Here's why:

* The Moon: The moon doesn't produce its own light. It reflects sunlight that falls on its surface. That's why we see different phases of the moon as the amount of sunlight reflected towards us changes.

* Planets: Planets, like the moon, don't produce their own light either. They reflect sunlight that falls on them. The amount of reflected light varies depending on the size, composition, and distance of the planet from the sun.

So, while they appear to shine, they are actually reflecting the sun's light!