Ptolemy, Claudius: A great astrologer, astronomer and geographer of the second century (ca. 100-178 A.D.) who developed the theory that Earth is the motionless center of the universe about which the planets, sun and Moon revolve. Ptolemy's work, recorded in his Tetrabiblos, was based in part upon the earlier works of Hipparchus (ca. 190-120 B.C.), who catalogued the known stars and, through his observations, discovered Precession of the Equinoxes. The Ptolmaic theory was widely accepted until replaced by the Copernican theory, put forth in the sixteenth century, which states that Earth is a moving planet, thus laying the foundation for later discoveries.

 

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Ptolemy, Claudius: A great astrologer, astronomer and geographer of the second century (ca. 100-178 A.D.) who developed the theory that Earth is the motionless center of the universe about which the planets, s . . . View Full Definition

Tetrabiblos: Ptolemy's four-volume treatise on astrology (second century). See also Ptolemy, Claudius.