The geocentric model, championed by the ancient Greek astronomer Ptolemy in the 2nd century CE, envisioned the Earth as the stationary center of the universe. This was presented as an improvement of Aristotle’s model. Celestial bodies like the sun, moon, planets, and stars were all believed to revolve around the Earth in intricate patterns. This model persisted for centuries, but its limitations eventually paved the way for a new perspective.

Basic tenets:

Earth as the Center: The Earth was considered the fixed and immovable center of the universe.

Spherical Heavens: The celestial bodies were thought to be embedded in a series of rotating crystalline spheres that carried them around the Earth.

Complex Orbits: To account for the observed motions of celestial bodies, the model incorporated epicycles and deferents, which were smaller circles traced by the bodies on larger circular paths.


The model provided a reasonably accurate prediction of planetary positions for naked-eye observations. It offered a framework for understanding celestial phenomena and served as a basis for calendars and navigation.


As astronomical observations became more precise, the model struggled to explain certain phenomena, such as the retrograde motion of planets. The need for increasingly complex epicycles became cumbersome and mathematically challenging.