StarDate

Billy Henry
  • 4.6 (242)
  • ASTRONOMY
  • UPDATED DAILY
StarDate

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

Episodes

  1. 1D AGO

    Moon and Spica

    You don’t need a thermometer to take a star’s temperature. All you need is your eyes. That’s because a star’s color is a direct result of its surface temperature. The hottest stars glow blue-white, while the coolest look reddish orange. One example is the star Spica. It rises below the Moon this evening, and the Moon moves closer to it during the night. Spica is a system of two stars locked in a tight orbit around each other. Both stars are bigger, heavier, brighter, and hotter than the Sun. The main star, Spica A, is by far the more impressive member of the system. Its surface is a broiling 45 thousand degrees Fahrenheit, compared to just 10 thousand degrees for the Sun. That makes the star look blue-white. Under dark skies, with no moonlight, that color is pretty easy to see with the eye alone. We can make out the color because Spica is both close and especially bright – more than 2,000 times the Sun’s brightness at visible wavelengths. But if our eyes could see other forms of energy, Spica A would appear even brighter. Because its surface is so hot, the star emits most of its energy as ultraviolet light – wavelengths that are too short for the eye to see. So when you add up all wavelengths, Spica A glows more than 20 thousand times brighter than the Sun – a blue-white spotlight that tonight snuggles close to the Moon. Tomorrow: bellying up to a cosmic bar. Script by Damond Benningfield

    2 min

  2. 2D AGO

    Julian Dates

    Happy Friday! It’s the 73rd day of the year. And to astronomers and a few others, it’s day 2,460,749. That’s the tally under the Julian Date system. Its starting point was more than 6700 years ago. The system was created by Joseph Scaliger, a French scholar and religious leader, in 1583. The system was named for his father, Julius. Scaliger was trying to integrate the many calendars that had been used throughout history. He picked a starting point long before any known calendar system. In the modern calendar, it was November 24th, 4714 B.C. That’s a date when long cycles of the Sun, Moon, and an ancient Roman cycle for collecting taxes all intersected. Astronomers use the Julian Date system to record observations and events. And they don’t add minutes or seconds – they convert those to decimals. That makes it easier to compare the timing of their work to observations made long ago, or under different calendar systems or time zones. They don’t have to figure out the permutations of the calendars or other details – just subtract one date from another to find the difference. A Julian day begins at noon Universal Time – 7 a.m. Central Daylight Time. So day 2,460,749 begins at 7 a.m. today, and ends 24 hours later – on the Ides of March. Script by Damond Benningfield

    2 min

  3. 3D AGO

    Lunar Eclipse

    The Moon will suffer a partial power failure tonight. It will grow dark as it passes through Earth’s shadow – creating a total lunar eclipse. Lunar eclipses occur only at full Moon, when the Moon aligns directly opposite the Sun. The Moon’s orbit is tilted a bit, so most months our satellite world passes above or below the shadow. But when the geometry is just right, the Moon passes through part or all of the shadow, creating a partial or total eclipse. For this eclipse, the Moon will plunge through the heart of the shadow, creating totality. Almost all of the Americas will see the entire eclipse sequence. The Moon will dip into Earth’s shadow, become fully immersed, then slip back into the sunlight. The Moon won’t go completely dark, though – sunlight scattered through Earth’s atmosphere will give it a deep orange or red glow. The partial eclipse, when the Moon is only partially covered by the shadow, begins at 12:09 a.m. Central Time, and will last about three and a half hours. Totality begins at 1:26 a.m., and will last an hour and five minutes. Anyone standing on the Moon would see a total solar eclipse, with Earth crossing in front of the Sun. Sunlight would create a bright orange outline around Earth. NASA and China plan to establish outposts near the Moon’s south pole in the coming decades. So before long, we may see some stunning views of these colorful alignments from an entirely new perspective. Script by Damond Benningfield

