(NASA Goddard Space Flight Center/Creative Commons)
Well, the fact is, the Sun is not a ball of fire. In fact, the light and heat that we feel from here on Earth are nothing more than the result of hydrogen gas heated to 2 million degrees Celsius. At that temperature, anything releases energy in the form of light and heat. Therefore, we have the impression that the star is made of fire. The difference is that the flame that comes out of bonfires is one of the products of the combination of certain compounds, such as wood, alcohol or gasoline, with oxygen in the atmosphere. In the case of the Sun, the energy comes from nuclear fusion. The violent pressure inside the star causes hydrogen atoms to stick together to form helium atoms. This union also releases light and heat, but on an incomparably greater scale.
This light is so intense that it strips electrons from the atoms that form the gaseous layer of the Sun, causing it to behave like a plasma, the same state in which the material that fills fluorescent lamps, for example, is. “The outer layer of the star looks like a luminous fluid, formed by a ‘paste’ of loose electrons and protons”, says astronomer Roberto Costa, from USP. Finally, a curiosity: the planets formed mainly by gases, such as Jupiter, Saturn, Uranus and Neptune, do not look like bonfires like the Sun. But, for those who observe them from space, their gaseous surfaces give the impression of being melting.