It's just a phaseDec 10, 2013
For celestial navigators (and voyagers who just like looking at the moon), below is a video from NASA that compresses the lunar phases for the entire year of 2014 into just five minutes. The video was made using images compiled by NASA's Lunar Reconnaisance Orbiter, which has been in orbit around the moon since the summer of 2009. One small side animation shows the position of the moon in its orbit as the phases change.
Question: Since the moon orbits through a point where it has the sun and earth on opposite sides once a month, why don't we have a monthly eclipse? If you're inclined, try your hand at answering the question in the comments below.