Full moon is a
lunar phase that occurs when the
Moon is on the opposite side of the
Earth from the
Sun, and when the three celestial bodies are aligned as closely as possible to a straight line. At this time, as seen by viewers on Earth, the hemisphere of the Moon that is facing the Earth (the
near side) is fully illuminated by sunlight and appears round. Only during a full moon is the opposite hemisphere of the Moon, which is not visible from Earth (the
far side), completely unilluminated.
Photo credit: Luc Viatour