Ptolemy, an Egyptian astronomer living in the second century A.D., devised
a powerful mathematical model of the universe based on constant motion
in perfect circles, and circles on circles. With the model, he was able
to predict the motions of the sun, moon, and stars, and even of the irregular
"wandering stars" now called planets.
| See Content Standard G History and
Nature of Science (grades 9-12): Historical Perspectives.
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