StarDate Online - Your guide to the universe

  • Cor Caroli

    Cor Caroli, the brightest star of Canes Venatici, the hunting dogs, is in the east-northeast at nightfall. It is the first meagerly bright star to the right of the tip of the Big Dipper’s handle.

  • Cor Caroli

    When healthy twins are born, they usually have the same life expectancy. Barring accidents or disease, they should live about the same amount of time.

    When twin stars are born, though, it’s a different story. One of them is likely to expire long before its sibling. And it’s pretty easy for astronomers to tell which one will go first.

    Consider Cor Caroli, the brightest star of Canes Venatici, the hunting dogs. It’s in the east-northeast at nightfall. It’s the first meagerly bright star to the right of the tip of the Big Dipper’s handle.

    Cor Caroli consists of two stars, which probably were born together, from the same cloud of interstellar gas and dust.

    One of the stars is about three times the mass of the Sun, while the other is only half that heavy. And when it comes to a star’s life expectancy, it’s all about the mass. Heavier stars consume the nuclear fuel in the cores at a much faster rate than less-massive stars, so they expire much more quickly.

    The heavier star of Cor Caroli, for example, will live as a “normal” star for about 350 million years. After that, it’ll puff up to giant proportions, shining hundreds of times brighter than it is now. Then it’ll cast its outer layers into space, leaving only its hot but dead core.

    When that happens, its lighter twin will still be going strong. The more leisurely rate of nuclear reactions in its core means that it’ll shine for a couple of billion years after its flashier twin expires.


    Script by Damond Benningfield

    Saturday, March 25, 2017
    Twins with different life expectancies
  • Moving Day

    Venus is losing its identity. After tonight, it will no longer be the “evening star.” Instead, it will be the “morning star,” as it crosses the line between Earth and the Sun. This crossing is known as inferior conjunction, and it happens every 584 days.

  • Moving Day

    Venus is losing its identity. After tonight, it will no longer be the “evening star.” Instead, it’ll be the “morning star,” as it crosses the line between Earth and the Sun.

    This crossing is known as inferior conjunction, and it happens every 584 days — about 19 months. During that interval, the planet goes through a series of phases like the phases of the Moon.

    At conjunction, Venus is “new” — the entire hemisphere that faces Earth is in the planet’s own shadow, so we’re looking at its nightside.

    After conjunction, Venus becomes a thin crescent, which grows fatter as the weeks roll by. It’s during its crescent phase that Venus shines at its brightest. The planet is close to Earth then, so it forms a relatively large target in our sky. That proximity also means that more of the sunlight that Venus reflects into space reaches Earth. The combination makes the planet especially bright.

    After that, Venus gets “fuller,” as sunlight illuminates more of its Earth-facing side. But it also moves farther away, so it doesn’t look as bright.

    Venus is “full” at superior conjunction, when it lines up behind the Sun. After that, Venus begins to wane again as it once again prepares to cross between Earth and the Sun.

    Venus is probably too close to the Sun for most of us to see it this evening. But it could be visible in the east shortly before sunrise tomorrow — and will definitely be putting in a great showing within a few days — as the “morning star.”


    Script by Damond Benningfield

    Friday, March 24, 2017
    Moving day for the “evening star”
  • The Argo

    Argo, the ship of Jason and the Argonauts, sails across the south tonight. It originally was a single constellation, but astronomers broke it into four smaller ones: Carina, the keel; Vela, the sail; Puppis, the poop deck; and Pyxis, the compass.

  • Major Storm

    A storm erupts on the Sun in this August 2012 image from a Sun-watching spacecraft. The storm includes a solar flare (bright white are) and a solar prominence (the loop extending above the Sun's surface). If a major storm was aimed at Earth, it could damage much of our electrical infrastructure, causing massive economic damage. [NASA/GSFC]

  • Storm Impact

    A major hurricane can cause tens of billions of dollars in direct damages. And it can cause tens of billions more in indirect damages — losses to the economy caused by destroyed businesses, fouled roads, power outages, and other problems.

    A major storm on the Sun, however, has the potential to dwarf those losses. A recent study by the American Geophysical Union found that under the right circumstances, a solar storm could trigger economic damages of up to almost 50 billion dollars a day.

    The Sun produces storms all the time — big eruptions of charged particles that race outward at millions of miles per hour. Most of the time, these storms miss Earth. But when they do hit, they can knock out satellites, disrupt communications and air travel, and even knock out power grids. In 1989, an especially big storm knocked out power to Quebec.

    In recent years, there’s been concern that if a monster solar storm hit Earth, it could knock out power across most of the United States. Not only that, but the currents might fry equipment that could take months to replace. That could leave big chunks of the country powerless for weeks or months.

    The recent report looked at the economic impact of such an outage. It found that damages could hit anywhere from a few billion dollars a day, up to 50billion. About half of that loss comes from a ripple effect that impacts vendors, customers, and others — a major impact from a stormy Sun.


    Script by Damond Benningfield

    Thursday, March 23, 2017
    Projecting damages from a big storm
  • Winter Circle

    Spring has already sprung, but a great pattern of stars named for winter still dominates the western evening sky. The Winter Circle includes some of the most prominent stars of all, including Sirius, the brightest star in the night sky.

  • The Next Generation

    The next big space telescope, James Webb, is being prepared for launch next year. And the one after that, which will look like a twin of the venerable Hubble telescope, is being developed.

    Yet even these instruments will leave many questions unanswered. So NASA is already planning the next generation of space telescopes. They’ll be bigger than anything launched before, and provide capabilities far beyond Hubble or Webb.

    A year ago, NASA picked four teams to outline concepts for the next big space telescope. They’ll keep at it for two more years. After that, the National Academy of Sciences will review the ideas and recommend which one to develop.

    One telescope would be like a super-sized version of Hubble. It would use a segmented mirror that could be as tall as a five-story building to look at a wide range of wavelengths. That would allow it to detect signs of life on planets in other star systems and watch the evolution of galaxies and black holes.

    Another concept would also provide details on other planets. It could photograph planets in Earth-like orbits, and monitor their atmospheres for signs of life.

    The other ideas would look only at wavelengths that are invisible to the human eye. That would allow them to study the earliest galaxies, or the disks of superhot gas around black holes.

    All of this will take time, though. Whichever concept NASA eventually picks, the telescope won’t launch until at least the 2030s.


    Script by Damond Benningfield

    Wednesday, March 22, 2017
    Space telescopes: the next generation
  • Milky Way Clouds

    The stars of the Milky Way intertwine with clouds of gas and dust that can span many light-years. Some of them are bright and colorful; others, dark and quiet. The dark clouds are giving birth to new stars. They are dark because their gas is cold.

  • Looking Deep

    Earth and the solar system’s other rocky planets probably grew as smaller blobs of rock and metal slammed together, forming ever larger bodies. As they grew, gravity pulled heavier materials — iron and nickel — toward the middle, forming their cores. Lighter materials floated toward the top, forming the mantle and crust.

    We can’t actually see the cores of these worlds. But a new NASA mission may be able to show us the next-best thing: the core of a possible protoplanet, one of the building blocks of planets.

    Psyche will orbit an asteroid of the same name. The asteroid is a chunk of metal about 150 miles in diameter — the biggest metallic asteroid in the solar system. It could be the surviving core of a protoplanet. The little object’s outer layers could have been blasted away by collisions with other asteroids, leaving only its dense metallic core.

    Observations by ground-based telescopes show that 90 percent of its surface is made of iron. The rest is made of various minerals. A close-up inspection of those minerals could confirm that Psyche is the leftover core of a protoplanet. On the other hand, it could show that the minerals came from impacts with other asteroids, telling us that Psyche never had a mantle or crust.

    Either scenario will reveal more about how the inner planets formed and how they grew, and perhaps give us a hint of what their metallic cores look like.

    We’ll talk about some other future missions of discovery tomorrow.


    Script by Damond Benningfield

    Tuesday, March 21, 2017
    Looking into the hearts of planets
  • Crater

    The constellation Crater, the cup, is visible this month in the southeastern evening sky. Its stars are faint, so you need dark skies to find it. To ancient European cultures, Crater represented the birthplace of storms.

  • Time Machines

    Two new NASA missions will take a look at relics from the birth of the solar system. Lucy (left) will explore six Trojan asteroids, which share the orbit of Jupiter, while Psyche (right) will orbit the metallic asteroid 16 Psyche, which could be the battered core of a would-be planet that never formed. Both missions are scheduled for launch in the next decade. [SWRI/SSL/Peter Rubin]

  • Time Machine

    Two new NASA missions are solar-system time machines. They’ll visit relics from the early solar system, providing a glimpse into the materials and processes that gave birth to the planets.

    Lucy will fly past seven asteroids — big chunks of rock, metal, and ice. One of them is in the asteroid belt, between the orbits of Earth and Mars. But the others share the orbit of Jupiter. Known as Trojans, they’re locked in place ahead of or behind the giant planet by the gravity of Jupiter and the Sun.

    Jupiter itself probably moved around a bit when it was young. It slid much closer to the Sun, then back out again. The Trojans might have formed with Jupiter and followed its migrations. On the other hand, they might have been captured by Jupiter as it moved. Studying them may help explain when and where they formed.

    In addition, the asteroids contain materials from the birth of the solar system. They probably haven’t changed much over the eons, so they preserve a record of conditions when the solar system was young.

