After years of observations from a city powder tower, mathematics professor Gustav Spörer in Anklam becomes Prussia’s most successful solar observer. At the age of 51, he is appointed to the newly established Astrophysical Observatory in Potsdam, whose director, Vogel, uses spectra on photographic plates to measure by use of a microscope the slow radial velocities of bright stars. His detection of the existence of very close binary stars such as the “Demon Star” Algol forms the first triumph for the very new astrophysics. In his final years, Spörer finds historical records of an almost 70-year pause in solar activity, which, after many decades of disbelief, is called the “Maunder minimum”.