system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why exactly do we see fire? And what makes it suddenly appear as visible?

I know about heat radiation, and that things that get too hot emit visible red light that's normally to low to see until it gets hotter (the hotter it is the higher the heat radiation light until it gets into human visible spectrum) .   


But while glowing steel falls under that, why does fire exactly start being visible, and is there fire even before we can see it? Fire is all wobbly and needs oxygen to burn. Or is it always on fire but before it's on the visible spectrum we can't see it?
gpt
Fire isn't a *thing* on to itself. It doesn't exist as an object in the same way steel exists as an object. 

Fire is a description of a proces: The rapid reaction of fuel with oxygen. What you're seeing is that reaction: which releases enough energy to emit heat, light, in addition to the actual byproduct of the reaction. It's less that fire needs oxygen to burn, and more that fire doesn't exist without oxygen and fuel that's being oxydized.