StarDate

StarDate Online - Your guide to the universe

  • Pherkad

    Just about every star varies a bit — it gets brighter and fainter over a period of time. And in most cases, astronomers can tell you what’s going on. Some stars pulse in and out like a beating heart. Others produce huge dark “starspots,” or brilliant eruptions known as flares. Even the Sun varies a tiny bit, over an 11-year magnetic cycle.

    One of the stars of the Little Dipper varies, too, but astronomers aren’t sure why. They’ve come up with several ideas, but none of them seems to work.

    Pherkad forms the lower outer corner of the dipper’s bowl. It’s about 500 light-years away. It’s a good bit bigger and heavier than the Sun, and about a thousand times brighter. Over a period of a couple of hours, though, that brightness varies by a few percent.

    Astronomers suspect the difference is caused by the star’s stage in life. It’s nearing the end of its “normal” lifetime, which is triggering a series of changes in the star. In stars of similar mass and life stage, those changes can cause the stars’ outer layers to pulse in and out. In fact, that’s happening to one of Pherkad’s neighbors — Polaris, the North Star, at the end of the dipper’s handle.

    Such stars don’t change brightness so quickly, though. Flares and starspots don’t cause such regular changes. And there’s no evidence of another object passing in front of the star, which would change the system’s brightness as well. So the cause of Pherkad’s changing brightness remains a mystery.

     

    Script by Damond Benningfield

    StarDate: 
    Sunday, October 22, 2017
    Teaser: 
    Deciphering a changing star
  • Pherkad

    The star Pherkad, which forms the lower outer corner of the Little Dipper’s bowl, is much bigger, brighter, and heavier than the Sun. Over a period of a few hours, though, its brightness varies by a few percent, and astronomers aren’t sure why.

  • Little Dipper

    If you’ve never seen the Little Dipper, this is a good time of year to look for it. And if you have seen it, you might want to look again, because you might not have seen what you thought you saw.

    This is a good time to find it because it stands almost directly above the Big Dipper, which is low in the northwest at nightfall. The Little Dipper’s bowl hangs upside down, like it’s pouring its water into the other dipper.

    The Little Dipper’s brightest star marks the end of its handle. And it’s one of the most famous stars of all: Polaris, the North Star. It serves as the hub of the northern sky — all the other stars appear to wheel around it.

    Overall, though, the Little Dipper is faint and obscure. You need pretty dark skies to see most of its stars. That means you can’t make out the pattern of the dipper at all unless you have dark skies, away from city lights.

    Quite a few people who think they’ve seen the Little Dipper have really seen the Pleiades — the star cluster that’s known as the Seven Sisters. Its stars do form a dipper. But it’s tiny. If you hold your hand out at arm’s length, you can cover the whole thing with the tip of your little finger. The Little Dipper is much bigger — you’d need your entire outstretched hand to cover it up.

    So if you can escape the glow of city lights, look above the Big Dipper for its fainter and lesser-known relative: the Little Dipper.

    We’ll talk about one of the stars in the dipper tomorrow.

     

    Script by Damond Benningfield

    Keywords:

    StarDate: 
    Saturday, October 21, 2017
    Teaser: 
    Dipping into a faint star pattern
  • Little Dipper

    The Little Dipper stands high above the Big Dipper, which is low in the northwest at nightfall. The Little Dipper’s bowl hangs upside down, like it’s pouring its water into the other dipper.

  • Orionid Meteor Shower

    The Orionid meteor shower should be at its most active late tonight. And there’s no Moon in the sky then, so it should be a pretty good show.

    The shower is known as the Orionids because all of its meteors appear to “rain” into the sky from Orion the hunter. The constellation climbs into good view after midnight, so that’s when the shower is at its best — between midnight and dawn.

    The meteors are bits of debris from Comet Halley. The comet sheds grains of dust as it orbits the Sun. When Earth crosses the comet’s path, some of those grains plunge into the atmosphere. They instantly heat up and vaporize, creating the streaks of light known as meteors.

