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  • Jupiter’s Great Red Spot appears to be on a diet. It’s slimmed down by thousands of miles, and the loss has accelerated in recent years. Planetary scientists say there’s no way to know what will happen next. Back in the 19th century, the oval-shaped storm was roughly 25,000 miles wide — about three times the diameter of Earth. By the time the Voyager spacecraft flew past Jupiter in the 1970s, the spot had shrunk to twice the diameter of Earth. And this year, Hubble Space Telescope measured its length at not much more than one Earth diameter. The Great Red Spot is flanked by strong jet streams. Interactions between the jet streams and the spot spin off eddies. They travel all the way around the planet, and then merge with the red spot, adding energy to the system. But Rita Beebe of New Mexico State, an expert on Jupiter’s atmosphere, says that fewer of these big eddies have merged with the red spot in recent years. BEEBE: We really think the way it has lived all these years is the same life cycle as in the ocean: big fishes eat little fishes. Big eddies eat little eddies on Jupiter, and the little eddies are not coming in so he can grab them right now. So we think the red spot has gone on a diet. The Great Red Spot may eventually begin growing again. Or it may stabilize at a smaller size. Or it could even disappear. About the only thing we can say for sure is that astronomers will keep an eye on it to see what happens. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Jupiter’s Great Red Spot may have been around for centuries. Yet during that long span it’s been anything but steady. It wiggles back and forth, it changes size, and it even changes color. In fact, just why the Great Red Spot is red is still a puzzler. The spot is a giant storm. At its peak it was wide enough to swallow three Earths, although it’s been shrinking for decades; more about that tomorrow. Its cloudtops tower several miles above the surrounding layers of clouds in Jupiter’s thick atmosphere. Winds are strongest near its edge, where they race along at hundreds of miles per hour, but quite calm at its center. Over the decades, the spot’s color has ranged from cherry red to orange to pink. Right now it’s more orange than red, although it still stands out next to the lighter-colored bands of clouds around it. The leading theory says the color comes from sulfur-rich compounds that the storm dredges up from deep within Jupiter’s atmosphere. As these compounds are pulled to the top of the clouds, ultraviolet radiation from the Sun splits them apart. The sulfur molecules then turn red. Yet that scenario hasn’t been confirmed. And even if it’s correct, scientists are uncertain just which sulfur compounds the storm plumbs from below, or from what depths it pulls them. It’s also not clear how those compounds are spread out across the storm. So there’s still a lot to learn about Jupiter’s most famous feature. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Jupiter's giant "eye," the Great Red Spot, stares outward from the planet in this 1979 image from the Voyager 1 spacecraft. The spot is the largest storm in the solar system, and may have been swirling since the 1600s or earlier. In recent decades, however, it has been shrinking; today, it's only about half as wide as in this image. Planetary scientists aren't sure whether the Great Red Spot will rebound or dissipate. [NASA/JPL/Björn Jónsson (IAAA)] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Astronomers have been looking at Jupiter through their telescopes for more than four centuries. And for a good bit of that time, they’ve seen Jupiter staring right back. The giant planet’s most prominent feature is a gigantic storm system that looks like a bloodshot eye — the Great Red Spot. It’s the biggest storm in the solar system — wider than Earth. It’s also the longest-lasting storm — although just how long it’s been around isn’t certain. Robert Hooke reported seeing a large, oval-shaped feature on Jupiter in 1664 — exactly 350 years ago. Its size and location match those of the Great Red Spot, although there was no mention of its color. Jean Dominic Cassini saw the same spot the following year, and tracked it for a quarter of a century. After that, however, the next mention of the spot didn’t come until the 19th century. That means there’s a bit of uncertainty about what Hooke and Cassini actually saw. It could have been the Great Red Spot, or it could have been a smaller storm system. In either case, the Great Red Spot has been spinning away for two centuries or longer. Despite the many years of observations, a lot of mysteries about the Great Red Spot remain. In fact, astronomers aren’t even certain about what’s responsible for its color. More about that tomorrow. Jupiter is just beginning a year-long arc across the night sky. The brilliant planet is low in the east at first light, a little above even brighter Venus. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The two brightest objects in the night sky other than the Moon will stand side by side at dawn tomorrow like a pair of headlights. They’re quite low in the eastern sky, though, so you need a clear horizon to see them. Venus is the brighter of the two. It’s on the far side of the Sun, and is preparing to pass behind the Sun this fall. So right now, most of the hemisphere that faces our way is awash in sunlight. Seen through a telescope, the planet looks like an almost-full Moon. Unlike the Moon, though, Venus isn’t brightest when it’s full because that’s when it’s farthest from Earth. Over the next few weeks, Venus will gradually drop lower into the dawn twilight as its orbit carries it behind the Sun. It’ll get lost in the Sun’s glare by late September or early October. Jupiter stands just a whisker to the right or upper right of Venus tomorrow. It’s heading in the opposite direction, away from the Sun. Over the coming months, it’ll rise a few minutes earlier each day, and stand a little higher in the sky at the first blush of twilight. By the time Venus disappears from view in early autumn, Jupiter will be standing half-way up the sky at first light — ready to dazzle skywatchers throughout the fall and winter. Again, look for Venus and Jupiter in the east-northeast at first light tomorrow. To see them, you’ll need a clear horizon, with no buildings or trees to block your view of these bright planetary headlights. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Two pairs of planets are teaming up the next few days — Venus and Jupiter at dawn, and Mars and Saturn in the evening. The morning planets are much brighter, but they’re also much lower in the sky, which makes finding them a little harder. Mars and Saturn are low in the southwest as night falls. Mars shines yellow-orange, with pale golden Saturn to its upper left. Mars and Saturn are almost equally bright right now — the difference between them is just a few percent. Planetary brightness depends on several factors, including the size of the planet, how much light it reflects, and its distance from Earth and the Sun. Saturn is almost 20 times the diameter of Mars, and its cloudy surface is much more reflective. But Saturn is about eight times farther than Mars is, which balances the scales. Mars is moving away from us in a hurry, so it’ll fade more quickly over the next few weeks. The two planets will move closer together over the next few evenings, and will pass each other in about a week. Venus and Jupiter are the brightest planets, with Venus the brightest of all. It’s reigned as the “morning star” for most of the year. Tomorrow, it stands just above Jupiter, which is the second-brightest pinpoint in the night sky. Venus is tiny compared to Jupiter, but it’s much closer to both Earth and the Sun, so it looks brighter. Venus and Jupiter will stand almost side by side on Monday morning, and we’ll have more about that tomorrow. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The solar system’s largest moon may be built like a layer cake — with real frosting. Ganymede is the largest moon of Jupiter — about half again the diameter of our own Moon. It has a solid core of rock and metal, and a crust made of ice. Spacecraft revealed that there’s probably a deep ocean of liquid water far below the crust, with a rime of ice at its bottom. But a recent study led by Steve Vance of the Jet Propulsion Laboratory suggested a more complex structure. The team used computer models that account for the water’s mineral content, the extreme pressures at great depths, and other factors. The models indicate that a layer of dense liquid water sits at the bottom of the layer cake, with alternating layers of ice and liquid water above it — up to six layers in all, spanning hundreds of miles. If water is in direct contact with Ganymede’s rocky center, then mineral-rich hot water could percolate up from the rock. That would provide the main ingredients for life: water, energy, and nutrients. So if the layered structure is confirmed, then Ganymede might move up a bit in the list of worlds that are considered possible homes for living organisms. Jupiter is climbing away from the Sun in the dawn sky. Tomorrow, it’s a bit below Venus, the brilliant “morning star,” and shines quite brightly on its own. It’ll pass Venus over the following couple of mornings, then pull away as it climbs higher into the sky each day. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Jupiter's largest moon, Ganymede, peeks out from behind the giant planet in this 2007 Hubble Space Telescope image. Recent research suggests that Ganymede's outer regions may be arranged like a watery layer cake, with alternating bands of liquid water and water ice. [NASA/ESA/E. Karkoschka (Univ. Arizona)] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Many of the star pictures that adorn the night sky are big and bold. The curving body of Scorpius, the scorpion, strides low across the southwestern horizon on August evenings, for example, while Cygnus, the swan, climbs high across the top of the sky. But many other constellations are much more difficult to see. They’re small or faint or both — little more than filler between the better-known star patterns. Three examples stairstep up the east as night falls. One of them is small but fairly easy to find, while the other two require some work and imagination. The easy-to-spot constellation is Delphinus, the dolphin. It’s about halfway up the eastern sky, to the lower left of the bright star Altair. It’s one of the smallest of the 88 constellations. But it stands out because its main stars really do form a pattern that resembles a dolphin, with its body to the left and its long tail to the right. An even smaller constellation is directly below Delphinus — Equuleus, the little horse. Unlike the much bolder Pegasus, the flying horse, which is next door, Equuleus is drawn as only the horse’s head. All of its stars are quite faint, so you need especially dark skies to see it. And Sagitta, the arrow, is above Delphinus. Its stars are faint as well. Under dark skies, though, you might just make out the shape of the arrow — four stars pointing roughly to the lower left — a tiny star picture in the broad summer sky. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Until the middle of the 19th century, the stars were little more than mysterious points of light. Astronomers could plot a star’s position in the sky, or record changes in its brightness, but that was about all. They couldn’t learn what the stars are made of, what makes them shine, or anything else. Painting of Anders AngstromOne of the people who changed that was Anders Angstrom, a Swedish scientist who was born 200 years ago today. Angstrom spent almost his entire career at the University of Uppsala. He developed interests in Earth’s magnetic field, and in the emerging science of spectroscopy, which splits a star’s light into its individual wavelengths or colors. Each chemical element imprints a unique “barcode” into a star’s spectrum, making it possible to determine which elements are present in the star. Angstrom helped develop the theory behind spectroscopy, and he became one of its first practitioners. In 1862, he announced that he’d discovered hydrogen in the spectrum of the Sun — its first detection in any star, but not the last, since hydrogen makes up the bulk of almost all stars. Angstrom soon discovered many other elements in the Sun, and he published a complete solar spectrum in 1868. In fact, he measured wavelengths in the spectrum that were just one ten-billionths of a meter wide. There was no name for that unit of measurement until 1905, when his fellow scientists named it the Angstrom — honoring the man who pioneered a new way to study the stars. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Powerful jets of charged particles race into space from the galaxy 3C 348 in this combined optical and radio image. The jets are powered by a black hole roughly 2.5 billion times as massive as the Sun. Gas and dust around the black hole are accelerated to high speeds as they circle toward the black hole. Strong magnetic fields direct some of this material into space from above the black hole's poles. Such jets of material can travel at almost the speed of light and stretch across hundreds of thousands of light-years. This image combines an optical view of the galaxy from Hubble Space Telescope with a radio view of the jets from the Very Large Array in New Mexico. [NASA/ESA/S. Baum and C. O'Dea (RIT)/R. Perley and W. Cotton (NRAO/AUI/NSF)/Hubble Heritage Team (STScI/AURA)] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Everything about M87 is big. The galaxy spans a million light-years, and is perhaps 200 times as massive as our home galaxy, the Milky Way. A black hole that’s many times bigger than our own solar system sits at the galaxy’s heart, encircled by a disk of superhot gas. And “jets” of charged particles shoot out from the black hole’s poles, stretching across hundreds of thousands of light-years. Similar jets shoot away from many black holes. They’re powered by the disks of hot gas and by strong magnetic fields. The gas comes from interstellar clouds, winds from nearby stars, or stars that have been pulled apart by a black hole’s gravity. As atoms in the disk drop closer to the black hole, they move faster and faster. They get so hot that they’re ripped apart, producing a soup of electrically charged particles. The spinning disk also produces a powerful magnetic field. And the black hole may spin as well, also generating a strong magnetic field. The field may catch some of the charged particles in the disk, hurling them back out into space from above the black hole’s poles in long, narrow jets. For a black hole that’s as massive as a star, the jets typically fire outward at a few million miles per hour. But for a supermassive black hole, like the one at the center of M87, the jets get close to the speed of light. Such jets can last as long as there’s gas to feed them — beaming into the universe for millions or billions of years. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The space around a newly forming star is a busy construction zone. A giant disk of gas and dust encircles the protostar — the blob of hot material that will someday form the star. Some of the material in the disk feeds into the protostar, while some squirts out into space in high-speed “jets.” The jets can be clumpy, and if one clump overtakes another, it forms a glowing cloud. Two such clouds are in Sagittarius, which is low in the southern sky at nightfall, with its brightest stars forming the outline of a teapot. The clouds are Herbig-Haro 80 and 81. They’re associated with a protostar that’s about 15 times as heavy as the Sun. The disk of gas and dust around it is many times wider than our own solar system. A powerful magnetic field snags charged particles and fires them into space above the protostar’s north and south poles. These jets of material span close to 20 light-years. The jets aren’t smooth, like the spray from a water fountain. Instead, they’re clumpy. The clumps can be several times heavier than Earth, and they shoot into space at hundreds of thousands of miles per hour. The clumps move at different speeds, though. Herbig-Haro 80 and 81 are regions where a faster clump has overtaken a slower one. That creates a shock wave that heats the gas, setting it aglow — creating a beautiful and rapidly changing cloud next door to a future star. We’ll talk about some even stronger jets tomorrow. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A full Moon is great for an evening stroll on the beach. Unfortunately, though, it’s not great for skywatching. Its glow overpowers most of the stars, leaving the sky looking murky and washed out. It also overpowers most of the “shooting stars” that streak across the sky. That’s a special problem the next few nights, because the Perseid meteor shower is at its peak. The Perseids occur every August as Earth sweeps through the orbital path of Comet Swift-Tuttle. The comet sheds grains of dust as it orbits the Sun. These bits of comet dust spread out along the comet’s path. When Earth plows through this trail of debris, some of the dust grains plunge into the atmosphere at tens of thousands of miles per hour. These grains vaporize as the glowing streaks of light known as meteors. The Perseids should be at their best after midnight Tuesday night. The shower has faded in recent years as Swift-Tuttle has moved away from the Sun. Even so, it generally produces up to a couple of dozen meteors per hour. Most of the meteors are relatively faint, though. And since the Moon is full today, it’ll still be quite bright on Tuesday night. And it’ll be in the sky during the shower’s peak hours, obliterating most of the meteors. A few of the brighter meteors should still shine through, though. To see them, get away from the glow of city lights, which make the sky even murkier. Then scan the sky for bright meteors — the calling cards of a comet. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The celestial scorpion curves above the southern horizon as night falls on summer evenings, with the bright orange star Antares as its bright heart. Antares is one of the most impressive stars in the galaxy — a supergiant that’s destined to explode as a supernova. But a fainter star that stands close to its right is pretty impressive, too. Sigma Scorpii consists of four stars, at least one of which will also end its life with a giant bang. Two of Sigma Scorpii’s stars form a tight pair — their surfaces are separated by about half the distance from Earth to the Sun. They’re so close together that even the biggest telescopes see them as a single pinpoint of light. But instruments that break the light into its individual wavelengths detect the presence of two stars, not one. Both stars are much bigger, brighter, and heavier than the Sun. Their details have proved a bit elusive, but a recent study found that the dominant member of the pair is about 14 times as massive as the Sun and about eight times the Sun’s diameter. Its companion is smaller and lighter, but still a stunner. The heavier star is almost certain to explode as a supernova sometime in the next few million years. But the companion’s fate is less certain. The star is near the mass limit for a star that will become a supernova. Above that limit, it goes boom. Below it, the star sheds its outer layers, leaving its hot, dense core — a dead star known as a white dwarf. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Astronomers have been discovering new planets almost faster than they can count them. They reported more than 750 in the first six months of this year alone, bringing the total number of confirmed planets in other star systems to about 1800. While the search for exoplanets continues, astronomers are also beefing up their efforts to study the planets they’ve already found. In the last few months, several new instruments have joined that effort. The telescope used for NESSI, in New MexicoOne of the biggest is the Gemini Planet Imager — an infrared camera attached to an eight-meter telescope in Chile. Scientists are using it to look at 600 target stars. The camera blocks out the light of the stars themselves, allowing it to see planets in orbit around the stars. And once it sees a planet, it’ll break apart the planet’s light to measure its chemical composition and other details. A similar European instrument entered service in May, also on a large telescope in Chile. In addition to hunting for planets, it’s also looking for rings of dust around its target stars — the raw material for making planets. And a third new instrument is beginning its work in New Mexico. Known as NESSI, it’ll target about 100 already-known planets that pass in front of their parent stars. Comparing a system’s light when the planet is in front of and behind the star will reveal details about the planet’s chemistry. These and other projects will help us get to know the many worlds in other solar systems. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Comet Churyumov-Gerasimenko looms close to the Rosetta spacecraft in this August 6 image, snapped from a range of 60 miles (96 km). Rosetta began keeping pace with the comet on August 6 after a 10-year journey. The comet has two main lobes connected by a narrow neck. Its crusty surface is marked by grooves, boulders, and other features. Rosetta's images show that the comet is dark, indicating that its surface is as much rock as ice. [ESA/Rosetta/NAVCAM] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A few of our stellar neighbors are hard to miss. Vega, which passes high overhead on August evenings, is just 25 light-years away. And Sirius, the brightest star in all the night sky, is nine light-years away. Yet many of our neighbors are so faint that you need a telescope to see them. That list includes the closest star of all, Proxima Centauri, at just four light-years. Astronomers are still working on the census of stars and other objects in our stellar neighborhood. One of the leaders in that effort is called RECONS. It got started 20 years ago this month. So far, it’s tallied about 270 systems within 10 parsecs of Earth — about 33 light-years. Those systems incorporate more than 400 individual objects — stars, planets, and brown dwarfs. Roughly three-quarters of the stars in the neighborhood are much smaller and fainter than the Sun — the cool cosmic embers known as red dwarfs. The faintest of them are only about one ten-thousandth as bright as the Sun, so it takes some effort to find them and measure their distances. The census has revealed fewer brown dwarfs than expected. These objects are more massive than planets, but not massive enough to shine as stars. Some astronomers thought we’d see as many brown dwarfs as true stars, but so far, only a few have been found nearby. Brown dwarfs are so faint, though, that a few could still await detection — adding to the census of our stellar neighborhood. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Rosetta spacecraft began flying along with Comet 67P/Churyumov-Gerasimenko on August 6, completing a 10-year journey to rendezvous with the icy body. This image, snapped from a range of 177 miles (285 km) on August 3, shows that the comet is dark and irregularly shaped. Rosetta will fly in formation with the comet, which is currently between the orbits of Mars and Jupiter, as it gets closer to the Sun. It is scheduled to deploy a small lander in November. [ESA/Rosetta/MPS for OSIRIS Team] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • In a time when astronomers are studying galaxies that are billions of light-years away, you might think that we know everything there is to know about our own cosmic neighborhood. But that’s not the case. Astronomers are still discovering stars and other objects that are close by — neighbors that we didn’t even know were there. Much of that work is being done by RECONS — the Research Consortium on Nearby Stars. It’s led by Todd Henry of Georgia State University. And it’s been going for 20 years. The project uses a 36-inch telescope in Chile to look at objects that move across the sky quickly — an indication that they’re close by. Team members compare the positions of those objects to the background of more-distant stars when Earth is on opposite sides of the Sun. That allows them to measure the distances to those objects. Initially, RECONS was looking for objects within 10 parsecs of Earth — about 33 light-years. A few years ago, the search was expanded to 25 parsecs — more than 80 light-years. In its two decades of work, the search has yielded more than 300 previously uncharted systems inside that 25-parsec zone. The list includes dead stars known as white dwarfs, and failed stars known as brown dwarfs. But most of them are red dwarfs — the smallest and faintest of all stars. In fact, RECONS has found that roughly three-quarters of all the stars in our neighborhood are red dwarfs. We’ll have more about that tomorrow. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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