    The mission will take advantage of existing technologies. Two of its instruments will be based on those used on New Horizons, which flew past Pluto. And a third will be based on another asteroid mission, Osiris-Rex.

    Lucy will launch in 2021, with arrival at Jupiter’s orbit six years later. By then, the second mission should be well on the way to its destination — the possible core of a would-be planet. More about that tomorrow.


    Script by Damond Benningfield

    Monday, March 20, 2017
    Traveling to the early solar system
  • Vernal Equinox

    Those of us in the United States will wake up to a new season tomorrow. Spring begins at 5:29 a.m. CDT, which is the moment of the vernal equinox. It occurs when the Sun crosses Earth’s equator from south to north.

  • Vernal Equinox

    Those of us in the United States will wake up to a new season tomorrow. Spring begins at 5:29 a.m. Central Daylight Time — the moment of the vernal equinox. It occurs when the Sun crosses Earth’s equator from south to north. It ushers in longer, warmer days here in the northern hemisphere, and shorter, cooler days in the southern hemisphere.

    Over the course of a year, the Sun moves north and south across the sky. That’s only an apparent motion, though. The Sun itself isn’t moving. Instead, that motion is caused by Earth’s tilt on its axis.

    As seen from the Sun, Earth doesn’t stand straight up and down. Instead, it slouches — by about 23 degrees. As Earth moves around the Sun, that causes the north and south poles to nod toward and away from the Sun. In June, the north pole aims toward the Sun. That brings longer days to the northern hemisphere. And in December, it’s the southpole that nods sunward, bringing lessdaylight to northern climes.

    The equinoxes come halfway between these extremes. Neither pole dips sunward, so both hemispheres experience roughly equal amounts of daylight and darkness. In fact, that’s where the name “equinox” comes from — it means “equal nights.”

    The equinoxes are also the only times of year when the Sun rises due east and sets due west. Unless you’re on the equator, it rises north or south of those points for the rest of the year.

    So enjoy the first day of spring — the start of a new season under the Sun.


    Script by Damond Benningfield


    Sunday, March 19, 2017
    Springing into a new season
  • Moon, Antares, Saturn

    The planet Saturn is in good view early tomorrow. It looks like a bright star to the lower left of the Moon at first light. The bright star Antares stands about the same distance to the lower right of the Moon.

  • Moon, Antares, Saturn

    Many of the gods and goddesses of the ancient world weren’t very nice. They lied, they cheated, they stole, and they even killed. And many of these actions were aimed at their own families.

    Consider the Greek god Kronos, who in Rome was known as Saturn. He was the father of an entire race of gods — the gods of Olympus. But to protect himself from his offspring, he swallowed them whole as soon as they were born — except for one.

    According to the story, Kronos was the ruler of the gods known as the Titans. His parents had foretold that one of his children would defeat him. So each time his wife, Rhea, gave birth to a new baby, Kronos swallowed it.

    Rhea wasn’t happy with that arrangement, though, so she tricked him. She hid her son Zeus in a cave. And — perhaps showing why you shouldn’t gobble your food — she gave Kronos a stone wrapped in a blanket.

    When Zeus grew up, he drugged his father, forcing him to regurgitate his now-grown-up children. They ganged up and waged war against the Titans. They won, and imprisoned the Titans in a pit at the edge of the world. With Zeus as their leader, these brothers and sisters then ruled the world from Olympus.

    The planet Saturn was named in honor of the god. And it’s in good view early tomorrow. It looks like a bright star to the lower left of the Moon at first light. And the bright star Antares is about the same distance to the lower right of the Moon.

    Tomorrow: springtime.

    Script by Damond Benningfield

    Saturday, March 18, 2017
    A planet with a nasty back story
  • Venus and Mercury

    The Sun’s two closest planets are staging a switcheroo. Mercury is climbing higher into the evening sky, while Venus is dropping out of the sky. Venus is the brilliant “evening star,” with much fainter Mercury close to its lower left tonight.

  • Venus and Mercury

    The Sun’s two closest planets are staging a switcheroo this month. Mercury is climbing higher into the evening sky, while Venus is dropping out of the evening sky. And if you look at just the right time, you can see them standing almost side by side the next few evenings.

    Mercury is the closest planet to the Sun. Since Earth is the third planet out, Mercury has a limited range of motion across our sky, so the little planet rarely climbs into really good view. At best, it’s visible for a little while before sunrise or after sunset, quite low above the horizon.

    Mercury passed behind the Sun earlier this month. Now, it’s moving away from the Sun, so it’s climbing into the evening sky. In fact, this is its best evening appearance for the entire year. It’ll climb higher over the next few nights, making it easier to see.

