On the evening of 11 November 1572, the 25-year-old Tycho Brahe walked back from his uncle's alchemical laboratory and looked up at the constellation Cassiopeia. He saw something that, by the medical-physical theory of the day, was not supposed to be possible. What was it?
A new star — what we now call a Type Ia supernova, SN 1572 — appeared in Cassiopeia and remained visible for sixteen months. Aristotelian cosmology held that the celestial sphere above the moon was unchanging; a new star above the moon was, by the prevailing theory, impossible. Tycho's parallax measurements demonstrated that the star sat well beyond the moon, demolishing the Aristotelian unchanging-heavens doctrine on observational grounds. His pamphlet *De Nova Stella* (1573) was one of the foundational publications of European astronomy. The other answers describe imagined celestial phenomena rather than the actual 1572 event.
Read the full story →On the evening of 11 November 1572 a bright new star appeared in the constellation Cassiopeia. It was visible for sixteen months. Tycho Brahe — twenty-five at the time — measured it carefully enough to prove it sat above the Moon. The Aristotelian heavens that were supposed to be unchanging had quietly changed.
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