The Copernican explanation for retrograde motion requires that:
A) the planets have circular orbits.
B) the planets move on epicycles.
C) the planets have different orbital periods.
D) only planets outside of Earth's orbit undergo retrograde motion.

Question

Quizplus · Accepted Answer

The Copernican model explains retrograde motion by recognizing that planets have different orbital periods. This difference in speed and orbital periods means that, from our viewpoint on Earth, it occasionally appears as if outer planets are moving backward (retrograde motion) when Earth overtakes them in its orbit.

The Copernican Explanation for Retrograde Motion Requires That