Why do we see different phases of the moon each month

Like the Earth itself, the Moon is roughly spherical in shape.  But instead of orbiting the Sun (once per year), it orbits the Earth instead (roughly once per month).

At any given point in its orbit, one side of the Moon is facing the sun and is lit up, while the other side faces away and is dark.  But because it's orbiting overhead, we see different sides of it:

All the other phases are just steps in between these.

2,407.2 miles. or 32 hours.