The planets were the "wandering stars." Their position relative to the
"fixed" stars changes from night to night. If observed over a course of
time, they will appear to travel across the background of the stars,
sometimes even going backwards for a brief period of days. Ptolomy
postulated the existence of "epicycles" to account for this retrograde
motion, but today's heliocentric model for the solar system works much
better.
Stephen Carlson
-- Stephen C. Carlson : Poetry speaks of aspirations, scarlson@mindspring.com : and songs chant the words. http://www.mindspring.com/~scarlson/ : -- Shujing 2.35