StarDate

StarDate Online - Your guide to the universe

  • Looking Back

    Earth and the Moon are small, glowing dots beneath Saturn's rings in this recent image from the Saturn-orbiting Cassini spacecraft. The Moon is the small, faint dot to the left of the brighter Earth. Cassini is beginning the final phase of its mission in late April, when it makes its first passage between Saturn and the inner edge of its rings. [NASA/JPL/SSI]

  • Hunting Dogs

    The constellation Canes Venatici, the hunting dogs, is high in the east this evening. To find it, look for bright yellow-orange Arcturus well up in the east as darkness falls. Canes Venatici is to the upper left of Arcturus.

  • Soyuz 1

    In the spring of 1967, the Soviet Union was getting ready to celebrate May Day, one of its most important holidays. And the celebration would be preceded by a spectacular mission in space: Two Soyuz spacecraft would rendezvous and dock, and two cosmonauts would walk in space.

    Soyuz was designed to carry cosmonauts to the Moon. But three unmanned tests had all resulted in failure. Even so, there was pressure to get on with the first manned flights. So 40-year-old cosmonaut Vladimir Komarov launched aboard Soyuz 1 on April 23rd, 1967.

    But the craft was a dud, rushed into space before it was ready. After launch, one of its solar panels failed to open, and systems designed to aim and maneuver the Soyuz failed as well.

    The launch of Soyuz 2 was canceled, and controllers set about trying to get Komarov back home. More problems delayed retro-fire by two orbits. Finally, after a day in space, Komarov fired his rockets and headed home.

    After reentry, though, the main parachute got stuck. A backup deployed, but got tangled with a smaller chute and never opened. Soyuz 1 hit the ground at 90 miles per hour, killing Komarov. Moments later, braking rockets fired, engulfing the capsule in flames.

    It took 18 months to redesign the Soyuz and get it back into space — a delay that scuttled any chances of winning the Moon race. Today, though, the Soyuz continues to fly — carrying Russians, Americans, and others to the International Space Station.

     

    Script by Damond Benningfield

    StarDate: 
    Monday, April 24, 2017
    Teaser: 
    A tragedy for the Soviet space program
  • Last Glance

    Orion, one of the most beautiful constellations, is about to disappear. There’s only about an hour of good viewing time now, between the end of twilight and the time Orion begins to set. In a couple of weeks it will be hard to see the hunter at all.

  • Last Glance

    This time of year is pretty inviting for a little evening skywatching. The evening hours are warm but not usually too hot, and thunderstorm activity generally hasn’t reached its peak — perfect conditions for watching the stars.

    Unfortunately, though, one of the most beautiful star patterns is dropping from view about now, so there aren’t many more days to enjoy it.

    Orion, the hunter, is low in the west as night falls. Its three-star belt stands almost parallel to the horizon. And its two brightest stars bracket the belt: orange Betelgeuse above, and blue-white Rigel below.

    Orion always climbs into prominence in the evening sky around Thanksgiving and Christmas. At that time of year, in fact, it’s in view for most of the night.

    As the months roll by, though, so does Orion. The constellation rises earlier each night, so by late February, it’s already halfway across the southern sky at nightfall.

    And now, it’s about to disappear from view. There’s only about an hour of really good viewing time — between the end of twilight and the time Orion’s stars begin to set. And that viewing window gets shorter by the night. In a couple of weeks, it’ll be hard to see the constellation at all.

    Fortunately, though, there’s still a lot to look at after Orion passes from view. And the hunter won’t stay gone forever. He’ll begin to climb into the morning sky in August — and will return to the evening sky during the long, chilly nights at year’s end.

     

    Script by Damond Benningfield

    StarDate: 
    Sunday, April 23, 2017
    Teaser: 
    A last good look at the hunter
  • Moon and Venus

    The two brightest objects in the night sky team up at dawn the next two days: the Moon and the planet Venus. Venus, the “morning star,” is close to the left or upper left of the Moon tomorrow, and to the upper right of the Moon on Thursday.

  • Moon and Venus

    The two brightest objects in the night sky team up at dawn the next couple of days: the Moon and the planet Venus. Venus stands close to the left or upper left of the crescent Moon tomorrow, and a little to the upper right of the Moon on Thursday. Venus is the brilliant “morning star.”

    The planet has no moons of its own, although for a couple of centuries it seemed that it might. From the late 1600s to the late 1700s, many astronomers reported seeing a moon close to the bright planet. Some of those astronomers were among the best observers of their time, so others took the sightings seriously.

