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37 Articles

What we owe stars

I hope that every day, at least for a moment, you think of the Sun — not necessarily because you’re a solar observer, but out of gratitude. If not for the Sun, of course, none of us would be here. Circumstances in our solar system’s formation and evolution led to Earth being in the right place to receive enough solar radiation to permit water, and, thus, life. Our local nuclear reactor in the sky gives us our existence, and we owe our lives to it. The subject of stars is a pretty fundamental one in astronomy. After all, stars are practically everywhere when we look up in the sky; galaxies are filled with them, and the universe is filled with galaxies. It’s a little funny thinking back over conversations with astronomers…

What we owe stars

We welcome your comments at Astronomy Letters, P.O. Box 1612, Waukesha, WI 53187; or email to letters@astronomy.com. Please include your name, city, state, and country. Letters may be edited for space and clarity. A keen eye I thoroughly enjoyed seeing the Moon get some love in the March issue with Michael E. Bakich’s “Explore the Moon at First Quarter.” I did notice one little erratum — he swapped the terms for scotopic vision (low light) and photopic vision (well lit). In a past job, I worked in the refractive surgery market writing software that imaged and measured a patient’s cornea with infrared light. We used infrared so the eye was fully scotopic, or dark adapted. The terms just jumped out at me when I saw them there, and of course I knew…

HUBBLE’S COSMIC REEF

On April 24, NASA celebrated the Hubble Space Telescope’s 30th anniversary with a starstudded image of NGC 2014 (right) and NGC 2020. Located in the Large Magellanic Cloud, the region is called the Cosmic Reef, in part for NGC 2014’s coral-like appearance. While NGC 2014 contains several stars 10 times the Sun’s mass each, its blue-hued neighbor is shaped by a single 15-solar-mass Wolf-Rayet star blasting material into space. HOT BYTES LIFTING OFF The Indian Space Research Organisation announced that its first crewed mission, named Gaganyaan, could launch three astronauts into low Earth orbit as early as December 2021. SLOW CRASH New data from the Gaia satellite suggest the Milky Way’s warped disk is the result of an ongoing collision between our galaxy and another, smaller one — possibly the Sagittarius Dwarf. LAVA-LESS A recent analysis of…

HUBBLE’S COSMIC REEF

GROWING SPACE SALAD

Aboard the International Space Station (ISS) in August 2015, Japanese astronaut Kimiya Yui trimmed a few leaves of red romaine lettuce and passed them to NASA astronauts Scott Kelly and Kjell Lindgren. Each drizzled a few drops of dressing onto the precious produce, then popped it into their mouths. “That’s awesome, tastes good,” Lindgren said. The 2015 harvest was too scant for a proper space salad, especially since half the crop was sent back to Earth for analysis. But the munchies marked a milestone in human spaceflight. It was the first time an orbiting crop had been grown with NASA hardware and then eaten (though scientists suspect astronauts might have stolen a few bites from a previous sample). We now know that space lettuce doesn’t just taste good. It’s also safe to…

GROWING SPACE SALAD

Curiosity views the martian horizon

Following the death of NASA’s Opportunity rover in 2018 due to a massive martian dust storm, Curiosity became the sole rover left exploring Mars’ surface. The car-sized scout has been churning out great science and images consistently for almost eight years, and it’s not done yet. Between November 24 and December 1, 2019, Curiosity used its Mastcam to capture more than 1,000 images that were later stitched together to create this highest-resolution panorama (almost 1.8 billion pixels) of Mars to date. Next year, Curiosity will get some new company when the Perseverance rover (and its more advanced Mastcam-Z camera) touches down in Jezero Crater.…

