When observing planetary motions from Earth, the phrase "retrograde motion" refers to the
A) apparent westward motion of the planet (and the Sun, the Moon, and stars) across the sky due to the rotation of Earth.
B) motion of the planet away from Earth during part of its orbit.
C) slow eastward motion of the planet from night to night compared to the background stars.
D) slow westward motion of the planet from night to night compared to the background stars.

Question

Quizplus · Accepted Answer

Retrograde motion is observed when a planet appears to move westward across the sky from night to night relative to the stars, which is a result of the relative positions and motions of Earth and the other planet.

When Observing Planetary Motions from Earth, the Phrase "Retrograde Motion