    Most of the dust grains are no bigger than pebbles. But a few are larger. They form brilliant streaks that are visible even in a moderately light-polluted sky. And some of them can leave glowing trails that remain visible for a couple of minutes.

    The shower has been declining in recent years. Halley’s Comet is near its greatest distance from Earth, so there aren’t as many bits of comet dust in this part of its orbital path. But the number of meteors appears to vary over a period of a decade or so. There’s evidence that the number is heading upwards, so the shower could produce 20 or more meteors per hour at its peak.

    To watch the Orionids, find a dark but safe site away from city lights. Bundle up against the autumn chill, then sit back and watch the sparks from Halley’s Comet.

     

    Script by Damond Benningfield

    StarDate: 
    Friday, October 20, 2017
    Teaser: 
    Sparks from a distant comet
  • Orionid Meteor Shower

    The Orionid meteor shower should be at its best late tonight, and there will be no Moon in the sky then to spoil the show. The shower is known as the Orionids because its meteors “rain” from Orion, although they can streak across any part of the sky.

  • Distant Rings

    Small moons orbit within the faint rings of the planet Uranus, as shown in this diagram. The rings form several narrow bands, shown in white, and a few wider bands, in blue and orange. Some of the moons acts as shepherds, keeping the ring material in place. Most of the rings particles are tiny, but some are as big as pickup trucks. [Ruslik0/Wikimedia]

  • More Uranus at Opposition

    Like peanut butter, planetary rings come in different textures. The rings of Jupiter and Neptune are smooth because the ring particles are tiny. But the rings of Saturn and Uranus are more chunky. They contain plenty of small particles, but they have big chunks mixed in. These different textures can reveal how the rings were made.

    The particles in the rings of Jupiter and Neptune probably flake off the moons of these planets when the moons are hit by big space rocks. The bits of debris then spread out to form rings.

    The small particles in the rings of Uranus probably form in the same way. But the rings of Uranus also contain chunks as big as pickup trucks. These pieces may be debris from a moon that was pulverized by a collision with a comet or asteroid.

    The rings of Uranus are darker than charcoal, so they were discovered just 40 years ago. Even then, they were found only because they blocked the light of a star that was passing behind them.

    There are several tight bands of material within the rings. These bands are no more than a few miles wide. They probably are “penned in” by small moons, which act like shepherds — their gravity keeps their flocks of ring materials from drifting away.

    And Uranus is putting in its best appearance of the year. It rises at sunset, in the constellation Pisces, and remains in view all night. It’s also closest to us for the year, so it shines brightest. Even so, you need binoculars to find it.

     

    Script by Damond Benningfield

    StarDate: 
    Thursday, October 19, 2017
    Teaser: 
    Smooth or chunky?
  • New Moon

    The new Moon will accompany the Sun as it climbs across the sky today. We can’t see the Moon because it is immersed in the Sun’s glare. The exact moment of new Moon is 2:12 p.m. CDT. The Moon will return to view after sunset tomorrow or Saturday.

  • Uranus at Opposition

    The planet Uranus is putting in its best appearance of the year this week. It rises at sunset and remains in the sky all night. It’s also closest to us for the year, at less than 1.8 billion miles, so it shines brightest. In fact, under especially dark skies, for those with very good vision, it’s barely visible to the unaided eye. Most of us, though, need binoculars to find it.

    Uranus is one of the giants of the solar system — only Jupiter and Saturn are bigger. But Uranus may be put together differently from its larger siblings.

    Jupiter and Saturn are balls of hydrogen and helium wrapped around solid cores. Uranus probably has a solid core, too, but it has a lot less hydrogen and helium.

    All of those elements that it does have are contained in an atmosphere that’s perhaps 3,000 miles thick — about one-fifth of the distance down from the tops of the planet’s clouds.

