In astronomy, the Geocentric Model is a description of the cosmos where Earth is at the orbital center of all celestial bodies. This model served as the predominant cosmological system in many ancient civilizations such as ancient Greece including the noteworthy systems of Aristotle and Ptolemy. As such, they assumed that the Sun, Moon, stars, and planets circled Earth.




     The Greeks were the first to treat astronomy as an important science, and the first models to explain the movement of the planets were invented by the Greeks in 4 BC. Ancient astronomers “could tell the difference between the stars and planets because stars remain fixed over time while planets move a noticeable amount in a short period of time." When Aristotle began his astronomical research, he was less concerned with models explaining the movements of the planets and was more concerned with why the planets were moving in the first place. He believed that the universe was made of spherical objects that circled around the earth. Aristotle’s view of the universe was accepted by society until Ptolemy enlarged his ideas and created a detailed model. This geocentric model of the universe became the worldview until Copernicus developed his heliocentric model, which stated that earth and the other planets revolved around the sun which remained stationary.




     The belief that the earth was the center of the universe was supported by two main observations. First, people observed that the stars, the sun, and the planets appeared to revolve around earth each day, which led them to believe that earth was in the center of all of the celestial bodies. The second observation which supported the geocentric model was the fact that the earth does not seem to move from our perspectives. From an observer on earth, our planet appears to be stable, solid, unmoving, and completely at rest.




     The medieval view of the universe states that “the central earth is surrounded by a series of hollow globes. Each of these transparent globes is situated above one another, and each sphere is larger than the one below. Fixed in each of the first seven spheres is one celestial body that all other planets revolve around. Beginning from the Earth, the order of the planets is Luna (the moon), Mercury, Venus, Sol (the sun), Mars, Jupiter and Saturn. Beyond Saturn lies the Stellatum, then the Primum Mobile, which leads into heaven." All power and movement “descended from God to the Primum Mobile and caused the spheres to rotate. The rotation of the Primum Mobile caused the rotation of the Stellatum, which caused the rotation of Saturn, which caused the rotation of Jupiter, and so on." -The Discarded Image