripple clouds, outer aureole essentially matched the size of Feb. 8, centered on a near First Quarter giving the sky a crinoline texture. Contrast the inner aureole. Moon. A volcanic glow lingers in the between the clouds and sky intensified around the time It is unclear how long the atmospheric effects will west. STEPHEN JAMES O’MEARA of sunset, when they underwent magnificent color linger or how widespread across the globe they will be. changes, morphing from silvery blue to tangerine As always, send any observations you have made of infused with lemon to a velvety scarlet reminiscent of these phenomena to [email protected]. Edvard Munch’s The Scream. As the Sun set, the clouds in the west appeared so optically thick that I couldn’t imagine starlight penetrating them. But come twilight, the stars and planets burned through them seemingly unimpeded. Over the next three days, the rippled sky put on phenomenal shows of light, color, texture, and tone. Even after the official start of night, volcanic glow and ruffled clouds remained visible to the unaided eye close BY STEPHEN to the western horizon for several minutes. JAMES O’MEARA Stephen is a globe- Bishop’s Ring BROWSE THE “SECRET SKY” ARCHIVE AT trotting observer who www.Astronomy.com/OMeara is always looking The rarest of the phenomena was the occurrence of for the next great Bishop’s Ring — an enormous single-ringed aureole of celestial event. light centered on the Sun or Moon. Typically, a solar or 14 ASTRONOMY • AUGUST 2022

OBSERVING BASICS Safely observe Fortunately, I also learned that I could still see the Sun with my little refractor by employing a simple technique the Sun Your eyes are worth protecting. called solar projection. All I had to do was aim my scope at the Sun, not with the finderscope, which should be capped or entirely removed, but using the scope’s shadow as a guide. I would adjust the telescope tube to make its shadow on the ground as small as possible. And once the telescope was on target, the eyepiece would light up with sunlight. I then held a piece of white cardboard about a foot away from the eyepiece and adjusted the focus until the bright circle of light (the Sun’s projected image) was sharp at the edges. Once again, I could follow the antics of sunspots — maybe not as clearly as I could with direct viewing, but at least with minimal risk to my eyes. During those early years of solar observing, I learned that my little refractor is an ideal telescope for projecting the Sun’s image. Lacking secondary mirrors, refracting telescopes are less likely to suffer internal heat damage than reflectors or catadioptrics. My scope’s modest 2.4- inch aperture also captures less sunlight (and therefore Seen through a hazy “Danger ahead!” You don’t usually associate heat) than a larger telescope. The 20mm Huygenian sky at sunset, the Sun this warning with a hobby as seemingly eyepiece that came with it yielded a magnification of 35x, in this two-exposure innocuous as backyard astronomy. Still, there ample for a celestial body that’s a half-degree across. shot features a large Moreover, the simple Huygenian design, scorned by seri- group of sunspots on ous amateur astronomers, is perfect for solar projection its eastern limb. The image was taken with is an inherent risk to life and limb any time you drive because it consists of two separated lenses. Concentrated a 2.6-inch refractor to and from a remote observing site or skygaze alone in solar heat can “cook” a more complex (and expensive) and a Canon 60Da an unfamiliar environment. Observers in desert areas eyepiece composed of one or more cemented lenses. June 30, 2014. ALAN DYER must worry about venomous snakes and scorpions. And Projecting the Sun’s image onto cardboard may have in humid climates, a mosquito or tick bite can lead to a been a sensible alternative to risking permanent blind- potentially fatal disease. Frigid wintry ness, yet I still yearned to view the Sun weather also brings its own hazards, like directly and safely. For that reason, I invested slippery ice and frostbite. With proper in a full-aperture mylar solar filter that However, perhaps the most dangerous equipment would fit my refractor. Unlike a screw-in astronomical undertaking — at least to the and a few solar filter, an aperture solar filter is affixed eye — is solar observing. I avoided this to the front of the telescope tube, filtering out activity during my early years as an amateur simple sunlight before it enters the scope. Whether astronomer. But in the summer of 1971, I techniques, comprised of mylar, glass, or polymer film, acquired a 60mm f/11 refracting telescope. at last, the this setup offers views of the Sun’s photo- Among its accessories was a solar filter that Sun was truly sphere without the risk of shattering solar screwed into the eyepiece. At last, the Sun mine to safely filters or cooking eyepieces. With proper was mine to explore! The filter produced a equipment and a few simple techniques, at “white light” image of the Sun, revealing explore! last, the Sun was truly mine to safely explore! activity on its surface, or photosphere. I Now it’s your turn to own the Sun. Be it remember the excitement of seeing sunspots by projecting its image with a small refractor for the first time. Day after sunny day, I watched, spell- or by viewing it directly with a larger scope fitted with bound, as they seemingly appeared from nowhere before an aperture filter, the Sun can be a safe, satisfying target eventually fading back into oblivion, all the while for backyard astronomers. Just watch out for rattle- BY GLENN CHAPLE drifting across the face of our life-sustaining star. snakes, mosquitos, and other drivers! Glenn has been an Several years passed before I learned that the glass in Questions, comments, or suggestions? Email me at avid observer since a friend showed screw-in solar filters has a nasty habit of shattering due to [email protected]. Next month: the answer to all him Saturn through excessive heat. Had this happened while I was peering into your backyard astronomy questions. Clear skies! a small backyard my scope’s eyepiece, a sudden blinding flash of unfiltered scope in 1963. and concentrated sunlight could have caused permanent BROWSE THE “OBSERVING BASICS” ARCHIVE eye damage. I thank my lucky stars that never happened. AT www.Astronomy.com/Chaple WWW.ASTRONOMY.COM 15

How NASA’s plucky probe has brought us WHENEVER JUPITER, unprecedented views of the solar system’s biggest planet, from its enigmatic aurorae thunderbolt-wielding lord of the to its dramatic storms. BY BEN EVANS gods in ancient Roman myth, misbehaved with the ladies, there was one person he most feared: his long-suffering yet ferocious wife, the goddess Juno. It was said that Jupiter conjured fog to hide his illicit 16 ASTRONOMY • AUGUST 2022

unmasked JUPITER liaisons from his wife. But Juno last six years, though, a spacecraft questions and uncovered new rid- Incredible bulk// always saw through her faithless bearing Juno’s name has watched dles to challenge us. Its onboard husband’s philandering to reveal Jupiter from orbit, stripping away camera, JunoCam, has turned Cloud belts swirl his every misdeed. its secrets and furnishing new Jupiter from a planet into an objet around Jupiter’s insights into its interior and d’art, capturing spectacular plan- southern hemisphere Like its mythical namesake, evolution. etscapes with sprawling storms. in this image captured the planet Jupiter guards its And the craft’s scientific toolkit by Juno at an altitude of secrets with jealous pride, its bulk This robotic Juno has has made it as much a force to be 8,453 miles (13,604 km) swaddled in thick clouds. For the answered many longstanding on Dec. 16, 2017. ENHANCED IMAGE BY KEVIN M. GILL (CC-BY) BASED ON IMAGES PROVIDED COURTESY OF NASA/ JPL-CALTECH/SWRI/MSSS

LEFT: New view// Blue cyclones encircle Jupiter’s south pole in this enhanced color image. NASA/JPL-CALTECH/SWRI/ MSSS/BETSY ASHER HALL/GERVASIO ROBLE BELOW: Red marble// Broad belts and swirling storms — including Jupiter’s Great Red Spot — are visible in this image taken by JunoCam Feb. 12, 2019. ENHANCED IMAGE BY KEVIN M. GILL (CC-BY) BASED ON IMAGES PROVIDED COURTESY OF NASA/JPL-CALTECH/SWRI/MSSS reckoned with as the goddess brimming with nine science North by north// The North North herself. instruments, including infrared and ultraviolet sensors, a radiom- Temperate Zone Little Red Spot is about Flying by Jove eter and magnetometer, and half the size of Jupiter’s Great Red Spot, energetic particle detectors. For but still measures roughly 5,000 miles The largest and most massive power, it relies on arrays of solar (8,000 km) across. NASA, JPL-CALTECH, SWRI, MSSS, planet in the solar system, Jupiter panels — a first for a spacecraft has been observed since antiq- at Jupiter, where sunlight is about PROCESSING: GERALD EICHSTADT, DAMIAN PEACH uity. But before the invention 4 percent as strong as at Earth. of the telescope, we knew little With its windmill-like trio of Launched on an Atlas V rocket of its nature, including its four 29-foot-long (9 meters) solar from Cape Canaveral Aug. 5, large Galilean moons (named arrays fully unfurled, the probe 2011, Juno voyaged 1.74 billion for their discoverer, the Italian spans about the same area as a miles (2.8 billion kilometers) to polymath Galileo Galilei) and basketball court. All previous reach Jupiter. Its convoluted its most striking atmospheric craft that had voyaged that deep 59-month trek carried it initially feature, the roiling Great Red into the solar system relied on beyond the orbit of Mars, but a Spot. Our knowledge has multi- nuclear generators. But a world- pair of maneuvers in August and plied since the dawn of the Space wide shortage of plutonium-238 September 2012 redirected it back Age, thanks to NASA’s Pioneer, nuclear fuel coupled with past Earth for a gravitational Voyager, and Galileo probes, advances in solar-cell technology slingshot maneuver in October which surveyed the giant planet made it both necessary and pos- 2013. This yielded an 8,800-mph between 1973 and 2003. sible for Juno to utilize the Sun’s (14,000 km/h) speed boost. On energy to power itself. Juno is the most advanced spacecraft yet to visit Jupiter, 18 ASTRONOMY • AUGUST 2022

