Tycho Brahe's Azimuth Quadrant, 1577.
© Science Museum / Science & Society Picture Library
Plate taken from Tycho Brahe's 'Astronomiae Instauratae - Mechanicae' (1602) 'Quadrans - mediocsis orichalcicus azimuthalis'. Considered to be the greatest pre-telescope observer, Brahe's (1546-1601) contributions to astronomy were enormous. Not only did he revolutionise astronomical instrumentation, by emphasising the importance of accuracy for the first time, but also profoundly changed observational practice. He was the first to observe the obrits of the moon and planets, and the first to make corrections for atmospheric refraction.