Answer:
by the moon turning.
Step-by-step explanation:
In the course of one month the Moon passes through all four phases. The Moon itself does not generate light; it is lit up by the Sun. Its looks like a shining rock up in the sky. As the Moon orbits the Earth, only one part of the moon is visible sometimes. And we can't see part of it because of the shadows. Giving rise to the phases of the Moon.