The best astronomical data before telescopes came from one nobleman's naked eyes

Tycho Brahe spent decades recording planetary positions with unaided-eye instruments accurate to about one arcminute, the best data of its kind ever compiled. After his death, his assistant Johannes Kepler used those records to work out that planets move in ellipses, not the circles astronomers had assumed for two thousand years.

— Tycho Brahe, Tycho Brahe — observations made at Uraniborg, 1570s–1590s