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The Moon is not uniformly illuminated by the Sun during its orbit around the Earth. The portion of the Moon that is illuminated, as observed from Earth, is known as the lunar phase. These phases change periodically throughout the month, and from Earth, we always see the same side of the Moon. There are eight recognized lunar phases, though more commonly, only the four principal phases are emphasized: New Moon, First Quarter, Full Moon, and Third Quarter. The most noticeable differences in the appearance of the Moon occur during the First and Third Quarter phases. In the First Quarter, the right side of the Moon is illuminated. For observers in the Northern Hemisphere, this indicates that the illuminated portion is increasing, or "waxing." Conversely, during the Third Quarter, when the right side of the Moon is dark, the illuminated portion is decreasing, or "waning." In the Southern Hemisphere, the Moon's phases are observed with an inverted perspective compared to the Northern Hemisphere.
