SOURCE: "The Tychonic System of the World," in The Lord of Uraniborg: A Biography of Tycho Brahe, Cambridge University Press, 1990, pp. 236-64.

In the following excerpt, Thoren examines the evolution of Brahe's planetary system and the slow publication of the astronomer's De mundi. Thoren concludes that the observations in Brahe's monograph were insufficient in themselves to overthrow the Aristotelian cosmology of solid celestial spheres, though they were necessary to set this process into motion.

At the time [Paul] Wittich came to Hven [in 1580], Tycho had probably not thought about planetary theory or cosmology since his deliberations on the comet [of 1577]. The same may have been true of Wittich, whose contemplations on the subject had occurred, oddly enough, at almost exactly the same time. But although Tycho's had been almost incidental thoughts, provoked only by his consideration of the comet, Wittich's had been self-conscious, explicit explorations of the various...