July 4, 2016, as Juno hurtled JUNO’S APPROACH TRAJECTORY was carefully planned to put the craft into a 53-day toward its target, a Jupiter Orbit Insertion (JOI) engine burn polar orbit that avoided Jupiter’s radiation belts and kept its solar panels constantly exposed to reduced its speed by 1,200 mph sunlight. The original mission plan (top) then called for Juno to tighten its orbit to a 14-day loop that (1,950 km/h), allowing the probe would precess over time, slowly increasing its exposure to the radiation belts. When the mission to thread a fine needle between team decided to cancel that maneuver due to a malfunctioning fuel valve, Juno remained in its the planet and its radiation belts. 53-day orbit for the duration of its prime mission (middle). Juno then entered an elliptical In July 2021, Juno began its extended mission (detailed at bottom) shortly after making a close orbit not around Jupiter’s equa- pass of Ganymede, which reduced the spacecraft’s orbital period from 53 to 43 days. A planned tor, but looping from pole to flyby of Europa in September 2022 will further shorten the orbit to 38 days. And two flybys of Io, in pole. This has given scientists December 2023 and February 2024, will trim it to 33 days. The extended mission is approved to last a perspective on Jupiter never until September 2025. seen by the Pioneer and Voyager probes, which made flybys of the WWW.ASTRONOMY.COM 19 jovian system in the 1970s, and even the Galileo mission, which girdled the planet in an equator- hugging orbit from 1995 to 2003. From this unique vantage point, Juno made the first obser- vations of the planet’s extreme northerly and southerly latitudes. It has also flown more than 10 times closer to its rollicking clouds, raging tempests, and savage radiation belts than any previous mission. In unmasking this multi-hued megaworld, Juno would have made its pansophical namesake proud. Juno’s initial orbit lasted 53 days, giving engineers time to prepare to test the craft’s instru- ments during a close passage to Jupiter that August. Then, in October 2016, Juno’s flight plan called for a Period Reduction Maneuver (PRM) to bring Juno in a tighter, 14-day orbit. Circling Jupiter every two weeks, Juno was expected to have an operational life of just 20 months. The main reason was the intense radiation belts at Jupiter, which had almost cooked the circuits of the earlier Pioneer probes. During their brief flybys, they sustained 1,000 times the human-lethal dose of radiation. NASA expected that Juno would endure the equivalent of over 100 million dental X-rays over its lifetime. To guard against the onslaught of charged particles

stainless steel braiding, and its the northern storms remained computers were shielded behind stable over time, scientists were the 0.4-inch-thick (1 centimeter) astonished in November 2019 walls of a 500-pound (200 kilo- when another cyclone — smaller grams) titanium vault. “Juno is than the rest, yet still the size of basically an armored tank going Texas — muscled its way into the to Jupiter,” said the mission’s southern group. The gatecrasher’s principal investigator Scott petulance did not go unpunished Bolton of the Southwest Research and within months, it had been Institute in a 2010 statement. pushed out and vanished. To “Without its protective shield, Bolton, “it almost appeared like or radiation vault, Juno’s brain the polar cyclones were part of a would get fried on the very first private club that seemed to resist pass near Jupiter.” new members.” Cyclone close-up// Juno made the closest-ever A flexible flight plan As well as spotlighting the storminess of the poles, Juno’s approach to Jupiter’s Great Red Spot on July 11, 2017, On Aug. 27, 2016, Juno experi- first perijove showed the planet’s taking this shot from just 6,100 miles (9,900 km) above enced its first close approach of magnetic fields and aurorae are the cloudtops. NASA/SWRI/MSSS/GERALD EICHSTÄDT/SEÁN DORAN Jupiter, or perijove, sweeping just much more powerful and exten- 2,600 miles (4,200 km) above sive than previously thought. It funneled by Jupiter’s magnetic Jupiter’s clouds, closer than any revealed the field is irregularly field, Juno’s electronics were spacecraft in history. This flyby shaped, lumpy in places, and — made with radiation-resistant provided our first ever high- at 7.766 Gauss — more than tantalum, its wiring was latitude glimpse of the north pole. 10 times as powerful as Earth’s wrapped in copper and It took almost two days to down- magnetic field at its strongest. load the 6 megabytes of data from perijove 1, but the results proved But despite a promising start, well worth the wait. “It’s bluer in all was not well. The PRM burn color up there than other parts of in October 2016 was postponed the planet, and there are a lot of due to worries about helium storms,” noted Bolton. “There is valves in the main engine’s pres- no sign of the latitudinal bands or surization system. Although the zones and belts that we are used valves opened on command, they to — this image is hardly recog- did so more sluggishly than nizable as Jupiter.” expected. Matters were com- pounded further when an unre- Juno revealed the poles are lated computer reboot threw Juno dominated by densely packed into safe mode for a few days in cyclones, all jostling for position. late October. In the north resides a central cyclone, encircled by eight others, The most efficient time to per- all around 2,000 miles (3,200 km) form the PRM was during the in diameter, as wide as the con- risky perijove passage, but an tiguous U.S. Clinging to the increasingly nervous NASA chose periphery of the pole, as if itching to weigh its options before trying for admission, are other tumultu- again. “There was concern that ous weather systems, including a another engine burn could result 5,000-mile-wide (8,000 km) behe- in a less-than-desirable orbit,” moth known as the North North said Project Manager Rick Temperate Little Red Spot 1, the Nybakken of the Jet Propulsion third-largest anticyclonic oval Laboratory in a statement. “The storm on Jupiter. bottom line is a burn represented a risk to completion of Juno’s sci- The planet’s deep south ence objectives.” proved no less tempestuous, har- boring a pentagon of five cyclones This risk ultimately decided around a central sixth. But while the issue. In February 2017, NASA announced that Juno 20 ASTRONOMY • AUGUST 2022

Dawn storms// The polar aurorae of Jupiter can suddenly intensify at morning in so-called dawn storms, which bear a resemblance to auroral storms on Earth. This image is a composite of visible light and ultraviolet data from Juno. NASA/JPL- CALTECH/SWRI/UVS/STSCI/MODIS/WIC/IMAGE/ULIÈGE would remain in its 53-day orbit ABOVE: Great Blue for the rest of the mission. Spot// This frame Researchers did not expect the longer orbit to impair the science, from a simulation of as the probe’s altitude during Jupiter’s magnetic field each perijove would remain the shows the Great Blue same as it would have during its Spot, an invisible region planned 14-day orbit. Indeed, the where the field is 53-day orbit meant that Juno particularly strong with would actually spend less time negative polarity. NASA/JPL- in the regions of most intensive radiation. “This is significant,” CALTECH/HARVARD/MOORE ET AL. said Bolton, “because radiation has been the main life-limiting LEFT: Newcomer// factor for Juno.” On Nov. 4, 2019, Juno Massively magnetic (8 million km) toward the Sun. saw a brand-new, And the Voyagers showed that Texas-sized cyclone A bonus of the 53-day orbit was the solar wind splays Jupiter’s (lower right) join the six the ability to spend more time in magnetic field back beyond the existing storms gyrating the poorly understood fringes of planet, forming a magnetotail around Jupiter’s south Jupiter’s magnetic field. Jupiter’s that extends 460 million miles pole. NASA/JPL-CALTECH/SWRI/ASI/ internal magnetism carves a vast (750 million km), almost out cavity into the solar wind, a mag- to Saturn’s orbit. INAF/JIRAM netic realm of influence with a field thousands of times stronger Later missions also visited than Earth’s. Researchers inferred Jupiter: In addition to Galileo’s its existence with ground-based extended stay, Ulysses passed radio and microwave observa- through the planet’s polar mag- tions in the 1950s. The Pioneer netosphere during a 1992 flyby missions flew through it and and New Horizons traversed the Ulysses probe found that 100 million miles (160 million km) Jupiter’s region of magnetic along its magnetotail in 2007 influence — or magnetosphere — extends about 5 million miles WWW.ASTRONOMY.COM 21

while en route to Pluto and the Scientists think that beneath to the planet’s visible surface, Kuiper Belt. But these were brief Jupiter’s outermost layers of above the liquid metallic hydro- encounters. It was left to Juno to molecular hydrogen resides an gen boundary. In May 2019, Juno undertake the first global map- electrically conducting shell of showed the field changes over ping campaign. liquid metallic hydrogen. The time — a phenomenon called existence of this exotic substance secular variation — and its effects Mapping the magnetosphere at Jupiter was first proposed in are particularly prominent near tells us more than just its extent. 1951. It has long been thought to an anomalous area of magnetism It’s also one of the few ways to near the equator. As the spot appears blue in maps produced Jupiter’s magnetic field is also capable with Juno data, scientists have of creating powerful aurorae many times dubbed it the Great Blue Spot. more energetic than Earth’s own. Jupiter’s magnetic field is also understand Jupiter’s gaseous play a key role in generating capable of creating powerful interior, including its magnetism Jupiter’s magnetic field, its rota- aurorae many times more ener- and core. The planet’s enormous tion acting as a dynamo. getic than Earth’s own. The gravity compresses its atmo- Voyagers witnessed polar dis- sphere so tightly that it is However, the magnetic field’s plays spanning 18,000 miles virtually impenetrable to lumpiness that Juno observed (29,000 km) that were accompa- remote-sensing tools. suggested that the field might be nied by whistling radio emis- created by dynamo effects closer sions. Analysis revealed these phenomena were partly triggered Jupiter blues// A blue-hued cloud system whirls across Jupiter’s northern hemisphere in this by material flowing along mag- netic field lines from Jupiter’s image taken by JunoCam Oct. 24, 2017, at an altitude of just 11,747 miles (18,906 km) — roughly the volcanic moon, Io. distance from New York City to Perth, Australia. NASA/JPL-CALTECH/SWRI/MSSS/GERALD EICHSTADT/SEAN DORAN, CC NC SA Juno’s time in Jupiter’s outer magnetosphere yielded an array of discoveries. In September 2017, researchers reported that Juno had found auroral electrons pouring into the atmosphere at energies approaching 400,000 electron volts, 10 times stronger than their counterparts on Earth. Yet, unlike at Earth, they don’t appear to be responsible for the strongest aurorae at Jupiter. This suggests that jovian lights are induced by a form of turbulence in the magnetic field that acceler- ates charged particles. More recently, Juno returned the first observations capturing the full birth and evolution of “dawn storms” — intense, short- lived events that regularly appear at sunrise, where the main auro- ral ovals that circle the planet’s poles broaden and brighten. Juno has also derived insights into Jupiter’s enigmatic X-ray-emitting aurorae and how they may heat the wider atmosphere. And in April 2021, Juno’s ultraviolet spectrograph linked auroral 22 ASTRONOMY • AUGUST 2022

TOP TO BOTTOM: ENHANCED IMAGE BY JASON MAJOR BASED ON IMAGES PROVIDED COURTESY OF NASA/JPL-CALTECH/SWRI/MSSS; ENHANCED IMAGE BY MIK PETTER (CC-NC-SA) BASED ON JUNOCAM’S VISUAL IMPACT cyclones lined up like strings of Pearly whites// IMAGES PROVIDED COURTESY OF NASA/JPL-CALTECH/SWRI/MSSS; IMAGE DATA: NASA/JPL-CALTECH/SWRI/MSSS, IMAGE PROCESSING: RITA NAJM CC BY pearls, and in December 2019, ALTHOUGH ALL serendipitously witnessed a pair The series of white OF JUNO’S NINE of storms colliding. It watched storms called the String INSTRUMENTS have Jupiter’s second-biggest storm, of Pearls is visible near Oval BA — the result of three the limb of Jupiter aided the probe’s scientific spots that merged in 2000 — in this image taken harvest, it is JunoCam’s change color from deep red to Dec. 16, 2017. NASA/SWRI/ spectacular imagery of almost white in 2015 and 2016. Jupiter’s swirling surface It measured vigorous winds that MSSS/GERALD EICHSTÄDT/SEÁN that has truly resonated in extend 1,800 miles (2,900 km) the wider world. The only deep and shear apart electrically- DORAN visible light camera on conducting material in the jovian the spacecraft, JunoCam interior, altering the shape of the was conceived not as planet’s magnetic field. And in a scientific instrument, 2020, Juno began tracking a small but as a tool for public storm found by South African outreach — and it has astronomer Clyde Foster, now been wildly successful. called Clyde’s Spot. Members of the public But of all Jupiter’s storms, have taken Juno’s raw none is bigger or longer lasting imagery and reworked it to than the famous Great Red Spot. present different artistic Continuously observed since the interpretations of Jupiter. 19th century, it may even be the One rendition uses two same storm found by the English glaring oval storms to scientist Robert Hooke in 1664. create a pair of eyes, which The counterclockwise-rotating Jason Major called Jovey spot now measures 10,000 miles McJupiterFace (top). Mik (16,000 km) in diameter, having Petter used mathematical noticeably shrunk in recent years. fractals to recreate Jupiter It has also shown dramatic varia- almost like a petri dish, tions in color, morphing from teeming with organisms brick-red to its present salmon- (middle). And Rita Najm pink. In July 2017, Juno flew enhanced the color and directly over the spot at a height contrast of one image to of just 5,600 miles (9,000 km), make a beautiful portrait of spying a tangle of dark, veinous Jupiter’s clouds, wrapped clouds weaving through it. around each other like the petals of roses (bottom). activity on Jupiter for the first Stormy weather time with charged particles at the boundary region between Juno has also been a prolific the magnetosphere and the storm-chaser, adept at tracking solar wind. Jupiter’s wild weather. The craft has seen series of Earth-sized WWW.ASTRONOMY.COM 23

