dipper@utastro.UUCP (Debbie Byrd) (10/04/84)
Earth's day is slowly getting longer. More on the length of a day on Earth -- right after this. September 28: The Length of Earth's Day The Earth spins on its axis once every 23 hours, 56 minutes and some seconds -- so a day on Earth is 24 hours long. Someday in the far distant future, though, Earth's day will be much longer -- and one face of our world will be turned at all times toward the moon. That's kind of like what the moon does now. One face of the moon continually stares toward Earth, no matter where the moon is in orbit. The moon is important to the length of Earth's day -- because this large satellite in orbit around our world is what's causing our day to get longer. The moon's gravity acts as a brake on Earth's rotation, and causes our spinning planet to spin more slowly. Earth's spin is slowing down in an extremely gradual way -- our day is only getting longer by about one second every 50 thousand years. That's an inconceivably long time to most folks -- but only a wink of an eye on astronomical time scales. Planet Earth will still be around millions, even billions, of years from now. And eventually, our world's spin will slow down so much that Earth will turn only once in the time it takes the moon to complete a single orbit. By some estimates, at that far-future time -- millions of years from now -- both motions will take about fifty-five of our present days. Then, as though the two worlds were connected with a rigid bar, the Earth and moon will always keep the same face toward each other. Script by Deborah Byrd. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin