Here's why:

* Stars are giant balls of hot gas. They generate their own light and heat through nuclear fusion reactions in their cores.

* Nuclear fusion is the process where lighter elements, like hydrogen, fuse together to form heavier elements, like helium. This process releases enormous amounts of energy in the form of light and heat.

* Planets and other celestial objects reflect light. They don't produce their own light but shine because they reflect sunlight.

So, while stars appear to "shine" in the sky, they are actually generating their own light through a powerful process, unlike planets or other objects that reflect light.