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Is the Sun really made of hydrogen and helium‑ How do we know?

I'm teaching an introductory astronomy course and want to present a more robust answer than "spectral lines tell us." While Fraunhofer lines are the direct proof, I know helioseismology and solar neutrino measurements provide independent, crucial constraints. Could you outline how these different methods converge to give us such a precise, confident measurement of the solar mix?

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By Kirti Answered 1 year ago

You're right to look beyond the spectrum. The Fraunhofer lines give us the photospheric composition. The deeper validation comes from two independent probes of the interior. First, helioseismology: the observed oscillation modes of the Sun are exquisitely sensitive to its internal density and temperature profile. The Standard Solar Model, built on a ~74% H, ~24% He mix, predicts these modes with remarkable accuracy. Second, solar neutrino detectors like Super-Kamiokande and Borexino measure the flux of particles from the core's proton-proton chain and CNO cycle. The detected rates match predictions only if the core's composition and nuclear reaction rates are as we've modeled. This three-fold agreement is why we're so certain.

 

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