Forma mundi. Copernicus' Preface in his books On the Revolutions; part two

Abstract

The article analyses the central part of Copernicus' Preface to his books On the Revolutions, in which he explains why he has decided to introduce the concept of Earth's movement to astronomy. Copernicus critically reviews the conditions of astronomy and exposes the problem of the precise determination of the duration of the year and the fact that astronomers do not use »the same principles and assumptions« (the model of homocentrics vs. the model of eccentrics and epicycles). What is more, each of the two astronomic traditions is, even when taken by itself, unsuitable: whereas the model of homocentric spheres does not enable the correct calculation of the position of celestial bodies, the model based on eccentrics and epicycles, breaks the principle of traditional astronomy regarding the uniformity of the movement of celestial bodies (the problem of equant). An additional and essential objection of Copernicus to Ptolemaic tradition is that it is unable to present »the principal«, »the structure of the world and the fixed symmetry of its parts«.