JOHANNES KEPLER

The Supernova of 1604

On October 1604, a bright new evening star (SN 1604) appeared, but Kepler did not believe the
rumors until he saw it himself. Kepler began systematically observing the star.

Astrologically, the end of 1603 marked the beginning of a fiery trigon, the start of the ca. 800-year cycle of great conjunctions; astrologers associated the two previous such periods with the rise of Charlemagne (ca. 800 years earlier) and the birth of Christ (ca. 1600 years earlier), and thus
expected events of great portent, especially regarding the emperor.

It was in this context, as the imperial mathematician and astrologer to the emperor, that Kepler described the new star two years later in his De Stella Nova. In it, Kepler addressed the star's astronomical properties while taking a skeptical approach to the many astrological interpretations
then circulating. He noted its fading luminosity, speculated about its origin, and used the lack of observed parallax to argue that it was in the sphere of fixed stars, further undermining the doctrine of the immutability of the heavens (the idea accepted since Aristotle that the celestial spheres were perfect and unchanging).

The birth of a new star implied the variability of the heavens.

In an appendix, Kepler also discussed the recent chronology work of Laurentius Suslyga; he calculated that, if Suslyga was correct that accepted timelines were four years behind, then the Star of Bethlehem — analogous to the present new star — would have coincided with the first great conjunction of the earlier 800-year cycle.