The probe’s microwave radi- Chance of mushballs// Pop-up clouds are thought to be the source of Jupiter’s ometer showed the spot extends further into the atmosphere than powerful thunderstorms. They can generate shallow lightning and mushballs — slushy its neighboring clouds, penetrat- hailstones made of water and ammonia — as depicted in this artist’s concept based on ing at least 200 miles (320 km) Juno data. NASA/JPL-CALTECH/SWRI/MSSS/GERALD EICHSTÄDT/HEIDI N. BECKER/KOJI KURAMURA deep. “The Great Red Spot’s roots go 50 to 100 times deeper than unpredictable electrical flashes passage reduced the spacecraft’s Earth’s oceans and are warmer at of light associated with thunder- orbital period from 53 to 43 days, the base than they are at the top,” storms — the first to be seen on with a Europa flyby in September said Andrew Ingersoll, a plan- a world other than our own. 2022 expected to shave this down etary scientist at Caltech, in a to 38 days. Two Io encounters, statement. “Winds are associated Time extension one in December 2023 and a sec- with differences in temperature, ond in February 2024, will cut it and the warmth of the spot’s base While Juno’s mission was origi- further to 33 days. explains the ferocious winds we nally scheduled to end in 2018, see at the top of the atmosphere.” the craft remains so productive As a result, Juno’s most that its mission has been extended remarkable discoveries may be still Juno has also detected hun- twice: first to July 2021 and again to come. And a probe expected to dreds of lightning discharges that through September 2025, or until survive just two years immersed gave off radio waves in the mega- it reaches the end of its life. in Jupiter’s fearsome radiation hertz and gigahertz ranges, far may spend almost a full decade more energetic than Earth’s own. These mission extensions have stripping back the secrets of this In results reported June 2018, its enabled it to take aim not just at most secretive of worlds. “We are Waves instrument recorded four Jupiter, but also its large moons not looking for trouble,” promised lightning strikes every second. Ganymede, Europa, and volcanic Scott Bolton. “We are looking for Io. One flyby in June 2021 saw data.” If she could know what her Shallow lightning originating Juno pass within just 645 miles robotic namesake has achieved, from ammonia-water clouds and (1,038 km) of Ganymede — the all-seeing Juno of myth would giant, slushy hailstones rich in closer than any spacecraft in be justly proud. But her philander- ammonia-ice, known as mush- a generation — and return ing husband, surely, would be less balls, were detailed in research spectacular infrared imagery than thrilled. published August 2020. And of its icy north pole. in October 2020, researchers Ben Evans has been fascinated reported that Juno had found The gravity-assisted tweaks by space since childhood. He has signs of sprites and elves — brief, afforded by repeat flybys of these written extensively on the history moons in the coming years will of human spaceflight. A striking scene// A stormy planetscape dotted naturally reshape Juno’s orbit. Last year’s close Ganymede with lightning strikes is rendered in this photoillustration combining a JunoCam image with artistic additions. At times, Juno recorded lightning at the rate of four strikes per second. NASA/JPL-CALTECH/SWRI/JUNOCAM 24 ASTRONOMY • AUGUST 2022

Catch PLUTO this summer Planet or not, Pluto is a worthy target. BY MICHAEL E. BAKICH IN 1929, Clyde William Tombaugh’s job was to comparator to see if any Be prepared search for Planet X, a world objects on the plates moved. Tombaugh, a farm boy that some astronomers It took him only until January Pluto reached opposition at who grew up in Illinois believed existed beyond 1930 to stumble onto Pluto. 2h UT on July 20. Observers and Kansas, began work- Neptune. Using the observa- always target planets (espe- ing at Lowell Observatory in tory’s 13-inch astrograph, Since then, amateur cially those beyond Saturn) Flagstaff, Arizona. The direc- Tombaugh exposed hundreds astronomers have regarded near opposition because that’s tor of the facility, renowned of glass plates. His search observing the distant, when they appear brightest. astronomer Vesto Slipher, strategy involved photograph- ever-so-faint world as a badge At that point, because the had hired Tombaugh based ing the same region of sky of honor. If you haven’t seen planet lies opposite the Sun on some high-quality sketches several days apart and then Pluto, this month offers yet in our sky, it rises at sunset, of Jupiter and Mars he sent to using a machine called a blink another chance to tick it off climbs highest at midnight, the observatory. your bucket list. and sets at sunrise. Rugged and complex terrain lines the western lobe of Sputnik Planitia, a heart-shaped basin on Pluto, in this image from NASA’s New Horizons probe. NASA/JHUAPL/SWRI

N July 10 15 E 20 25 Path of Pluto 30 SAO 188756 Aug. 1 5 SAO 188737 10 15 20 SAO 188701 0.05° SAGIT TARIUS M75 SAO N E 188829 SAO 188795 SAO 188701 tiny dot and enough faint stars around it so that you SAO SAO 188667 Because our July issue was can identify it. But if you 188756 SAO 188737 devoted to space art, this can go bigger, do it. story is appearing slightly SAGIT TARIUS after that event. At opposi- And the scope is only the tion, Pluto glowed weakly at beginning of this odyssey. Terebellum 1° magnitude 14.9. Don’t fret if You’ll also need to transport you didn’t see it on that night, it to an observing site that SAO 188795 N j2 however. Its distance from the has great seeing (a measure / m Sun changed so little that, on of the atmosphere’s steadi- M75 SAO 188829 Aug. 26 — the night closest ness). If the Moon is any- SAO 188737 SAO 188667 k to New Moon this month — where in the sky, forget it will have faded by a mere finding Pluto. Our atmo- E 0.2 magnitude. sphere scatters the Moon’s Terebellum light, raising the background As you might imagine, a glow to a point where you SAGIT TARIUS magnitude 14.9 dot is going to will not see the world. be tough to identify. Pluto was o a slightly easier catch — at Track it down magnitude 13.8 — when it 3° c was at perihelion, the point Use the charts on this page of its orbit closest to the Sun. to help you to identify Pluto. Start your search for Pluto with the wide-field view of Sagittarius (bottom), But that was Sept. 5, 1989, and Illuminate them with a dim which shows stars down to magnitude 8, including the Teapot asterism at right. the planet has been moving red light; that color has the Locate Tau (τ) Sagittarii, the lower left corner of the Teapot’s handle, and then farther from the Sun ever least impact on your eyes’ move to Terebellum, 11° east. In the binocular view (middle), stars are shown since. It won’t start approach- dark adaptation, but even down to magnitude 10. You should be able to find the magnitude 7.6 star ing our daytime star again red light will ruin your night SAO 188737 just over 3° north of Terebellum. On July 19, Pluto will be until 2114. So, the longer you vision if it’s too bright. approaching a tiny triangle of stars; the telescopic view (top) includes wait, the less chance you have stars as faint as magnitude 16. ALL MAPS: ASTRONOMY: ROEN KELLY of bagging this elusive quarry. On July 19, the dwarf planet lies in eastern Let me be honest here. An Sagittarius, about 2° from that 8-inch telescope will give constellation’s border with great views of clusters, nebu- Capricornus. It also lies 2° lae, and some galaxies — but west-southwest of globular not Pluto. To track it down, cluster M75, which is worth a you need to think bigger. An look through a medium to 11-inch scope will reveal the large telescope. Pluto’s right ascension is 19h58m, and its 26 ASTRONOMY • AUGUST 202 2

ABOVE: The haze layers of Pluto’s thin but complex atmosphere are backlit in this view from NASA’s New Horizons probe. NASA/JHUAPL/SWRI RIGHT: Clyde Tombaugh got his start as an astronomer by building his own telescopes and observing from his family’s farm in Kansas. NMSU LIBRARY ARCHIVES AND SPECIAL COLLECTIONS declination is –22°50'. The SAO 188756 anchors a trio several nights later, remember east through the stars. But planet first entered Sagittarius of stars, all brighter than to allow the Moon to set. The around opposition, Earth, in in December 2006 and reaches Pluto, angling northwest. Just main chart on page 26 shows its orbit, passes Pluto, causing Capricornus in early 2024. to the northeast is a smaller background stars to magni- it to appear to travel west. and fainter but similarly tude 16, so you should be able This apparent reversal is Start with the wide-field angled trio of stars. It forms to locate Pluto, which glows called retrograde motion. view at the bottom of page 26 one side of an equilateral tri- slightly brighter than this and identify the Teapot, the angle with a star of nearly the limit. Be patient, though: This Pluto is an object that eight stars that make up same brightness. The faintest isn’t a sight that will instantly every amateur astronomer Sagittarius’ main asterism. of this group just barely out- reveal itself to you. should see. Even though the From magnitude 3.3 Tau (τ) shines your target. If you process is a bit difficult, Sagittarii, the star in the lower locate these stars early in the Also, remember that Pluto you’ll feel a sense of accom- left corner of the Teapot’s evening and return to this is moving westward. Outer plishment having done it. handle, move 11° east to mag- view six or eight hours later planets generally move to the Good luck! nitude 4.7 Terebellum (Omega (owners of motorized tele- [ω] Sagittarii). It’s part of a scope drives can just leave Michael E. Bakich is a contributing editor of Astronomy who group of four similarly bright them on), you may notice that co-authored Atlas of Solar Eclipses: 2020–2045 with Michael Zeiler. stars. one object has changed its position. That’s Pluto. From Terebellum, move slightly more than 3° north It’s tough to remember and find the magnitude 7.8 such fine details, however, star SAO 188737. Pluto now especially when a plethora will lie within the eyepiece, a of stars surrounds the ones mere 25' northeast of that star. you’re trying to target. A To get there, look 15' to the much better strategy is to northeast for magnitude 8.9 sketch the region. Then come SAO 188756. (Note that these back to it a few hours later. instructions are for those Even better, return the follow- without computerized drives. ing night (or two or three If your telescope sits atop a nights later), and re-sketch. go-to drive, all SAO stars are Pluto will be the only point probably in its database. So, of light whose position is just enter “SAO 188756” and different. If you do return hit “Go To.”) WWW.ASTRONOMY.COM 27

for city-dwellers Don’t let bright lights prevent you from exploring cosmic sights. BY PHIL HARRINGTON MANY ASTRONOMY enthusiasts just need to know what telescope is best So, where will you keep your telescope for you and your location. when it is not in use? If you must lug the live under the veil of light pollution, equipment up and down stairs every either from local sources like poorly When it comes to buying a telescope, night, you’ll want to be able to carry it all aimed lights on neighboring houses or most people immediately consider their in one trip. The same applies if you need the enormous light domes enveloping budget. No one wants to spend beyond to walk or take public transport to a large cities. It can be quite discouraging their means. But for those who live in nearby park or other open area. If, how- at first. a city, there are a few other matters to ever, you have first-floor access and a ponder, as well. The most important yard of your own with a clear view, then But it doesn’t mean you can’t be an considerations are ease of use and stor- taking couple of trips is less burdensome. active observer. Anyone can enjoy age. Unless a telescope is convenient to wonderful views every clear evening use, it will quickly become consigned to Also remember that you won’t just be without venturing far from home. You the closet. Many a stargazer’s enthusiasm transporting the telescope, but its mount has turned to apathy upon the harsh as well. If you must haul the setup a sig- City light pollution largely washes out the stars realization that hauling out and setting nificant distance, avoid heavier designs above Calgary, Alberta. But with the right up a telescope can be a daunting task. like German equatorial mounts. equipment, you can still get lost in the sky. ALAN DYER

