StarDate

William Lassell made a fortune selling beer to factory workers in Liverpool. He used that money to set up his own astronomical observatory, called Starfield, outside Liverpool. And he equipped it with telescopes he built himself – some of the best in the world.

Using one of those instruments, Lassell made a major discovery 175 years ago this week. Make that two discoveries: two large moons of the planet Uranus. They were named Ariel and Umbriel, after characters from the works of William Shakespeare and Alexander Pope.

The moons are almost exactly the same size – about 720 miles in diameter. And they have a similar makeup – mixtures of rock and frozen water and methane.

But they look different. Umbriel is dark, and it’s covered by many large impact craters. That suggests the moon is quiet and still – not much happens there.

Ariel is brighter, and it’s much more interesting. It’s crossed by giant canyons and cliffs, with few craters. Liquid water may bubble to the surface from an underground ocean. At the surface, it freezes. That may push the surrounding crust, causing it to crack. So Ariel may be an active world orbiting a giant planet.

Uranus is an easy target for binoculars. It’s halfway between Aldebaran – the bright eye of the bull – and the Pleiades star cluster. They climb into good view in late evening. But the view will be better before dawn, after the Moon has dropped from sight.

Script by Damond Benningfield

The modern constellations offer a convenient way to appreciate the beauty of the night sky. Using the outline of a scorpion or a lion as a landmark makes it easier to find your way around. It’s also a good way to exercise your imagination.

Our imaginations don’t all show us the same pictures, though. The western constellations were passed down from ancient Greece and Rome. And many of them are even older – they came from ancient Babylon and Sumeria. But just about every culture had its own star pictures – its own map of the night sky.

An example is Capricornus. In western mythology, it represents a sea-goat – half goat and half fish – perhaps a story about the god Pan. But records from ancient China describe something different.

Six of the stars in that region formed an ox, known as Niu – a sacrifice for mid-winter. Three others formed dams to hold water for the emperor’s fields, which were also in Capricornus. And other stars formed parts of different pictures – different stories in the night sky.

Capricornus is low in the south at nightfall. The constellation isn’t especially bright, so it’s invisible from light-polluted cities. Under darker skies, you can see the outline of a wide triangle. Tonight, the gibbous Moon is near the triangle’s eastern point. That makes it easier to find where the sea-goat is, but harder to see its faint outline.

Script by Damond Benningfield

Some high-speed bullets are firing across the night sky this week. They’re the bits of debris that produce the Orionid meteor shower – small pebbles left behind by Comet Halley. They hit the atmosphere at about 150,000 miles per hour. They vaporize almost instantly, forming the glowing streaks known as meteors.

Halley visits the inner solar system once every 76 years or so. On each approach, the Sun’s heat vaporizes some of its frozen surface. That releases bits of rock and dirt. Over time, they spread out along the comet’s orbit. Earth flies through this path twice a year, sweeping up some of the particles.

But the comet dust isn’t evenly spread out. Halley produces a new “streamer” with each pass. So the strength of the shower depends on which of these ribbons we encounter, and how deeply we pass through it.

Most years, the Orionids produce up to a couple of dozen meteors per hour. But if we pass through a denser stream, or if we pass through its middle, the rate can go up. In 2006, for example, the shower produced up to a hundred meteors per hour.

Experts aren’t forecasting that kind of performance this year. Still, the shower is worth checking out. You need a dark skywatching site, far from city lights. And the best view comes in the wee hours of the morning, after the Moon has set. The meteors can appear anywhere in the sky, so sit back, look up, and enjoy the show.

Script by Damond Benningfield

Meteorology is the study of Earth’s atmosphere and its weather and climate. Despite the name, it has nothing to do with meteors – at least not directly. But more broadly, meteors and meteorology are related – in their names. Both words come from a Greek word that meant “the heavens above” or “things high up.”

Meteorology was first used by the Greek philosopher Aristotle, around 340 B.C. A “meteor” was any particle in the sky, or that fell from the sky.

Over time, meteors were clumped into four classes. Aerial meteors referred to the wind. Aqueous meteors were rain, snow, or hail – any wet stuff that fell from above. Luminous meteors were anything that glowed, such as rainbows or the northern lights. And igneous meteors were anything that flashed through the sky in an instant – lightning and “shooting stars.”

Until a couple of centuries ago, it was thought that shooting stars had a strictly atmospheric origin – something triggered in the sky itself. It wasn’t until the early 1800s that scientists figured out their true origin: bits of space rock that are burning up in the atmosphere. So without the atmosphere, there would be no glowing meteors to light up the night sky.

The word “meteor,” by the way, refers only to the streak of light. When a rock is still in space, it’s a meteor-oid. And one that s hits the ground is a meteor-ite – a “thing on high” that fell to Earth.

More tomorrow.

Script by Damond Benningfield

The oldest objects on Earth didn’t come from our home planet. They were born in space more than four-and-a-half billion years ago. They fell to Earth as the most common type of meteorite.

Chondrites account for about 85 percent of all meteorites. They’re named for tiny round beads of material known as chondrules. The beads formed in the disk of gas and dust that encircled the newborn Sun. Grains of dust clumped together. The chondrules then mixed in with other particles to form asteroids. Collisions sent pieces of the asteroids racing off into space. Some of them plunged through Earth’s atmosphere, falling as meteorites.

Chondrites haven’t changed much since they formed, so they preserve a record of the early solar system. They tell us what kinds of materials came together to form Earth and the other planets.

There are three main classes of chondrites. The differences reveal where they formed. Some were born quite close to the Sun; others, near the inner edge of the asteroid belt; and still others even farther out. The different classes tell us about conditions in different regions of the early solar system.

Many chondrites contain a lot of water, so they may provide clues to the origin of water on Earth. And they contain some of the chemical building blocks of life, perhaps telling us about the origin of life itself – lessons from relics from the birth of the solar system.

More about meteorites tomorrow.



Script by Damond Benningfield