Moon phases. Composite time-lapse image of the phases of the Moon, as seen in Earth's night sky during a lunar (synodic) month. A full Moon is at upper centre, with pairs of (from inner to outer) gibbous Moons, quarter Moons, crescent Moons and new Moons. The lunar phases occur because the Moon does not produce its own light, but reflects that of the Sun. As it travels around the Earth during its 29.53-day orbit, parts of the Moon's surface which are visible from Earth become shadowed by the Moon itself. New Moons occur when the Moon lies between the Earth and Sun, and full moons occur when the Moon is furthest from the Sun.