StarDate PodcastAuthor: McDonald Observatory
16 Jan 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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    Kepler 90

    If you squished the planets of our solar system much closer to the Sun, you’d have something similar to the system known as Kepler 90. The smaller planets are closer to the star, while the giant planets are farther out.

    The star is bigger, brighter, and heavier than the Sun, and about half the Sun’s age. Most important, it’s the only star system besides ours with eight known planets. The planets that are close to the star are a little bigger than Earth, the ones in the middle are bigger still, and the two at the outer edge of the system are giants.

    There’s one big difference between Kepler 90 and the solar system. The Sun’s farthest major planet is Neptune — about 30 times farther from the Sun than Earth is. But at Kepler 90, the most-distant planet is only as far out as Earth. That means the planets are crowded together — smushed in close to their sun.

    When our solar system was young, its giant planets moved much closer to the Sun. That could have scattered any planets that were even closer. But the planets of Kepler 90 appear to be stable. They align in such a way that the gravity of each planet helps keep the others in place — a tightly packed family of planets.

    Kepler 90 is in Draco. Although the star is much too faint to see without a telescope, you can get an idea of its location. It’s low in the northwest at nightfall, to the upper right of the bright star Vega. And it’s in the northeast at dawn, to the left of Vega.
     

    Script by Damond Benningfield

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  • Posted on 15 Jan 2022

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    The Leviathan

    A beautiful spiral galaxy spins into view in the northeast this evening, near the tip of the Big Dipper’s handle. It actually consists of two galaxies: a large one that’s interacting with a smaller one, with a “bridge” of stars and gas between them.

    M51 is the first galaxy whose spiral nature was seen. It was revealed by the Leviathan of Parsonstown — the largest telescope in the world at the time. It entered service in 1847 — 175 years ago.

    The Leviathan was the invention of William Parsons, the Earl of Rosse, in Ireland. He owned and operated a large estate, but was also interested in astronomy. And he designed a telescope that far outclassed anything else of the time.

    Its main mirror spanned six feet — two feet wider than the second-largest. The metal mirror had to be taken out and polished every six months, so Parsons made two of them. The mirrors fit into a tube that was 58 feet long. It was suspended between two brick walls, and assistants used cables and pulleys to move it.

    Parsons did some of the observing himself, but he also hired a professional. Together, they studied the odd, fuzzy objects known as nebulae. Astronomers hadn’t figured out what they were. The Leviathan revealed that some are clusters of stars. But more than a hundred were spirals. Decades later, astronomers showed that these objects are separate galaxies of stars — beautiful spirals first resolved with the Leviathan of Parsonstown.
     

    Script by Damond Benningfield

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  • Posted on 14 Jan 2022

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    Moon and Aldebaran

    The Moon is bashful — it never shows us its backside. The same hemisphere always faces Earth. There’s a bit of a “wobble” that allows us to see around the edges a little. In all, though, two-fifths of the Moon is always hidden from view.

    That part of the Moon is known as the back side, the far side, or the dark side.

    People sometimes complain when it’s called the dark side. They argue that, over a cycle of phases, the near side and the far side receive equal amounts of sunlight. As a result, the far side is no darker than the side we always see. And they’re absolutely right.

    The “dark-side” tag doesn’t refer to how much sunlight it gets, though. Instead, it refers to the fact that the far hemisphere is hidden from us. And until the Space Age, we had no idea what it looked like — it was completely unknown. It’s a lot like dark energy. It might not be dark, and it might not even be energy. For now, though, it remains unknown — a “dark” mystery for scientists to solve.

    Today, of course, we know a lot about the dark side of the Moon. Orbiting spacecraft have mapped it in great detail. It has fewer dark volcanic plains than the near side, and lots more of the jumbled-up bright areas.

    Most of the near side is in good view tonight — lit up by the Sun. And the bright star Aldebaran is close by. They wheel high across the sky during the night and set in the wee hours of the morning.

    Tomorrow: Putting a leviathan to work.
     

    Script by Damond Benningfield

    Support McDonald Observatory


  • Posted on 13 Jan 2022

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    Life in the Red

    Life on Earth is sustained by photosynthesis. Plants and some bacteria combine water, carbon dioxide, and sunlight to make sugars and oxygen, which they release into the air and water. Without that process, modern life wouldn’t exist.

    Scientists have been wondering whether the most common stars in the galaxy might sustain photosynthesis on their planets.

    M dwarfs are the smallest and coolest of all stars. But they probably account for more than half the stars in the galaxy, which makes them of special interest in the search for life. In addition, M dwarfs live a long time, so there’s plenty of time for life to develop. And because the stars are small and cool, any possible life-bearing planets would be close in, making them easier to find.

    The light produced by M dwarfs is different from sunlight. It’s much redder, and there’s a lot more infra-red. Scientists have considered whether those wavelengths could support photosynthesis.

    One study said that M dwarfs don’t produce enough ultraviolet light. But another said the spectrum of an M dwarf should be just fine for life. And yet another one, released last year, agreed. That study subjected bacteria that live by photosynthesis to lighting conditions like those around M dwarfs. And the organisms did well.

    The issue is complicated by the fact that most M dwarfs produce big outbursts of X-rays. But it seems at least possible that microscopic life could get by on these little but common stars.
     

    Script by Damond Benningfield

    Support McDonald Observatory


  • Posted on 12 Jan 2022

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    Double Earths?

    Astronomers have discovered thousands of planets in other star systems. So far, though, only a few can possibly be described as “Earth-like.” And two of those are in the same star system.

    Teegarden’s Star is a close neighbor — just 12 light-years away. But it’s so small and faint that it was discovered only a couple of decades ago. It’s a fraction the size and mass of the Sun, and less than a thousandth as bright.

    Its two known planets are cataloged as objects “b” and “c” in the system. Both planets are just a few percent bigger and heavier than Earth. And both of them appear to lie in the “habitable zone” — the region where temperatures are just right for life. Since the star is so feeble, that zone is quite close — just a few million miles out.

    A study a couple of years ago said that both planets could have comfortable atmospheres and liquid water. But a study last year said otherwise. It found that gravitational interactions between the planets and the star could have caused problems. They could have turned b into something like Venus, with a hot, thick atmosphere. And c could have been turned into a world of volcanoes — making both planets unfit for life as we know it.

    Teegarden’s Star is in Aries, the ram, which is high in the southern sky on January evenings. The star is much too faint to see without a telescope. But its location is easy to spot tonight — just above the Moon.

    More about extraterrestrial life tomorrow.
     

    Script by Damond Benningfield

    Support McDonald Observatory


  • Posted on 11 Jan 2022

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