Astronomy

your observations well before Ring C (obscuring globe) or after opposition. Equatorial Zone Study Saturn’s face South Compared to Jupiter, Saturn’s Equatorial Band Equatorial Zone face is a more delicate object North of study. While it too displays North Equatorial dark belts and bright zones, Belt (S) North Tropical Zone many are of low contrast. This is because we see them through North Equatorial North Temperate Zone a high-altitude haze in Saturn’s Belt (N) upper atmosphere, which hides North Temperate Belt North North the finer details beneath. But North Polar Region Temperate Zone Saturn is known to surprise. North North Temperate Belt (polar hexagon) Small scopes generally show the world's Equatorial Zone split on occasion. In some North Equatorial Belt, as well ABOVE: The nomenclature (by far the brightest), bordered observations, the bright as a prolonged white spot and for Saturn’s dark belts and by dark Equatorial Belts. The North North Temperate plume activity in the Equatorial bright zones is shown planet’s Tropical and Temperate Zone (just south of the North Zone. Meanwhile, this year, as here, with the planet regions are more difficult to Polar Region) persisted into of early May, some low-contrast oriented north down. define, and they generally November before solar white spot activity has been appear as a wide, bright yellow conjunction. imaged in the planet’s North NASA, ESA, AMY SIMON (NASA-GSFC), wash. Meanwhile, the planet’s Tropical Belt. MICHAEL H. WONG (UC BERKELEY); North Polar Region usually This year, observers should PROCESSING: ALYSSA PAGAN (STSCI) takes on a dusky appearance also be on the alert for pro- So keep an eye out, because that gradually darkens toward nounced white-spot activity. more intense white-spot activ- LEFT: Saturn’s tiny moon the pole. However, early White spots, which can vary ity potentially could be linked Pan (marked by arrow) observations this year show dramatically in size and inten- to spoke propagation. As plan- steadily orbiting around the planet’s dark cap appear- sity, are the result of powerful etary scientist Geraint Jones of the gas giant allows it to ing like an island in a brighter atmospheric storms hurling University College London and carve out a small path, polar region. water and other molecules high his colleagues have proposed, called the Encke Gap, in into Saturn’s atmosphere, where energetic beams of electrons the fringes of Ring A. NASA/ This somewhat placid view they freeze out to form white produced above powerful thun- changes once one images the clouds. Two bright white spots derstorms (related to white-spot JPL-CALTECH/SPACE SCIENCE INSTITUTE ringed planet under excellent detected in the North North activity) could be transported seeing conditions or uses a Temperate Zone may have to the rings by Saturn’s mag- This year, larger high-quality telescope caused the zone to temporarily netic field. There, the electrons observers with substantial magnification. increase in brightness last charge the dust, lifting it out of should also Then, much more structure apparition, and such activity the ring plane to create the be on the pops into view, including intri- appears to be ongoing early this spokes. alert for cate banding, different-colored time too. Several intriguing pronounced zones and belts, and white-spot smaller white spots were also Whether you decide to study white-spot activity. detected at varying latitudes the details of Saturn’s face or activity. last year, including one in the not, don’t miss out on this Last apparition, Saturn’s face year’s opposition display. After was well banded, with the all, ask any observer and they’ll North Polar Region taking on tell you: Views of the ringed the appearance of a hexagon. world through instruments of Amateur astronomers were able all sizes never disappoint. It is to capture the North Polar the most beautiful planet in our Hexagon (within which resided solar system, no matter how a very small dark cap) on sev- much or little detail you seek. eral instances. By this year’s opposition, however, the hexa- Stephen James O’Meara is a gon will likely recede from view. Overall, the yellow long-time contributing editor and Equatorial Zone appeared columnist at Astronomy. brighter and more intensely colored to the north, while the dusky Equatorial Band was WWW.ASTRONOMY.COM 51

stargazingTheABCs of Take a seat at your scope and brush up on your observing vocabulary. BY MICHAEL E. BAKICH DARK ADAPTATION I compiled my first version of this list in 2004 as a list of tips to help you get In the first 30 minutes in a dark the most out of your time at the eyepiece. Well, it’s time for an update. This setting, the sensitivity of our time, I’m not going to list something for every letter (I still don’t know any vision increases 10,000-fold, with amateurs who have X-ray telescopes!), but I’ll make up for that with a few little gain after that. Brief expo- multiple-letter entries. Most are new, but several have stood the test of time. I sure to bright light temporarily discovered some of these myself, while others were passed on to me by friends reverses the gain, though how at nearby telescopes. I hope they’ll all help you become a better observer. much you lose depends on how long the light is on; a strobe flash Barlow lens 2x Barlow doubles the focal Binoculars that lasts just an instant does less length and the eyepiece will damage than a bright light lasting This type of lens (which you provide twice the power. If High-quality binoculars a few seconds. If you need to turn insert in the telescope’s focus- you choose your eyepieces should be part of every on a light during your observing er and then put an eyepiece carefully, adding a Barlow can observer’s kit. For mag- session, opt for a red light. At into) increases the effective give you a much wider range nification, choose 7x, 8x, night, your eyes are most sensi- focal length of a telescope of magnifications. or 10x. The front lenses, tive to this wavelength, so you’ll and magnifies its image. A however, should be at least need less light to see clearly. ABOVE: Using red lights will help preserve your night vision, as seen in this six-hour exposure at a California desert star party. CHRIS COOK 52 ASTRONOMY • SEPTEMBER 202 2

