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  • For Ceres, timing was everything. Had the largest asteroid formed just a few million years earlier, it likely would be almost completely dry. Instead, water appears to account for about half of its volume. Most of the water is frozen, but some may be liquid.

    We should learn more about that over the next few months as a spacecraft known as Dawn takes a close look at Ceres, which is also classified as a “dwarf planet.” Dawn is scheduled to enter orbit around it this week. It’ll become the first craft ever to orbit two different solar system objects beyond Earth.

    Ceres is roughly 600 miles in diameter — about a quarter the size of the Moon. It’s in the asteroid belt, between the orbits of Mars and Jupiter.

    Water probably was common in that zone when Ceres and the other asteroids took shape. But the first big asteroids to form also incorporated large amounts of radioactive elements from a nearby supernova. These elements heated the growing bodies and boiled off much of their water. Ceres probably formed a few million years later, after the radioactive elements had decayed, so it stayed cool enough to keep much of its water.

    Today, its surface consists mainly of clay, which forms in a wet environment. And a space telescope discovered wisps of water vapor around Ceres, suggesting that water may be squirting into space from below ground. So Dawn could see geysers or other evidence of water on the surface of this intriguing little world.

     

    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • An asteroid-chasing spacecraft is about to make history. If all goes well, it’ll enter orbit around the largest asteroid this week. That will give it two notes in the history books: It’ll be the first spacecraft to study Ceres from close range, and it’ll be the first to orbit two bodies beyond Earth.

    Dawn was launched seven-and-a-half years ago. It entered orbit around its first target, the asteroid Vesta, in July 2011, and stayed there for 14 months. It then fired up its engines again and headed toward Ceres.

    Those engines are quite different from those on most spacecraft. Most missions use chemical rockets to get around, like those on the big boosters that blast them into space. Such engines produce a lot of power, but they’re heavy and they burn through a lot of fuel.

    Dawn is powered by ion engines. They use an electric charge to fire out molecules of xenon. That produces only a tiny amount of thrust, but an engine can fire for days without stopping, so the “kick” adds up. And the engines need only a fraction as much fuel as standard rockets. In fact, without the ion engines, Dawn would have been much too big and heavy to even launch.

    Although Dawn will enter orbit around Ceres this week, it’ll take several more weeks to reach the right orbit to conduct its scientific observations. After that, it’ll spend many months looking at Ceres — a world that may have an ocean of liquid water beneath its rocky crust. More about that tomorrow.


    Script by Damond Benningfield, Copyright 2015


    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The dwarf planet Ceres spins on its axis in this animation compiled from 27 images from the Dawn spacecraft, which will enter orbit around Ceres on March 6. These images were snapped from roughly 26,000 miles (47,000 km) on February 19. They show impact craters, including some fairly recent ones that may have exposed ice below the surface, as well as two mysterious bright spots on the floor of a crater. This sequence shows almost a full turn, which takes about 9.5 hours. [NASA/JPL/Caltech/UCLA/MPS/DLR/IDA]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The almost-full Moon glides past the heart of Leo, the lion, tonight. Regulus huddles close to the lower left of the Moon at nightfall. The planet Jupiter, which far outshines Regulus, stands well above them.

    Because it was the brightest star of a prominent constellation, Regulus played a major role in the astronomy and skylore of many cultures. And they gave it names to match. In fact, Regulus means “the little king.”

    That name was bestowed by Nicolaus Copernicus, the 16th-century astronomer who showed that Earth orbits the Sun, not the other way around. He adapted the name from an earlier one, Rex, which means “the king.”

    Less than a century after Copernicus came up with Regulus, German astronomer Johann Bayer devised another name that’s also still in common use: Alpha Leonis, indicating that it’s the brightest or most important star of Leo.

    Bayer labeled more than 1500 stars with a letter of the Greek alphabet followed by the name of its constellation. “Alpha” usually was applied to a constellation’s brightest star, but not always. Sometimes, Bayer labeled the stars based on their location, not their brightness.

