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  • To the people of ancient Persia, four bright stars ruled the night sky — the four “guardians of heaven.” The guardian of the southern sky is one of the highlights of autumn. Fomalhaut is low in the southeast not long after nightfall right now. It’s a lonely beacon in that part of the sky, so it’s hard to miss. It reaches its highest point around midnight, when it stands due south. Like many of the gems in the night sky, Fomalhaut shines so brightly for a couple of reasons. For one, it is fairly bright — it shines about 16 times brighter than the Sun. And for another, it’s quite close — just 25 light-years away. Fomalhaut is also quite young — only about one-tenth the age of the Sun. In fact, it’s still encircled by a broad disk of debris that’s left over from its formation — blobs of ice and rock known as planetesimals, plus vast clouds of dust. Many of these bodies stuck together to make at least one large planet around Fomalhaut, and perhaps more. Some of the leftovers may still be sticking together to give birth to other planets in the future. But many of these “dirty snowballs” are slamming together at such high speed that they pulverize each other, releasing big puffs of gas and dust. That feeds the disk around Fomalhaut with fresh material. Recent observations have shown that Fomalhaut has more than its one known planet to keep it company. It’s gravitationally bound to at least two stars. More about that tomorrow.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • 27,000 years ago, Earth was locked in an Ice Age. Glaciers covered much of North America, and sea level was hundreds of feet lower than it is today. People were painting in caves and on canyon walls, and they were developing such weapons as the bow and arrow. Scientists have pieced together that view of the ancient past through centuries of excavations and lab work. But they can see one remnant of that time directly — the light from the heart of the Milky Way galaxy. That illustrates the vastness of our home galaxy. Light travels at 670 million miles per hour — almost six million million miles in a year. Yet it takes light about 27,000 years to cross the great gulf from the galactic center to Earth, which is a little more than half-way out to the galaxy’s edge. So if a star explodes in the galactic center tonight, no one on Earth will see the fireworks for another 27,000 years. Unfortunately, we can’t see the center of the Milky Way with our eyes alone because it’s veiled by vast clouds of dust. To study it, astronomers must use instruments that are sensitive to wavelengths that are invisible to the human eye. We can see where the galactic center is, though. It’s just above the “spout” of teapot-shaped Sagittarius, which is low in the south-southwest as night falls. That’s right about where the Moon stands this evening — pointing the way to the distant hub of the Milky Way galaxy. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • There’s a sweet alignment in the southwest as night falls this evening: the Moon, the planet Mars, and the star Antares. Mars and Antares are among the brightest pinpoints of light in the night sky, and both shine with a distinctly orange color. They line up below the Moon. Although Mars and Antares look almost identical, they couldn’t be more different. Mars is a planet — a ball of rock that’s about half as big as Earth. It shines only by reflecting sunlight. Antares, on the other hand, is a star — a ball of hot, glowing gases. Not only that, but it’s a supergiant star that’s many hundreds of times wider than the Sun. To put that in perspective, imagine placing Antares so that its surface was the same distance as Mars is right now — about 140 million miles, or roughly half-again the distance from Earth to the Sun. At that range, Antares would span half of the daytime sky. And it would shine thousands of times brighter than the Sun. It would be so bright, in fact, that you’d probably need to wear a helmet with dark, thick glass to keep you from going blind. No matter how you looked at it, though, the view wouldn’t last long. The star’s tremendous heat would quickly vaporize Earth’s atmosphere and oceans, leaving nothing more than a hot, barren rock. And even that wouldn’t last long. Sometime in the next million years or so, Antares will explode as a supernova — a blast that will pulverize any nearby planets. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Mission scientists have chosen a landing spot for Philae, a small probe that's scheduled to land on Comet 67P/Churyumov–Gerasimenko on November 12. Marked by a cross on this image, it features a relatively smooth surface, which provides a safe landing spot. The probe will fire a harpoon into the comet to prevent it from drifting away, then will study the comet's surface and sub-surface. [ESA/Rosetta] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Moon cruises between two planets early this evening. Saturn looks like a bright star to its lower right, with slightly brighter Mars to its left. The star Antares is below Mars, and shines almost the same color — bright orange. Saturn has more than 60 moons of its own. Mars has only two, but their discovery presents an interesting history. Jonathan Swift, Gulliver's travels, and the Mars moons Phobos (top left) and DeimosJonathan Swift wrote about them in his 1726 novel, Gulliver's Travels. Although his descriptions of the moons were accurate, there was a problem: The moons had not yet been discovered. American astronomer Asaph Hall found them in 1877. Swift based his descriptions of the moons on the astronomical knowledge of the day. Earth had one moon, and Jupiter was known to have four. Since Mars was between them, many assumed that it would have two moons. But since no one had yet discovered them, Swift deduced that they were small and close to Mars, where they were hidden in the planet’s glare. Swift was right. Hall found the moons by blocking out Mars itself and scanning the space near the planet. He named his discoveries Phobos and Deimos — fear and panic — after two attendants to the god Mars. Both moons may be asteroids that Mars captured early in its history. Many impact craters mark their surfaces. One of the biggest craters on Deimos is named for a man who wrote about the moons long before their discovery: Jonathan Swift. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Cassini spacecraft may have captures a small new moon taking shape at the outer edge of Saturn's rings. This image shows a small, bright arc at the bottom of the rings. Planetary scientists say this could be ring material clumping together to form a new moon. Small moons may come and go fairly often in the rings. [NASA/JPL/SSI] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Saturn is encircled by beautiful rings and more than 60 known moons. And there may be a link between the two — an idea supported by what appears to be a small moon taking shape inside the rings. The possible moon is less than a mile across — too small to see directly. Last year, though, images from the Cassini spacecraft revealed a bright arc at the outer edge of Saturn’s A ring, the outermost of the planet’s main rings. The arc was hundreds of miles long, and may have formed when something hit the small moon and kicked off debris from its surface. Planetary scientists think this part of the A ring is ripe for forming new moons. That’s because a larger moon, Janus, orbits beyond the A ring’s outer edge. The gravitational pull of Janus causes ring particles to crowd together. Some of these particles may merge, forming an ever-growing ball. Eventually, the ball may get big enough to form a moon. Scientists don’t know when the new moon formed. It could have been during the past decade, or it could have been millions of years ago. Scientists hope to use Cassini to verify the discovery. It’s scheduled to pass close to the rings in 2016, possibly allowing it to see the moon directly — confirming what may be Saturn’s newest moon. And Saturn is quite close to our own Moon this evening. The giant planet looks like a bright golden star close to the upper left of the crescent Moon as night falls. They set about an hour later. Script by Ken Croswell, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Science isn’t just about explaining why things are — it’s also about explaining why things aren’t. Astronomer Daniel Kirkwood, for example, is best known for explaining gaps in the asteroid belt and the rings of Saturn — zones that are clear of the normal debris. Daniel Kirkwood look toward a dark gap in the rings of SaturnKirkwood was born 200 years ago tomorrow in Maryland. He grew up on a farm, and was educated at a small country school. As a teenager, he became a teacher, and he taught himself algebra. He liked it so much that he studied math in college, and began applying that knowledge to astronomy. In 1856, he joined the faculty of the University of Indiana, where he stayed for 30 years. Kirkwood didn’t observe the heavens with a telescope. Instead, he used other people’s observations to develop new theories. As astronomers discovered more and more asteroids in a belt between Mars and Jupiter, for example, Kirkwood noticed that there were gaps — certain distances from the Sun that were bereft of asteroids. He calculated that Jupiter’s gravity would nudge asteroids away from those distances, clearing out the gaps. He also calculated that the gravity of moons of Saturn would do the same thing, clearing out the wide gaps in Saturn’s rings. Today, those types of gaps are named in Kirkwood’s honor. Kirkwood also came up with the correct explanation for meteor showers — they’re bits of debris from comets. Those discoveries have earned him an honored spot in the history of American astronomy. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Two orange pinpoints of light huddle close together in the southwestern sky the next few evenings — the planet Mars and its “rival,” the star Antares — names that are related to that orange color. Mars reminded long-ago skywatchers of the color of blood, so they named the planet for the god of war. In Greece, he was known as Ares; in Rome, he was Mars. Mars’s path across the sky periodically takes it by Antares, which marks the heart of Scorpius, the scorpion. The two so closely resembled each other that the star was called “anti-Ares” — in other words, the rival of Mars. The two bodies come by their color in completely different ways. Mars is colored by iron-rich dust that covers much of its surface. But Antares looks orange because of its temperature. Like all stars, it’s a glowing ball of gas. The color of that gas depends on its temperature — cool stars shine red or orange, while hot stars are blue or white. Antares is at the cool end of that range, with a surface temperature thousands of degrees cooler than the Sun — making it shine bright orange. Look for these orange pinpoints of light as night falls. This evening, Antares is to the lower left with Mars to the upper right. Over the next few nights, though, Mars will move up and over Antares. It’ll stand directly above the star on Tuesday, then quickly move away over the next few nights — leaving its bright orange rival behind. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • India joined the ranks of planetary explorers on September 24 with the arrival of its Mars Orbiter Mission at the Red Planet. It becomes the fourth entity, after the United States, Soviet Union, and Europe, to successfully place a spacecraft in Mars orbit. The mission is designed primarily to help India develop the capabilities for more advanced planetary missions, although it will study the Martian surface and atmosphere. MOM arrived just three days after the latest American mission, MAVEN, also entered orbit. [ISRO] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A huge star in Canis Major, the big dog, is probably about to go “boom.” The star could explode as a supernova within the next hundred thousand years. VY Canis Majoris is one of the largest stars in the entire galaxy. Until the last few years, in fact, many thought it could be the biggest of all. But better measurements of its distance show that it’s a bit closer than thought — less than 4,000 light-years — so it’s not quite as big as thought. Even so, it’s still a stunner — more than 1400 times the diameter of the Sun. Only a handful of stars are bigger. It’s also a couple of dozen times as massive as the Sun, and several hundred thousand times brighter. Such massive stars burn through their nuclear fuel in a hurry, so they die quickly. So even though VY Canis Majoris is only a few million years old, it’s nearing the end of its life. As it’s aged, changes in its core have caused its outer layers to puff up. The star also blows a powerful “wind” of hot gas from its bloated surface — enough material to make a star as massive as the Sun in just a few thousand years. As this material races into space, it sticks together to form solid particles. That’s encased the star in a churning cocoon of dust. The cocoon veils the star from view. The big dog is in in the south-southeast at first light. VY Canis Majoris is to the left of the dog’s hindquarters. But because of its cocoon, you need a telescope to see it — for now. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Cepheus, the king, rotates high across the north on autumn evenings. In that position, its brightest stars form a pattern that looks a bit like an ice cream cone. The constellation is home to several of the largest stars yet discovered — monsters that are more than a thousand times the diameter of the Sun. If they took the Sun’s place in our own solar system, they’d engulf Mercury, Venus, Earth, Mars, and Jupiter, and some of them would get pretty close to Saturn. There are two keys to the size of these “hypergiants,” as they’re sometimes called: They’re many times heavier than the Sun, and they’re nearing the ends of their lives. A star shines by fusing lighter-weight atoms in its core to make heavier ones. At each step of this process, the core shrinks and gets much hotter. The radiation from the core pushes on the gas around the core, making the star’s outer layers puff outward. Stars like the Sun puff up to a few dozen times the size of the present-day Sun. But the most massive stars grow to hundreds of times that size. It’s a bit difficult to measure the sizes of these stars. For one thing, there’s some uncertainty in their distances. And for another, a lot of gas blows off the star’s surface and out into space, so it’s tough to define the star’s edge. Even so, some of the hypergiants of Cepheus could be more than 1600 times the Sun’s diameter — the monsters of the Milky Way. We’ll talk about a doomed hypergiant tomorrow. Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The oldest astronomical instrument is the calendar. It records and predicts the motions of three heavenly bodies — Earth, Sun, and Moon. But while people have been making calendars for thousands of years, they still disagree on many of the details. One example is the dates on which the seasons change. Under the astronomical calendar, today is the September equinox. The Sun crosses the equator from north to south, marking the start of autumn in the northern hemisphere and spring in the southern hemisphere. The equinoxes and solstices divide the astronomical seasons because they’re precise moments in time, and they’re easy to predict far in advance. But there are other ways to define the changing seasons. In the meteorological calendar, autumn begins on September 1st. And many households mark the beginning of autumn at the start of the new school year. In centuries past, many cultures used the equinoxes and solstices as the middle points of the seasons, not the beginnings. In these cultures, the seasons began on what are known as cross-quarter days, which are roughly halfway between a solstice and an equinox. But each culture picked its own dates for these markers, so there was no standardized way to note the changing of the seasons. Even so, we still commemorate many of these dates, with events such as Groundhog Day and Halloween — events tied to the changing of the seasons, no matter which calendar you use. Script by Damond Benningfield, Copyright 2014   For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Modern-day Mars is the planetary equivalent of a high desert — cold and dry. But just how it got that way isn’t fully understood. Planetary scientists hope to pick up some clues from an orbiter that’s scheduled to arrive at Mars this evening. There’s abundant evidence that the young Mars was warm and wet, with a thick atmosphere and water standing on the surface — perhaps even an ocean that covered up to a third of the planet. Over the past four billion years, though, Mars lost most of its atmosphere to space, and the water disappeared as well. Some of the water probably is locked up in the polar ice caps, in beds of ice below the surface, or in aquifers of liquid water. But it’s likely that much of it also escaped into space. MAVEN is designed to study how that might have happened, and how the process is continuing even now. The craft will probe the chemistry of Mars’s upper atmosphere. In particular, it’ll look to see how much water, carbon dioxide, and other molecules are escaping into space. MAVEN also will look at the interactions between the atmosphere and the radiation and particles from the Sun. The Sun’s ultraviolet radiation should split apart molecules in the upper atmosphere, allowing the solar wind to whisk them into space — further depleting the Red Planet’s thinning blanket of air. And MAVEN should start off by studying a different target: a comet that’ll pass about 85,000 miles above the Martian surface next month. Script by Damond Benningfield, Copyright 2014 For 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.

  • The next American mission to Mars, known as MAVEN, entered 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.

  • 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.

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