50 millimeters across. Smaller from? Numerical designa- Astronomical twilight ones just don’t collect enough tions for stars brighter than light. about 7th magnitude first In the evening, astronomical twilight lasts until the Sun sinks 18° below appeared in Historia Coelestis the horizon. JOSH FELISE Circumpolar star Britannica, a star catalog by English astronomer John Astronomical twilight happens when the Sun is 108° from the This term describes a star that Flamsteed published in 1725. zenith — that is, when the Sun is 18° below the horizon. Unless always lies above an observer’s He numbered roughly 3,000 your target is the Moon, which you can observe much earlier, horizon, no matter the time of stars. astronomical twilight is “go time” for amateur astronomers. After day or season. At the equator, astronomical twilight (or before, if you’re viewing in the morning), no star is circumpolar. At the Gegenschein there’s no sunlight to hinder viewing. North or South Pole, all stars are circumpolar. At any other Also known as the coun- BAYER LETTER latitude, a star whose declina- terglow, this faint light is tion is greater than 90° minus sometimes visible at a point Greek letter designa- the observer’s latitude will be 180° from the Sun. It occurs tions first appeared on circumpolar. as sunlight is reflected from star maps in interplanetary dust particles. Uranometria, a work by Collimation You’ll see it best in Pisces in German astronomer September and western Virgo Johann Bayer in 1603. Owners of Newtonian in March because those two He assigned the first or Schmidt-Cassegrain areas of the ecliptic are far- letter, Alpha (α), to telescopes who don’t have thest from the Milky Way, the brightest star in them set up in a permanent which will hide the gegen- each constellation. location should collimate schein’s faint glow. Then came Beta their scope, or align its (β), Gamma (γ), components, prior to each Horizon and so on. Well, observing session. I know it mostly. Bayer’s can be a pain, but to ignore We usually define the horizon rankings have a it means your telescope as where the celestial sphere few mistakes (see Orion, won’t perform at its best. intersects Earth at every for example). My point is, if (For more on the topic, see point. Here’s the problem: you’re going to use star charts, “How to collimate your Most non-ocean locations you’ll find it helpful to learn to scope” in the May 2019 issue.) don’t offer a true horizon identify the Greek letters. — that is, one 90° from the Eye patch zenith. Mountains, hills, trees, ABOVE: Bayer’s original and buildings can all obstruct designations were not always Cover your observing eye your view. Be aware that the accurate. In this drawing with a patch when you start times celestial objects rise and from his Uranometria, to set up, and by the time set will be affected by your Betelgeuse is designated you finish, you’ll have a local horizon. the alpha star of Orion fully dark-adapted eye. Then despite the fact that Rigel switch the patch to your other Intoxication outshines it in reality. eye so you can keep both eyes open at the eyepiece, a tech- Ever notice that all observ- NATIONAL LIBRARY OF POLAND nique that reduces eye fatigue. ing guides recommend you Oh, and before you use your bring non-alcoholic bever- RIGHT: Binoculars let you scan faint red light, move the patch ages when you observe? The the sky with a wide-field view. But back to your observing eye. reason is simple: Alcohol like telescopes, the larger the impairs vision. aperture, the more light they collect. Focus Know your UROSE/DREAMSTIME Here’s the most important tip equipment on this list. Each time you put WWW.ASTRONOMY.COM 53 your eye to your eyepiece, and You just bought a new tele- whenever you change eyepiec- scope. Don’t be in a rush to es, focus. If you don’t, you’re take it to a remote site. Set it wasting good observing time. up at home first, and in the daytime. (Just don’t point it Flamsteed number at the Sun.) Any problem you uncover in the light will be Ever wonder where the des- one less issue you’ll have to ignation “61 Cygni” comes

