StarDate

Billy Henry
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  • Astronomy
  • Updated twice weekly

StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

Episodes

  1. 1 day ago

    Cold Skies

    It’s early in the long winter night at the south pole. But a few dozen scientists and others have settled in at a research base there. They monitor the weather and climate, listen to rumbles in the ice below, and watch auroras dancing in the dark skies above. And they operate observatories that study the universe beyond. One of those observatories is buried in the ice. Known as IceCube, it’s a set of thousands of light detectors. They look for evidence of neutrinos – particles that are produced in the Sun, exploding stars, and other powerful objects and events. They almost never interact with other matter. But when one does interact, by smashing into an ice molecule, it produces a quick flash of light. Studying that flicker reveals details about the neutrino, including its origin. And that tells scientists more about the body that created it. Another observatory, the South Pole Telescope, studies the “afterglow” of the Big Bang. Known as the cosmic microwave background, it’s a sort of “haze” that fills the entire universe. Tiny fluctuations in the haze reveal details about the birth of the first stars and galaxies. Water vapor in the atmosphere absorbs microwaves. But the south pole is almost two miles high, and it’s so cold that there’s almost no water vapor in the skies above it. That allows the 10-meter dish to study the background glow in great detail – under the clear, dark skies at the bottom of the world. Script by Damond Benningfield

    2 min

  2. 2 days ago

    Blue Moon

    The Moon can be like a painter’s canvas, dabbed with many colors: the silver of a frosty night, the gold of honey, the orange of a ripe cantaloupe, even the deep red of blood. But it’s almost never blue – at least not in appearance. It sometimes is blue in name, though – including tonight. That’s because it’s the second full Moon of May – a repeat appearance known as a Blue Moon. The color of the Moon – full or not – depends on several factors. When the Moon is low in the sky, as it rises or sets, its light passes through a thicker layer of air. Molecules in the atmosphere scatter blue wavelengths of light, allowing the red to shine through. As the Moon climbs higher, we see more of its true color – gray. But the Moon is so bright that it looks white or silver. During a lunar eclipse, the Moon passes through Earth’s dark shadow. But sunlight filtering through Earth’s atmosphere makes the Moon look dark orange or red. In rare cases, the Moon can actually look blue. That happens after volcanic eruptions or big forest fires. These events pump out particles that scatter red light, allowing the blue to shine through. After the eruption of Krakatoa, in 1883, the Moon appeared blue for months around the entire globe. Whatever its color, enjoy tonight’s Blue Moon. And look quite close to it throughout the night for the star Antares, the heart of the scorpion. They’ll be closest as they set. Script by Damond Benningfield

    2 min

  3. 3 days ago

    First Glimpse

    For most American skywatchers, the star Capella is just peeking into view in the morning twilight. It’s bright, but it’s quite low as the sky brightens. You need precise timing and a clear north-northeastern horizon to spot it. A star’s first appearance is called the heliacal rising – a term that means “with the Sun.” It takes place at the same time every year, as the Sun completes a full circuit through the background of stars. In many ancient cultures, the heliacal rising of certain stars was crucial. The best example is Sirius, the brightest star in the night sky. In Egypt, it first appeared just before the annual flooding of the Nile – the most important event of the year. So the star’s return marked the start of a new year. Several cultures looked for the Pleiades star cluster. Its appearance marked a time to plant crops, or to gather them, depending on a culture’s location. Capella might have been important to the Zapotec, who lived in present-day Mexico. A half-century ago, researchers proposed that a building in the city of Monte Albá‡n was intentionally aligned at a right angle to Capella’s rising point. The star first appeared there at the time the Sun passed directly overhead at noon – a key date in the calendar. But later work disputed that finding. Capella isn’t nearly as important in modern times. But it reminds us that the stars once held great power over much of everyday life. Script by Damond Benningfield

