Tycho Brahe (Uraniborg Observatory)
On the island of Ven, Tycho Brahe measured stars and planets for two decades to about one arcminute without a telescope; Kepler used his Mars data to show that orbits are ellipses.
Open in the interactive tree →King Frederick II of Denmark funded Tycho's observatory Uraniborg on the island of Ven, begun in 1576. With large metal quadrants and sextants and about thirty assistants over the years, he recorded planet positions for roughly two decades, at best to about one arcminute, and compiled a catalogue of about 1,000 stars. His measurements of the 1572 supernova and the 1577 comet showed that the heavens were not unchanging. After his death in 1601, Kepler used the Mars observations: a mismatch of 8 arcminutes was too big to blame on measuring error, which led him to the ellipse and to the laws that prepared Newton's gravity.
Prerequisites
- Ancient Astronomy~150 ADHis instruments continued the ancient art of measuring star positions.
- Heliocentrism (Sun at the Centre)1543Rival models of the heavens could only be tested with exact planet positions.
Unlocks
- Falling Bodies & Planet Orbits1609Kepler derived his laws from Tycho's Mars observations.