A new star, in a sky that could not change

Tycho Brahe walked home to supper, looked up, and saw a star brighter than Venus in a place where there had never been one.

He measured it for months and could find no parallax at all, which meant it was further away than the Moon — and the heavens beyond the Moon were supposed to be perfect and unchanging. It was a supernova. The Moon is the ruler in that argument: anything nearer shifts against the stars as you move, and anything further does not.