StarDate PodcastAuthor: McDonald Observatory
27 Feb 2017

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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    Annular Eclipse

    Skywatchers in parts of South America and Africa are in for a treat today: a solar eclipse. Unfortunately, though, it’s not a total eclipse, but an annular one. That means a thin but bright ring of sunshine will outline the intervening Moon.

    Solar eclipses occur when the new Moon passes directly between Earth and the Sun. When the alignment is just right, the Moon covers the entire solar disk, briefly turning day into an awe-inspiring twilight.

    But the Moon follows a slightly elongated path around Earth. So if an eclipse occurs when the Moon is farthest from us, the Moon isn’t quite big enough to cover the entire Sun, leaving a ring of sunlight.

    And that’s just what happens this morning across a narrow path that stretches from South America, across the Atlantic Ocean, and into southern Africa. The Moon will cover up to 98 percent of the Sun, leaving plenty of sunlight. Still, the sky will turn dusky, the air will get cooler, and beams of sunlight shining through leafy trees will project bright rings on the ground — good clues that something important is happening in the sky.

    This is the first of two solar eclipses this year. The second takes place in August. It will slice across the width of the United States. Even better, it’s a total eclipse, so the Moon will cover the entire Sun. That will briefly expose the Sun’s hot but faint outer atmosphere, known as the corona — one of the most awe-inspiring of all astronomical sights.

    More about the Sun tomorrow.


    Script by Damond Benningfield

  • Posted on 26 Feb 2017

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    Mars and Uranus

    The giant planet Uranus hasn’t received a visit from Earth since 1986, when Voyager 2 gave us our only close-up view of the planet and its known moons. The spacecraft also found several new moons. And scientists recently have seen hints of two more satellites in the Voyager observations.

    Uranus has 27 known moons. That’s a lot fewer than Jupiter and Saturn. Perhaps that’s because Uranus is smaller and less massive. Or perhaps it’s just harder to find moons because Uranus is farther away, and it’s farther from the Sun, so there’s less light to reveal its moons.

    But scientists analyzing old Voyager data have found wavy patterns in two of the rings of Uranus. Each pattern may arise from the gravitational influence of a small, dark moon just beyond the ring. If the moons exist, they’re no more than a few miles across — smaller than any other Uranian moon yet seen.

    Hubble Space Telescope may be able to find them. If not, though, a future mission to the planet may spot these elusive bodies — or else rule out their existence.

    And with binoculars, the next few evenings offer a good chance to look for Uranus. Tonight, it stands close to the upper left of Mars, which itself is to the upper left of Venus, the “evening star.” Through binoculars, the solar system’s third-largest planet looks like a faint star, with perhaps a hint of blue-green. Mars and Uranus will stand almost side by side tomorrow night, with Mars above Uranus on Monday.


    Script by Ken Croswell, Copyright 2016

  • Posted on 25 Feb 2017

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    Supernova 1987A III

    Astronomers have kept a keen eye on Supernova 1987A since it first flashed in the night sky 30 years ago this week. It was the closest and brightest supernova in centuries — bright enough to see with the unaided eye, and to study in detail with telescopes.

    They’ve watched the explosion fade away; a blast wave from the star ram into rings of material around the star; and atoms from the exploding star stick together to make solid particles.

    The blast wave raced outward at millions of miles per hour. A few years after the explosion, it rammed into rings around the star — one around its equator, and two others above its poles.

    Those rings probably formed after the star expelled a lot of material about 20,000 years before it exploded — perhaps as the result of a merger with another star. The supernova shockwave heated the rings, causing them to glow. As the shockwave continues to expand, it’s ripping the rings apart.

    As the exploding material expands and cools, atoms are sticking together to form solid particles. How and where they form helps astronomers better understand the original star and its explosion. It also helps them understand how the particles get scattered through space.

    Other supernovae are thought to have contributed many of the particles that make up our planet and our own bodies. So studying the particles around 1987A can provide new insights into the birth of our own solar system — continuing discoveries from a fascinating supernova.


    Script by Damond Benningfield

  • Posted on 24 Feb 2017

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    Supernova 1987A II

    Thirty years ago today, scientists caught the ghosts of an exploding star. The discovery helped confirm how the star died, and the kind of corpse it likely left behind.

    Supernova 1987A was the brightest and closest supernova in centuries. It exploded in a small galaxy that’s about 165,000 light-years away.

    Theory said the explosion took place when the star’s core could no longer produce energy from nuclear reactions. Without that radiation to push outward, the core collapsed. The star’s outer layers fell inward, then rebounded and blasted into space, forming the supernova.

    The collapsing core was squeezed so tightly that electrons and protons were smashed together to form neutrons and neutrinos. The neutrons stayed in the core, forming a super-dense neutron star.

    But the neutrinos raced outward. These ghostly particles almost never interact with other matter. The core’s collapse should have produced so many of them, though, that if even a tiny percentage interacted with the surrounding layers of gas, they’d help power the supernova. The rest would race into space unimpeded — including many aimed at Earth.

    And on February 23rd, 1987, detectors on Earth caught a couple of dozen neutrinos from the supernova — a huge haul. A few hours later, the light from the blast reached Earth as well. The neutrinos matched what the theory predicted — helping to confirm what happens deep in the heart of a supernova.

    More tomorrow.


    Script by Damond Benningfield


  • Posted on 23 Feb 2017

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    Supernova 1987A

    Astronomers have been hunting a neutron star for 30 years. They know where it is, and they’re almost certain it’s there. Yet they still can’t see it, even with the most powerful telescopes on the ground and in space.

    The neutron star would be the remnant of Supernova 1987A, an exploding star that was first seen 30 years ago this week. It’s in the Large Magellanic Cloud, a galaxy that’s about 165,000 light-years away.

    At that range, 1987A is the closest supernova seen since the invention of the telescope. That’s allowed astronomers to study it in greater detail than any other supernova.

    Their observations have shown that the exploding star was a blue supergiant. That would make it similar to Rigel, the brightest star of Orion, which is high in the south at nightfall, to the lower right of Orion’s three-star belt.

    The star exploded when it could no longer produce nuclear reactions in its core. The core collapsed, and the star’s outer layers blasted into space, forming the supernova.

    From the mass of the original star, astronomers expected the collapsed core to become a neutron star — a super-dense ball no bigger than a city, but about twice as heavy as the Sun. But despite a diligent search, they haven’t seen a thing. That could mean that the core collapsed even more, forming a black hole. Or it could mean that the neutron star is simply hidden from view — waiting for better observations to reveal its presence.

    More about 1987A tomorrow.


    Script by Damond Benningfield

  • Posted on 22 Feb 2017


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