dipper@utastro.UUCP (Debbie Byrd) (12/23/85)
This is the anniversary of the discovery of one of Saturn's moons. More on the moon we call Rhea -- in just a moment. December 23: The Discovery of Rhea On today's date in the year 1672, Giovanni Cassini found a moon of the planet Saturn -- the one we now call Rhea. This was the third moon discovered for Saturn -- the second discovered by Cassini. Rhea brought the total number of objects known to be orbiting the sun to fourteen -- and coincidently, the ruler of France at that time was Louis XIV. Cassini brought this fact to the attention of the king -- who it is said was sufficiently impressed to have a commemorative medal struck. It's not known what Cassini said to the king when he found two more moons for Saturn a dozen years later. Well, now we know many moons for the planet Saturn. The number increased to nearly two dozen when the two Voyager spacecraft passed near the planet in 1980 and '81. Now the official count on Saturn's moons is 17. Thanks to Voyager, we now know each moon individually in a way that Cassini never could. For example, we know that the surface of Rhea has both light and dark colored terrain -- with some areas that have a wispy appearance. Both the light and dark regions are totally covered by craters, with fewer large craters in the dark regions than the light. It's likely that the two kinds of terrain represent two different episodes of bombardment by meteorites in the early solar system. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin