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Copernicus Epicycles versus Kepler's Ellipses
Copernicus Epicycles versus Kepler's Ellipses
Contrary to common belief, the Sun is not precisely at the center of the Copernican universe, nor do the planets orbit around it in perfect circles. In order to describe the angular motion of the planets, Copernicus moved the Sun slightly from the center and let the planets describe oval orbits obtained as a combination of two uniform circular motions. The agreement with observations was good but not perfect. It took all Kepler's genius to understand that the data could be perfectly explained by assuming that the orbits are ellipses with the Sun at one of the foci, traveled in such a way that the line joining the Sun with the planet sweeps out equal areas in equal times.