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Greek astronomer and mathematician who based his astronomy on the belief that all heavenly bodies revolved around Earth. Ptolemy's model of the solar system endured until the 16th century when Nicolaus Copernicus proposed that the heavenly bodies in the solar system orbited the Sun.
An ancient Greek astronomer, living in 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.