Curiosity views the martian horizon

AURORAL SIGNAL Astronomers think they’ve found a terrestrial-mass exoplanet some 30 light-years away by spotting aurora-like radio signals in the star’s magnetic field, caused by the potential planet’s presence. FAREWELL, AL Al Worden, Command Module Pilot of Apollo 15, died March 18 at the age of 88. In 1971, Worden set the record for “most isolated human being” while orbiting the Moon some 2,235 miles (3,597 km) away from his crewmates on the lunar surface — greater than the separation between other Apollo crews. EX-THEORY? Astronomers searched the Milky Way for an X-ray signal seen in other galaxies and thought to come from dark matter. However, they saw no such signal in our own galaxy. The team says their result, which is still highly controversial, rules out the theory that these X-rays come from dark…

Astronomers find 139 new minor planets

Researchers searching through data from the Dark Energy Survey, or DES, have discovered 139 new minor planets orbiting the Sun. These worlds, called trans-Neptunian objects (TNOs), orbit beyond Neptune, which sits about 30 astronomical units from the Sun. (One astronomical unit, or AU, is the average Earth-Sun distance.) The method that allowed the team to spot so many small worlds is now expected to reveal thousands of distant objects in coming years — making these first hundred or so just the start. Currently, we know of nearly 3,000 TNOs, but astronomers estimate the total number is closer to 100,000. Taken together, the newfound distant objects, as well as those to come, could possibly resolve one of the most fascinating questions in modern astronomy: Is there a massive and mysterious world called…

Astronomers find 139 new minor planets

DECODING THE HERTZSPRUNG-RUSSELL DIAGRAM

CRYSTAL BALL. Since it was developed in the early 1900s, astronomers have used the Hertzsprung-Russell (HR) diagram to categorize stars by size, temperature, and brightness. The HR diagram is a simple but extremely powerful tool for understanding a population of stars. A given star’s location on this diagram is related to its age and mass; these properties allow astronomers to predict how that star will evolve by calculating the track it will follow through this diagram over time. Main sequence stars, such as the Sun, are in the relatively stable hydrogen-burning phase of their lives. As these stars age and run out of hydrogen fuel, they will move off the main sequence and onto the giant branch as they fuse helium or heavier elements in their cores. The most massive…

DECODING THE HERTZSPRUNG-RUSSELL DIAGRAM

Researchers map dark matter via slime mold

A brainless, single-celled organism with a knack for finding food is helping astronomers study the largest, most mysterious structure in the universe: the cosmic web. And things could get a bit … slimy. The cosmic web is a vast network of interconnected filaments made of dark matter and cold gas that forms the scaffolding upon which the entire universe is built. These filaments can stretch hundreds of millions of light-years, connecting groups and clusters of galaxies together. However, because the cosmic web is incredibly faint and the dark matter within it doesn’t interact with light, it’s extremely difficult to map. To tackle this challenge, researchers at the University of California, Santa Cruz, sifted through archived data for more than 37,000 galaxies to chart their positions in the sky. They then used a…

Researchers map dark matter via slime mold

OLD STAR REVEALS YOUNG JETS

Planetary nebulae occur when Sun-like stars puff off their outer layers late in life. These layers glow for a short cosmic time as radiation from the star strikes them, pushing them outward. Although some planetary nebulae are round, others are bipolar, shaped like a butterfly or an hourglass. Bipolar nebulae are particularly interesting to astronomers, but they are also hard to study because the gas and dust from the star hides the innermost regions from optical telescopes. To see past this veil, astronomers recently used the Atacama Large Millimeter/submillimeter Array (ALMA) to study W43A, a planetary nebula 7,000 light-years away, at radio wavelengths. ALMA revealed the star’s fast-moving bipolar jets (blue), which are blasting away from the star at about 109 miles (175 kilometers) per second. Based on this speed…

OLD STAR REVEALS YOUNG JETS

Iron rains from the sky on this world

On the exoplanet WASP-76 b, the nighttime forecast often calls for rain. But the droplets aren’t made of water. Instead, the downpour is made of iron. WASP-76 b is slightly smaller than Jupiter and sits some 640 light-years from Earth in the constellation Pisces. Its bizarre weather is caused by its truly extreme orbit. Gas giant worlds like WASP-76 b are called hot Jupiters because they orbit uncomfortably close to their home stars — in this case, nearly 10 times closer than Mercury is to our Sun. That proximity leaves WASP-76 b tidally locked to its star, with one side permanently baking in light and the other stuck in eternal darkness. As a result, WASP-76 b’s dayside gets hit with thousands of times more radiation than Earth receives from the Sun. Daytime…

