Tycho Brahe (14 December 1546 – 24 October 1601) is commemorated in one of my favourite craters on the moon (crater Tycho) and he’s well worth remembering. Tycho made many observations of the positions of the planets and stars in the days just before the invention of telescopes. By observing new stars – we call now them novas – and showing by their position observed over time that they must lay outside of the atmosphere, Tycho proved that they were not atmospheric phenomena. Thus, he proved that the realm of the stars was not immutable.
Perhaps his greatest contribution to astronomy was in fact sharing his observations with his protégé Johannes Kepler, who then used the detailed location information for the planets in the developing of his laws of planetary motion.
He was a complex and colourful character. For more details, take a look at the profile of his life and contributions on Wikipedia: http://en.wikipedia.org/wiki/Tycho_Brahe