The Muslim Scientists

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Embedding Scientific Ideas as a Mode of Science Transmission


At a different occasion I had attempted to survey the results that have already been reached regarding the transmission of scientific ideas from the world of Islam to the scientists of the European Renaissance.’ In that survey, I included some of those details which have been well known in the literature since the late fifties of the last century, while I added others that were either less known, or have been more recently explored and documented. I used the discipline of astronomy as a template to record the transmitted ideas and hoped that other people, who work on other disciplines, would do the same, all in an effort to paint a fuller picture of the situation that prevailed around the Mediterranean during the sixteenth and seventeenth centuries.

Problems of Detecting Contacts

In the field of astronomy, which happens to be the most fecund of all the scientific fields, tracing the transmission of astronomical ideas from the Islamic world to Europe proves to be rather challenging for two main reasons: When texts were plainly and admittedly translated from Arabic into Latin, and that happened mainly during the Middle Ages, sometime between the tenth and the fourteenth centuries, the problem that was hardest to answer was: why some texts were translated while others were not? Why were the works of Muhammad b. Musa al-Khwarizmi (d. c. 850) translated, his Indian arithmetic, his algebra, as well as his astronomical tables, while the astronomical tables and other mathematical works of his contemporary, and in many ways just as brilliant, Habash al-Hasib (d. c. 870) were not?

In the case of the Renaissance the situation becomes much more complex. For by that time, that is, after the fifteenth and during the sixteenth centuries, we rarely find Arabic books that were explicitly translated into Latin, as was the case in medieval times. Of course we are not talking about the conscious efforts by people like Andreas Alpagos who undertook the challenge to re-translate the works of Avicenna in particular, for those were simply revisions of translations already completed before. Nor are we talking about the very few attempts that were made during the seventeenth century to translate one book here or one treatise there as was the case during the earliest stages of what later became the tradition of Orientalism. Those attempts are a category by themselves for they were mainly executed with an archaeological purpose in mind and were mostly motivated by the curiosity that became notorious during the later colonial period, and prepared the ground for the fictitious Orient that was finally created in the European mind, an Orient that became the hallmark of Orientalism.[2] The complex issues that began to appear in the Renaissance, and were rarely recognized before, had to do with a completely different kind of transmission of scientific ideas. The phenomenon I wish to single out, and which I would call embedding rather than transmission, is that of a transmission process through which Renaissance scientists, and sometimes also humanists, read texts in the original Arabic, grasped the ideas contained in those texts, and then incorporated those ideas in their own works. Of course, their resulting works were produced in Latin.

During this process, detecting lines of transmission, especially in the case of humanistic texts, becomes much more difficult, and at times even contentious. Issues of whether Dante read the Mi`raj stories of prophet Muhammad before he wrote his Divine Comedy or not, give only one sample of such difficulties. And if true, such a process of embedding could be barely detected in the works of Dante, notwithstanding the disputes that surround it and still stir up much debate. This very process of embedding may in fact be a forerunner of what seems to have happened at a much larger scale during the Renaissance.

Those who work with scientific texts are slightly more fortunate than their fellow humanists simply because it is slightly easier to prove the process of embedding in scientific texts than it is in humanistic ones. It is the very nature of those scientific texts that allowed someone like Neugebauer, Kennedy and generations of the latter’s students after him to pronounce immediately that what they saw in the lunar model of Copernicus (d. 1543) was in fact a case of embedding the lunar model of Ibn al-Shatir (d. 1375). And yet, we can still hear people arguing for the case of independent discovery, and that one should not yet talk of embedding or transmission of the ideas of Ibn al-Shatir by or to Copernicus without demonstrating the exact route by which Ibn al-Shatir’s ideas reached Copernicus. Independent discovery is in fact a plausible argument, and we have many examples of such occurrences in the history of science. But the case of Ibn al-Shatir’s lunar model, the story of coincidence is slightly more complex. To start with, it is a geocentric model unlike the other Copernican models, not only because it fits better with an Aristotelian cosmology, but because the moon is in fact an earthly satellite. Second, Ibn al-Shatir’s model was designed to solve in one stroke two major problems in the Ptolemaic lunar model: (a) it solved the equant-like behaviour of the Ptolemaic model, and (b) it resolved the distortion that the Ptolemaic model introduced to the apparent size of the lunar disk at quadrature. Third, Ibn al-Shatir’s model was also designed to dispense with the concept of prosneusis that had bedeviled the Ptolemaic model and had caused much controversy in Islamic astronomy. When all those factors are taken into consideration it becomes clear that all those purposes that motivated Ibn al-Shatir’s model, and the multiple layers of technical intricacies it resolved, make it highly unlikely that two people would coincidentally come upon it unless they were both seeking to resolve all those problems of the Ptolemaic model and from within the same Aristotelian cosmology. To think that the same complexities and the same motivations could be attributed to Copernicus in order to explain his adoption of Ibn al-Shatir’s lunar model complicates the story of independent discovery, not to say that it makes it incredible. Let us at least say that one’s imagination has to be stretched a little in order to believe that such coincidences could occur.

