was aware of this and could not present any observational "proof" in his manuscript, relying instead on arguments about what would be a more complete and elegant system. From publication until about 1700, few astronomers were convinced by the Copernican system, though the book was relatively widely circulated (around 500 copies are known to still exist, which is a large number by the scientific standards of the time). Many astronomers, however, accepted some aspects of the theory at the expense of others, and his model did have a large influence on later scientists such as Galileo and Johannes Kepler, who adopted, championed and (especially in Kepler's case) sought to improve it. Galileo's observation of the phases of Venus produced the first observational evidence for Copernicus' theory.
The Copernican system can be summarized in seven propositions, as Copernicus himself collected them in a Compendium of De revolutionibus that was found and published in 1878:
1. Orbits and celestial spheres do not have a unique, common, center.
2. The center of the Earth is not the center of the Universe, but only the center of the Earth's mass and of the lunar orbit.
3. All the planets move along orbits whose center is the Sun, therefore the Sun is the center of the World. (Copernicus was never certain whether the Sun moved or not, claiming that the center of the World is "in the Sun, or near it.")
4. The distance between the Earth and the Sun, compared with the distance between the Earth and the fixed stars, is very small.
5. The daytime motion of the Sun is only apparent, and represents the effect of a rotation that the Earth makes every 24 hours around its axis, always parallel to itself.
6. The Earth (together with its Moon, and just like the other planets) moves around the...
Copernicus' major work, was the result of decades of labor. It opened with an originally anonymous preface by Andreas Osiander, a theologian friend of Copernicus, who urged that the theory did not necessarily have implications outside the limited realm of astronomy. Copernicus' actual book began with a letter from his (by then deceased) friend, the 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 (calendar reform then being an important question and one of the major reasons for Church funding of astronomy.