StarDate

StarDate

  • Meteorites III

    The Lyrid meteor shower is building toward its peak on Tuesday night. The best views come in the wee hours of the morning, when your part of Earth turns most directly into the meteor stream. And there’s no moonlight to spoil the view.

    The meteors are particles of rock from a comet. They splash into Earth’s atmosphere at blazing-fast speeds, so they vaporize as streaks of light.

    The particles in a meteor shower are so small that they completely burn up. But a few random meteors are big enough to survive their fiery plunge and reach the surface. Such survivors are known as meteorites.

    Thousands of meteorites hit Earth each year. Most plop into the oceans or onto rocky terrain where they’ll likely never be found. A few are discovered — although it generally takes an expert to identify them.

    In fact, most meteorites don’t look unusual at all. They’re fairly angular, although their edges may have been rounded by their plunge through the atmosphere. They’re generally fairly smooth, with no pits on their surfaces. Those that have fallen recently are covered with a shiny black layer known as a fusion crust.

    Most meteorites contain large amounts of iron, so they’re attracted to a magnet. And most also contain small, round blobs of once-molten rock — a feature not found in Earth rocks.

    Most rocks that people think are meteorites are just ordinary Earth rocks. But a rare few really are rocks from outer space.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Meteorites II

    The solar system is about four-and-a-half billion years old. One of the major lines of evidence to determine that age comes from meteorites.

    Most meteorites are pieces of asteroids — chunks of rock and metal that orbit the Sun. Some of these meteorites contain radioactive elements and their daughter elements, which form when the radioactive materials decay.

    The radioactive materials were created by a supernova that exploded shortly before the birth of the solar system. Debris from the supernova “seeded” the cloud from which the solar system formed with many elements.

    The radioactive elements form a natural atomic clock.

    Scientists know how long it takes any radioactive element to decay to form its daughter element. Uranium-238, for example, has a half-life of four-and-a-half billion years. At the end of that time, half of a given sample of the element will have decayed to form lead-206. So comparing the amount of uranium to lead in a meteorite tells you how much of the original uranium has decayed, which tells you how long the sample’s “clock” has been ticking.

    Scientists look at several elements to get a more complete understanding of the age. And they have to make a few assumptions about the composition of the cloud that gave birth to the solar system.

    Any way they look at it, though, they get the same age. The oldest meteorites are a bit more than four-and-a-half billion years old, which means the solar system is that old as well.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Over the Top

    The Dawn spacecraft snapped a series of images of Ceres, the largest member of the asteroid belt, on April 10, roughly one month after entering orbit. The images are looking down on the north pole from a distance of about 21,000 miles (33,000 km). Dawn is scheduled to begin full science observations of Ceres later this month, when it has moved closer to the dwarf planet. To see the animated sequence, click on the full-size version of the image. [ 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.

  • Meteorites

    Our planet Earth offers many natural treasures, from gold and other precious metals to diamonds and other carbon-based compounds. But some treasures come from beyond Earth. They’re bits of asteroids or other bodies.

    These rocks are known as meteorites, and they’re treasures in many ways. Collectors will pay dearly for them, and scientists value them for the information they contain about the history of the solar system.

    Most meteorites are pieces of asteroids — rocky bodies left over from the solar system’s birth. Collisions break off small chunks that spiral around the Sun. Occasionally, one of these chunks plows into Earth’s atmosphere, forming a blazing streak of light known as a meteor. If it’s big enough, then part of the rock may survive and hit the ground.

    Most meteorites are known as chondrites. They’re made mainly of rock. They contain small, round bits of crystallized rock that melted, then cooled and solidified. These bits may have formed when shockwaves hit asteroids as the solar system was taking shape, or when asteroids collided with enough force to melt some of their rock.

    Other meteorites consist almost entirely of iron and nickel, or of a roughly equal mix of metal and rock.

    A few meteorites appear to come from the Moon or Mars. Most of them are a lot younger than the meteorites that come from asteroids, and their chemistry matches what we know about the Moon or Mars — special treasures from beyond Earth.

    More tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Future Quadruplets

    An interstellar cloud in the constellation Perseus is giving birth to quadruplets. And at least three of the four are likely to stick close together after they’re born.

    The cloud is known as Barnard 5. It contains enough cold gas and dust to make about a thousand stars as massive as the Sun. Some of that material is collapsing into dense knots. A few of those knots have given birth to new stars over the last few million years, while others are incubating stars even now.

