What was the Ptolemaic universe?

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The Ptolemaic system was named after Claudius Ptolemy, a philosopher in the first century A.D. who developed it. Essentially, Ptolemy conceived the universe as geocentric, with the Earth at its center. The Earth was held to be less perfect than the rest of the universe, which was composed of objects that moved along spheres. By the medieval period, the Ptolemaic system was the accepted cosmological model for the universe, held as orthodoxy by the Catholic Church because it appeared to line up fairly strongly with Biblical descriptions of the universe, and because it emphasized that the earth was changing and corruptible, and the rest of the universe, made of a so-called "fifth element," was immutable and perfect. The geocentric universe came under challenge in the sixteenth century, most famously by Copernicus and Galileo, whose works were condemned by the Church. As better instruments made more precise observations possible, the geocentric conception of the universe gave way to first a heliocentric one, and then a recognition of the universe as almost infinitely massive, with the Earth and its solar system in a galaxy known as the Milky Way.

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