StarDate Podcast

Textbook views of the Milky Way show a long bar of stars in the middle, with several spiral arms wrapping around it. But that picture is incomplete. And some of it might not be right. In fact, astronomers are still trying to develop a complete and accurate diagram of our home galaxy. The problem is that they’re trying to map the Milky Way from the inside. It’s like trying to map a million square miles of forest from a single spot deep inside it. Not only can you not see the rest of the...

The star Regulus stands just a whisker away from the Moon tonight. They climb into good view by about 8:30 or 9, with the lion’s bright heart to the right of the Moon. Regulus is a bit more than 79 light-years away. That means the light you see from Regulus tonight actually left the star more than 79 years ago — at the start of World War II. So when a particle of light from Regulus hits your eye, it’s ending a journey of 79 years. Of course, as with many things astronomical, it’s all...

Gamma Cassiopeia is a busy star system. The main star is surrounding itself with a disk of gas and dust. The star is interacting with an invisible companion. And it’s building up to an impressive demise. Gamma Cass is the middle point of the letter M or W formed by the stars of Cassiopeia, which is high in the northern sky at nightfall. Gamma Cass is the most distant member of that pattern, at 550 light-years. The main star — the one visible to the eye alone — is between 15 and 20 times the...

In a bit of a coincidence, a total lunar eclipse will shine through American skies for the second January in a row. The entire eclipse will be visible from all of North America, with Hawaii seeing most of the action as well. Lunar eclipses occur when the full Moon passes through Earth’s long shadow. But the Moon’s orbit is tilted a bit with respect to Earth’s orbit around the Sun. So during most months, the full Moon passes a bit above or below the shadow. When the geometry is just right,...

At the ends of their lives, stars like the Sun do a double dip. They puff up to giant proportions, then shrink, then puff up again, even bigger than the first time. The star at the end of the tail of Draco, the dragon, is in the midst of that second period of puffing up. It’s about 70 times wider than the Sun, and almost 900 times brighter. Lambda Draconis is low in the north at nightfall right now, with the rest of the dragon stretching to its left. The star wheels high overhead later...

We give full Moons all kinds of names. The full Moon of January, for example, traditionally is known as the Old Moon, Wolf Moon, or Moon After Yule. A second full Moon in a month is known as a Blue Moon. And a full Moon that occurs when the Moon is especially close to Earth is a supermoon. And there’s a supermoon coming on Sunday night. The Moon will be full only half a day before it reaches its closest point to Earth for its current orbit — and its third-closest point for the year. And it...

Glaciers keep secrets. They hide rivers, hills, and other surface features. They conceal the bodies of animals that roamed the landscape tens of thousands of years ago, and enfold the debris of crashed airplanes. And a glacier in Greenland has hidden evidence of a cosmic impact — a 20-mile-wide crater blasted out by an asteroid. Scientists used several lines of evidence to discover the crater, which is below the Hiawatha glacier on Greenland’s northwestern coast. They used radar scans made...

In the first pictures of the far side of the Moon, one feature stood out: a dark circular patch. Since those photos were snapped by a Soviet spacecraft, the feature was named the Sea of Moscow. Most lunar “seas” are on the near side — the hemisphere that always faces Earth. In fact, seas cover about a third of the near side, but only about one percent of the far side. The seas are plains of dark volcanic rock. They formed when asteroids punched holes in the Moon’s crust. Molten rock...

In many sci-fi movies and TV shows, orbiting spacecraft take up “stationary” positions over New York, London, or some other major landmark. That’s not possible, though. It is possible to assume a stationary position — but only if the spacecraft is above the equator. Such a spot is called a geosynchronous orbit. It’s achieved at an altitude of about 22,000 miles. At that distance, a craft’s orbital speed carries it around Earth in exactly one day. So the craft appears to “stand still” above...

Every object in the solar system is orbiting something else. Moons orbit planets, for example, and planets orbit the Sun. And even the Sun goes around something: the barycenter of the solar system. As the Moon goes around Earth, it doesn’t orbit the center of our planet. That’s because both Earth and the Moon have mass — they weigh something. So both of them orbit the center of mass of the combined Earth-Moon system — a point known as the barycenter. Because Earth is the heavier object, the...

