Moon and Mars
The Moon follows Mars across the sky tonight. Mars looks like a fairly bright orange star. It's closest to the Moon at nightfall, with the Moon moving slightly farther from it during the night. They set about two or three hours before sunrise.
Both worlds are marked by countless craters -- the scars of collisions with big space rocks.
Most of the craters on the Moon are ancient.
During the solar system's first billion years or so, the bodies of the inner solar system were subjected to a severe pounding by boulders as big as states. This pounding created big craters. There's no water or air on the Moon to erode them, so the only thing that wears them away is the impacts that create more craters. A steady "rain" of tiny meteoroids steadily pounds at the craters, softening their edges a little.
Many of the craters on Mars are more recent.
Mars has a thin atmosphere, so winds and blowing dust erode or bury the craters. Mars also has big volcanoes, which have covered ancient craters with lava. And in the distant past, Mars was much warmer and wetter than it is today. Water probably flowed across its surface, and rain may have poured from the sky -- also erasing ancient craters. So while Mars took a heavy pounding early on, just as the Moon did, there's little record of it left on the Martian surface.
Watch for Mars and the Moon soaring high overhead this evening, and setting in the northwest in the wee hours of the morning.
Script by Damond Benningfield, Copyright 2007
For more skywatching tips, astronomy news, and much more, read StarDate magazine.