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 Earth.
B) Earth must rotate so an observer can see the Moon.
C) the Moon's orbit is tilted with respect to Earth's rotational axis.
D) 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 Earth moves in its orbit around the Sun, requiring the Moon to travel a bit further to complete the cycle of phases as seen from Earth.

The Moon's Sidereal Period Is 2