According to Ptolemy's model,a planet undergoing retrograde motion on the sky would be moving on its epicycle:
A) in the opposite direction to the orbit of the epicycle's center.
B) in the same direction to the orbit of the epicycle's center.
C) away from Earth.
D) toward Earth.

Question

Quizplus · Accepted Answer

In Ptolemy's model, a planet's retrograde motion is explained by the planet's motion along an epicycle that is moving in the opposite direction to the planet's uniform motion along its deferent. Therefore, the planet undergoing retrograde motion on the sky is moving on its epicycle in the opposite direction to the orbit of the epicycle's center.

According to Ptolemy's Model,a Planet Undergoing Retrograde Motion on the Sky