During the thirteenth and fourteenth centuries several Arab astronomers developed mathematical techniques similar to that of Copernicus, including the previously mentioned al-Urdi, al-Tusi, and al-Shatir. The underlying suggestion is that Copernicus was most likely influenced by previous astronomical theories. According to Saliba “research conducted in the history of Arabic astronomy after 1957 has managed to demonstrate that the very same theorems of Tusi and Urdi as well as the model for the moon by Ibn al-Shatir were also used by Copernicus to construct his own alternative astronomy.”
The influences of Islamic astronomers on European contemporaries is uncertain, but Copernicus discussed al-Battani in De Revolutionibus Orbium Coelestium suggesting a possible influence of the Arab astronomer. In the tenth chapter entitled The Order of the Heavenly Spheres, Copernicus writes that planets “are tiny bodies in comparison with the sun. Venus, although bigger than Mercury, can occult barely a hundredth of the sun. So says Al-Battani of Raqqa, who thinks that the sun’s diameter is ten times larger [than Venus’s], and therefore so minute a speck is not easily descried in the most brilliant light.” Without looking further than his own text, Copernicus was certainly familiar with works of Islamic astronomers. Whether they influenced his mathematical conclusions remain open to debate.
Reductionist revisions to history have claimed the superiority of Islamic sciences because several astronomers in the dar al-Islam touched on the possibility of a heliocentric universe. These included Ibn al-Haytham, Abu-Rayhan Biruni, and Qutb al-Din al-Shirazi. However, there was no general consensus among Muslim astronomers for a heliocentric option to replace geocentric models. Often astronomers suggested a heliocentric model only to expressly deny its possibility. Although heliocentric theories already existed in ancient scientific writings, this model did not come to replace geocentric opinion until long after Copernicus himself. That other astronomers came to think of it first thus remains remarkably unimportant until the time of Galileo and Newton. Only in hindsight have historians of science taken note of heliocentric models that were touched up, even though they were dismissed by contemporary medieval and early modern astronomers.
Although the connection between astronomers of the Maragha School and Copernican scholars is uncertain, Saliba proposes that it is almost certainly likely. Mere coincidence does not explain, for example, the nearly identical lunar models of Copernicus and al-Shatir. The main distinction is that the Maragha School astronomers remained geocentric as opposed to the heliocentric model of Copernicus. “That feature of Copernican astronomy entails the transformation of geocentric mathematical models to heliocentric ones by the reversal of the vector connecting the sun to the earth, while leaving the rest of the mathematical models intact.” (Saliba, p 266) While the innovation of contemporary heliocentric visions of the universe are attributed to Copernicus, his actual mathematics remained little distinguished from earlier and contemporary astronomers.
Other similarities between Copernicus and the Maragha School exist. Like the Maragha astronomers, Copernicus was concerned with preserving the Ptolemaic equant instead of arguing against it. “The real Copernican indebtedness to the Maragha astronomers not only lies in the fact that he uses these same theorems to build his own models, but that he also uses them at the identical points in the models where they were used earlier by the Maragha astronomers.” (Saliba, p 269) Both the Tusi Couple and the ‘Urdi Lemma figured in Copernicus’ theorems. The only certainty in the actual transmission of astronomical information to Christian Europe, during and before the time of Copernicus, was a Byzantine Greek manuscript showing the Tusi Couple and “a poor rendering of Ibn al-Shatir’s lunar model” (Saliba, p 271) which was located in the Vatican Collection by 1453. Whether Copernicus actually saw this document is not known.
What is known is that the Islamic sciences remained an active force into the sixteenth century and even later. Two notable Islamic contemporaries of Copernicus were ‘Abd al-‘Ali al-Birjandi (d. AD 1525 or 1526) and Shams al-Din al-Khafri (fl. AD 1525). Al-Birjandi debated the Earth’s motion, defending natural philosophy and metaphysics in astronomy in direct opposition to the arguments of al-Qushji. “In developing his position, al-Birjundi makes an interesting analysis of what might occur if the Earth were rotating (which he himself rejects) and hypothesizes something quite close to Galileo’s notion of ‘circular inertia.'” (Ragep, p 63-4) While modern science has generally moved toward secularism, medieval and early modern European and Islamic astronomers worked within a religious context that affected the development of their work.