1 23 4 TELESCOPE IMAGES IN ORDER: HIGH POINT SCIENTIFIC; CELESTRON; CELESTRON; EXPLORE SCIENTIFIC; IOPTRON; Fortunately, nowadays there are many In some cases, you will need to manually Fully assembled, it weighs 52.2 pounds SKYWATCHER USA; STELLARVUE; TELE VUE; TELE VUE; MEADE small mounts that are light enough to input that information and go through a (23.7 kilograms), so it’s an excellent choice easily carry, yet sturdy enough to support one- or two-star alignment process using for those who don’t have to carry their a portable telescope. The lightest, most pre-selected bright stars. Other systems telescope up and down flights of stairs. compact mounts are altitude-azimuth automatically complete all that using designs. With these, the telescope moves GPS technology. 2 Celestron NexStar up and down in altitude and left to right Evolution 6 in azimuth, which might be more intui- For more details on the different types tive for novice observers. of telescopes, see my article, “First scopes This portable 6-inch Schmidt-Cassegrain for adults,” in the June 2022 issue. But for telescope comes on a one-armed comput- Many setups also feature computer- now, here are 10 scopes, arranged in erized mount with a built-in battery that ized go-to mounts, which automatically alphabetical order, that might serve you lasts up to 10 hours on a single charge. aim the telescope toward a preselected well when viewing the sky from an urban The total kit weighs 38 pounds (17.2 kg) object. That’s a big plus if light pollution environment. and features an integrated handle for obliterates everything fainter than the easy carrying. Moon and brighter planets and stars. But 1 Apertura AD8 Dobsonian be aware that a go-to mount’s “brain” This 8-inch Newtonian reflector rides 3 Celestron NexStar 8SE must first know its location, as well as on a simple altitude-azimuth mount If you have a bigger budget, the time and date, before it will work. made of wood, making it a Dobsonian. consider the 8-inch NexStar 8SE

Earth’s city lights are on full display in this image created using data from orbiting Defense Meteorological Satellite Program (DMSP) craft. DATA: MARC IMHOFF (NASA/GSFC ), CHRISTOPHER ELVIDGE (NOAA/NGDC); IMAGE: CRAIG MAYHEW, ROBERT SIMMON (NASA/GSFC). Schmidt-Cassegrain. The telescope creates an advanced, highly portable lens, which eliminates the chromatic attaches to its computerized, single- system small enough to carry onboard aberration that can plague traditional armed altitude-azimuth mount using airplanes. achromatic refractors. The scope’s image a dovetail plate for easy setup. quality is exceptional, but note the 6 Sky-Watcher SkyMax 127 mount is sold separately. 4 Explore Scientific AZ-GTi Explore FirstLight 8 Tele Vue-NP101is 102mm Doublet Refractor This 127mm Maksutov-Cassegrain You can achieve breathtaking views weighs 9.7 pounds (4.4 kg), and mea- and images with this 101mm NP101is This 102mm refractor has enough aper- sures 15 inches (38 cm) long, so is easy to refractor, thanks to its four-element ture to reveal the Moon, brighter plan- carry and store. It sits atop the AZ-GTi apochromatic objective lens system. ets, binary stars, and bright deep-sky altitude-azimuth go-to mount, which The mount is sold separately. objects, but is still small enough to easily adds another 8.6 pounds (3.9 kg) to the transport. package. 9 Tele Vue-85 The 85mm TV-85 refractor from 5 iOptron SmartStar 7 Stellarvue Triplet Apo Tele Vue combines portability, crafts- Cube-A-MC90 SVX080T-25FT manship, and excellent optics in a small package. Again, the mount is sold iOptron’s innovative CubePro mount The Stellarvue SVX080T-25FT separately. (not shown) paired with their compact refractor features a 3.1-inch (80 mm) 90mm Maksutov-Cassegrain scope three-element apochromatic objective 7 56 8

EXIT PUPIL Field Eye Apparent TARGET TYPE EXIT PUPIL (mm) lens lens field of view Large star clusters, 3 to 4 Edge-of-field Exit pupil full lunar disk 1 to 3 light rays Small deep-sky objects 0.5 to 1 To telescope (especially planetary nebulae and smaller galaxies), double Barrel Observer's stars, lunar details, and planets eye on nights of poor seeing Eye relief Double stars, lunar details, and The exit pupil is the diameter of the cylinder of light that leaves an eye- planets on exceptional nights piece and enters your eye. Choosing the optimal exit pupil depends on what type of target you are observing. ASTRONOMY: ROEN KELLY, AFTER PHIL HARRINGTON 10 Meade Coronado is especially important for Newtonian the eyepiece in millimeters by the tele- Personal Solar reflectors because the focuser is so close scope’s focal ratio (its f/ number, which Telescope to the front of the tube. Make a slip- has no units). Let’s say you have a 6-inch on dew shield that extends at least one f/10 Schmidt-Cassegrain and a 12mm Let’s not forget about solar observing, telescope-tube diameter in front of the eyepiece. That combination yields an exit especially as we rise out of the dol- focuser and paint the inside of the tube pupil of 1.2 mm (12 mm/10). drums of solar minimum. A dedicated flat black to dampen reflections. Hydrogen-alpha (Hα) solar scope, such As you are selecting eyepieces, make as the 40mm Meade Coronado Personal Additionally, amateurs often overlook sure they include rubber eyecups. Solar Telescope, will reveal amazing the importance of eyepieces. While many Eyecups are designed to block localized details, including prominences, fila- purchase eyepieces based on their focal light from entering the corner of the ments, and active regions. (Remember: lengths and the resulting magnification observer’s eye, and they can be a Never observe the Sun without proper for a given telescope, the real key is exit game-changer. equipment!) pupil. The exit pupil is the diameter of the cylinder of light exiting the eyepiece Also be sure to use a broadband light Make the most of your and entering your eye. The size of the pollution reduction (LPR) filter. Many observing session exit pupil will change as magnification outdoor lights do not shine uniformly changes. across the entire visible spectrum. No matter what you choose, to get the Instead, they emit light at only a few best out of your urban scope, you’ll want Depending on which type of target discrete wavelengths. For instance, high- to optimize it with a few simple tricks. you are interested in observing, using the pressure sodium streetlights principally One of the most helpful techniques to right eyepiece combination to get the shine in the yellow wavelengths. LPR enhance the view is to add a short tube optimal exit pupil will really enhance filters suppress the broad portion of the extension, called a dew shield, to the your view. See the table above for some visible spectrum that includes those front of the telescope. The extension suggestions. wavelengths, while allowing others to slows dew formation on the lens or cor- pass through. Unfortunately, they are rector plate, as well as blocks stray light To find out how large the exit pupil not as effective against incandescent from entering from the side. The latter will be with a specific telescope/eyepiece bulbs and LED lights, since those emit combination, divide the focal length of across the entire spectrum. LRP filters 9 may not magically whisk you away to 10 that perfect dark sky, but they will go a long way toward darkening your field of view and improving contrast. Urban stargazing can be great fun with the right equipment. With a bit of consideration and preparation, you’ll be treated to years of entertainment viewing the sky — without hours of travel. Phil Harrington is a longtime contributor to Astronomy and the author of many books. 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 AUGUST 2022 The solar system’s giant planets take center stage on August nights. The Giant planet time time is ripe to look for stunning detail in the rings of Saturn (left) and on Midsummer observing southward along the horizon. By — difficult to see in bright twi- Jupiter’s disk (right). ARIEL ADORNO means giant planets, Aug. 14, it fades to magnitude 0 light. Try spotting it in binocu- with Jupiter and Saturn visible and stands 5° high due west lars on the 28th and 29th, as a Saturn rises in the east soon before midnight. Both planets 30 minutes after sunset. crescent Moon enters the scene. before 9 P.M. local time on offer hours of amazing views. Mercury lies 9.5° left of the Aug. 1. It reaches opposition Saturn is visible all night, while Mercury reaches greatest Moon on the 28th and 6.5° Aug. 14, so it is visible all night. Jupiter rises a bit later. You eastern elongation Aug. 27 below the Moon on the 29th. The best time to view the planet might catch elusive Mercury in and fades to magnitude 0.3 is when it is highest in the the early evening if you’re lucky. southern sky, around 1 A.M. And the morning sky carries Get an early start Markab local time (local midnight using the glories of a growing Mars PEGASUS daylight saving time). It briefly and a brilliant Venus. Hamal brightens to magnitude 0.2 mid- Mercury modestly hugs ARIES Algenib month and is unmistakable the western horizon all month. Uranus within Capricornus the Sea It’s a favorable apparition for Mars PISCES Saturn Goat as the brightest object in Southern Hemisphere observers this part of the sky. but is more challenging for Menkar A Q UA R I U S those in the Northern You’ll find 3rd-magnitude Hemisphere. On Aug. 3, soon Jupiter Neptune Deneb Algedi Deneb Algedi (Delta [δ] after sunset, you’ll find it only CAPRICORNUS Capricorni) near Saturn, 1.7° 0.8° north of Regulus, although Skat southeast of the planet as the pair sets within an hour of August opens. Saturn’s retro- the Sun. Try 30 minutes after CETUS Fomalhaut grade motion is easy to spot as sunset to spot magnitude –0.5 Diphda the ringed planet wanders slowly Mercury 4° high; use binocu- westward at about 0.5° per week. lars to find fainter Regulus. 10° August’s Full Moon, also oppo- Mercury’s elevation after site the Sun in the sky, lies sunset doesn’t improve much Aug. 1, 3 A.M. within 5° of Saturn overnight as August progresses, although Looking southeast on Aug. 11/12, shortly before the its elongation from the Sun Perseid meteor shower peaks. increases. Mercury slides As August opens, Mars and Uranus sit 1.4° apart in the predawn sky. Center binoculars on Mars to find the more distant ice giant. Also visible are Jupiter, It’s the best time of the year Neptune (requires binoculars), and Saturn. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY to view Saturn’s rings, since the planet is closest to Earth at opposition (824 million miles), rendering the planet and its ring system at their largest apparent size to Earth dwellers. Saturn’s disk spans 19\" across the 32 ASTRONOMY • AUGUST 2022

