Thanks for the hints. I ordered two promising books in German language: "Astronomie" by Pearson and "Astronomie in Theorie und Praxis" (3 volumes) by Erik Wisc

Thanks for the hints. I ordered two promising books in German language: "Astronomie" by Pearson and "Astronomie in Theorie und Praxis" (3 volumes) by Erik Wischnewski. Thats some 2000 pages of stuff to read, so let's see where this takes me.