Kepler’s Copernican Campaign and the New Star of 1604

Abstract

In a letter of 27 October 1604, David Fabricius (1564–1617) eagerly reported to Johannes Kepler (1571–1630) his observations of a brilliant new luminary in the constellation of Sagittarius. Fabricius had first observed the new luminary “near the location of the great conjunction,”¹ which had occurred just 10 months earlier. His eyes had been drawn to the area by the proximity of the three superior planets when “Mars and Jupiter were conjoined and Saturn had by then returned directly to the location of the great conjunction.”² There, Fabricius had identified “a new star, with no motion of its own,” in the outer sphere encasing the cosmos.³ The star had surpassed Jupiter “in diameter and silvery splendor,”⁴ and its scintillation had proven incomparably swift.