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

I shall now recall to mind that the motion of the heavenly bodies is circular, since the motion appropriate to a sphere is rotation in a circle.

I can easily conceive, most Holy Father, that as soon as some people learn that in this book which I have written concerning the revolutions of the heavenly bodies, I ascribe certain motions to the Earth, they will cry out at once that I and my theory should be rejected.

So far as hypotheses are concerned, let no one expect anything certain from astronomy, which cannot furnish it, lest he accept as the truth ideas conceived for another purpose, and depart from this study a greater fool than when he entered it.

Mathematics is written for mathematicians.

Therefore, having obtained the opportunity from these sources, I too began to consider the mobility of the earth.

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