As viewed from the Earth, some planets appear to double back in their orbits for a while (retrograde motion). This is due to:

Question

A.
The planets really do reverse their motion through space, because of outside forces.

B.
The planets move on secondary orbits called epicycles, whose centers are in orbit about the Earth.

C.
The fact that the planets are in orbit about the Sun rather than about the Earth.

D.
The wobble of the Earth's axis of rotation.

Answer 1

The correct answer is:

C. The fact that the planets are in orbit about the Sun rather than about the Earth.

Retrograde motion occurs due to the relative positions and motions of the Earth and the other planets in their orbits around the Sun. As the Earth passes by an outer planet (like Mars), it makes the planet appear to move backward (retrograde) against the background stars for a time.