The first years of the 17th century were expected to be very portentous. December 1603 brought into conjunction Jupiter with Saturn in Sagittarius, the start of the fiery trigon in astrology. The last time that happened marked the rise of Charlemagne, whose Carolingian Empire swept across much of Europe, establishing the Catholic church as the arbiter of all things culture and shaping much of Western Europe as it stands today. The previous cycle, around 6 A.D., was the time of Jesus Christ and might have accounted for the fabled Star of Bethlehem. Astrologists and astronomers alike were looking up at the skies in expectation.

On this day, October 8, in 1604 the supernova designated now as SN-1604 was first sighted. For a while it was easily the brightest object in the sky, and could even be seen in daytime. Kepler himself began observations of it starting October 17.

No major epoch-changing events came out of the fiery trigon, but on the other hand, Kepler’s observations recorded the last known star supernova to occur within the Milky Way Galaxy, and he used it to further his case against the immutability of the heavens. He argued that the way all the stars in the sky are arranged is the way they always were.