The ring of fire

It's not just a Johnny Cash song. Inside the Sun, very hot, ionized gas (plasma, which is essentially the same thing as fire), circulates deep below the layer that produces most of the optical light we see (called the photosphere). However, we can infer its properties based on its observable effects when it happens to skim the Sun's "surface." Go here to read how it might be responsible for the very few Sun spots being detected over the last few years.