Why does the moon seem to have different shapes?
As the Earth rotates on its axis and the moon revolves around the Earth, we get to see the moon in various different positions with respect to the sun. At any given time, half of the moon is facing the sun, but an observer on the surface of the Earth may only be seeing part of the illuminated surface. The part that is not illuminated is invisible from Earth, so the moon seems to be of different shapes.
