What is a Lunar Phase?
A lunar phase is the appearance of the illuminated part of the moon’s surface as seen from earth. One half of the moon is always lit because of the sun, but how much of the illuminated part is shown can vary from 0% to 100% or new moon to full moon, respectively. The variances in the lunar phases are caused by the different viewing geometries, not by the moon moving behind the earth and the earth casting a shadow upon the moon. In fact, the full moon occurs when the moon and the sun are on different sides of the earth.
