In first place we must observe that the universe is spherical. This is either because that figure is the most perfect, as not being articulated, but whole and complete in itself; or because it is the most capacious and therefore best suited for that which is to contain and preserve all things.
Nicolaus CopernicusFor it is the duty of an astronomer to compose the history of the celestial motions through careful and expert study.
Nicolaus CopernicusThe two revolutions, I mean the annual revolutions of the declination and of the centre of the Earth, are not completely equal; that is the return of the declination to its original value is slightly ahead of the period of the centre. Hence it necessarily follows that the equinoxes and solstices seem to anticipate their timing, not because the sphere of the fixed stars moves to the east, but rather the equatorial circle moves to the west, being at an angle to the plane of the ecliptic in proportion to the declination of the axis of the terrestrial globe.
Nicolaus CopernicusTo 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