As we have noted, modern astronomy is built on the interplay between quantitative observations and testable theories that attempt to account for those observations in a logical and mathematical way. A crucial ingredient in the Copernican revolution was the acquisition of more precise data on the motions of objects on the celestial sphere.

Precise Observations before the Invention of the Telescope

A Danish nobleman, Tycho Brahe (1546-1601), made important contributions by devising the most precise instruments available before the invention of the telescope for observing the heavens. Brahe made his observations from Uraniborg, on an island in the sound between Denmark and Sweden called Hveen. The instruments of Brahe allowed him to determine more precisely than had been possible the detailed motions of the planets. In particular, Brahe compiled extensive data on the planet Mars, which would later prove crucial to Kepler in his formulation of the laws of planetary motion because it would be sufficiently precise to demonstrate that the orbit of Mars was not a circle but an ellipse.