To fully describe the apparent motion of the planets in the sky, Ptolemy's model invoked
A) ellipses.
B) constant speeds.
C) a heliocentric view.
D) epicycles.
E) Occam's Razor.

Question

Quizplus · Accepted Answer

Ptolemy's model involved the use of epicycles, which were small circles that planets would move along while also moving along their larger circular orbits. This was done to explain why planets sometimes appeared to move backwards in the sky (retrograde motion).

To Fully Describe the Apparent Motion of the Planets in the Sky