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.

As the Moon approaches its New Moon phase, only a decreasingly thin crescent remains (position H in the diagram below). The waning (shrinking) crescent Moon rises after midnight, transits the meridian after sunrise and sets after noon. The waning crescent 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.