Sethus Calvisius

Sethus Calvisius or Setho Calvisio, originally Seth Kalwitz (21 February 1556 – 24 November 1615), was a German music theorist, composer, chronologer, astronomer, and teacher of the late Renaissance.
Biography.
He was born into a peasant family at Gorsleben in present-day Thuringia. By the exercise of his musical talents he earned money enough for the start, at Helmstedt, of a university career, which the aid of a wealthy patron enabled him to continue at Leipzig. He became director of the music-school at Pforta in 1572. In 1594 he was transferred to Leipzig in the same post, including directing the Thomanerchor at the Thomaskirche. He retained this post until his death in Leipzig, despite the offers successively made to him of mathematical professorships at Frankfurt and Wittenberg.
Calvisius was also a significant astronomer: in his "Opus Chronologicum" (Leipzig, 1605, 7th ed. 1685) he expounded a system based on the records of nearly 300 eclipses. An ingenious, though ineffective, proposal for the reform of the calendar was put forward in his "Elenchus Calendarii Gregoriani" (Frankfurt, 1612); and he published a book on music, "Melodiae condendae ratio" (Erfurt, 1592). He composed choral pieces including "Unser Leben währet siebzig Jahr".