RISING MOON I Historic record THE UPRIGHT crescent Moon that opened Julius Caesar and Rima Ariadaeus August waxes into a world of striking detail up and down the terminator, the line dividing day OBSERVING from night. The hours shortly after lunar sunrise Julius HIGHLIGHT exaggerate the apparent height of features Caesar thanks to the long shadows cast by the low Sun. SATURN reaches opposition Arago Lamont Along the curved limb under a higher Sun, the Aug. 14 and is visible all topography seems to have vanished. The north- night this month. south wrinkle ridges crossing the plains of Mare Tranquillitatis really stand out on the 2nd, when sunlight first touches the ramparts of the sharply defined crater Arago. Just to the southeast, the equator, but only 17\" from pole rim of the buried crater Lamont buckles the lunar Rima Ariadaeus to pole — the planet’s somewhat surface. Ariadaeus N By the 3rd, the Moon’s illumination nearly matches this image. How did nature create flattened disk is now evident as this weird landscape? Scientists have E the tilt of the rings reveals more pieced together the likely story that of the southern polar regions. an asteroid slammed into the young The low Sun angle early in the month Moon, carving out a huge, deep basin. highlights the roughness of the terrain The rings span nearly 43\" Later, smaller impactors scooped out the near Rima Ariadaeus. CONSOLIDATED LUNAR across and 10\" along the minor ATLAS/UA/LPL. INSET: NASA/GSFC/ASU axis. Compare this year’s view 50-mile-wide Julius Caesar and others, called the Ariadaeus rille. It is a collapsed val- to last summer’s, and you’ll including Lamont. Several times lava welled ley a half-mile deep created as two zones pulled notice the distinct change in up through cracks in the larger basin, flooding apart. A number of shallower rilles extend parallel ring tilt. By 2025, the rings it. Because Julius Caesar formed on a slope, its to the shores of Tranquillity. Ariadaeus Crater is will appear edge-on. eastern rim was lower, allowing the rising lava to the larger of the snowmanlike doublet at the breach that wall but not the higher western one. rille’s east end. Return the following night, the Titan, Saturn’s largest moon, Its central peak was swallowed. Much later, a 4th, when the equally interesting Hyginus rille to is an easy target for small smattering of impacts dotted the solidified Sea the west is revealed. Note how the wrinkles near scopes. You’ll find it north of of Tranquillity. Arago have vanished under the higher Sun, while Saturn Aug. 5 and 21, and due Rima Ariadeus is in the act of disappearing. south Aug. 13 and 29. On The long line to the south of Julius Caesar is Aug. 19, a field star slightly Rima Ariadaeus (pronounced Ah-ree-ah-day-us), dimmer than Titan’s magnitude 8.5 appears southwest of the METEOR WATCH I The brightest prevail planet; don’t confuse it for the moon, which lies southeast. Closer to the rings, Perseid meteor shower THIS YEAR’S famous Perseid 10th-magnitude Tethys, Dione, and Rhea orbit with periods Radiant Algol ARIES Uranus meteor shower is heavily affected by ranging from two to five days. C AME LOPA R DA L IS a Full Moon one day before maximum on Aug. 12. Its light hides all but the Two-toned Iapetus’ leading brightest meteors, severely attenuat- hemisphere is dark, causing the ing hourly rates. The Perseids are active from July 17 through Aug. 24. moon to appear faint at eastern PERSEUS Pleiades Mars The radiant in Perseus rises late at night, reaching a respectable 60° elongations (12th magnitude) Capella TAURUS altitude by 4 A.M. local time. and brighter at western ones The more favorable time this year (10th magnitude). This month, Aldebaran to view the Perseids is the few days prior to the peak. Each day before Iapetus is brightest Aug. 7, when AURIGA Aug. 12 will give you an extra hour of moonless predawn skies. For it reaches western elongation example, on Aug. 10, the Moon sets by 4 A.M. local time, with nearly an 9' west of Saturn. It moves to LYNX Betelgeuse hour before twilight begins. superior conjunction early Aug. 27 for U.S. observers. Castor Don’t forget that the occasional Perseid fireball whistles through our Usually, Iapetus skims Pollux GEMINI ORION atmosphere; even with a Full Moon, these will be hard to miss. past the northern hemi- PERSEID METEORS 10° sphere of Saturn’s disk, but the current shallow tilt of Active dates: July 17–Aug. 24 Aug. 12, 4 A.M. its orbital plane causes an Peak: Aug. 12 Looking northeast occultation instead. It’s a Moon at peak: Waxing crescent Maximum rate at peak: Focus on catching Perseid meteors in the — Continued on page 38 last hour before morning twilight, when 100 meteors/hour you’re on Earth’s leading hemisphere. WWW.ASTRONOMY.COM 33

STAR DOME N a _ C A M E L OPA R DA L I S HOW TO USE THIS MAP NGC 884 P E R SE U S M82 M81 This map portrays the sky as seen INOGPCE8I6A9 near 35° north latitude. Located ANDROMEDA S b ¡ inside the border are the cardinal directions and their intermediate ` CAS URSA points. To find stars, hold the map MINOR overhead and orient it so one of NE M33 _ a a the labels matches the direction d NCP _ you’re facing. The stars above Polaris the map’s horizon now match CEPHEUS what’s in the sky. ` a ` The all-sky map shows M31 `f how the sky looks at: b +c ` 11 P.M. August 1 b d d f 10 P.M. August 15 _ _ LACERTA _ c 9 P.M. August 31 k DRACO b Planets are shown d at midmonth Deneb a HERCULES a Path of the Sun (eclipti ` ` CYGNUSb d i d MAP SYMBOLS ¡ ` / c M13 c _a _ Open cluster Globular cluster _c + PEGASUS r Vega ¡ Diffuse nebula E a LYRA Planetary nebula Galaxy P V M57 STAR I ` + MAGNITUDES b S M27 a U ` Sirius 0.0 3.0 C _ LPECU 1.0 4.0 2.0 5.0 E M15 S Enif S D _ AG a E I ` T ¡ LP Altair a LA _ _ e `_ TA ` OPHIUCHUSg H E c) I c b Q N U U _ AQUARIUS _ S SERPENS CAUDA U L E U S ` e A d _ Q UI h ` M11 L A d _ b Saturn a b SCUTUM i M16 CAPRICORNUS M17 d P IAS CUISST R I N U S /j + M20 M22 SE STAR COLORS om h e M8 A star’s color depends on its surface temperature.   The hottest stars shine blue S A G I T TA c b a M6 •• Slightly cooler stars appear white MICROSCOPIUM R I US ¡ M7 • Intermediate stars (like the Sun) glow yellow • Lower-temperature stars appear orange h • The coolest stars glow red • Fainter stars can’t excite our eyes’ color _ CORONA d gp ` f NGC 623 receptors, so they appear white unless you _ AUSTRALIS use optical aid to gather more light ` TELESCOPIUM e d BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT _ www.Astronomy.com/starchart. _ ARA S

e AUGUST 2022 SUN. MON. TUES. WED. THURS. FRI. SAT. c Mizar s NGP 1 23456 b a _ M64 NW 7 8 9 10 11 12 13 ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY _ VIRGO c ¡ 14 15 16 17 18 19 20 ` 21 22 23 24 25 26 27 URSA MAJOR d¡ 28 29 30 31 M51 Note: Moon phases in the calendar vary in size due to the distance _` from Earth and are shown at 0h Universal Time. CVAENNE SAT I C I S E C I ` A a EN BOÖTES CBOEMR _b Arcturus _ W CALENDAR OF EVENTS d CORONA 1 Mars passes 1.4° south of Uranus, 5 A.M. EDT BOREALIS 4 Mercury passes 0.7° north of Regulus, 1 A.M. EDT 5 First Quarter Moon occurs at 7:07 A.M. EDT ¡ 7 Venus passes 7° south of Pollux, 6 A.M. EDT 10 The Moon is at perigee (223,587 miles from Earth), 1:09 P.M. EDT S CSAEPRUPTE N S ` 11 Full Moon occurs at 9:36 P.M. EDT _ The Moon passes 4° south of Saturn, midnight EDT M5 12 Perseid meteor shower peaks 14 The Moon passes 3° south of Neptune, 6 A.M. EDT ¡b ` Saturn is at opposition, 1 P.M. EDT 15 The Moon passes 1.9° south of Jupiter, 6 A.M. EDT c 18 The Moon passes 0.6° north of Uranus, 11 A.M. EDT a 19 Last Quarter Moon occurs at 12:36 A.M. EDT LIBRA The Moon passes 3° north of Mars, 8 A.M. EDT 22 Asteroid Vesta is at opposition, 3 P.M. EDT _ The Moon is at apogee (251,915 miles from Earth), 5:52 P.M. EDT ` 24 Uranus is stationary, 11 A.M. EDT 25 The Moon passes 0.7° south of dwarf planet Ceres, 3 P.M. EDT b m The Moon passes 4° north of Venus, 5 P.M. EDT Antares _ m / 27 New Moon occurs at 4:17 A.M. EDT o M4 P I SW US Mercury is at greatest eastern elongation (27°), noon EDT ¡ SCO 29 The Moon passes 7° north of Mercury, 7 A.M. EDT R + d LUPUS 31 a c WWW.ASTRONOMY.COM 35

PATHS OF THE PLANETS AUR PER AND LAC UMa LYN GEM CYG LMI Ceres Venus Path of the Moon TRI LYR LEO ARI SER SCT Path of PEG VUL Uranus SGE Mars the Sun (ecliptiPc)S C EQU DEL TAU Sun CNC ORI Pallas CMi Jupiter AQL LEP COL Juno Saturn appears at its best for the year in August SEX Neptune H YA MON ERI CET CAP CMa Pluto ANT PYX FOR Asteroid Vesta reaches MIC VEL opposition August 22 PUP CAE SGR PHE CrA HOR TEL Moon phases Dawn Midnight 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 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 Jupiter Uranus THE PLANETS IN THE SKY IN THEIR ORBITS Neptune These illustrations show the size, phase, Arrows show the inner and orientation of each planet and the two brightest dwarf planets at 0h UT for the dates planets’ monthly motions in the data table at bottom. South is at the top to match the view through a telescope. and dots depict the outer planets’ positions at midmonth from high above their orbits. Saturn Venus Opposition is August 14 Mercury Mars Pluto Ceres Ceres Venus Mars Jupiter PLANETS MERCURY VENUS Earth Date Aug. 31 Aug. 15 Mercury Magnitude 0.4 –3.9 Greatest eastern elongation Angular size 7.7\" 10.4\" Illumination 48% 95% is August 27 Distance (AU) from Earth 0.878 1.608 Distance (AU) from Sun 0.719 Right ascension (2000.0) 0.460 Declination (2000.0) 12h11.1m 8h24.3m –4°12' 19°52' 36 ASTRONOMY • AUGUST 202 2

