StarDate PodcastAuthor: McDonald Observatory
19 Oct 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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    Losing Weight

    Planet Earth turns on its axis like a spinning gyroscope — one turn every 23 hours and 56 minutes. And because of that spin, you’d weigh less at the equator than at the poles.

    The spin is pretty fast — a point on the equator moves at more than a thousand miles per hour. That creates an outward “push” on material at the equator. That gives Earth a slight “bulge” in its waistline — about 27 miles wider through the equator than through the poles.

    Since a person standing at one of the poles is a little bit closer to the center of Earth than a person at the equator, the person at the pole would feel a stronger gravitational pull.

    The difference would be magnified by Earth’s rotation. A person at the equator would be pushed outward by the same force as Earth itself. That acceleration would decrease their weight.

    When you add up the effects, a person who weighs 150 pounds at the poles would weigh almost a pound less at the equator.

    The same thing would happen on the other planets of the solar system, although to varying degrees. Venus has the slowest rotation, and it’s the “roundest” planet, so the difference would be tiny.

    On Jupiter and Saturn, though, it would be much more pronounced. Both planets are giant balls of gas, and they both spin much faster than Earth does. As a result, they’re much more “squashed” than Earth is. So if you floated through the clouds at the poles, you’d weigh many pounds more than at the equator.


    Script by Damond Benningfield


  • Posted on 18 Oct 2018

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    Moon and Mars

    The seasons are changing on Mars. Today is the first full day of winter in the planet’s northern hemisphere. The new season follows what turned out to be a nasty autumn.

    Mars has seasons for the same reason Earth does: The planet is tilted on its axis. As it orbits the Sun, the north and south poles take turns dipping toward the Sun. As a result, the northern and southern hemispheres take turns getting more and less sunlight — creating seasons.

    The seasons are more complicated than those on Earth, though. That’s because Mars follows a more lopsided orbit around the Sun. The planet is closest to the Sun during northern winter, and farthest during summer. So summers and winters are milder in the north than in the south.

    The changes in sunlight can trigger big dust storms. As the surface warms, it creates wind currents that stir up the powdery dust that covers much of Mars.

    That’s just what happened back in May. Just days after the spring equinox on Mars, a storm whirled to life in the northern hemisphere. By the end of June, it encircled the entire planet. Rovers on the surface saw day turn almost to night. The Sun vanished from view, and the sky turned dark red.

    It’s taking months for the dust to settle out of the atmosphere — creating a hazy winter in the northern hemisphere.

    Look for Mars to the left of the Moon as darkness falls this evening. It looks like a bright orange star. It’ll be even closer to the Moon as they set, after midnight.


    Script by Damond Benningfield


  • Posted on 17 Oct 2018

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    Close Visitor

    A space rock the size of a building will buzz near Earth tomorrow. There’s no risk of it hitting us. But it’s a reminder that other members of the solar system often pass this way. And some of them could be hazardous.

    Asteroid 2014 US7 will miss Earth by about 750,000 miles — three times the distance to the Moon. Most of the time, the asteroid stays well inside Earth’s orbit. But its orbital path is elongated, so it sometimes passes close to our planet.

    2014 US7 probably is between about 40 and 100 feet wide. That’s about the same size as an asteroid that exploded over Russia in 2013. The explosion shattered windows and caused other damage.

    Asteroids in this size range pass near Earth all the time. This year alone, in fact, several dozen of them have passed inside the Moon’s orbit. And one of them actually hit us. It was only about six feet wide, so it wasn’t discovered until a few hours before impact. It exploded harmlessly over southern Africa in June, raining small fragments on the surface.

    Astronomers have been hunting and plotting the orbits of near-Earth asteroids over the past quarter century. The goal is to identify anything on a collision course long before it could hit us. And they’ve found most of the big asteroids, which could decimate life on a regional or global scale. Now they’re trying to find ones that are smaller, but still big enough to cause big problems — trying to keep Earth safe from space rocks.


    Script by Damond Benningfield


  • Posted on 16 Oct 2018

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    Collision Zones

    Planetary systems can be dangerous. Like race cars zipping around a track, planets can ram into each other. That can destroy one or both of the planets, and create massive piles of debris. Some of that debris may then fall onto the parent star.

    Astronomers have seen the likely aftermath of several such collisions. The most recent is in a star system in Auriga. The charioteer climbs into view in the northeast by about 10 p.m. It’s marked by the bright star Capella.

    Astronomers have been intrigued by a star system known as RW Aurigae for decades. It consists of two stars in a tight orbit around each other. They’re only a few million years old.

    The system periodically gets much fainter. In 2011, for example, it faded for about six months. It faded again in 2014, and stayed faint for more than two years.

    A recent study says the dimmer switch probably was flipped by a collision between two small planetary bodies. The impact created a big cloud of dust and gas. The cloud passed in front of the star, blocking some of its light. And some of that material appears to be falling onto the star.

    Such a discovery isn’t surprising. There’s evidence that young stars gobble up some of their close planets. Eventually, though, the systems calm down. Yet even then, collisions between planets and smaller bodies happen all the time — maintaining the danger level. We’ll have more about that tomorrow.


    Script by Damond Benningfield


  • Posted on 15 Oct 2018

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    Moon and Saturn

    Saturn is the second-largest planet in the solar system — only mighty Jupiter outranks it. And it generates the second-largest magnetic “bubble” — a region of space dominated by Saturn’s magnetic field. It’s molded into a “teardrop” by the solar wind.

    Saturn’s magnetic field is generated deep inside the planet. A core of rock and metal probably is surrounded by a layer of metallic hydrogen. The core and the hydrogen rotate at different rates. That creates a dynamo effect, like an electric motor, which generates the magnetic field.

    Charged particles get trapped in the field. And many of those particles come from Enceladus, a small moon. It squirts geysers of water into space. Radiation zaps some of the water molecules, giving them an electric charge. The Cassini spacecraft found that some of the particles then flow toward Saturn in waves. So do particles from the planet’s rings.

    Cassini recorded energy emitted by the waves. Mission scientists then converted some of the observations to sound. The sounds have been speeded up to make the patterns more audible.

    Cassini’s observations confirm that an electric “circuit” connects Saturn and Enceladus — powered by the giant planet’s magnetic field.

    And Saturn huddles quite close to our own Moon tonight. The giant planet looks like a bright golden star to the lower left of the Moon.


    Script by Damond Benningfield


  • Posted on 14 Oct 2018

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