it is not shrinking in a shinking kind of way. It is however burning the gases and therefore will eventually burn itself out. Estimates are around one million years from now.

No, it's not shrinking. Sol is in it's mid life and is considered to be what is called a main sequence star. Not big, not small and still using hydrogen as it's fuel source. It's pretty happy in it's current state. The amount of energy that it's producing is counteracting the force of garvity, due to it's mass. In effect it's equally pushing out as much as gravity wants to pull it back in. In about 6 billion years Sol will run low of hydrogen and not produce as much energy. Gravity will then win the battle and our sun will begin to contract. This contraction ain't the end. Now Sol will begin fusing the ashes of the hydrogen, helium and out we go again taking the helium and converting it to carbon, releasing more energy again in the fuel switch and consuming any hydrogen left that was in the outer shell of the star. What's next? Yup, we got a yo yo. Not that it will matter to us, we'll have been crispy critters for some time. Back down in size she goes again to stabilize out as a white dwarf. In reference to Glenn's post: http://imagine.gsfc.nasa.gov/docs/science/know_l2/stars.html http://zebu.uoregon.edu/~soper/StarLife/starlife.html http://home.case.edu/~sjr16/stars_lifedeath.html http://www.umich.edu/~gs265/star.htm All agree that the core doen't undergo any collapse until the star has exhausted readily avaliable hydrogen and not DURING the hydrogen fusion process. It occurs AFTER. The corona doesn't expand until this time, either. Edit: I actually have Glenn, as well as doing a quick check of the dozen or so astonomical books and my collection of 3 years of Sky and Telescope and Atronomy magazines. The issue I have in your answer is that you state the core collapses before the sun switches to helium. That's it. Look at your wording. As to hydrogen being consumed later, yes, it does happen, in the outer shell, not in the core. Read that reference again, it's clearly stated.

No the Sun is not shrinking in any significant way. It is loosing some mass as it is converted hydrogen into helium, but the amount of mass that it is losing is miniscule compared to its over all mass. Also, I would like to clear up a few misconceptions in some of the other answers. 1) The sun has a total expected life span of about 10 billion years of which it has 5 billion left. 2) As it begins to run out of hydrogen to burn the core will collapse while the outer layers expand. **************** "scubabob: Glenn, the core collapses at the final stage, when it's using carbon, not during the hydrogen fusion stage or helium stage. The core remains constant until the helium is gone. Carbon is left. It's heavier and denser, causing contraction of the core." No, as helium builds up in the core, hydrogen burning gets forced further out into the star. Eventually there is not enough heat production in the star's core to resist gravity and it starts to collapse. This causes the temperature in the core to rise through adiabatic heating until it gets hot enough (approximately 100 million Kelvins) for helium to start fusing to create carbon. The energy released by this reaction temporarily stops the cores collapse. This, by the way is where energy production will stop in the Sun. It does not have sufficient mass to generate the temperatures required to start burning carbon. So, carbon is where it will stop. **************** scubabob, I think that it is time that you state the authority upon which you make your assertions. I make mine based on the information that I got from "Astronomy: The Cosmic Journey", the textbook from which I spent 2.5 years teaching a college-level astronomy course. As further support for what I have asserted, I also refer you to the following sites. Note that one is from is hosted by Cornell University and the other is hosted by NASA. I would expect that both of these sources are more knowledgeable about astronomy then the two of us combined. http://curious.astro.cornell.edu/question.php?number=38 http://observe.arc.nasa.gov/nasa/space/stellardeath/stellardeath_1b.html