High-altitude observing Amateur astronomers routinely travel to mountaintops to observe. Be aware that this alters your color perception and raises your limiting magnitude. Most people notice small changes when they travel 2,000 feet (600 meters) above where they live, but the higher you go, the more change you’ll see. Observing at high altitude gets you above Earth’s atmosphere, improving the visibility of the night sky. But be aware that reduced oxygen also impacts your vision. KAT LAWMAN Mosquitoes deal with in the dark. And if New General you do come across an issue, Catalogue (NGC) Mosquito repellent is an essential part of an astronomer’s toolkit — at least you’ll be familiar with unless you happen to live in Iceland or observe exclusively during the the scope! Most observers are familiar winter. WIKIIMAGES/PIXABAY with at least the main Messier Mosquitoes are attracted to heat, carbon dioxide, and move- Limiting magnitude objects. The NGC is a more ment, so swatting at one is essentially an open invitation to extensive catalog of deep-sky others. The most effective mosquito repellents contain DEET, The best way to get a feel for objects published by Danish which stops a mosquito from biting by jamming the insect’s the quality of your observing astronomer John Louis Emil antennae cells that are sensitive to lactic acid. Treat your site is by measuring its limit- Dreyer in 1888. The original clothing as well as exposed skin. ing magnitude (LM). Most listed 7,840 objects and was observers determine LM by followed by a supplement (the 54 ASTRONOMY • SEPTEMBER 2022 identifying the faintest star Index Catalogue) of 5,386 they can see at the zenith. more. Get familiar with the Others like to use the region designations and positions around Polaris (Alpha Ursae of some of the most impres- Minoris) because the same sive NGC objects to expand stars are visible year-round. your repertoire. A few of the brighter ones to consider are Meridian NGC 457 (the Owl Cluster), NGC 869 and NGC 884 (the An observer should always Double Cluster), NGC 5139 know the position of the (Omega Centauri), and meridian. It’s the great circle NGC 7293 (the Helix Nebula). that passes through the zenith and the celestial poles. So, Observing chairs find Polaris, draw a line to and ladders the zenith, and continue south. When an object lies on When observing, comfort is the meridian, it has reached everything, and nothing says its highest point and is best comfort like a high-quality placed for observing. observing chair. Good ones

have sturdy construction and Position angle free. An air mass warmer TERMINATOR padded seats, and are easily than the ground can hold adjustable. And while chairs Learn where north is when lots of dust, but images will Features along this line, work fine for refractors and you look in your eyepiece. be steadier. If a cold front has which marks the boundary Schmidt-Cassegrains, large Many times, observing guides just passed your site, the see- between the sunlit and dark Dobsonian-mounted scopes will give the position angle ing probably won’t be good for hemispheres of the Moon, require a ladder. In this case, (P.A.) of one object in relation at least 24 hours. Seeing can should be your targets each you’re looking for ones that to another, brighter object. be good if thin cirrus clouds time you observe our lone feature wide, rubber-coated This angle is measured from are above you, except when natural satellite. At the steps and a utility tray. north through east. For a they combine with low-level terminator, it’s either lunar double star, it’s the line join- crosswinds. sunrise or sunset, and ing the primary with the shadow detail is at its best. companion star. Site selection The shadows at the terminator Questions When you’re looking for an accentuate lunar terrain ideal observing site, three features. This photo along the Good observers have a list things count. First, it must be terminator of the rugged Fra of questions memorized that free of most light pollution. Mauro Highlands was snapped they answer when viewing an Second, the air must contain by astronauts aboard the object. For a planetary nebula, few aerosols (dust, air pol- Apollo 12 mission. IMAGE SCIENCE AND questions might be: “Can you lution, and water droplets). see the central star? At what And third, it should be at an ANALYSIS LABORATORY, NASA-JOHNSON SPACE magnification?” “What shape altitude between 5,000 and CENTER is the nebula?” “Is any color 8,000 feet (1,500 and 2,500 m). apparent?” A common set of Of course, not everyone can VITAMIN A questions reminds you to look get to such a site, but choose for common details, espe- the one that best approximates Your eyes need vitamin A. cially when you’re tired. these features. An amateur astronomer whose diet is low in this Seeing and Your speed nutrient won’t have great transparency night vision, and a severe Some observers spend an hour deficiency can cause night Seeing is a measure of or more on a single object, blindness. You can get it the steadiness of the air. endeavoring to glean every bit from eggs, cheese, liver, Transparency is a measure of of detail possible. Others take a carrots, and most green how clear the sky is. Weather leisurely pace between five and vegetables. has a huge impact on both. 15 objects per hour. Take the An air mass colder than the time to discover what observ- Kale, like most green ground will produce unsteady ing speed works best for you. vegetables, is a rich source air, but it’s also usually dust of vitamin A. RADIANT Zoom eyepieces If your budget for observing JENIFOTO406/DREAMSTIME accessories is limited, con- sider a zoom eyepiece. Such an accessory will provide a range of magnifications at a cost much less than each of the individual eyepieces in its range combined. And fortu- nately, the quality of today’s zoom eyepieces is much better than those of even a decade ago. The streaks of light from a meteor shower appear to emanate from a single Michael E. Bakich is point on the sky, called the radiant. This composite image of the Geminids a contributing editor of was taken in China’s Heilongjiang province. JEFF DAI Astronomy. He always carries a bottle of mosquito repellent When you head out to observe a meteor shower, memorize in in his observing bag. advance the position of its radiant. This point, toward which Earth is traveling in its orbit, is the shower’s apparent origin. All the shower meteors’ paths trace back to it.

