Here's why:
* The Sun is a star: It generates its own light and heat through nuclear fusion, releasing enormous amounts of energy.
* The Moon is a reflector: It doesn't produce light but reflects sunlight. The light we see from the moon is simply sunlight bouncing off its surface.
While the moon can appear bright in the night sky, it's only because the sun is so far away. The moon is much closer to us, and it's reflecting a small portion of the sun's powerful light.
If you were to stand on the surface of the moon during the day, the sun would appear just as bright as it does from Earth. The moon itself would be completely dark.
