StarDate PodcastAuthor: McDonald Observatory
21 Feb 2018

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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    Canis Major

    Winter brings out the big dogs — some of the most prominent constellations of all. And one of those really is a dog: Canis Major, the big dog. It’s best known for its leading light: Sirius, the Dog Star, the brightest star in the night sky. It’s a third of the way up the southeastern sky at nightfall.

    But there’s more to Canis Major than just Sirius. It includes several bright stars, most of which are below or to the right of Sirius. When you link them up, they really do look like the outline of a dog.

    Like all constellations, Canis Major consists of more than just a connect-the-dots pattern of stars, though. It covers a patch of sky that includes the area outside that pattern as well. And within those borders, you can find several deep-sky objects — objects like star clusters, which are far beyond most of the individual stars visible in Canis Major.

    Perhaps the best known is M41. It’s not far below Sirius, and is an easy target for binoculars. It’s about 2300 light-years away, and consists of about a hundred stars.

    The cluster probably is about 200 million years old. At that age, its biggest, heaviest stars have already expired, leaving small, dense corpses known as white dwarfs. The next-heaviest stars will soon follow that same path. Those stars have puffed up to become red giants. They’re easily visible through binoculars — sparkling red and orange jewels along the “collar” of the big dog.

    More about Canis Major tomorrow.

    Script by Damond Benningfield

  • Posted on 20 Feb 2018

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    Doomed Moons

    Some moons lead dangerous lives. Two moons of the planet Uranus, for example, are likely to be destroyed in a million years or so when they smash into each other.

    Uranus has 27 known moons, and nine of them form the most tightly packed system of satellites in the solar system. Their orbits all lie within just 11,000 miles of one another.

    In that busy environment, accidents are inevitable. Although the moons are small, each moon’s gravity still tugs at all the others. Over long periods of time, that can make a moon swerve into the wrong lane, causing a collision.

    Astronomers recently deduced the mass of the moon Cressida by studying its effects on one of the rings of Uranus. This work indicates that the moon is massive enough to perturb another moon, Desdemona. That will make them crash into each other in about a million years — not long compared with the solar system’s age of four-and-a-half billion years.

    These moons aren’t the only ones whose days are numbered —the moons Cupid and Belinda are likely to collide as well.

    Impacts like these may explain why Uranus has a couple of rings near the moons. The rings may contain the debris from earlier collisions — the remnants of moons that crashed into their neighbors.

    Uranus is too faint to see with the eye alone. But it’s easy to see its position tonight. It’s above the Moon, by less than the width of a fist held at arm’s length. Binoculars will show the planet as a tiny orb amidst the stars.

    Script by Ken Croswell

  • Posted on 19 Feb 2018

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    Here’s a phrase that you probably haven’t heard before: solar antapex. It’s the location in the sky that’s opposite the direction that Sun and Earth are moving through the galaxy. It’s marked by the constellation Columba, the dove, which scoots quite low across the south on February nights.

    Like all the other stars in the Milky Way, the Sun is orbiting the center of the galaxy. And its path is taking it in the direction of Vega, a bright star in the summer constellation Lyra. That direction is known as the solar apex. So the opposite direction is the ant-apex.

    That point may be the most interesting thing about Columba, which is to the lower right of Sirius, the brightest star in the night sky.

    The constellation was created in 1592 by a Dutch astronomer. He used it to fill in a gap between some brighter star patterns.

    Columba’s leading light is Alpha Columbae, which actually is quite impressive. It’s perhaps four-and-a-half times the diameter of the Sun, and a thousand time the Sun’s total brightness. But it’s also 260 light-years away — a distance that dulls its luster. So as seen in Earth’s night sky, it’s not much to look at.

    Over the ages, though, it’ll get brighter. The star is finishing up the original hydrogen fuel in its core. When the hydrogen is gone, the core will get smaller and hotter. That’ll cause the star’s outer layers to get bigger and brighter. So the dove will have something besides the solar antapex to set it apart.

    Script by Damond Benningfield

  • Posted on 18 Feb 2018

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    Mercury in Conjunction

    The smallest of the solar system’s major planets is hiding in the Sun’s glare right now. That’s because Mercury is at superior conjunction — it lines up behind the Sun as seen from Earth. As it moves away from the Sun, it’ll climb into decent view in the early evening sky in a couple of weeks.

    Mercury’s motion around the Sun played a big role in the development of Albert Einstein’s theory of gravity, known as General Relativity.

    Mercury’s path around the Sun is lopsided, so the little planet’s distance from the Sun varies by quite a bit. Astronomers plotted that path, and used the laws of gravity devised by Isaac Newton to predict where Mercury should appear in the future. But they discovered that each time Mercury comes closest to the Sun, it’s a little farther along in its orbit than predicted.

    Einstein saw gravity not as a force — something that pulls two objects together — but as a warp in space caused a massive object — in this case, the Sun. The closer to the Sun you get, the more pronounced that warp becomes. So each time Mercury comes closest to the Sun, it gets pulled forward a bit by the warp in space.

    Mercury’s orbit was the first bit of tangible evidence in support of General Relativity. In fact, Einstein discussed it in his early papers on the subject. Since then, much more evidence has confirmed Einstein’s ideas — showing us that, for now, General Relativity is the best explanation of gravity.

    Script by Damond Benningfield

  • Posted on 17 Feb 2018

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    Flying Across Titan

    Most of the spacecraft that have touched down on other worlds have been either stationary landers or wheeled rovers. But a possible mission to the biggest moon of Saturn would take a big jump in mobility — it would fly from point to point like a helicopter.

    Dragonfly is one of two finalists for a mission that will launch in about a decade. The other is called Caesar. It would touch down on Comet Churyumov-Gerasimenko, which was studied in detail by an earlier spacecraft. Caesar would grab a sample from the comet’s surface and return it to Earth.

    Dragonfly would study the moon Titan for about two years. The small drone would have a set of rotors, like a helicopter, to carry it from place to place. Each hop could cover dozens of miles, allowing the craft to visit dozens of locations across a wide area. It would spend several Earth days at each spot, studying Titan’s weather, surface chemistry, and more.

    Titan is one of the most intriguing bodies in the solar system. Its frigid atmosphere is thicker than Earth’s, and it contains large amounts of organic compounds — the chemical building blocks for life. Liquid methane and ethane form lakes and seas on the surface. Titan also may have a massive ocean of liquid water deep below the surface. That combination means that Titan could be a good place to look for microscopic life.

    NASA plans to pick the winning concept next year — setting the stage for a visit to a solar system neighbor.

    Script by Damond Benningfield

  • Posted on 16 Feb 2018


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