Here's why:

* The Moon doesn't produce its own light. It's a large, rocky body in space that doesn't have its own light source.

* Sunlight illuminates the Moon. The sun's rays strike the moon's surface, and a portion of that light is reflected back into space.

* We see the reflected light. This reflected light is what we see as the moon shining in the night sky.

The moon's surface is dusty and rocky, so it reflects light differently than, say, a mirror. This is why the moon appears to have different phases, depending on how much of the sunlit side is facing us.