Ask A Scientist© Astronomy Archive

Author:      carl w gamauf, jim, prairie view,  and  mike gucwa
Will the Sun ever burn out?

Response #:  1 of 4
Author:      jasjeet s bagla
Yes.  Sun converts Hydrogen into Helium and by radiating this energy it
maintains its stability.  When the hydrogen content goes down and there is
not any left to be converted, it will cool down and end its life.  This will
happen after a few billion years.

Response #:  2 of 4
Author:      asmith
Probably not - the Sun is too small to blow up.  However, when the Sun gets
really old (about 5 billion years in the future?) it will expand outward and
probably grow so big that the Earth will be within the Sun's atmosphere,
probably destroying the planet.

Response #:  3 of 4
Author:      samuel p bowen 
When the Sun has fused all of the hydrogen atoms into helium atoms it will
be finished.  It would then start to cool and expand.  Unfortunately we
think it would expand out beyond Earth's orbit.  We would be cooked.  This
is not expected to happen for billions of years.  It is hard to think that
humans will still be around.  We will have left or may not have survived. 
Nothing to worry about for the next several million years.  

It is true that when the Sun runs out of its current fuel, hydrogen and
starts to cool down, it will expand into a red giant and could expand out to
Jupiter.  These are the estimates I have seen quoted before.  The end of the
Sun is billions of years away.

Response #:  4 of 4
Author:      asmith
Yup.  About 5 billion years from now, according to our best theories of the
way stars get older.  The first thing it will do is expand the outer surface
of the star, probably too close to the Earth's orbit, which will be pretty
much the end of things here.