Iron rains from the sky on this world

Pop-up robot scouts practice their skills

NASA’s Jet Propulsion Laboratory (JPL) has a new team of small scouts ready to explore the Moon. The Autonomous Pop-Up Flat Folding Explorer Robot, or A-PUFFER, is a shoebox-sized robot designed to go where astronauts cannot, including lunar craters or caves that humans might find inaccessible. Here, one of three A-PUFFERs tackles the Moon-like terrain of JPL’s Southern California Mars Yard during a test in February. These robots are designed to work together in teams, collaboratively and autonomously reconnoitering an area quickly to generate maps of previously unexplored regions. NASA hopes a team of A-PUFFERs could be on its way to the Moon within a few years. 23.5 The number of hours in a day on Earth about 70 million years ago, based on a study measuring how fast ancient clams grew.…

Pop-up robot scouts practice their skills

A tribute to carbon

Join me and Pulse of the Planet’s Jim Metzner in my podcast, Astounding Universe, at www.astoundinguniverse.com We astronomers love carbon. Though now-a-days it gets unrelenting bad press thanks to climate change, carbon is so essential to life that it grabs attention wherever we detect it. Who doesn’t perk up when reading about organic compounds found in comets or in martian soil, or causing the redness on Titan? Indeed, an entire field — organic chemistry — is devoted to the study of material containing carbon. Carbon is the universe’s fourth-most abundant element. During stellar life cycles, nuclear fusion turns hydrogen into helium, and helium into carbon and oxygen. So, when reaching old age, Sun-like stars collapse into tiny balls of oxygen and carbon. If blown outward, carbon becomes lots of fun even when…

A tribute to carbon

How stars are BORN AND DIE

We live in a relatively quiet district of a galaxy 100,000 light-years across that contains around 200 billion stars arranged in a disk beset with spiral arms. As galaxies go, it’s pretty big, though the supermassive black hole at the center is relatively small, just 4 million solar masses. There is ample evidence from the Milky Way’s rotation that our galaxy, like all others, contains considerable dark matter, whose role in star formation eludes us. But many of the processes of stellar evolution have become apparent, most notably that through death comes life. Stellar evolution is cyclic, with new stars replacing those that pass away. Stellar building blocks To forge a star you need gas, dust, gravity, and violent stirring. From a dark location in northern summer and fall, an observer can…

How stars are BORN AND DIE

Meet the most EXTREME STARS

SYMBOL KEY R⊕ = 1 Earth radius M⊕ = 1 Earth mass R⊙ = 1 solar radius M⊙ = 1 solar mass L⊙ = 1 solar luminosity THE SUN IS a pretty boring star. Still burning through the hydrogen in its core, our middle-aged Sun is comfortable at its current, relatively petite size. And though it will stay this way for about 5 billion years more, our star will eventually run low on hydrogen and switch to fusing helium deep within. This will inflate the Sun into a red giant over the span of just a couple of hundred million years. After engulfing the innermost planets, possibly including Earth, the Sun will continually shed its outer layers, eventually leaving behind a smoldering white dwarf surrounded by a beautiful planetary nebula of glowing gas. That’s the picturesque life…

Meet the most EXTREME STARS

STELLAR NEIGHBORS CLOSE-UP

KEY What do we really know about our Sun’s nearest stellar neighbors? We get so consumed with what’s beyond our galaxy that we forget that our own stellar neighborhood is pretty fascinating. Sure, we’re surrounded by mostly faint red dwarf stars, but they are our nearest stellar neighbors and we interact with them on timescales of tens of thousands of years. With the exceptions of Sirius, the brightest star in the night sky, and Alpha Centauri, none of these stars shows up easily to the naked eye. But they have influenced our solar system’s evolution in the past and will continue to do so in the future. We often hear about our neighbors in the Alpha Centauri system, which includes Proxima Centauri, the closest known star to Earth at only 4.2 lightyears away. But…

