Abstract
Tycho Brahe is known as the greatest astronomer of his time and his observations had great significance for the development of science. Tycho received in 1576 the island Hven not far from Copenhagen as a gift from the Danish king Frederik II and he worked there with many collaborators during twenty years. But Tycho must share the credit for renewing astronomy with Landgrave Wilhelm IV in Kassel as has been better recognized recently. About 1566 Wilhelm achieved a better accuracy of star positions than any astronomer before. Twenty years later, an accuracy about one minute of arc was obtained in Kassel, and soon after also by Tycho Brahe. We shall follow this evolution and the mutual process of learning between Kassel and Hven - which was not without drama. %ZHamel, J., Rothenberg, E., & von Mackensen, L. 1998, AcHA, 2, 1
Høg, E. 2018, RMxAC, 50, 1