This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows AUGUST 2022 JULYand colored dots show motions and locations of solar system objects during the month. 1 Jupiter HER CVn UMa LYN Callisto 2 LMi CrB BOÖ COM 3 Io 4 Ganymede LEO Europa 5 Europa Sun Io OPH SER Mercury 6 Celestial Comet VIR SEX Ganymede 7 Callisto equator C/2017 K2 JUPITER’S 8 CRV CRT H YA MOONS 9 10 LIB Dots display 11 positions of 12 ANT PYX Galilean satellites 13 at 4 A.M. EDT on SCO LUP the date shown. ARA South is at the CEN VEL top to match the view through a Early evening telescope. 8 7 6 5 432 1 31 30 29 28 27 26 25 14 15 Jupiter 16 17 Saturn S 18 WE 19 20 N 10\" 21 Uranus Neptune Pluto 22 23 MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO 24 25 Aug. 15 Aug. 15 Aug. 15 Aug. 15 Aug. 15 Aug. 15 Aug. 15 26 0.0 8.6 –2.8 0.2 5.8 7.7 15.1 27 8.9\" 0.4\" 46.9\" 18.8\" 3.6\" 2.4\" 0.1\" 28 85% 100% 99% 100% 100% 100% 29 1.055 3.547 4.202 8.857 100% 30 1.402 2.572 4.958 19.606 29.058 33.688 31 9.869 19.690 29.916 34.584 3h38.3m 8h54.6m 0h31.5m 21h37.5m 3h04.9m 23h41.9m 19h55.6m 17°52' 23°03' 1°45' –15°33' 17°00' –3°17' –22°59'

WHEN TO SKY THIS MONTH — Continued from page 33 VIEW THE Kepler’s laws in motion by 5 A.M. local time (an hour PLANETS before sunrise) on Aug. 1, and EVENING SKY Io’s shadow S by 3 A.M. on Aug. 31. Mercury (west) W Jupiter Small telescopes reveal paral- MIDNIGHT Ganymede’s shadow lel dark equatorial belts, while Mars (east) Io larger scopes show progressively Jupiter (east) more detail, tempered by local Saturn (south) Ganymede seeing conditions. The planet’s Uranus (east) temperate zones contain many Neptune (southeast) spots, including the Great Red MORNING SKY Aug. 16, 1 A.M. EDT 30\" Spot that features every alternate Venus (east) night on average. All these fea- Mars (southeast) The dual transit of Io and Ganymede (and their shadows) Aug. 15/16 highlights tures move quickly across the Jupiter (south) these moons’ orbital motion. Europa and Callisto lie farther east at this time. planet’s face, carried by Jupiter’s Saturn (southwest) roughly 10-hour rotation period. Uranus (southeast) challenging event, given the night. Jupiter shines a brilliant Neptune (southwest) The four Galilean moons brightness of Saturn and its magnitude –2.7 most of the orbit Jupiter every two to 16 rings, combined with Iapetus’ month and reaches magnitude days. Dual transits are fascinat- paltry 11th-magnitude glow. –2.8 in the last week of August. ing to follow; a fine example Digital imaging is likely to best The giant’s apparent diam- occurs Aug. 15/16. Less than an Ganymede 36\" east of Io — note capture the event. Iapetus lies eter spans 49\" by late August. hour after Jupiter rises in the this for later. Io is the innermost just above the rings and begins The best views are in the early Midwest, Io’s shadow begins large moon and moves faster to disappear around 12:25 A.M. morning hours, when the planet a transit at 11:24 P.M. EDT. Io than more distant Ganymede. EDT Aug. 27 (late on Aug. 26 stands high in the southern sky. itself stands 19\" east of the plan- Beginning at 11:59 P.M. EDT, in all other U.S. time zones). It lies due south at 53° altitude et’s limb at this time. Also spot Ganymede’s shadow appears Other moons also undergo eclipses and transits across the planet’s disk; these will increase Iover the next few years. COMET SEARCH It’s all about the dust Neptune is an easy binocular object at magnitude 7.7. It starts THE ENJOYMENT is set to con- Comet C/2017 K2 (PanSTARRS) the month in southwestern tinue as C/2017 K2 (PanSTARRS) Pisces, 5° due south of Lambda glows at 7th magnitude. Catch it Aug. 1 N (λ) Piscium, the Circlet’s south- from the suburbs with a 4-inch r easternmost star. You can also scope or easily sweep it up with home in on Neptune by looking binoculars from a dark sky. 5 M107 13.5° southwest of Jupiter. The PanSTARRS starts August in 10 region is best viewed starting a Ophiuchus, about 2.5° northwest couple of hours after midnight, of 8th-magnitude M107 and 10.5° Path of Comet PanSTARRS 15 LIBRA when Neptune rises above 35° southwest of M10. All three tar- OPHIUCHUS q d altitude in the southeastern sky. gets are fairly compact and well E defined, but the comet will be e Through binoculars on lopsided: very sharp on the Aug. 1, you’ll find a star of southern flank where the solar r 20 similar brightness 0.4° to the wind hits and soft to the north- s planet’s east. Neptune’s motion east as the dust spreads outward i` g carries it westward; on Aug. 31, t the pair is 1° apart. A telescope t1 25 h will reveal the distant planet’s t2 30 dim bluish disk, spanning a SCORPIUS mere 2\". Neptune reaches oppo- sition in September. into a stubby fan. 2° l M80 b For a comet some four times bigger than Halley, imagers might Compare Comet PanSTARRS to globular clusters M10 (to the northeast, not expect to capture the green glow shown) and M107. Which does it resemble more? from excited dicarbon molecules. But at a distance of 2.5 astronomical units (AU, where 1 AU is the average Earth-Sun distance), this mecha- Jupiter lies in northwestern nism won’t have switched on. Comet dust reflecting our Sun’s light will be neutral compared to the globu- Cetus. It rises in the hour before lars, whose red giant stars give them a slightly warmer hue. midnight on Aug. 1 and soon Later in the month, PanSTARRS slides through the beautiful binocular and telescopic fields of the before 9 P.M. local time by the Scorpion’s face. Note the gorgeous wide double pair of Beta (β) and Omega (ω) Scorpii. Imagers with 31st. It moves westward each 135mm lenses can capture the comet along with the colorful Rho (ρ) Ophiuchi clouds to the east. 38 ASTRONOMY • AUGUST 2022

Morning stars LOCATING ASTEROIDS I LYNX Getting up there Castor GEMINI HOW HIGH UP the asteroid list are you? 704 is the biggest num- Pollux ber you’ll see from the suburbs with a 4-inch scope, not counting the unusual near-Earth rocks. Floating in front of Pegasus’ nose, CANCER CANIS MINOR main-belt asteroid Interamnia vaults up the southeastern sky. M44 Venus Procyon Use the bright star Enif (Epsilon [ε] Pegasi) to jump westward 10° into Equuleus the Little Horse and land on magnitude 3.9 Alpha (α) Equulei, logically named Kitalpha. From the 23rd through the Aug. 17, 1 hour before sunrise month’s end, 200-mile-wide Interamnia lies within 1° of the star. Looking east Before that, we can use the old-timer’s trick of letting the sky Venus sits near the Beehive open cluster (M44) the morning of Aug. 17. drive for us. On Aug. 1, set your scope on Kitalpha, turn off any Center your binoculars on the bright morning star to enjoy the meetup. motors, and wait 23 minutes for Interamnia to come into view. By the 15th, it’s down to an 11-minute drift. We can do this when both objects’ declination is nearly the same. Interestingly, 704 is the fifth-largest asteroid in the main belt! The reason it took so long to find is its high orbital inclination — 17° — which for long periods keeps it away from the ecliptic search zones. It’s also darker than average and lies mostly outside the orbit of Ceres. Interamnia is the Latin name for Teramo, Italy, where Vincenzo Cerulli built his observatory and later made his discovery in 1910. Wild horses southeast of Io’s shadow. Now target of advanced imagers in N b two shadows race across the recent years, and some elusive jovian cloud tops, but faster Io’s cloud features can be captured Enif will stay well ahead. Io itself using high-speed video. PEGASUS begins a transit 24 minutes later. Visually in a telescope, Uranus renders a 4\"-wide featureless E By 1 A.M. EDT (midnight disk. A Last Quarter Moon CDT), Io has caught up with ventures within 4° of Uranus EQUULEUS Ganymede’s shadow and passes the morning of Aug. 18. ` it within 30 minutes. Io’s Path of Interamnia shadow departs the western Mars moves eastward and 5 10 15 20 25 30 limb of Jupiter at 1:38 A.M. EDT, crosses into Taurus Aug. 9, Aug. 1 followed just under an hour while Uranus remains in Aries; later by Io. Ganymede’s huge already, 4.7° separate them. _ shadow lingers until just before Mars treks 6° south of the 1° 3 A.M. EDT. If you stay up Pleiades between Aug. 16 and another few hours, you’ll catch 19. The 19th is also when the Asteroid 704 Interamnia arcs through Pegasus and Equuleus, the Ganymede itself beginning its Last Quarter Moon catches up Winged Horse and the Little Horse respectively, this month. transit at 4:09 A.M. EDT. It and lies less than 3° from Mars. leaves by 5:39 A.M. CDT, just as In the predawn sky, telescopes — smaller than recent years but continues declining, reaching twilight arrives in the Midwest. might show the contrasting the best for some time to come. 14° by Aug. 31. Fortunately, its dark Syrtis Major and the bright brilliance still renders it visible Mars and Uranus rise Hellas basin on the tiny disk. Venus is a brilliant morning even in the bright dawn sky. together in Aries soon after star at magnitude –3.9 all midnight local time on Aug. 1. By Aug. 31, Mars stands 5.7° month. On Aug. 1, it rises in Through a telescope, Venus Mars is easy to find, shining at northwest of similarly orange- Gemini two hours before the changes from a 93-percent-lit magnitude 0.2. Uranus is much red Aldebaran, the brightest Sun. The planet crosses into disk spanning 11\" on Aug. 1 to fainter, requiring binoculars to star in Taurus. Cancer on Aug. 10 and by 97 percent lit and 10\" across on spot at magnitude 5.8. Center Aug. 17 stands just under 1° Aug. 31. Mars in your binoculars and Mars season is now upon us: west of the Beehive Cluster you’ll find Uranus 1.4° north of The Red Planet grows in appar- (M44). Look for the pairing in Martin Ratcliffe is a the Red Planet. Its bluish hue ent size from 8\" to 10\" during binoculars about 4° high one planetarium professional with will contrast nicely with Mars. August. By the time it reaches hour before sunrise. Evans & Sutherland and enjoys opposition in December, Mars observing from Wichita, Kansas. Uranus has become the will be nearly double this size Catch the waning crescent Alister Ling, who lives in Moon 6.5° northwest of Venus Edmonton, Alberta, is a longtime GET DAILY UPDATES ON YOUR NIGHT SKY AT Aug. 25 before sunrise. Venus’ watcher of the skies. www.Astronomy.com/skythisweek. elongation from the Sun WWW.ASTRONOMY.COM 39



