As the earth revolves about the sun, the moon revolves once about the earth in a period of about 30 days. In connection with tide, the moon revolves about the earth in the same direction as the earth rotates, resulting in a time period of about 24 hours and 50 minutes for the earth to complete one rotation with respect to the moon. Since the moon completes one rotation every 30 days, the same side is always facing toward the earth. The moon like the planets is illuminated by the sun, the size and shape of the visible portion of the moon as viewed from the earth is constantly changing. The names given to the various visible portions or phases of the moon are. NEW MOON, CRESCENT, FIRST QUARTER, GIBBOUS, FULL MOON, GIBBOUS, LAST QUARTER, CRESCENT.
Once in awhile the moon passes directly between the sun and the earth, casting a shadow across the surface of the earth. When viewed from within the shadow zone, it seems to the observer as though the sun disappears behind the superimposed moon,this is called a solar eclipse.
At other times, the moon's orbit takes it through the shadow zone cast by the earth, creating a lunar eclipse visible to observers on the dark side of the earth. This has little scientific value, but is interesting to see.
