The Moon's sidereal period is 2.2 days shorter than the period during which the Moon's phases change because:
A) the Moon always keeps the same side turned toward the Earth
B) the Earth must rotate so an observer can see the Moon
C) the Moon's orbit is tilted with respect to the Earth's rotational axis
D) the Earth moves significantly in its orbit around the Sun during that time
E) the Moon's orbital speed varies

Question

Quizplus · Accepted Answer

The Moon's sidereal period is shorter because the Earth moves in its orbit around the Sun, requiring the Moon to travel a bit further to complete a full cycle of phases as seen from Earth.

The Moon's Sidereal Period Is 2