Polish astronomer. At the time when Europe sees its perception of the Earth upset by the discovery of the New World, the work of Copernic marks, at the level of cosmos, another decisive date.

However, will be needed, to seize all the consequences of them, nearly two hundred years, time that the heliocentric system, which inaugurates the “scientific revolution” of the XVIIe century, substitutes for the world closed and arranged hierarchically of Antiquity and the Middle Ages the unlimited Universe of the modern time.    

Nicolas Copernic is born on on February 19th, 1473 in Torun, in Poland. His/her mother is of Torun even, and his/her father, rich commercial from Cracow and sympathizer of the Prussian Union (allied in Poland), came to be established there in 1454.  

Italian formation
In 1495, Nicolas Copernic, with the support of his uncle Lucas, reaches the dignity of canon, the chapter of Frauenburg (today Frombork). For an ecclesiastical career, it leaves for Italy to study the canon law and the Greek. In October 1496, its name is registered on the register of the university of Bologna; it will remain there more than three years. If one believes of it his future disciple, biographer and editor, Rheticus, it will also continue studies of astronomy and works with the astronomer Domenico Maria Novara, of which he is “more the assistance and the collaborator that the pupil”.  

In July 1501, Copernic must return to Poland to take possession of its seat of canon to the cathedral of Frauenburg. But, hardly installed, it obtains a new grant for two years in Italy; it goes this time to Padoue, where it undertakes studies of medicine; however, knowing that it will not be able to complete this formation, it is authorized to present to Ferrare, on on May 31st, 1503, a thesis in canon law, which confers the title of doctor to him.  

Thus, seemingly, nothing prepares really Copernic with becoming the largest astronomer of its time. From 1503 to 1512, he lives initially in Heilsberg (in Polish Lidzbork) near his uncle, to which he is used as secretary, to advise and of doctor. The day before the death of this one, in 1512, Copernic joined its diocese of Frauenburg, of which the chapter impatient, in this Warmie which it will not leave any more until its death, on on May 24th, 1543.

The revolution of the “revolutions of the spheres”

If, like all the great minds of its time, Copernic had many activities, whose diversity can astonish today (it made in particular work of administrator in Warmie and continued research in economy, summarized in its Test on the striking of the currency written in 1517), all its glory is due to its work in astronomy, which however occupied only one small portion of its time. This fame is not due even that to one single work, Of revolutionibus orbium coelestium libri VI, published for the first time at Nuremberg, in 1542-1543.  

Design and structure of work
If the fundamental idea which directs Of revolutionibus, the heliocentrism, seems, according to the testimony even of Copernic, to be to him appeared around 1505 or 1506, its first writing of astronomy, Commentariolus, circulates only around 1513 and the final drafting of work will continue at least until 1532. Moreover Copernic will not cease correcting it and modifying it until the end of its days.  

End of the anthropocentrism
Of revolutionibus, which counts six books, consists of three different units. In the first eleven chapters of book I, Copernic poses the bases of its heliocentric system (which makes Sun around the star whose the rotation of planets is carried out) - what leads it to polemize lengthily against the theories of Old, Aristote and Ptolémée, holding of the geocentric system, according to which the Earth is the center of the world and the celestial movements. For Copernic, the Earth not being more motionless in the center of the Universe, occupied from now on by the Sun, it takes the statute of simple planet launched in the sky. It rotates in one year around the Sun, and in 23:00 and 56 min; moreover, its axis of rotation is affected of a movement that Copernic believes, wrongly, essential so that this axis keeps a constant direction compared to stars considered as fixed. Then, in the three final chapters of book I, it presents trigonometrical concepts, mathematical tool obliged for the detailed construction of its system.  

The last five books are devoted to a description as complete as possible of the Universe according to the assumption heliocentrist: book II is a talk of spherical astronomy which a catalog accompanies by stars; the following books (III to VI) provide the detail of the theories of the various movements (apparent and real) of the Sun and the Earth, the Moon and planets.  

Critical of Old
Fourteen centuries after Almageste de Ptolémée, with a structure of presentation similar, it is a new exhaustive description of the skies.  

However, Copernic, which read and studied all the philosophical works dealing with the structure of the Universe, does not seek as well to destroy the systems previously suggested as to improve them, in particular that of Ptolémée. Although he admires this last, there reproaches him for not having known to remain faithful to the basic principle of the uniformity of the circular motion of the celestial bodies and to have given up it and distorted by the introduction of the équants. Other criticizes of Copernic: the system of Ptolémée, where each star must be treated like a particular case, gives an irrational image of the Universe.  

The heliocentric system
At the base of the system of Copernic there is thus a will of simplification. For this purpose, this one takes again on its account the assumption of Greek authors of IVe and IIIe front centuries J. - C. like Héraclide of the Bridge or Aristarque, assumption seemingly absurd of the rotation of the Earth around the Sun, and he discovers that it offers a remarkable explanation of the celestial phenomena; moreover, it leads to the image of a perfectly ordered Universe. Thus, initially, Copernic is persuaded that it made more understandable the planetary mechanisms. However, it is a recognized fact as of the time of Ptolémée which the planets do not turn according to perfect circles with a uniform speed. To give an account of these irregularities and to preserve the thesis of the circular motions of the celestial objects, while giving up the équants, Copernic is brought to complicate its system by the introduction of a whole combination of épicycles and the deferent ones. It does not give up either the “spheres”, these spheres material which are supposed to carry planets and make it possible to explain the movement of it (they are the spheres which turns, involving planets). Its system introduces only one difference, but it is capital: it is that the Sun is found in the center of the Universe, and that the Earth, like another planets, is carried by a sphere - from where the title of its work, revolutions of the celestial spheres.  

