Astronomy and the Archduke: Unpublished Letters on SN1604 by Brengger, Coignet, and Kepler in the Archives of Albert VII of Austria

Abstract

The State Archives of Belgium, in particular, the archives of Archduke Albert VII of Austria, hold a letter which possibly is a copy of the letter, or an excerpt of the letter, of Kepler to Emperor Rudolf II of October 1604 on SN1604, that is, the first letter of Kepler on the subject. Together with this letter, there are other letters on SN1604, written by Johannes Brengger and Michiel Coignet. In one of these letters, the very observation by Brengger which Kepler cites can be found. The letters are in Albert’s archive because he asked his Court Mathematician Coignet about the phenomenon. It is less clear why Albert was interested in the phenomenon, given the lack of interest in science at his court.