    A team of astronomers studied one of those incubators with an array of radio telescopes in New Mexico. They found that it contains one proto-star — a dense clump that’s about ready to ignite the fires of nuclear fusion and shine as a true star. It also contains three other clumps that aren’t quite that far along. They’re probably going to give birth to stars sometime in the next 40,000 years or so.

    Each of the new stars will be a good bit smaller and less massive than the Sun. And they’ll be separated by billions of miles. The researchers say the gravitational interactions of the stars is likely to eject one of the quadruplets from the family. But the other three may remain bound to one another — circling through the Milky Way as a tight-knit family.

    And Perseus is low in the west as night falls right now — a couple of intersecting chains of stars spread out to the right of Venus, the “evening star.”

     

    Script by Damond Benningfield, Copyright 2015

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

  • Venus and Aldebaran

    One of the most feminine of all astronomical symbols passes by one of the most masculine the next few evenings. Venus, the brilliant “evening star,” scoots a few degrees to the right of Aldebaran, the bright orange eye of Taurus, the bull.

    The contrast between them is profound. Venus is a planet — a ball of rock about as big as Earth — while Aldebaran is a star that’s dozens of times wider than the Sun.

    It’s fairly easy to see why Venus and Aldebaran got their mythological identities. Venus outshines everything in the night sky except the Moon, so it’s one of the most beautiful objects in the sky. Because of that, ancient skywatchers associated it with the goddess of love and beauty. In Greece, she was known as Aphrodite; in Rome, she was Venus.

    Aldebaran stands at the top left point of a letter “V” formed by several stars — a configuration that clearly resembles a face. And Aldebaran’s orange glare makes it look stern and angry, so many cultures associated the face with that of a bull. In fact, the earliest depictions of the celestial bull may have been drawn in caves more than 15,000 years ago.

    The bull’s horns extend well above the V, with its shoulder marked by the sparkly Pleiades star cluster, which is to the lower right of Venus right now.

    Venus will move past Aldebaran over the next couple of nights, then begin to slowly pull away from the star — a separation of the sexes in the evening sky.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Crackling Star

    Compared to the Sun, the star known as GJ 1243 is a dull ember. It’s about a quarter of the Sun’s size and mass, but less than one percent as bright. Yet there’s one way in which it puts the Sun to shame: It produces more of the powerful explosions known as flares, which can be stronger than anything from the Sun.

    GJ 1243 is a red dwarf. These tiny stars outnumber all the other classes of stars put together. But because they’re the least-massive stars, their light is feeble — not a single one is visible to the unaided eye.

    Because of its size, though, a red dwarf behaves a little differently from stars like the Sun. All of the gas outside its core is like a big pot of boiling water, with gas circulating between the core and the surface.

    That generates a powerful magnetic field, which in turn produces big “starspots” — magnetic storms on the star’s surface. The activity also produces flares — powerful outbursts of particles and energy.

    Astronomers used the planet-hunting Kepler space telescope to keep an eye on GJ 1243 for 300 days. They found that about three percent of the star’s surface was covered by starspots — a far larger percentage than on the Sun. And they detected more than 6,000 flares — more than have been seen on any star other than the Sun. Many of the flares were small, but quite a few were stronger than any solar flares — making this faint star crackle like a Fourth-of-July fireworks display.

     

    Script by Damond Benningfield, Copyright 2015


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

  • The Search Continues

    Venus is continuing its long reign as the brilliant “evening star” this month. It’s in the west as night falls, in the middle of Taurus. That’s right where a planet-hunting space telescope is aiming right now. It’ll have to turn away in a couple of weeks, though, because the bull is dropping toward the Sun in our sky, and soon will be lost in the Sun’s glare.

    The Kepler spacecraft has already discovered more than a thousand confirmed planets, with another three thousand awaiting confirmation. Technical problems halted its initial search a couple of years ago. But a new one allows it to look for planets around a smaller number of stars in different regions of the sky. It aims at one patch for about three months, then turns to a new one as that part of the sky moves behind the Sun.

    The new mission is known as K2, and it’s already yielded at least one planet. The new world is bigger and heavier than Earth, and orbits quite close to its parent star, which is a bit smaller and cooler than the Sun.

    K2 is also studying the stars as well as their planets. Its observations will look at stars that are particularly active, for example, or clusters of young stars that are just taking shape — yielding many more discoveries for astronomers to study.

