The Ptruth About Ptolemy

A case of fraud?

Claudius Ptolemy, the second-century Greek mathematician whose word on the heavens was law for some 1,400 years, has long been considered the king of ancient astronomers. Now an iconoclastic physicist is seeking to dethrone him. After an eight-year study of the Syntaxis, Ptolemy's 13-volume collection of celestial observations, Robert R. Newton of the Applied Physics Laboratory at Johns Hopkins University has concluded that Ptolemy faked his figures. In his just-published The Crime of Claudius Ptolemy (Johns Hopkins University Press; $22.50), Newton minces no words: "Ptolemy is not the greatest astronomer of antiquity, but he is something still more unusual. He is the most successful fraud in the history of science."

Newton bases his charges on a meticulous examination of Ptolemy's work, which revealed an internal consistency that would not have been possible with that ancient astronomer's techniques. Newton also conducted a backward extrapolation from modern astronomical data, which demonstrated certain anomalies in Ptolemy's observations. Ptolemy claimed, for example, that he had observed an autumnal equinox at 2 p.m. on Sept. 25, A.D. 132; he stressed that he had measured the phenomenon "with the greatest care." But, says Newton, back calculation from modern tables shows that an observer in Alexandria, Egypt, where Ptolemy made his observation, should have seen the equinox at 9:54 a.m. on Sept. 24, more than a day earlier.

Why the difference? To Newton, the evidence suggests that Ptolemy accepted the observations of an earlier astronomer, Hipparchus, without checking them against his own. Newton feels that Ptolemy may also have followed a technique used by mediocre students throughout history: he worked backward to prove the results he wanted to get, and sometimes made up his data. Whatever he did, Ptolemy got away with it for 18 centuries.

At least one scientist has come to Ptolemy's defense. Astronomer and Science Historian Owen Gingerich of Harvard admits that the Syntaxis contains "some remarkably fishy numbers." But he is convinced that any deception was honestly motivated, and that Ptolemy, like many a modern-day scientist, merely chose to publish the data that best supported his theories. These ideas are outdated anyway. Ptolemy's theories were all aimed at proving that the earth was the center of the universe. By 1543 Copernicus had proved Ptolemy wrong.

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