1. Superior planets (Mars, Jupiter, Saturn) generally appear to move toward the east against the background of stars. However, they will occasionally move "backwards" - to the west relative to the stars. At this time the planets appear brighter than they normally are. This period of increased apparent brightness and reversed direction is termed retrograde.

A. Under the Geocentric Model of Ptolemy, what was the explanation for retrograde behavior in planets such as Mars? (A small sketch would be useful).

B. Under the Heliocentric Model of Copernicus, what was the explanation for retrograde behavior?

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