StarDate

StarDate Online - Your guide to the universe

  • Moon and Mercury

    As twilight begins to paint the dawn sky tomorrow, a couple of planets appear near the crescent Moon. Saturn stands to the upper right of the Moon, with little Mercury below the Moon. Mercury is best seen from southern latitudes.

  • Moon and Mercury

    As twilight begins to paint the dawn sky tomorrow, a couple of planets appear near the crescent Moon. One of them is easily visible from the entire country. The other, though, is best seen from southern latitudes — south of about Oklahoma City or Raleigh, North Carolina.

    The easy target is Saturn, the second-largest planet in the solar system. It looks like a golden star to the upper right of the Moon at first light. And the difficult target is Mercury, the smallest planet. As the dawn brightens, it stands below the Moon. It looks like a fairly bright star, but it’s quite low in the sky, so you need a clear horizon to spot it.

    Although Mercury is little, it’s also quite dense — the planetary equivalent of a bowling ball. More than half of its volume consists of a core that’s made of iron and nickel.

    There are several possible reasons for that. One is that the region where Mercury was born was so hot that most of the lightweight materials near the Sun vaporized and were blown farther into space by the Sun’s radiation. That left mainly the heavier materials to make up the little planet.

    Another is that Mercury had more of the lightweight materials when it was born, but they there were blasted into space by a collision with another planet-sized body. That left mainly the dense, heavy core.

    Whatever the reason, Mercury is a heavy little bowling ball of a planet rolling around the Sun.

    Tomorrow: the influence of a “shocking” star.

     

    Script by Damond Benningfield

    StarDate: 
    Tuesday, January 24, 2017
    Teaser: 
    A bowling-ball planet
  • Moon and Saturn

    Saturn is part of a beautiful pairing in the pre-dawn sky tomorrow. The giant planet looks like a fairly bright golden star, quite close to the lower right of the crescent Moon. A telescope will reveal Saturn’s rings.

  • Moon and Saturn

    Every year or two, it seems, there’s a new explanation for the rings of Saturn — how and when they formed. Some researchers have said they formed at about the same time as the planet itself, perhaps from the shattered fragments of a large moon. Others have said they formed much more recently, from the fragments of two moons that rammed together.

    And late last year, another group came up with yet another idea: the rings formed about four billion years ago, from a Pluto-sized object that wandered too close to Saturn and was partially pulled apart by Saturn’s gravity.

    Saturn’s rings are made mainly of ice, with smaller amounts of rock and dust. And that’s the key to the new idea.

    Researchers in Japan simulated encounters between Saturn and objects like Pluto, which should have been plentiful in the early solar system. Their models showed that if one of these objects passed close to Saturn, the planet’s gravity could have sheared off the object’s outer layers, which consisted mainly of ice. Some of this material could then have been captured into orbit around Saturn — enough to account for its rings.

    And Saturn is part of a beautiful pairing in the pre-dawn sky tomorrow. The giant planet looks like a fairly bright golden star, quite close to the lower right of the crescent Moon. A telescope will reveal Saturn’s rings — which are beautiful no matter how they formed.

    We’ll talk about the Moon and another planet tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Monday, January 23, 2017
    Teaser: 
    A new idea about the rings of Saturn
  • Moon, Antares, Saturn

    The crescent Moon will slide past several bright companions over the next few mornings. Tomorrow, the bright orange star Antares is to the lower right of the Moon at first light, with the golden planet Saturn to the lower left of the Moon.

  • Moon, Antares, Saturn

    Early risers, take note: The crescent Moon will slide down past several bright companions over the next few mornings, creating some beautiful configurations in the pre-dawn sky.

    First up are the star Antares and the planet Saturn. Bright orange Antares stands to the lower right of the Moon at first light, with golden Saturn about the same distance to the lower left of the Moon.

    Antares and Saturn are among the few objects in the night sky to show any color. Antares looks orange because of its surface temperature — it’s thousands of degrees cooler than the surface of the Sun. Saturn, on the other hand, looks yellow because of the composition of its upper atmosphere.

    The giant planet is a big ball of hydrogen and helium gas, with a tiny mixture of other chemical elements. Those elements combine to form layers of clouds at the top of the atmosphere.

    The clouds in the top layer are made of ammonia. Those in the layers below probably are made of water, ammonia, and a compound that includes ammonia and sulfur.

    These compounds are all white. But above Saturn’s visible cloudtops, several compounds react with sunlight to form hydrocarbons, which have an orange or red color. Tiny amounts of them fall into the ammonia clouds, adding a bit of color. When we see Saturn in the night sky, the colors blend together to give the giant planet a subtle golden hue — a rare bit of color in the starry night sky.

    More about Saturn and the Moon tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Sunday, January 22, 2017
    Teaser: 
    Subtle color for a giant planet
  • Leading the Dog

    Two “dog stars” hunker low in the east and southeast as night falls at this time of year. From most of the U.S. one of them, Procyon, rises a bit before the Dog Star Sirius, the brightest star in the night sky. The name Procyon means “before the dog.”

  • Leading the Dog

    Two “dog stars” hunker low in the east and southeast as night falls about now, and scamper higher across the sky later on. One of them rises a bit earlier than the other — a fact reflected in its name: Procyon means “before the dog.”

    Procyon is the brightest star of Canis Minor, the little dog. It rises a few minutes earlier than Sirius, the brightest star in all the night sky. Sirius is also the leading light of Canis Major, the big dog, so it’s known as the Dog Star.

    Because of their relative locations in the sky, Procyon always rises before Sirius — but only from north of roughly 30 degrees north latitude. Below that line, Sirius rises first.

    Although Procyon isn’t as bright as Sirius, it’s still one of the most prominent stars in the night sky. In fact, the two stars look so bright for the same reasons — they are fairly bright, but more important, they’re both close neighbors.

    Sirius is about 26 times brighter than the Sun, but it’s also less than nine light-years away — closer than only a few other star systems. Procyon is only about a third as bright as Sirius, and it’s about three light-years farther, so it looks a good bit fainter as it leads the Dog Star across the night sky.

    The two stars are quite low as the sky gets good and dark tonight. Procyon stands due east, with Sirius well to its right, posing a little lower in the sky as seen from most of the United States.

    Tomorrow: subtle color for a big planet.

     

    Script by Damond Benningfield

    StarDate: 
    Saturday, January 21, 2017
    Teaser: 
    One dog leads another across the sky
  • More Fornax

    The constellation Fornax, which is low in the south at nightfall, has only one modestly bright star, Alpha Fornacis. Binoculars show that it consists of two stars. One is bigger and heavier than the Sun, while the other is smaller than the Sun.

  • More Fornax

    There’s no fountain of youth to make people look younger. But there is one for stars. It’s a process that sounds like a story from a 1950s B movie — “stealing” life from another star.

    A good example of a rejuvenated star is in the constellation Fornax, which is low in the south as night falls. It has only one modestly bright star, Alpha Fornacis, which is 46 light-years away.

    To the eye alone, it’s not much to look at. Binoculars, though, reveal that it consists of two stars. One of them is bigger and heavier than the Sun. It’s nearing the end of its life, even though it’s almost two billion years younger than the Sun.

    The other star of Alpha Fornacis is smaller than the Sun, and its surface is cooler than the Sun’s, so it glows orange. Yet it should be even redder than it is. And that’s where the story of rejuvenation comes in.

    The star has been identified as a blue straggler. That means its color shifted to slightly bluer wavelengths as the star aged. It might have done so by merging with another star, which would rev up its nuclear reactions, making it hotter and bluer. On the other hand, it might have changed color by simply stealing gas from a third star in the system.

    And there is some evidence of a third member of Alpha Fornacis — the corpse of a once-normal star. If it’s there, it may be about half as massive as the Sun, and quite close to the blue straggler — a dead star that gave part of its life to a stellar companion.

     

    Script by Damond Benningfield

     

    StarDate: 
    Friday, January 20, 2017
    Teaser: 
    Drinking from the fountain of youth
  • Giant Storm

    A sunspot forms a dark blotch on the Sun in this recent image from ALMA, a set of telescopes in Chile that look at the universe in millimeter and submillimeter wavelengths, a portion of the radio spectrum. Sunspots are relatively cool magnetic storms on the Sun's surface. The number of spots waxes and wanes on a roughly 11-year cycle. The Sun is currently on the downward slope of one such cycle, so few sunspots have been observed in recent years. This spot is roughly twice the diameter of Earth. [ALMA (ESO/NAOJ/NRAO)]

  • Fornax

    Fornax, the furnace, is quite low in the south as night falls right now. Created in the 17th century, it originally was called Fornax Chemica, after a small heater that was used for chemistry experiments. The name was shortened a few decades later.

  • Fornax

    Almost a century ago, astronomers partitioned the celestial sphere into 88 constellations. Most of them — the famous ones — date from ancient times. But 14 of them — none of which is famous — were created by a single man, in the 18th century.

    Nicolas Louis de la Caille was a French astronomer. In 1751, he set up an observatory at the Cape of Good Hope in South Africa to study the stars of the southern hemisphere. Over the following year, he cataloged about 10,000 stars. And later, he used those stars to draw new constellations in regions of the sky that weren’t visible from most of Europe.

