StarDate PodcastAuthor: McDonald Observatory
07 Jul 2022

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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    Roswell Incident

    On a stormy night 75 years ago, something crashed in the desert near Roswell, New Mexico. The military says it was a balloon carrying top-secret instruments for sniffing out atomic-bomb tests in the Soviet Union. But others say it was a flying saucer carrying visitors from another world — the most famous and persistent UFO story to date.

    Saucer mania gripped the country that summer. Thousands of sightings were reported. And Roswell was a perfect place for a close encounter. Robert Goddard had tested his rockets just outside town during the 1930s. The first atomic bomb was detonated not a hundred miles away, the army was testing V-2 missiles at White Sands, and the local air base housed the world’s only atomic-bomb group.

    The story of the Roswell Incident broke on July 8th, 1947. Roswell Army Air Field issued a press release saying it had recovered a “flying disk” from a ranch near town. The army soon backtracked, saying the disk was nothing more than a weather balloon.

    The story died, but it didn’t rest in peace. Decades later, the base intelligence officer said he really had discovered a flying saucer. He said it was fashioned of a thin, tough metal covered with odd markings. Later versions of the story said investigators had recovered alien bodies, too.

    It’s a great story, but scientists will tell you it’s only that — a story — and we’ll tell you why tomorrow — on Star Date.
     

    Script by Damond Benningfield

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  • Posted on 06 Jul 2022

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    Messier 71

    Objects in the night sky aren’t always what they seem. Take Messier 71, a star cluster in Sagitta, the arrow. Originally, it was classified as an open cluster. In recent decades, though, it’s been reclassified as a globular cluster.

    Both types of clusters are big groups of stars that were born together, from the same cloud of gas and dust. But that’s where the similarities end.

    Most globular clusters contain a hundred thousand stars or more. The stars clump together in a tight ball. The clusters move well beyond the galaxy’s wide, flat disk. And their stars are among the oldest in the entire Milky Way — typically 10 billion years or older.

    Open clusters, on the other hand, generally contain a few hundred to a few thousand stars, they’re concentrated in the disk, and they tend to be young. The combined gravity of their stars isn’t enough to hold a cluster together, so most open clusters vanish within a couple of billion years.

    M71 has many of the traits of an open cluster: It’s in the galaxy’s disk, its stars are widely spread, and they’re younger than those in most globulars. But recent work has shown that M71 has more stars than first thought, the stars are older than expected, and the cluster travels far outside the galaxy’s disk. So M71 is a globular cluster — a not-too-big, not-too-tight family of ancient stars.

    M71 is due east at nightfall, a third of the way up the sky. Through binoculars, it looks like a small, hazy patch of light.
     

    Script by Damond Benningfield

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  • Posted on 05 Jul 2022

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    Mars Pathfinder

    In “The Martian,” when astronaut Mark Watney is stranded on the Red Planet, he turns to an old NASA mission for help. He travels to an ancient floodplain called Ares Vallis, where he grabs Mars Pathfinder. Later, he uses the parts to contact Earth and help arrange his rescue.

    “The Martian” is fiction, but Pathfinder was real. The lander and rover touched down on Mars 25 years ago today, and operated for almost three months. It was the first landing on Mars in two decades, and the first rover on any other planet.

    Pathfinder was designed mainly to test out new technologies for landing and operating on Mars. The craft bounced to a halt inside a cocoon of airbags, for example.

    Yet Pathfinder also carried scientific instruments, on both the lander and the rover, which was named Sojourner. The rover weighed about 25 pounds and was the size of a microwave oven. In all, it traveled roughly the length of a football field.

    It measured the composition of the rocks and soil, and found that liquid water had once flowed across the surface. And it demonstrated that a rover could be guided along the Martian surface, setting the stage for more-capable machines in the future.

    The lander monitored the weather and snapped more than 16,000 pictures. They revealed clouds of water ice in the early morning, and dust devils twirling across the desert landscape later in the day — a quarter of a century ago.
     

    Script by Damond Benningfield

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  • Posted on 04 Jul 2022

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    Far from the Sun

    It probably doesn’t sound right on a hot summer day, but Earth is actually farthest from the Sun for the entire year about now — more than 94 million miles.

    Earth’s orbit around the Sun is a bit lopsided. The average distance to the Sun is about 93 million miles. But during the year, the distance varies by about three percent in either direction.

    That slight variation is known as the “eccentricity” of the orbit. The orbits of all the planets are eccentric, but by different amounts. Venus’s orbit is the least eccentric — less than one percent. Mercury’s is the most eccentric — about 20 percent.

    In fact, it’s almost impossible for one body to have a perfectly circular orbit around another. Earth and the other planets of the solar system, for example, are pushed and pulled by the gravity of all the other planets. And collisions with other bodies have also skewed their orbits.

    As Earth’s distance from the Sun changes, so does the amount of energy we receive from the Sun. At our closest, in January, we get about six percent more total energy than we’re getting right now.

    Surprisingly, though, there’s little impact on Earth’s climate. The atmosphere and oceans store the heat and distribute it around the planet. That’s why we can have really hot days during summer here in the northern hemisphere, even though the Sun is three million miles farther than during the dead of winter.
     

    Script by Damond Benningfield

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  • Posted on 03 Jul 2022

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    Moon and the Sickle

    A bit of danger looms above the crescent Moon this evening: a sickle. It’s a curved pattern of stars that forms the head, mane, and heart of Leo, the lion. The handle is Regulus, the lion’s heart, to the left of the Moon. And Leo’s next-brightest star is near the middle of the sickle — looming above the Moon.

    Algieba is a binary — two stars locked in orbit around each other. The system is about 130 light-years away. By astronomical standards, that’s nothing more than a hop. And the two stars are separated by about four times the distance between the Sun and Pluto.

    Even so, the system still isn’t all that well understood. Astronomers know that both stars are into their final phase of life. They’ve used up the original hydrogen fuel in their cores, which has caused them to swell up. So both stars are a good bit bigger and brighter than the Sun.

    Estimates for one star say it’s about 30 times wider than the Sun, although it could be even bigger. The size of the other star is even less well known — astronomers can only make a rough guess.

    We do know that the better-known star has a planet. It’s about nine times the mass of Jupiter, the giant of our own solar system. It’s just a little bit farther out than Earth is from the Sun. There’s evidence of a second planet much farther out. But so far, that’s unconfirmed — one more thing to learn about a bright star system in the sickle.
     

    Script by Damond Benningfield

    Today's program was made possible by Mercer Caverns, in Calaveras County in California's historic Gold Country.

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  • Posted on 02 Jul 2022

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