Here's why:

* The Moon is a large, rocky body in space. It doesn't have its own source of energy like the Sun, which generates light through nuclear fusion.

* Sunlight shines on the Moon. When sunlight hits the Moon's surface, some of that light bounces back towards Earth, making the Moon appear bright in our sky.

* The amount of light we see depends on the Moon's phases. During a full moon, the entire side of the Moon facing Earth is illuminated by the Sun. During a new moon, the side facing Earth is in shadow.