The fact that we still do not know the exact route by which Copernicus knew of Ibn al-Shatir’s lunar model, before he decided to adopt it, and yet we can make such claims of indebtedness on the part of Copernicus, is only a feature of the nature of scientific texts that allow such conjectures.

As we just said, the scientific intricacies of Ibn al-Shatir’s model and its complexity and multiple purposes, as well as its demonstrable equality with that of Copernicus, angle for angle, sphere for sphere, and the historical fact that Ibn al-Shatir died exactly a hundred and sixty-eight years before Copernicus, make the story of independent discovery much less likely. And yet it is not impossible to imagine.

Had the story stopped with the lunar model, this particular case of embedding would have remained a tantalizing conjecture, and we would have all continued to wait for the day when we could indeed account for what is sometimes called “the smoking gun” that would demonstrate the route through which Copernicus came to know of Ibn al-Shatir’s work.

The plot thickened, however, when it was found out that Copernicus also used a mathematical theorem, now commonly known as the Tusi Couple, which was discovered by another astronomer, Nasir al-Din al-Tusi (d. 1274), who lived even another hundred years earlier than Ibn al-Shatir. As it turned out, Copernicus did not only use this theorem, but offered to prove it. It was in the proof that he reproduced the same geometric points that were used by Tusi before. One could still stretch his imagination and say that it was a series of coincidences. But then there was a “smoking gun” in this case. There was one geometric point that indicated the center of the smaller sphere in the Iasi Couple where Dig had designated it with the Arabic letter “zain”. All other points were the same, that is the Arabic letters used by Tusi were duplicated, point for point, with their Latin phonetic equivalents by Copernicus. For this particular point, Copernicus used the Latin letter “F”, instead of the expected “Z”. This single variation could only mean that he, or someone helping him, obviously misread the Arabic “zain” for an Arabic “fa”‘. In fact the two letters are very similar in the Arabic script, and, depending on the manuscript that he or his assistant were working from, it would be very easy to mistake a “fa”‘ for a “zain”. Thus the likelihood that Copernicus would have his own random selection of alphabetic designators to mark the same points that were marked by Tusi with the same phonetic equivalences is very slim indeed, and in light of that one has to begin to loose faith in the theory of independent discovery.

But when it was further found that Copernicus also used the same model for the upper planets that was used by Tusi’s colleague and friend Mu’ayyad al-Din al-Urdi (d. 1266), of course after making the easy mathematical shift from geocentrism to heliocentrism, and this time neglecting to prove the lemma that was devised by ‘Urdi and proven by him for the purpose, the problem of independent discovery became even harder to maintain. This lapse in Copernicus’s construction of ‘his own’ mathematical model for the upper planets prompted Kepler to write to his teacher Maestlin and inquire about this particular proof of this rather simple theorem, now dubbed as the ‘INT lemma, and Maestlin duly complied with his request.[3] One can see how complex scientific texts could allow us to reach such conclusions regarding the embedding of scientific ideas even if we had no clue regarding the route through which Copernicus must have known about these earlier results.

The coup de grace came when Copernicus reached the construction of his model for the planet Mercury. There too, Ibn al-Shatir had constructed a model of his own that avoided the equant problem of Ptolemy’s model, but preserved the essential features of the Ptolemaic observational results, namely, that the planet Mercury should have one apogee in the constellation of Libra and two perigees at ± 120° on either side of it. The very problem of two perigees came about from the Ptolemaic observational problem where it was thought that Mercury had its maximum elongations from the sun at those two points, i.e. it appeared to the observer, on the earth, to have the largest epicycle at those points. In order to achieve all these cosmological purposes and remain faithful to the Ptolemaic observational results, Ibn al-Shatir had to use the Tug Couple within the construction of the model in order to allow Mercury’s epicycle to expand and contract, so that it would look small at apogee, and large enough at the two perigees. This was relatively simple for Ibn al-Shatir since the Tusi Couple was specifically designed to take care of such cases of expansion and contraction while remaining within the conceptual domain of Aristotelian cosmology. Put simply, the Tusi Couple was developed specifically to obtain linear motion, the expansion and contraction in this case, as a result of the Aristotelian required uniform circular motion.

