The moon, in common with other planets and satellites of the solar system, does not shine by any light of its own. We see it because it reflects back some of the light from the sun that falls on it. Blot out the sun and the moon will cease to shine. It is because of this that the moon shows phases. At any time half of its surface is in sunlight, the other half is in darkness. If we are facing toward the sunlit side, we say it is full moon ; if we are facing the dark side we say it is new moon.