The sun is a nuclear fusion reactor

George Porter

The sun is a nuclear fusion reactor which derives its energy principally from the fusion of hydrogen atoms into helium. This reaction has been going on for about 5 billion years and will continue for about as long again before the fuel begins to run out. The inside temperature is several million degrees but the surface temperature corresponde very approximately to that of a black body at 6,000 ºC. The energy maximum in the radiation which reaches the earth’s surface occurs near the middle of the visible region in the green, as one would expect of a well adapted eye: 40% of the total radiation is in the visible, 51% in the infra-red and 9% in the ultra-violet region below 400 nm.

Fonte: Porter, G. 1975. Life under the sun. Proceedings of the Royal Institution of Great Britain 48: 173-82.