    Below that may be a liquid or partially frozen mixture of water, methane, and rocky minerals. Unlike the boundary between the oceans and air here on Earth, though, there probably isn’t a sharp boundary between the layers of Uranus. The pressure is so great that the liquid and gas merge in a slushy transition zone.

    Uranus climbs into view in the southeast an hour or two after sunset, near the eastern edge of the constellation Pisces. Through binoculars, it looks like a faint blue-green star — a giant world far from the Sun.

    We’ll have more about Uranus tomorrow.

     

    Script by Damond Benningfield

    Keywords:

    StarDate: 
    Wednesday, October 18, 2017
    Teaser: 
    A giant world with a difference
  • Uranus at Opposition

    The planet Uranus is putting in its best appearance of the year this week. It rises at sunset and remains in the sky all night. It’s also closest to us for the year. It’s still so faint, though, that you need binoculars to find it.

  • Sniffing Venusian Air

    A Soviet stamp commemorates the flight of Venera 4, which parachuted through the atmosphere of Venus in October 1967. It made the first direct measurements of the atmosphere of any planet beyond Earth, determining that Venus's "air" consists mainly of carbon dioxide. It also measured high temperatures and pressures before its battery died at an altitude of about 15 miles. [Wikimedia]

     

  • Moon and Venus

    The beautiful “morning star” shines above the crescent Moon at dawn tomorrow. It’s not a star at all, though — it’s Venus, our nearest planetary neighbor. It shines so brightly in part because its surface is completely covered by clouds. They hide not only the surface, but the planet’s atmosphere as well. In fact, scientists got their first direct measurements of the atmosphere half a century ago.

    Venera 4 was a Soviet spacecraft that arrived at Venus 50 years ago tonight. It dropped a probe into the atmosphere — the first craft to plumb the atmosphere of any planet other than Earth.

    Venera’s parachute opened at an altitude of more than 30 miles. The probe’s instruments then transmitted readings for an hour and a half, until Venera reached an altitude of about 15 miles.

    Because of the cloud cover, there was no consensus on what Venera 4 would find. Estimates of surface temperature and pressure, along with the atmosphere’s composition, varied wildly.

    The probe put a lot of that uncertainty to rest. By the time it stopped working, atmospheric pressure was already more than 20 times the surface pressure on Earth, and temperatures had reached 530 degrees Fahrenheit. And Venera found that carbon dioxide made up more than 90 percent of the atmosphere.

    Several later missions made it all the way to the surface, providing a more complete picture of Venus’s atmosphere — a hot, dense, toxic brew hiding beneath a beautiful blanket of clouds.

     

    Script by Damond Benningfield

    StarDate: 
    Tuesday, October 17, 2017
    Teaser: 
    Dropping in on a neighbor
  • Moon and Venus

    The beautiful “morning star” shines above the crescent Moon at dawn tomorrow. It’s not a star at all, though. Instead, it’s Venus, our nearest planetary neighbor. It shines so brightly in part because its surface is completely covered by clouds.

  • Moon and Mars

    Earth’s geologic history is divided into several eras. Today, we’re in the Cenozoic era, which began about 66 million years ago.

    The current geologic era on Mars has been going on a lot longer. Known as the Amazonian period, it’s been underway for three billion years. That means that not much has changed on the planet during that time.

    During earlier eras, the Martian surface changed quickly. Rivers flowed across the landscape, carving channels and canyons. They filled lakes and seas, and perhaps even an ocean. There was a lot of volcanic activity as well.

    By the start of the Amazonian, though, things were slowing down. Mars had cooled off, so some of its water froze. But much of the water escaped into space, because Mars’s weak gravity couldn’t hold on to the planet’s atmosphere. Without an atmosphere, standing water vaporized, water molecules were split apart by sunlight, and the hydrogen in the water was whisked away by the solar wind.

    That doesn’t mean things have been static over that period, though. Volcanic activity continued, and winds in the thin atmosphere sculpted the landscape — a process that’s still going on. Yet Mars is much quieter than it was during its youth — a world little changed over most of its long history.

