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  • It’s lonely out beyond the edge of the galaxy. The nearest neighbors would be hundreds if not thousands of light-years away. About the only thing in sight, in fact, would be the hazy disk of the Milky Way, glowing like a small, cloudy slash across the dark sky. The Milky Way’s disk spans about a hundred thousand light-years. We see its outline as a hazy band of light across a dark night sky. But most of the galaxy’s mass is found outside the disk, in a huge volume of space known as the halo. It consists mostly of invisible dark matter, but it also contains a smattering of stars. The most distant of those stars yet seen appear to be far beyond the galaxy’s disk. A team of astronomers found two red-giant stars that are deep into the halo. Red giants are puffy stars that shine dozens or hundreds of times brighter than the Sun, so they’re visible across great distances. One of the stars is about 775,000 light-years from the center of the galaxy, while the other is more than a hundred thousand light-years farther. That makes them the most distant members of the Milky Way yet seen. The stars probably didn’t form that far out because there’s not enough gas in the halo to give birth to stars. Instead, they could have been kicked out of the disk by gravitational encounters with other stars. Or they could have been stripped away from smaller galaxies — turning them into remote sentries on the lonely outskirts of the Milky Way.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • You don’t need big telescopes or electronic instruments to learn about the universe. Sometimes, you can learn a great deal with not much more than your eyes alone. 2200 years ago, for example, the Greek astronomer Hipparchus learned that the stars change position relative to the Sun from year to year. He did so by measuring the position of Spica, the brightest star of Virgo. Spica is in good view in the east at dawn tomorrow, close to the upper right of the crescent Moon. During a lunar eclipse, Hipparchus measured the angle from Spica to the middle of the Moon. And from that, he calculated Spica’s position relative to the Sun. He found that the star had moved about two degrees since another eclipse 150 years earlier — about the width of a finger held at arm’s length. He realized that the entire celestial sphere — the background of fixed stars — rotated with respect to the Sun. That rotation is known as the precession of the equinoxes. It’s caused not by the stars, but by Earth. Our planet “wobbles” on its axis like a spinning gyroscope that’s running down. As it does so, the stars appear to shift position relative to the Sun. It takes about 26,000 years to complete one full wobble and have the stars return to their starting positions. The precession of the equinoxes was an important discovery because it showed that the heavens can change — a discovery made with some simple tools and the nimble mind of Hipparchus.   Script by Damond Benningfield, Copyright 2011, 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Sun, which is shown setting behind the Davis Mountains near McDonald Observatory, sets earliest for the year from the northern United States in mid-December. The earliest sunsets for more southerly latitudes took place earlier in the month. Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The shortest day of the year is still almost a week away, yet for most of the country, the Sun is already starting to set a little later than it did just a few days ago. The difference isn’t much, though — you have to pay close attention to notice it. The shortest day of the year is the winter solstice. In the northern hemisphere, it comes on December 21st, when the Sun stands farthest south for the entire year. You might expect the latest sunrise and earliest sunset on the solstice as well. But that’s not the case. The earliest sunsets came around the first of December for those in Miami, about a week later for those in the country’s middle latitudes, and a few days later still for those in the north. There are several reasons for the early sunsets. One is related to Earth’s tilted axis. Another is Earth’s orbit around the Sun. Right now, we’re near our closest point to the Sun, so our planet moves a little quicker and covers a slightly greater distance than average each day. That means that Earth has to turn a little bit farther for the Sun to return to “local noon” each day — its highest point in the sky. And that takes a bit more time, so local noon occurs later each day. And if noon comes later, so do sunrise and sunset. If you add it up, the earliest sunsets take place a few days or weeks before the solstice, while the latest sunrises occur after the solstice. It’s all part of the precise but complicated workings of the solar system.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Many of the myths of ancient Greece sound like they were written for Hollywood. There’s beauty, mystery, and treachery, with enough nasty monsters to occupy passels of computer animators. One of the nastiest is Cetus, the sea monster, which crawls across the southern sky on December evenings. His story begins with Cassiopeia, the queen of Ethiopia. She was beautiful but vain — she bragged that she was the most beautiful of all. That didn’t sit well with the sea nymphs, who were also great beauties. They asked their father, Poseidon, to punish Cassiopeia for her boasting. He did, by sending Cetus to destroy Ethiopia. Cetus is often depicted as having the head and forelegs of a land creature, but the body of a sea serpent. And he was huge — big enough to destroy entire villages. The oracles told King Cepheus that the only way to save his kingdom was to sacrifice his daughter, Andromeda. So he ordered her to be chained at the shoreline as a sacrifice to Cetus. Just as the monster approached, though, Perseus, the hero, came to the rescue. Depending on which version of the tale you read, he either hacked the monster up, or turned him to stone with the head of Medusa, another nasty creature. Either way, Andromeda was saved, and Cetus was banished to the stars. The constellation is in the south and southeast at nightfall, and due south around 9 o’clock. It offers few bright stars, so you need dark skies to see this vanquished sea monster.