Phobos, the innermost moon of Mars, has an orbital period that is less than 1 Martian day. This means that, as seen from Mars, Phobos appears to:
A)hover over one position all the time in a synchronous orbit.
B)rise in the west, moving eastward.
C)oscillate back and forth in the sky, never rising or setting from a given location.
D)rise in the east, traveling westward.

Question

Quizplus · Accepted Answer

Phobos orbits Mars faster than the planet rotates on its axis, which means it appears to rise in the west and move eastward across the Martian sky, unlike most celestial objects as seen from Earth.

Phobos, the Innermost Moon of Mars, Has an Orbital Period