What evidence is there that the "stars" in the night sky (the sun could be a different matter, being close to us compared to the night sky "stars") are stars?

Could they be giant flashlights? With noble gases?

Or UFOs?

or UFOs with giant flashlights with noble gases?

Or something else?

No views yet.

Now the views appeared.

Spectroscopy, star forming regions, their intensity. There are thousands of experimental pieces of evidence and it's improved everyday, the closeness to the maths is really very good indeed. Most astrophysics undergrads do some observable tests on stars. Any decent star formation textbook say would provide the answers.