EARTH’S GREATEST

LONG BEFORE HUMANS CAME to inhabit the area, a massive space rock slammed into woodlands that are now the Arizona desert. Mammoths, giant sloths, and other Pleistocene animals may have glanced up as explosions tore through the sky — only to be vaporized an instant later. Estimated to be about This so-called Giant Impact 160 feet (50 meters) wide and weighing as much as 330,000 We live in a Hypothesis explains a great deal tons (300 million kilograms), about why Earth and the Moon share the incoming mass of iron ionized the atmosphere as it cosmic shooting such similar compositions. And streaked toward Earth at some although Earth has since continued 27,000 mph (43,000 km/h). The meteorite hit with a force 150 gallery, with to be pummeled by asteroid-sized times more powerful than the impactors, fortunately, none can atomic bomb dropped on Hiroshima. Shock waves propa- our planet the compare to the sheer amount of gated through the ground and air inevitable target destruction wrought by Theia. alike, destroying everything for miles. In the blink of an eye, the of incoming Extinction factor impact excavated a hole 0.75 mile The small town of Chicxulub in (1.2 kilometers) wide and 560 feet (170 m) deep. space rocks. Yucatán, Mexico, is very near the Evidence of the collision’s true center of one of the largest impact power can be seen in the uplifting of massive limestone blocks, shocked BY RAYMOND craters on Earth. The town’s beauti- rock formations, and even micro- ful beaches belie the epic event that scopic diamonds formed by the intense pressure and heat of the SHUBINSKI took place there some 66 million strike. Ejected fragments from the largely vaporized meteorite have since years ago. been recovered miles away. The strike that created Meteor Recent research suggests it was Crater was surely dramatic and devas- tating. However, that impact pales in spring in the Northern Hemisphere comparison to the long-term beating Earth has endured since its formation. size of Mars collided with our home when an asteroid or comet, moving at world, nearly destroying it. nearly 45,000 mph (72,500 km/h), The rogue object, named Theia, impacted Earth near the coast of the was largely obliterated by the collision. Yucatán Peninsula. The object may Everything but its core was vaporized have been as large as 8 miles (13 km) and spewed into space, along with across. The strike released the power most of Earth’s crust. Within 100 years of a 100-million-megaton blast, carv- or less, our planet was encircled by a ing out a crater more than 100 miles ring of debris. Under the unyielding (160 km) wide and penetrating force of gravity, these leftovers began 12 miles (20 km) into Earth’s crust. to clump together, ultimately forming Earthquakes, volcanoes, and a the Moon. monster tsunami that reached the A rough start The budding solar system was a chaotic and violent place. The Sun was forged from a massive, rotating nebula of gas and dust some 4.6 billion years ago. And about 4.5 billion years ago, when Earth was still in its infancy, a protoplanet roughly the LEFT: According to the Giant Impact Hypothesis, 4.5 billion years ago, a planetesimal the size of Mars, dubbed Theia, slammed into Earth. The debris ejected by the impact entered orbit around our planet, eventually forming the Moon. RON MILLER RIGHT: Standing on the rim of Meteor Crater in Arizona gives a spectacular view of the best- preserved impact site on Earth. DAVID J. EICHER WWW.ASTRONOMY.COM 57

