text: what do you call one revolution of the moon? seriously..?   a lunar cycle:  this explanation can be a bit confusing, so have patience. the moon takes 27 1/3 days to orbit the earth once, but the number of days between one full moon and the next full moon is 29 1/2 days. why are these two "months" not the same? the answer has to do with the earth and moon relationship to the sun. if you chart the moon's position every night for a full month, you could compare its position with a bright star, and then wait to see how long it takes for the moon to come back to its position relative to that star. the answer would be about 27 1/3 days. but during this time, the earth has moved nearly 1/12 of the way in its orbit around the sun. so to get from one full moon to the next would take about two days longer, 29 1/2 days, because the moon would have to travel a little further around the earth to get to "full" again.