    2 min

  4. 4D AGO

    Earth’s Shadow

    It’s hard to look away from a stunning sunset. If you turn around, though, you might see another colorful show, although one that’s more subdued than the main event. As the Sun drops below the western horizon, Earth’s shadow climbs into view above the opposite horizon. It forms a dark blue band that climbs higher as the evening progresses. It’s also visible in the dawn sky, shortly before sunrise. The band forms a thin wedge where it intersects the horizon, and grows thicker as it approaches the point directly opposite the Sun. At the same time, a band of bright pink appears above the shadow. It’s known as the anti-twilight arch. It’s created when the red hues of sunlight strike particles in the atmosphere on the opposite horizon, causing them to shine reddish pink. It’s also known as the Belt of Venus. And right now, Venus – the “evening star” – is directly opposite that band in early evening. As the fuzzy line that separates the two bands climbs higher, it gets even fuzzier. Soon, it reaches a height where the atmosphere is thinner, so less red light is scattered there. The pink belt fades to blue, and both the Belt of Venus and Earth’s shadow merge into the darkening night. Earth’s shadow extends far into space. When the geometry is just right, the Moon passes through the shadow, creating another beautiful show: a lunar eclipse. And an eclipse is coming up tomorrow night. We’ll talk about that on our next episode. Script by Damond Benningfield

    2 min

  5. 5D AGO

    Moon and Regulus

    Hundreds of valleys meander across the Moon. Many of them look like river valleys on Earth. And some of them might have been formed in the same way – by flowing liquid. There’s no water on the Moon, though, so the channels were carved by lava. The channels are known as rilles – from a German word that means “grooves.” They come in three basic forms. One form probably took shape as pieces of crust pulled apart, leaving a wide, straight gap between them. The second category follows a gently curving path. These rilles probably formed when a river of lava cooled and condensed, sinking into the ground. The final group looks most like Earthly riverbeds. “Sinuous” rilles twist and turn across the surface – sometimes dramatically. They probably formed from flowing lava. The lava either carved a channel on the surface or tunneled below the surface, and the empty tube later collapsed. Sinuous rilles often begin at a crater, which probably is the “vent” where lava poured onto the surface. Apollo 15 landed near one of these rilles. Known as Hadley Rille, it’s about 75 miles long, a mile wide, and a thousand feet deep. Astronauts looked into its depths and gathered samples from its rim – the edge of a “river valley” on the Moon. The almost-full Moon is in the east at nightfall. Regulus, the brightest star of Leo, is close below it. They move closer during the night, and are almost touching as they set, before dawn. Script by Damond Benningfield

    2 min

  6. 6D AGO

    Venus and Mercury

    The Sun’s closest planets are appearing close to each other in the early evening sky. Venus is the brilliant “evening star.” Mercury is close to its lower left this evening, but will slide above Venus over the next few nights. Mercury is the Sun’s closest planet. It’s also the smallest planet – a dense ball of rock and metal about half-again the diameter of the Moon. At its equator, noontime temperatures climb to about 800 degrees Fahrenheit. But some deep craters near the poles never see daylight. So temperatures there hit a couple of hundred below zero. That’s not the case on Venus – not even close. Even though Venus is tens of millions of miles farther from the Sun, it’s much hotter. That’s because Venus is more massive than Mercury, so its surface gravity is stronger. That’s allowed Venus to hold onto its atmosphere. Heat from the Sun has baked gases out of its rocks, making the air especially thick – the surface pressure is about 90 times the pressure on Earth. And the atmosphere is made mainly of carbon dioxide, which traps heat, preventing the heat from escaping into space. So the average temperature across the planet is about 865 degrees. It’s blazing hot even at the poles. The only places that aren’t that hot are mountaintops – the cool spots on the solar system’s hottest planet. Venus and Mercury are quite low in the west during evening twilight. They’ll stand side by side in a couple of days. Script by Damond Benningfield

    2 min

  7. MAR 9

    Pole Stars

    The North Star is one of the most important beacons in the sky. It serves as a compass, pointing the way due north. And it also serves as the hub of the sky – all the other stars appear to circle around it as Earth turns on its axis. More than 4,000 years ago, the architects of Egypt used the North Star to align the pyramids of Giza. And more than four decades ago, Apollo astronauts used it to help guide them to the Moon. But the two groups were aided by different north stars. The Egyptians used a star called Thuban, in Draco, the dragon. The astronauts used Polaris, at the end of the handle of the Little Dipper. Thuban didn’t explode or fade away – it’s still in plain sight. Instead, Earth’s axis turned away from the star – an effect called precession. It’s caused by the gravitational tug of the Sun and Moon, which cause our planet to wobble like a spinning top. As it wobbles, the axis points toward different stars. Four thousand years ago, it aimed at Thuban. Today, it aims at Polaris. Over the next century, the pole will take slightly better aim at Polaris. Right now, the star is about two-thirds of a degree from where the axis is pointing. Around the year 2100, it’ll be less than half a degree from that spot. After that, though, the pole will move away from Polaris. By around the year 4100, it’ll take aim at a star that’s one constellation over, in Cepheus – a North Star to guide future generations. Script by Damond Benningfield

