Why does the appearance of the Moon change in a pattern that repeats about every 30 days?

Answer 1

The appearance of the Moon changes in a pattern that repeats about every 30 days because of its orbit around the Earth. As the Moon orbits the Earth, the angle between the Earth, Moon, and Sun changes, causing different portions of the Moon to be illuminated by the Sun. This changing angle creates the different phases of the Moon, such as the full moon, new moon, waxing crescent, and waning gibbous. This cycle takes about 29.5 days to complete, which is why we see the same phases repeating every month.