The Ptolemaic model of planetary motion is a geocentric model of the solar system that was proposed by Claudius Ptolemy, a Greek astronomer, in the 2nd century AD. In this model, the Earth is stationary at the center of the universe and the celestial objects, such as the sun, moon, and planets, revolve around it in circular orbits.
The Ptolemaic model was a refinement of the epicycle and deferent system proposed by Hipparchus, which was used to explain the retrograde motion of celestial objects. Ptolemy added equants to the model in order to better match observations of planetary motion with the predictions of the model. Despite its limitations, the Ptolemaic model became almost universally accepted as the correct explanation of planetary motion for many centuries and was used as the basis for celestial predictions and observations for over 1000 years.
However, the Ptolemaic model eventually faced challenges from the observations and theories of other astronomers, such as Nicholas Copernicus, who proposed a heliocentric model of the solar system in which the sun was at the center and the Earth and other planets revolved around it. The Ptolemaic model was eventually replaced by more accurate models, such as the heliocentric model of Copernicus and the laws of planetary motion proposed by Johannes Kepler. Despite its eventual obsolescence, the Ptolemaic model remains an important contribution to the history of astronomy and the understanding of the solar system.
Ptolemy proposed that the planets were located on small, rotating epicycles that in turn moved on larger deferent circles. He added equants to the model in order to adjust the angular speed of the epicycles and better match observations of planetary motion with the predictions of the model. Ptolemy also moved the Earth away from the center of the deferent and allowed for a wobble of the deferent itself in order to improve the accuracy of the model.