Ancient astronomers often had difficulty explaining _____, the occasional westward motion of the planets.
A) parallax
B) eccentrics
C) retrograde motion
D) deferents
E) epicycles

Question

Quizplus · Accepted Answer

Retrograde motion is the term used to describe the apparent backward or westward motion of the planets as observed from Earth. This phenomenon puzzled ancient astronomers because it didn't fit with the simple geocentric model of the universe they initially proposed.

Ancient Astronomers Often Had Difficulty Explaining _____, the Occasional Westward