StarDate PodcastAuthor: McDonald Observatory
21 Jul 2017

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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    Hot Weather

    The objects known as brown dwarfs are oddballs. They’re heavier than planets, but not heavy enough to trigger the nuclear reactions that would make them shine as true stars. In fact, they’re often described as failed stars.

    Yet they share some traits with both stars and planets. Like stars, their surfaces are hot, with temperatures of up to several thousand degrees. But like planets, those surfaces may be topped by layers of clouds and giant storms.

    Astronomers have discovered “weather” on the surfaces of several brown dwarfs. They can’t actually see the clouds and storms. But they know they exist because the brown dwarfs get fainter and brighter in different wavelengths as they rotate. The sometimes-dramatic change in brightness indicates that the surface of a brown dwarf consists of layers of clouds with embedded storm systems.

    The clouds and storms are quite different from those on Earth, though. The clouds are so hot that they’d be made of small particles of iron or silicon, not water. And the storms might be a lot like Jupiter’s Great Red Spot — cyclones big enough to swallow an entire planet.

    Indeed, a stormy brown dwarf might look a lot like Jupiter, with bands of clouds circling all the way around it, and big storms whirling through the clouds. But the brown dwarf would also provide its own inner glow — its heat would make it shine dull red or orange, with the clouds forming dark bands across its stormy surface.


    Script by Damond Benningfield

  • Posted on 20 Jul 2017

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    Moon and Venus

    Early risers are in for a skywatching treat at first light tomorrow — a close pairing of the crescent Moon and the planet Venus. Venus looks like a dazzling star just to the left or upper left of the Moon.

    Venus is the second planet out from the Sun, while Earth is third. Because of that, Venus has a limited range in our sky. At best, it’s visible for a few hours before sunrise or after sunset.

    Also because of that arrangement, Venus shows phases, just as the Moon does — from a bare crescent to almost full. It’s a crescent around the time it passes between Earth and Sun, and almost full just before it passes behind the Sun. We don’t see it when it’s full because it’s too close to the Sun then.

    Right now, the planet is roughly at a right angle to the Sun, so it’s about half full. So if you look at it with a telescope, you’ll see that half of the hemisphere that faces our way is in sunlight, while the other half is in darkness.

    You might expect the planet to be brightest when it’s full, and faintest when it’s a crescent, but that’s not so. Venus is much closer to us when it’s a crescent, so it covers a larger fraction of the sky. We also catch more of its reflected sunlight then. So Venus is at its brilliant best a little before and after it passes between Earth and the Sun.

    Venus is always bright, though, so it’s an easy target. For now, look for it in the east at first light — tomorrow, near the crescent Moon.


    Script by Damond Benningfield

  • Posted on 19 Jul 2017

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    The stars that dust the night sky are all moving around the center of the galaxy at hundreds of thousands of miles per hour. Yet they’re so far away that their motion is imperceptible across not just a human lifetime, but hundreds of lifetimes. In fact, even one of the fastest stars as seen from Earth will move just one degree over the next 5,000 years — less than the width of a finger held at arm’s length.

    Altair is the brightest star of Aquila, the eagle. In fact, the name “Altair” means “the flying eagle.” The star is in the east at nightfall, at the lower right corner of the bright, widespread Summer Triangle.

    Altair is only about 17 light-years away — closer than all but a handful of the stars that are visible to the unaided eye. That’s the main reason it’s moving in such a hurry. It’s like watching race cars on opposite sides of a track. Although the cars are all moving at about the same speed, those on the side closest to you cover a larger angle in the same amount of time than those on the far side.

    Yet that motion is too tiny to plot with the eye alone. Instead, astronomers make extremely precise measurements of its position against the background of more-distant stars. Comparing Altair’s position over a period of years reveals its apparent speed across the sky.

    Again, look for Altair almost due east at nightfall, climbing high across the south during the night, and almost due west at first light.

    Script by Damond Benningfield

  • Posted on 18 Jul 2017

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    Eagle Nebula

    One of the most beautiful and inspiring regions in the galaxy climbs across the south on summer nights. Binoculars reveal some of its stars, and a telescope shows its hazy outline. But its true glory comes through best in long-exposure images.

    The Eagle Nebula is a vast complex of stars, newly forming stars, and the raw material for stars — clouds of gas and dust. The nebula was discovered by comet hunter Charles Messier. But it was made famous a couple of decades ago by an image from Hubble Space Telescope, known as the Pillars of Creation.

    The pillars of cold gas and dust span several light-years. They’re sculpted by winds and radiation from hot, young, massive stars. The stars erode the outer regions of the pillars, but they also create shock waves that squeeze them. The shock waves compress dense knots of gas and dust, helping them collapse to form new stars.

    The nebula has given birth to hundreds of stars in a wide variety of sizes and masses.

    There’s evidence that one of its heavy stars has exploded as a supernova. If so, then a shockwave from the star is racing outward. In fact, it’s probably already plowed through the pillars, blasting away most of the material for making more stars. Because the system is about 6500 light-years away, though, we won’t see that happen for another millennium or so. That means we can enjoy the inspiring beauty of the Eagle Nebula for many more centuries.

    Script by Damond Benningfield

  • Posted on 17 Jul 2017

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    The Dolphin II

    Most constellations bear little resemblance to their namesakes. You need a great imagination to see a king in the stars of Cepheus, for example, or a “sea goat” in Capricornus.

    One constellation that does resemble its namesake is the dolphin, Delphinus. It’s a small grouping of stars that’s low in the east at nightfall, and swims high across the south later on. And that little group of stars really does look like a dolphin jumping through the edge of the starry Milky Way.

    In Greek mythology, Delphinus carried a poet to safety when he jumped overboard to escape some nasty sailors. The poet and the dolphin were commemorated in several coins that were issued around 500 B.C. And the dolphin gained longer-lasting recognition through its own constellation.

    None of the individual stars of Delphinus is particularly interesting. The brightest is Beta Delphini. It’s near the center of the constellation, and marks the end of the dolphin’s torso. The dolphin’s body stretches to the left as it climbs higher in the sky, and its tail to the right.

    Beta Delphini is actually a binary. The two stars were born from the same cloud of gas and dust, and they remain bound to each other by their mutual gravitational pull. They orbit each other once every 27 years.

    Look for the beautiful dolphin swimming into view in the east as darkness falls, and climbing high across the south during the night.


    Script by Damond Benningfield

  • Posted on 16 Jul 2017


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