What determines the phases of the moon?
Phases are determined by the position of the moon in its orbit around the earth, with respect to the sun. There are four specific phases, which can be said to happen at a particular moment: New moon: when the moon is between the earth and the sun. First quarter: when the moon is halfway between new and full. Full moon: when it is opposite us from the sun. Last quarter: when it is halfway between full and new. In between those phases are general phases which cover a period of about a week and they vary in degree: Between new and first quarter is waxing crescent. Between first quarter and full is waxing gibbous. Between full and last quarter is waning gibbous. Between last quarter and new is waning crescent.
