Saturn on August 17, 1564, by means of an ordinary pair 

 of compasses. For a few years after, his attention was 

 given to other scientific subjects, but the appearance of 

 a remarkable new star in the constellation of Cassiopeia 

 in 1572 re-awakened his activity and fixed his career. 



Thenceforth, he devoted his life to the accurate 

 determination of the positions and motions of celestial 

 bodies, and started a renaissance of astronomical 

 measurement. Until he began observations at his 

 observatory at Uraniborg on the island of Huen, the 

 astronomy of the ancients had remained practically 

 undisturbed. No advance had been made in the know- 

 ledge of the positions of the fixed stars or of the moon's 

 motion so important for navigation ; and the positions 

 of the planets could not be foretold with anything like 

 reasonable accuracy. 



No astronomer had yet made up his mind to take nothing 

 for granted on the authority of the ancients ; but to determine 

 everything himself. Nobody had perceived that the answers to 

 the many questions which were perplexing astronomers could 

 only be given by the heavens, but that the answers would be 

 forthcoming only if the heavens were properly interrogated by 

 means of improved instruments capable of determining every 

 astronomical quantity anew by systematic observations. The 

 necessity of doing this was at an early age perceived by Tycho 

 Brahe. Dr. J. L. E. Dreyer. 



For twenty-five years Tycho Brahe patiently and 

 diligently measured the positions of stars and other 

 bodies upon the celestial sphere, using instruments of 

 his own design and attaining an accuracy of observation 

 little short of marvellous. Upon the basis of these 

 observations Kepler constructed his three famous laws 

 of planetary motion. 



Johann Kepler was born at Weil, in the Duchy of 

 Wiirtemberg, in 1571. Refused as a divine, he pursued 



