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

Those who know that the consensus of many centuries has sanctioned the conception that the earth remains at rest in the middle of the heavens as its center, would, I reflected, regard it as an insane pronouncement if I made the opposite assertion that the earth moves.

Mathematics is written for mathematicians.

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

We regard it as a certainty that the earth, enclosed between poles, is bounded by a spherical surface.

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

To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.