月相

ses of the moon occur because the moon is spherical in shape. Sunlight illuminates the side of the moon closer to the sun, resulting in daytime. Conversely, the bulge in the moon casts shadows, causing the side opposite the sun to become nighttime. The moon orbits the Earth, causing the angle between the sun, moon, and Earth to change by approximately 12 degrees each day. Therefore, when viewed from Earth, we see the moon's phases changing in size in a cycle, as shown in Figure 1, which takes approximately 30 days.