STELLAR NEIGHBORS CLOSE-UP

Feast on a full planetary lineup

Visible to the naked eye Visible with binoculars Visible with a telescope All seven major planets are on display these short summer nights. Take in Saturn’s rings, Jupiter’s dynamic atmosphere, and the red deserts of Mars late at night. Stay up for dramatic views of Venus and its phases near a waning crescent Moon and two bright star clusters in Taurus. Binocular views of Uranus and Neptune, plus Mercury’s late July predawn show, provide a full course of planetary delights. On July 1, a gibbous Moon is already in the southeastern sky as night falls. As the sky darkens between 9:30 and 10 P.M. local time, you’ll spot Antares, the brightest star in Scorpius, about 10° southeast of the Moon. At first, no planets seem visible, but both Jupiter and Saturn rise in the…

Feast on a full planetary lineup

MUCH OF THE MOON’S history is encapsulated in one feature: the crater Schickard, way down in the lunar southwest. Protective measures are necessary to carry out this observation. Screw in a dark filter, mask off part of your scope’s aperture, or pump up the magnification to reduce the glare of an almost-full lunar disk. Start on the evening of the 2nd, when the rays of sunlight strike the flooded crater at a glancing angle, highlighting the differences in height among the smaller features. This is an old crater, its rounded rim pounded down across the ages. The splatter of smaller craters across the smooth floor sport the classic sharp edges of relative youth. The western wall, steep at the instant of formation, slumped abruptly down into terraces that remain visible to…

Southern Delta Aquariid meteors SOUTHERN DELTA AQUARIID METEORS Active dates: July 12–August 23 Peak: July 29 Moon at peak: Waxing gibbous Maximum rate at peak: 20 meteors/hour JULY IS A GOOD MONTH for meteor observing, with warm weather and increasing hours of darkness as the month progresses. Some minor showers are active, all contributing to an overall increase in summertime meteor rates. A Full Moon occurs on July 5, so the best viewing is later in the month, when the Southern Delta Aquariids are active (July 12 to August 23). New Moon occurs on July 20 and the predawn hours are the best time to look for shower members, although sporadic meteors can occur any time of night. In late July, the Perseids begin, quietly at first, but the waxing Moon interferes most of the night in…

HOW TO USE THIS MAP This map portrays the sky as seen near 35° north latitude. Located inside the border are the cardinal directions and their intermediate points. To find stars, hold the map overhead and orient it so one of the labels matches the direction you’re facing. The stars above the map’s horizon now match what’s in the sky. The all-sky map shows how the sky looks at: midnight July 1 11 p.m. July 15 10 p.m. July 31 Planets are shown at midmonth MAP SYMBOLS Open cluster Globular cluster Diffuse nebula Planetary nebula Galaxy STAR MAGNITUDES Sirius 0.0 1.0 2.0 3.0 4.0 5.0 STAR COLORS A star’s color depends on its surface temperature. The hottest stars shine blue Slightly cooler stars appear white Intermediate stars (like the Sun) glow yellow Lower-temperature stars appear orange The coolest stars glow red Fainter stars can’t excite our eyes’ color receptors, so they appear…

PATHS OF THE PLANETS

THE PLANETS IN THEIR ORBITS Arrows show the inner planets’ monthly motions and dots depict the outer planets’ positions at midmonth from high above their orbits. and colored dots show motions and locations of solar system objects during the month. JUPITER’S MOONS Dots display positions of Galilean satellites at 11 p.m. EDT on the date shown. South is at the top to match the view through a telescope. THE PLANETS IN THE SKY These illustrations show the size, phase, and orientation of each planet and the two brightest dwarf planets at 0h UT for the dates in the data table at bottom. South is at the top to match the view through a telescope.…

