Science and Invention


What was the Ptolemaic System?

It was a scheme devised by the ancient Greek astronomer Ptolemy (c. 170–c. 100 B.C.). He proposed a system that placed Earth directly at the center of the universe—with the sun, the moon, and the planets all orbiting around Earth. However, Ptolemy observed that the movement of the planets did not match his scheme and so he added small orbits (called epicycles) to the model to try to make it work. Even though it was erroneous—and complicated—the Ptolemaic system was functional enough to make predictions of planetary positions. The system took hold, influencing thinking for 1,400 years. The Roman Catholic Church adopted the system as part of its doctrine, which the church hierarchy held to even when Polish astronomer Nicholas Copernicus (Mikolaj Kopernik; 1473–1543) refuted it in 1543, arguing that the sun, not Earth, is the center of the universe. In the 1570s accurate measurements of planet positions that had been taken by Danish astronomer Tycho Brahe (1546–1601) proved that the Ptolemaic system was inaccurate. But it was not until 1609, when German astronomer Johannes Kepler (1571–1630) devised a better explanation of planetary orbits, that the Ptolemaic system was put to rest.


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