My+Moon

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The phases are a function of the moon's orbit around planet earth. there is always one half of the moon that is unlit by the sun, and one half that is lit. Our changing view of the moon's night-and-day sides are what we call moon phases. the new moon occurs when the moon is positioned between the earth and sun. The three objects are in approximate alignment. The entire illuminated portion of the moon is on the back side of the moon, the half that we cannot see. At a full moon, the earth, moon, and sun are in approximate alignment, just as the new moon, but the moon is on the opposite side of the earth, so the entire sunlit part of the moon is facing us. The shadowed portion is entirely hidden from view. The first and third quarter moons happen when the moon is at a 90 degree angle with respect to the earth and sun. So we are seeing exactly half of the moon illuminated and half in shadow. After the new moon, the sunlit portion is increasing, but less than half, so it is a waxing crescent. After the first quarter, the sunlit portion is still increasing, but now it is more than half, so it is a waxing gibbous. After the full moon, the light continually decreases. So the waning gibbous phase occurs next. Following the third quarter is the waning crescent, which wanes until the light is completely gone. The reason this all happens is the position of the earth between the moon and sun. wherever it is matters how big or small the shadow is on the moon.