# Abundance of hydrogen in Sun

1. Jun 30, 2011

### shirin

Hi everyone,
There is problem that asks how many hydrogen atoms are there in sun for each helium atom.
I don't know which solution is correct:
1) to count all the hydrogens and heliums participating in one solar pp chain,
or,
2) as X=0.71 and Y=0.26, there is (0.71/0.26)*2 H for each He.
Thanks for help.

2. Jul 1, 2011

### qraal

The figures X & Y are mass fractions. In terms of numbers of atoms of each we need to divide by their relative masses, roughly 1:4, giving us 0.71 and 0.052, then divide those by the sum I.e. 0.71/0.762 & 0.052/0.762 which gives their atomic proportions. Divide the hydrogen figure by the helium figure and you have how many hydrogens for every helium.

3. Jul 2, 2011

thank you.

4. Jul 2, 2011

### phyzguy

The 26% He by weight is more representative of the composition of the sun at the time of formation. The sun has been burning H to He for 4.5 billion years, so according to the standard solar model, the interior of the sun is now over 60% He. To calculate the atomic ratio, you would need to integrate over the whole volume - I don't know the answer, but I'm sure it is more than 26% He by weight when averaged over the whole sun. Here are a couple of references with Figure 2 in the first reference showing the mass fraction as a function of radius, and Table 1 in the second reference giving the He mass fraction in the core at >60%.

http://www.pha.jhu.edu/~france/PAPERS/solmodel.pdf [Broken]

http://arxiv.org/abs/astro-ph/0204331

Last edited by a moderator: May 5, 2017