What Causes the ‘Phases of the Moon’ and Why Do They Change?

The Moon changes shape because it moves around the Earth, and we see different parts of it from our spot on Earth.

Imagine you have a round ball, like a basketball, and you're holding a flashlight. The flashlight is like the Sun, and the basketball is like the Moon. When you move the basketball around your head, which is like the Earth, sometimes more of the side facing the light shows up, and sometimes less does.

When the Moon is on the opposite side of the Earth from the Sun, we see the whole lit-up part, that’s a full moon. When it's between the Earth and the Sun, we don’t see any lighted part at all, that’s a new moon.

Sometimes the Moon is half between those two spots, that’s a half-moon, or first quarter or last quarter depending on where it is in its path. It's like playing with shadows, as the Moon moves, we see more or less of the part lit by the Sun.

So no magic, just movement and light!