An inferior planet moves more or less directly toward Earth at greatest eastern elongation. What does this mean for an observer is watching the night-by-night motion of this planet against the background stars?
A) The planet appears to remain stationary for a few days.
B) The planet appears to be moving at its fastest motion against the background.
C) The planet is invisible in the sky because it is moving toward Earth.
D) The planet's motion against the background will appear to be normal, that is, direct motion, because apparent motion is always constant in a circular orbit.

Question

Quizplus · Accepted Answer

At greatest eastern elongation, an inferior planet (one that orbits closer to the Sun than Earth, such as Mercury or Venus) appears to pause in its motion against the background stars from Earth's perspective. This is because it is transitioning from moving eastward relative to the stars (direct motion) to moving westward (retrograde motion), creating a moment where its motion relative to the stars appears to halt.

An Inferior Planet Moves More or Less Directly Toward Earth