Ptolemy (aka Claudius Ptolemaeus, Ptolomaeus, Klaudios Ptolemaios, Ptolemeus) lived in Alexandria, Egypt and has an important role in the history of astronomy and geography. We know very little of Ptolemy’s life, including his birth and death dates. Various sources report different years, however, the first observation made by him which we can date exactly was on 26 March 127 while the last was on 2 February 141. Some experts believe his life spanned the years 87 – 150. During his lifetime, he did much to advance the sciences of astronomy and geography.

We get a few clues about him from his name, Claudius Ptolemy, which is a mixture of the Greek Egyptian ‘Ptolemy’ and the Roman ‘Claudius’. This seems to indicate that he was descended from a Greek family living in Egypt and that he was also a citizen of Rome. This could only have happened as a result of a Roman emperor rewarding one of his ancestors with this favor.

Around 1360, Theodore Meliteniotes claimed that Ptolemy was born in Hermiou (Northern Egypt. Alexandria is slightly farther south.) Due to the fact that Meliteniotes lived more than a thousand years after Ptolemy, and there is no corroboration, there is a lot of skepticism. In fact no evidence exists that he ever lived anywhere other than Alexandria.

Ptolemy was an astronomer, mathematician and geographer. He classified the Greek geocentric view of the universe, and calculated the apparent motions of the planets, as they were known in his time by synthesizing and extending Hipparchus’s system of epicycles and eccentric circles to explain his geocentric theory of the solar system. He used at least 80 epicycles to explain the motions of the Sun, the Moon, and the five planets known in his time.

This system came to be called the Ptolemaic System and was the center of astronomical beliefs for nearly a millennium and a half. It predicted the positions of the planets accurately enough for naked-eye observations.

Ptolemy described his system in his book, Almagest (Also known as Mathematical Syntaxis). It was a thirteen book mathematical explanation of astronomy, containing a wide variety of information. He also included a star catalog that contained 48 constellations, all with the same names still in use today.

The Ptolemaic System was the accepted wisdom until the Polish scholar Copernicus proposed a heliocentric view in 1543. In fairness, Ptolemy’s system is actually more accurate than Copernicus’s. The heliocentric calculations for the movement of planets does not improve on Ptolemy’s until Kepler’s Laws were added. Some people also doubt that Ptolemy truly believed his own system, rather he merely used it as a method of calculating positions.

Not just an astronomer, Ptolemy was very important in the history of geography and cartography. He was well aware that the Earth is a sphere. His is the first known projection of the sphere onto a plane. His work, “Geography” remained the principal work on the subject until the time of Columbus. It was amazingly accurate for the time, but had Asia extending much too far east. This may have been a deciding factor in Columbus’s decision to sail west for the Indies.


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