Waning gibbous Moon. The lunar phases arise as the Earth-Moon-Sun angle changes as the Moon orbits the Earth. This waning gibbous Moon is 18 days into its 28-day cycle. On a waning Moon, the day-night line (terminator) marks the lunar sunset as night falls over the Earth-facing side of the Moon. The Moon is gibbous when it is more than half full. This image, published in 2015, uses data from the Lunar Reconnaissance Orbiter. The image is part of a sequence of lunar phases (see images C030/3708-3714), orientated for the northern hemisphere.