StarDate

StarDate

StarDate Online

  • The star that anchors the Big Dipper’s handle is a bit of an outcast. The five stars that make up the dipper’s middle are members of the same family — the Ursa Major Moving Group. They were born from the same cloud of gas and dust, and they move through space together. The stars at the ends are different. Tens of thousands of years from now, they will have moved a good distance from the others as seen from here on Earth, pulling the “dipper” apart. Alkaid is the end of the dipper’s handle. It’s farther away than the members of the moving group — 100 light-years. And it’s only about 10 million years old, which is far younger than the members of the moving group. Ten million years isn’t long on the astronomical time scale — the Sun is four-and-a-half billion years old. Even so, Alkaid is getting well along in life because it’s more than six times as massive as the Sun. The cores of heavy stars are much hotter than those of lighter stars, which revs up their nuclear reactions. They consume their nuclear fuel at a much faster rate, so they burn out much more quickly. Alkaid, for example, will live a “normal” lifetime of less than a hundred million years, versus 10 billion years for the Sun — a short life for a stellar outcast. Look for Alkaid in the north as night falls, with the rest of the dipper hanging below it. The dipper rotates down toward the northern horizon during the night, ready to scoop up a dipperful of stars.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The star Aldebaran, which represents the eye of Taurus, the bull, is nearing the end of its life, so it has puffed up to dozens of times the size of the Sun. The Sun will undergo this same process in several billion years. [Wiki] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A star is the product of a delicate balancing act between gravity and radiation. They remain in balance for most of a star’s life. But as the star ages, the balance changes, causing big changes in the star itself. An example of that process is visible at dawn tomorrow. Aldebaran, the bright orange eye of Taurus, stands just below the Moon. Gravity squeezes a star tightly, smashing its gas together into a compact ball. At the middle of the ball, the gas is heated to millions of degrees — hot enough to ignite nuclear fusion. The fusion produces radiation, which pushes outward, keeping the star in balance. As the star ages, though, it uses up the hydrogen fuel in its core, leaving an “ash” of helium. The helium doesn’t fuse at the same temperature as hydrogen, though. Without nuclear fusion, there’s no radiation to push outward, so gravity squeezes the core even tighter. As the core shrinks, it gets hotter. Eventually, it gets hot enough to ignite fusion in the helium. That achieves a new balance — one with a smaller, hotter core. The radiation from the hotter core exerts a stronger outward pressure, causing the surrounding layers of gas to puff outward like a giant balloon. And that’s what’s happened to Aldebaran. The star has used up its hydrogen, so it’s now beginning to burn its helium. So Aldebaran has puffed up to many times the size of the Sun, causing its outer layers to cool — giving the bull a glowing orange eye.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Pleiades star cluster is climbing higher into the pre-dawn sky each day. Tomorrow, it’s well up in the east at first light, not far to the left or upper left of a thick crescent Moon. In western skylore, the Pleiades represent seven sisters — the daughters of Atlas. To Chinese skywatchers, though, they represented Mao — a spear or a fuzzy head of hair. The earliest confirmed reference to Mao comes from a box found in the well-preserved burial place of Zeng Hou Yi. He was a governor who lived more than 2400 years ago, when seven feudal kingdoms were fighting for supremacy. The box is decorated with an astronomical map that shows the Pleiades with a Chinese character for spear, known as Mao. When a historian wrote a famous book two centuries later, though, he used another character for Mao. It has almost the same pronunciation, but it means “hairy head.” Some speculate that’s because the historian thought the Pleiades looked like the fuzzy fringe of a spearhead. Whether spear or fuzzy fringe, the Chinese version of the small dipper-shaped cluster is composed of seven stars, just like the Pleiades. They’re commonly referred to with the word Mao followed by the Chinese word for the numbers one through seven. Again, look for the Pleiades about a third of the way up the eastern sky at dawn tomorrow, near the Moon. The cluster will rise a few minutes earlier each night, eventually moving into the evening sky of autumn.   Script by Robert Tindol and Paris Liu, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Aquila, the eagle, soars across the southern sky on summer nights. It’s in the east as night falls and high in the south after midnight. It’s marked by Altair, one of the brightest stars in the summer sky. But almost a century ago, Altair was dwarfed by a “new” star that popped into view near by. Known today as V603 Aquilae, it was a nova — the explosion of hot gas on the surface of a white dwarf. It briefly shined as brightly as any star in the night sky. Over the decades, astronomers have used various techniques to try to measure the power of nova explosions. These observations seemed to show that all novae were basically alike — they exploded and faded from view in the same way. Recently, though, a team of astronomers used Hubble Space Telescope to get the most accurate distances yet to V603 Aquilae and three other old novae. The distance of a nova reveals its maximum brightness, providing clues about what’s happening in the explosion. McDonald Observatory astronomer Fritz Benedict, a member of the Hubble team, explains that the observations showed that nova explosions aren’t all alike: BENEDICT: The big piece of information is that these things are very individualistic. The assumption that the same energetics are always involved is wrong. We thought we knew what was going on, and now we know we don’t know what’s going on. You look for the “Aha!” moment, but you also have an aha moment when you say, “Ha, we were dead nuts wrong about that, we need to do it some other way.” So there’s a lot more work to be done to explain the explosions of these “new” stars.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • At Christmas of 1934, a bright “new” star exploded to life in Hercules. For a few days, it was one of the brightest stars in the night sky. It made the front pages of newspapers, and astronomers tracked it for months as it slowly faded from sight. The star is known as DQ Herculis, and astronomers are still tracking it today. In fact, a team of astronomers has used Hubble Space Telescope to study DQ Herculis and three similar stars. Their work has demonstrated that some of the ideas about this class of stars are wrong. Each of these stars erupted as a nova — a powerful explosion on the surface of a dead star known as a white dwarf. The white dwarf stole gas from a nearby companion star. When enough gas piled up on the star’s surface, it triggered a runaway nuclear explosion. But when the four target stars first appeared, in the early 20th century, the cause of these outbursts was still unknown. All that astronomers knew was that a bright star suddenly appeared where no star had been seen before. Yet they observed these enigmatic objects in detail. Using their eyes and their knowledge of the night sky, they tracked how bright each nova looked as it faded from view over the weeks or months. In the decades since, other astronomers have used those observations and those of similar stars to try to draw some conclusions about all novae. But the recent Hubble observations demonstrated that some of those conclusions were wrong. More about that tomorrow.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A white dwarf sounds harmless enough. It’s the small, dead core of a once-normal star like the Sun. But to a close companion star, a white dwarf is anything but harmless. It’s the living dead. Although a typical white dwarf is only about as big as Earth, it’s half as massive as the Sun or heavier, so its surface gravity is quite strong. So if a companion is close enough, the white dwarf can pull hot gas off its surface — like a vampire drinking the blood of the living. Over time — anywhere from a few decades to a few centuries — a layer of gas many miles thick can build up atop the white dwarf. This gas gets hotter and hotter until it triggers a nuclear explosion, like a giant hydrogen bomb. For a while, the white dwarf shines thousands of times brighter than normal. As seen from Earth, a “new” star suddenly appears where none was seen before, so such an outburst is known as a nova, which is the Latin word for “new.” In a few weeks or months, though, the nova once again fades from sight as the exploded material dissipates. So the white dwarf “dies” once again. This cycle of death, rebirth, and re-death has led some astronomers to give novae another name: zombie stars. And the cycle can repeat. After an explosion, the white dwarf can once again begin sucking the gas from its companion. Over the decades, that can lead to another nova explosion — once again reviving a stellar zombie. We’ll have more about novae tomorrow.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The first fragment of Comet Shoemaker-Levy 9 strikes the planet Jupiter while the others (including the rocky objects in the foreground) line up for their own collisions in this artist's concept. The impact took place on July 16, 1994, with the others following over the next few days. Jupiter's gravity had shattered the comet into about 20 large chunks plus countless smaller bits of debris. They hit Jupiter with the energy of thousands of hydrogen bombs, leaving dark scars in the planet's upper atmosphere that persisted for weeks. [Don Davis/NASA] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Our solar system can be a dangerous place. The most striking evidence of that came 20 years ago today, when the first fragment of a shattered comet blasted the planet Jupiter. Another 20 pieces of the comet followed over the next week, creating dark blemishes that lasted for months. Comet Shoemaker-Levy 9 was discovered in 1993. By then, Jupiter’s gravity had already pulled