TO HIS HOLINESS, POPE PAUL III,
From NICOLAUS COPERNICUS
A PREFACE TO HIS BOOKS ON THE REVOLUTIONS
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Chapter 10
THE ORDER OF THE HEAVENLY SPHERES
Of all things visible, that the highest is the heaven of the fixed stars, is doubted by nobody. But the ancient philosophers, assuming that, among objects moving equally fast, those farther away seem to travel more slowly, as is proved in Euclid's Optics. The moon revolves in the shortest period of time because, therefore, it runs on the smallest circle, nearest to the earth. The highest planet, on the other hand, is Saturn, which completes the biggest circuit in the longest time. Below it is Jupiter, followed by Mars.

According to Plato 's followers, all the planets, being dark bodies, shine because they receive sunlight. Thus, they must be above the sun, otherwise we would see them sometimes obscured by shadows, which we do not.

In my judgement, therefore, we may look to the ideas of Martianus Capella, the author of an encyclopedia, and other Latin writers, who thought that Venus and Mercury do not circle the earth, but have "other circles". And what other circle might there be, but that of the sun? If anyone seizes on this notion, may he not also think likewise of Saturn, Jupiter, and Mars, and of the earth too?

Hence I feel no shame in asserting that the moon and the earth traverse a grand circle amid the rest of the planets in an annual revolution around the sun. Moreover, since the sun remains stationary, whatever appears as a motion of the sun is really due rather to the motion of the earth. This should be admitted, I believe, in preference to perplexing the mind with an almost infinite multitude of spheres, as must be done by those astronomers who try to fix the earth in the middle of the universe. On the contrary, we should rather heed the wisdom of nature, which especially avoids producing anything superfluous or useless, and frequently endows a single thing with many effects.

All these statements are difficult and almost inconceivable, being of course opposed to the beliefs of many people. Yet, as we proceed, with God's help I shall make them clearer than sunlight, at any rate to those who know some astronomy. So, if the size of the spheres is measured by the length of time of their rotation, the order of the spheres is the following:

The first and the highest sphere is of the fixed stars, which contains everything, and is therefore immovable.
This is followed by the sphere of the first planet, Saturn, which completes its circuit in 30 years. After Saturn, Jupiter revolves in 12 years. Then Mars in 2 years. The fourth place is the earth, together with its moon. In the fifth place Venus in 9 months. Lastly, in the sixth place, Mercury, which revolves in 80 days.
At rest, however, in the middle of everything is the sun. For in this most beautiful temple, who would place this lamp in another or better position than that from which it can light up the whole thing at the same time? For, is not the sun called 'the lantern of the universe' and, 'its mind' and by others 'its ruler'? Hermes the Thrice Greatest calls it 'a visible god', and Sophocles' Electra, 'the all-seeing'. Thus indeed, as though upon a royal throne, the sun governs the family of planets revolving around it.

In this arrangement, therefore, we discover a marvelous symmetry of the universe, a harmonious linkage between the motion of the spheres and their size, such as can be found in no other way. From this, the attentive student may explain the many and curious motions of the planets. Yet no such curiosities appear in the fixed stars. This proves their immense height, which makes the sphere of their annual motion vanish from before our eyes. For, every visible object has some measure of distance beyond which it is no longer seen, as is demonstrated in optics. From Saturn, the highest of the planets, to the sphere of the fixed stars there is an additional gap of the largest size. This is shown by the twinkling lights of the stars. By this token in particular they are distinguished from the planets, for there had to be a very great difference between what moves and what does not move. So vast, without any question, is the divine handiwork of the most excellent Almighty.