Sunny Days.... By the numbers

I found myself needing the specific times and places carbon and oxygen arose in the universe. This led me to fusion in the sun. It turns out our sun will make it as a main sequence star going into red giant phase by smashing helium atoms together. Carbon and oxygen didn’t come from the big bang which only produced hydrogen and helium. Larger stars produce elements up to the atomic number of iron but iron won’t ‘burn’ (fuse) because it takes more energy to force more protons together than is released in the process of doing so.

So anyway, I found the sun burns 700 million tons of hydrogen (I am calling it ‘burning’ but that is not correct, burning is a chemical process that makes use of electric force but fusion is energy from the strong nuclear force when .7 percent of the mass of 4 hydrogen atoms is converted into energy) eac second! 700 million tons of hydrogen a second. Makes you wonder how long this sort of thing can continue. They say the sun has been around for about 5 billion years and has about 5 more billion to go before it becomes a red giant and boils earths oceans. But I wanted to see for myself. The sun is composed of about 70 percent hydrogen for fuel. It is about 330,000 times more massive than the Earth. All of it can not be used because it is only the hydrogen at the core that is hot enough from the pressure of gravity to fuse 4 protons into a helium nucleus of 2 protons and 2 neutrons. The energy thereby released from the .7 percent mass loss and e = mc squared causes an hydrogen bomb like explosion that couteracts the force of gravity in all directions equally causing the sun to have the shape of a sphere. But only 10 percent of all the sun’s hydrogen (arguably 10-15 percent) can be used for fuel because the rest is used for the pressure to make it hot enough to fuse to begin with.

The Sun is 70% hydrogen p71 Lecture 19 UU

4.512325 x 10 exp 26 tons x .7 = 3.1586275 x 10 exp 26 tons of hydrogen in the Sun (University Physics 11’th Edition Young and Freedmon)

Only 10% of this can be used for fuel p71 UU Lecture 19

3.1586275 x .1 = 3.15826275 x 10 exp 25 tons of hydrogen the Sun has to burn.

The Sun is about 5 billion years old

3.15826275 x 1025/2 = 1.57931375 x 10 exp 25 tons of hydrogen remaining in the Sun approximately.

1.57931375 x 10 exp 25 available tons hydrogen available to burn per second/700,000,000 tons per second

= 2.2561625 x 10 exp 16 seconds x 1 min/60 sec x 1 hr/60 min x 1 day/24 hr x 1 year/365 days = 7,154,244,356 years of hydrogen fuel left to burn.

Over 7 billion years left for the Sun to burn hydrogen!

A closer estimate is with the Sun being 4.6 billion years old. (p76 Lecture 20 Understanding the Universe by Professor Alex Filippenko at Berkeley)

But out of a 10 billion year history this means it is greater than 7 billion years.

Certainly nothing to worry about until at least next Thursday… :slight_smile: Better think about meteors and comets instead…

Actually I already have all these numbers like the mass of the sun and earth etc all typed up so all I had to do was plug them in and crunch.

Mike Dubbeld