StarDate

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 “intriguing” category.

For one thing, it’s the only moon with a thick atmosphere — more than half again as thick as Earth’s. And like Earth, the atmosphere supports a cycle of rainfall and evaporation.

The rains fill lakes near Titan’s poles, but just how that works is unclear. It could be that the lakes remain at least partially full year-round, and the rains just top them off. Or the lakes may dry up during summertime and refill during winter.

Perhaps most intriguing of all, Titan contains many of the building blocks for life — not just methane, but many of the other compounds from which life arose on Earth. So Titan may well be a chillier version of an early Earth — a world with all the ingredients for life.

Saturn stands near the upper left of our own moon this evening. It looks like a bright star. Through a small telescope, Titan looks like a tiny star quite close to the giant planet.

More about Saturn and the Moon tomorrow.

Script by Damond Benningfield

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 thousands of dollars to buy the third-largest telescope in the world.

By late 1843, he had enough money and pledges to lay the cornerstone, atop 500-foot Mount Ida.

Adams was 77 years old then, living in Massachusetts. He spent days traveling by rail, boat, and stage coach. Adams spoke on November 9th, 1843. Before a large crowd, he talked for more than an hour, extolling the virtues of science and of the new observatory. To honor the ex-president, Cincinnati renamed the hill Mount Adams — the name it still holds today.

The building was completed, and the new telescope was delivered from Germany, in 1845. The observatory operated there for three decades. By the mid-1870s, though, the smoke from chimneys and coal-burning industry had blotted out the stars. So the cbservatory moved to a new site, farther from town. And it’s still there — 175 years after its illustrious founding.

Script by Damond Benningfield

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 of charged particles that travels at millions of miles per hour. They also studied the Sun’s magnetic field and other phenomena.

Magnetic activity on the Sun is responsible for space weather here on Earth. Big storms can produce outbursts of particles and energy. When those outbursts reach Earth, our planet’s magnetic field can funnel the charged particles toward the surface.

When the particles strike atoms and molecules, they produce colorful aurorae — the northern and southern lights. They can disrupt the ionosphere — a charged layer of the atmosphere that bounces radio waves around the planet. And at the surface, they can cause power blackouts.

Pioneer 9 operated for 15 years, with some of the other craft going even longer. A planned fifth member of the network was destroyed during launch in 1969. Even without it, though, the Pioneers helped scientists begin to understand space weather, and develop ways to forecast this threat from the Sun.

Script by Damond Benningfield

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 150,000 light-years — a bit bigger than the Milky Way. It has a bright ring of older, redder stars in its middle, with a brighter ring of younger, bluer stars outside it. Wispy spiral arms connect the rings.

The Cartwheel probably was a normal spiral galaxy until a smaller galaxy plunged through it. The collision created a wave that rippled outward, like a rock thrown into a still pond. The wave disrupted the galaxy’s spiral structure. It also squeezed clouds of gas and dust, causing them to give birth to new stars.

Another well-known ring galaxy is Hoag’s galaxy. It has a yellow ball of stars in its middle, with a bright ring of blue stars around it. There’s not much between them, though — no spiral arms to link them. Astronomers aren’t sure if Hoag’s galaxy gained its structure from a collision or some other mechanism. All we know for sure is that it’s a beautiful cosmic bulls-eye, spinning through the universe.

Script by Damond Benningfield

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 elongated orbits around the galaxy’s center. That “stretches out” the center, forming the bar.

Gas can be funneled into the bar, where it can give birth to new stars. But most of the stars in a bar are old and faint, so the bar looks yellow. The spiral arms that wrap off its ends, on the other hand, contain a lot of young, vigorous stars, so the arms look bright blue.

Barred spirals can take many forms. Some have just one arm extending from each end of the bar, so they look like a twirler’s baton with ribbons streaming off the tips. Others have more spiral arms, so they look like pinwheels.

That includes the Milky Way. Because we’re inside the galaxy, we can’t easily see its overall structure. So the bar was discovered only recently. And there’s still some uncertainty about its size. But it certainly extends across many thousands of light-years — a sweet collection of stars in the heart of the Milky Way.

More about spiral galaxies tomorrow.

Script by Damond Benningfield

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 they’re not as impressive.

Most spirals actually form disks that are roughly 10 times wider than they are thick. The spiral arms are regions where material has piled up, like a traffic jam on a highway. Individual cars move through the jam, but the pile-up remains.

In the case of a galaxy, stars and clouds of gas and dust move into the wave, which moves slower than the galaxy’s overall rotation. Material is denser in the wave, which causes the clouds of gas and dust to collapse and give birth to new stars. Many of these stars are hot, bright, and blue. It’s these stars that make the spiral arms so prominent.

Such stars burn out quickly, though. So as they move through the wave, they fade from view. That leaves the regions that flank a spiral arm looking dark and empty.

Spirals come in many varieties. In some, the central “bulge” forms a long bar. More about that tomorrow.

Script by Damond Benningfield

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 several minutes. When you consider that a Venusian day lasts 243 Earth days, that’s not much. But it’s still a puzzler.

Observations by the most recent Venus orbiter have suggested an explanation: The atmosphere may push on mountain ranges near the equator, speeding up or slowing down Venus’s rotation.

Scientists developed that scenario based on observations by Akatsuki. The Japanese craft has orbited the planet for three years — more than four Venus days. Each afternoon, it’s seen a big wave develop over mountains near the equator. The waves move at a different speed from the rest of the upper atmosphere.

Simulations showed that the waves could be caused as the air warms a bit in the afternoon. That would allow the flow of the dense, heavy atmosphere to crest the mountains and climb high into the sky. The transfer of energy between the atmosphere and the solid planet could change Venus’s rotation rate — altering the length of its day.

Script by Damond Benningfield

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 in the sky. In some cities, the time was kept by observatories, which had telescopes for measuring the Sun’s position.

But as railroads expanded in the 19th century, standard time zones became important. Trains ran through thousands of cities and towns, with the clocks set a little differently in each one. That made scheduling tough and confusing.

Scientists were concerned about timekeeping, too. An astronomer, for example, had set up the country’s first network of weather observers. But coordinating the reports was hard to do. So he led an effort by scientists to create standard time zones.

It took the railroads to get the job done, though. In 1883, they established four time zones for their own use. Some towns and states adopted the zones, but others stuck with local time, which kept things a bit jumbled.

The situation wasn’t resolved until 1918, when Congress enacted the time zones into law — bringing order to the way we keep time.

Script by Damond Benningfield

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 is near its top right corner — part of a pentagon of faint stars.

Gamma Piscium is a stellar giant. It’s nearing the end of its life, so it’s beginning to get bigger and brighter. Right now, it’s about 10 times the diameter of the Sun, and more than 60 times the Sun’s brightness. That makes it faintly visible to the eye alone, even though it’s more than 135 light-years away.

Perhaps the most interesting fact about Gamma Piscium, though, is its speed. It’s moving across the sky at about 350,000 miles per hour — faster than all but a few other visible stars. At that rate, it’ll move the equivalent of the Moon’s diameter in less than 1500 years.

The star’s composition hints that it came from outside the disk of the Milky Way — the part of the galaxy that includes the Sun. The star has very few heavy elements. That suggests it formed outside the disk, and just happens to be passing through — zipping by like a speeding bullet.

Script by Damond Benningfield

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 Kessel run is fictional, the parsec isn’t. In fact, it’s the most commonly used unit of distance in modern astrophysics. It measures the distances to objects beyond the solar system — stars, galaxies, and others. It’s equal to about three and a quarter light-years.

The word “parsec” is short for “parallax second.” It’s based on the apparent motion of an object as Earth moves from one side of the Sun to the other. As a result of that shift, the viewing angle to an object changes over the course of a year. How much it changes reveals the object’s distance. The angles are so tiny, though, that the technique works best for objects that are within a few thousand parsecs.

A star whose distance is easily measured with the technique is in good view early tomorrow: Regulus, the bright heart of Leo. It’s close to the upper right of the Moon at first light. The best measurements to date say the star is about 79 light-years away — just 24 parsecs.

Script by Damond Benningfield