Cecilia Helena Payne - Gaposchkin (May 10, 1900 -- December 7, 1979) was a British -- American astronomer and astrophysicist who, in 1925, proposed in her Ph. D. thesis an explanation for the composition of stars in terms of the relative abundances of hydrogen and helium.
who discovered the sun is made of hydrogen
Cecilia Helena Payne - Gaposchkin