Waning crescent Moon Image of Optical image of a waning decreasing in apparent size crescent Moon days into its day cycle The lunar phases arise as the Moons orbit of the Earth shows the Earthfacing side moving into and out of the light of the Sun This Earthfacing 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 On a waning Moon the daynight line terminator marks the lunar sunset The Moon is crescent when it is less than half full Taken in October A sequence of the monthly cycle of Moon phases is shown on images R
