Perhaps the most important other student was Unsöld who then went into astrophysics, and he... during my studies discovered that the sun and other stars mostly consist of hydrogen and not of the same material as the Earth. Astrophysicists before him, especially Eddington who really put astrophysics on a firm basis, had assumed that the same elements prevail in the sun as on Earth, and that gave Eddington a terribly high temperature at the center of the sun, about 40 million degrees. Then came Unsöld, and at the same time Russell, Henry Norris Russell in America, who said well... the spectrum of the sun and of other stars is richest in the lines of hydrogen, therefore it is very likely that hydrogen is the dominant element in all stars. And this was then taken up by Eddington and Strömgren who independently made a star, mostly made out of hydrogen. So this was probably the most important student at my time.