The shape of the Moon as seen from the Earth keeps changing. The changing shapes of the Moon are called phases. When the side of the Moon that faces the Earth is turned away from the Sun, we are unable to see the Moon. This phase is called the New Moon. As the Moon travels in its orbit around the Earth, we start to see a small portion of the Moon that is lit up by the Sun. This is called the Crescent Moon. The lit up portion seen by us slowly increases, and we see a Half Moon, then a Three-quarter Moon. When the Moon completes a half orbit around the Earth, we can see the entire disc lit up by the Sun – the Full Moon.