Evidence of transmission of Islamic intellectual knowledge to Europe resides in the great translation movement, although the extent that astronomical texts were translated has yet to undergo serious research. Starting in the eleventh century, Arabic manuscripts began to be translated to Latin in earnest. The translation of Hellenistic scientific and philosophical works were mostly done further East in the tenth century, arriving in Muslim al-Andalus throughout the tenth and eleventh centuries. There they were often translated into Hebrew and, later, Latin and European vernaculars which transmitted this information to Europe. For example, Ibn Rushd’s works on Aristotle were translated first to Hebrew and then to Latin, important to the introduction of Aristotelian cosmology to Christian Europe. The most important ancient and medieval texts available in the Islamic world were translated by the thirteenth century. More research remains to be done on the extent to which astronomical texts were translated and subsequent correlation between Muslim and Christian scientific achievements.
The traditional separation of Islamic and Christian astronomical history continues to be defied by obvious intellectual connections in the early modern period. George Saliba draws an interesting parallel between Copernicus and al-‘Urdi. The latter assumed that his model was true (as most astronomers did), and that the burden of proof belonged to Ptolemy who was the one that made mistakes “corrected” by al-‘Urdi. “This is exactly the same sentiment expressed by Maestlin some three centuries later when he explained this same point in Copernicus’s astronomy to his student Kepler.” (Saliba, p 298) Because of Copernicus’ the relative neglect to explain the ‘Urdi Lemma it became the subject of a correspondence between Kepler and his teacher Maestlin, where Kepler asked his teacher specifically about this theorem in Copernicus’s astronomy and its proof. Maestlin supplied the proof to the theorem in his answer to his student Kepler.
In summary, exact influences of Islamic astronomical texts are unknown. A case in point is the unsure extent of the work of al-Shatir on Copernicus. What is known about the work of al-Shatir is that clear equivalences are seen in the Copernican models. Since al-Shatir and other significant astronomers were well known in the Islamic intellectual world, it can be assumed that there is a history of “a natural and gradual development that had started some three centuries earlier.” (Saliba, p 304) Such a historical progression cannot be found for Copernicus, who appears unique in European history where astronomy is generally seen as progressing from a Ptolemaic stagnation of two thousand years to a sudden heliocentric revolution relatively shortly after Copernicus’ work was published. The missing link should most probably be attributed to a lack of research in the intellectual transmission and cultural interaction between astronomers in the Islamic and Christian worlds.
Aside from mathematical similarities, religious dedications by Muslim astronomers are not a far cry from Christian astronomers. Copernicus (1473-1543) opened De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Spheres) with:
“I can readily imagine, Holy Father, that as soon as some people hear that in this volume, which I have written about the revolutions of the spheres of the universe, I ascribe certain motions to the terrestrial globe, they will shout that I must be immediately repudiated together with this belief For I am not so enamored of my own opinions that I disregard what others may think of them. I am aware that a philosopher’s ideas are not subject to the judgment of ordinary persons, because it is his endeavor to seek the truth in all things, to the extent permitted to human reason by God.”
This reflects a concern with keeping astronomical observation within a religiously acceptable realm of Godly creation. Copernicus adopted the doctrine of Aquinas in believing that God’s will included a proper reason given humans to comprehend his creation – a parallel can be drawn to Islamic debates over the relationship between god and astronomy.
While Copernican science led to controversy within the Christian world, the Ottoman empire absorbed his theory as one among many others. The heliocentric model “was not made a subject for polemics. One probably reason may be that there were no religious dogmas concerning the system of the cosmos.” (p 41) Ottoman sciences were generally directed toward practical matters, and interest in the works of Copernicus, Tycho Brahe, Kepler, and Newton appear to have remained unimportant to contemporary Ottoman astronomers. Instead of an interest in astronomy as a science to explain the cosmos, Ottoman concern was “in the developments concerning calendar making and timekeeping which were necessary for the State and religious affairs and daily life.” (p 41) Generally, by the seventeenth century in the Ottoman state there appear to have been little controversy between astronomy and religion. Whether this was a result of Ottoman state formation specifically or the “success” of Islamic astronomers in consolidating their science with religion is unclear.
While much has been written about Islamic astronomy in early and medieval times, many more manuscripts remain untranslated into the English language. Clear parallels and connections between Islam and the role of astronomy remain unexplored at this time, including any detailed analysis of political and religious relationships in scientific progression or the status of astronomers in society. Islamic astronomers inherited the sciences of the Ancients and quickly translated and added onto this work. Between the eight and fifteenth centuries, these astronomers created new theories of the planets. More significantly, their work brought astronomy into a science in its own right, freed from astrology and philosophy. Metaphysical connections to Islam were not negated although over the course of time the science gained an increasing independence from theology. By then the Holy Office attempted to restore religious unity in Europe after the split in the Church, at the expense of anyone who spoke too loudly in disagreement with the views of the Roman Catholic Church. As Galileo stood in the crux of the bitterest moment of European astronomical history, the Islamic world never felt a similar controversy although astronomy was always a diverse field of opinion.
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