The Sudbury Neutrino Observatory, designed to detect solar neutrinos, was Observatory’s detectors qui- other buildings in the town) housed within a cavern in Creighton Mine in Sudbury, Ontario, Canada. SNOLAB etly waited for solar neutrinos was built using suevite, a mix to pass through the ground of coarse-grained, fused rock. center of North America were into Earth some 1.8 billion and interact with a massive Suevite also contains glass, only some of the aftereffects years ago. The impactor was tank filled with heavy water. shocked crystals, and even of this powerful event. A long an estimated 6 to 10 miles The Sudbury project, along diamonds. It is estimated that period of cooling also began (10 to 16 km) across and with help from the Super- the cathedral alone has 5,000 as trillions of tons of dust and moving at about 45,000 mph Kamiokande collaboration in carats of diamonds embedded debris were blasted into the (72,000 km/h). A cloud of Japan, proved that neutrinos in its walls, and the crater may atmosphere, nearly bringing debris enveloped our planet change form as they leave the hold as much as 72,000 tons of a stop to all photosynthesis. after the strike, and ejected Sun — a process that requires diamonds — most microscopic, rocks were thrown as far as them to have mass. This but a few as big as 0.01 inch Over time, weather and current-day Minnesota. impact-enabled discovery (0.3 millimeter) across. erosion eventually erased ultimately won Takaaki Kajita most of the visual evidence This collision may have of the University of Tokyo Southwest of the town of of this devastating impact, even opened a fissure in and Arthur McDonald of Nördlingen, near the city of which wiped out an esti- Earth’s crust, releasing Queen’s University in Limoges, France, lies the mated 70 to 80 percent of all magma. As the magma Kingston, Canada, the 2015 ancient Rochechouart Crater. species on Earth, including flowed upward, it carried Nobel Prize in Physics. This site was gouged out when the dinosaurs. Nonetheless, large amounts of nickel, cop- a large asteroid hit Earth some life slowly recovered. New per, gold, and platinum to the Cathedrals and 207 million years ago, around and diverse forms of life ulti- surface. Near the end of the cluster strikes when the Triassic-Jurassic mately reclaimed the planet. 19th century, mines opened to Those familiar with gems mass extinction occurred. claim these precious metals. and minerals likely know of (That extinction event is now Fortunately, an Earth- a beautiful emerald-green understood to have been a altering event like this only From 1999 to 2006, scien- glass called moldavite, a type slow, multi-million-year happens, on average, about tists carried out a search of of tektite formed from terres- process that wiped out nearly every 100 million years. their own in Creighton Mine, trial material ejected during 80 percent of all species; while almost 7,000 feet (2,100 m) an impact. Researchers now the Rochechouart impact may Riches and neutrinos below Sudbury Crater. believe that moldavites, found have helped the extinction In Sudbury, Ontario, lies However, these scientists were mainly in the Bohemian along, it was not the cause.) one of the oldest and larg- not searching for metals to region of the Czech Republic, est impact craters yet found harvest, nor even for evidence are the byproduct of a specific Other craters seem to have on Earth. Scientists believe of the ancient impact. Instead, massive meteorite that struck this crater formed when a shielded from cosmic radia- Germany some 15 million With a population of around 20,000, giant space rock slammed tion, the Sudbury Neutrino years ago. the town of Nördlingen in Bavaria, Germany, is situated within an impact Studies show that the crater known as Nördlinger Ries. roughly 0.6-mile-wide (1 km) asteroid plowed into Earth at WOLKENKRATZER/WIKIMEDIA COMMONS an oblique angle. The impact ejected thousands of tons of material, which became fluid due to heat and shock. The ejecta rained down, creating a blanket of impact rubble over the newly formed crater, now known as Nördlinger Ries, or simply the Ries. It is within this 15.5-mile- wide (25 km) impact crater that, more than a millennium ago, humans built the town of Nördlingen. Recent research has shown that St. George Cathedral (along with many 58 ASTRONOMY • SEPTEMBER 202 2

formed near the same time it 7 million years older than ground 2 billion years ago. hit, Earth was just being — the Eye of Quebec, for Rochechouart Crater. These rings make up the released from the grips of example. An unusual circular Vredefort Dome, a 43-mile- a global ice age, so the feature officially named Staying power wide (70 km) area of uplift Yarrabubba asteroid must have Manicouagan Reservoir, the Most craters on Earth are where the ground rebounded crashed into ice several miles “eye” is actually the eroded slowly erased by erosion after the hit. But the full cra- thick. Computer simulations inner ring of a huge impact and plate tectonics. That’s ter, which has eroded away, show that the impact released crater. An almost perfectly certainly the case for the was much larger, perhaps as between 100 billion and round ring lake surrounds two oldest-known impact large as 186 miles (300 km). 5.5 trillion tons of water vapor, René-Levasseur Island, at the which then spread throughout center of which is Mount ZIRCON CLOCK Earth’s atmosphere. That Babel, the uplifted peak that atmospheric water vapor could formed when Earth’s crust One of the earliest minerals to form on Earth is zircon. In every have sparked a greenhouse rebounded from the impact. crystal, there is a tiny amount of uranium, which slowly decays effect, warming Earth, speed- With an outer diameter of into lead at a well-established rate. However, when zircon is ing the great thaw, and usher- 60 miles (100 km), this is one subjected to the heat and pressure of a massive cosmic impact, ing in a new era of life. of the largest craters on Earth. the rate of decay “resets,” starting the clock all over. This allows Impacts such as those Because the date of researchers to work backward and determine the highlighted here represent the impact corre- timing of past impacts with great precision. — R.S. tremendous natural disasters, sponds closely with but they also often led to the event that formed BJÖRN WYLEZICH/DREAMSTIME Nestled in Western unexpected consequences. Rochechouart Australia’s landscape of With nearly 8 billion people Crater, as well as craters: Vredefort ancient rock is a 40-mile-wide now living on our planet, the others located in Crater in South (64 km) crater excavated a next cosmic strike could be a Ukraine, Manitoba, and Africa and Yarrabubba whopping 2.23 billion years major turning point for the North Dakota, some scientists Crater in Western Australia. ago, according to a recent human race — good or bad. initially suggested all these Nonetheless, there are still study of the ratio of uranium But nothing helps us prepare craters were formed by the signs of them — some visible, to lead in ancient zircon crys- for the future like thoroughly same event, perhaps due to an and others detectable only by tals collected from the site. understanding the past. impactor fragmenting before modern techniques. (Uranium decays into lead striking Earth in multiple From space, partial ring at a known rate.) Raymond Shubinski is a locations. However, more structures are obvious at the contributing editor of Astronomy recent research suggests location where the Vredefort When the 4.3-mile-wide Manicouagan Crater is some impactor smashed into the (7 km) Yarrabubba asteroid who collects meteorites from 214 million years old, making impacts and always wishes upon a shooting star. Sometimes called the Eye of Quebec due to its appearance when viewed from space, Canada’s Lake Manicouagan is actually the inner ring of one of Earth’s largest and oldest-known impact craters. Captured here in true color by NASA’s Terra spacecraft, the crater is some 214 million years old. NASA/GSFC/LARC/JPL, MISR TEAM WWW.ASTRONOMY.COM 59

