c. 400 BCE

Greek Geocentrism

Plato (427–347 BCE), Aristotle (384–322 BCE)

Ancient Greece established a number of important legacies that strongly influenced Western civilization for thousands of years. These included a cosmological worldview that was derived primarily from the teachings and writings of two of the most prominent thinkers of the classical era: the mathematician and philosopher Plato, and his student Aristotle, who mastered almost all of the arts and sciences of the day. Plato and Aristotle created the basic foundations upon which modern Western philosophy and science—including physics and astronomy—were built.

The basic focus of ancient Greek astronomical thinking (and science in general) was to try to seek mathematical, physical explanations and models for observed phenomena. It was natural to turn to the geometry and trigonometry pioneered by Pythagoras for solutions. Plato used geometry to divide the universe into two realms: the fixed sphere of the Earth, and the nested, constantly moving spheres of the Sun, Moon, five known planets, and known stars—all of which revolved around a motionless Earth. To the region of the cosmos beyond the sublunary sphere—the region between Earth and the Moon composed of the basic elements earth, water, air, and fire—Aristotle added the element aether, which he believed constituted the rotating heavenly spheres that contained the stars and planets.

This geocentric view of the cosmos was a major feature of Greek cosmology. Furthermore, the quest for symmetry and simplicity implied that the heavenly spheres should move in uniform circular motions or combinations thereof, an interpretation consistent with much of the available astronomical data of the time. But Plato’s model could not explain all of the observed motions of the sky. The concept of perfect circular motions was expanded upon by the Egyptian astronomer Ptolemy during the Roman Empire, but it would be challenged by later astronomers until the seventeenth century, when the observational and theoretical work of Copernicus and Kepler officially put the geocentric model to rest.

A Renaissance-era depiction of the geocentric celestial spheres model of the cosmos. The outer shell is labeled “The Firey Heavens, Home of God and All of the Chosen Ones.”