Two competing models attempt to explain the motions and changing brightness of the planets: ptolemy's geocentric model and copernicus' heliocentric model. sort the characteristics according to whether they are part of the geocentric model, the heliocentric model, or both solar system models.

Ptolemy's geocentric model depended on the possibility that Earth is the focal point of the universe, while Copernicus' heliocentric model was created around the possibility that the Sun is in the middle. While these two models depended on restricting thoughts, they shared a typical confidence in uniform round movement and the utilization of epicycles. In any case, Copernicus' heliocentric model does not utilize epicycles to clarify retrograde movement like Ptolemy's geocentric model. With a specific end goal to clarify retrograde movement, Copernicus utilizes the diverse orbital places of the planets as a clarification to the appearance in reverse movement of the planets in the sky.