StarDate

Billy Henry
  • 4,3 (6)
  • Astronomie
  • Tous les jours

StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

Épisodes

  1. -1 j

    Total Eclipse

    A total solar eclipse is coming up on Wednesday. The Moon will cover the Sun, turning day to night across a narrow slice of the globe. Parts of Alaska and the northeastern United States will see a partial eclipse. The timing of the eclipse is known down to the second, and has been for decades; astronomers can predict eclipses far into the future. But making such predictions isn’t easy. It requires a detailed knowledge of the Moon’s orbit around Earth, Earth’s orbit around the Sun, and even the shapes of Earth and the Moon. Just when the first prediction was made is unclear. There’s no doubt that people have been predicting lunar eclipses for thousands of years. But they’re easier to forecast. Earth’s shadow is roughly 35 times wider than the Moon’s, so you don’t need to be quite as precise to get it right. There are stories that the Chinese were predicting solar eclipses more than 4,000 years ago, but no confirmation. An eclipse in 585 BC that stopped a war supposedly was predicted by a Greek scientist. But many present-day scientists doubt that. The first confirmed prediction was made by Edmond Halley, using the laws of gravity recently devised by Isaac Newton. Halley forecast that an eclipse would cross England on May 3rd, 1715. And he was right. So the event is known as Halley’s Eclipse – honoring the prediction of an astronomical spectacle. Script by Damond Benningfield

  2. -2 j

    Moon and Gemini

    The Moon forms a nice triangle with the twins of Gemini at dawn tomorrow – the stars Castor and Pollux. Castor is to the left of the Moon, with brighter Pollux about the same distance to the lower left. Castor consists of six known stars. We haven’t found planets orbiting any of them. Pollux is a single star. And it has one likely planet – a giant that’s much heavier than any of the planets in our own solar system. The planet was discovered 20 years ago, by astronomers at McDonald Observatory. They’d seen evidence of the star earlier, but they couldn’t confirm it. The planet is known as Pollux b. It also has a formal name – Thestias – a variation of the name of Pollux’s mother in Greek mythology. The planet is almost three times the mass of Jupiter, the Sun’s largest planet. It’s farther from Pollux than Earth is from the Sun. But that’s much too close for the planet to be habitable. That’s because Pollux has passed beyond the prime phase of life. It’s puffed up to about nine times the Sun’s diameter, so it’s much brighter than the Sun. That extra energy makes Thestias much too hot to have liquid water at its surface – a key ingredient for life. The temperature could have been more comfortable in the past. The planet itself probably is a big ball of gas – not a good place to live. But if it has any moons, it’s possible that they could have offered better environments for life. Script by Damond Benningfield

  3. -3 j

    Moon and Mars

    Mars and the Moon hang out in tomorrow’s early-morning sky. Mars looks like a bright star to the right of the Moon at first light. The Moon is a thin crescent, and it’s getting thinner by the day. That means the Moon is about to cross between Earth and the Sun, so the Sun is lighting up less of the lunar hemisphere that faces our way. But you can make out the nighttime part of the disk because it’s lit up by earthshine – sunlight reflected from Earth. If anyone were standing on that part of the Moon, the earthshine would be bright enough to read by. That’s because Earth is in its gibbous phase – it’s almost fully in daylight. Earth is much bigger than the Moon, and its surface is much more reflective. So a gibbous Earth is dozens of times brighter than a gibbous Moon. From Mars, both Earth and the Moon appear gibbous. That’s because Earth and Mars line up more or less on opposite sides of the Sun. But over time, Earth and the Moon would appear to go through a full cycle of phases, just as the Moon does as seen from Earth. And their phase would always be the same. As the Moon orbits Earth, the angle between them would vary. So sometimes, Earth and the Moon would appear so close together that they’d form a single bright point. But at their widest separation, it would be easy to see them as individual points, with Earth especially bright, and the Moon a good bit fainter. Script by Damond Benningfield

  4. -4 j

    Moon and Taurus

    The terms that describe the phases of the Moon can be a little confusing. Take tomorrow morning, for example. From most of the United States, the Sun will light up one-quarter of the lunar hemisphere that faces Earth. You might think that would make it a “quarter” Moon – but no. A “quarter Moon” doesn’t describe the Moon’s appearance – it describes the position in its month-long cycle of phases. The cycle begins when the Moon is new. The Moon crosses the line between Earth and the Sun then, so it’s hidden in the Sun’s glare. A bit more than a week after that, the Moon is a quarter of the way through the cycle – it’s at first quarter. It lines up at a right angle to the Earth-Sun line, so the Sun lights up half of the visible disk. A week later comes full Moon. And a week after that comes last quarter – three-quarters of the way through the cycle. Once again, half of the lunar disk is illuminated – but it’s the opposite half from the first-quarter Moon. Then the Moon rolls back around to new – starting a new cycle. The next cycle starts on Wednesday. And this time it brings a rare treat – a total solar eclipse. In the meantime, look for the Moon passing through Taurus tomorrow. Aldebaran, the bull’s bright eye, is to the right of the Moon. Elnath, the tip of one of its horns, is closer to the lower left of the Moon. As a bonus, Mars is below them, and the Moon will pass close to it on Sunday. Script by Damond Benningfield

  5. -5 j

    Dog Days

    The Dog Star is just beginning to emerge from the Sun’s glare in the dawn sky. By tradition, that means we’re just getting into the Dog Days of summer. Sirius is the brightest star in the night sky. It’s climbing into view in the morning glow of the brightest star in all the sky – the Sun. Sirius is quite low in the east-southeast shortly before sunrise. It’s best seen from the southern tier of states, although it’ll pull into better view from the northern states over the coming days and weeks. Sirius is also the leading light of the constellation Canis Major, the big dog, so it’s known as the Dog Star. And that’s where we get the name for this part of summer – the Dog Days. Sirius makes its closest approach to the Sun during summer, disappearing for a few weeks in the Sun’s glare. In ancient times, it returned to view in the morning by early July – just as the weather was reaching its hottest. At the time, it seemed logical to associate the bright star with the sweltering weather. So the people of ancient Greece and Rome named that stifling time of year in the star’s honor. Thanks to an effect known as precession, the stars shift position with respect to the Sun over the centuries. So Sirius now returns to view a few weeks later than it did thousands of years ago. So the heat is already in full force at northern latitudes – the Dog Days of summer. Script by Damond Benningfield

  6. -6 j

    NGC 6397

    NGC 6397 seems like a pretty ordinary globular star cluster. It’s not especially big or bright, and nothing about its stars is going to strike anyone as odd. Yet it’s been an important astronomical laboratory. Among other things, it’s helped astronomers determine the age of the galaxy, and the minimum “weight” of a star. NGC 6397 is in the constellation Ara, the altar. It’s below the tail of Scorpius, the scorpion. That puts it so far south that it’s visible only from the southernmost United States. Hubble Space Telescope has monitored the cluster for decades. It contains several hundred thousand stars, packed into a ball only a few dozen light-years across. The Milky Way contains about 150 of these clusters, which are the galaxy’s oldest inhabitants. Over the decades, Hubble has monitored many of the cluster’s stars. The observations helped astronomers lock down the minimum mass for an object to shine as a true star – about eight percent the mass of the Sun. Another set of observations helped measure the cluster’s distance – just 7800 light-years – one of the closest of all globulars. That number is important for determining the cluster’s age – 13.4 billion years. That means that NGC 6397 – and its home galaxy, the Milky Way – took shape when the universe was just 400 million years old. Script by Damond Benningfield

  7. 4 août

    The Altar

    The gods of ancient Greece weren’t great parents. One of the ancient gods known as the Titans, for example, swallowed his newborn children. Eventually, though, the kiddos escaped and overthrew him. Their victory is commemorated in the stars, as the altar where they swore allegiance to each other. It’s the constellation Ara, and it’s below the tail of the scorpion. In the story, Cronus was the king of the Titans. He’d come to power by defeating his own father. A prophecy said that one of his children would defeat him. To prevent that, he swallowed each of his first five children. But his wife, Rhea, got tired of that plan. When the last child was born, she hustled him away to an island and gave Cronus a rock wrapped in a blanket. That child was Zeus. When he grew up, he returned home and forced his dad to cough up his brothers and sisters. They pledged to defeat the Titans, and won a 10-year war. Zeus became the king of the new gods and ruler of the sky. To celebrate the victory, he placed the altar among the stars. The altar is so far south that most of it’s visible only from far-southern parts of the United States – places like Florida, South Texas, and especially Hawaii. Ara is one of the smaller constellations, with only a couple of moderately bright stars. But it does have some good deep-sky objects, and we’ll talk about one of them tomorrow. Script by Damond Benningfield

