Pythagorean astronomical system

Lore & Background

Philolaus (c. 470 to c. 385 BC) was a follower of Pythagoras of Samos and has been called one of the three most prominent figures in the Pythagorean tradition. He may have been the first to commit Pythagorean doctrine to writing. Most of what is known about the Pythagorean astronomical system is derived from his views, though scholars are not absolutely certain he developed it; it may have been created by someone else in the late fifth century BC. Before Philolaus, knowledge of Pythagorean astronomy is limited, and no evidence of Pythagoras's own work on astronomy remains. One surviving theory from earlier Pythagoreans, the harmony of the spheres, is first mentioned in Plato's Republic and presented by Aristotle as a physical doctrine.

Reader's Guide

The Pythagorean astronomical system is significant as an early departure from geocentric thinking, moving the Earth from the center and making it a planet. However, how much of the system was intended to explain observed phenomena and how much was based on myth, mysticism, and religion is disputed. Other than the inclusion of the five visible planets, very little of the system is based on genuine observation, and in retrospect Philolaus's views are seen as less like scientific astronomy than like symbolical speculation. The system's erroneous concepts of a Central Fire distinct from the Sun and a Counter-Earth were later rejected, but its insight that apparent celestial motion results from the observer's real motion was a conceptual advance. The system influenced later thinkers such as Johannes Kepler, who believed Philolaus's Central Fire was actually the Sun.

Did You Know?

• Philolaus may have believed the Sun was a mirror reflecting the heat and light of the Central Fire.
• The system included a nonexistent Counter-Earth, which along with the Central Fire was never visible from Greece.
• Ancient sources describe the Earth as rotating daily, but the idea of one hemisphere always facing the Central Fire is a modern speculation not clearly attested in surviving fragments of Philolaus.