    Regulus qualifies as the alpha star on both counts. Not only is it the lion’s leading light, but it’s also at the bottom of a pattern that outlines the lion’s head and mane. So this “royal” star is the most prominent member of a royal constellation: Leo, the king of the beasts.


    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Most of astronomy is strictly “hands-off.” Astronomers can look at the objects they’re studying, but they can’t touch them. Sometimes, though, they can simulate those objects in the lab. That helps them better understand what they see with telescopes and spacecraft.

    An example is a recent study of Jupiter’s Great Red Spot — a storm that’s wide enough to swallow Earth.

    Scientists have pieced together a pretty good picture of the Great Red Spot. They’ve mapped its clouds and winds and taken its temperature. Yet they’re still not sure why it’s red. The color could come from compounds pulled up from deep inside Jupiter, or from interactions between Jupiter and the Sun.

    A team of scientists recently conducted laboratory simulations of conditions at the top of the Great Red Spot. The scientists zapped compounds found in Jupiter’s atmosphere with ultraviolet radiation, like that produced by the Sun. The UV caused two of those compounds — ammonia and acetylene — to turn red.

    The researchers also looked at observations that show that the red is found only at the top of the Red Spot, which towers much higher than the surrounding clouds. That suggests that the Great Red Spot gets its color from interactions between Jupiter and the Sun — a “hands-on” discovery about the solar system’s biggest planet.

    And Jupiter is putting in a big appearance tonight. It’s close to the upper left of the Moon at nightfall, and looks like a brilliant star.

     

    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The stars can be like a time machine — they let us see what our own solar system was like when it was young. These snapshots in time are showing that many planetary systems may evolve in the same way as our own.

    One especially early snapshot is the system known as HD 95086. It’s only around 15 million years old, compared to four-and-a-half billion years for the solar system.

    The star is a bit bigger, brighter, and heavier than the Sun. A big disk of warm dust orbits close to the star, while an even bigger disk of cold dust orbits farther out. A jumbo planet inhabits the gap between the disks, and astronomers expect to find more.

    The layout is similar to that of our solar system, which has a band of warm material close to the Sun — the asteroid belt — then a zone of giant planets, and finally a zone of cold debris beyond the planets.

    A slightly older system shows a similar structure.

    HR 8799 is roughly 30 million years old. The star is similar to the one in HD 95086. And it also has warm and cold dust sandwiching a realm of giant planets. Four planets have been seen so far, and all of them are more impressive than Jupiter, the giant of the solar system.

    No one has found small planets like Earth in either system. But there’s plenty of room for them, because both systems are like scaled-up versions of our own. So there may be more to see as we get better snapshots of these young planetary systems.

     

    Script by Damond Benningfield, Copyright 2015

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A bright star in Cassiopeia is in a short but impressive phase of life: it’s beginning to puff up like a giant balloon.

    Beta Cassiopeia is in the northwest early this evening, at the bottom of a sideways letter W formed by some of the constellation’s brightest stars.

    Beta Cass is probably less than half the age of the Sun. But it’s almost twice as massive as the Sun, so it burns through its nuclear fuel much more quickly. In fact, it’s probably already consumed the original hydrogen fuel in its core, converting it to helium. Gravity is causing the core to shrink and get hotter, which eventually will allow it to start burning the helium to make even heavier elements.

    In reaction to the changes in the core, Beta Cass’s outer layers are starting to puff up. Right now, the star is roughly four times the diameter of the Sun. That’s big, but not nearly as big as the star will be. Over millions of years, it’ll puff up to dozens of times the Sun’s diameter. It’ll then shrink and cool a little as it goes through another series of changes, before puffing up to even bigger proportions.

    At the end of that second cycle, Beta Cass will shed its outer layers into space, briefly surrounding itself with a glowing bubble of gas and dust. The bubble will quickly dissipate, though, leaving only the star’s now-dead core — a hot but tiny cosmic ember known as a white dwarf: a stellar corpse that will slowly cool and fade away into the long cosmic night.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • It’s clear that Mars was much warmer and wetter in the distant past. What’s not so clear is whether any living organisms ever basked in those comfy conditions. The Curiosity rover recently found organic compounds in a rock and bursts of methane in the atmosphere — both of which could be evidence of life. And pieces of the Red Planet continue to show intriguing signs of ancient microscopic life.

    Those signs are found in meteorites — pieces of Mars that were blasted into space when large asteroids slammed into the planet, and that later found their way to Earth.

    A couple of decades ago, a team of scientists reported evidence of ancient microscopic life in one of these rocks. But many other scientists discounted the findings. Even so, similar evidence has been reported in a few other meteorites over the years.

    The most recent came in December. An international team found organic material in one meteorite that appears to have been produced by living organisms.

    The meteorite fell in the desert of Morocco in 2011, and pieces of it were quickly recovered. Scientists found possible products of life inside cracks in one of the rocks. They ruled out the possibility that these organic compounds entered the rock after it hit Earth. The team says the most likely source is Martian life.

    Mars is in pretty good view in the early evening sky right now. It’s low in the west as night falls, close to the lower right of Venus, the “evening star.”

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Two bright spots glare from inside a crater on Ceres, the largest member of the asteroid belt. The Dawn spacecraft, which is scheduled to enter orbit around Ceres on March 6, snapped the image from a range of 29,000 miles (46,000 km) on February 19. Scientists have no explanation for the bright spots, although some speculate that they could be volcanic in origin, perhaps pouring fresh ice onto the dwarf planet's surface. [ NASA/JPL/Caltech/UCLA/MPS/DLR/IDA]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • One of the busiest stellar nurseries in the galaxy stands about half way up the southern sky at nightfall right now. The Orion Nebula has given birth to thousands of stars, with many more taking shape even now.

    As the universe has aged, sights like the Orion Nebula have become less common — far fewer stars are born today than when the universe was young.

    In fact, the rate at which new stars are born reached its peak billions of years ago, and has been dropping ever since. According to a study published a couple of years ago, the universe is giving birth to only one-thirtieth as many stars today as it did about 11 billion years ago. In fact, the study says that 95 percent of all the stars that will ever be born have already taken shape.

    In part, the drop in the stellar birth rate is because much of the original supply of gas for making stars has been used up. The universe is also bigger now, so the gas for making new stars is more spread out. And hot gas around giant black holes creates radiation that may shut down the process of starbirth in many galaxies. Yet these ideas can’t fully account for the dramatic drop in starbirth — leaving astronomers to ponder why so few stars are born today.

    Stars are still being born in the Orion Nebula, though. Look for it below the three stars of Orion’s Belt. Under dark skies, the nebula looks like a large but fuzzy star — a massive stellar nursery less than 1400 light-years away.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • It’s a bit hard to believe when you look at it, but we’re not seeing the star Aldebaran at its best.

    Aldebaran is quite close to the lower right of the Moon this evening. It shines brightly even through the lunar glare. In fact, it’s the 14th-brightest star system in the night sky, so it’s always easy to spot.

    At visible wavelengths, Aldebaran shines about 150 times brighter than the Sun. That’s mainly because the star is much bigger than the Sun, so there’s a lot more surface area to radiate light into space.

    When you add up all wavelengths of light, though, Aldebaran is about 450 times brighter than the Sun. Most of that energy is in the infrared, which is invisible to the human eye.

    That, too, is a result of Aldebaran’s great size. The star is nearing the end of its life, causing its outer layers to puff up to giant proportions. As those layers expanded they also got cooler — much cooler than the Sun. That gives Aldebaran its orange color — cooler stars are orange or red, while hotter ones are blue or white.

    Cooler stars actually radiate most of their energy at wavelengths beyond the red end of the visible spectrum — the infrared. And that’s the case with Aldebaran. Earth’s atmosphere absorbs most of the infrared energy from stars. But from outside the atmosphere, if our eyes were tuned to the infrared, Aldebaran would look even brighter than it does now. Only then would we see this bright star at its absolute best.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Canopus, the second-brightest star in the night sky, has served as a beacon for travelers for centuries. Today, it guides spacecraft to the Moon and other worlds. Appropriately enough, this picture of the giant star was snapped by an astronaut aboard the International Space Station. [NASA]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • If you’re south of about Dallas, the star Canopus can serve as a navigational beacon tonight. It passes due south around 9 or 9:30. And it’s the second-brightest star in the night sky, so it really stands out. But it’s quite low, so you need a clear horizon to find it.