the comet apart, creating what was described as a string of pearls — almost two dozen bright chunks of rock and ice. The first of the pearls hit Jupiter on July 16th, 1994. It hit on the back side of the planet as seen from Earth, so the impact itself wasn’t visible. But a spacecraft en route to Jupiter did see the flash, and measured the temperature of the fireball at about 45,000 degrees. The fireball was about 2,000 miles tall — tall enough for telescopes on Earth to see before the impact site rotated into view. The largest fragment of the comet hit a few days later, exploding with the force of millions of nuclear bombs. It and the other impacts created dark scars in Jupiter’s clouds that were as big as Earth. In the two decades since, a couple of other large objects have plowed into Jupiter, creating similar dark scars. And a small asteroid exploded in the skies above Siberia last year. These and other events, along with a lot of close calls, show that impacts between planets and smaller bodies are common — an ever-present danger in our own solar system.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Our home galaxy, the Milky Way, is a giant, encompassing every individual star the unaided eye can see. But the Milky Way hasn’t always been so huge. Instead, it grew over time, as smaller galaxies smashed together, squeezing their gas clouds and triggering the birth of new stars. Astronomers have recently seen this process in action near the edge of the galaxy’s disk. The Milky Way is so large that many lesser galaxies go around it the way moons orbit a planet. The two brightest of these satellite galaxies are the Magellanic Clouds. They’re named for Portuguese explorer Ferdinand Magellan, who described them as clouds in the southern sky. The clouds abound with gas, which is the raw material for making new stars. The two galaxies are shedding a stream of gas that wraps around much of the Milky Way. Try though they might, though, astronomers couldn’t find any stars in this ribbon of gas until recently. A study examined the stream and detected six bright, young stars within it. The stars likely were born as the gas from the Magellanic Clouds collided with gas at the edge of the Milky Way. That squeezed the gas from the Magellanic clouds, causing it to collapse and give birth to new stars. The newborn stars add even more luster to the Milky Way. And they illustrate how our home galaxy has grown into a giant that’s home to hundreds of billions of stars. We’ll talk about a collision right here in the solar system tomorrow.   Script by Ken Croswell, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The large and small Magellanic clouds, which are companion galaxies to the Milky Way, glow above the antennas of ALMA, a radio telescope in Chile. Each galaxy contains a few billion stars, and lie within about 200,000 light-years of the Milky Way. The Magellanic clouds are visible the unaided eye, but only from the southern hemisphere and the lowest latitudes of the northern hemisphere. [C.Malin/ESO] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • About two dozen satellite galaxies orbit the Milky Way. By far the brightest are the Large and Small Magellanic Clouds, both of which are within about 200,000 light-years of Earth. They’re best seen from the southern hemisphere, where they look like small, glowing clouds. In the past decade, our view of these two galactic neighbors has undergone a pretty big makeover. Astronomers used to think the Magellanic Clouds orbited the Milky Way once every one or two billion years. But in 2006, observations by Hubble Space Telescope suggested that the clouds had a wider orbit and thus a longer orbital period. And last year, new Hubble observations found that this period is at least four billion years and possibly much longer. Meanwhile, other studies show that only a few percent of giant galaxies like the Milky Way boast a pair of bright, star-making satellites as close-in as the Magellanic Clouds. The Milky Way’s other satellites are dead — they’re devoid of any star-making gas, so they no longer give birth to new stars. Put it all together and a new view emerges. The Magellanic Clouds are bright and vigorous, full of gas and new stars, only because until recently they’ve avoided the Milky Way, which steals gas from its satellites. And the two clouds probably orbit each other. Each galaxy’s gravity stimulates the birth of bright new stars in the other, making both of them stunning celestial sights. More tomorrow.   