When did a planet undergo retrograde motion in Ptolemy's model of the solar system?
A)When the deferent of a planet carried it closest to the Earth
B)When the Earth passed the planet as they both orbited the Sun
C)When the planet was dimmest and most distant
D)When the planet was on the part of its epicycle that was nearest the Earth

Question

Quizplus · Accepted Answer

According to Ptolemy's model, retrograde motion occurred when a planet was on the part of its epicycle that was nearest the Earth. The epicycle was a small circle that a planet's orbit traced as it moved along its deferent, a larger circle around the Earth. During retrograde motion, the planet appeared to move backwards in the sky relative to the stars.

When Did a Planet Undergo Retrograde Motion in Ptolemy's Model