    We’ll have more about the Kepler mission tomorrow.

    In the meantime, look at Kepler’s current search area in the western sky beginning as night falls — a patch of sky around the evening star.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Evidence of an Encounter

    A kink in one of its spiral arms suggests that the galaxy M66 recently staged a close encounter with a nearby companion galaxy. The kink is near the center of this image, and is marked by a bright red blob of newly forming stars. M66 is about the size of the Milky Way, as is its companion, M66. Gravitational interactions between the two galaxies may have distorted M66 and spurred the birth of many new stars. [NASA/ESA/Hubble Heritage]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Galactic Companions

    Our home galaxy, the Milky Way, and the Andromeda galaxy are the two largest members of the Local Group, a gathering of dozens of galaxies. They’re all gravitationally bound to one another, so even as the universe expands, their gravitational pull will keep them close together.

    But the Local Group is hardly the only galaxy group in the universe. In fact, on spring nights the eastern sky features two large galaxies that resemble Andromeda and the Milky Way.

    M65 and M66 are near Denebola, the bright star that marks the tail of Leo, the lion. Like Andromeda and the Milky Way, both are spiral galaxies. And also like the Milky Way, each is about a hundred thousand light-years across. M66 is a bit off-kilter, suggesting a fairly recent encounter with another galaxy. The encounter squeezed giant clouds of dust, causing them to give birth to millions of new stars.

    M65 and M66 are a similar distance from us — a bit more than 30 million light-years. And they’re quite close to each other. In fact, they’re probably bound to each other just as the Milky Way and Andromeda are, so they’ll remain partners long into the cosmic future.

    And you can see these two galaxies tonight. Look for Leo rising in the east as night falls. If you have a dark sky and a good pair of binoculars or a small telescope, the two galaxies should appear in the same field of view. They show us what our Local Group would look like if we could view it from afar.

     

    Script by Ken Croswell, Copyright 2015

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

  • Local Environment

    Our solar system is a bit like a Russian matryoshka doll. It’s inside an interstellar cloud, which in turn is inside an interstellar bubble.

    The bubble, known as the Local Bubble, spans a few hundred light-years. It was carved out millions of years ago by the shockwave and radiation of one or more exploding stars. There’s much less gas and dust inside the bubble than in the surrounding galaxy. But the gas that does fill the bubble is much hotter than the surrounding galaxy — also the result of the exploding stars.

    The Local Interstellar Cloud is inside the bubble. Its gas and dust are denser and cooler than the bubble, although less dense than many other interstellar clouds.

    The solar system is moving through this cloud at tens of thousands of miles per hour. As a result, a breeze of helium atoms blows through the solar system at that same speed. The Sun’s gravity focuses the breeze into a long tail that’s downwind of the Sun. Earth passes through that tail in December, so right now we’re upwind of it — on the opposite side of the Sun.

    Several spacecraft have measured this wind. And one craft may even have caught some of it and brought it back to Earth.

    The solar system will exit the Local Cloud sometime in the distant future, into the Local Bubble. Over time, it’ll enter much denser clouds — producing a much brisker “wind” through our space environment.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Interstellar Clouds

    Venus, the “evening star,” blazes in the west as night falls this evening. And if you look carefully, you’ll see another famous celestial object close to its upper right — the Pleiades star cluster.

    The eye alone reveals several bright stars that form a tiny dipper. But long-exposure photographs show many more stars, all surrounded by a blue glow — a veil of dust known as a nebula.

    There are several kinds of nebulae — vast clouds of gas and dust that fill the space between stars. The Pleiades is surrounded by a reflection nebula. It consists of tiny grains of dust. These grains are the right size to scatter blue wavelengths of light. It’s similar to what happens in Earth’s atmosphere — molecules of air scatter blue light, which is why the sky looks blue.

    Another prominent nebula is well to the left of Venus and the Pleiades, a little below the three-star lineup of Orion’s Belt. The Orion Nebula is bright enough to see with the eye alone. It looks like a fuzzy star.

    It is an emission nebula — one that produces its own light. It’s part of a giant nursery that’s given birth to thousands of stars. The hottest, brightest stars zap the leftover atoms of hydrogen gas, causing them to glow.

    There’s one other type of nebula — a dark one. Its gas and dust are so cold that they don’t produce any visible light. Instead, the dust grains absorb the light of the stars behind them - creating dark “voids” in the night sky.

