StarDate PodcastAuthor: McDonald Observatory
11 Jul 2020

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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    Venus and Aldebaran

    The “morning star” and the eye of the bull are staging a brilliant encounter in the dawn sky. They’ll be quite close to each other for about a week, providing plenty of time to see them.

    At first light tomorrow, Venus, the morning star, will stand directly above Aldebaran, the star that marks the eye of Taurus. Over the following few days Venus will slide down to the left of Aldebaran, then stand side by side with it. After that, Venus will drop away from the star, with the gap between them getting wider each day.

    Although Venus looks brighter, that’s only because it’s much closer to us than Aldebaran is. If you lined them up at the same distance, Aldebaran would look billions of times brighter.

    That indicates that they’re completely different kinds of objects. Venus is a planet about the size of Earth. It doesn’t “shine” on its own. Instead, sunlight reflects off the clouds that top its atmosphere. The combination of the clouds and Venus’s proximity to both Earth and the Sun makes it look bright.

    Aldebaran is about nine million times farther than Venus is this week. But it’s a star, and a big one at that — about 40 times wider than the Sun, and five thousand times the size of Venus. Nuclear reactions in its core produce energy. By the time it reaches the star’s surface, much of that energy is in the form we see with our eyes — the beautiful glow of a giant star.

    Tomorrow: another pairing in the early morning sky.


    Script by Damond Benningfield

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  • Posted on 09 Jul 2020

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    Galactic UFO

    A UFO has been spotted in a galaxy more than two billion light-years away — an ultra-fast outflow. It’s a “wind” created by a disk of hot gas around a supermassive black hole in the galaxy’s heart. And soon, it may sweep away all the gas and dust for making new stars.

    PDS 456 is in Serpens Cauda — the tail of the serpent. The constellation is a third of the way up the southeastern sky at nightfall. The galaxy is far too faint to see without a telescope.

    Even so, it’s the brightest “quasar” within billions of light-years. It’s powered by a black hole that’s a billion times the mass of the Sun. Gas and dust fall toward the black hole, forming a wide disk around it. Material in the disk is heated to extreme temperatures, so it emits a lot of radiation and charged particles. They produce the UFO — a heavy wind that blows at a quarter of the speed of light, and carries as much energy as a trillion Suns.

    The wind blows in every direction. And it acts like a galaxy-wide broom — it sweeps gas and dust away from the galaxy’s core. Right now, it’s pushing enough material to make 250 million stars as heavy as the Sun. And in fact, as that material piles up, clumps of it do give birth to some new stars.

    That won’t be the case for long, though. At the current rate, the wind from the black hole will sweep all the gas and dust out of the galaxy in a few million years — leaving PDS 456 unable to make any more stars.


    Script by Damond Benningfield

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  • Posted on 08 Jul 2020

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    Red Square

    A star in the constellation Serpens appears to be staging a colorful demise. It’s surrounded itself with a cloud of gas and dust that glows bright red — the Red Square Nebula.

    The star is known as MWC 922. And astronomers have been piecing together its story since the discovery of the nebula a decade and a half ago.

    A study last year, for example, said the system probably consists of two stars. The main star is about 15 times the mass of the Sun. It’s passed the end of its “normal” lifetime, so it’s puffed up to giant proportions. It blows a thick “wind” into space. Its unseen companion helps sculpt that wind into two cones, which flow in opposite directions. We happen to view the system in profile, so we see the outlines of the cones as a bright “X.”

    There’s also a thin disk of gas between the cones, and a thicker disk outside them — all glowing bright red.

    If the main star really is as heavy as the study says, then its demise is about to get even more dramatic. The star will explode as a supernova. As debris rams into the material in the Red Square Nebula, the entire system will glow even brighter — sculpted into new and beautiful shapes not by a dying star, but by a dead one.

    MWC 922 is in Serpens Cauda, the tail of the serpent. It’s about a third of the way up the southeastern sky at nightfall. The star is far too faint to see without a telescope, though — at least for now.

    More about Serpens tomorrow.


    Script by Damond Benningfield

    Support McDonald Observatory


  • Posted on 07 Jul 2020

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    Serpens Nurseries

    Our home galaxy, the Milky Way, gives birth to new stars at a leisurely rate — the equivalent of one Sun per year. But you wouldn’t think the rate was that low if you looked deep into Serpens Cauda — the tail of the serpent. Several stellar nurseries there are busily churning out baby stars — some of which are really big babies.

    The nurseries all appear to belong to the Serpens Molecular Cloud. Its gas and dust are cold and dark. But a few million years ago, something rippled through the cloud. That caused knots of gas and dust to begin collapsing to form stars.

    Today, that’s taking place mainly in three big clusters. They’re known as Serpens Main and South, and Westerhout 40. In all, they appear to contain at least 2,000 young stars or future stars — some of the objects are so young that they’re just now igniting the nuclear fires in their cores. And some aren’t even that far along — they’re dark knots that are the seeds of future stars.

    Most of the stars in these clusters are small and faint. But a few are members of the most impressive classes of stars. One of them, in the center of Westerhout 40, is especially hot and bright. It’s blowing away the nearby gas and dust. That will shut down the birth of new stars close by, but perhaps trigger the birth of stars farther away. And the star has blown a colorful bubble around itself that resembles a butterfly — the result of starbirth in the serpent.

    More about Serpens tomorrow.


    Script by Damond Benningfield

    Support McDonald Observatory


  • Posted on 06 Jul 2020

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    Moon and Planets

    Two bright planets accompany the Moon across the sky tonight. Brilliant Jupiter, the solar system’s largest planet, is close to the upper right of the Moon as they climb into good view around 10:30 or 11. And fainter Saturn — the second-largest planet — is about the same distance to the left of the Moon.

    Today, scientists can tell you the distance of both planets to within a tiny margin of error. Jupiter, for example, is about 386 million miles away right now, with Saturn about 840 million miles.

    But such big numbers are unwieldy. So when talking about distances inside star systems, astronomers typically use the astronomical unit, or AU. That’s the average distance between Earth and the Sun — about 93 million miles. So Jupiter is a little less than 4.2 AU away, with Saturn at nine AU.

    The distance from Earth to the Sun isn’t constant, though. Over the course of a year, it varies by about one and a half percent in either direction. Yesterday, for example, we were farthest from the Sun for the entire year: 1.017 AU.

    Today, we’re moving back toward the Sun. We’ll be closest to our star on January 2nd, during the dead of winter in the northern hemisphere. The change in distance does little to change Earth’s overall temperature, though. The air and oceans distribute heat around the entire planet — no matter how far we are from the Sun.

    Tomorrow: slithering along with the serpent.

     

    Script by Damond Benningfield

    Support McDonald Observatory


  • Posted on 05 Jul 2020

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