Michael Mästlin und Galileo Galilei; Michael Mästlin und Galileo Galilei; Michael Mästlin and Galileo Galilei.

In the earlier literature it is incorrectly claimed that Mästlin, when travelling through Italy, converted Galilei to copernicanism. We know today that Galilei was first introduced to Copernicus' work through Chr. Wursteisen. In 1610, Martin Horký published a note against Galilei's Sidereal Messenger, which also came into the hands of Kepler who forwarded it to Mästlin. While Kepler was infuriorated, Mästlin concurred with the author, and hoped in vain to win Kepler against Galilei's cause. We analyze this historically peculiar attempt, and in addition, we analyze a letter of Thaddaeus Hagecius to Martin Mylius, which deals with Mästlin's work on the new star of 1572, and which shows the remarkable relation between Hagecius and Mästlin.