歳差とコペルニクス体系の生成
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In this paper I discuss the genesis of the Copernican system. It is well known that Copernicus himself explained, both in some chapters of On the Revolutions and in its dedication to Pope Paul III, how he began to conceive motion of the earth against the traditional opinions of astronomers. As far as Copernicus is concerned, astronomers did not agree among themselves in the investigation of the heavenly bodies, especially they were so uncertain about the motion of the sun and moon that they could not establish and observe a constant length even for the tropical year. In spite of those remarks, his train of thought to a revolutionary heliocentrism remains obscure because he did not specifically mention which observations he thought could definitely undermine the traditional astronomy. This sense of dissatisfaction with the rationale with which Copernicus fortified his arguments against the Ptolemaic geocentric world has induced historians to look for a more likely point of departure for his revolution in scientific thinking. The first astronomical phenomenon that might have induced Copernicus to reform the traditional cosmological system is supposed by some historians to be the irregular motions of the five planets; to be the In this paper I discuss the genesis of the Copernican system. It is well known that Copernicus himself explained, both in some chapters of On the Revolutions and in its dedication to Pope Paul III, how he began to conceive motion of the earth against the traditional opinions of astronomers. As far as Copernicus is concerned, astronomers did not agree among themselves in the investigation of the heavenly bodies, especially they were so uncertain about the motion of the sun and moon that they could not establish and observe a constant length even for the tropical year. In spite of those remarks, his train of thought to a revolutionary heliocentrism remains obscure because he did not specifically mention which observations he thought could definitely undermine the traditional astronomy. This sense of dissatisfaction with the rationale with which Copernicus fortified his arguments against the Ptolemaic geocentric world has induced historians to look for a more likely point of departure for his revolution in scientific thinking. The first astronomical phenomenon that might have induced Copernicus to reform the traditional cosmological system is supposed by some historians to be the irregular motions of the five planets; to be the abnormally huge epicycle of Venus by others: to be the curious coincidence of the periods of revolution of the sun, Venus and Mercury by yet others: and so on. Those seem to me to be all probable, but conjectural and arbitrary to some extent. I think that those who desire to figure out, as objectively as possible, how Copernicus conceived the motion of the earth should pay attention to the evidence which Rheticus gave us in The First Report which was composed under the watchful eyes of Copernicus. In one of its chapters entitled "Why We Must Abandon the Hypotheses of the Ancient Astronomers," Rheticus enumerated six principal reasons for the new system, of which I find the first one to be the most crucial to our subject. Rheticus says that the indisputable precession of the equinoxes and the change of the obliquity of the ecliptic persuaded his teacher to assume that the motion of the earth could produce most of the appearances in the heavens, or at any rate save them satisfactorily. This evidence should be considered seriously, since there was no astronomer who could have more intimate contact with Copernicus than Rheticus, the only disciple of the astronomer who lived in the "very remote corner of the earth" which is V raniewo in Poland in modern terms. If you reread Copernicus carefully in this light, you will notice that the greatest reformer of modern astronomy tells you the same motive as found in Chapter 5, Book 1 of his immortal work: "If we assume its (the earth's) daily rotation, another and no less important question follows concerning the earth's position (in the universe)." Consequently, as far as I know, all the historians are wrong in arguing that Copernicus conceived the annual revolution of the earth prior to its daily rotation. The precession of the equinoxes was discovered by Hipparchus in archaic Greek times and it was confirmed about 400 years later by the Roman astronomer Ptolemy. According to the author of Almagest, all the fixed stars, besides their daily rotation, revolve uniformly around the poles of the ecliptic from the west to the east for the period of 36,000 years. His assumption is essentially correct except for the numerical value of the period which counts for about 26,000 years in contemporary astronomy. However, something extremely curious though inevitable happened to all the Renaissance astronomers including Copernicus. To the contrary of their great predecessor of Alexandria, they insisted on the anomaly of the precession of the equinoxes since the observations that progressively accumulated in the long course of astronomy appeared to them to point to this. The truth is that the data of the ancients were wrong because of their poor techniques of observation. Accordingly, the anomaly of the precession of the equinoxes was an imaginary construct. As well as other astronomers, Copernicus struggled with the wrong observations to save the pseudo anomaly of the noblest heavens and supposed that the irregular motion of the fixed stars could be composed of the uniform rotations of four heavenly spheres, in addition to the other two assigned to the daily rotation and the mean precession of the eqiunoxes. Surely, if the firmament needed six spheres and moved in an uttermost complicated way, it would never deserve the name of visible god! So I conclude that Copernicus wanted first of all to replace the confusion of the god-like heavens with a complexity of the humble earth's motions that accorded with the most fundamental principle of heavenly beauty and harmony grounding ancient Greeks cosmology. I admit, however, that another important question is still open as to how Copernicus took a further step from the earth's daily rotation on its axis to its annual revolution around the sun, and this theme will be discussed in my next paper.
- 信州大学教養部の論文
- 1993-03-25