Why does the moon have phases?

You can recreate the phases of the Moon with nothing more then a dark room, bright lamp, basketball, and baseball. Imagine the dark room is space and the bright lamp is the rays of light from our sun. Mark anywhere on the basketball. This represents where you are standing on Earth. Looking from this point, rotate the baseball (our Moon) around the basketball (our Earth) to see how the baseball becomes more and less illuminated as the Moon goes through phases.