For it is the duty of an astronomer to compose the history of the celestial motions through careful and expert study.

At rest, however, in the middle of everything is the sun.

The massive bulk of the earth does indeed shrink to insignificance in comparison with the size of the heavens.

When, therefore, I had long considered this uncertainty of traditional mathematics, it began to weary me that no more definite explanation of the movement of the world-machine established in our behalf by the best and most systematic builder of all, existed among the philosophers who had studied so exactly in other respects the minutest details in regard to the sphere.

For I am not so enamoured of my own opinions that I disregard what others may think of them.

Finally we shall place the Sun himself at the center of the Universe.

Yet the widespread planetary theories, advanced by Ptolemy and most other astronomers, although consistent with the numerical data, seemed likewise to present no small difficulty. For these theories were not adequate unless they also conceived certain equalizing circles, which made the planet appear to move at all times with uniform velocity neither on its deferent sphere nor about its own epicycle's center.