# Have scientists always known that the Sun was not a fuel+air system?

Astronomy is far older than nuclear physics. So there was a long time in which fire was a reasonable explanation for the sun burning.

Has any scientist figured out the sun cannot possibly be a normal fuel+air fire? I guess such a scientist must be familiar with Newton's orbital mechanics since people prior believe the universe is filled with air.

I got inspired from this Phys.SE question: Why can there be fire in space while there is no oxygen?