PATHS OF THE PLANETS

BRIGHTER THAN MANY of Virgo’s Messier galaxies, Comet PanSTARRS (C/2017 T2) will appear in a 4-inch scope under a country sky. Follow the 9th- to 10th-magnitude fuzz across the Milky Way’s north polar region as it gradually fades on its return to the Oort cloud. On June 30, our ball of ice and dust is nearly equal to the interesting NGC 4485/90 pair. The Moon interferes in early July; on the 10th and 11th, leverage the two hours of evening darkness to jump between PanSTARRS and the nearby galaxies of Coma Berenices. July is also globular cluster season, so compare M53 and NGC 5053 to the comet for brightness, shape (morphology), and character. Observe intently at different magnifications to examine which objects have well-defined edges, bright cores, and fading flanks. The…

LOCATING ASTEROIDS

THE EASIEST TIME to pick out an asteroid is when the backdrop goes black. The Great Rift splitting our summer Milky Way does just that. The prominent Scutum Star Cloud just below Aquila sports a metaphorical cliff on its western (right) edge, where a field chock-full of stars suddenly empties to a couple of dozen. The dark swath of dust and gas that cloaks the bulge of our galaxy is so dense it caught the attention of E.E. Barnard, pioneer of dark nebula photography. Beginning at the fabulous star cluster Messier 11, push your scope westward past a small inky circle cataloged as Barnard 103 and onto the near emptiness. 56 Melete starts out the month just east of a 6.3-magnitude star that it grazes on the 3rd. Look farther west…

LOCATING ASTEROIDS

The Sun’s LOST SIBLINGS

Somewhere in the galaxy, we have a long-lost family. At this very minute, there are hundreds to thousands of stars that began to form and shine in the same dust cloud as our Sun, whose current locations are unknown in the sea of other stars. But what if it were possible to test stars to find our stellar siblings, like a DNA test can reveal unknown family members for humans on Earth? Astronomers think it’s doable — and, what’s more, we may have already done it. The beginning Although the Sun was born billions of years ago, we know roughly how the process happened by studying “stellar nurseries” we see today, called nebulae. Nebula means “cloud” in Latin, and each consists of interstellar gas, primarily hydrogen and helium with trace amounts of…

The Sun’s LOST SIBLINGS

IS ETA CORVI a window to our past?

Our solar system’s comets are believed to have delivered a wealth of material to early Earth. Among the icy visitors’ suspected gifts were rare gases, small amounts of water, and organic material — all of which could have helped terrestrial life form and evolve. But while ancient Earth received only a moderate influx of comets, any planets around young nearby star Eta Corvi are likely raking in cometary currency. After planets form in a fledgling system, the host star is surrounded by a disk of leftover gas and dust that didn’t get molded into new worlds. In our solar system, this surplus of material settled into two bands: the asteroid belt between Mars and Jupiter and the Kuiper Belt beyond Neptune. While members of the asteroid belt are rocky and relatively…

IS ETA CORVI a window to our past?

HOW PULSATING STARS unlock our universe

Earth is fortunate to be orbiting a star that is fairly constant in its light production. The amount of light energy reaching Earth from the Sun has varied by much less than 1 percent over the past few hundred years. Our star is stable because the balance between the inward force of gravity and the outward force exerted by the hot gas in its interior allows it to maintain a constant radius and thus a constant luminosity. But this will not always be the case. The Sun is a typical main sequence star fusing hydrogen into helium in its core. In about 5 billion years, when it runs out of hydrogen in its core, the Sun will evolve into a red giant, and soon after, it will enter the “horizontal branch”…

HOW PULSATING STARS unlock our universe

WHAT IS THE HORIZONTAL BRANCH?

