December 12, 2011, 12:28 pm
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Ptolemy (c. 90-c. 170) was Greek philosopher who synthesized and extended Hipparchus's system of epicycles and eccentric circles to explain his geocentric theory of the solar system. Ptolemy believed the planets and Sun to orbit the Earth in the order of Mercury, Venus, Sun, Mars, Jupiter, Saturn. This system became known as the Ptolemaic system and predicted the positions of the planets accurately enough for naked-eye observations. The fusion of Ptolemy's model with the cosmology and physics of Aristotle was adopted in the late antiquity and medieval Western world and defined the dominant view of the universe for over a millennium. Ptolemy also made important contributions to geography and cartography.


Cleveland, C. (2011). Ptolemy. Retrieved from


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