StarDate Online

  • Algol

    Four stars in Perseus represent the Gorgons, the mythological sisters whose heads were covered with snakes. For a couple of hours every three days, the brightest of them, Algol, fades dramatically as one member of the binary system covers the other.

  • New Moon

    The Moon is new today at 12:38 p.m. CDT as it crosses the line between Earth and Sun. Our satellite world is lost in the Sun’s glare, but will return to view as a thin crescent shortly after sunset tomorrow or the next day.

  • Venus and Saturn

    Two planets are slipping past each other in the early evening sky. Venus is the “evening star.” The fainter planet Saturn stands to the upper right of Venus this evening, and a bit farther from it on succeeding nights.

  • Eridanus

    Eridanus, the river, flows into the evening sky this month. This long, winding trail of stars begins to rise around 8 or 9 p.m., but it is so long that its easternmost stars don’t clear the horizon until about midnight.

  • Moon and Jupiter

    Jupiter is in great view at dawn tomorrow. The solar system’s largest planet looks like a brilliant star a whisker to the upper right of the crescent Moon. Jupiter is the brightest object in the sky at that hour other than the Moon.

  • VV Cephei

    Cepheus the king wheels high across the north on autumn evenings. It hosts one of the largest stars in the galaxy, VV Cephei. If it took the Sun’s place, it would swallow Mercury, Venus, Earth, Mars, Jupiter, and maybe Saturn.

  • Cepheus

    Cepheus the king stands high in the north this evening, and looks like an upside-down child’s drawing of a house. It was passed down to us from ancient times through the Almagest, a famous text written almost 2,000 years ago by Claudius Ptolemy.

  • Moon and Regulus

    Regulus, the brightest star of Leo, the lion, will crouch close above the Moon at dawn tomorrow. Regulus actually consists of at least four stars, which are split into two close pairs. The system is almost 80 light-years from Earth.

  • Big Neighbor

    Our closest neighbor, the Moon, is 240,000 miles away—equal to 10 trips around Earth’s equator. The closest planet, Venus, the “evening star,” is always at least a hundred times farther. And the closest star system, Alpha Centauri, is a million times farther still.

  • Lost and Found

    Mars Reconnaissance Orbiter may have found the failed Schiaparelli lander, which plummeted to the Martian surface on October 19. A picture taken on October 20 (bottom) shows two spots that were not on an image of the same region in May (top). The image, also shown in a larger view at right, reveals a dark spot and a bright spot. The bright spot may be the lander's parachute, while the larger dark spot could be debris from the lander itself. The European Space Agency reports that Schiaparelli's retrorockets appear to have shut down when the lander was still a mile or two above the surface, not a few feet as planned. The lander was designed to test technologies for landing a rover on Mars in 2020. [NASA/JPL/MSSS]

  • Andromeda

    Andromeda is one of the largest constellations. Its main figure is two streamers of stars that form a skinny V. But it takes some patience to find it. Right now, it is well up in the east and northeast at nightfall, and passes high overhead by midnight.

  • Andromeda

    Andromeda is a pretty big constellation — it rates 19th out of 88. It’s also ancient — it was first drawn several thousand years ago. And it’s fairly famous, too — its namesake was featured in plays by the ancient Greeks, and in more recent times in movies and TV shows.

    Yet it’s a bit disappointing to look at. Andromeda’s main figure is two streamers of stars that form a long, skinny V. But it’s not an attention grabber — it takes some patience to find it. Right now, it’s in the east and northeast at nightfall, and passes high overhead by midnight.

    The constellation represents a princess from the mythical land of Ethiopia.

    The princess was chained at the shore as a sacrifice to a sea monster. The monster was sent to punish the country after Andromeda’s mother, Cassiopeia, boasted that she was more beautiful than the sea nymphs. But the young maiden was rescued at the last moment by Perseus, and the gods placed all of them in the stars.

    Andromeda’s brightest star, Alpha Andromeda, forms the top of the V. Beta Andromeda, which is only slightly fainter, stands to its lower left during the early evening hours.

    The constellation’s real stars, though, are its galaxies. Three of them are easy targets for small telescopes, and one is visible to the unaided eye. In fact, it’s the farthest object you can see without any optical aid: M31, which is two-and-a-half million light-years away. We’ll have more about M31 tomorrow.


    Script by Damond Benningfield

    Saturday, October 22, 2016
    A big but inconspicuous constellation
  • Almach

    The colorful star system Almach climbs high across the sky on autumn nights. A telescope reveals one star that looks yellow-orange, and another that looks blue. Almach is one of the brightest stars of Andromeda, which passes high overhead early tomorrow morning.

  • Almach

    One of the most colorful star systems around climbs high across the sky on autumn nights. A telescope reveals two stars — one that looks yellow-orange, and another that looks blue.

