The first known calculation of the (inverse) golden ratio as a decimal of "about 0.6180340" was written in 1597 by Maestlin in a letter to Kepler.

Although he primarily taught the traditional geocentric Ptolemaic view of the solar system, Maestlin was also one of the first to accept and teach the heliocentric Copernican view. Maestlin corresponded with Kepler frequently and played a sizable part in his adoption of the Copernican system. Galileo Galilei's adoption of heliocentrism was also attributed to Maestlin.[via]