Moon phases

The Moon does not emit any light on its own. All the moonlight we see is the light coming from the Sun that is reflected off the surface of the Moon, but,  from the Earth, we can only see the illuminated part of the half facing us.

During its orbit around the Earth the area of the moon’s disk which is visible changes. The new moon occurs when the moon is on the sun’s side of the Earth and shows us its shadowed face. When it lies on the opposite side of the Earth from the sun, the moon presents a fully illuminated disk which we call the full moon. The 29 days which separate two new moons are called a lunar month or a lunation.
The Lunar Cycle begins with the conjunction of the Sun and the Moon. This is the new moon.