StarDate Online - Your guide to the universe

  • Coma Berenices

    The constellation Coma Berenices, which represents the hair of a legendary queen, is well up in the east by mid-evening. It is about half way between the bright stars Arcturus and Regulus, which highlight the eastern sky.

  • PicSat

    A French satellite that’s small enough to hold in your hand is looking for a big planet to make a move. The planet is expected to pass in front of its star in the next year or so, causing the star’s light to fade a bit. When the satellite sees that happen, it’ll notify a large telescope on the ground, which will study the event in detail.

    Picsat consists of three cubes stacked together. Combined, they’re a foot tall, and weigh about eight pounds. One of the cubes holds a two-inch telescope.

    The telescope can be small because its target, Beta Pictoris, is bigger and brighter than the Sun. And it’s just 63 light-years away, so it’s easily visible to the unaided eye.

    Beta Pic is only about 25 million years old. And it’s surrounded by material for making planets — a wide disk of gas and dust. The disk already has given birth to at least one planet, which is much heavier than Jupiter, the giant of our own solar system.

    Its orbit is aligned so that the planet is expected to pass in front of the star once every 18 years. If astronomers get a good look at such a passage, they can determine the planet’s size, telling them about its composition, and measure its atmosphere as starlight filters through it.

    So Picsat will keep a constant eye on Beta Pic. It’ll also measure smaller drops in the star’s light as comets and asteroids pass in front of it. That will tell us more about how planetary systems form — big science from a small satellite.


    Script by Damond Benningfield

    Wednesday, March 21, 2018
    A tiny satellite for a big planet
  • Winter Circle

    Spring arrives in the northern hemisphere today, but the most prominent stars of winter remain in good view. They form a big loop known as the Winter Circle, which is in the southwestern quadrant of the sky this evening.

  • New Hunter

    NASA's next planet-hunting spacecraft is being prepared for launch in the next few weeks. TESS (Transiting Exoplanet Survey Satellite) will look for planets to cross in front of their stars, causing a small, brief dip in the star's light. It is the same technique used by the highly successful Kepler space telescope, which has discovered thousands of confirmed or likely planets. TESS will monitor the light from several hundred thousand bright, nearby stars. That will make it easier for astronomers to follow up on any discoveries with detailed observations by ground-based telescopes. [NASA/GSFC]

  • Planet Hunter

    The next planet hunter is getting ready for launch. It’ll sweep the skies within a few hundred light-years of Earth. Astronomers say its discoveries could include a few hundred worlds that are similar to Earth — about the same size, and at the right distance from their stars to support life.

    TESS — the Transiting Exoplanet Survey Satellite — will use the same technique used by Kepler, a small space telescope that’s discovered thousands of confirmed or possible planets. It will monitor the light of several hundred thousand stars. If a planet passes in front of a star, the star will get a bit fainter for a while. Just how faint will reveal the size of the planet.

    While Kepler concentrated on a single small patch of sky for much of its mission, TESS will scan almost the entire sky. Its cameras will monitor bright stars that are fairly close. That will make it easier to study any planets it discovers using other telescopes in space and on the ground. The follow-up observations can provide a thorough dossier on a planet, including whether it has an atmosphere, and the atmosphere’s composition.

    TESS’s cameras will scan 26 patches of the sky for about a month at a time. They’ll begin with the southern hemisphere, then move to the north a year later.

    If TESS works as planned, it could add hundreds or thousands of worlds to the list of known exoplanets — including some that could be among our closest neighbors in the entire galaxy.

    Script by Damond Benningfield

    Tuesday, March 20, 2018
    Hunting for nearby planets
  • Vernal Equinox

    The Sun will cross the celestial equator tomorrow. The crossing marks the vernal equinox, which is the beginning of spring in the northern hemisphere. It also marks the starting point for measuring the length of the year.

  • Vernal Equinox

    The Sun will cross a special point in the sky tomorrow. The crossing marks the beginning of spring in the northern hemisphere — the vernal equinox. It also marks the starting point for measuring the length of the year. And for much of human history, it also marked the start of the year — the equinox was New Year’s Day.

    The equinox probably gained its significance because spring is a time of birth and renewal. The days are getting longer, flowers are beginning to bloom, and other signs of life are popping up. So it made sense that the calendar year would begin then, too. In fact, Britain and its American colonies didn’t switch the start of the year to January 1st until 1752.

    Astronomically, the equinox is one of two points where the Sun’s path intersects the celestial equator — the projection of Earth’s equator on the sky. The other is the autumnal equinox, in September. Astronomers selected the vernal equinox as the starting point for their system of sky coordinates — the equivalent of latitude and longitude. At the equinox, the Sun stands at point zero-zero.

    The definition of a “year” is the interval between the Sun’s passages across the equinox point. On average, that’s 365 days, 5 hours, 48 minutes, and 46 seconds. Those extra hours and minutes are why we have leap years — to keep the calendar in sync with the seasons.

    And one of those seasons begins tomorrow at 11:15 a.m. Central Time — the time of the vernal equinox.

    Script by Damond Benningfield

    Monday, March 19, 2018
    A special point for the Sun
  • Moon and Companions

    The vanishingly thin crescent Moon has a couple of companions after sunset this evening, the planets Venus and Mercury. Venus is the “evening star,” to the right of the Moon. Much-fainter Mercury is about the same distance to the upper right of Venus.

  • Moon and Companions

    The vanishingly thin crescent Moon has a couple of companions after sunset this evening — the planets Venus and Mercury. Venus is the brilliant “evening star,” to the right of the Moon. Much-fainter Mercury is about the same distance to the upper right of Venus.

    Mercury is tough to see in the early twilight, but its proximity to the brighter lights can help you pick it out.

    In fact, this is an especially good time to look for the little world. It’s the closest planet to the Sun, so most of the time it’s hidden in the Sun’s glare. A few times a year, it climbs into view either just before sunrise or just after sunset. For many of those apparitions, though, it stays quite low in the sky, so it’s tough to see even though it can get pretty bright.

    Mercury was brightest for this evening appearance a few weeks ago, when it was still quite close to the Sun. It’s been getting fainter as it’s pulled away from the Sun. But because it appears farther from the Sun, it stays in view later, when the twilight isn’t as bright.

    Like the Moon, Mercury goes through a cycle of phases. It just passed between Earth and the Sun a few weeks ago, so right now it’s a thick crescent. As it loops back around behind the Sun, sunlight will illuminate more and more of the side that faces Earth. At the same time, though, Mercury will be moving farther from us, so it’ll get fainter. It won’t shine this brightly again until May — this time in the morning sky.

    Script by Damond Benningfield

    Sunday, March 18, 2018
    An elusive companion for the Moon
  • Owl Nebula

    The Owl Nebula stares out from the Big Dipper. It is a set of concentric bubbles of gas blown into space by a dying star. It’s round, and seen through a telescope or in photographs, it has two dark patches that look like an owl’s eyes.

  • It's a Hoot

    The Owl Nebula stares at us from near the Big Dipper, in Ursa Major, the great bear. It is the death mask of a star. Nuclear reactions have ceased in the star's core, and the star's outer layers are blowing into space. The layers of gas are energized by ultraviolet radiation from the dying core, which will form a white dwarf. The contours of the surrounding gas show two relatively empty regions, which form the owl's dark "eyes." The glowing gas will continue to expand into space, eventually growing so thin that it will no longer shine. Estimates of the distance to the nebula, which is also known as Messier 97, vary widely, from about 1,000 to 3,000 light-years. [Calar Alto Observatory/Vicent Peris/José Luis Lamadrid/Jack Harvey/Steve Mazlin/Juan Fabregat/Gilles Bergond]

  • Owl Nebula

    An owl stares at us from the Big Dipper — the death mask of a star. It consists of several concentric “bubbles” of gas blown into space by the dying star. It’s nice and round, and seen through a large telescope or in photographs, it has two dark patches that look like the eyes of an owl.

    Astronomers have been keeping an eye on the Owl Nebula since it was discovered more than two centuries ago. Yet quite a bit about the nebula is still poorly understood. That includes its distance. Estimates published in the last decade and a half range from about a thousand light-years to about three thousand. Without knowing its distance, you can’t pin down its size, either. And without knowing its size, you can’t tell just when the nebula began to form.

    One of the most extensive studies of the Owl says it began forming about 8,000 years ago as seen from Earth.

    Because of changes in the nuclear reactions in the star’s core, it had puffed up to gigantic proportions. As those reactions began to shut down, gas at the surface flowed out into space, forming a faint “halo.” Later, much moregas flowed outward, forming the nebula’s outer shell. And later still, a faster wind began blowing, forming the inner shell. A cavity inside that shell contains less material, so it forms the eyes — the visage of a celestial owl.

    And the Owl Nebula is near the top right corner of the Big Dipper’s bowl as darkness falls right now — the beautiful death mask of a star.

    Script by Damond Benningfield

    Saturday, March 17, 2018
    Sculpting a celestial death mask
  • New Moon

    The Moon will be “new” early tomorrow as it crosses the line between Earth and the Sun. It is lost from sight in the Sun’s glare, but should return to view on Sunday, as a thin crescent quite low in the west at sunset.

  • The Future

    The future of the universe looks dark. The stars will fade away, matter may disintegrate, and even black holes may vanish. That will leave a cold, dark void containing only the most basic bits of matter and energy.

    This future scenario depends on the nature of dark energy — a mysterious something that’s causing the universe to expand faster as it ages. Current theory says that dark energy will become more dominant as the eons roll by, causing the universe to expand ever faster.

    As space is stretched, clusters of galaxies will be so far apart that they’ll be isolated from each other. So if the inhabitants of a cluster look toward intergalactic space, they won’t see any galaxies other than the ones that are close by.

    And as time passes, there won’t be much to see in their own cluster, either. The last stars will form tens of trillions of years from now. The smallest and faintest of them will last for perhaps 10 trillion years more. After that, the galaxies will be populated only by stellar corpses — white dwarfs, neutron stars, and black holes — and by the failed stars known as brown dwarfs.

    One of the basic building blocks of atoms — the proton — eventually may decay. If so, then all the atoms in the universe will fall apart.

    And even black holes probably won’t last forever. They should evaporate, creating torrents of energy that will quickly fade.

    After that, only cold and darkness — a dead universe that may expand forever.


    Script by Damond Benningfield

    Friday, March 16, 2018
    Outlining a cold, dark future
  • Arcturus

    One of spring’s most prominent stars is Arcturus, in the constellation Bootes, the herdsman. This yellow-orange star rises in the middle of the evening and soars high across the sky during the night.

  • Before the Big Bang

    Scientists pretty much agree that our universe — everything that we can see and touch — evolved from a single moment of creation, known as the Big Bang. It happened 13.8 billion years ago, and it created not just matter and energy, but space and time as well.

    But there’s absolutely no agreement about what came before the Big Bang. Some say that there was nothing at all. It’s an idea supported by Stephen Hawking, who has said that the universe wasn’t created, it just is.

    Others, though, have developed models in which there was something before the Big Bang. One of those says the universe began when a previous universe ended in a “big crunch.” Everything in that universe smashed together into a single point of almost infinite temperature and density. That point then rebounded as the Big Bang.

    Another idea says that the universe had existed as a single point for a very long time — perhaps an infinitely long time. But 13.8 billion years ago, something caused it to begin expanding, creating the present universe.

    And yet another idea says that our universe is the offspring of another universe — a parent that could have given birth to an infinite number of other universes. That raises the possibility that ouruniverse alsocould be a parent.

    There aren’t many ways to test these ideas. But scientists hope that new tools in the future may tell us what came before the Big Bang.

    We’ll talk about the futureof our universe tomorrow.

    Script by Damond Benningfield

    Thursday, March 15, 2018
    Looking before the beginning
  • Cancer

    Cancer, the crab, is well up in the east at nightfall. Although it is part of the zodiac, its stars are dim. The brightest, Beta Cancri, is so faint you may not be able to see it from a suburb, let alone a bright city.

  • Zero to 13.8 Billion

    The history of the universe is depicted in this diagram, which begins with the Big Bang at the far left and ends with the present-day universe at right. The imprint of the Big Bang was left at 380,000 years, when the universe became thin and cool enough for particles to stick together to form atoms. The earliest stars yet seen formed about 180 million years after the Big Bang. Since then, galaxies have continued to form and spread out as the univere expands as the result of the Big Bang and dark energy, which increases the rate of acceleration. [N.R. Fuller/NSF]

  • The Big Bang

    The universe contains hundreds of billions of galaxies. All but a few of them are moving away from us, with galaxies that are farther moving faster than those that are closer. That’s because the universe is expanding as a result of the Big Bang.

    In fact, the discovery that the universe is expanding is what caused astronomers to think of the Big Bang in the first place. If all the galaxies are moving away from each other today, then they must have been closer together in the past. And that suggests that in the far-distant past, everything was jammed together into a single point.

    There’s no agreement about what that point was. But scientists do agree that 13.8 billion years ago, it began to expand. It wasn’t a giant explosion in space, though. Instead, scientists like to say that it was an explosion of space — space didn’t exist until the Big Bang. Neither did time, matter, or energy.

    Time and energy sprang into existence first. Some of the energy was converted to the most basic particles of matter. And as the universe expanded and cooled, some of those particles combined to form atoms — mainly hydrogen and helium, the simplest elements. That period left an “afterglow” in the sky — a background of radiation that’s seen across the entire universe. Both the radiation and the chemistry match what Big Bang theory predicts — supporting this model of how the universe was born.

    We’ll talk about what came beforethe Big Bang tomorrow.

    Script by Damond Benningfield

    Wednesday, March 14, 2018
    Getting the universe off to a fast start
  • Eternal Stars

    As Earth turns, most stars rise in the east and set in the west. But a few remain visible all night, every night. These stars are called circumpolar, meaning “around the pole.” In ancient Egypt they were known as the eternal stars.

  • Counting Galaxies

    Leo, the lion, springs across the sky on March nights. He’s in the east at nightfall, marked by his prominent “heart,” the bright star Regulus, which is a third of the way up the sky.

    If you scan the sky below and to the left of Leo with a telescope, you’ll see clusters of galaxies. They contain thousands of galaxies in all. Each galaxy is an “island universe” similar to the Milky Way — a vast assemblage of millions or billions of stars.

    A couple of years ago, a group of astronomers estimated that, if we had big enough telescopes, we could see about two trillion galaxies. Most of those are small “puffballs” from the very early universe, when the first galaxies were being born.

    We see those galaxies as they looked when the universe was only about a billion years old. In other words, we see what they looked like about 13 billion years ago. By today, none of them look as they did then. Most of them probably have merged with other galaxies to form giant galaxies similar to our own.

    On the other hand, there probably are many more galaxies that are out of sight — they’re so far away that their light, traveling at a limited speed, hasn’t had time to reach Earth. And for many of those galaxies, it never will. Because the universe is expanding, light can’t travel fast enough to cover the ever-widening gulf. So there are vast regions of the universe that we can’t see — and never will.

    We’ll have more about the early universe tomorrow.


    Script by Damond Benningfield

    Tuesday, March 13, 2018
    Counting up the galaxies
  • Leo

    The constellation Leo is in the east as night falls, with Regulus, its leading light, about a third of the way up the sky. Denebola, the lion’s tail, is far to the lower left of Regulus.

  • Zosma

    The proper names of the three brightest stars of Leo, the lion, all sound like destinations from a spy thriller: Regulus, Denebola, and Algieba. And the fourth-brightest star sounds pretty exotic, too: Zosma. It’s from a Greek words that means “girdle,” because the star marks the lion’s hip.

    Unfortunately, though, the star itself isn’t all that exotic. It’s in the prime of life, so it’s fusing the hydrogen in its core to make helium. It’s the same phase of life the Sun is in, known as the main sequence.

    But for Zosma, that phase won’t last nearly as long as it will for the Sun. That’s because Zosma, which is also known as Delta Leonis, is a bit more than twice as heavy as the Sun. And as a star’s mass increases, so does the rate of nuclear reactions in its core. So while the Sun will spend about 10 billion years on the main sequence, Zosma will stay there for only about one billion years.

    And it’s getting toward the end of that span already. Astronomers estimate it will end its “prime” lifetime in just a few hundred million years. After that, it’ll puff up to giant proportions, and shine hundreds of times brighter than it is now — making the lion’s “girdle” a bit more exotic.

    Leo is in the east as night falls, with Regulus, its leading light, about a third of the way up the sky. Zosma stands well to the lower left of Regulus, and directly above Denebola, the lion’s tail.

    Tomorrow: counting galaxies.

    Script by Damond Benningfield

    Monday, March 12, 2018
    A “girdle” for the king of the beasts
  • Doggie Treats

    Sirius, the brightest star in the night sky, highlights this view of the front of Canis Major, the big dog. The constellation is low in the south as night falls in March, and is easy to pick out even from light-polluted cities. The star Mirzam shines to the right of Sirius, with the star cluster M41 below Sirius, near the bottom of the image. Under dark skies, the cluster is just visible to the unaided eye, although you'll need binoculars to find it under brighter skies. [Christos Doudoulakis/Wikimedia]

  • Milky Way Clusters

    If you have access to a dark skywatching site, far from the glow of city lights, this is a great evening to look at the Milky Way. It arcs high overhead as darkness falls, so it’s quite a sight. And the Moon doesn’t rise until the wee hours of the morning, so it won’t spoil the show.

    That faint, milky band of light outlines the disk of the Milky Way galaxy. It’s the combined glow of millions of stars. The stars are so far and faint that we can’t see them individually with our eyes alone.

    If you look carefully, though, you’ll see some slightly brighter spots within the Milky Way. Many of those are star clusters — big groups of stars that move through space together. They congregate in the band of the Milky Way because they, too, belong to the galaxy’s disk.

    One of the easiest to spot is Messier 41. That’s because it’s close below Sirius, the brightest star in the night sky, which is in the south at nightfall. M41 is just bright enough to see with the eye alone, as a hazy smudge of light. But binoculars will reveal some of the cluster’s individual stars.

    A string of Messier clusters stretches high across the sky: M35, 36, 37, and 38. They line up to the left of Capella, a brilliant yellow-orange star that’s high in the northwest. They’re fainter than M41, but all of them are good targets for binoculars — vast families of stars glowing within an even bigger family: our home galaxy, the Milky Way.

    Script by Damond Benningfield

    Sunday, March 11, 2018
    Families of stars in the Milky Way
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