Full Moon. Image 14 of 27. Optical image of a full Moon 14 days into its 28-day cycle. The Moon is full when the Earth-facing side is fully lit by the Sun. The continuing motion of the Moon in its orbit around the Earth will begin to move this Earth-facing side out of the sunlight. Darkness will encroach (here, from the right-hand side) as the lunar night falls on a waning Moon. The Earth- facing side of the Moon is locked in place by the gravitational influence of the Earth. This results in a lunar day that equals the length of the lunar Earth orbit. Taken in October 2001. A sequence of the monthly cycle of Moon phases is shown on images R340/644-670.