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Unformatted text preview: Sun and three extra spheres for each planet for retrograde motion. Total of 27 spheres. Aristotle (384-322 BC) postulated gravity and physical laws of motion Aristotles Cosmology: Two worlds: heavenly ether and sub-lunar Earth, Water, Air and Fire. Introduced 56-sphere geocentric model but still in error. He couldnt explain variation in Moons size and variation in planets brightness but his model that Earth is in the center of the Universe stood for 2000 years. After Aristotle, the models became more quantitative. Eratosthenes (300 BC): measures size of Earth to 1% accuracy....
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- Fall '11