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.
Nicolaus Copernicus

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.
Nicolaus Copernicus

Those things which I am saying now may be obscure, yet they will be made clearer in their proper place.
Nicolaus Copernicus

I am aware that a philosopher's ideas are not subject to the judgment of ordinary persons, because it is his endeavour to seek the truth in all things, to the extent permitted to human reason by God.
Nicolaus Copernicus

The earth also is spherical, since it presses upon its center from every direction.
Nicolaus Copernicus

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.
Nicolaus Copernicus

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.
Nicolaus Copernicus

Accordingly, since nothing prevents the earth from moving, I suggest that we should now consider also whether several motions suit it, so that it can be regarded as one of the planets. For, it is not the center of all the revolutions.
Nicolaus Copernicus