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.

Finally we shall place the Sun himself at the center of the Universe. All this is suggested by the methodical relation of phenomena and the harmony of the Universe, if only we face the facts, as they say, 'with both eyes open'.

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

Therefore, when I considered how absurd this opinion would appear to those who knew that the earth was fixed in the middle of the universe, and that the heavens revolved around it, I hesitated for a long time whether I should publish my commentaries.

The motion of the earth alone, therefore, can explain so many apparent inequalities in the heavens.

For who could take a better guide than truth?

To know the motions of the heavenly bodies is to know the most beautiful things in the world.

The universe is a sphere, and the earth is a sphere, and the planets are spheres.

The earth, too, has a motion, and this motion is not simple, but composite.

For it is not the earth that moves, but the heavens.

The planets revolve around the sun, and the moon revolves around the earth.

The order of the planets is as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn.

The sun is the center of the universe, and all the planets revolve around it.

The earth rotates on its axis once every day, and revolves around the sun once every year.

The moon revolves around the earth once every month.

The stars are fixed in the heavens, and do not move.

The universe is infinite, and there are an infinite number of stars.

The earth is not the center of the universe, but merely one of the planets.

The motion of the earth causes the apparent motion of the sun and stars.

The earth is a planet, and like all other planets, it revolves around the sun.