Waning crescent Moon. Optical image of the waning crescent Moon. The Moon is said to wane when it is diminishing in apparent size. The phases of the Moon are due to its orbit around Earth. When it lies in between the Earth and the Sun, only the unlit side faces us, and it is called a new Moon. When it has moved round so that the Earth lies between it and the Sun, we see the full lit face, called a full Moon. North is at top. For the sequence of the Moon's phases, see images R340/526-532.