Many people hold the mistaken belief that the phases of the moon are caused by the shadow of the earth. Though not true (the phases are caused by the varying angle of the sun on the lunar disk throughout the month), the earth's shadow DOES effect the appearance of the moon, but only during a lunar eclipse, which can only occur during a full moon. Above are two shots, one of a standard gibbous moon, and the other of the full moon in partial eclipse. Note the curvature of the shadow's edge on the second photo. This is one small segment of the large, circular shadow of the earth.