    But the sightings were sporadic. And it was impossible to combine them all to calculate an orbit for the possible moon, so the subject fizzled out for a while.

    Then, in 1884, another astronomer thought he had a solution. The sightings weren’t a moon, he decided, but a small planet. Its orbit was synchronized with Venus’s in such a way that they appeared close together once every three years. He named this rarely seen world Neith, after an Egyptian war and sky goddess who was sometimes known as the veiled goddess.

    A few years later, though, the veil was lifted for good. A thorough analysis of all the sightings found that there was neither moon nor planet. Instead, they were all sightings of stars that just happened to line up close to Venus — simple coincidences. The subject was closed — and our closest neighbor world remained moonless.

     

    Script by Damond Benningfield

    StarDate: 
    Saturday, April 22, 2017
    Teaser: 
    Looking for a neighboring moon
  • Through the Gap

    Saturn's rings arc above the Cassini spacecraft while storms in the planet's atmosphere pass below it in this artist's concept of the final phase of the Cassini mission. The craft will fly close to Titan, Saturn's largest moon, on April 21, reshaping Cassini's orbit. Beginning the following week, it will make 22 passes between Saturn and the inner edge of its rings, flying just a few thousand miles above the planet itself. Cassini will end its mission in September by diving into Saturn's clouds, which will destroy the long-operating craft. [NASA/JPL/Caltech]

  • Hercules

    The constellation Hercules rises in early evening and stands clear of the northeastern horizon a couple of hours after sunset. The constellation is defined by a lopsided square of stars known as the Keystone.

  • Through the Gap

    An amazing mission of discovery is scheduled to enter its final phase tomorrow. Cassini, which has been orbiting the giant planet Saturn since 2004, will change its flight path. The new course will take the craft between Saturn’s cloudtops and the inner edge of its beautiful rings.

    Cassini has studied the rings in great detail during its journey. It’s found that the system consists of hundreds or thousands of individual rings. Most of the particles in the rings are made of ice, with a smattering of rock and dust.

    Cassini has also discovered many small “moonlets” in the gaps between rings. These bodies are like shepherds tending their flocks; their gravity keeps the ring particles in their proper place.

    The innermost ring is fairly thin and faint. Its inner edge reaches to within just a few thousand miles of Saturn itself. Bits of material from this ring probably drop into Saturn’s atmosphere, where they burn up as meteors.

    To protect itself against possible impact, Cassini will use its large radio dish as a shield as it plunges through the plane of the rings. That should keep its instruments and electronics safe.

    Tomorrow, Cassini will fly close to Titan, Saturn’s biggest moon. That’ll change Cassini’s path, setting up its first loop inside the rings next week. It’ll make 21 more passages over the next five months, leading up to its final act in September: a fatal dive into Saturn’s atmosphere, bringing its mission to an end.

     

    Script by Damond Benningfield

    StarDate: 
    Friday, April 21, 2017
    Teaser: 
    A spacecraft begins its final act
  • Lyrid Meteors

    The Lyrid meteor shower is at its best the next couple of nights. The Moon doesn’t rise until a couple of hours before sunrise, leaving a few dark hours to watch the shower.

  • Last Visit

    The Cassini spacecraft has been orbiting Saturn for almost 13 years. During that time, it’s made many visits to the giant planet’s moons. It’s paid special attention to the biggest moon, Titan, passing less than a thousand miles from it dozens of times. And on Saturday, it’ll make one final pass by the big moon — its final close encounter with any of Saturn’s moons.

    Titan is veiled by smog — an orange haze that makes it impossible to see the surface. But Cassini has viewed the moon at wavelengths that are invisible to the eye. Those wavelengths pass through the haze, allowing Cassini to study the surface in detail.

    Among other things, those observations have revealed sand dunes that can be hundreds of miles long, and lakes and seas that are filled with liquid hydrocarbons. The largest is bigger than Lake Superior. Occasional rains may fill rivers, which then flow into the lakes and seas.

    Cassini has also given us hints of even more liquid far below Titan’s surface — an ocean of water mixed with ammonia. It could be many miles thick, and contain far more water than in all of Earth’s oceans.

