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

Not only the phenomena of the others followed from this, but also it so bound together both the order and magnitude of all the planets and the spheres and the heaven itself, that in no single part could one thing be altered without confusion among the other parts and in all the universe.

So if the worth of the arts were measured by the matter with which they deal, this art-which some call astronomy, others astrology, and many of the ancients the consummation of mathematics-would be by far the most outstanding. This art which is as it were the head of all the liberal arts and the one most worthy of a free man leans upon nearly all the other branches of mathe matics. Arithmetic, geometry, optics, geodesy, mechanics, and whatever others, all offer themselves in its service.

Astronomy is written for astronomers

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

More stars in the north are seen not to set, while in the south certain stars are no longer seen to rise.

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