The purpose of using epicycles and deferents to explain the motion of the planets in the night sky was to account for
A)prograde motion.
B)Mercury's and Venus's limited angular distance from the Sun.
C)retrograde motion.
D)non-uniform speed of the planets in their orbits.
E)precession of the equinoxes.

Question

Quizplus · Accepted Answer

Epicycles and deferents were used to account for retrograde motion, which is the apparent backward motion of planets in the night sky. The retrograde motion was observed by ancient astronomers and could not be explained by the simple model of circular orbits. Epicycles and deferents allowed astronomers to explain the retrograde motion as a result of the complex motion of the planets around the Earth.

The Purpose of Using Epicycles and Deferents to Explain the Motion