The strange case of the eyeball These tidally locked planets worlds could be the key to finding life in the universe — if they exist. BY MICHAEL CARROLL HUMANS HAVE LONG IMAGINED what life on ABOVE: A tidally locked exoplanet orbits a red dwarf in this artist’s concept. another world may look like. And as we entered a golden age ESO/M. KORNMESSER/N. RISINGER (SKYSURVEY.ORG) of exoplanet discovery, the hunt picked up for Earth 2.0, a twin to our planet orbiting within its star’s habitable zone. LEFT: Seen from a nearby moon, a tidally locked ocean world simmers beneath But so far, searches have turned up empty, leading scientists the light of its red dwarf sun. The sea along the terminator — the day/night to use some out-of-the-box thinking to find another haven boundary — freezes as it approaches the cold nightside, but temperatures at for life in the universe. the point directly under the star may be quite temperate, with liquid oceans amenable to life. MICHAEL CARROLL The habitable zone, or Goldilocks zone, is the region surrounding a star where water can exist on the surface of an orbiting planet or moon. The hotter the star, the farther away its habitable zone sits. Take red dwarfs, for example: Of the hundreds of billions of stars in our galaxy, astronomers esti- mate that about 80 percent of them are red dwarfs. At a mere 0.08 to 0.5 times the mass of the Sun, these stars only reach surface temperatures around 4,000 to 6,700 degrees Fahrenheit (2,200 to 3,700 degrees Celsius). Thus, the habitable zone is quite close to these stars. That proximity makes it much easier to spot any planets that pass in front of the tiny star, as such eclipses tend to block a large fraction of starlight and make the presence of an exoplanet clear. During its nine-year mission, the planet- hunting Kepler space telescope found 2,709 planets through this transit method; another 2,057 are still awaiting confir- mation. And most of Kepler’s finds are worlds circling close to red dwarf suns, some of which are similar in size to our own. WWW.ASTRONOMY.COM 41

TRAPPIST-1 e Distance from Earth: 41 light-years Mass: 0.69 Earths Radius: 0.92 times Earth Year: 6.1 days The TRAPPIST-1 system is home to seven Earth-like A member of one of the most famous stellar systems, exoplanets. Of them, TRAPPIST-1 e (second from the TRAPPIST-1 e is one of seven exoplanets around Trappist-1. right) is the most likely to host life, as it may have Several of the worlds may be eyeball planets. But while all held onto any water on its surface. NASA/JPL-CALTECH the planets could also have water, only three lie firmly within the star’s habitable zone. Among these Earth-like exoplanets, there exists a bizarre class known as A hot, bright, early stellar phase may have caused eyeball planets. These worlds orbit so all the evolving planets to look like Venus: any early near to their suns that they are tidally oceans long since evaporated, leaving behind a thick, locked, with one hemisphere always fac- uninhabitable atmosphere. But according to a 2018 study ing toward the star and the opposite one published in the Astrophysical Journal, Trappist-1 e is the in eternal night. Scientists are beginning most likely to have managed to retain water, perhaps to realize that eyeball worlds are more even hosting an Earth-like ocean. than just curiosities — they’re key to understanding how common life might All seven of the Trappist-1 planets have similar be in the universe. Their arrangement densities, making the system very different from our own. of an always-lit and always-dark side Such similar densities suggest the planets also all have causes fascinating weather and unusual similar compositions. The James Webb Space Telescope surface conditions. These characteristics will be able to probe further into the atmospheres of may make eyeball planets within the these exoplanets, searching for elements that could Goldilocks zone prime candidates for hint at the presence of life. hosting life, but they could also make otherwise habitable planets inhospitable. the body’s rotation until it becomes tid- Eyeball planets initially got their ally locked. We have a good example of moniker when astronomers noted that Oceanic eyes such synchronous rotation on our own in the habitable zone, tidally locked cosmic front porch: The Moon orbits worlds covered by water would become After coalescing around its star, a planet Earth once a month and takes the same frozen starting at the terminator (the has some spin. But over time, the host amount of time to turn once on its axis. edge of night) while the seas would star’s gravity pulls at the world, slowing This means that we always see the same remain clear near the substellar point face of our Moon. (the point that directly faces the star). 42 ASTRONOMY • AUGUST 2022

This dark blue central ocean surrounded TYPES OF EYEBALL PLANETS by sea ice gives the appearance of an eyeball. Terrestrial planet Red dwarf As astronomers racked up exoplanet A rocky planet 0.5 to 2 times discoveries over the last 30 years, they the size of Earth. realized eyeball planets may be plentiful Example: TRAPPIST-1 e among planetary systems and that a wide range of worlds may take on an eyeball Super-Earth Habitable zone form. One common example is super- Earths, worlds that are larger than Earth An exoplanet larger than Earth Where liquid water can but smaller than Neptune. but smaller than Neptune. exist on a planet’s surface. Example: Proxima b Allison Youngblood, an astrophysicist ASTRONOMY: ROEN KELLY at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has been using On smaller eyeball planets, desert conditions likely reign supreme on the dayside, while the nightside of the the Hubble Space Telescope to study world freezes. The terminator may be a haven for potential life, as liquid water could exist there. ESO/L. CALÇADA super-Earths orbiting near red dwarfs. “There’s some evidence of super-Earths has found a way to thrive despite a salt waters, the ice cools the ocean as it melts. with thick atmospheres and some with concentration above 30 percent. So, it Gradually, more and more of the ocean thin or no atmospheres at all,” but obser- isn’t impossible for salt-loving bacteria freezes, even on the dayside. At that vations point to many of these worlds to likewise exist on Proxima b in this point, only an atmosphere with abundant being “really cloudy and hazy,” she says. scenario. greenhouse gases could prevent global This would make spotting life difficult, freezeover. but some astronomers believe that, in Open oceans aren’t the only possible the right scenario, super-Earths hold the surface conditions for Proxima b. A But, according to Eric Wolf, a most promise for life beyond the solar paper published in Nature Astronomy research associate at the Laboratory for system. in 2019 suggests that oceans beneath Atmospheric and Space Physics in the substellar point might freeze over Boulder, Colorado, other models have One such scenario is on eyeball super- because of sea-ice dynamics. Modeling shown the opposite scenario. Just as ice Earths. These worlds are likely covered conditions on Proxima b, the researchers can drift from cold regions to warm in vast oceans. On the night hemisphere, found that as sea ice drifts into warmer regions, heated waters can also serve as the planet suffers arctic conditions while the dayside swelters, the heat burning away clouds and, in extreme scenarios, the ocean itself. The habitability of such a planet depends on a lot of factors, including the day/night temperature, the activity of the host star, the density of the planet’s atmosphere, and even the saltiness of the ocean. As it so happens, a prime target for habitability sits just at our interstellar back door. Proxima b is an eyeball super- Earth orbiting within the habitable zone of Proxima Centauri, the closest star to our solar system. A 2017 study published in Astrobiology modeled potential cli- mates of the exoplanet, assuming a variety of conditions. The researchers concluded that a Proxima b “with an atmosphere similar to modern Earth’s can have a habitable climate with a broad region of open ocean, extending to the nightside.” How far the ocean extends depends upon the amount of salt assumed in the water, but even with an ocean with high salinity, Proxima b could theoretically host life. One only has to look as far as Earth’s infamous Dead Sea, where life WWW.ASTRONOMY.COM 43

On an ocean-covered eyeball planet, there may lie a Even if an eyeball planet lies within the region near the terminator where the icy nightside habitable zone, its surface can range wildly gives way to liquid water. NASA/JPL-CALTECH/T. PYLE (IPAC) from endless ocean to frozen wasteland. a transporter of heat from warm regions Rock-solid places surface may remain above freezing. But to cold regions and melt the ice, warm- if the air is thin or stagnant, tempera- ing the climate instead. “Depending While super-Earth eyeball planets are tures will drop precipitously, even if the on the details,” Wolf says, “the climate ocean-covered orbs cocooned in dense planet is on the inner edge of its star’s could very literally be anything from atmospheres, smaller Earth-like tidally habitable zone. the cold, icy states shown by [the locked worlds have rockier surfaces. 2019 study] to Venus-like, hot, Where the planet’s star blazes overhead, However, these smaller eyeball planets CO2-dominated worlds, or they could desert conditions blanket the landscape. face a larger problem than temperature even look like [Saturn’s moon] Titan Closer to the nightside, the environment in terms of habitability: atmospheric with [methane] and hazes.” Not to men- becomes more clement, perhaps allow- erosion. An atmosphere is crucial for tion that if continents are included in ing for liquid water within that twilight life’s survival, but, orbiting close to their the mix, he adds, “all bets are off zone. Also within that twilight region, red dwarf suns, these small worlds face because the presence and location of provided the planet has enough atmo- ferocious stellar winds that can strip continents significantly changes the sphere with strong wind currents, the away even the densest of atmospheres. patterns of ocean transports.” So even if an eyeball planet lies within the habitable zone, its surface can range wildly from endless ocean to frozen wasteland. 44 ASTRONOMY • AUGUST 2022

Proxima Centauri b Distance from Earth: 4.2 light-years Mass: 1.27 Earths Radius: estimated 1.08 times Earth Year: 11.2 days Proxima Centauri b — often shortened to just Proxima b — is a super-Earth discovered through the subtle wobble of Proxima Centauri itself. As the star is pulled toward and away from us by its unseen planet, its light shifts toward the blue and then the red end of the spectrum, respectively. Proxima Centauri is also home to two other planets. Likely a large terrestrial world, Proxima b is within its star’s habitable zone. But the planet probably receives bouts of ultraviolet radiation hundreds of times greater than that Earth receives from the Sun. This radiation may have stripped away Proxima b’s atmosphere. Even if Proxima b does have an atmosphere, it’s difficult to model the planet’s surface because scientists don’t know its radius. Most exoplanets have been found using the transit method — when the world happens to pass in front of its star. This technique also allows researchers to measure an exoplanet’s radius. But Proxima b is not known to transit, so its radius is unknown. Exoplanet expert Avi Mandell of NASA’s Astronomers recently discovered that Proxima Centauri is home to three exoplanets. Proxima b, the Goddard Space Flight Center points out innermost world, is a super-Earth, but likely receives too much radiation to host life. ESO that “some amount of atmosphere will always be eroded — we’re losing some a planet reaches this point, there is no But there are ways around this run- atmosphere from Earth all the time due stopping the erosion. Researchers think away loss, giving life on small eyeball to our own Sun.” But, if not replenished this phenomenon could explain planetary planets a lifeline. It’s likely that both quickly enough by gases leaking out from atmospheres that appear mysteriously Venus and Earth saw hydrodynamic the planet’s interior, an atmosphere may drained of oxygen, nitrogen, and heavier escape early in their evolution, yet lose the compounds that are needed to noble gases. they have managed to retain thick sustain life, or simply evaporate entirely. Youngblood suggests that the amount of atmospheric loss will depend on what kind of atmospheric escape is occurring. The most troublesome escape is known as hydrodynamic escape. Today, only a handful of different atoms are escaping Earth from the top of the atmosphere. But in the case of hydrodynamic escape, that trickle becomes a gush, with escap- ing atoms acting like a fluid that drags still-heavier atoms and molecules along for the ride. Ultimately this kind of atmo- spheric escape is driven by heat and, once WWW.ASTRONOMY.COM 45

