In Ptolemy's geocentric model, retrograde motion occurs when the planet is closest to us, on the inside portion of the

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In Ptolemy's geocentric model, retrograde motion is explained by the planet moving along a small circle called the epicycle, which itself moves along a larger circle called the deferent. When the planet is on the inside portion of the epicycle, it appears to move backward (retrograde) relative to the stars.

In Ptolemy's Geocentric Model, Retrograde Motion Occurs When the Planet