    There’s evidence that Canopus helped folks get their bearings for centuries. And it’s still a popular beacon today — not for people, but for spacecraft.

    One early use for Canopus may have been as a calendar marker in ancient Arabia. Its first appearance in the early morning sky may have heralded the start of a new year.

    Later, Canopus helped Polynesian sailors navigate from island to island. It also helped European sailors when they began to journey through the southern hemisphere.

    When NASA began planning missions to the Moon and planets in the 1960s, it needed a star to serve as a handy navigational beacon. Locking on to the star and the Sun would keep a craft on target.

    Canopus was the obvious choice. Not only is it bright, it’s also well away from the ecliptic — the Sun’s path across the sky. That means there’s always a good separation between Sun and star, so they’re both always in view. And there are no other bright stars or planets around it to confuse the tracking system.

    Canopus made its debut with the Surveyor missions to the Moon and Mariner missions to the planets. And it still helps guide spacecraft today — on journeys across the solar system and beyond.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Until the last couple of decades, the second-brightest star in the night sky was a bit of a mystery. Astronomers couldn’t get a good handle on its distance, so they couldn’t tell whether it was simply big and bright, or super big and bright.

    Canopus is the leading light of the constellation Carina, the keel. From the southern U.S., it’s quite low above the southern horizon this evening, well below Sirius, the only star that outshines it.

    Canopus is far enough away that it’s difficult to measure its distance from the ground. Estimates ranged from a couple of hundred light-years to more than a thousand. But if you don’t know a star’s distance, you can’t tell that much about it. It might look bright because it really is bright, or just because it’s close by.

    In the early ’90s, though, a space telescope measured the distance to Canopus with unprecedented accuracy: it’s about 300 light-years away. That yielded the star’s true brightness — about 13,000 times brighter than the Sun.

    And that allowed astronomers to compile a better profile of the star. It’s about 8 to 10 times as massive as the Sun, and more than 70 times the Sun’s diameter. The great size tells us that Canopus is nearing the end of its life, so it’s puffed outward. Over the next million years or so it may get even bigger and brighter. And while the star is already a good beacon for interplanetary travel, the extra brilliance would enhance that role. More about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • Sirius, the brightest star in the night sky, arcs across the south this evening. And if you live in the far southern latitudes of the United States — south of about Phoenix or Atlanta — the second-brightest star sneaks into view as well. Canopus is due south around 9 o’clock, just a few degrees above the horizon. It’s so bright, though, that you shouldn’t have much trouble spotting it.

    Canopus is the brightest star of Carina. The constellation represents the bulk of the Argo, the ship that carried Jason and the Argonauts on their adventures.

    Canopus may be named for a sailor with another mythological vessel. According to the story, Canopus was the helmsman for Menelaus, the king of Sparta. Canopus piloted the boat on the expedition to retrieve the king’s wife, Helen of Troy. On the way back, a storm blew the boat off course, and it landed in Egypt. When Canopus went ashore, he was bitten by a cobra and died. Helen and Menelaus buried him, and Menelaus established a town there. He named both the town and a bright star that was in the night sky then in the helmsman’s honor.

    Although the star Canopus looks only about half as bright as Sirius, that’s only because of its greater distance — it’s more than 300 light-years away, compared to nine light-years for Sirius. If you lined them up at the same distance, Canopus would shine more than 500 times brighter.

    It took awhile to lock down the distance to Canopus, though; more about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • A February 14 image of Comet Churyumov-Gerasimenko from the Rosetta spacecraft reveals details as small as an office desk. Mission scientists have named the smooth, dust-covered area at the top of the image Imhotep after an Egyptian vizier who is considered to be an early astronomer. The large, round boulder in the top of this zone is named Cheops, the Greek name for the pharaoh Khufu, who built the first and largest of the Giza pyramids. This image was snapped from a distance of just six miles (9 km), which was Rosetta's closest approach to the comet to date. [ESA/Rosetta/Navcam]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • You don’t have to be LeBron James or Tim Duncan to score a double double tonight. Just look in the western sky in early evening. The solar system offers up two close pairings. Each of them consists of one bright, prominent object plus a much fainter one.

