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I guess we should start from beginning. In the beginning, man stood on some earth, and we called it the Earth. And we looked up and saw some stars, the Sun, and the Moon. And looking up night after night, we noticed some of the stars didn't behave like the other stars, but wandered about on their own, and we called them wanderers, or "planets" in Greek. And over our lifetimes they appeared to wander in peculiar patterns, and we sensibly began, around 1200 BC, to record their movements and picked up a knack for predicting where they would wander to next. Around the time of Eodoxus in 400 BC, we began to devise models of how such patterns could be described geometrically by rotating spheres. And the first sphere was called a deferent.
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