    Cassini will fly about 600 miles above Titan on Saturday, giving scientists a farewell look at the intriguing moon. As a bonus, Titan’s gravity will reshape Cassini’s orbit, placing it on a course that’ll carry the craft between Saturn and the inner edge of its rings — beginning the final phase of its lifetime of discovery. More about that tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Thursday, April 20, 2017
    Teaser: 
    A final visit to a big moon
  • Grand Spiral

    Bright waves of new stars, lanes of dark dust, and a central clump of billions of older stars highlight this Hubble Space Telescope view of Messier 100, one of the leading members of the Virgo Cluster, a collection of hundreds of galaxies. M100 is bigger and more massive than our home galaxy, the Milky Way. It is about 56 million light-years away. [ESA/NASA/STScI]

  • M100

    A small telescope reveals the spiral galaxy Messier 100 shining in the corner of the constellation Coma Berenices, to the lower left of Leo. Slightly bigger telescopes begin to reveal its great beauty — a spiral galaxy whirling through the cosmos.

  • M100

    For sheer grandeur, no astronomical object beats a spiral galaxy. And one of the grandest of them all climbs high across the sky on spring nights: Messier 100. We see it face-on, providing an amazing view of its delicate spiral arms.

    The galaxy is one of the leading members of the Virgo Cluster — a couple of thousand galaxies that travel through the universe together.

    M100 is bigger and more massive than our home galaxy, the Milky Way. But like the Milky Way, it’s a wide, flat disk. Waves ripple through the disk, squeezing clouds of gas and dust and causing them to give birth to new stars. Many of the newborn stars are especially hot and bright, so they outline the waves, forming the spiral arms.

    M100 has another thing in common with the Milky Way: It has a couple of smaller companion galaxies. The gravity of these galaxies is tugging on M100. That may be responsible for a slight offset in one side of the spiral, making at least one of the spiral arms look a bit deformed.

    A couple of decades ago, Hubble Space Telescope discovered some stars in the galaxy that are good mile markers. That allowed astronomers to make a good measurement of M100’s distance: about 56 million light-years.

    And a small telescope reveals M100 shining from that great distance in the corner of the constellation Coma Berenices, near Virgo. A slightly biggertelescope begins to reveal its great beauty — a grand spiral galaxy whirling through the cosmos.

     

    Script by Damond Benningfield

    StarDate: 
    Wednesday, April 19, 2017
    Teaser: 
    The grandeur of a spiral galaxy
  • Last-Quarter Moon

    The Moon reaches last quarter at 4:57 a.m. CDT tomorrow. At first and last quarter, the Moon looks as though it were sliced through from top to bottom like a ripe melon. Half of the side facing Earth is in sunlight, while the other half is in shadow.

  • Virgo Cluster

    Galaxies don’t like to be alone. They congregate in clusters — collections of a few dozen to a few thousand of them, all bound by their mutual gravitational pull. Our own galaxy, the Milky Way, belongs to a small cluster known as the Local Group.

    The nearest big cluster is about 50 million light-years away. It’s in the constellation Virgo, so it’s known as the Virgo Cluster. It contains a couple of thousand galaxies.

    Most of them are puffballs — dwarf galaxies that are only a fraction the size and mass of the Milky Way. But a few are giants — they’re the size of the Milky Way or bigger, and some may contain dozensof times as many starsas the Milky Way.

    The Virgo Cluster is at the center of a much larger collection of galaxies: the Virgo Supercluster. It includes several clusters that move through space as a unit, tied together by gravity. Membership includes the Local Group, which is on the supercluster’s outskirts. We’re becoming more tightly integrated into the supercluster, though, as the Local Group is pulled toward the Virgo Cluster.

    And it’s easy to spot the cluster’s location right now. It’s high in the east and southeast at nightfall. It’s roughly between the planet Jupiter, which is the brightest object in the sky at that hour, and the tail of Leo, the lion. Binoculars reveal a few of the galaxies as hazy smudges of light, while a small telescope brings several galaxies into sharper view.

    Moreabout the Virgo Cluster tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Tuesday, April 18, 2017
    Teaser: 
    Galaxies that hang out together
  • Island Universes

    NGC 6503 is a beautiful spiral galaxy spinning through the constellation Draco, the dragon. It is about 18 million light-years away, and spans about 30,000 light-years, which is less than one-third the size of our home galaxy, the Milky Way. It contains tens of billions of stars. The visible universe contains more than 100 billion galaxies, ranging from mere puffballs to behemoths much larger than the Milky Way. Because they are self-contained systems of stars, gas clouds, and planets, they are often called "island universes." [NASA/ESA/D. Calzetti (Univ. Mass.);H. Ford (Johns Hopkins Univ.)/Hubble Heritage Team]

  • Virgo Cluster

    The Virgo Cluster, a giant collection of galaxies, is high in the east and southeast at nightfall, between the planet Jupiter, the brightest object in the sky at that hour, and the tail of the lion. Binoculars reveal a few galaxies as hazy smudges of light.