    2 min

  4. 4 days ago

    Manhattanhenge

    Thousands of New Yorkers and visitors will crowd the major east-west streets of Manhattan the next couple of afternoons – all to watch the setting Sun. Weather permitting, the Sun will be perfectly framed by the island’s urban canyons as it descends over the Hudson River. The event is known as Manhattanhenge. It’s named for Stonehenge, the ancient monument in England. Its stones appear to have been aligned with key sunrise and sunset points, and other events. Manhattan produces its own alignments. The island is laid out in a perfect grid, and there are no obstructions along the horizon to block the Sun. The special sunset alignment occurs twice per year, about three weeks before and after the summer solstice, in June. Today, the Sun will be half above and half below the horizon at the peak viewing time. Tomorrow, the full solar disk will stand directly atop the horizon. That sequence is reversed on the nights of July 12th and 13th. Manhattanhenge has become a popular tourist attraction. The streets are clogged by a half hour before sunset. And some venues hold special events to celebrate the view. New York isn’t the only city where you can see the Sun setting between the buildings. But few offer the same alignment of streets and the open horizon provided by Manhattan. Script by Damond Benningfield

    2 min

  5. 5 days ago

    Vega Planets

    The star Vega is a bit of a puzzler. Over the years, astronomers reported evidence of several planets orbiting the bright star. But none of the planets has been confirmed. And observations by two space telescopes revealed nothing. But they left open the possibility of planets. Vega is low in the east-northeast at nightfall, and soars high overhead later on. It’s about 25 light-years away. It’s a bit bigger, brighter, and heavier than the Sun. And it’s younger – just 10 percent the Sun’s age. A disk of dust encircles Vega. It’s tens of billions of miles wide. Hubble Space Telescope recently found a “halo” of tiny dust grains that extends tens of billions of miles beyond the disk. Hubble and James Webb Space Telescope took a good look at the system. They showed that the disk is quite smooth. It’s probably renewed by comets and asteroids. They shed material as they orbit the star, and even more when they slam together. The smoothness of the disk means there are no giant planets orbiting within it. If there were, they would clear out wide gaps. There is one gap. But it’s not completely open. So a planet several times the mass of Earth could orbit in that zone, partially clearing it out. And there could be smaller planets elsewhere in the system – especially close to Vega. But so far, there are no confirmed planets – leaving Vega to travel through space alone. Script by Damond Benningfield

    2 min

  6. 6 days ago

    Richard Carrington

    On September 1st of 1859, Richard Carrington was studying the Sun, as he did every day. The British astronomer used a small telescope to project an image of the Sun on a screen. That allowed him to map the dark features known as sunspots. But on this day, Carrington saw something he’d never seen before. Bright features mingled with the sunspots. They were the first solar flares ever recorded – and still the most powerful. So the outburst is called the Carrington Event in his honor. Carrington also linked the flares to brilliant auroras seen across the globe the following day – the first observations of space weather. Carrington was born 200 years ago today, in London. He originally studied theology, but became hooked on astronomy. He joined an observatory, but left after a couple of years. He built his own observatory, in Surrey. Carrington watched the skies both day and night. He compiled star catalogs. And he made the most impressive studies of the Sun to that time, revealing some crucial details about the Sun. For one thing, it rotates faster near its poles than at the equator. For another, during the 11-year sunspot cycle, the spots move from middle latitudes to near the equator. Carrington eventually had to give up his research. When his father died, he had to take over the family brewery. His health failed as well. He died in 1875 – a pioneer at studying the Sun. Script by Damond Benningfield

    2 min

  7. 25 May

    Mars Lightning

    Lightning may flash through the skies of Mars. But don’t expect to see big, jagged streaks like those produced by storms on Earth. Instead, they may be tiny sparks – like fireflies twinkling through a summer evening. On Earth, lightning is generated by the motions of bits of ice inside clouds. As the particles move past each other, they build up an electric charge. They dis-charge as lightning. The clouds on Mars are high and thin, so there’s no way for them to make big lightning bolts. But the dust grains that swirl through the Martian atmosphere might generate their own discharges. And two recent studies found evidence of them. In the first, researchers combed through recordings made by a microphone on the Perseverance rover. They found 55 instances of small “crackling” sounds near the rover. Almost all of them happened during dust storms, or when small dust devils passed the rover. The scientists decided the most likely explanation for the crackles was tiny discharges – “lightning” bolts about a centimeter long. In the second study, a team looked at observations made by the MAVEN orbiter. The scientists looked for radio waves produced by lightning, which are different from other types of radio from the planet. They found a single example – a possible flicker in Martian skies. Even if lightning is small and rare, it could interfere with future Mars landers – perhaps endangering instruments and people on the Red Planet. Script by Damond Benningfield