    More tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Filling the Void

    Billowing clouds of gas and dust fill this Spitzer Space Telescope image of part of the Milky Way galaxy. Most of this material isn't visible at optical wavelengths, but it does glow in the infrared, which Spitzer investigates. This material forms the interstellar medium, a thin mixture that permeates the space between stars. Especially cold dust forms dark ribbons in this false-color image. The dust in those lanes may someday collapse to give birth to new stars. [NASA/JPL/Caltech]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Interstellar Medium

    The weather can be a bit blustery at this time of year, with strong winds stirring dust into the sky. The dust can make the setting Sun look especially orange or red.

    Astronomers see that same “redness” when they look at the stars beyond the Sun, and for the same reason: clouds of dust. In fact, the space between the stars is far from empty. It’s filled with gas and dust that form the interstellar medium. This material accounts for about 15 percent of all the “normal” matter in our home galaxy, the Milky Way.

    The interstellar medium is an extreme vacuum by any standard — it’s far emptier than any vacuum created in the laboratory. But there’s a lot of space between the stars, so the gas and dust adds up.

    Most of the interstellar medium consists of hydrogen — atoms that were created in the Big Bang. But there’s also a smattering of other atoms and molecules, plus the tiny solid particles known as dust.

    Many of the dust grains are about the size of the particles in cigarette smoke. That’s the right size to scatter blue wavelengths of light. In fact, that’s similar to what makes the sky blue, and what makes the Sun look redder when it’s shining through a thick layer of air.

    Interstellar dust makes distant stars look redder than they really are, too. So to fully understand the stars, astronomers need to know how much dust they’re looking through — dust that reddens the view of the distant stars.

    More tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Moon, Saturn, and Antares

    Every star is remarkable — a giant ball of hot gas that beams light far across the universe. Yet some are more impressive than others. One of the most impressive shines near the Moon tonight.

    Antares is the leading light of Scorpius. It stands to the lower right of the Moon as they rise after midnight. Another bright light, the planet Saturn, is about the same distance to the upper right of the Moon.

    Antares ranks in the top one percent of the top one percent of stars in just about every category.

    It’s roughly 700 times the diameter of the Sun, for example. If it took the Sun’s place in our own solar system, it would engulf the four innermost planets, including Earth, and come close to the fifth planet, Jupiter.

    It’s also extremely bright — about 10,000 times the Sun’s brightness at visible wavelengths. But its surface is relatively cool, so most of its energy is in the infrared. When you add that in, Antares is many times brighter still.

    Finally, it’s one of the most massive stars around — roughly 15 to 20 times heavier than the Sun. Such supergiants burn through their nuclear fuel in a hurry, so they live relatively short lives — in the millions of years, compared to billions of years for stars like the Sun.

    And when their lives are over, stars like Antares don’t go quietly into that good night. Instead, they blast themselves to bits — a fate that could befall remarkable Antares at just about any time.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Family Portrait

    The Cassini spacecraft saw this glorious view of Saturn and its family of rings in 2013. The spacecraft was viewing Saturn's nightside, with the Sun eclipsed by Saturn itself. This view spans roughly 400,000 miles (650,000 km). The 'classic' rings, which were first seen in the 1600s, shine in shades of gold and brown, while the outer 'E' ring, which contains primarily water ice, looks blue. Prominent gaps are visible throughout the ring system. Earth is visible in the image as well, as a small blue dot at the edge of the E ring to the lower left of Saturn. [NASA/JPL/SSI]

    Text ©2015 The University of Texas at Austin McDonald Observatory

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

  • Moon and Saturn

    The rings of Saturn are among the most beautiful objects in the solar system — and perhaps among the most ephemeral as well. They may undergo dramatic changes, with old rings disappearing and new rings forming over millions of years.

    Pan, a small moon of Saturn, moves through the Encke Gap, which is outside the A ring, in this Cassini view [NASA/JPL]The main set of rings spans about two-thirds of the distance from Earth to the Moon. The rings are named with the letters A through D. The D ring is closest to Saturn, beginning just a few thousand miles above the planet’s cloudtops. And the A ring is farthest, with its outer edge almost 50,000 miles out.

    Each of these rings actually consists of hundreds of smaller rings. They’re made of various mixtures of ice, rock, and dust, so each major set of rings looks different from the others.

    That may be because they were born from different parent bodies. The rings likely are the remains of one or more moons that were pulverized by collisions with other bodies, or by the tug of Saturn’s gravity. The debris from such collisions grinds together, creating smaller and smaller pieces.

