dipper@utastro.UUCP (Debbie Byrd) (07/29/85)
Earth has its oceans -- but the moon is completely dry. We'll tell you why -- in a moment. July 29: Why the Moon is Dry If there were lakes or oceans on the moon, we'd sometimes see sunlight reflecting from them. We DON'T see these reflections -- so it's easy to see that large bodies of water just aren't there. Earth has oceans because we're located at a favorable distance from the sun -- close enough to keep the water from turning to ice, but far enough to prevent it from boiling away. But the moon is located this same distance from the sun -- so why doesn't it have any water? The reason is the moon's small size, or mass. The moon is smaller than Earth, and its gravity is much weaker. Earth's stronger gravity keeps our oceans from escaping into space as a gas. Long ago, when the planets condensed from a disk of gas surrounding the sun, the moon probably had the ingredients to make oceans. But its gravity couldn't hold them -- they escaped the moon forever. Still, there ARE seas on the moon -- but they aren't made of water. The dark patches on the lunar surface are calld "maria" which in Latin means "seas." The maria are actually ancient lava beds. They got their name because early astronomers imagined that the moon was like Earth, with alternating water and land. You can see the so-called seas -- or maria -- with the naked eye. They're the same dark patches that make the face of the "man in the moon." The moon is waxing toward full now -- so any evening around now, take a look! Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin