What causes the phases of the Moon?

The phases of the Moon happen because of the way sunlight hits the Moon as it orbits Earth. As the Moon moves around our planet, we see different parts of its sunlit side. This creates phases such as new moon, crescent, first quarter, full moon, and last quarter. The whole cycle takes about 29.5 days. The Moon doesn’t produce its own light—it reflects sunlight. When the Moon is between the Earth and Sun, we can’t see it well (new moon). When it’s opposite the Sun, we see the entire lit side (full moon).