StarDate Podcast

Pluto isn’t an easy target for skywatching. It’s so small, remote, and faint that it’s visible only through a good-sized telescope. Today, though, you can get a good idea of its location in the sky because the Moon will pass quite close to it. In fact, as seen from some parts of the globe, the Moon will pass in front of Pluto, briefly blocking it from view. Pluto is a fascinating world. Although it’s only about two-thirds the diameter of the Moon, it has a dynamic surface. Massive glaciers...

We don’t know whether anyone will ever establish an outpost on the Moon. If they do, though, the residents will need a source of supplies, including water, oxygen, rocket fuel, and many others. And they may be able to get some of those things from the Moon itself. They’re warehoused at the Moon’s poles — in big deposits of frozen water. The first evidence of that ice was obtained a quarter century ago, by a spacecraft in lunar orbit. And the strongest evidence yet was obtained by another...

There are only two bodies in the solar system where rain falls on a solid surface, carving riverbeds and filling lakes and seas. One of them is Earth. The other is Titan, the largest moon of Saturn. But there’s one big difference between them: Titan is more than 300 degrees colder than Earth is, so the liquid that falls from its skies is not water, but methane. Titan is the second-largest moon in the solar system — about as big as the planet Mercury. But it ranks second to none in the...

Shortly after John Quincy Adams became president, in 1825, he asked Congress to build a “lighthouse of the skies” — a national astronomical observatory. Congress rejected the idea. But Adams didn’t lose his enthusiasm for astronomy. In fact, his last public speech came 175 years ago today, at the founding of the Cincinnati Observatory — the first major public observatory in the United States. The observatory was the handiwork of Ormsby MacKnight Mitchel, a teacher and astronomer. He raised...

One threat facing our technology-powered world is space weather. Storms on the Sun can cause big problems here on Earth. They can knock out power grids, disrupt some radio signals, and damage or destroy satellites. We began to learn how space weather works in the 1960s, with a network of Sun-watching spacecraft. The fourth and final member of the network, Pioneer 9, was launched 50 years ago today. The Pioneers monitored solar activity. They measured the solar wind, for example — a stream...

Galaxies frequently collide with each other. And the results can be spectacular. The encounters can pull out great streamers of stars, making the galaxies look like tadpoles. They can trigger intense bouts of starbirth. And they can scramble a galaxy’s stars and gas clouds, creating beautiful rings that look like cosmic bulls-eyes. One well-known example is the Cartwheel galaxy. It’s in the constellation Sculptor, which is low in the south on November evenings. The Cartwheel spans about...

The Milky Way bar is more than just candy. It’s a key part of our home galaxy. That’s because the Milky Way is a barred spiral. Its beautiful spiral arms extend from the ends of a thick bar of stars that spans the galaxy’s middle. And the Milky Way isn’t alone. In today’s universe, up to two-thirds of all spiral galaxies appear to have bars. Simulations reveal that bars should be a natural development for spiral galaxies. Gravitational disturbances can cause stars in a spiral to follow...

Few sights in the universe can beat a spiral galaxy. Beautiful streamers wrap around a dense core, creating a whirlpool or a pinwheel. Such a galaxy can span a hundred thousand light-years or more, and contain hundreds of billions of stars. And we live in a spiral galaxy — the Milky Way. The spiral arms that define such a galaxy are a bit of an illusion, though. There are plenty of stars in the gaps between the arms. Such stars are older and fainter than those in the spiral arms, though, so...

Venus is returning to view — as the brilliant “morning star.” It’s quite low in the east as twilight paints the dawn sky. It’s so bright, though, that, if you have a clear horizon, it should be easy to spot. And right now, the crescent Moon points the way. Venus will be below the Moon tomorrow, and closer to the right of the Moon on Tuesday. Over the last 40 years, several spacecraft have orbited Venus. And they’ve found something odd: The length of Venus’s day has appeared to vary by...

Daylight Saving Time ends tonight. We’ll set our clocks back an hour as we revert to Standard Time. Standard Time wasn’t always standard, though. In fact, the time zones we use today weren’t formalized until 100 years ago. For the first century of American history, timekeeping wasn’t much of an issue. People didn’t travel much, and they certainly didn’t travel very far. So it was most convenient for cities and towns to keep their own time. It was noon when the Sun reached its highest point...