    And Mars is in good view at dawn tomorrow. It stands to the right of the crescent Moon, and looks like a moderately bright star. The much brighter planet Venus stands below them. More about that tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Monday, October 16, 2017
    Teaser: 
    A long period of quiet on Mars
  • Moon and Mars

    The planet Mars is in good view at dawn tomorrow. It stands to the right of the crescent Moon, and looks like a moderately bright star. The much brighter planet Venus stands below them.

  • Surprising Monster

    The giant galaxy UGC 1382, which is in the constellation Cetus, the sea monster, is a bit of a surprise. At visible wavelengths alone (left), it looks like a dull elliptical galaxy, which has already used up all of its gas and is no longer giving birth to new stars. A few years ago, though, scientists took a closer look at it in ultraviolet wavelengths (center), which revealed bright spiral arms around the galaxy's core. Adding radio wavelengths (right, in green) reveals massive clouds of hydrogen gas around the galaxy, indicating that it has plenty of materials for making many more stars. [NASA/JPL/Caltech/SDSS/NRAO/L.Hagen and M.Seibert]

     

  • Monster Galaxy

    Astronomers got quite a surprise recently. What they thought was a fairly ordinary galaxy turned out to be one of the largest galaxies they’d ever seen.

    UGC 1382 had been classified as an elliptical galaxy — a type that no longer gives birth to new stars. But a closer look revealed an enormous disk of stars around the galaxy’s center. The disk includes spiral arms that are giving birth to new stars. The stars are so spread out, though, that the disk is hard to see.

    Our galaxy, the Milky Way, is also a giant spiral. Its disk of stars spans more than a hundred thousand light-years. But UGC 1382’s disk is more than 500,000 light-years across — several times the diameter of the Milky Way’s disk.

    The galaxy doesn't stop there, though. Beyond the stellar disk is a disk of gas, just as there is in the Milky Way. When you count that, UGC 1382 is a whopping 700,000 light-years across. That’s nearly a third of the distance between the Milky Way and the Andromeda galaxy, the closest big galaxy to our own.

    Gargantuan though this galaxy is, it isn’t unique. Three decades ago, astronomers found a similar galaxy, Malin 1. But UGC 1382 is much closer. That will make it easier for astronomers to study — and figure out how such a monster galaxy came to be.

    Appropriately enough, this galactic monster is in Cetus, which represents a sea monster. It clears the horizon in late evening, spanning much of the southeastern quadrant of the sky.

     

    Script by Ken Croswell, Copyright 2017

    Keywords:

    StarDate: 
    Sunday, October 15, 2017
    Teaser: 
    A monster within a monster
  • Andromeda Galaxy

    The Andromeda galaxy is in good view right now. Tonight, it’s in the east-northeast as darkness falls, and overhead later on. It looks like a faint, fuzzy star. Small telescopes reveal its true nature: a family of hundreds of billions of stars.

  • Moon and Regulus

    Regulus is a big star — it’s three times the Sun’s diameter. Even so, the heart of the lion will wink out of sight in an instant early tomorrow for skywatchers across almost all of the United States.

    Nothing is happening to the star itself. Instead, it’ll be covered by the crescent Moon — an event known as an occultation. It’s one of a series of occultations that began last December and will continue through April.

    The Moon can occult Regulus because the star lies right on the ecliptic, which is the Sun’s path across the sky. The Moon stays close to that path, too. But the Moon’s orbit is tilted a bit with respect to the ecliptic. So most months, the Moon misses Regulus.

    In fact, it misses the star most years as well. That’s because the Moon veers back and forth across the ecliptic over a period of years. So its occultations of Regulus come in clumps — when the Moon’s position relative to the ecliptic is just right.

