StarDate PodcastAuthor: McDonald Observatory
18 Dec 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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    If a scientist on an alien world aims a telescope at Earth, it might pick up some interesting signals. The telescope might see the chemical signatures of oxygen, ozone, and methane, for example. And it might see a green color that’s missing on most planets. From those observations, the scientist might reach a startling conclusion: life inhabits this small, rocky world.

    Scientists here on Earth are starting to look for similar signs of life on some of the thousands of planets discovered in other star systems. In particular, they look for a planet to pass in front of its parent star. If the planet has an atmosphere, some of the star’s light filters through it. That adds the “fingerprints” of chemicals in the atmosphere to the light from the star itself.

    Some of those chemicals could be produced by life. On Earth, for example, plants “exhale” oxygen. In the upper atmosphere, some of the oxygen is converted to ozone. And cattle and other animals produce methane.

    Detecting those chemicals is no guarantee that a planet is inhabited, though. Scientists must take many factors into account — the size and mass of the planet, its distance from its star, the radiation it receives from the star, and many others.

    The observations are tough to make with current technology. But future space telescopes, as well as giant telescopes on the ground, should make it easier to look for signs of life among the stars. More about that tomorrow.

    Script by Damond Benningfield

  • Posted on 17 Dec 2018

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    Messier 37

    A 500 million-year-old star cluster climbs high overhead during late fall and winter. It’s not quite visible to the unaided eye, but it’s a fairly easy target for binoculars.

    Messier 37 probably is about 5,000 light-years away, and it contains about 500 known stars. And it could have even more stars, but they’ve been too faint, or too far from the cluster’s packed center, for astronomers to pick them out.

    We know the cluster’s age because of its population of stars. When a cluster like M37 forms, it has a mixture of stars of all sizes and masses.

    M37 is basically bereft of the two heaviest classes of stars, which burn out quickly. But it has quite a few of the next class, which last longer.

    Since we know how long it takes all of those stars to expire, we have a pretty good idea of the cluster’s age: Longer than the lifespans of the heaviest stars, but shorter than the spans of medium-mass stars. When you plug in all the numbers, it works out to about half a billion years — barely more than one-tenth/the age of the Sun.

    Auriga is in the east-northeast as darkness falls. It consists of a pentagon of stars, with brilliant Capella at its top left point. M37 is a little below the figure. In modest binoculars, it looks like a fuzzy star. Higher-power binoculars, though, reveal many of the cluster’s individual stars — a family of stars that’s still quite young.

    Tomorrow: looking for signs of life.

    Script by Damond Benningfield

  • Posted on 16 Dec 2018

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    The Charioteer

    The tales that describe many of the ancient constellations can be romantic, tragic, heroic, or majestic. But some are just weird.

    A prime example is Auriga. The constellation is low in the east-northeast as night falls right now, and climbs high across the sky later on. It’s marked by a pentagon of stars. And it’s easy to pick out thanks to the brightest member of that figure, Capella — one of the brightest stars in the entire night sky.

    Although Auriga is described as a charioteer, the character usually isn’t depicted with a chariot. But he is shown with a goat and her two kids on his shoulder.

    There are several versions of his story. In one, he was Erichthonius, an early king of Athens. He was raised by the goddess Athena. Among other things, she taught him how to tame horses. He was so good at it that he became the first person to harness four horses to a chariot, like the chariot that carried the Sun across the sky. Zeus, the king of the gods, was so impressed that he placed the charioteer in the stars.

    The goat, which is represented by Capella, isn’t actually a part of any of the legends of Auriga. It may represent the goat that suckled the infant Zeus, who placed her and her children in the sky in gratitude.

    The goat and kids may once have formed their own small constellation. Today, though, they ride on the shoulder of the charioteer — who rides on nothing at all.

    We’ll have more about the charioteer tomorrow.


    Script by Damond Benningfield

  • Posted on 15 Dec 2018

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    Moon and Mars

    A trip to Mars takes a while — with current rockets, about six months to get there and six months to get back. And thanks to the alignment of the planets, the layover between flights is a year or so.

    All of that time in space and on Mars would expose astronauts to large doses of radiation. According to a European spacecraft, they’d be exposed to the equivalent of about 6,000 chest X-rays just during the round trip. Their time on Mars would add even more.

    We don’t have to worry about space radiation here on Earth — we’re protected by the planet’s magnetic field and its atmosphere. The magnetic field also offers some protection to astronauts in Earth orbit.

    Outside that field, though, crews would be exposed to solar storms, and to cosmic rays, which come from outside the solar system.

    No one is sure how the radiation would affect astronauts — there aren’t enough studies. But they could suffer from radiation sickness, higher chances of cancer, or other problems.

    NASA and others are looking at ways to protect Mars travelers. They’re trying to develop lightweight shielding, for example, or Star Trek-like force fields. And they’re studying ways to enhance a person’s resistance to radiation — everything from gene therapies to suspended animation. So far, though, there are no good solutions to the problem of space radiation.

    Mars is in great view tonight. The planet looks like a bright star just above the Moon as night falls.

    Script by Damond Benningfield

  • Posted on 14 Dec 2018

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    Comet Wirtanen

    It’s prime time for the celestial bull. Taurus is well up in the east at nightfall, and climbs high across the sky later on. Look for his bright orange “eye” — the star Aldebaran — with his shoulder — the Pleiades star cluster — standing above it. And over the next few nights, a visitor will streak across the constellation.

    Comet Wirtanen just made its closest approach to the Sun for its current orbit, a bit outside Earth’s orbit. As the comet heads away from the Sun, it’ll fly past Earth. It’ll make its closest approach on Sunday night, at a distance of about seven million miles. That’s the 20th-closest approach by a comet ever recorded.

    Astronomers are taking advantage of that approach. They’re measuring the size and rotation of the comet’s nucleus, which is less than a mile across. And they’re measuring the composition of the comet and its long tail.

    Because we record our show in advance, we can’t tell you how bright the comet will become. But some predictions say that, under dark skies, it could be bright enough to see with the unaided eye. From brighter areas, you’ll probably need binoculars or a telescope.

    Tonight, Wirtanen will stand far to the right of Aldebaran and the Pleiades. But it will pass between them on Sunday night — closer to the Pleiades than Aldebaran. After that, it’ll sweep off to their left, quickly leaving the bull behind — but perhaps staying bright enough to watch for a few more weeks.

    Script by Damond Benningfield

  • Posted on 13 Dec 2018


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