StarDate PodcastAuthor: McDonald Observatory
29 Sep 2021

StarDate Podcast

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

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    Dusty Skies

    Most of the dust in your home has an earthly origin: bits of dirt and pollen from the yard, skin cells from you and your pets, and even dust mites. But some of it probably comes from outer space — tiny bits of debris from comets and asteroids. In fact, a recent study says that almost 6,000 tons of that debris falls to Earth every year.

    As comets orbit the Sun, they shed tiny grains of rock and dirt. And asteroids ram together, spraying similar grains into space. The particles spread out. And some of them enter Earth’s atmosphere and settle on the surface.

    Estimates of how much reaches the surface vary by quite a bit. The numbers have been based on how much cosmic dust is found in sediments, how much is captured by high-altitude research aircraft, or how much is detected by spacecraft.

    The recent study examined layers of ice in Antarctica. Over the last 20 years, researchers dug near Concordia Station, a European research base a few hundred miles from the south pole. They counted the number of cosmic dust grains found in different layers. When they projected the same rate across the entire planet, they came up with an annual fall of about 5700 tons.

    They also compared the types of grains to models of how dust is scattered through the solar system. That told them that about 80 percent of the grains probably come from comets, with the rest from asteroids — extra sources of dust for your kitchen cabinets.
     

    Script by Damond Benningfield

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  • Posted on 27 Sep 2021

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    The Little Horse

    Pegasus, the flying horse, is climbing across the night sky. It’s in the east as night falls. It’s preceded by another horse, which is to the upper right of Pegasus.

    Equuleus is far smaller and less prominent than its equine cousin. In fact, of all the constellations passed down from the ancient world, it’s by far the smallest — you can cover it with your palm held at arm’s length.

    Unlike most ancient constellations, there’s not much of a story associated with Equuleus. And as it’s drawn in the sky, it’s not even a full horse — only a head, which is outlined by a lopsided rectangle of four meager stars.

    The brightest of the four is Alpha Equulei, which actually is a pair of stars locked in a tight orbit around each other. Both stars are about twice as massive as the Sun, with one slightly heavier than the other.

    The difference in heft has made a big difference in the lives of the two stars. The heavier one has already ended its “normal” lifetime, and is entering one of its final stages. That’s caused the star to puff up like a balloon.

    The smaller star is still in the prime of life. Yet as the bigger star puffs up, the surfaces of the two stars may get so close that the stars will swap some of their gases — altering the evolution of both stars.

    Equuleus is in the southeast at nightfall. It’s below Delphinus, the dolphin — another small constellation, but one that’s much easier to pick out.
     

    Script by Damond Benningfield

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  • Posted on 26 Sep 2021

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    Moon and Aldebaran

    Although the Moon looks bright, its surface is actually one of the darkest of any major body in the solar system. On average, it reflects only about a tenth of the sunlight that strikes it. That makes the Moon almost as dark as charcoal.

    There is one prominent bright spot on the Moon, though — a crater named Aristarchus. Although it’s tiny as seen from Earth, it’s such a contrast to the surrounding landscape that it’s visible to the unaided eye. It’s near the left edge of the Moon as the Moon rises late this evening, above the bright star Aldebaran, the “eye” of the bull.

    Aristarchus is about 25 miles across, and a couple of miles deep. A mountain peak rises from its floor like a skyscraper. The crater is surrounded by bright “rays” of debris that were blasted out by the impact that made it.

    Observations by spacecraft in lunar orbit show that the crater floor contains a lot of minerals that are rich in titanium. They probably came from far below the surface, and were brought to the surface by the impact.

    There’s some evidence that the area around Aristarchus is volcanically active. Observers have reported seeing flashes of light or odd glows in the area, including in the crater itself. And instruments have revealed traces of a radioactive gas. That could mean that gas sometimes erupts from below the surface — briefly adding to the luster of this bright lunar feature.

    Tomorrow: drawing up a little horse.
     

    Script by Damond Benningfield

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  • Posted on 25 Sep 2021

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    A Passel of FRBs

    Fast radio bursts are among the most powerful objects in the universe. Many of them are hundreds of millions of light-years away. Despite their great power, though, there’s no consensus on what they are. But a whole passel of new discoveries may help.

    Fast radio bursts were first seen in 2007. But they last only a tiny fraction of a second, which makes them hard to track down.

    By earlier this year, astronomers had seen about 140 of them. But a few months ago, they got 535 more to study. The new ones were discovered by CHIME — a radio telescope in British Columbia that scans the entire northern sky.

    Most of the objects in the new catalog have produced a single outburst. But a few have repeated themselves. Their outbursts last a little bit longer than the others, and they have a tighter range of frequencies. That suggests there are two classes of “bursting” objects.

    The class that repeats may be produced by magnetars — the super-dense and ultra-magnetic corpses of once-mighty stars. They spin up to hundreds of times per second, beaming energy into space with each turn.

    In fact, CHIME and other telescopes detected a radio outburst from a magnetar in our own galaxy. So repeating bursters could be powered by one mechanism, while those that are seen only once are powered by something different. Detailed study of all the new observations — as well as future outbursts — will help astronomers figure it out.
     

    Script by Damond Benningfield

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  • Posted on 24 Sep 2021

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    September Equinox II

    The flow of the seasons has taken on a different feel over the past year and a half. Children spent months at home instead of in the classroom, so spring break and summer vacation felt no different from any other time. Adults didn’t leave home for days or weeks at a time, so conditions outdoors made little difference to the routine. And busy downtowns closed up, so they looked deserted regardless of the time of year.

    We mention all of that because today is the first full day of autumn in the northern hemisphere. It’s the time of the equinox, as the Sun crosses the equator from north to south. Over the next three months, it’ll move even farther south, so we’ll see shorter, cooler days.

    The equinoxes and solstices mark the starting points of the astronomical seasons. They’re convenient points for marking the seasons because they’re precise and easy to predict.

    But there are many other ways to mark the changing seasons. The meteorological season, for example, began on September 1st. And in centuries past, some cultures used the equinoxes and solstices as the mid-points of the seasons, not the beginnings. These cultures picked various dates for these markers, so there was no common way to mark the seasons.

    And in modern times, we’ve marked the seasons by school and work calendars, vacation schedules, and other everyday events. COVID scrambled those cycles — making it a bit harder to follow the rhythms of the seasons.

    Tomorrow: radio outbursts by the hundreds.
     

    Script by Damond Benningfield

    Support McDonald Observatory


  • Posted on 23 Sep 2021

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