Moon and Saturn

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• 24 of 1969
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The Moon keeps company tonight with the giant planet Saturn, which looks like a bright golden star. They rise in mid evening, with Saturn just a whisker to the upper left of the Moon. They're high in the southwest at first light.

Saturn has a bunch of moons of its own, including one of the largest and most intriguing in the solar system. Titan is about half again as big as our Moon. What makes it intriguing, though, is that it's like a supercold version of Earth.

Because it's so far from the Sun, Titan's surface temperature is hundreds of degrees below zero. Yet the big moon has an atmosphere that's thicker than Earth's. And its surface is altered by falling and flowing liquids -- not water, which is frozen as hard as rock, but liquid methane and ethane.

Using radar to peer through Titan's hazy atmosphere, the Cassini spacecraft has mapped hundreds of lakes and seas on Titan. Most of them are in the far north, although the craft is starting to look at the far south, too. The largest is bigger than Lake Superior.

The lakes and seas are filled by a rain of methane and ethane. These supercold liquids also carve rivers, just like the rains on Earth. These rivers sculpt Titan's terrain.

As the seasons on Titan change, the methane and ethane evaporate and form clouds, which then rain on other areas, filling other lakes and seas. It's a chilly cycle that just keeps repeating -- just like the cycle of water here on Earth.

Script by Damond Benningfield, Copyright 2007

For more skywatching tips, astronomy news, and much more, read StarDate magazine.