    Almach is one of the brightest stars of the constellation Andromeda, the princess. It’s about half-way up the northeastern sky as night falls, and passes high overhead in the wee hours of the morning.

    The system is about 350 light-years away. At that great distance, the eye alone sees only a single pinpoint of light. It takes a telescope to reveal Almach’s double identity.

    The orange star is nearing the end of its life, so it’s going through a series of big changes. Its core has gotten smaller and hotter, so its radiation pushes more strongly at the surrounding layers of gas. That’s caused the star to puff up to giant proportions — it’s several dozen times wider than the Sun. And that expansion has caused the star’s surface to get cooler, which is why it looks yellow-orange.

    The blue star actually consists of three stars. One is visible through a small telescope, a second comes into focus with a bigger telescope, and the third reveals its presence only to special instruments.

    All three stars are bigger and more massive than the Sun. They’re also hotter, so their surfaces are white with a hint of blue. Seen next to their orangey companion, their combined light looks even bluer than it really is — making Almach one of the most beautiful double stars in the galaxy.


    Script by Damond Benningfield

    Friday, October 21, 2016
    A colorful double star
  • Orionid Meteors

    The Orionid meteor shower should be at its best late tonight. Unfortunately, the Moon rises around midnight, so it will cast its glow in the sky during the shower’s peak. The Moon also will be quite close to Orion, making things even worse.

  • Orionid Meteors

    Halley’s Comet won’t return to the inner solar system for almost half a century. But it makes its presence known at this time of year with a meteor shower. The shower isn’t named for the comet, though, but for the region of the sky in which the meteors appear to “rain” into the atmosphere — the constellation Orion.

    A meteor shower takes place when Earth flies through the path of a comet, which is a big ball of frozen water and gases mixed with bits of rock and dirt. As the comet gets close to the Sun, some of the ices vaporize, releasing some of the solid particles. Over time, these bits of dust spread out along the comet’s path.

    Halley has made a lot of trips around the Sun, so it’s shed a lot of debris, which has spread out all along its orbit. Earth flies through this path every October. As the particles of comet dust hit the atmosphere they vaporize, forming the glowing streaks known as meteors.

    The Orionids are pretty reliable, although not usually spectacular. At their peak, they produce a couple of dozen meteors per hour.

    This year’s shower should be at its best late tonight. Unfortunately, the Moon rises around midnight, so it’ll cast its glow in the sky during the shower’s peak. And the Moon will be quite close to Orion, making things even worse.

    The best chance to see the meteors is to get away from city lights, and hope for some bright ones to puncture the sky — some bright “calling cards” of Halley’s Comet.


    Script by Damond Benningfield


    Thursday, October 20, 2016
    Faint meteors and bright moonlight
  • M31

    M31, the Andromeda galaxy, is visible to the unaided eye as a hazy smudge of light. It stands about half-way up the eastern sky as night falls. At a distance of 2.5 million light-years, it’s the farthest object that is easily visible to the eye alone.

  • Runaway Giant

    A massive star in a nearby galaxy is on the run. It’s moving faster than any other known star — fast enough to escape its home galaxy.

    The star is a member of M31, the Andromeda galaxy. Under dark skies, the galaxy is visible to the unaided eye as a hazy smudge of light. Right now, it’s about half-way up the eastern sky as night falls. At a distance of two-and-a-half million light-years, it’s the farthest object that’s easily visible to the eye alone.

    Astronomers discovered the runaway while looking for red supergiants in M31. These stars are much bigger, heavier, and brighter than the Sun. They’re also nearing the ends of their lives, which is one reason they’re so puffed up.

    One of the supergiants is moving in our direction far faster than any other star in the survey. The astronomers estimated that its overall speed relative to the rest of M31 is about 650,000 miles per hour.

    The star probably was born with a cluster of other massive stars. Gravitational interactions among the stars may have kicked this one out of the cluster. The kick was so powerful that the star may be moving fast enough to escape from M31.

    Or it would escape if it lived long enough. The star is expected to explode as a supernova in the next million years or so — long before it can escape the galaxy. But the blast probably will leave a dead, heavy core. It will continue to race away from M31 — and may eventually escape into intergalactic space.


    Script by Damond Benningfield

    Wednesday, October 19, 2016
    A giant star that’s running away from home
  • Moon and Aldebaran

    The Moon has been playing a game of hide-and-seek all year. Most months it has passed in front of Aldebaran, blocking the bright eye of Taurus from view. It will do so again tonight. The disappearing act will be visible across most of the United States.

  • Moon and Aldebaran

    The Moon has been playing a game of celestial hide-and-seek all year long. Almost every month, it’s passed directly in front of Aldebaran, blocking the bright eye of Taurus the bull from view. And it will do so again tonight. The disappearing act, known as an occultation, will be visible across a wide swath of the United States.

    The Moon’s orbital path is such that the Moon passes close to Aldebaran every month. But that path carries the Moon north and south of Aldebaran’s position in the sky. The path overlaps Aldebaran during cycles that last about four years. The current cycle began in January of last year, and continues through September of 2018. After that, we won’t see another occultation of Aldebaran for another 15 years.

    Tonight’s occultation will be visible to the south and east of a line that runs from about Los Angeles to Minneapolis and on through the middle of Lake Superior.

    The exact timing depends on your location. From Baltimore, for example, the occultation begins when Aldebaran disappears behind the Moon at about 1:38 a.m., and lasts for more than an hour. From Chicago, it starts at 12:38 a.m., and lasts for about 44 minutes. And from San Antonio, it starts a little after midnight and continues for an hour.

    The view is especially beautiful before and after the occultation, as bright Aldebaran snuggles quite close to the Moon — an act that’ll be repeated many times over the next couple of years.


    Script by Damond Benningfield

    Tuesday, October 18, 2016
    Four years of hide-and-seek
  • Two for Mars?

    ExoMars, a joint project of the European and Russian space agencies, appears to have achieved mixed results at Mars. Trace Gas Orbiter (at right in this artist's concept) successfully entered orbit on October 19, and will spend a year refining its orbit before beginning full science operations. It is designed to sniff out traces of methane and other gases that could have a biological origin. Engineers lost contact with the other half of the mission, the Schiaparelli lander (at left, shown shortly after separation from the orbiter), moments before its scheduled landing. The lander is a technology demonstrator for a future Mars rover. If ground controllers can regain contact, it is scheduled to operate for only a few days before its batteries die. [ESA/ATG Medialab]

  • Epsilon Eridani

    One of our closest stellar neighbors is just visible to the unaided eye in the constellation Eridanus, well to the lower right of the Moon. Epsilon Eridani, which is about 10 light-years from Earth, rises around 10:30 p.m. The star has at least one planet, and probably more.

  • More ExoMars

    In four years, the European Space Agency plans to send a rover to Mars. It’ll be the agency’s most ambitious planetary mission yet; the rover will drill into the Martian surface to hunt for signs of life.

    The mission team hopes to get in a rehearsal for the rover’s landing this week. A probe is scheduled to land on Mars on Wednesday. It has limited battery power, so it’ll last for only a couple of days. But it’ll provide experience at landing on Mars, and check out some of the equipment for the rover mission.

    The probe is half of a larger mission called ExoMars. It was launched by a Russian rocket earlier this year.

    The other half of the mission is known as Trace Gas Orbiter. It’ll enter orbit on Wednesday, then spend the next 14 months lowering its altitude before beginning its observations.

    Its mission is to sniff the upper atmosphere for gases that are related to life, especially methane.

    Most of the methane in Earth’s atmosphere comes from living organisms. And traces of methane have been detected in the atmosphere of Mars. That suggests that microscopic organisms could be living below the Martian surface.

    But the methane could also be produced by geologic processes instead of life. The instruments aboard Trace Gas Orbiter are designed to determine which is the case — perhaps telling us whether the future rover is likely to find signs of life below the Martian surface.


    Script by Damond Benningfield

    Monday, October 17, 2016
    A dress rehearsal for a Mars rover
  • ExoMars

    Mars perches low in the south as night falls. It looks like a bright orange star to the left of teapot-shaped Sagittarius. A European spacecraft, ExoMars, is scheduled to arrive at Mars later this week.

  • ExoMars

    A European probe to Mars is scheduled to arrive on Wednesday. One part of the ExoMarsmission, called Schiaparelli, will land on the Red Planet. The other, known as Trace Gas Orbiter, will study the Martian atmosphere from orbit.

    The lander will operate for only a couple of days. Although it’ll make some scientific observations, its main goal is to pave the way for a Mars rover in a couple of years. It will allow European engineers and scientists to gain experience at landing on Mars.

    To help make that landing as precise as possible, navigators here on Earth are getting help from quasars. These cosmic beacons are brilliant disks of hot gas around supermassive black holes in distant galaxies.

    Navigators use more than one tracking station here on Earth to triangulate the craft’s position. But Earth’s atmosphere can alter its radio waves. So the tracking stations also monitor one or more quasars at the same time.

    The radio characteristics of the quasars are well known. Any change in the quasar signal tells engineers what’s happening to radio waves in the atmosphere. That allows them to correct signals from ExoMars. Engineers say that’ll make it possible to pinpoint the craft’s position to within about a half mile — making it easier to hit the bullseye on Mars.

    We’ll have more about ExoMars tomorrow. In the meantime, look for the planet low in the south as night falls. It looks like a bright orange star, to the left of teapot-shaped Sagittarius.


    Script by Damond Benningfield

    Sunday, October 16, 2016
    Lining up an approach to Mars
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