In 1939, Grotrian had identified the red corona line as a forbidden transition of the highly ionised iron atom, but he never addressed the needed enormous corona temperature. As director of the Astrophysical Observatory in the early 1950s, he tracked the temporal progression of sunspot magnetic fields in order to understand the mechanism of the 11-year activity cycle. As one of the few East German intellectuals, he emphatically but ultimately unsuccessfully advocated for a young assistant affected by Soviet Stalinism. After his early death, no successor of international reputation could be found due to the political situation in East Berlin after 17 June 1953.