Astronomers use a tool call the Hertzsprung-Russell (HR) diagram to easily characterize stars. The HR diagram plots a star’s temperature and luminosity, or brightness. Where a star falls on the HR diagram can tell researchers how far along the star is in its life cycle, as the temperature and brightness of a star change as it evolves. Stars located on the main sequence part of the diagram, like our Sun, are fusing hydrogen into helium. After a star exhausts the hydrogen in its core and becomes a red giant, it begins fusing hydrogen in a spherical shell just outside the core. It also moves onto the giant branch of the HR diagram. Next, helium fusion ignites in the core, as the star fuses helium into carbon. This process causes the star’s…

WHAT IS THE HORIZONTAL BRANCH?

Is T CrB rising?

BY STEPHEN JAMES O’MEARA Stephen is a globe-trotting observer who is always looking for the next great celestial event. The extraordinary dimming of Betelgeuse (Alpha [α] Orionis) that began in October 2019 captured the attention of astronomers worldwide. The star’s dip was a golden moment for Edward Guinan and colleagues at Villanova University, who have been monitoring the star for the past 25 years. They were the first to report its recent dimming. Betelgeuse’s brightness varies on three known cycles: one between 100 to 180 days, one about every 425 days, and one about every 5.9 years. “The current faintness of Betelgeuse appears to arise from the coincidence of the star being near the minimum light of the 5.9-[year] light-cycle as well as near the deeper than usual minimum of the 425-[day] period,”…

Is T CrB rising?

The coolest cat on the web

BY JEFF HESTER Jeff is a keynote speaker, coach, and astrophysicist. Follow his thoughts at jeff-hester.com The other day, a friend showed me what has to be the coolest thing on the internet. It’s an app that turns you into a human version of Schrödinger’s cat (minus the whole dead-in-a-box thing, of course). You read Astronomy magazine, so you know the basics. A cat is sealed in a box, along with a Geiger counter and a radioactive source with a half-life of one hour. The Geiger counter is rigged so that if it registers a single radioactive decay, it will break a vial of deadly hydrocyanic acid. Bye-bye, kitty. Schrödinger probably needed therapy. Anyway, in quantum mechanics (which, having never made an incorrect prediction, is the crème de la crème of theories), physical systems are…

The coolest cat on the web

Summertime observing

BY GLENN CHAPLE Glenn has been an avid observer since a friend showed him Saturn through a small backyard scope in 1963. One of the all-time classic summer-themed hits is the 1902 song “In the Good Old Summertime,” written by George Evans (music) and Ren Shields (lyrics). I don’t know much about either song-writer, but I can make the following statement with the utmost confidence: Neither was an amateur astronomer. Summertime astronomy for Northern Hemisphere observers, especially those who live in higher latitudes, is nothing less than a nightmare. We suffer from three seasonal ills: god-awfully late sunsets, god-awfully hazy and humid weather, and god-awfully annoying mosquitoes. What can we do to combat these summertime maladies? We’re pretty much at the mercy of late summer sunsets. In mid-northern latitudes, July sunsets don’t happen until…

Summertime observing

Riches of the Scorpion

BY PHIL HARRINGTON Phil is a longtime contributor to Astronomy and the author of many books. This month, we dive head-first into the deep end of the summer Milky Way by visiting everyone’s favorite bad guy, Scorpius the Scorpion. In one Greek myth, the goddess of the hunt Artemis and her mother, Leto, dispatch Scorpius to kill Orion after the hunter brags that he could slay any animal on Earth. Another version puts the blame on Artemis’ twin brother, the god Apollo. Either way, the scorpion prevails. To memorialize Orion and Scorpius, Zeus places them in the sky directly opposite each another, so they are never visible at the same time. Like Orion, Scorpius is also famous as the home to one of the largest stars visible to the naked eye. Antares (Alpha…

