Galileo's famous letter to his friend Castelli, dated December 21, 1613, is where, for the first time, he joins fully in the debate over the relations between science and theology. The letter to Castelli was disseminated in numerous manuscript copies, some of which were maliciously altered; it would lead to many denunciations of Galileo to the Inquisition. Convinced that the Church would look foolish if it were to denounce heliocentric cosmology, Galileo stood firm, rejecting a request that he consider Copernican theory as a mere hypothesis by saying that Copernicus 'could not be altered', that it was necessary either 'to accept him or to reject him completely'.
The letter to Cristina de Lorena, Grand Duchess of Tuscany, was probably written in mid-1615 and is the longest of the Copernican letters; in it Galileo expands on the issues raised in the letter to Castelli and cites Saint Augustine and other authorities in defence of his thesis. Having first thought of sending this letter to a member of the religious community (probably Castelli), Galileo decided instead to address it to the Grand Duchess, who had shown interest in the topic, and thus repeated a strategy that had proved to be advantageous for him earlier when he had named the satellites of Jupiter the 'Medicean planets' in honour of his patrons (in the 1616 trial of Galileo before the Inquisition this letter was not mentioned, most probably so as not to incriminate its illustrious recipient).
The letter of Galileo to the Grand Duchess is an indispensable text, both for the study of the conflict between the Catholic Church and Copernicanism and for understanding Galileo's concept of nature and the importance of the new scientific methodology of contrasting hypotheses.
For the translation we have used Antonio Favaro's edition of the works of Galileo, Galileo Galilei, Opere, Edizione Nazionale, first published in Florence between 1890 and 1910 and later reprinted with some additions. The text of the Copernican letters is found in Volume V, among writings in defence of the Copernican system.
Another article by Olaf Pedersen entitled Galileo and the Council of Trent: the Galileo affair revisited was published in J. Hist. Astronom. 14 (1) (1983), 1-29. It gives an interesting perspective on events and we indicate its contents by quoting from the Introduction:-
Very few episodes in the history of science have caused more discussion than the ecclesiastical condemnation of the Copernican system in 1616 and the ensuing personal persecution of Galileo in 1633. The debate began at the time of these very events and continues today with unabated fervour.
One of the more enigmatic features of this affair is that the debate has gone on for 350 years without producing any real convergence of opinion which would once and for all settle the matter, by providing an answer to the fundamental question of why the ecclesiastical authorities of the seventeenth century were able to make a decision which was nothing but a serious blunder. Today we can provide a rather precise answer to the first important question, 'What happened?', although there may still be one or two obscure points concerning the proper understanding of the mere historical facts. Also the second question, 'How did it happen?', is now much better understood than before. Only the third question, 'Why did it happen', still divides scholars and others to such an extent that no one can pretend that even an approximate solution has been reached.
In this paper we concentrate on this third question and argue that the lack of consensus may be due to the fact that the Galileo affair has been examined in a perspective which often has been too narrow. It has usually engaged the attention of historians of science with little or no interest in the history of theology; and certainly the fate of Galileo and the Copernican system must always remain one of the crucial episodes in the emergence of modern science. On the other hand, it may well be that the key to a more satisfactory understanding of the ultimate causes of the condemnation will be found if we so extend the perspective that the whole affair is seen not only as an episode in the history of science, but also as an important event in the history of theology. But before this point is argued it may be useful briefly to touch upon the first two of the questions mentioned above.
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