SECRET SKY A deep-sky devil design spiral galaxy only 20° from edge-on. Its minute angular extent (4.6' by 1.9'), small central bulge, and low surface brightness (23.6 magnitudes per square arcsec- The spiral galaxy NGC 6118 is fiendishly difficult to find. ond) are all hallmarks of a true dark-sky object. High contrast between the galaxy and background sky is needed to see it — seriously, add just a hint of light, moisture, or dust to the sky and this devil will drown. Seeing NGC 6118 through small- to moderate-sized telescopes requires knowing exactly where to look. Use low power to find the field, then immediately switch to 25x to 40x per inch of aperture for your search. Look for a faint fleck of misty light that swells in fast phantom flashes. At times, just the nuclear region appears. Then a fine oval mist manifests before every- thing vanishes just as quickly as it appeared, like a shy spirit. Try moving the telescope in slow creeps (not sweeps) back and forth, as your eyes perceive objects better if they are in motion. Any gain in altitude should also help with the view. Jay Reynolds Freeman had success spying NGC 6118 through a 2.2-inch f/8 Vixen fluorite refractor from an Use this Digitized Sky altitude of about 2,700 feet (820 meters) in Fremont Survey image to Peak State Park near San Juan Bautista, California. locate NGC 6118, Here’s a bit of trivia. Admiral William Henry Using only magnifications of 22x and 37x, he saw “a which lies only about Smyth (1788–1865), author of the celebrated faint, diffuse, and not very centrally concentrated glow, 15' southwest of a A Cycle of Celestial Objects, is also noted for popping in and out at the limit of averted vision, at the 6th-magnitude star, seen at upper left. another work: The Sailor’s Word-Book, a classic dic- charted position. Jiggling the telescope, or moving it DIGITIZED SKY SURVEY/STSCI/ tionary of nautical (and related astronomical) terms. slightly with the slow motions, helped a bit.” Others OSCHIN SCHMIDT TELESCOPE/UK The volume is filled with fascinating phrases. In it, have seen it through 4- and 5-inch telescopes quite SCHMIDT TELESCOPE for instance, we learn that a blazing star was the popular distinctly from high-altitude observing sites, as well. name sailors used for a comet, that blue moon meant an Plan to spend an evening solely on this object. Take indefinite period, and that star-glint was a your time. Make sure your eyes do not common name for a meteor. strain. As you observe, periodically relax Smyth’s Word-Book also informs us about You are the and take deep breaths (hyperventilate). Keep the origins of the phrase between the devil both eyes open. If extraneous light is a prob- and the deep blue sea. The devil referred to master of lem, use a blanket or cloth to cover your “the seam which margins the water-ways” of your art, so head. Do not settle for one possible glint; a ship’s hull. As the seam was close to the learn from repeat sightings are key. Sometimes, quick waterline, caulking it in rough waters was glances are more efficient than prolonged looking. dangerous; there was risk involved in any stares, which can fatigue the eye. You are the course of action a sailor took or didn’t take. master of your art, so learn from looking. This month, we honor Smyth by asking observers By the way, in Smyth’s Word-Book, the phrase blink using small to moderate-sized telescopes to weigh of the ice refers to the flickering appearance of a miraged anchor and try to fix their gaze upon a devil of a galaxy: iceberg. This term aptly applies to NGC 6118, which is, NGC 6118, which lies only about 2° south of the night in fact, popularly known as the Blinking Galaxy, as it sky’s “waterline” (the celestial equator) in Serpens flickers in and out of view depending on the position of Caput. Many observers consider NGC 6118 to be the your eye when you look through the telescope. This most difficult object on the Herschel 400 list, the popu- effect involves not only averted vs. direct vision, but also lar selection of targets plucked from John Herschel’s whether the galaxy hits your eye’s “hot spot” — the most BY STEPHEN General Catalogue of Nebulae and Clusters. Let’s see if sensitive region of your eye’s retina. JAMES O’MEARA we can’t heighten the chances of success in the hunt. As always, send reports of what you see or don’t see Stephen is a globe- trotting observer who A “blink-of-the-ice” target to [email protected]. is always looking for the next great NGC 6118 is a photographic delight and a visual observ- BROWSE THE “SECRET SKY” ARCHIVE AT celestial event. er’s menace. We see this roughly magnitude 11.5 grand www.Astronomy.com/OMeara 60 ASTRONOMY • SEPTEMBER 2022

