The new moon occurs when the moon is positioned between the earth and the sun. At a full moon the earth, moon and sun are in approximate alignment. The first quarter and third quarter moons happen when the moon is at a 90 degree angle with respect to the earth and sun. After the new moon, the sunlit portion is increasing but less than half, so it is a waxing crescent. After the first quarter the is still increasing but now it is more than half, so it is a waxing gibbous. After the full moon the light continually decreases this is called a waning gibbous. Following the third quarter is the waning crescent, which wanes until the light is completely gone. Hope this helps.
