nomical writings.
             To create a new plan for the solar system, Copernicus would have to somehow debunk Ptolemy's long-standing method. Ptolemy's universal system had been firmly established for almost 1500 years when Copernicus was born; this system was a mathematical model based on Aristotelian thinking and thus the idea that the planets rotate on crystal spheres in perfect motion. Ptolemy had to discard the idea of perfect motion because of the obvious fact of retrograde motion; this led him to invent "epicycles" or small, backwards circles that a planet makes in order to maintain the proper motion in the sky, "the eccentric", which meant that the earth was slightly off-center, and finally, the "equant" which was the focal point opposite the eccentric in the center. The point of these efforts was to assure that the planets would have precisely circular motions around the earth so that they could follow the crystal spheres. But Ptolemy had abandoned the idea of planetary mechanics in order to save
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