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A S K A S T R O Astronomy’s experts from around the globe answer your cosmic questions. ELECTROMAGNETIC James SPECTRUM Webb Planck Hubble Coandra X-ray Observatory MICROWAVES VISIBLE X R AYS 700 nm 600 nm 500 nm 400 nm RADIO WAVES Wavelength (meters) INFRARED U LTR AVIOLE T 103 102 101 1m 10-1 10–2 10–3 10–4 10–5 10–6 10–7 10–8 10–9 10–10 10 cm 1 cm 1 mm 100 ̀m 1 nm 0.1 nm 1,000 m 100 m 10 m 1m 10 ̀m 1 ̀m 100 nm 10 nm ALMA Scientists use The full telescope are also tailored to different wavelengths. telescopes capable of spectrum Many detectors are made from semiconductor materials, viewing the universe so that when light hits the detector, it releases electrons, across the entire Q I HOW DO WE CREATE TELESCOPES which we then measure and translate into an image. electromagnetic THAT SEE DIFFERENT PARTS OF Different semiconductor materials respond to light with spectrum. ASTRONOMY: THE ELECTROMAGNETIC SPECTRUM? different energies and therefore different wavelengths. ROEN KELLY Frank Coulter Finally, we can further restrict the wavelengths we Pauanui Beach, New Zealand observe by putting a filter in front of the detector. A filter is just a piece of glass that only lets through certain A I The range of colors or wavelengths that a tele- wavelengths. Astronomical cameras usually have sev- scope can observe depends on the design of eral filters mounted on a wheel, and astronomers can both the telescope itself and the cameras attached to it. then select which one they want to use to make their observations. For instance, if you’re building a telescope that will observe mostly in infrared, usually the mirror is coated It may seem like a lot of work, but seeing the cosmos in silver or gold. For the mirrors of telescopes designed through every possible wavelength is critical for deep- to observe in both optical and infrared, aluminum, ening our understanding of the universe we inhabit. which reflects light fairly well over a wide range of wavelengths, is a better choice. Juan Carlos Muñoz-Mateos European Southern Observatory Media Officer, Garching, Germany Mirrors in X-ray telescopes are usually coated with gold or iridium. But there’s a problem: If you aim a mir- Q I COULD NEUTRINOS ACCOUNT FOR ror directly at an X-ray source, the photons (light) won’t DARK MATTER? be reflected — they will either go through the mirror Richard Goering or get absorbed. To solve this, mirrors in X-ray tele- Centennial, Colorado scopes are shaped like a funnel. This way, the incoming light grazes the mirror at a very shallow angle, like a A I Neutrinos as physicists understand them can- stone skimming on a lake, allowing instruments at the not constitute dark matter. The Standard Model bottom of the funnel to catch the light. explains how the basic building blocks — fundamental particles — and three of the four known forces created The detectors that register the light captured by a the universe. Fundamental particles are subatomic par- ticles that do not consist of any other particle; electrons are an example, and so are neutrinos. 62 ASTRONOMY • SEPTEMBER 202 2

Fermi Gamma-ray Space Telescope GAMMA R AYS observed. But researchers have seen neutrinos interact ABOVE: Sometimes a with other particles through the weak force. body’s gravity isn’t 10–11 10–12 10–13 10–14 10–15 enough to keep it 0.01 nm Hopefully dark matter isn’t fully invisible; otherwise spherical if another 0.001 nm 0.0001 nm 0.00001 nm 0.000001 nm we could never detect it directly by “seeing” it. And mass has a greater because dark matter has been confirmed to interact pull on it. In the case What rules neutrinos out of the running for dark gravitationally, astronomers and particle physicists are of WASP-103 b, the matter is that in the Standard Model, they are considered hopeful that it has some highly suppressed interactions planet is orbiting so “hot” particles, meaning they travel at speeds close to yet to be seen. close to its star that the speed of light. For a particle to constitute dark mat- the world has been ter, it must be “cold,” or travel slowly compared to light. Kaliroe Pappas warped, as shown in Graduate Student, Laboratory of Nuclear Science, this artist’s concept. The major role dark matter played in the formation of the universe was to clump itself up into large masses, MIT, Cambridge, Massachusetts ESA whose gravity then attracted regular matter, forming the large-scale structures of the universe. If dark matter Q I WHY ARE PLANETS AND STARS BELOW LEFT: were hot, the particles would have been moving too fast ROUND? Astronomers have to create these clumps, meaning there would be no Richard Fulton been able to catch galaxies (at least, not on the scales we observe them). San Diego, California dark matter hidden We still observe these dark matter clumps, or dark mat- within the Bullet ter halos, surrounding galaxies. A I Small celestial bodies, like comets or dwarf Cluster. The normal planets, can sometimes have bizarre shapes — matter (pink) doesn’t Another aspect of neutrinos that rules them out as just look at ‘Oumuamua, the interstellar visitor whose account for the dark matter candidates is that they aren’t actually invis- strange, elongated form sparked endless theories as majority of matter in ible — at least, not in the way that physicists define it. it passed through our solar system. So, what’s stop- the galaxy cluster When a scientist refers to an invisible particle, it usually ping large moons, planets, or even stars from coming (blue). X-RAY: NASA/CXC/CFA/ means a collision with another particle has never been in not only all sizes, but all shapes? It all comes down to gravity. M. MARKEVITCH; OPTICAL AND LENSING MAP: NASA/STSCI, No matter how irregularly shaped an object is, its self- MAGELLAN/U.ARIZONA/D. CLOWE; gravity pulls equally in all directions. But when an object LENSING MAP: ESO WFI becomes massive enough that its gravity can overcome the internal forces between atoms that bond its irregular SEND US YOUR features in place, protrusions will want to fall toward the QUESTIONS center of the body, creating a sphere. So, as a body collects more mass, it smooths out any edges, preventing any Send your cube- or pyramid-shaped planets. astronomy questions via email to askastro@ But not every planet or moon is perfectly round. This astronomy.com, or has to do with their rotation, which causes the material write to Ask Astro, around the equator to want to spin off, like mud from P.O. Box 1612, a tire. But gravity is too strong, so the body just gains Waukesha, WI 53187. some extra width around its middle, called an equato- Be sure to tell us rial bulge. In our solar system, slowly rotating Mercury your full name and and Venus are nearly perfect spheres, while Jupiter and where you live. Saturn bulge out near their equators. Even Earth isn’t a Unfortunately, we perfect sphere. Our world is about 0.3 percent thicker cannot answer all in the middle. Stars also bulge out near their equators questions submitted. for this reason. Caitlyn Buongiorno Associate Editor WWW.ASTRONOMY.COM 63

READER GALLERY Cosmic portraits 1 2 1. SEAGULL AND SUPERHERO The Seagull Nebula (IC 2177, left) spreads its wings over Thor’s Helmet (NGC 2359, right) in this wide-field view straddling Canis Major and Monoceros. The imager took 61 hours of observations, nearly all of it from the light-polluted skies of Las Vegas. He used SHO filters and a 2.8-inch scope for the Seagull and HO filters with a 5-inch scope for Thor’s helmet. • Antoine Grelin 2. NORTHERN LIGHT SHOW Aurorae dance in the skies over Paeskatun, Norway, in this shot from February 2022. Other celestial attractions visible include the Andromeda Galaxy (M31) and Cassiopeia at right, with the Alpha Persei Cluster (Melotte 20) positioned in between the auroral V at center. The Pleiades (M45) lie behind the auroral curtain to the left of the V. The image was taken with a 14 mm f/2.8 lens and a 10-second exposure at ISO 1000. • Debbie Troy 64 ASTRONOMY • SEPTEMBER 2022

3 6 3. ETNA’S LIGHT SHOW nebula. The photographer took Stars and lava fragments alike leave nearly 13 hours of exposure with a trails arcing through the sky in this 12-inch scope in HαLRGB filters. shot of Italy’s Mount Etna, which has • Gerald Rhemann been erupting since February 2021. 4 This image comprises 163 seven- 6. THAT’S NO SPACE STATION second exposures at ISO 6400 with An ominous sliver of the Moon a 35mm f/1.4 lens. • Gianni Tumino hangs in the sky during the May 16 total lunar eclipse, as seen from 4. AT THE LAGOON’S SHORES Montevideo, Uruguay. The exposure NGC 6559 is a star-forming was 1/800 of a second at ISO 400 interstellar cloud with dense threads with a 400 mm f/5.6 lens. of dust that sits just 1° east of the • Ruben Rodolfo Perez de Paula more famous Lagoon Nebula (M8) in Sagittarius. This RGB image was made with 15 hours of exposure time on a 24-inch scope. • Adam Block/Telescope Live/Mount Lemmon Skycenter/University of Arizona SEND YOUR IMAGES TO: 5. JUG AND CLARET Astronomy Reader Gallery, P.O. Box 1612, Waukesha, WI 53187. The dusty cloud and arcing streams Please include the date and of reflection nebula IC 2220 gives location of the image and the object its popular name, the complete photo data: telescope, Toby Jug Nebula. But this image camera, filters, and exposures. also shows faint shells of Hα Submit images by email to emission surrounding the reflection [email protected]. 5 WWW.ASTRONOMY.COM 65

BREAKTHROUGH RED SKY AT NIGHT IS A SAILOR’S DELIGHT Dust often obscures the view of objects in the plane of our galaxy, but this colorful region in the southern constellation Vela the Sails stands out. The bright circular cloud at the image’s center is Gum 15. Intense radiation from embedded newborn stars excites hydrogen atoms in the surrounding nebula, causing them to emit red light. Directly below Gum 15, near the image’s bottom, resides the region’s brightest star: 4th-magnitude d Velorum. The large emission nebula Gum 17 lies to the star’s left, while the outskirts of the Vela supernova remnant, the remains of a massive star that exploded some 11,000 years ago, appear as wispy tendrils at bottom right. ESO/DIGITIZED SKY SURVEY 2 66 ASTRONOMY • SEPTEMBER 202 2

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