| Chapter 1: | The New Astronomy |
he wished to reduce everything to its imagined stability. He put the two well-resolved Ancient Planets—the Sun and Moon—into geocentric orbits and allowed the remaining five wandering planets to orbit the Sun (figure 1.6). The fact that his arrangement led to planetary orbits that intersected was no impediment—he broke with Ptolemaic thinking and dispensed with crystalline spheres, letting planets move freely through space where he hoped (with judicious choice of orbital parameters) they need not collide. He justified smashing the concept of crystalline spheres using the observed properties of the Comet of 1577, which he found lay at least six times farther away than the Moon and crossed the spheres that were supposed to carry the planets in prior models.
Because Tycho believed that every cranny of the Universe served a purpose, he devised a plenum with as little wasted space as possible. His model was about 70% smaller than Ptolemy's, making it—comparatively
Figure 1.6. The bounded geo-heliocentric model of Tycho Brahe, from Liber Secundus (1588).
