An ancient Greek astronomer, living in Egypt (see also Egypt), who proposed a way of calculating the movements of the planets on the assumption that they, along with the sun and the stars, were embedded in clear spheres that revolved around the Earth. The system of Ptolemy, called the Ptolemaic universe, prevailed in astronomy for nearly fifteen hundred years, until the modern model of the solar system, with the sun at the center and the planets in motion, was developed from the ideas of Copernicus.
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