  8. 3 août

    Desolate Planet

    The formal name for a planet almost 50 light-years from Earth is Kua’Kua – a Costa Rican name that means “butterfly.” But there’s nothing beautiful or delicate about this world. Its surface is a desolate landscape of volcanic rock. The planet is in the system LHS 3844. Its star is a cool, faint ember known as a red dwarf. Kua’Kua – LHS 3844 b – is a super-Earth. It’s bigger and heavier than Earth, and it’s made of rock and metal. The planet is only about half a million miles from the star, and the same hemisphere always faces the star. So the dayside sizzles at more than 1300 degrees Fahrenheit. Every 11 hours, the planet passes behind the star as seen from Earth. Astronomers have watched several passages with Webb Space Telescope. Watching before and after a passage revealed the combined make-up of the star and planet. But when the planet disappeared, that left only the star in view. Comparing the readings revealed details about the surface of the planet. In fact, it’s the first “exoplanet” for which we have such a close look. The surface appears to be made of dark volcanic rock that could have been deposited recently, making it fairly smooth and unbroken. But the surface also could be much older. In that case, a constant pounding by radiation and meteorites could have pulverized the surface. Either way, Kua’Kua is not a good place to go hunting for butterflies. Script by Damond Benningfield

  9. 2 août

    Moon and Saturn

    There’s just one place to catch a wave outside Earth: Titan, the largest moon of Saturn. It’s the only other world in the solar system with bodies of liquid on its surface. And the waves there could reach heights of 10 feet. But future surfers will need to dress carefully; the surface temperature is almost 300 degrees below zero. Titan is half-again the size of Earth’s moon, and it has a dense atmosphere. Rain fills its lakes and seas with liquid methane, ethane, and nitrogen. The largest sea covers about 200,000 square miles – twice the area of all the Great Lakes combined. It could be several hundred feet deep. The Cassini spacecraft used radar to measure Titan’s ponds. It saw waves of no more than an inch or so high. But a recent study says the waves could get a lot bigger. Based on 20 years of observations of waves on Lake Superior, scientists built a computer model of how waves might work on other worlds. The model accounted for gravity, the pressure of the atmosphere, and the properties of the liquid. When the model was applied to Titan, it showed that even gentle breezes could whip up some big waves. But the waves would move more slowly than those on Earth – a slow-motion trip across the sea. Saturn looks like a bright star close to our moon the next couple of mornings. It’ll stand to the left of the Moon at dawn tomorrow, and the lower right of the Moon on Tuesday. Script by Damond Benningfield

  10. 1 août

    Morning Mercury

    The dawn twilight has a bright visitor the next few mornings – the planet Mercury. It’s farthest from the Sun for its current morning appearance. It looks like a bright star, but it’s so low in the sky that it’s tough to find. Mercury holds an important spot in the history of astronomy and physics. It provided some of the first confirmation of General Relativity – Albert Einstein’s theory of gravity. Mercury’s orbit around the Sun is lopsided, so the planet’s distance from the Sun varies. For a long time, astronomers had seen that the orbit’s closest point shifted a tiny bit over time. Isaac Newton’s laws of gravity explained most of the difference. But there was still a tiny amount that couldn’t be accounted for. Einstein’s theory of gravity held that massive bodies warp the space around them. Since Mercury is the Sun’s closest planet, its orbit is influenced by that “warpage” more strongly than any other planet’s. In fact, general relativity accounted precisely for the shift in the orbit. So Mercury’s orbit provided some of the first evidence to support general relativity – a new way of thinking about gravity. Look for Mercury quite low in the eastern sky during the waxing twilight. It’ll shine a little brighter each day over the next few mornings. But it’ll also drop a little closer to the Sun, so you’ll need a clear horizon to spot it. Tomorrow: catching waves. Script by Damond Benningfield

  • 10 épisodes

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À propos

StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

Informations

  • Créateur
    Billy Henry
  • Années d’activité
    2017 - 2026
  • Épisodes
    10
  • Classement
    Tout public
  • Copyright
    © 2022 The University of Texas McDonald Observatory
  • Site Web de l’émission
    StarDate

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