Riches of the Scorpion

H-alpha scope DayStar Filters Warrensburg, Missouri DayStar’s SE Grade 127-QT Prominence model features a 5-inch clear aperture and a 2,667-millimeter focal length in a carbon fiber tube. The tube with rings weighs 13.6 pounds (6.2 kilograms) and measures 31.1 inches (79 centimeters) long with its dew shield retracted. $5,995 866.680.6563 www.daystarfilters.com Observing journal Gleg Photography Georgetown, Kentucky Gleg Photography’s Astronomy Observer’s Journal is a perfect-bound paperback measuring 7½ by 9½ inches (19 by 24 cm). With it, an observer can record site conditions, object notes, and equipment used. It also has an area for sketching the object or for making additional notes. $19.88 859.333.9743 www.gleg.photography Teaching tool Armstrong Metalcrafts Albany, Oregon Armstrong Metalcrafts’ Cometarium demonstrates Kepler’s second law: An object in orbit sweeps out equal areas in equal amounts of time. The Cometarium uses elliptical gears with an eccentricity of 0.65 to achieve the correct motions. Armstrong…

The Sun’s light

Q IN WHAT PART OF THE ELECTROMAGNETIC SPECTRUM DOES THE SUN EMIT ENERGY? Jason PerryPhoenix, Arizona A The Sun emits light in virtually every part of the electromagnetic spectrum, albeit some more than others. The sunlight that we see — aptly named visible light — falls into only a very narrow range of the spectrum, from about 400 to 750 nanometers (a nanometer is one-billionth of a meter, or about 400 millionths of an inch). The Sun also emits at longer wavelengths, in the infrared, microwave, and radio. Our Sun emits light at progressively shorter wavelengths, too: the ultraviolet, X-ray, and even gamma-ray parts of the spectrum. But most of the Sun’s light is in the infrared, visible, and ultraviolet parts of the electromagnetic spectrum. Its output at the longest (radio) wavelengths is…

The Sun’s light

Cosmic portraits

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

Cosmic portraits

VIRGO’S STRIKING SUPERNOVA FACTORY The loosely wrapped spiral arms of NGC 5468 sparkle with brilliant star clusters glowing blue from the high-energy radiation pouring from the hot young stars within. A more careful look also reveals a smattering of pinkish nebulae well on their way to creating a new generation of dazzling clusters. This face-on galaxy lies about 140 million light-years from Earth in eastern Virgo. With a diameter of 110,000 light-years, NGC 5468 closely matches the Milky Way’s size. But the stars in this distant galaxy explode at a far greater rate than those in our home system. Astronomers have observed five supernovae in NGC 5468 in the past 21 years, but haven’t seen one in the Milky Way in more than 400 years. ESA/HUBBLE AND NASA/W. LI ET AL.…

Jupiter and Saturn excel

With spring arriving this month and the nights growing warmer, September offers nearly perfect conditions for observing the Sun’s two largest planets. Both Jupiter and Saturn stand high in the northeast during evening twilight and pass almost over-head within a couple of hours. Jupiter appears far brighter than its companion. The magnitude –2.5 planet actually outshines every other point of light in the evening sky. The giant world remains nearly stationary this month against the backdrop of eastern Sagittarius. Jupiter’s high altitude makes it a showpiece object through any telescope. Even the smallest instrument shows two dark cloud belts straddling a brighter zone that coincides with the planet’s 43"-diameter equator. You can also track the planet’s four bright moons as they circle the planet from night to night. Beautiful Saturn follows less than…

HOW TO USE THIS MAP This map portrays the sky as seen near 30° south latitude. Located inside the border are the cardinal directions and their intermediate points. To find stars, hold the map overhead and orient it so one of the labels matches the direction you’re facing. The stars above the map’s horizon now match what’s in the sky. The all-sky map shows how the sky looks at: 10 p.m. September 1 9 p.m. September 15 8 p.m. September 30 Planets are shown at midmonth MAP SYMBOLS Open cluster Globular cluster Diffuse nebula Planetary nebula Galaxy STAR MAGNITUDES Sirius 0.0 1.0 2.0 3.0 4.0 5.0 STAR COLORS A star’s color depends on its surface temperature. The hottest stars shine blue Slightly cooler stars appear white Intermediate stars (like the Sun) glow yellow Lower-temperature stars appear orange The coolest stars glow red Fainter stars can’t excite our eyes’ color receptors, so they…

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