Usually, historians point out the preference of Tycho Brahe for "practical astronomy'. In fact, from his youth, he made systematic observations of stars and planets. However, the lack of a well-developed Tychonic World system is due to circumstances more than to Tycho's pour interest in the matter. His illness and early death in Prague curtailed any elaboration of the planetary models he was planning to include in such system.
Nevertheless, Tycho's theoretical work was remarkable:
i. He established the super-Lunar position of transient phenomena such as new stars and comets. This meant that he undermined the Aristotelian conception of the immutability and incorruptibility of the heavens.
ii. On the ground that comets revolved around the Sun and that the minimal distance of Mars from the Earth was sometimes less than the distance of the Sun, Tycho demolished the traditional idea that planets were carried by crystalline spheres.
iii. Last, Tycho and his assistant Christen S?rensen Longberg (1562?1647), also known as Longomontanus, discovered and computed the main anomalies of Lunar motion.