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Mars is snuggling especially close to the Sun right now. It was at its closest just yesterday, at a distance of about 128 million miles — 14 million miles closer than average. Like the orbits of all the planets, the orbit of Mars is an ellipse — like a flattened circle — so Mars’s distance from the Sun varies. In the case of Earth, the change in distance isn’t much. But Mars’s orbit is much more lopsided. The dramatic difference in the distance between Mars and the Sun has a dramatic impact on the Martian seasons. When Mars is closest to the Sun, it receives about 45 percent more solar energy than when it’s farthest. The point of closest approach occurs just before the start of winter in the northern hemisphere and summer in the south. So southern summers are much warmer than those in the north, while southern winters are much colder. The change in seasons can bring large dust storms. Mars’s polar ice caps are topped by frozen carbon dioxide. CO2 in the atmosphere freezes onto the polar cap that’s experiencing winter, then vaporizes and flows back into the atmosphere during summer. Since the south pole gets colder, it develops a larger ice cap. But that also means that when summer arrives, more carbon dioxide rushes into the atmosphere. The difference in temperature between the cold air and the Sun-warmed ground can generate strong winds. The winds can kick up big dust storms — some of them big enough to blanket the entire planet.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Geminid meteor shower is at its best the next couple of nights. You can look any time after it gets dark, but there are more meteors after midnight, when your part of Earth faces more directly into the meteor stream. By then, though, the Moon will be in the sky, so its glare will interfere with the fireworks. Like all meteor showers, the Geminids are named for a constellation — in this case, Gemini, the twins, which is high overhead around 2 or 3 a.m. If you trace the paths of the Geminids across the sky, they all appear to “rain” into the atmosphere from Gemini. But meteor showers aren’t caused by the constellations. In fact, even though a meteor is sometimes called a “shooting star,” it has nothing to do with stars at all. Instead, it’s a bit of cosmic rock that’s burning up as it plows into the atmosphere. Meteor showers occur when we encounter dense clouds of these bits. Most meteor showers are spawned by icy comets. But the Geminids come from an object that resembles both a comet and a rocky asteroid. 3200 Phaethon may be an extinct comet — one that’s lost all or most of its ice, leaving only a ball of rock. Bits of that rock fleck off the surface and stream into space — providing the raw meterials for a meteor shower. To watch the shower, find a safe viewing site away from city lights. Despite the glare of the Moon, you might still see a handful of bright meteors streaking across the sky the next couple of nights.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Geminid meteor shower will be at its best after dark on Saturday, December 13 and before dawn on Sunday, December 14, according to the editors of StarDate magazine. read more

  • Observations by an orbiting spacecraft suggest that one of the large volcanic plains on the Moon may have formed when the Moon's early crust cooled and contracted. That caused the crust to crack, allowing molten rock to bubble up to the surface, filling lower terrain and creating the Ocean of Storms. That origin would be difference from most of the dark volcanic plains, which formed after impacts by large asteroids. This image combines a Lunar Reconnaissance Orbiter view of the Ocean of Storms with an artist's depiction of the cracks around its edges. [NASA/Colorado School of Mines/MIT/JPL/GSFC] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A bright trio climbs high across the southern sky late tonight — the Moon, the planet Jupiter, and Regulus, the brightest star of Leo, the lion. They climb into good view by midnight, and are high in the sky at first light. 1960s view of the Ocean of StormsMuch of the portion of the lunar disk that’s visible tonight is covered with dark volcanic plains — beds of rock that were deposited billions of years ago. Many of them formed when asteroids punched holes in the Moon’s crust. Molten rock then bubbled to the surface, filling the basins created by the impacts. But the largest of these dark features may have a different origin. The Ocean of Storms covers a million-and-a-half square miles. If you leave out Alaska and Hawaii, that’s about half the size of the United States. Unlike many other volcanic plains, its outline is ragged, suggesting it wasn’t formed by an asteroid. Observations from a recent NASA mission suggested a different origin. GRAIL measured the Moon’s gravitational field, which revealed four deep cracks around the Ocean of Storms. Those cracks may have formed when part of the crust of the young Moon cooled and contracted, opening deep rifts in the lunar surface. Molten rock then oozed through the cracks, eventually spreading out to form the volcanic plains that are visible today. The Ocean of Storms is on the left side of the Moon as it rises late tonight — a dark volcanic plain that may have formed when the lunar surface cracked open.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • http://stardate.org/store/2015-sky-almanac Images Our special 32-page January/February issue delivers skywatching tips, anniversaries in astronomy and spaceflight, and more for each month, as well as the scoop on next year’s meteor showers and eclipses. Get your copy today.

