Geocentric model  

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In astronomy, the geocentric model of the universe is the theory that the Earth is at the center of the universe and the Sun and other objects go around it. Belief in this system was common in ancient Greece. It was embraced by both Aristotle and Ptolemy, and most Greek philosophers assumed that the Sun, Moon, stars, and naked eye planets circle the Earth. Similar ideas were held in ancient China. Aristarchus of Samos proposed a heliocentric model of the solar system.

Two common observations were believed to support the idea that the Earth is in the center of the Universe. The first is that, for observers in the northern hemisphere, the stars (including the Sun and planets) appear to revolve around the Earth each day, with the northern stars circling around the pole and those stars nearer the equator rising and setting each day and circling back to their rising point. The second is the common sense perception that the Earth is solid and stable; it is not moving but is at rest.

The geocentric model was usually combined with a spherical Earth by ancient Greek and medieval philosophers. It is not the same as the older flat Earth model implied in some mythology. The ancient Greeks also believed that the motions of the planets were circular and not elliptical, a view that was not challenged in western culture before the 17th century.

The geocentric model held sway into the early modern age; from the late 16th century onward it was gradually replaced by the heliocentric model of Copernicus, Galileo and Kepler. Today, geocentric cosmology survives in the work of some creationist fundamentalist Protestant elements of Christianity, as well as literary treatments within alternate history science fiction.

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