    He called one of them Mons Mensa — table mountain. It honored a feature near la Caille’s observatory. He named all the others for tools that had scientific uses, such as the telescope and microscope, or artistic uses, such as the painter’s easel.

    One of those constellations is Fornax, the furnace, which is quite low in the south as night falls right now.

    It was originally called Fornax Chemica, after a small heater that was used for chemistry experiments. Another astronomer shortened the name a few decades later.

    Fornax isn’t much to look at — at least not with the eye alone. It contains only one modestly bright star, Alpha Fornacis, which we’ll talk about tomorrow. But a telescope reveals many treasures within its borders, including some beautiful individual galaxies, plus a giant cluster of galaxies — fiery visions in the celestial furnace.

     

    Script by Damond Benningfield

    StarDate: 
    Thursday, January 19, 2017
    Teaser: 
    Firing up a celestial furnace
  • Morning Mercury

    Mercury, the solar system’s smallest planet, will be at its greatest distance from the Sun in the morning sky tomorrow. It looks like a fairly bright star quite low in the southeast as dawn brightens, to the lower left of Saturn, another planet.

  • Fast Bursts

    When astronomers find a new type of object that goes “boom,” it takes a while to explain it. They have to figure out how far away the objects are, which reveals how bright they are. And they have to see them at different wavelengths to understand what they’re doing.

    They’re just starting that process for a class of objects known as fast radio bursts — blasts of radio waves that last no more than a few thousandths of a second. The first was discovered in 2007, and a few dozen others have been seen since then.

    Theorists have proposed several explanations for the bursts — from mergers between stellar corpses, to flares on the surfaces of highly magnetizedcorpses.

    The effort to understand them has been stymied because astronomers hadn’t seen any of the bursts at other wavelengths. But that changed with a burst that was discovered in November of 2013.

    A space telescope was looking at the same region of sky where the radio burst was discovered. An analysis, reported late last year, showed that the burst was accompanied by a blast of gamma rays, which are produced by some of the most violent events in the universe.

    That means that this particular burst took place far outside our home galaxy, so it had to be extremely energetic. That eliminates some possible explanations for the burst. But astronomers say that different bursts could have different causes. So it’ll take a while to fully understand the diverse nature of fast radio bursts.

     

    Script by Damond Benningfield

     

    StarDate: 
    Wednesday, January 18, 2017
    Teaser: 
    Explaining a new kind of outburst
  • Orion Nebula

    The Orion Nebula is a fuzzy patch of light just below the three bright stars that represents Orion’s Belt. The nebula is a vast cloud of gas and dust that has given birth to thousands of stars over the last few million years.

  • Super Supernovae II

    A supernova that was discovered a couple of years ago has astronomers doing a lot of head scratching. The explosion appears to be a couple of hundred times brighter than a typical supernova. But none of the models of how stars explode can fully explain why the blast was so bright.

    Supernova 15LH is thought to be the violent death of a massive star. Such a star dies when it can no longer produce energy in its core. The core collapses, and the surrounding layers are blasted into space.

    It’s not easy to explain a blast as powerful as 15LH, though — but that hasn’t stopped the theorists from trying.

    One team, for example, says that the energy could be coming from the interaction between the supernova blast wave and a shell of gas and dust around the star. The material would have been expelled from the star long before the explosion, and was moving away from the star.

    Other groups have come up with other ideas. One says that the supernova was powered by a magnetar — the star’s collapsed core. The super-dense, highly magnetized core would be spinning about a thousand times per second, pumping energy into the material around the core with each turn.

    And yet another idea says that 15LH wasn’t a supernova at all. Instead, it was the death throes of a star that was ripped apart by a supermassive black hole.

    With all these competing ideas, it’s likely to take a while to explain Supernova 15LH.

    We’ll talk about another stellar blast tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Tuesday, January 17, 2017
    Teaser: 
    Explaining a brilliant explosion
  • Last Walk

    Eugene Cernan, the last astronaut to walk on the Moon, died on January 16, at age 82. Cernan, shown here with the Moon's Taurus mountains in the background, commanded the Apollo 17 mission, which landed on the Moon in December 1972. Cernan and crewmate Harrison Schmitt, a geologist, spent three days in the Taurus-Littrow Valley, and conducted three long moonwalks. They also used a lunar rover (at right) to cover about 22 miles during their explorations. Cernan also piloted the Gemini 9 mission, during which he conducted a spacewalk that left his visor fogged and his heart rate at dangerous levels. He also served as lunar module pilot for Apollo 10, which was a dress rehearsal for the first landing mission, Apollo 11. [NASA]

  • Aries

    One of the dimmest but best-known constellations of the zodiac is in fine view right now. Aries, the ram, stands high in the sky at nightfall, and drops down the western sky during the evening.

