Why is there a two day difference in the sidereal and synodic months?
A)The Moon speeds up at perigee, and slows down at apogee.
B)The sidereal day is four minutes shorter than the solar day, and it adds up.
C)The Earth is closer to the Sun during the sidereal month.
D)The Earth is also revolving around the Sun, so the Moon must "catch up."
E)The Moslem lunar year is only 354 days long, on average.

Question

Quizplus · Accepted Answer

The two-day difference between the sidereal and synodic months is due to the Earth's revolution around the Sun. As the Earth moves in its orbit, the Moon needs to travel a bit further to complete a full phase cycle from new moon to new moon, which is the basis of the synodic month. This additional distance causes the synodic month to be longer than the sidereal month, which is the time it takes for the Moon to return to the same position against the background stars.

Why Is There a Two Day Difference in the Sidereal