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  • The next American mission to Mars, known as MAVEN, is scheduled to enter orbit on September 21. The spacecraft will study the Martian atmosphere and its interaction with the solar wind to help scientists understand how the Red Planet lost most of its water and air over the past four billion years. [NASA/GSFC] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • For the star Regulus, the secret of looking young just may be cannibalism. Regulus is the brightest star of Leo, the lion. It’s close to the left of the crescent Moon at dawn tomorrow. Regulus actually consists of at least four stars. Only one of them is bright enough to see with the eye alone — the one we call Regulus. It’s many times brighter and bigger than the Sun. But it may not always have been that impressive. One of its companions is a tiny stellar corpse that’s only a few million miles away from Regulus. A study a few years ago said that when the system was born, the companion was actually the more impressive star. The star was more massive than Regulus, so it evolved more quickly. As it neared the end of its life, it puffed up to gigantic proportions. The hydrogen gas in its outermost layers began to pour onto the surface of Regulus, making the star bigger and heavier and causing it to spin rapidly. Today, all that’s left of the companion star is its hot but tiny core — a white dwarf. Most estimates have put the age of the system at no more than about 250 million years, compared to four-and-a-half billion years for the Sun. But the study said that the infusion of fresh hydrogen may have made Regulus look younger than it really is. So Regulus may actually be roughly a billion years old, but was kept looking young by an act of stellar cannibalism. Tomorrow: Studying Mars’s changing climate. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • If you’re a fan of smoldering volcanoes, then you can always visit such exotic locations as Hawaii, Iceland, or Italy. Or you might check out Io, one of the largest moons of Jupiter. It’s the most active body in the solar system, with hundreds of working volcanoes. That activity is the result of a tug-of-war between Jupiter and the giant planet’s other large moons. Like our own Moon, Io is locked so that the same hemisphere always faces its parent planet. As the other moons sweep by Io, though, their gravity tries to pull Io out of that locked position. That stretches and twists Io’s interior, heating it and creating vast pools of molten rock. The magma forces its way to the surface. Some of it forms vast pools, with temperatures of more than 2,000 degrees Fahrenheit. But some of it forms towering volcanoes. They can blast material hundreds of miles above the surface. In fact, some of that material gets swept away by Jupiter’s magnetic field, forming a ring of charged particles around the planet. All of this activity gives Io a unique appearance. Its surface is marked with blobs and rings of red, orange, yellow and black, making Io look like a scarred persimmon — a surface unlike any other in the solar system. And Jupiter shines like a brilliant star to the upper left of our Moon early tomorrow. Binoculars reveal Io and a few other large moons — an entourage of intriguing worlds around the solar system’s largest planet. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Moon has a couple of bright companions before dawn tomorrow. The brilliant planet Jupiter stands to the lower left of the Moon, with the star Procyon a little farther to the Moon’s right or upper right. Procyon is the brightest star of Canis Minor, the little dog, which represents one of the hunting dogs of nearby Orion, the hunter. The other hunting dog is well to the lower right of Procyon — Canis Major, the big dog. It contains the “Dog Star” Sirius, the brightest true star in all the night sky. Sirius and Procyon are quite similar. Both stars are bigger, heavier, and hotter than the Sun, and each has a “dead” companion — the small, hot core of a once-normal star. The bright systems are among our closest stellar neighbors. Sirius is almost nine light-years away, with Procyon about three light-years farther. The two are related in the lore of the sky as well. The name Procyon means “before the dog.” It tells us that, from most of the northern hemisphere, Procyon rises a little before Sirius. For many ancient cultures, that made Procyon an important sky marker. In the Mediterranean, for example, the first appearances of Sirius in the dawn sky heralded the end of summer’s heat and the start of cooling autumn rains. From those regions, Procyon first appeared in the dawn twilight a few days before Sirius did — providing a hint of the change in seasons. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A star with a demonic reputation climbs the northeastern sky this evening. Algol represents the head of Medusa, a monster that’s part of the constellation Perseus. The star periodically fades and brightens, which may have helped inspire its reputation. The person who first proposed why the star acts so oddly was born 250 years ago today. John Goodricke came from a well-to-do family. That was important because while he was quite young, Goodricke was afflicted with a disease that left him completely deaf. But his family was able to send him to one of the few schools for the deaf, in Scotland. After completing his education, Goodricke returned to the family home, where he befriended Edward Pigott, a neighbor who’d built an observatory. They decided to study variable stars — those whose brightness changes. Algol was one of their first targets. They found that its brightness varies with a period of 2.8 days. Goodricke suggested that the change was the result of a faint star or a large planet passing in front of a brighter star — an explanation that was later proved correct. The 19-year-old’s work was rewarded by the Royal Society, England’s leading scientific organization. Three years later, Goodricke was elected to membership in the society, at the age of 21 — one of the youngest members ever. Yet he never learned of the honor. He died of unknown causes just days later — ending a brilliant career before it could really get started. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A brilliant aurora glows around the International Space Station in this image snapped in early September by European astronaut Alexander Gerst. An aurora occurs when electrically charged particles from the Sun zap atoms and molecules in the upper reaches of Earth's atmosphere, causing them to emit energy. The green color comes from oxygen, while the red can come from either oxygen or nitrogen. The space station orbits at an altitude of more than 250 miles (400 km), which is at or beyond the upper edge of most aurorae. [NASA/ESA] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The next wave of Mars explorers should be getting ready to enter orbit around the Red Planet. A NASA mission will arrive on Sunday night, with a craft from India following three days later. The two missions share a scientific goal — to better understand how Mars lost its water and most of its atmosphere over the past few billion years. NASA’s an old hand at the Mars exploration business. Its first successful mission took place almost 50 years ago. The agency has launched roughly a score of missions in all, and about three-quarters have succeeded. India, on the other hand, is a Mars neophyte. It has sent a successful mission to the Moon, but the country is trying to expand its exploration of the solar system. As a first step, it launched the Mars Orbiter Mission last November. AUDIO: 3, 2, 1, 0, plus 1, 2, 3, Liftoff! Liftoff normal... The mission’s main goal is to test the technologies needed for further exploration, from the spacecraft and its instruments to tracking systems on Earth. But it’ll also conduct research while it’s there. It’ll study how Mars is losing water to space, map minerals on the Martian surface, and look for traces of methane in the upper atmosphere, which could be a marker of microscopic life. And Mars is in view in the southwest as night falls, shining like a bright orange star. Not far to its left, look for equally bright Antares, a star that shines with the same orange color. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Mars boasts plenty of features an Earthling would recognize, including deserts, canyons, and polar ice caps. And planetary scientists recently discovered another similarity. Mars once had supervolcanoes like the one that erupted more than 600,000 years ago in what is now Yellowstone National Park. These dramatic eruptions may have altered the Red Planet’s climate — for better or for worse. Prior to this discovery, scientists already knew that Mars had mighty volcanoes — some of them are far taller and wider than any on Earth. But the newfound supervolcanoes erupted so violently that they tore themselves apart. In fact, on first glance their remains looked more like impact craters. The supervolcanoes last erupted billions of years ago, and they must have affected the Martian climate. On Earth, even ordinary volcanoes can alter the climate by ejecting ash that reflects sunlight into space, making the planet a little cooler. But volcanoes also vent carbon dioxide and water vapor, which warm a planet by trapping heat from the Sun. Four billion years ago, Mars was much warmer and wetter than it is today. Since then, though, the climate has gotten colder and drier, and no one knows exactly why. The supervolcanoes may have played a role, perhaps emitting so much ash that they caused the planet to cool. Or perhaps they played a positive role, emitting large amounts of greenhouse gases that tried to keep Mars warm even as the planet turned frigid. Script by Ken