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. 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. Read more