What changes in the way that the moon appears as it orbits the earth?

As the Moon orbits the Earth, it goes through a cycle of phases due to its position relative to the Earth and the Sun. These phases include the New Moon, First Quarter, Full Moon, and Last Quarter, resulting in varying amounts of the Moon's surface being illuminated. The changing appearance is primarily a result of the angle at which sunlight hits the Moon, causing it to appear as a crescent, half, or fully illuminated disk. This cycle takes about 29.5 days to complete, known as a lunar month.