See part one here
Thirty years after that supernova made its remarkable appearance in Earth’s skies, the Danish astronomer Tycho Brahe would recall his first sight of it:
Amazed, and as if astonished and stupefied, I stood still with my eyes fixed intently upon it. When I had satisfied myself that no star of that kind had ever shone forth before, I was led into such perplexity by the unbelievability of the thing that I began to doubt my own eyes.
Like John Dee and Francis Bacon in England, Tycho knew that according to the Ptolemaic system that had been firmly in place for hundreds of years, the real problem was “that [the supernova] was in the celestial, not the Elementary Region” — that is, that is was not within the cycles of the planets, which were known to move and change (the word “planet” means “wanderer”) but in the more distant realm of the so-called “fixed stars,” the supposedly unchanging backdrop to the celestial machinery. Whether or not the exploding star was a God-sent sign to King Charles of France or not, it was a powerful blow to the Ptolemaic system.
In a lucid essay on this event, the noted astronomer Owen Gingerich writes that “Tycho had, first of all, the imagination to formulate an interesting research strategy, secondly, the ingenuity to devise the instruments to carry out the research, and thirdly, the ability to draw significant conclusions from his results.” John Dee may have understood the general import of the event but only Tycho went about exploring it in a serious way. Gingerich is interested primarily in the technical challenges that Tycho faced, and triumphantly met, but he notes in passing that the Cassiopeia nova “was by no means the end of Aristotelian cosmology, but it was the beginning of the end.”
This is perhaps an understatement. C. S. Lewis in his The Discarded Image comments that “the great Nova in Cassiopeia of November 1572 was a most important event for the history of thought.” Lewis points to F. R. Johnson’s 1937 book Astronomical Thought in Renaissance England: A Study of the English Scientific Writing from 1500 to 1645 — which is still worth reading, by the way — for evidence that the community of natural philosophers in England at least, and presumably elsewhere, were deeply shaken by the nova’s appearance.
It’s a really fascinating moment in intellectual history. The Ptolemaic theory was already being challenged and would in any case have eventually fallen, but this single event did more rapid and serious harm to it than any articulated theory could have. A whole system of belief was effectively brought to its knees by a few incontrovertible astronomical observations.