    Venus is the second planet from the Sun. It’s getting ready to cross between Earth and Sun, so it’s dropping lower in the sky each evening — ready to move into the morning sky in about a week.

    For now, though, look for Venus quite low in the west beginning about 15 minutes after sunset. It’s the “evening star,” so if you have a clear horizon, you can’t miss it. Tonight, much fainter Mercury is close to its lower left, but you probably need binoculars to pluck it from the twilight glow. The two worlds will stand side by side tomorrow night, with Mercury climbing away from Venus — and into better view — on succeeding nights.


    Script by Damond Benningfield

    Friday, March 17, 2017
    A close pass in the evening sky
  • Giant Cannibal

    Betelgeuse, the bright orange shoulder of Orion, is high in the south-southwest as night falls, above the hunter’s three-star belt. Recent research says that when Betelgeuse was younger, it might have swallowed a companion star as massive as the Sun.

  • Living Dangerously

    A white dwarf star perches precariously close to a black hole in this artist's concept of 47 Tucanae X9, a binary system in the globular star cluster 47 Tucana. The white dwarf, which is the dead core of a star that was once like the Sun, is just 600,000 miles (1 million km) from the black hole, according to a team of astronomers that analyzed observations from Chandra X-Ray Observatory, a space telescope (a Chandra image is shown in the inset). It is the closest companion to a black hole yet discovered. The black hole's powerful gravity is pulling oxygen-rich gas from the white dwarf's surface. This material forms a disk around the black hole. Material in the disk eventually disappears into the black hole. 47 Tucana is about 15,000 light-years from Earth, in the southern constellation Tucana, the toucan. [NASA/CXC/M. Weiss; inset: NASA/CXC/University of Alberta/A. Bahramian et al.]

  • Giant Cannibal

    Given the chance, a star can easily become a cannibal — a bigger star can swallow a smaller one. The star that gets eaten can leave its mark on the surviving star, though. Among other things, it can trigger an eruption or change the way the star rotates.

    An example of that just may be found in Betelgeuse, the bright orange shoulder of Orion. It’s high in the south-southwest as night falls, above the hunter’s three-star belt.

    When Betelgeuse was young, it was probably a few dozen times the diameter of the Sun. As it aged, though, changes in its core caused its outer layers to puff outward. Today, it’s many hundreds of times the Sun’s diameter.

    And as Betelgeuse expanded, it just might have swallowed a companion star. That’s the conclusion reached by University of Texas astronomer Craig Wheeler after a team of his students used a computer model to study how Betelgeuse spins on its axis.

    Wheeler says its rotation rate is unusually fast for a star of its size. The computer model shows that the star would spin that fast if it swallowed a Sun-sized companion. As the star spiraled in, it transferred its orbital motion to Betelgeuse’s outer layers, making the star spin faster.

    A shell of gas surrounds Betelgeuse. It could have been expelled from the star when it swallowed the companion. Judging from the size and motion of the shell, that would have happened about a hundred thousand years ago — when Betelgeuse might have become a cannibal.


    Script by Damond Benningfield

    Thursday, March 16, 2017
    A giant star becomes a cannibal
  • Quasars

    Amateur telescopes reveal amazing sights. Perhaps the most amazing looks like an average star. It’s a maelstrom of gas around a massive black hole 2.5 billion light-years away. Known as 3C 273, it’s in the east at nightfall, above the brilliant planet Jupiter.

  • Quasars

    Modern amateur telescopes reveal some amazing sights, from the colorful death throes of stars that are thousands of light-years away, to spiral galaxies millions of light-years away. Perhaps the most amazing sight of all, though, looks like an average star. But it’s really a maelstrom of gas around a supermassive black hole. It’s two and a half billion light-years from Earth, which means we see it as it looked two and a half billion years ago.

    3C 273 is a quasar — one of the most powerful objects in the universe. It’s powered by a black hole that’s hundreds of millions of times as massive as the Sun. The black hole’s gravity pulls in gas, dust, and stars from the galaxy around it.

    This material swirls around the black hole, forming a disk that’s about as wide as our solar system. Friction heats the material to millions of degrees, so it shines brighter than an entire galaxy of stars.

    Magnetic fields direct some of the superhot gas in the disk into jets that shoot into space. The jets produce enormous amounts of radio waves. One of the jets aims at Earth, so we get a powerful blast of energy from it.

    Astronomers have cataloged a couple of thousand quasars. Some are even more energetic than 3C 273. But they’re also farther away, so they don’t look as bright. That leaves 3C 273 as the most-distant object visible through most amateur telescopes. Right now, it’s in the east a couple of hours after night falls, well above the bright planet Jupiter.


    Script by Damond Benningfield


    Wednesday, March 15, 2017
    Looking deep into the universe
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