  • Galaxies

    There are lots of ways to think of galaxies. We might look at them as cosmic cities, each with a densely populated “downtown” and more thinly settled suburbs. More poetically, we might think of them as “island universes” — collections of stars, gas, and all the other stuff that makes up the universe, all in one big, bright, beautiful package.

    However you look at them, galaxies are the biggest individual objects in the universe. They contain anywhere from a few million stars to trillions. And they span anywhere from a few thousand light-years to a million or more.

    These giant agglomerations are dynamic — they grow and evolve. Their clouds of gas and dust collapse to give birth to stars, for example. That can happen steadily, like the drip of a leaky faucet — just what’s happening now in our home galaxy, the Milky Way. Or it can happen in a hurry, like the rush of a fire hose — usually when two galaxies interact with each other — passing close to each other, or even merging.

    In fact, big galaxies like the Milky Way probably got so big through mergers. In the early universe, most galaxies were pretty small. They were packed together so tightly, though, that their gravity pulled them together. Today, big galaxies continue to grow by gobbling up smaller ones; the Milky Way is ingesting several right now.

    Gravity also holds together big groupsof galaxies, known as clusters. And we’ll talk about one of the most impressive clusters tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Monday, April 17, 2017
    Teaser: 
    “Island universes” across the cosmos
  • Gienah

    Gienah, the brightest star of Corvus, the crow, stands in the southeast as night falls, and due south around midnight. The constellation’s brightest stars form the outline of a small sail, with Gienah at the sail’s top right corner.

  • Gienah

    Most stars consist almost entirely of hydrogen and helium, the lightest and simplest chemical elements. But there’s a smattering of other ingredients as well — everything from oxygen to platinum. These elements can be tough to detect, though. For one thing, there’s not much of them — they add up to only a fraction of one percent of all of a star’s atoms. And for another, they’re usually concentrated deep inside the star, where they’re hidden from astronomical instruments.

    But one class of stars likes to show off some of those elements. The stars in this class all have about the same surface temperature — they’re much hotter than the Sun.

    They’re known as mercury-manganese stars, because they can show concentrations of these and similar elements that are thousands of times greater than in other stars.

    They don’t really have more of these elements, though. Instead, more of the elements have been dredged up from deep inside. Radiation from the star’s core may push these elements to the surface, where astronomers can see them. On the other hand, gravity pulls other types of elements toward the core, so the stars show unusually low levels of them.

    One good example of a mercury-manganese star is known as Gienah. It’s the brightest star of Corvus, the crow. The constellation is in the southeast as night falls, and due south around midnight. Its brightest stars form the outline of a small sail. Gienah is at the top right corner of the sail.

     

    Script by Damond Benningfield

    StarDate: 
    Sunday, April 16, 2017
    Teaser: 
    Stirring up a star’s ingredients
  • Moon and Saturn

    Saturn follows the Moon across the sky late tonight. The ringed planet looks like a bright star, and perches close to the lower left of the Moon at first light tomorrow.

  • Moon and Saturn

    Saturn follows the Moon across the sky late tonight. The planet looks like a bright star, and perches close to the lower left of the Moon at first light tomorrow.

    The Moon is in its “gibbous” phase now. That means that sunlight illuminates more than half of the hemisphere that faces our way.

    The portion that’s in view offers a good look at the contrast between the two main landforms on the Moon: the dark “seas” and the lighter highlands.

    As the name implies, the highlands are generally at a higher elevation than the seas. They’re the fractured remains of the Moon’s original crust. They consist mainly of a mineral known as anorthosite. It’s not very heavy, so when the Moon formed, it floated to the top. It contains a lot of calcium, which is why it has a lighter color.

    Over the eons, impacts by space rocks blasted the crust, churning it up — like pounding the tiles on your kitchen floor with a hammer. That created a jumbled landscape of hills, mountains, canyons, and other dramatic features.

    Some of the biggest impacts blasted holes all the way through the crust, or created deep cracks in the crust. That allowed molten rock to bubble up from below, forming volcanic plains. This rock, known as basalt, contains a higher concentration of dark materials, so the plains look dark. They reminded long-ago skywatchers of bodies of water, so they were called maria, the Latin word for “seas” — dark seas of rock on the surface of the Moon.

     

    Script by Damond Benningfield

    StarDate: 
    Saturday, April 15, 2017
    Teaser: 
    Light and dark on the lunar surface
  • Moon and Antares

    Antares, the brightest star of Scorpius, stands below the Moon at dawn tomorrow. Antares is a supergiant star that is nearing the end of its life. Within the next million years or so, it is likely to blast itself apart as a supernova.

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