To impose its system, Copernic is obliged to refute a certain number of arguments which underlie the classical theory since Aristote and Ptolémée. To start, he criticizes the principle of Aristote according to which the Universe would be composed, on the one hand, of the sublunary matter, that of the Earth and space to the “sphere” of the Moon, and, on the other hand, of a matter ethereal, that of planets, the Moon or stars, perfect and insensitive, inter alia, with the effects of acceleration: one of the main arguments against the rotation of the Earth was that such a rotation would subject this one to a centrifugal force which would make it burst. For Copernic, the Earth is a planet among the other of comparable nature ones that it and whose orbital characteristics can be described according to the same rules. Their movement is not as well related to their substance as with their form, from where importance of the circle and the sphere; indeed, it is allowed that the spherical bodies have as a “natural” movement the circle, in other words which they do not have need for engine. So Copernic will never go until considering an elliptic circulation of planets.  

But the system of Copernic operates another fundamental change, starts of a intellectual revolution much major: Copernic declares, against Aristote, that it is absurd to make be driven all the Universe around this tiny point which the Earth constitutes. As it maintains the existence of the sphere of the fixed ones, on which the stars are, it is obliged to increase dimensions of the Universe considerably - it multiplies by more than 2 ' 000 its ray -, so that the effects of parallax, which had with the rotation of the Earth compared to fixed stars, are not perceptible. If such a manner of designing the Universe can appear, at the time, to raise of a petition of principle, it is clear, now, that with Copernic a new vision of the world is in gestation. Because its system, although it is, in the final analysis and in spite of its intentions first, neither simpler nor more precise than that of Ptolémée, confers on the other hand on the Universe, for the first time since nearly two millenia, of new dimensions as well as a harmony and a unit ever expressed hitherto.

However, the astronomy of Copernic remains strongly influenced by the theses of Old. Through the prevalence granted to the circular motions, the importance of the spherical shape of the stars and, more still, the conviction that the Sun occupies in the Universe a central place, Copernic is undoubtedly let guide by considerations metaphysics. Thus, the role of the Sun is not determined by requirements of a mechanical nature but by a belief concerned with the Platonic tradition: from its perfection, because it gives to the world its light, the Sun must be in central position; “the Sun sitting on the royal throne directs the round of the family of the stars”, Copernic writing in Of revolutionibus. In spite of that, the Sun is not the pivot of the Universe: the movements of the stars in fact are deferred to the center of terrestrial the “sphere”, excentré compared to the Sun.  

All these nuances brought to the comprehension of the system of Copernic force to modulate what one understands by “revolution copernician”. If it is undeniable that it is put an end to a certain way of thinking the world and the place of the Earth (and the man) in this one, and that such an inversion inaugurates the beginning of the modern time, it does not remain about it less than with many regards Copernic remains culturally a man of the Middle Ages. One thus could write that its revolution was a “revolution without revolutionist”, which does not exclude a certain intellectual courage: Copernic will know, in its dedication with the pope Paul III, to plead in a very convincing way for the right of the scientist to express his ideas.  

Publication and posterity of work
If the first complete edition of revolutionibus were not the clap of thunder which one could have supposed, it is that it has partly escaped with its author. The publication of the final text, supervised by Rheticus, was indeed undertaken, as from 1542, in Nuremberg. But, towards the end of the year, this one had to give up the work of edition to the one of his/her friends, the theologist Lutheran Andreas Osiander. This last believed good to decorate the work of a not signed foreword which, by presenting the heliocentric system like a simple mathematical model making it possible to improve calculations, attenuated the range seriously of it. At the beginning of 1543, Copernic, seriously sick, undoubtedly did not have the possibility of correcting such an interpretation of its work, and it may be even that it never was informed of it. On the other hand, this foreword, which was a long time allotted to him, allowed a broad diffusion of work and, initially, crossed short to many negative reactions, initially in the Protestant mediums then among catholics: it will be necessary to wait until 1616 and the “Galileo business” so that Of revolutionibus is put at the Index and the firmly condemned heliocentrism.  

First step towards Newtonian mechanics
At the time of Copernic three “bolts” blocked the development of astronomy: geocentrism; the division of the Universe in a sublunary world and a cosmos, basically opposite; the requirement to bring back all the celestial movements to a composition of uniform circular motions. In the great upheaval of the astronomy - and of what, starting from the philosophy of the nature of Aristote, will become physical sciences - which, through Kepler and Galileo, will lead to Newtonian mechanics, it is Copernic which opens the first breach in the Aristotelian fortress. It makes jump the first “bolt”, the geocentrism, and consequently, implicitly, the second. Galileo will also pulverize this one with the publication of the celestial Message in 1610, after, on theological considerations, Giordano Bruno has, him, at the extreme end of the XVI E century, explodes the limits of the Universe and even denied the central place of the Sun. In Kepler, partisan convinced of the system of Copernic, it will return with the publication of his three laws, between 1609 and 1619, to remove astronomy from the uniform circular motions, while being based on the precise observations and the rigorous statements of Tycho Brahe. Contrary to this last which, in spite of the quality of its work, never gave up placing the Earth out of the center of the world, Kepler not only will endorse the system of Copernic, but still will transfigure it by the introduction of the elliptic orbits.  

It “will not remain” more in Newton but to provide, between 1665 and 1686, the total and final explanation of this celestial mechanics.