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Abundance of hydrogen in Sun

  1. Jun 30, 2011 #1
    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,
    2) as X=0.71 and Y=0.26, there is (0.71/0.26)*2 H for each He.
    Thanks for help.
  2. jcsd
  3. Jul 1, 2011 #2
    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.
  4. Jul 2, 2011 #3
    thank you.
  5. Jul 2, 2011 #4


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    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]

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