Orion, the hunter, strides boldly across the southern sky on winter nights. The big, bright constellation is low in the east shortly after nightfall, with its famous “Belt” of three bright stars pointing up from the horizon. Orion’s brightest star, blue-white Rigel, is to the right of the Belt, representing the hunter’s foot. A mighty foot can get mighty tired, so long-ago skywatchers gave Orion a footstool to rest it on — a pattern of four relatively faint stars that’s above Rigel during...

A big star with a bigger future climbs across the south on winter nights. It’s already one of the biggest and brightest stars in our region of the galaxy. Over the next few million years, though, it’s likely to puff up even more, then end its life as a supernova. Rigel represents one of the feet of Orion, the hunter. It’s to the right of Orion’s three-star belt in early evening. Rigel is quite bright, and shines blue-white. Actually, Rigel is a system of several stars. But only one of...

To the eye alone, Orion may be the most impressive of all the constellations. It consists of a bright rectangle of stars with a “belt” of three stars in the middle, and a massive stellar nursery along the hunter’s sword. If we could view the constellation in X-rays, though, it would look even more impressive. That’s because it’s home to a superbubble — a globule of million-degree gas that spans hundreds of light-years. At such high temperatures, the gas emits most of its energy as...

Little stars can pack a wallop. They can produce giant explosions of radiation and charged particles. And that could be bad news for the prospects for life on planets around such stars. The smallest true stars are red dwarfs. They can be as little as just eight percent the mass of the Sun. Such stars are small, cool, and faint — only about one ten-thousandth as bright as the Sun. The stars are quite turbulent. Giant bubbles of gas rise from such a star’s core to the surface, where they...

The most brilliant steadily shining objects in the universe aren’t giant stars or even galaxies of stars. Instead, they’re big pancakes of gas and dust. The pancakes are known as accretion disks. They form as gas and dust fall toward a massive central body. The material flattens out, forming a wide, thin disk — like a pancake. The brightest of these disks are found around black holes. And much of their energy is in the form of X-rays. The gas and dust don’t fall directly toward a black...

X-rays pass right through human flesh, making it possible to study what’s under the skin. But they don’t pass through the atmosphere — not very far, anyway. So to study what’s under the skin of X-ray-producing stars and galaxies, astronomers must loft their telescopes into space. X-rays are important for diagnosing what’s happening in some of the most interesting objects and events in the universe. That includes the environments around black holes, the remnants of exploded stars, and...

Not many astronomical objects are also units of measurement. But one that is stands high in the east at nightfall, near the tip of one of the horns of Taurus, the bull. You need a telescope to see the Crab Nebula because it’s not very bright at visible wavelengths. In X-rays, though, it’s one of the brightest objects in the sky. In fact, its X-ray brightness is defined as one crab — the basic unit for the brightness of all X-ray targets. The nebula is the remnant of a supernova — a massive...

A star pattern that runs along the spine of the Milky Way is quite prominent at this time of year. It’s the Northern Cross — part of the constellation Cygnus, the swan. During summer evenings, the swan flies parallel to the horizon, so it really does resemble a graceful bird. Now, though, it stands almost straight up from the western horizon at nightfall. In that configuration, it forms a cross. Its brightest star is Deneb, at the top of the cross. If you have a dark skywatching site,...

The Skull Nebula is well named. It’s the stripped-off “skin” of a once-impressive star. All that remains of the star is its dying core. The nebula is about 1600 light-years away, in the constellation Cetus. It began forming about 6600 years ago as seen from Earth. The star, which was about four times as massive as the Sun, could no longer produce nuclear reactions in its core. The core began collapsing to form a white dwarf — a small, dense ball of carbon and oxygen. It continues to shine,...

Over the holidays in late 1943 and early ’44, Gerard Kuiper was on leave from military duty in Europe. Instead of taking in the sights of home, though, he took in the sights of the solar system. Kuiper was an astronomer at the Yerkes and McDonald observatories. During his time off, he used McDonald’s 82-inch telescope to study several worlds. His list included Titan, the largest moon of the planet Saturn. It’s about 3200 miles in diameter — larger than Mercury, the smallest of the Sun’s...