Waxing gibbous Moon. Image 9 of 27. Optical image of a waxing (increasing in apparent size) gibbous Moon 9 days into its 28-day cycle. The lunar phases arise as the Moon's orbit of the Earth shows the Earth-facing side moving into and out of the light of the Sun. This 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. On a waxing Moon the day-night line (terminator) marks the lunar dawn. The Moon is gibbous when it is more than half full. Taken in September 2001. A sequence of the monthly cycle of Moon phases is shown on images R340/644-670.