The Copernican Revolution
Of all the motions there were, motions of the heavenly bodies most occupied the thoughts of ancient thinkers. The Pythagoreans put Earth at the center of the universe and the planets (including our Sun and Moon) on spheres turning around it. Variations of this model were proposed (most notably by Aristarchus in about 200 BC), but the matter was essentially settled by Plato when he posed the problem of finding the best combinations of circular orbits to explain the motions of the planets. The most successful attempt was by Claudius Ptolemy in about 100 AD. Using the idea of epicycles proposed by Hipparchus over 200 years earlier, he created a complex model (the Ptolemaic system) that could predict the motions fairly accurately - Plato's problem had been solved. The Ptolemaic system was accurate enough (although modified - and made more complex - over time) to stand for fifteen centuries until, looking for a simpler way, Nicolaus Copernicus moved the center of the World to the Sun.
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