  • Planetary scientists often deal with sizes and distances that are beyond anything in the everyday world — measurements in the thousands, millions, or even billions of miles. And yet for some things, a single inch will do. Two examples where that’s the case are close together late tonight: Jupiter and the Moon. Jupiter looks like a brilliant star to the lower left of the Moon as they rise in late evening. The Moon is our nearest neighbor, at an average distance of about a quarter-million miles. By bouncing laser beams off special reflectors left on the Moon by Apollo astronauts, though, scientists have found that the Moon is moving away from us — at about an inch and a half per year. That recession is a result of the tides. The Moon’s gravity raises tides in the oceans, while Earth’s gravity raises smaller tides in the solid surface of the Moon. The combination causes Earth to rotate a bit slower, and the Moon to move a bit farther away. In the case of Jupiter, the “inch” is related not to its distance, but its size. Jupiter is the largest planet in the solar system — about 11 times Earth’s diameter, and more than 300 times our planet’s mass. Such a massive object produces a strong gravitational field. It’s so powerful that it causes Jupiter to shrink — by about an inch per year. Look for Jupiter and the Moon climbing into good view around midnight, and high in the sky at first light. More about the Moon tomorrow.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Ancient rocks are stacked like the layers of a cake in this recent image from the Curiosity rover on Mars. Mission scientists say the layers probably formed several billion years ago, at or near the mouth of a river, as the river deposited sediments carried from up stream. The images confirm that Curiosity's surroundings, inside a large crater, were once warm and wet, providing a possible habitat for life. This image, which is in false color, spans about five feet, so each rock layer is no more than an inch or two thick. [NASA/JPL/MSSS] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • When a supply capsule docked with the International Space Station a couple of months ago, its cargo included something that had never been to space before: a 3D printer. Astronauts are checking it out to see how it works in microgravity, and making sure it’s safe. 3D printing builds objects one layer at a time. A laser or electron beam fuses together the raw materials, from paper to plastic to metal. The technology uses fewer raw materials than conventional technology, and can cut manufacturing time and costs. It’s already being used to make models, prototypes, works of art, and other objects. 3D printing could be a critical technology for starshipsSpace scientists are using the technology as well. NASA recently made fuel injectors for a new booster rocket that way, and they passed an early test firing. And in the future, small satellites may be made entirely on 3D printers. And in the far future, the technology may be used to make everything from food to replacement parts on Mars expeditions and other long-duration missions, like a slower version of the replicators found on the starships of the Star Trek universe. And if we ever build real starships, 3D printing or its follow-on technologies could be critical. Taking enough spare parts for all of a ship’s systems would add a lot of weight. With 3D printing and recycling, a crew could start out with tanks full of raw ingredients, then make anything it needed on the way — making it a little bit easier to reach the stars.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • NASA and other space agencies have long offered paper models of their spacecraft. Just print out the plans, cut them out, and fold them up to make your own Mars rover or other probe. But the European Space Agency recently took the model building to a whole new level of detail. It posted detailed overviews of the comet that’s being studied by its Rosetta mission. Download them, manipulate them with the right software, and print out a fully realistic solid model of the comet. There’s only one minor drawback: you need a 3D printer. 3D printing builds an object layer by layer, using a variety of materials — from paper to plastic to metal. It’s becoming popular in everything from art to manufacturing, because it makes it possible to build intricate objects more easily than with conventional techniques. So far, it’s mainly used for making models and prototypes, but it could one day be a popular method of mass production. It offers advantages for science as well. Astronomers can build 3D models of comets, dying stars, magnetic fields, and other things that are normally seen only in two dimensions. That helps them understand how such objects form and evolve. 3D printing is likely to be especially helpful to space exploration. Engineers could put together spacecraft components — and even entire satellites — in one operation. They could also build parts that otherwise would be impossible to make. 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.

