The Moon does not emit its own light, shining instead by reflecting sunlight. Depending on the relative positions of the Earth, Sun and Moon, varying amounts of the lunar surface appear to be illuminated.

A few days after the First Quarter Moon, the Moon’s disk is nearly completely illuminated as seen from the Earth (position D in the diagram below). The waxing (growing) gibbous Moon rises after noon, transits the meridian after sunset and sets after midnight. The waxing gibbous phase repeats every 29.531 days – one synodic month.

The Moon’s motion around the Earth, with the Sun illuminating only one side of the Earth and Moon.