How does the Sun keep burning?
The central part of the Sun is like a nuclear reactor. It combines four
Hydrogen atoms to make Helium and some energy in form of radiation. It is
this energy that we receive. A star as big as the Sun may live on this
reaction for about 9 billion years. We think the Sun is about half that
Jasjeet S Bagla
Update - 1/24/2005
We say that the sun is "burning," but it is not burning in a chemical sense
like wood or oil. The sun is kept hot by nuclear reactions taking place
inside of it, but these are different from the reactions in a nuclear
Nuclear reactors split heavy atoms (like uranium) to release energy. In
contrast, the sun fuses together light atoms (like hydrogen) to release
The hydrogen reaction is more complicated than just four hydrogen atoms
(mass 1) fusing together into a helium (mass 4).
The correct sequence is two normal hydrogen nuclei (protons) combine into a
heavy hydrogen nucleus (with an electron left over). Then a normal and
heavy hydrogen combine into a light helium. Then two light heliums combine
to form a normal helium (with two protons left over).
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Update: June 2012