  • If you’re in the southern half of the United States, you can look for something a bit unusual in the early evening sky over the next few weeks: the Big Dipper rising. Like all the stars in the northern sky, those of the Big Dipper constantly wheel around the North Star, Polaris, as Earth spins on its axis. The stars of the Dipper are closer to the North Star than most, though, so they make a tight loop around it. From the northern U.S. — cities like Seattle and Minneapolis — Polaris is so high in the sky that the Dipper never sets. It scoots low above the northern horizon, but never quite dips below it. As you head south, though, the North Star drops lower and lower in the sky — and so does the Dipper. From the latitude of Denver, the star at the tip of the Dipper’s handle disappears. And by the time you get as far south as Dallas, almost the entire Dipper scoops below the horizon. Even so, it doesn’t remain out of sight for long. From Dallas, for example, most of the Dipper is below the horizon as night falls this evening. But the bowl climbs into view low in the north-northeast by about 10 o’clock. And the handle clears the horizon after midnight — returning the entire Dipper to view. The Dipper rotates higher in the sky during the rest of the night, and stands high in the north at dawn. Its bowl is upside down, so it looks like it’s pouring its contents down on the North Star — the constant hub of the northern sky.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Summer is long gone, and winter’s just a couple of weeks away. Yet one of the signature star patterns of summer remains in good view in the evening sky. The Summer Triangle is well up in the west at nightfall. Its brightest point is the star Vega, about a third of the way up the sky. Deneb stands directly above it, with Altair well to the left of Vega. Deneb represents the tail of Cygnus, the swan. At this time of year, though, the swan is nose-diving toward the horizon. In this position, the star pattern looks more like a crucifix, so it’s also known as the Northern Cross. It stands directly atop the horizon around 10 o’clock. Every star and constellation has its own season. That’s because there’s a difference in the time it takes the Sun and the other stars to return to the same position in the sky. The background stars — those we see at night — return to the same position every 23 hours and 56 minutes. But in that span, Earth moves a good distance in its orbit around the Sun. As a result, it takes four minutes longer for the Sun to return to the same position in the sky. The difference means that the distant stars all rise and set four minutes earlier each night, or two hours each month. The Summer Triangle first appears at nightfall around the start of summer. Over the following months it climbs high overhead, then drops down the western sky in autumn and into early winter — a remnant of the warmer months of summer.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The full Moon stages a close conjunction with the bright star Aldebaran tonight. At their closest, they’ll be separated by less than the width of your finger held at arm’s length. Aldebaran is 65 light-years away. In other words, it takes light 65 years to cross from Aldebaran to Earth, so we see the star as it looked 65 years ago. Today, though, astronomers typically use another unit to measure the distances to stars and galaxies: the parsec. The name is a contraction of “parallax second.” An object that’s one parsec away has a parallax of one second of arc. Parallax is a tiny back-and-forth shift in a star’s apparent position against the background of more-distant stars when it’s viewed from different angles. It’s like looking at an object that’s close to you with first one eye, then the other — the object appears to jump back and forth a bit compared to objects that are farther away. Astronomers measure parallax by looking at a star when Earth is on opposite sides of the Sun. The star shifts a tiny bit between the two views. The size of the shift reveals the star’s distance — the wider the angle, the closer the star. In the case of Aldebaran, the angle tells us that the star is 20 parsecs away. Again, watch Aldebaran tonight as it snuggles close to the full Moon. The orange “eye” of Taurus is below the Moon as they rise. The two are closest in the evening hours, with the Moon pulling away from Aldebaran after midnight.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • On the human timescale, a star system seems eternal. It can last anywhere from a few million years to a few trillion. Even so, it can change in a hurry — especially when it’s young. A couple of years ago, for example, astronomers were using Spitzer Space Telescope to keep an eye on a system in the constellation Vela. The system is less than one percent the age of the Sun. It’s still surrounded by the building blocks of planets — chunks of rock and ice, plus clouds of dust. Astronomers hoped that watching the system would provide clues about how these materials come together to make planets. Spitzer had to avoid the star for a few months because it was lost in the glare of the Sun. When the telescope turned toward the system again, it detected a vast cloud of dust that hadn’t been there before. It probably was the aftermath of a collision between two asteroids, which pulverized both of them. Yet that act of destruction is also part of the process of making rocky planets like Earth. Smaller chunks of rock stick together to make bigger chunks. If enough of them stick together, they make a planet. But it’s a messy process. The rocks can collide too violently to stick together. Or a small rock can hit a larger one, blasting some of the material into space. Or two large ones can hit, creating a field of debris that coalesces to form a moon — something that happened to Earth when our own solar system was young.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A powerful outburst of energy and charged particles erupts from one of the stars of DG Canum Venaticorum in this artist's concept. The outburst, which was recorded by an X-ray satellite, was 10,000 times stronger than any ever recorded on the Sun. DG Canum consists of two red-dwarf stars, each of which is much smaller, cooler, and fainter than the Sun. The companion star is depicted at top left. [NASA/GSCF/S. Wiessinger] 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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