-Draws a planet bouncing around in space.
-The built-in image is a map of the earth (extracted from `xearth'),
-but you can wrap any texture around the sphere, e.g., the planetary
-textures that come with `ssystem'.
+The Earth, bouncing around in space.
+
+If you would like it to display a different planet, the texture maps
+that come with "ssystem" work well.