    2 min

  8. 24 May

    Martian Climate

    Stargazers on Mars might face one of the same challenges that often hampers a night under the stars here on Earth: clouds. A recent study found that clouds on the Red Planet tend to be thicker at night than during the day. They’re thickest in early morning and evening, especially when Mars is coldest. A fleet of orbiters and landers has been scanning the planet for decades. The probes have told us quite a bit about the Martian climate. The cloud study came from a craft that’s been in orbit since 2021. It watched the clouds both day and night. It amassed the most complete view of the nighttime sky to date. Another study looked at Martian winds. Researchers used AI to sift through more than two decades of images collected by two orbiters. The program identified more than a thousand dust devils – twisting columns of air that sweep dust high into the sky, such as this one recorded by the Perseverance rover. [dust devil sounds] Tracking the motions of the little devils allowed scientists to plot the speed and direction of the winds across the whole planet. The study revealed peak wind speeds of almost a hundred miles per hour – far faster than anything ever recorded by instruments on the surface. These studies and others are helping scientists better understand how the Martian climate works – day and night, in every season. More about Martian climate tomorrow. Script by Damond Benningfield

    2 min

  9. 23 May

    Martian Clock

    Time is tricky. There’s no “universal” clock ticking along at a constant rate. Instead, every clock in the universe ticks at its own rate, influenced by its motion and by the gravity of the matter around it. Those influences are built into the clocks of GPS satellites; without them, the system would fail within days. Scientists recently calculated how clocks would tick on Mars – an average of 477 millionths of a second faster per day than clocks on Earth. But as Mars orbits the Sun, that rate varies by up to 226 millionths of a second. The scientists used Albert Einstein’s theories of gravity and motion. Stronger gravity and faster motion both make a clock move more slowly as seen by an outside observer. The surface gravity of Mars is only about a third as strong as Earth’s. And because the planet is farther from the Sun, it orbits the Sun more slowly. But Mars’s orbit is more lopsided than Earth’s, so its orbital speed varies more dramatically. The changing distance also alters the gravitational influence of the Sun, as well as that of Earth and the Moon. The researchers incorporated all of these variables – and many others – to figure out the ticking of Martian clocks. Mars is working its way into the morning sky. It’s quite low in the east during dawn twilight. But the planet will climb a little higher day by day, and will be in good view this summer. More about Mars tomorrow. Script by Damond Benningfield

    2 min

  10. 22 May

    Moon and Regulus

    The Moon creeps up on the heart of Leo tonight, the star Regulus. Regulus is close to the upper left of the Moon at nightfall. The Moon will move closer before they set, around 2 a.m. They’ll be closest together as seen from the West Coast. The star we see as Regulus is called Regulus A. It’s several times bigger and heavier than the Sun, and much brighter. A tiny companion star is so close that it’s impossible to see through the glare. That duo appears to have two more companions, Regulus B and C. They form their own pair, orbiting each other once every 600 years or so. Regulus B is about 80 percent the size and mass of the Sun, and one-third as bright. Regulus C is a third of the Sun’s mass and size, and just two percent as bright. Regulus B and C are 79 light-years from Earth – the same distance as Regulus A. And they’re moving through space in the same speed and direction as the brighter star. That suggests that they’re bound to Regulus A. But they’re a long way from it – several thousand times the distance between Earth and the Sun. So astronomers haven’t watched the system nearly long enough to calculate a mutual orbit for the two pairs of stars. Estimates say it would take more than a hundred-thousand years for them to complete one circuit. So it’s possible that they’re not really bound at all – just a chance alignment at the bright heart of the lion. Script by Damond Benningfield

    2 min
  • 10 Episodes

Hosts & Guests

About

StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

Information

  • Creator
    Billy Henry
  • Years Active
    2017 - 2026
  • Episodes
    10
  • Rating
    Clean
  • Copyright
    © 2022 The University of Texas McDonald Observatory
  • Show Website
    StarDate

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