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Claudius Ptolemy

2nd Century

Claudius Ptolemaeus was a native of Alexandria, Egypt, in the 2nd century C.E. We know very little about Ptolemy’s life, not even his date of birth or death. Nevertheless, we do have a few clues about him from his name which is a combination of the Greek ‘Ptolemy’, and the Roman ‘Claudius’. This would suggest that he was descended from a Greek family living in Egypt, and that he was also a citizen of Rome, perhaps through an ancestor of his who had been rewarded with citizenship.

Regarding the length of Ptolemy’s career, we can say with certainty that the first recorded date of an observation made by him is March 26, 127 C.E.; and that the last recorded date of an observation from him is on February 2, 141 C.E.

Astronomer, mathematician, and cartographer/geographer, Ptolemy has played an important role in the history of Western civilization. He standardized the Greek geocentric view of the universe, and calculated the apparent motions of the planets, as they were known at that time, by synthesizing and extending Hipparchus’ theory of epicycles and eccentric circles that explained the geocentric model of the Solar System.

His work in this field came to be known as the Ptolemaic system, and it was the centre of astronomical, and religious, beliefs for nearly a millennium and a half. In his 13-volume work known as the Almagest, Ptolemy elaborated some 80 epicycles to demonstrate the motions of the Sun and Moon, and the five planets known at that time. (His predictions of the positions of the planets were accurate enough for naked-eye observations.) The Almagest also included Ptolemy’s star catalogue of 48 constellations, all of which are still known by the same names today.

The Ptolemaic system was the accepted wisdom until the Polish scholar, Nicolaus Copernicus, proposed a heliocentric view in 1543. However, heliocentric predictions only became more accurate than the Ptolemaic system in 1609 when Johannes Kepler published his laws of planetary motion in his revolutionary work, Astronomia Nova.

In the field of geography and cartography, the volumes of Ptolemy's work published under the title Geographia remained the principal references on the subject until the time of Columbus. He knew that the Earth was a sphere, but in his maps of the known world he projected Asia too far east, and this may have convinced Columbus into believing that the voyage west to the East Indies was shorter than it was in reality.