    But some debris may eventually coalesce to form a new moon, which may then be blasted apart in another collision. This process may have repeated itself over the eons many times — giving Saturn a succession of moons and rings.

    And Saturn is in good view tonight. It’s just below the Moon as they climb into view after midnight, and looks like a bright star. The bright true star Antares is not far below Saturn, and we’ll have more about that tomorrow.

     

    Script by Damond Benningfield, Copyright 2015

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

  • The Next Phase

    2015 has already been a big year for little solar system objects. The Rosetta spacecraft has been orbiting a comet, for example, providing extraordinary views from just a few miles away. And the Dawn spacecraft has entered orbit around Ceres, the largest member of the asteroid belt.

    And beginning this week, a third spacecraft is ramping up its observations of yet another solar system little guy: Pluto.

    New Horizons has been snapping pictures of Pluto since early January. It’s been so far away, though, that Pluto and its biggest moon appear as little more than tiny blobs of light.

    But the craft is drawing almost a million miles closer to the Pluto system every day, so the view is getting better. So New Horizons is beginning the second phase of its observations. It’ll soon start taking pictures with its color cameras. And by about a month from now, those images will offer a sharper view than anything snapped by Hubble Space Telescope, which has provided the best views of Pluto so far.

    This phase of the encounter is scheduled to last until late June, when New Horizons will be just three weeks away from Pluto. At that point, it’ll switch on most of its instruments and start studying Pluto and its four known moons in great detail. New Horizons will speed by Pluto on July 14th — providing what should be some big views of a small world on the edge of the solar system.

    Tomorrow: remaking the beautiful rings of Saturn.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Twin Monsters

    “Frankenstein” was born in Switzerland during the dark and stormy summer of 1816. But the spark that gave life to Mary Shelley’s classic novel may have happened half a world away and more than a year earlier — with a planet-altering event that began 200 years ago today.

    Mount Tambora rose above a small island in Indonesia. It staged a powerful eruption on April 5th, 1815. It rumbled for a few days more, than blew itself to bits on April 10th — the most powerful eruption ever recorded. The mountain turned to “liquid fire,” and dozens of cubic miles of smoke and ash were blasted into the sky.

    The smallest particles of ash made it all the way to the stratosphere, almost 30 miles high, where they spread around the entire planet. They reflected a lot of sunlight back into space, causing the global temperature to drop by a couple of degrees.

    The drop was even steeper in parts of America and Europe, where 1816 was called the “year without a summer.” Crops failed, farmers were bankrupted, and the hungry staged food riots.

    That summer, Shelley was vacationing in Geneva with her future husband — the poet Percy Shelley — as well as Lord Byron and one other writer. Cold, stormy weather trapped them indoors. In the gloom they told ghost stories, and staged a contest to see who could create the scariest.

    Mary Shelley’s contribution was Frankenstein — the tale of a monstrous creation — inspired by a monstrous explosion half a planet away.

     

    Script by Damond Benningfield, Copyright 2015

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

  • Moon and Spica

    The just-past-full Moon has a bright companion tonight: Spica, the brightest star of Virgo. It’s quite close to the lower right of the Moon at nightfall, and stays close as they arc low across the southern sky during the night.

    If you take time to look at the Moon, you’ll notice random dark markings across its surface. They reminded long-ago astronomers of bodies of water, so they gave these features names like the Sea of Crises, the Sea of Tranquility, and the Ocean of Storms.

    Those features aren’t bodies of water, though — they’re volcanic plains. They were created billions of years ago, when giant asteroids slammed into the Moon. The impacts formed wide, deep basins that filled with molten rock from below the lunar crust.

    Yet they’re not completely dry. In fact, there’s quite a bit of water on the Moon — all in the form of ice.

    Spacecraft have discovered large deposits of ice inside craters at the lunar poles. The bottoms of these craters never see the Sun’s rays, so they stay cold enough to hang onto the ice.

    And samples returned by Apollo astronauts, as well as observations by automated spacecraft, have shown that tiny grains of ice are mixed with the lunar “dirt” across much of surface.

    If we ever build colonies on the Moon, the water could be put to good use — providing not just drinking water, but oxygen for breathing, and oxygen and hydrogen for rocket fuel — precious resources from our not-quite-dry satellite world.

     

    Script by Damond Benningfield, Copyright 2015

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

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