    This occultation begins in the wee hours of the morning — around 5:45 a.m. from New York, and earlier as you move farther west. Regulus will disappear behind the lighted portion of the Moon, then return to view from the dark portion. The occultation will last about 30 minutes to an hour, with Regulus remaining hidden longer from more southerly latitudes.

    Those on the Pacific coast won’t see the occultation at all — it’ll be over by the time the Moon and Regulus rise, with the bright star standing just above the Moon.

     

    Script by Damond Benningfield

    StarDate: 
    Saturday, October 14, 2017
    Teaser: 
    A big star disappears from view
  • Moon and Regulus

    Regulus will wink out of sight early tomorrow across most of the U.S. The star will be covered by the crescent Moon, an event known as an occultation. It’s one of a series of occultations that began last December and will continue through April.

  • Capricornus

    The roster of constellations includes some weird and wonderful creatures. There’s a dragon, a unicorn, and twocentaurs. But perhaps the weirdest of all is Capricornus, the sea-goat. It’s half goat and half fish.

    In Greek mythology, it’s associated with the god Pan, who was half goat and half man. The story says that he was about to be attacked by the monster Typhon, so he jumped into the water to escape. At the same time, he tried to transform himself into a fish to speed his getaway. But he botched the spell, and turned his human half into a fish, but kept the half that was a goat.

    The constellation is low in the southern sky as darkness falls at this time of year. Its brightest stars form a wide triangle. None of the sea-goat’s stars is especially bright, though, so you need a fairly dark sky to make them out.

    The brightest forms the left point of the triangle. It’s known as Deneb Algedi — “the tail of the goat.” It’s actually a system of at least two stars. The leader is about twice as big and heavy as the Sun, and shines several times brighter. The other is quite similar to the Sun.

    The two stars orbit each other about once a day. As they do so, each star passes in front of the other for a bit. When the fainter star crosses the brighter one, the system’s overall brightness drops by about a quarter. That’s just enough for a skilled observer to notice with the eye alone — a slight flicker for one of the night sky’s oddest creatures.

     

    Script by Damond Benningfield

    StarDate: 
    Friday, October 13, 2017
    Teaser: 
    The weird and wonderful sea-goat
  • Capricornus

    Capricornus, the sea-goat, is low in the southern sky as darkness falls at this time of year. Its brightest stars form a wide triangle. None of the sea-goat’s stars is especially bright, though, so you need a fairly dark sky to make them out.

  • Protecting Earth

    When a double asteroid swings close to Earth in 2024, it just might get a nasty reception. NASA is studying a mission that would slam a spacecraft into the smaller of the two bodies. Astronomers would then measure how much the impact affected the orbit of the two asteroids around each other — vital information that could help us deflect an asteroid on a collision course with Earth.

    An impact by a large asteroid could have devastating effects across a region or even the entire planet. But with enough lead time, it could be possible to nudge an asteroid onto a safe course. One way to provide the nudge might be to ram into the asteroid, changing its speed and direction by a tiny bit.

    The new mission, known as DART, would test that technique.

    The current concept calls for it to target Didymos, a system of two asteroids that orbit the Sun as a pair, bound by their mutual gravitational pull. The larger body is about half a mile in diameter, while the other is only about 500 feet across.

    DART would hit the smaller asteroid at about 13,000 miles per hour. That should alter the asteroid’s orbit around its companion just enough for astronomers to measure the change.

    NASA gave the okay to begin preliminary design work on the mission back in June. If DART is launched, it could be a first step in developing a way to protect our planet from potentially deadly space rocks.

    Tomorrow: odd but beautiful Capricornus, the sea-goat.

     

    Script by Damond Benningfield

    StarDate: 
    Thursday, October 12, 2017
    Teaser: 
    Protecting Earth from space rocks
  • Last-Quarter Moon

    The Moon is at its last-quarter phase at 7:25 a.m. CDT, so sunlight illuminates half of the lunar hemisphere that faces Earth. The illuminated portion of that hemisphere will grow smaller each day until the Moon is new on October 19.

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