Osiander. This cleric stated that Copernicus wrote his heliocentric account of the Earth's movement as a mathematical hypothesis, not as an account that contained truth or even probability. Since Copernicus' hypothesis was believed to contradict the Old Testament account of the Sun's movement around the Earth (Joshua 10:12-13), this was apparently written to soften any religious backlash against the book. However, there is no evidence that Copernicus himself considered the heliocentric model as merely mathematically convenient, separate from reality. Copernicus' actual compendium began with a letter from his (by then deceased) friend Nikolaus von Schönberg, Cardinal Archbishop of Capua, urging Copernicus to publish his theory. Then, in a lengthy introduction, Copernicus dedicated the book to Pope Paul III, explaining his ostensible motive in writing the book as relating to the inability of earlier astronomers to agree on an adequate theory of the planets, and noting that if his system increased the accuracy of astronomical predictions it would allow the Church to develop a more accurate calendar. At that time, a reform of the Julian Calendar was considered necessary and was one of the major reasons for the Church's interest in astronomy. The work itself is divided into six books: The first is a general vision of the heliocentric theory, and a summarized exposition of his idea of the World. The second is mainly theoretical, presenting the principles of spherical astronomy and a list of stars (as a basis for the arguments developed in the subsequent books). The third is mainly dedicated to the apparent motions of the Sun and to related phenomena. The fourth is a description of the Moon and its orbital motions. The fifth is a concrete exposition of the new system, including planetary longitude. The sixth is further concrete exposition of the new system, including planetary latitude. Early criticisms From publication until about 1700, few astronomers were convinced by the Copernican system, though the work was relatively widely circulated (around 500 copies of the first and second editions have survived, which is a large number by the scientific standards of the time). Few of Copernicus' contemporaries were ready to concede that the Earth actually moved. Even forty-five years after the publication of De Revolutionibus, the astronomer Tycho Brahe went so far as to construct a cosmology precisely equivalent to that of Copernicus, but with the Earth held fixed in the center of the celestial sphere instead of