Not everyone readily accepted Copernicus’ heliocentric model of the universe, but some astronomers did try to reconcile Copernicus’ observations with a geocentric model.

The geocentric model is a debunked theory that the Earth is the center of the universe, with the sun and planets revolving around it.

In the geocentric model this means that the motions of the deferent and the epicycle are in the same sense (counterclockwise as drawn).

A diagram of the geocentric trajectory of Mars. Kepler’s investigation of the Red Planet’s orbit would lead to his first two planetary laws. (Image credit: Johannes Kepler/PD-US) ...