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 week after Full Moon, the Moon reaches its Last Quarter. In this phase, the Moon is in quadrature (elongation = 270o, position G in the diagram below), and one half of the Moon’s disk is illuminated as seen from Earth.

The Last Quarter Moon rises at midnight, transits the meridian at sunrise and sets at noon. The Last Quarter 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.