The Sun

[kermit911]

How can we tell how much Hydrogen is left on the sun to burn? and If there are large amount of Hydrogen on the sun, why doesn't the sun blow up?

[jake-the-peg]

The sun does not "burn" hydrogen like hydrogen burns on Earth - that is a chemical reaction between Hydrogen and oxygen, there's precious little oxygen on the Sun.

The Sun shines due to a fusion reaction from hydrogen nuclii joining together to make helium.

In a sense the sun is constantly blowing up but is being constantly held together by it's massive gravity.

We know the mass of the sun because of it's gravity and we can tell the relative abundance of all the elements in the sun by looking at the spectrum that you get from splitting it's light.

[Catso]

When you look at the sun, what you are seeing is an unshielded nuclear reaction; like looking into the centre of an ongoing nuclear bomb explosion.

[mibn2cweus]

The fusion of hydrogen into helium takes place within the center of the Sun's sphere. This is caused by the combined mass of the Sun pressing in from all directions around its center. When hydrogen atoms combine to make helium there is some extra mass left over that is released as energy. This energy presses outward heating and expanding the Sun's matter, keeping the Sun with all of its mass from collapsing in upon itself.