Script by Ken Croswell, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The planet Mars and the star Spica team up for a beautiful showing in the southwest this evening. As night falls, bright orange Mars is just a degree or two above Spica — less than the width of a finger held at arm’s length. If you draw a line from Spica to Mars and continue it upward by less than the width of your fist, you’ll come to two members of our own solar system that are staging an even closer encounter — Ceres and Vesta. They’re not quite bright enough to see with the eye alone, though — you need a telescope to spot them. Ceres is the largest object in the asteroid belt — a wide band of rubble between the orbits of Mars and Jupiter. It’s a ball of rock and ice about one-quarter the diameter of the Moon. Despite its diminutive size, a few years ago Ceres was classified as a dwarf planet — one of five objects to receive that designation so far. Vesta is the second most-massive asteroid after Ceres. It’s about half the size of Ceres, but it’s also closer to Earth, and its surface is more reflective, so it’s the brightest asteroid. Although it’s not a dwarf planet, it’s built a bit like a planet, with a dense core surrounded by a mantle and crust of lighter rock. We learned a lot more about Vesta from the Dawn spacecraft, which orbited the big asteroid for more than a year. Dawn left orbit in late 2012, and is en route to Ceres. It’ll arrive next February — providing our first close look at any dwarf planet.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • This false-color image shows the last gasp of a dying star. Known as M27, the Dumbbell Nebula, it is a giant cloud of gas expelled at the end of a star's life. The nebula spans more than one light-year, and will slowly fade from sight as it continues to expand in the coming millennia. It was discovered 250 years ago by Charles Messier. [George Jacoby (WIYN/NSF)] Text ©2014 The University of Texas at Austin McDonald ObservatoryFor more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Most stars end their lives with a blaze of color — an expanding bubble of gas and dust known as a planetary nebula. Comet-hunting astronomer Charles Messier discovered the first planetary nebula 250 years ago today. It’s known as M27 — the 27th entry in Messier’s catalog of comet-like objects. A planetary nebula forms when a star exhausts the nuclear fuel in its core. The core collapses to form a dense, hot cosmic ember called a white dwarf. Radiation from the white dwarf pushes away the star’s outer layers, creating an ever-expanding bubble. The radiation also causes the gas to glow like a fluorescent bulb. As seen from afar, these clouds can look like rings, cat’s eyes, pearl necklaces, or glowing atoms. And M27 resembles a hand weight like you’d use at the gym — hence another of its names, the Dumbbell Nebula. The Dumbbell has been expanding for thousands of years, and will remain visible for thousands of years more. Eventually, though, it will become so large and thinly spread that it’ll fade from sight. But its story won’t be done. Millions or billions of years in the future, some of the Dumbbell’s gas and dust may be incorporated into new stars and planets — an act of rebirth from the remains of a dead star. The Dumbbell is in Vulpecula, the fox, which is high in the east at nightfall. The nebula is about halfway between Deneb and Altair, the two bright stars that mark the bottom of the Summer Triangle.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Mercury and Venus, the Sun’s closest planets, team up in the eastern sky at dawn the next few mornings. Venus is the “morning star,” so it’s an easy target. Mercury is fainter, but it’s not far to the lower left of Venus, which will help you pick it out. Mercury is a little more than a third of Earth’s distance from the Sun, while Venus is roughly two-thirds of the Earth-Sun distance. So it would make sense for Mercury to be the hotter of the two planets. And it is indeed quite warm — noontime temperatures at Mercury’s equator can reach 750 degrees Fahrenheit. But since Mercury doesn’t have an atmosphere, it doesn’t retain that heat at night, so temperatures plunge to hundreds of degrees below zero. And at the planet’s poles, the temperature can remain below freezing all the time. Venus, on the other hand, does have an atmosphere. It’s about 90 times denser than Earth’s, and it consists almost entirely of carbon dioxide. The combination turns Venus into a planet-sized oven, with steady temperatures of about 850 degrees — day and night, across the entire planet. That makes Venus the hottest planet in the solar system. Again, look for Venus low in the eastern sky at dawn, with Mercury to its lower left. Mercury is easier to spot from the southern states, where it rises a little straighter into the sky. The planet will get a bit brighter over the next few days before it begins to fade and drop away into the morning twilight.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A bright star and a brighter planet are staging a beautiful encounter in the evening sky. They’re quite close together tonight, and will pass even closer over the next few nights. Look for them about a third of the way up the southwestern sky as the last blush of twilight fades away. The planet Mars is the brighter of the two objects. It shines with a distinctly orange hue — the color of the iron-rich dust that coats much of its surface. The star Spica is just to the lower left of Mars. It shines white or blue-white — the result of surface temperatures of tens of thousands of degrees for the system’s two bright stars. Spica is so far away that it remains “fixed” in the same position in our sky — it takes centuries to see any motion at all. But Mars is a close planetary neighbor — the next planet outward from our own Earth — so it moves across the sky fairly quickly. If you plot its position against the background of stars, you can often notice a change from one night to the next. That’s especially true when Mars is passing a bright star like Spica — you don’t need a telescope or a chart or any other aid to notice its motion across the sky. Mars will move closer to Spica over the next couple of nights, then pass over the top of it on Sunday and Monday. After that, Mars will quickly leave its stationary companion behind — heading toward a couple of other prominent encounters in August. We’ll keep you posted.