Tycho Brahe
A new star — in a sky that never changes?
That time, that place
A Danish nobleman who lost part of his nose in a youthful duel and wore a metal prosthesis for life. The king granted him the whole island of Hven, where he built the observatory Uraniborg. He belonged to the last generation to measure the sky by eye, before the telescope.
Why this question
In 1572 a new star appeared, bright enough to see by day.
This was not supposed to be possible. Since Aristotle, the world above the Moon did not change; change belonged below, to the earthly realm. So people said it must be something happening in the atmosphere.
What was found
Tycho decided to measure. Something nearby shifts against the background when you move your viewing position. He hunted that shift night after night, and however precisely he measured, it never appeared.
No shift means very far away. This new star stood well beyond the Moon — inside the realm that was supposed never to change. Today such a star is called a supernova: not a newborn star but a dying one, blazing briefly as it explodes.
He applied the same method to the comet of 1577 and got the same answer. That was worse: if transparent crystalline spheres really carried the planets, a comet could not pass through them.
The world above the Moon never changes
A parallax that never appeared, however carefully he looked for it
He never accepted heliocentrism, proposing a compromise of his own. But his twenty years of observations passed to his assistant, Kepler