Croswell, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Some of the brightest and best-known star patterns form a beautiful arch across the sky on September evenings. The curving body of Scorpius, the scorpion, and the teapot shape of Sagittarius hunker low in the south and southwest at nightfall. The Northern Cross — also known as Cygnus, the swan — soars high overhead. And W-shaped Cassiopeia is about a third of the way up the northeastern sky. One advantage to this lineup is that you can see it even from most cities, where artificial light sources overpower the fainter stars. But if you can get away from that glow, the view goes from impressive to breathtaking. That’s because those bright star patterns are immersed in the silvery glow of the Milky Way — the combined light of millions of stars in the disk of our home galaxy. And the longer you gaze at the Milky Way, the better it looks. It takes up to 20 minutes for your eyes to completely adapt to the dark. As they do, you’ll start to see structure in the Milky Way — the dark outlines of clouds of dust, and the brighter glow of dense fields of stars. And to see the Milky Way at its most impressive, find a safe skywatching spot far from the glow of pesky city lights. Tonight, the best view comes before midnight, when the Moon climbs into view. But the Moon will rise later on succeeding nights, providing even more time to appreciate the silvery arch of the Milky Way.   Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Moon creeps toward the two most prominent star clusters late tonight — the Pleiades and the Hyades. Both are in the constellation Taurus. The Pleiades represents the bull’s shoulder, while the Hyades forms his face. The Hyades is to the lower left of the Moon as they climb into good view after midnight. It forms a V, with the point aiming to the right. The brightest star in the V is Aldebaran, the bull’s orange eye. It’s not actually a member of the cluster, though — it just happens to line up in the same direction. The Hyades is the nearest major star cluster — just 150 light-years away. It contains several hundred stars, all of which are several hundred million years old. The stars were born together, from a single giant cloud of gas and dust. They still move through the galaxy together, bound by their mutual gravitational pull. The Pleiades is above or to the upper left of the Moon as they rise. Its brightest stars form a small dipper. The Pleiades is much younger than the Hyades, so it contains more hot, massive stars, which burn out more quickly than smaller, fainter stars. These stellar show-offs make the Pleiades easy to see even though the cluster is about three times farther than the Hyades. Again, look for these families of stars near the Moon tonight. The whole group climbs into view by about 1 a.m., and stands high in the south at first light. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The stars range in age from newborns to more than 13 billion years. Astronomers recently discovered that two faint red stars just 20 light-years away are so young that they haven’t yet ignited their nuclear furnaces. That makes them the closest “pre-main-sequence” stars to Earth. Most stars, including the Sun, are on the “main sequence.” These stars generate energy by converting hydrogen to helium in their cores. But a pre-main-sequence star isn’t yet producing those nuclear reactions. So instead, it shines simply because gravity is squeezing it, which makes it hot. Our Sun spent 50 million years in this phase of life. But it lasts a good bit longer for lightweight stars, like those of EQ Pegasi, which are only a few percent as massive as the Sun. The stars are probably 50 million to 100 million years old — just one or two percent the age of the Sun. Because of their youth, the stars may have planets that are still glowing from the heat of their formation. And since the system is so close, astronomers may be able to take pictures of those planets — offering a glimpse of some young planetary neighbors. EQ Pegasi is in Pegasus, the flying horse, which is well up in the east at nightfall. Look for its Great Square of four fairly bright stars, which is tilted a bit so that it looks more like a diamond than a square. Despite their proximity, the stars of EQ Pegasi are too faint to see without a telescope. Script by Ken Croswell, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A giant family of stars arcs across the southeastern sky on September evenings. M15 is a globular cluster — a family of more than a hundred thousand stars packed into a tight ball. The cluster is about 375,000 times brighter than the Sun. That’s a lot of light. On the other hand, quite a few individual stars in the galaxy shine even brighter. That tells us that M15 is dominated by old, faint stars. In fact, M15 is probably at least 12 billion years old — almost three times the age of the Sun. Its most brilliant stars burned out quickly, leaving ultra-dense corpses known as neutron stars. A neutron star forms when the core of a massive star can no longer produce energy. The core collapses, while the outer layers blast into space as a supernova. Today, almost all the stars that are left are the mass of the Sun or smaller. Occasionally, one of these stars reaches the end of its life and puffs up to giant proportions, shining thousands of times brighter. It then sheds its outer layers, exposing its dead core — a white dwarf, which is bigger but less massive than a neutron star. So one by one, the stars of M15 are going out — slowly draining the luster of this ancient family of stars. M15 is in the east-southeast at nightfall, well to the upper right of the Great Square of Pegasus. It’s too faint to see with the eye alone, but through binoculars, it looks like a fuzzy star — the combined glow of a hundred thousand suns. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Thousands of stars shine in the packed core of M15, a globular cluster that contains more than 100,000 stars, in this Hubble Space Telescope image. At about 12 billion years, the cluster's stars are some of the oldest in the galaxy. Most of the stars are small and faint, although one occasionally flares much brighter as it nears the end of its life. Through binoculars, the cluster looks like a small, fuzzy patch of light well on the upper right of the Great Square of Pegasus on September evenings. [NASA/ESA] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The brightest star of Pegasus, the flying horse, is a bit difficult to pin down. Depending on how you define the constellation, two stars can claim the title. And one of those two changes brightness, so other stars in Pegasus can outshine it. The brightest star in the classical connect-the-dots picture of Pegasus is known as Alpheratz. It’s in the Great Square, a pattern of four stars that outlines the horse’s body. In the 1930s, though, astronomers drew precise boundaries for all the constellations. In this system, Alpheratz is just across the border of Andromeda, where it’s that constellation’s leading light. That leaves Pegasus with a fainter luminary: Enif, from an Arabic name that means “the horse’s nose.” Enif is a supergiant. It’s perhaps a couple of hundred times wider than the Sun, and thousands of times brighter. Enif doesn’t shine steadily, though. Instead, its brightness varies by a few percent. The change doesn’t follow any discernible pattern, so no one knows exactly how bright the star will appear on any given night. And to complicate matters even more, Enif has been seen to flare several times brighter than average for brief periods. Such outbursts might be the result of giant explosions on the surface of the star. Such flares would be brighter than our entire Sun, and blast enormous amounts of particles and energy into space — briefly enhancing the brilliance of the flying horse’s leading light. More about Pegasus tomorrow.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • More than two years after it arrived at Mars, the Curiosity rover continues to explore the Red Planet. This mosaic, made from four images snapped on September 4, shows the rover's surroundings inside a large crater. Curiosity is moving toward the mountains, where its instruments should be able to probe millions of years of Martian history in exposed rock layers. [NASA/JPL/MSSS] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A quartet of above-average stars climbs the eastern sky this evening. The stars form the points of the Great Square of Pegasus — the body of the flying horse. The square is tilted as it comes into view, so it looks more like a diamond than a square. All four of the stars are giants or sub-giants, which makes them much bigger and brighter than the Sun. And all of them are at the end of their “normal” lifetimes, so they’re undergoing a series of changes. In fact, that’s why the stars look so impressive. For most of its life, a star shines by fusing together hydrogen atoms in its core to make helium — a process that releases a lot of energy, making the star shine. When the hydrogen is gone, the core shrinks and gets hotter. The core itself no longer produces energy, although the star burns a layer of hydrogen around the core. Soon, though, the core gets hot enough to ignite the helium, which fuses to make carbon and oxygen. This cycle of changes causes the star’s outer layers to expand, so the star gets bigger and brighter. Two of the stars of the Great Square are just beginning this cycle, so they’re classified as sub-giants. They’re bigger and brighter than the Sun, but they’ll get even bigger and brighter in the future. The other two stars are well into the cycle, so they’re classified as giants — stars in the final stages of life. A star that’s near the Great Square is even more impressive, and we’ll talk about it tomorrow. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Many cultures have given names to the full Moons. The names reflected local conditions at the time of year in which the full Moon appeared, so they varied from place to place. But there was wide agreement on what to call the full Moon closest to the autumnal equinox: the Harvest Moon. And that’s what we have tonight — a full Moon just two weeks before the equinox, which makes it the Harvest Moon. Harvest Moon is more than just a name, though. It does occur around the time most cultures were ready to harvest their crops. But it also helped farmers by casting enough light to allow them to work at night. And at high northern latitudes, the Moon rises at about the same time for a few nights after the full Moon, so farmers didn’t have to take a break after sunset — they could keep right on working far into the autumn nights. The modern definition of Harvest Moon is the full Moon that’s closest to the equinox. Most years, that places it in September, including this year — but just barely. The equinox takes place about 14 days and one hour after the full Moon, with the next full Moon a bit less than 15-and-a-half days after that. So if this month’s full Moon had come just a few hours earlier, Harvest Moon honors would have slipped into October. The time of the full Moon, by the way, is 8:38 p.m. Central Daylight Time, as the Moon lines up opposite the Sun in our sky — lighting up the night of the Harvest Moon. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The serpent bearer has a fat head. Ophiuchus, the serpent bearer, is in the south-southwest as night falls this evening. Its brightest star is Rasalhague, from an Arabic name that means “head of the serpent bearer.” The system actually consists of two stars. The one we see as Rasalhague is more than twice as massive as the Sun, and about 25 times brighter. Unlike the Sun, which is a near-perfect sphere, this star bulges outward — it’s about 20 percent thicker through the equator than through the poles. That distension is caused by the star’s rotation. Its equator spins more than a hundred times faster than the Sun does — so fast that the star is close to flinging itself apart. That pushes gas outward, creating the bulge around the star’s middle. Because the gas at the equator is much farther from the star’s power source — its hot core — than gas at the poles, the equator is thousands of degrees cooler than the poles. The equator also radiates less energy into space, so it looks darker than the poles. Rasalhague is nearing the end of its “normal” lifetime. So over the next few million years, it’ll puff up dramatically — giving the serpent bearer an even “fatter” head. Rasalhague is high in the south-southwest at nightfall. To see it, find bright orange Antares, which is much lower in that direction. Then loft your gaze directly above Antares until you come to the first moderately bright star — the head of the serpent bearer. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The little-known 13th constellation of the zodiac rolls across the sky this evening. It’s in the southwest as night falls, and begins to set after midnight. It covers such a huge chunk of sky, though, that it takes several hours for the whole thing to drop below the horizon. Ophiuchus is known as the serpent bearer. It represents Asclepius, a son of Apollo and the god of medicine in ancient Greece. His healing powers were so great, the legend says, that he could even resurrect the dead. That was bad for business for Hades, the god of the underworld. So he convinced Zeus, the king of the gods, to smite Asclepius with a lightning bolt. But that angered Apollo, so Zeus made Asclepius immortal by placing him in the stars. The modern constellation incorporates much more than just the original connect-the-stars picture of the serpent bearer. It covers a large, jagged patch of sky that extends almost all the way down to Antares, the heart of Scorpius, and the teapot shape of Sagittarius. The Sun crosses the southern part of this big constellation in early December, although it doesn’t touch any of the ancient star picture. A few year ago, some astrologers re-drew the zodiac to add Ophiuchus, recognizing the Sun’s passage across the constellation’s extended borders. The ancient star picture looks a bit like a big coffee pot, with the constellation’s brightest star, Rasalhague, at the top. We’ll talk about that star tomorrow. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Moon will pass in front of Dabih, one of the brightest stars of Capricornus, in the early hours of September 6. This illustration shows the configuration about an hour before the Moon covers the star. The view is best from the western half of the country, where the Moon and Dabih will still be well clear of the horizon as the occultation begins. Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

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