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Detailed explanation-1: -The Ptolemaic Model By the time of Ptolemy Greek astronomers had proposed adding circles on the circular orbits of the wandering stars (the planets, the moon and the sun) to explain their motion. These circles on circles are called epicycles.

Detailed explanation-2: -The original system proposed by Hipparchus used epicycles which were able to model retrograde motion and to explain the dimming and brightening of the planets by placing them at times closer, then farther away from earth.