In the diagram above, you can see the Moon always has a lit side (facing the Sun) and a dark side (facing away from the Sun). From the Earth, we can only see the part of the Moon that is facing toward us at any time (which is often called the near side of the Moon) and we cannot see the part of the Moon facing away from Earth ( called the far side of the Moon). The phase of the Moon, or the shape of the lit part of it, that we see at any time is then determined by the combination of these two factors - which part of the Moon is lit by the Sun and visible to Earth at the same time!
The StarChild site is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC.
The StarChild Team
StarChild Graphics & Music: Acknowledgments
StarChild Project Leader: Dr. Laura A. Whitlock
Responsible NASA Official: Phil Newman