Claudius Ptolemy was a Greco-Egyptian mathematician, geographer, astronomer, and poet. He lived in Rome in 100 AD. Ptolemy's model of the solar system assumed that the Earth was the center of the universe. According to Ptolemy, each planet moved on a small sphere or circle called an epicycle, that moved on a larger sphere (circle), called a deferent. He assumed that the stars moved on a celestial sphere around the outside of the planetary spheres. The Ptolemaic conception of the universe was accepted by society and not challenged for 1,300 years.
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