What is the main characteristic of Ptolemy's geocentric model?

Ptolemy's geocentric model is primarily characterized by the concept that Earth is at the center of the universe. This model, prevalent from ancient times until the Copernican revolution, posited that all celestial bodies, including the sun, moon, and stars, revolve around a stationary Earth. This viewpoint aligned with the philosophical and observational perspectives of the time, where the Earth was seen as the most significant and stable point in the cosmos.

While other models, such as Copernicus's heliocentric theory, proposed a sun-centered universe, orbits in Ptolemy's model were not elliptical as later described by Kepler. Moreover, retrograde motion was explained through complex systems of epicycles rather than varying orbital speeds alone. These details highlight the geocentric model's focus on an Earth-centered universe, making it a cornerstone of ancient astronomical theory.