  • Super Supernovae

    Every supernova is a brilliant beacon — a stellar explosion that can outshine an entire galaxy. But in recent years, astronomers have logged a few dozen supernovae that take “brilliant” to extremes — they shine anywhere from about 10 to hundreds of times brighter than a typical supernova. And theorists are still trying to understand why.

    The first examples of “superluminous” supernovae were discovered more than a decade ago by Robert Quimby, a graduate student at the University of Texas at Austin. He was looking for supernovae across large patches of the sky when he discovered a couple of exceptionally bright examples. Since then, other astronomers have joined the search, leading to many new discoveries.

    These super-bright explosions appear to come in two varieties. One contains a lot of hydrogen — the element that makes up the bulk of most stars. The other type shows no hydrogen.

    The hydrogen-rich variety may involve a shell or bubble of hydrogen gas around the star that was expelled from the star before it exploded. If the bubble has expanded to just the right size, then the collision with the debris from the supernova could make it extremely hot. At such high temperatures, it would radiate enormous amounts of light — making it a superluminous supernova.

    The hydrogen-poor variety is a bit more mysterious. Theorists have proposed several explanations — from the magnetic cores of dead stars to stellar encounters with black holes. More about that tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Monday, January 16, 2017
    Teaser: 
    Making a super-duper supernova
  • Bright Stars

    From southern latitudes of the U.S., the two brightest stars in the night sky line up in the south tonight. The brighter star is Sirius, which is high in the south in late evening. The other is Canopus, which is well below Sirius and a little to the right.

  • Scary Asteroids

    Astronomers compile catalogs of all kinds of objects: variable stars, black holes, binary stars, and many others. One of their most important catalogs keeps getting bigger — it passed 15,000 entries a couple of months ago.

    The catalog lists N-E-Os — Near-Earth Objects. These asteroids and comets follow paths that approach or cross Earth’s orbit around the Sun. Such objects have the potential to hit our planet, so it’s important to find and track them. With enough warning, it might be possible to deflect an object that’s on a collision course.

    Most of that work is done by automated searches in Arizona and Hawaii, which scan the sky most clear nights of the year. A new search is scheduled to begin next year in Europe, with another, using a giant new telescope in Chile, to follow soon after.

    Scientists estimate that they’ve found more than 90 percent of NEOs that are at least a kilometer in diameter. Such giant space rocks could cause widespread damage if they hit us. In fact, just such an impact is thought to be responsible for the demise of the dinosaurs.

    In recent years, searchers have been looking for even smaller objects. Such objects wouldn’t be big enough to trigger global problems if they hit, but they could destroy a city. But smaller objects are also fainter, so it takes much more effort to find them.

    So far, the searches haven’t discovered any problems — none of the 15,000 cataloged NEOs is on a threatening course.

     

    Script by Damond Benningfield

    StarDate: 
    Sunday, January 15, 2017
    Teaser: 
    Cataloging scary space rocks
  • Moon and Regulus

    Look for Regulus, the heart of Leo, quite near the Moon as they climb into view in mid evening, and a little farther to the right of the Moon at first light tomorrow.

  • Moon and Regulus

    Regulus is one of the brightest stars in the night sky, so people have been looking at it since the beginning. And astronomers have been studying it since the invention of the telescope. And it’s quite close — less than 80 light-years away. So you might think that we’ve known all the important details about it for a long time.

    You’d be wrong. Astronomers continue to learn about the system. Less than a decade ago, for example, they found that the bright star we see as Regulus has a close companion. That star tells us a lot about the bright star’s history.

    The companion is small, faint, and quite close to the bright star, which is known as Regulus A. So it’s impossible to see the companion directly. Instead, astronomers detected it by measuring the system’s individual wavelengths of light. They reveal a slight shift in the star’s motion caused by the gravitational tug of the companion.

    The companion is a white dwarf — the tiny corpse of a once-normal star. That star had to be born with more mass than Regulus A, so it aged faster. It puffed up, then dumped much of its outer layers of gas onto Regulus A. That made Regulus A bigger and hotter, and it made the star spin much faster.

    That discovery shows that there’s still a lot to learn about the stars — even the ones we think we know well.

    Look for Regulus just above the Moon as they climb into view in mid-evening, and a little farther to the right of the Moon at first light tomorrow.

     

    Script by Damond Benningfield

    StarDate: 
    Saturday, January 14, 2017
    Teaser: 
    Learning about a familiar star
  • Auriga

    Auriga, the charioteer, rides high across winter’s evening skies. To find it, look for its brightest star, Capella, which stands high overhead around 10 or 11 p.m. Capella is one of the brightest stars in the night sky, and shines pale yellow.

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