You can always count on the stars. Over the course of a human lifetime, their configuration doesn’t change — they don’t appear to move at all. That static appearance is an illusion, though. The stars are all so far away that we don’t see any motion. Yet they’re all moving in a hurry. And one of the fastest is in view on autumn evenings. Gamma Piscium is the second-brightest member of Pisces, the fishes. The constellation stretches across the east and southeast at nightfall. Gamma Piscium...

In the original “Star Wars” movie, Han Solo brags that his ship, the Millennium Falcon, can make the Kessel run in less than 12 parsecs. Since a parsec is a unit of distance, not time, that didn’t seem to make any sense. But in “Solo,” the most recent movie, it’s explained that the Kessel run isn’t a straight path — it maneuvers around several objects along the way. A good ship and a good pilot, though, can take a dangerous shortcut — and cut the distance down to about 12 parsecs. While the...

Like other buildings, observatory domes sometimes outlive their usefulness. They may not be big enough for the latest telescopes, for example. Encroaching cities can make it hard for them to see the heavens. Or time may just catch up to them. Many domes and related buildings have been torn down. Others have been converted to offices or libraries. And still others have been abandoned — left to the elements and the inevitable passage of time. Several of these buildings are scattered around...

The Skidi Pawnee of Nebraska were avid skywatchers. They used the stars to tell them when to plant corn and conduct other affairs. They worshipped many of the stars as gods. And they even built their dwellings with the stars in mind: The lodges faced the rising Sun, and they included posts that depicted the four stars that held up the sky. And they had a hole in the ceiling, in part, to make sure the residents could see the sky. And just in case they missed the stars, one Pawnee recorded...

One of the prime stars of summer continues to dazzle in the autumn sky. Vega is quite high in the west at nightfall. It’s the brightest member of the Summer Triangle. Vega is known by many names. One of the most important is HD 172167. That’s its listing in the Henry Draper Catalog. The first volume was published a century ago. People have been compiling star catalogs for a long time. One of the earliest was done more than 2,000 years ago. It recorded the positions of more than a thousand...

We still don’t know if anything has ever lived on Mars. But the evidence that something could have lived there keeps getting stronger. So does the evidence that conditions could still be okay for life today. There’s little doubt that early Mars was much warmer and wetter than it is now — conditions that were favorable for microscopic life. And a Mars rover recently found evidence of the building blocks of life in three-billion-year-old sediments. The Curiosity rover is poking around inside...

Stars come in all types, from brilliant to feeble. The brilliant ones are easy to see. But the feeble ones are a challenge just to discover, let alone study. This month marks the 75th anniversary of the discovery of the most feeble star then known. Georges Van Biesbroeck was an astronomer at Yerkes Observatory in Wisconsin. He specialized in double stars — two stars locked in a mutual orbit around each other. He measured the positions of known double stars, and discovered new ones. In...

Sagittarius is disappearing into the evening twilight. Look for the outline of a teapot low in the south and southwest as darkness falls. The teapot is pouring its starry brew toward the horizon. A giant star cluster lurks near the star that connects the lid and the spout. Through binoculars, NGC 6624 looks like a slightly fuzzy star. A small telescope reveals many of its individual stars. A recent study says that a middleweight black hole may inhabit the center of the cluster. If so, it’s...

Fifteen years ago as seen from Earth, a star in a distant galaxy suffered a violent death: It was pulled apart by a black hole. As the star was ripped to shreds, it produced an outburst of X-rays. Over the following decade, it slowly cooled and faded. Astronomers have seen this scenario play out dozens of times. But this one was special. It may have been created by a middleweight black hole — a type that’s rarely seen. Earlier events were powered by supermassive black holes. They’re...

The problem with black holes is that they’re black — they don’t produce any detectable energy at all. So astronomers find and study black holes by observing their effects on the stuff around them. They pull at nearby stars, for example. And they sometimes “feed” on gas and dust, which glows brightly as it spirals toward a black hole. One of the most spectacular effects is when a black hole rips apart a star. Known as a tidal disruption event, it can be as bright as a supernova. It can shoot...