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Over the decades, when astronomers wanted a subject for testing new techniques for studying the stars, they frequently turned to Vega, the brightest star of Lyra, the harp. It’s one of the brightest stars in the night sky, it shines pure white, and it climbs high overhead as seen from most of the northern hemisphere, making it an excellent target. In 1850, Vega became the first star other than the Sun to have its picture taken. In 1872, it became the first star to have its spectrum photographed — a development that allowed astronomers to study the chemical composition of stars in detail. And it was also one of the first stars with an accurate measurement of its distance. More recently, Vega helped astronomers calibrate their observations of other stars. Under the stellar brightness scale, in which a lower number indicates a brighter star, Vega shines at “magnitude zero.” Astronomers could accurately measure the brightness of other stars by comparing them to Vega — a bright and familiar target in the summer sky. Right now, Vega is high in the east at nightfall and crowns the sky around midnight. Deneb, the tail of Cygnus, the swan, is to the lower left of Vega as the sky gets dark. And Altair, the brightest star of Aquila, the eagle, is a little farther to the lower right of Vega. These three stars form the bright but wide-spread Summer Triangle, which remains in view not only in summer but all the way through autumn as well.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Moon forms a gentle arc with two bright pinpoints of light tonight. Antares, the brightest star in Scorpius, is to the lower left of the Moon as night falls, with the slightly brighter planet Saturn to the right or upper right of the Moon. Both Antares and Saturn belong to families of similar objects. Saturn is the second largest of the eight major planets in our own solar system. And Antares is the largest member of a family of stars known as Upper Scorpius — part of a larger complex of stars that spans many light-years. Upper Scorpius contains hundreds of stars that formed from a single giant cloud of gas and dust about 10 million to 12 million years ago. Despite their similar ages, though, they’re not all in the same phase of life. For most stars, an age of a few million years is quite young. In fact, most of the stars of Upper Scorpius haven’t even arrived at stellar adulthood. These stars will live hundreds of millions to billions of years. Antares is the same age as those stars, but it’s already well into its final stages because it’s one of the giants of the galaxy — roughly 17 or 18 times as massive as the Sun. The nuclear furnaces at the cores of such massive stars run at a furious rate, “burning” through their original nuclear fuel in a hurry. Sometime in the next million years or so, Antares is likely to explode as a supernova — while most of its stellar siblings are just getting started.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • When Giovanni Cassini discovered four new moons of Saturn in the 1670s and ’80s, he named them for his patron, King Louis XIV of France. Other astronomers weren’t so keen on the idea, though, so the “Stars of Louis” never caught on. Instead, a couple of centuries later the moons were named for the Titans — the giants who ruled before the gods of Olympus. The Titans were led by Cronus, the Greek version of Saturn. Giovanni Cassini tried to name the moons of Saturn for Louix XIV of FranceNaming astronomical objects has always been a bit of a problem. In the early 20th century, for example, several astronomers had published maps of the Moon with their own sets of names. That made it difficult to discuss individual features at conferences or in papers. So in 1919, astronomers agreed to give the job to the International Astronomical Union — a job it still does today. It not only names moons and other bodies, but it also names the features on those bodies. The names are suggested by scientists who want to report on particular features. IAU committees review and approve the names, which must fall into specific categories for each body and each type of feature. On Saturn’s largest moon, Titan, for example, mountains are named for mountains in Tolkien’s Middle Earth, while bright streaks along the surface are named for rain gods. And Saturn is in great view tonight. It looks like a bright star close above the Moon as night falls, and just to the right of the Moon as they set in the wee hours of the morning.   Script by Damond Benningfield, Copyright 2014 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Valid XHTML & CSS | Template Design LernVid.com and ah-68