Here's why:
* The moon doesn't produce its own light: It reflects sunlight.
* The amount of reflected light depends on the angle: When the moon is full, we see the entire sunlit face, and when it's half, we see half of that sunlit face.
* It's not a linear relationship: The brightness doesn't decrease by half when the moon goes from full to half. It's more complicated due to the way light reflects off the surface of the moon and the angle at which we view it.
Roughly speaking, a full moon is about twice as bright as a half moon. This is a general estimate, and the actual difference in brightness can vary slightly depending on factors like atmospheric conditions.