atmospheres today. According to atmosphere, the world could remain says. Hubble sees from the ultraviolet to Youngblood, mitigating the atmospheric habitable at the substellar point. near-infrared, but Webb is sensitive to a erosion “partly depends on the composi- Conditions warm if the planet is home different part of the infrared. tion of the atmosphere — what atoms to an Earth-like atmosphere, but or molecules are present high in the become inhospitable relatively quickly Already, researchers plan to use atmosphere that absorb the stellar as more carbon dioxide is injected JWST to observe several eyeball planet radiation that drives escape.” into the modeled atmosphere. candidates. In some cases, Webb will watch a planet as it transits its star. An example of what various atmo- Therefore, even atmospherically When a world moves in front of its star, spheric conditions can look like on a challenged eyeball exoplanets could it’s possible to not only spot the planet, small eyeball world lies a mere 40 light- contain regions of habitability under but also determine what molecules exist years away. The TRAPPIST-1 system is the right conditions. in its atmosphere. Just as the planet famed for hosting seven Earth-like exo- blocks starlight with its solid surface, so planets. Of them, TRAPPIST-1 e is a JWST: The ophthalmoscope too can the molecules in the atmosphere small eyeball world and the most likely absorb light from the planet’s sun, creat- to be suitable for humanlike life, accord- Eyeball experts now have a new tool: ing dips in the spectrum of light we ing to a 2017 study published in The the James Webb Space Telescope receive from the star. Studying these Astrophysical Journal Letters. (JWST). Outer planets researcher Heidi missing wavelengths of starlight can Hammel, a member of the JWST team, give scientists insight into the chemical The study modeled what the world looks forward to new revelations from composition of the planet’s atmosphere. may look like under a variety of atmo- the powerful observatory. “Webb’s spheric conditions. Without greenhouse strength is in atmospheric chemistry; In other cases, JWST will observe a gases, TRAPPIST-1 e would be a cold it will be complementary to what the planet as it passes behind its star, an world, but, even with just a thin Hubble Space Telescope is doing,” she effective technique for measuring how much of the system’s total light is LHS 1140 b reflected by the dayside of the planet. This can give researchers insight into both the chemical composition of a world and its temperature. Distance from Earth: 48.8 light-years BELOW: Some 40 light-years from Earth lies Mass: 6.4 Earths LHS 1140 b. In 2020, the Hubble Space Telescope spied potential evidence of water in this eyeball Radius: 1.6 times Earth world’s spectrum. ESO/SPACEENGINE.ORG Year: 24.7 days Discovered in 2017, LHS 1140 b is promising as an Earth- like exoplanet for a few reasons. At 0.1 astronomical unit (AU, where 1 AU is the average Earth-Sun distance) from its star, LHS 1140 b is within the habitable zone and receives 46 percent of the radiation from its star that Earth does from the Sun. An ocean of lava could cover the surface of the planet, according to a 2017 study published in Nature. Instead of preventing habitability, however, the lava could feed steam into LHS 1140 b’s atmosphere, replenishing the planet with water. A 2020 study in Astronomy and Astrophysics suggests that habitability on LHS 1140 b depends on the composition of its atmosphere — with life possibly able to survive in atmospheres dominated by nitrogen, hydrogen, and carbon dioxide. Researchers hope to use JWST to gain further insight into LHS 1140 b’s atmosphere.

RIGHT: 55 Cancri e likely has an atmosphere thicker than our own, hiding its lava-covered surface from our view. NASA-JPL/CALTECH BELOW: Tidally locked to its star, 55 Cancri e promises visitors an ocean of lava. NASA-JPL/CALTECH 55 Cancri e Distance from Earth: 41 light-years Mass: 7.99 Earths Radius: 1.9 times Earth Year: 0.7 day Orbiting a star called Copernicus (also known as 55 Cancri A, or just 55 Cancri), 55 Cancri e is uninhabitable, thanks to a molten surface with a temperate greater than 3,000 degrees Fahrenheit (1,600 degrees Celsius). When the planet was first discovered, researchers suggested that its host star’s high ratio of carbon to oxygen could indicate 55 Cancri e was covered in a thick layer of diamond. But further analysis showed that Copernicus contains more oxygen than carbon after all, eliminating this fanciful possibility. Currently, climate models can vary habitable zones.” And some of them are widely as scientists move beyond the eyeball planets. strict Earth-centric models they’ve used in the past. Adding new data from While conditions would be different JWST, scientists will be able to put fur- than Earth, alien life could exist beneath ther constraints on the atmospheric such exotic skies. And they could see a models that can be applied to an eyeball plethora of landscapes: frozen waste- planet, giving them a better idea of what lands, rugged mountains, parched des- conditions may exist on its surface. erts, or oceans from horizon to horizon. Only time will tell what strange and Already, JWST is slated to study wondrous forms life could take under many eyeball planets that Hammel the angry glare of a red dwarf sun. calls “the usual suspects.” She says, “Any of the exoplanet systems that you can Michael Carroll is a writer, lecturer, and name are targets for Webb — like the artist. He has published over 30 books in TRAPPIST planets or 55 Cancri e — print. His latest novel is Plato’s Labyrinth: so there are about 68 exoplanets on the Dinosaurs, Ancient Greeks, and Time list, including five or six terrestrials in Travelers (Springer, 2021). WWW.ASTRONOMY.COM 47

Capturing the in high res The digital revolution has enabled amateur astronomers to take crisp, clear images that would have been the envy of professionals just a few decades ago. BY LEO AERTS AND KLAUS BRASCH 48 ASTRONOMY • AUGUST 2022

F ew technological advances have impacted astronomy routinely uses an AstroTechniek as much as the digital revolution. That’s been true atmospheric dispersion corrector, in the professional realm since the 1980s, and it’s especially when his target is below been true for amateur astrophotographers like us 40° high in the humid Belgian skies. since the turn of the millennium. Perhaps nothing These handy optical devices have illustrates this seismic shift more vividly than comparing historic two rotatable prisms made of sili- photographs of the Moon with their more modern counterparts. cate glass, which can be adjusted to introduce a degree of native For instance, take the great Although Aerts has used many chromatic aberration that counter- lunar crater Clavius, imaged in older model webcams, including acts that of our atmosphere. the 1950s with what was then the several DMK CCD models, they world’s largest telescope, the operated at relatively low capture In short, a typical imaging run 200-inch Hale telescope at Palomar rates of 30 to 60 frames per second for Aerts varies depending on his Observatory. If you compare that (fps). His current favorite cameras webcam’s field of view and seeing shot (see the top of page 51) with a are ZWO CMOS models, an ASI conditions. He’ll collect anywhere corresponding image taken in 2005 178MM with a 2.4 micrometer (μm) between 4,000 and 5,000 frames using a standard 14-inch consumer pixel size, and an ASI 290MM with for a full shot of the Moon and scope and one of the first commer- 2.9 μm pixels. These models per- 15,000 to 20,000 frames for a cially available CCD cameras, the form very well up to 150 to 250 fps, close-up of a lunar region of inter- differences in resolution, sharpness, with low levels of noise and high est. Of those, about 800 to 900 of and dynamic range between the infrared sensitivity. Aerts also the best frames are combined with two are striking. his preferred stacking software, So, what are some AutoStakkert. If seeing conditions So, what are some of the tools of the tools and are excellent, he caps the number and methods for cutting-edge lunar methods for cutting- of selected frames at about 10 per- imaging now available to those with edge lunar imaging cent of the total shot, provided the telescopes suitable for amateurs now available noise level allows it. Aerts uses (6 to 14 inches)? Apart from good to those with FireCapture for image capture and optics and a solid mount, most telescopes suitable practitioners can employ any num- for amateurs? Author Leo Aerts’ optically superb telescope, ber of excellent webcam models or an Opticon 10-inch f/15 “planetary” Schmidt- laptop computers (with appropriate Cassegrain, is shown at left. Above, Aerts and his image-capture software), as well as full setup are ready for an exciting imaging session sophisticated image-stacking and in his backyard. ALL IMAGES BY LEO AERTS UNLESS OTHERWISE NOTED processing software. In addition, for close-up, high-resolution imaging of select lunar features, quality Barlow lenses or Powermates — which both extend focal lengths — are essential, as are atmospheric dispersion cor- rectors and, typically, near-infrared filters to minimize the effects of less-than-perfect seeing conditions. Shooting from his home near Brussels, Belgium, one of this arti- cle’s authors, Leo Aerts, routinely uses a custom-built Opticon 10-inch f/15 “planetary” Schmidt- Cassegrain (with only a 25 percent central obstruction) and a Celestron 14-inch f/11 scope, both on movable Losmandy G-11 equatorial mounts. The telescopes are stored in his home garage and wrapped in ther- mal insulating material to prevent overheating during daytime hours. WWW.ASTRONOMY.COM 49

Photoshop 10 for final processing. Who among us have been an incomparable adven- Any refining or elimination of noise hasn’t imagined ture. And while few of us are likely levels is done with the unsharp what an incredible to experience that in person, we can masking application or the wavelets experience it must accomplish it virtually thanks to function of Astra Image. have been for the the magic of digital imaging. Apollo astronauts One common misstep for new to approach and The first stop on our lunar tour imagers is not monitoring seeing circle the Moon just is the path of one of the most scien- conditions throughout observing. a few miles above tifically productive Apollo missions: During an extended imaging run, Apollo 15. In 1971, the astronauts conditions can vary considerably, its surface? landed in the Hadley–Apennine which can ruin a good portion of region near the Montes Apenninus your session. Limit your image cap- by NASA’s Lunar Reconnaissance (Apennine Mountains), in the ture to periods of favorable seeing, Orbiter (LRO). To bring that point northern hemisphere of the Moon pausing when necessary, and only home, we have put together a sort of bordering Mare Imbrium (Sea of resuming once seeing stabilizes virtual tour of the lunar landscape, Rains). Their assignment was to again. It may be overwhelming at featuring some of its highlights, as investigate and collect samples in first, but, as with any new endeavor, well as the more captivating aspects the area around Rima Hadley consistency, patience, and persis- of familiar regions across the (Hadley Rille), a volcanic channel tence are essential. Moon’s spectacular surface. Except likely formed during the Moon’s where otherwise indicated, all early history. To accomplish this, Digital technology has reached images were taken by Aerts with David Scott and James Irwin were a level of precision that allows ama- a standard 14-inch Celestron. equipped with the first Lunar teur practitioners to generate pic- Roving Vehicle, allowing them to tures rivaling those produced by Flying over the Moon roam and explore a sizeable area early space probes, and even some near their landing site. of the lower-resolution images taken Who among us hasn’t imagined what an incredible experience it With consumer equipment, the Rima Hadley must have been for the Apollo snaking valley of Rima Hadley, only astronauts to approach and circle roughly 1 mile (1.6 kilometers) Palus Putredinis Mons Hadley the Moon just a few miles above its wide, is easily visible, as well as both surface? Seeing that otherworldly Mons Hadley and Mons Hadley Rima Hadley Julienne Apollo 15 panorama of craters, mountains, Delta, the massive mountains that St. George smooth lava plains, and endless surround their landing site. Mons Hadley Delta horizons in brilliant detail must Chasing shadows One of the most absorbing activities seasoned observers can undertake is following the gradual changes in the shadow patterns of selective Hadley C 1b Taizo Carlos Béla Jomo 1a 1A AND 1B The Apollo 15 landing site and nearby features are shown in this photo of the Hadley-Apennine site taken from lunar orbit (1a). A similar-scale shot taken Aug. 24, 2016, with a Celestron-14 reveals even finer detail (1b). LEFT: NASA/JSC/ARIZONA STATE UNIVERSITY 50 ASTRONOMY • AUGUST 2022