    One of the doubles is anchored by the crescent Moon. Sunlight illuminates about one-eighth of the lunar disk, with the rest of it in darkness. Yet you can easily make out the entire disk because it’s bathed in earthshine — sunlight reflected off of our own Earth. It gives the “dark” portion of the Moon a ghostly appearance.

    The Moon’s companion is the planet Uranus. It’s only about a degree or so to the lower right of the Moon — less than the width of a finger held at arm’s length. The planet is just below the edge of visibility right now. But it should be easy to spot with binoculars. It looks like a tiny star, with perhaps a hint of blue-green.

    The other double is far to the lower right of the Moon. Its anchor is the planet Venus, the brilliant “evening star.” It far outshines all the other planets and stars in the night sky, so you just can’t miss it.

    Venus’s companion is the planet Mars, just a whisker to its upper right. Mars is only about one percent as bright as Venus right now, but the proximity to its bright sibling will help it stand out.

    So enjoy the beautiful double double in the evening sky — the result of the precise choreography of the solar system.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • The Moon and the planets Venus and Mars stage a spectacular encounter early this evening. Venus is the brilliant “evening star” to the left of the Moon. And Mars is just a fraction of a degree from Venus. It’s much fainter, though, so you may need to look carefully to spot it.

    Venus and Mars flank our own planet Earth. Venus is the next planet in toward the Sun, while Mars is the next planet outward.

    Like Earth, both planets are small and rocky. But their surfaces are quite different. That’s partially because of their different locations, and partially because of their different sizes.

    Venus is only a bit smaller than Earth is. Early on, it may have had an atmosphere similar to that of Earth. But because it was so much closer to the Sun, it was much hotter. Any water on the planet boiled away into space or combined with other compounds to make rocks. Over time, carbon dioxide baked out of the rocks and into the atmosphere. This trapped heat from the Sun. So today, Venus’s surface roasts at about 860 degrees Fahrenheit, under an atmosphere that’s about 90 times denser than Earth’s.

    Mars is only about half as big as Earth, and it’s about twice as far from the Sun as Venus is. It, too, probably had a warm, wet atmosphere early on. But the planet’s gravity wasn’t strong enough to hold on to its air, so most of it leaked away into space. That leaves Mars cold and dry, with an atmosphere less than one percent as dense as Earth’s.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • With spring training just getting under way, baseball fans are dreaming of pennants, hitting records, and perhaps even that most elusive of defensive gems, the triple play. They might not get one on the diamond, but there’s a great one in the evening sky the next few nights — a tight grouping of the Moon and the planets Venus and Mars.

    This close encounter is made possible by the way the solar system is laid out. The Sun is in the middle, with the planets circling around it in almost the same plane — as if they’re all on a tabletop. The Moon stays close to this plane as well.

    Venus, Mars, and the Moon are at different distances from Earth and the Sun, so they move across the sky at different rates.

    The Moon completes one loop against the background of stars every 27-and-a-third days. But the motions of the planets across the sky are more complicated. Venus wiggles back and forth between evening and morning sky, and never strays far from the Sun. Mars loops all the way across the starry background, but periodically stops and changes direction. So getting these three worlds together is a complicated task.

    But they are close together tonight. The crescent Moon is quite low in the sky as night begins to fall. Venus, the brilliant “evening star,” stands to its upper left, with much fainter Mars directly above Venus. The three will be much closer together tomorrow night, and we’ll have more about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2014

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

  • This diagram shows the structure of the Milky Way galaxy, including its major and minor spiral arms. Our solar system is in the Orion Spur (shown below the yellow bar that marks the galaxy's center), a relatively short arm that contains some of the brightest stars in our night sky. [NASA]

    Text ©2015 The University of Texas at Austin McDonald Observatory

    For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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