ccording to Aristotle, is the naturalmovement of Earthly matter from all places downwards, to a center, around which asphere of matter will build up. "Only circular motion is capable of endless repetitionwithout a reversal of direction, and rotary motion is prior to linear because what isexternal, or at least could have always existed, is prior, or at least potentially prior, towhat is not."(North,80) In Aristotle's book De Caelo (On the Heavens), he speaks of thecelestial sphere, the Earth's center being the same shape, and dismissing the idea of theEarth rotating at the center of the universe. He also dismisses the idea of an orbitalmotion of the Earth. (North, p.81) Contradicting Aristotle, Heracleides, an astronomer,believed in the rotation of the Earth on it's axis and is known to be the earliest astronomerto stand by it. He was thought to have taken the first step toward heliocentricity. It isbelieved in the years to follow that Copernicus was said to have mentioned Heracleides'name in this connection. (North, p.85) Aristarchus of Samos was the first astronomer to clearly put forth a truesun-centered theory, learned from Archimedes. (North, p.85) "...Aristarchus' hypothesesare that the fixed stars and the Sun are stationary, that the Earth is carried in a circularorbit around the Sun, which lies in the middle of it's orbit, and that the spheres of fixedstars, having the same center as the Sun, is so great in extent that the circle on which theEarth is supposedly carried is in the same ratio to the distance of the sphere has to itssurface." (North, p.85-6) If Aristarchus believed in heliocentrism, he still couldn’texplain the differences in the Earth's motion and seasons, which explains its failure to beaccepted. Although scientists such as Eudoxus, Callippus, and Aristotle all came up withEarth-centered systems based by providing a center for all motions, Ptolemy wastriumphant for he was able to explain sphere sizes and ...
