This "Phoenix among Astronomers"--as Kepler calls him,[150]--was the father of modern practical astronomy.[151] He also propounded a third system of the universe, a compromise between the Ptolemaic and the Copernican. In this the Tychonic system,[152] the earth is motionless and is the center of the orbits of the sun, the moon, and the sphere of the fixed stars, while the sun is the center of the orbits of the five planets.[153] Mercury and Venus move in orbits with radii shorter than the sun's radius, and the other three planets include the earth within their circuits. This system was in harmony with the Bible and accounted as satisfactorily by geometry as either of the other two systems for the observed phenomena.[154] To Tycho Brahe, the Ptolemaic system was too complex,[155] and the Copernican absurd, the latter because to account for the absence of stellar parallax it left vacant and purposeless a vast space between Saturn and the sphere of the fixed stars,[156] and because Tycho's observations did not show any trace of the stellar parallax that must exist if the earth moves.[157] [Footnote 150: Kepler: _Tabulæ Rudolphinæ_. Title page.] [Footnote 151: Dreyer: 317-363.] [Footnote 152: As stated in his Book on the Comet of 1577 (pub. 1588).] [Footnote 153: Dreyer: 168-9.] [Footnote 154: Schiaparelli in Snyder: 165.] [Footnote 155: Brahe: _Op. Om._, pt. I, p. 337.] [Footnote 156: Ibid: 409-410.] [Footnote 157: The Tychonic system has supporters to this day. See chap. viii.] Though Tycho thus rejected the Copernican theory, his own proved to be the stepping stone toward the one he rejected,[158] for by it and by his study of comets he completely destroyed the ideas of solid crystalline spheres to the discredit of the scholastics; and his promulgation of a third theory of the universe helped to diminish men's confidence in authority and to stimulate independent thinking. [Footnote 158: Dreyer: 181.] Copernicus worked out his system by mathematics with but slight aid from his own observations. It was a theory not yet proven true. Tycho Brahe, though denying its validity, contributed in his mass of painstaking, accurate observations the raw material of facts to be worked up by Kepler into the great laws of the planets attesting the fundamental truth of the Copernican hypothesis.