Nicholas Copernicus’ Revolutions

Abstract

In the preceding Book to the best of my limited ability I explained the phenom-ena caused by the motion of the earth around the sun, and through the same procedure I intend to analyze the motions of all the planets. Therefore the moon’s motion confronts me now. This must be so, because it is principally through the moon, which takes part in the day and the night, that the positions of any asters whatever are found and verified. Secondly, of all [the heavenly bodies] only the moon relates its revolutions as a whole, even though they are very irregular, to the center of the earth, to which it is in the highest degree akin. Therefore the moon, taken by itself, gives no indication that the earth moves, except perhaps in its daily rotation. All the more for that reason it was believed that the earth was the center of the universe and the common center of all the revolutions. In ex-pounding the moon’s motion I do not disagree with the ancients’ belief that it takes place around the earth. But I shall also present certain features at variance with what we have received from our predecessors and in closer agreement with one another. By means of those features I may determine the lunar motion too with greater certainty, as far as possible, in order that its secrets may be more clearly understood.