    2 min

  8. MAR 8

    Moon and Mars

    Follow the water is NASA’s mantra for Mars exploration. Water is a key ingredient for life. So missions to the Red Planet have sought out regions that show evidence of water, either past or present. Such regions should be the most likely to hold evidence of life. But some scientists think the search ought to be expanded. Don’t just follow the water – follow the salt. The Viking landers of the 1970s carried several experiments to look for microscopic life. They fed a bit of Martian dirt into small chemical laboratories. The experiments added water, nutrients, or other ingredients. They then looked for gases or radioactive elements that might be produced by such organisms. A couple of the experiments found just what they were looking for. But most scientists later decided that the evidence was produced by chemical reactions. Others maintained that they really were produced by life. A recent paper argued that the composition of the soil at the landing sites was very salty. On Earth, some organisms live in such conditions. They draw their water from the salts. But if you add water, they die. So the Viking landers might have found life – then killed it off. So NASA might need to expand the search – by following the salt. Mars is especially easy to see tonight. It’s right next to the Moon at nightfall, and looks like a bright orange star. They’ll be a little farther apart as they set, in the wee hours of the morning. Script by Damond Benningfield

    2 min

  9. MAR 7

    Dark Energy

    For centuries, the far side of the Moon was called the dark side – not because it doesn’t get any sunlight, but because it was always hidden from view. Astronomers couldn’t shed any light on what it looked like – making it dark. Today, scientists are trying to shed a little light on another darkness – dark energy. It appears to be making the universe expand faster as it ages. And it accounts for about 70 percent of all the energy and matter in the universe. But so far, there’s no widely accepted explanation for what constitutes dark energy. Scientists have a lot of ideas, but none of them has been confirmed. One of the leading ideas is that dark energy is constant, because it comes from the vacuum of space itself. As the universe expands, the amount of matter stays the same, but it’s spread across a greater and greater volume. That means each bit of matter feels a weaker gravitational pull from all the other matter. At the same time, as more space is created, so is more dark energy. It overpowers gravity, causing the universe to expand faster. Some recent research has found support for that idea by looking at how the universe has expanded over the eons. But the same result could support the idea that dark energy isn’t constant – that it’s evolved over time. That has important implications for the fate of the universe – whether it will continue to expand forever, or someday collapse – ending in a “Big Crunch.” Script by Damond Benningfield

    2 min

  10. MAR 6

    Martian ‘Wiggle’

    If astronomers ever see a “wiggle” in the orbit of Mars, it might be the fault of a passing black hole. A study last year suggested that tiny black holes might pass through the inner solar system once every decade or so. They’re not likely to run into Earth or anything else. But their gravity might give the inner planets a minuscule nudge. And if Mars is the one getting shoved, we might be able to measure it. The universe might be filled with “primordial” black holes created in the Big Bang. They’d be as tiny as atoms, but as massive as asteroids hundreds of miles wide. Such black holes might account for much of the “dark matter” in the universe. It makes up about 85 percent of all matter, but it produces no energy, so we can’t see it. We know it’s there only because its gravity pulls on the visible matter around it. Scientists have suggested it might consist of subatomic particles, but efforts to find them have come up empty. If primordial black holes make up the difference, they would zip through the solar system fairly often. The study found that it would be hard to measure the effect of such a black hole on Earth or the Moon. But if one passed within a few hundred million miles of Mars, its gravity could change the planet’s orbit by a tiny amount. Over a few years, the change would add up, allowing astronomers to measure it. So if the orbit of Mars gives a little wiggle, it just might be caused by a passing black hole. Script by Damond Benningfield

    2 min
  • 10 Episodes

    4.6
    out of 5
    242 Ratings

    About

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

    Information

    • Creator
      Billy Henry
    • Years Active
      2017 - 2025
    • Episodes
      10
    • Rating
      Clean
    • Copyright
      © 2022 The University of Texas McDonald Observatory
    • Show Website
      StarDate

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