AUTHOR'S PREFACE.

...the motions of the world's spheres were different from those established by those who teach mathematics in the schools. And indeed, I first found in the writings of Cicero that Nicetas original: Nicetum; Copernicus refers to Hicetas of Syracuse, a 4th-century BCE philosopher who believed the Earth rotated on its axis. had sensed that the earth moves. Afterward, I also found in Plutarch that others were of the same opinion. I have chosen to write down his words here, so that they may be available to everyone:

Others say that the earth stands still, but Philolaus the Pythagorean says that it travels in a circle around the fire in an oblique path, similar to the sun and the moon. Heraclides of Pontus and Ecphantus the Pythagorean also grant motion to the earth, not in the sense of changing its position, but like a wheel turning from west to east around its own center.

Copernicus provides this quote in the original Greek from Plutarch’s Opinions of the Philosophers. It highlights that the idea of a moving Earth was not a new "heresy" but a rediscovered ancient theory.

Taking the opportunity from this, I too began to think about the mobility of the earth. And although the opinion seemed absurd, yet because I knew that others before me had been granted this liberty—to imagine any circles they wished to explain the phenomena of the stars—I thought it might easily be permitted to me as well to test whether, by assuming some motion of the earth, more reliable demonstrations of the revolutions of the celestial spheres could be found than those produced by others.

And so, having assumed the motions which I attribute to the earth later in this work, I finally found—after many long observations—that if the motions of the rest of the wandering stars The planets. are compared to the circulation The orbital revolution. of the earth, and calculated according to the revolution of each star, not only do their phenomena follow as a result, but the orders and sizes of all the stars and spheres, and the heaven itself, are so linked together that in no part can anything be moved without throwing the other parts and the whole universe into confusion.

Therefore, in the course of this work, I have followed this order: in the first book I describe all the positions of the spheres, together with the motions I attribute to the earth, so that this book contains what is essentially the general constitution of the universe. In the remaining books, I then compare the motions of the rest of the stars and all the spheres with the mobility of the earth, so that it can be gathered from them to what extent the motions and appearances of the rest of the stars and spheres can be saved In astronomy, "saving the appearances" means creating a mathematical model that matches observed data. if they are compared to the motions of the earth. Nor do I doubt that ingenious and learned mathematicians will agree with me, if they...

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