models of the planet systems, based on his background as a mathematician. Eudoxus's model was geocentric, with the Earth being a stationary sphere at the center of the system, surrounded by 27 rotating spheres. The farthest sphere carried stars, which he declared to be fixed within the sphere. Thus, though the stars were moved around the Earth by the sphere which they occupied, they themselves did not move and were therefore considered fixed.

Aristotle

Aristotle, who lived from 384 to 322

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