Expert: Steve Nelson - 4/17/2008

Question
Hi, A fireman friend asked me this question yesterday and it has been driving me mad, so hopefully you can clear it up for me.  If things need oxygen to burn, and there is no oxygen present in space - which we are told is a void - then how does the sun burn?  And what does it burn?  Any help you could give would give my brain a rest and be very much appreciated!
warmest regards
Lucy

Answer
The sun doesn't burn oxygen like a flame to create energy with a chemical reaction like an Earth-type fire from your normal experience.  It actually burns hydrogen in nuclear fusion to create energy from a nuclear reaction!  That's why it's so super-powerful, gravity has compressed and heated the gases to the point where their actual nuclei (their little centers where all the heavy stuff is that gives them weight) actually combine, not just the outer electrons that float around the outside like in a chemical reaction.

The Sun is far more dense than the Earth.  Imagine that it's like a dense metal.  Its gravity pulls it in, it's a million times the mass of the Earth.  And it's almost all hydrogen, so it's super-compressed fuel!  Does that help?  If not, perhaps here:

http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/procyc.html