StarDate PodcastAuthor: McDonald Observatory
25 May 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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    Tharsis Ridge

    If Mars colonists want to look for adventure, they’ll probably visit Tharsis Ridge. It’s a vast plateau of volcanic rock with some of the most spectacular features on the planet. Giant volcanoes loom at one side of the ridge, with canyons that dwarf the Grand Canyon on the other.

    The ridge is several thousand miles across, and bulges several miles higher than the planet’s average elevation. It built up at least 3.7 billion years ago, when a massive pool of molten rock pushed upward from deep below the surface. “Hotspots” within the molten rock built giant volcanoes.

    The most prominent of these volcanoes are known as Arsia Mons, Pavonis Mons, and Ascraeus Mons. They rise almost 10 miles high, and their bases are up to 300 miles across.

    The biggest volcano on Earth is Mauna Loa, in Hawaii. It’s only 75 miles across and six miles tall. The difference is the way the crusts of the two planets are made. Earth’s crust consists of interlocking plates, which are in constant motion. They move across the pools of molten rock that build volcanoes. So over time, one volcano shuts down and another takes its place. Mars’s crust, on the other hand, is a solid sheet, so the volcanoes keep building in the same spot.

    On the opposite side of the ridge is Valles Marineris. It’s a system of canyons that’s more than 2500 miles long, up to 375 miles wide, and six miles deep — another amazing landmark on Tharsis Ridge.

    More about Mars tomorrow.

    Script by Damond Benningfield

  • Posted on 23 May 2018

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    Martian Autumn

    The shortest season on Mars arrives today — autumn in the northern hemisphere, and spring in the south. The season will last just 142 Mars days. That’s 52 days shorter than northern spring.

    The difference is the result of Mars’s lopsided orbit. The distance between Mars and the Sun varies by about 25 million miles. When Mars is farthest from the Sun, it moves slower than when it’s closest to the Sun. That stretches one season, and compresses another.

    The differing seasons would make it hard to create a Martian calendar that’s tied to the seasons. That hasn’t stopped people from trying, though. They’ve come up with several ideas.

    Some schemes divide the year into 12 equal months, like those on Earth. Others use 18 months, or even 24. And still others have tried months of different lengths.

    The concept of a “month” wouldn’t be as important on Mars as it is on Earth. A month here is based on the Moon’s cycle of phases, which lasts 29 and a half days. But the two Martian moons move across the sky much faster. The tiny outer moon, Deimos, completes its cycle of phases in just five and a half days. And the bigger inner moon, Phobos, crosses the sky twice every day. So the moons probably won’t be much help in designing a calendar for the Red Planet.

    And Mars is climbing into better view by the day. Right now, it’s about a third of the way up the southern sky at first light, and looks like a bright orange star.

    More tomorrow.

    Script by Damond Benningfield

  • Posted on 22 May 2018

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    Moon and Regulus

    The first-quarter Moon snuggles especially close to a bright companion tonight. Regulus, the heart of Leo, the lion, will stand just a degree or so from the Moon as night falls — less than the width of your finger held at arm’s length. The Moon will pull away from the star later on, but they’ll still be quite close together as they set in the wee hours of the morning.

    Their closeness is just an illusion — they just happen to line up in the same direction in the sky. In reality, they’re an extraordinary distance apart.

    The Moon is a quarter of a million miles away. That’s a vast distance on the human scale, but the tiniest baby step by astronomical standards.

    Regulus, on the other hand, is a bit more than 79 light-years away. In other words, traveling at the speed of light — about 670 million miles per hour — it takes light a bit more than 79 years to reach Earth. So a beam of light that leaves the surface of Regulus tonight won’t arrive at Earth until the year 2097. To put that in perspective, it’s just a few months longer than the life expectancy of a baby born in the United States. So we can truly say that Regulus is a lifetime away.

    There’s a bit of uncertainty in the distance to any star. In the case of Regulus, it’s about seven-tenths of a light-year. That doesn’t sound like much until you consider this: That slight margin of error is equal to about 17 million times the distance to the Moon.

    Script by Damond Benningfield

  • Posted on 21 May 2018

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    Dragon’s Eyes

    A pair of eyes stares down from the northeast as night falls right now — the eyes of Draco, the dragon. They’re above brilliant Vega, one of the night sky’s most prominent stars.

    The brighter of the eyes is the star Eltanin, the dragon’s leading light. The name means “the serpent,” because the star once represented the entire dragon.

    Eltanin is an orange giant. It’s a good bit bigger, heavier, and brighter than the Sun. That makes it easy to see even though it’s more than 150 light-years away.

    It should get a lot easier to see in the coming millennia. That’s because Eltanin and the Sun are moving closer together. In about one and a half million years they’ll be at their closest — just 28 light-years apart. Assuming Eltanin hasn’t changed much by then, it’ll be the brightest star in the night sky — about as bright as the current champ, Sirius.

    The other eye, Rastaban, is just above Eltanin. Its name means “head of the serpent.” It’s more than twice as far as Eltanin. It’s also a giant, but a much bigger and brighter one — a thousand times as bright as the Sun. So it’s only a little fainter than Eltanin despite the extra distance. It’s about the same color as the Sun, though — yellow-white.

    The rest of Draco curves to the left and above the dragon’s eyes, and curls around Polaris, the North Star. The eyes stare in the opposite direction — toward Hercules, who killed the dragon before both of them were placed in the heavens.

    Script by Damond Benningfield

  • Posted on 20 May 2018

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    VW Cephei

    Many stars are binaries — two separate stars in orbit around each other. In some cases, though, the two stars are so close to each other that they’re actually stuck together. These contact binaries are surprisingly common. And with a pair of binoculars, you can see one tonight, in the constellation Cepheus, the king.

    In 1926, astronomer Jan Schilt observed the star after another astronomer told him its spectrum resembled that of the best-known contact binary. Schilt found that the star’s brightness varied as the two stars went around each other. The variation in brightness occurred across the entire orbit. That meant the stars were so close together that one or the other was always blocking some of its companion’s light.

    Today, the system is known as VW Cephei. It’s 90 light-years from Earth. No telescope in existence can see it as two stars instead of one. But the constant change in brightness means the stars are so close that they are indeed stuck together. If you lived on an orbiting planet, your sun would look like a glowing peanut, with the two lobes whirling around each other every 6 hours and 41 minutes.

    If you have binoculars and a good star map, you can see VW Cephei for yourself. It’s so far north that for anyone in the United States it never sets. Over just a few hours, the system’s brightness rises 60 percent from minimum to maximum, as the two stuck-together stars race around each other in the far northern sky.

    Script by Ken Croswell

  • Posted on 19 May 2018


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