Now, in his own construction of the Mercury model, Copernicus adopts the same technique as Ibn al-Shatir, that is, he used the same Tusi Couple for the same expansion and contraction purposes that were used by Ibn al-Shatir. And he also accounted for the equant in exactly the same way it was accounted for by Ibn al-Shatir. But here again there was another “smoking gun”. In adopting Ibn al-Shatir’s very complicated model Copernicus got confused between the absolute size of Mercury’s epicycle and the size it would appear to an observer on earth, and made the absurd statement that the model would yield a maximum elongation at a distance of 90° from the apogee. He apparently forgot that size depended on two variables: the absolute size of the object, and the distance of the object from the observer. For although Mercury’s epicycle does in fact reach its maximum expansion at 90° away from the apogee, for an observer at the earth it would still not look as big as the contracted epicycle which would be brought closer by the motion of the model to the observer at 120° on either side of the apogee. When Swerdlow noted this discrepancy in Copernicus’s construction of the Mercury model, as he translated Copernicus’s earliest astronomical treatise, the Commentariolus, he had this to say about it:

There is something very curious about Copernicus’s description. […] Copernicus apparently does not realize that the model was designed, not to give Mercury a larger orbit (read epicycle) when the Earth (read center of the epicycle) is 90° from the apsidal line, but to produce the greatest elongations when the Earth (read center of the epicycle) is ± 120° from the aphelion (apogee).”[4]

He then went on to say:

This misunderstanding must mean that Copernicus did not know the relation of the model to Mercury’s apparent motion. Thus it could hardly be his own invention for, if it were, he would certainly have described its fundamental purpose rather than write the absurd statement that Mercury “appears” to move in a larger orbit when the Earth is 90° from the apsidal line. The only alternative, therefore, is that he copied it without fully understanding what it was really about. Since it is Ibn ash-Shatir’s model, this is further evidence, and perhaps the best evidence, that Copernicus was in fact copying without full understanding from some other source, and this source would be an as yet unknown transmission to the west of Ibn ash-Shatir’s planetary theory.” [italics mine][5]

The series of “coincidences” mentioned before, as well as the misreading and “misunderstanding” just mentioned, makes it clear that Copernicus was not working independently of the Arabic texts that had been written in the previous two centuries or so. The fact that we can assert such claims demonstrates the power of scientific texts which allow us to determine indebtedness, incorporation, embedding, direct and indirect transmission, etc., without necessarily knowing the manner in which those contacts took place. Similar cases in humanistic texts would be much harder to establish.

Other instances of such embeddings are a little easier to establish in the opposite direction, that is, when we know the Arabic texts that were read by Renaissance scientists, but we still do not know exactly how they were used by those scientists in their Latin habitat. I have had occasion to study Arabic manuscripts that were read by one of Copernicus’s younger contemporaries, Gillaume Postel (1510-1581). One of those manuscripts is preserved at the Vatican Library, while the other at the Bibliotheque Nationale de France. Both manuscripts have Postel’s handwritten annotations on their margins. I used those manuscripts for an article, which I published on the internet, in order to raise the question: whose science was Arabic science in Renaissance Europe?[6] In that article I demonstrated how someone like Postel would read Arabic astronomical manuscripts one day, annotate them, and in some instances even correct them, and the next day he would deliver his lectures at the Institut Royal, now College de France, obviously in Latin. Just think of the complexity of ideas being originally in Arabic, themselves written to challenge Greek astronomy, and after being digested by Postel were embedded in his lectures which were obviously delivered in Latin.

I used that example to question the applicability of such concepts as Arabic science, Latin science, Greek science and the like when we know, as in the example of Postel, how ideas were actually constructed through many layerings of those languages, religions, and cultures to which those sciences are usually ascribed. In it I called for a new historiography of science that accounts for such instances of embeddings as Postel’s and Copernicus’s.

One More Incorporation: The Case of Ighnatius Ni`matallah (d. c. 1590) and the Gregorian Reform of the Calendar

Now that we have shed a badly needed light on the poorly studied phenomenon of embedding as a mode of transmission that was apparently quite common during the Renaissance, a phenomenon that did not involve specific texts being translated as was done during the Middle Ages, we can then approach the Renaissance with a much more open mind. Once we do that, we are likely to find many more contacts than the ones we have already mentioned. In what follows, I will focus on one particular instance where transmission was not specifically sought out by Renaissance orientalists, as was done by Postel and others, but by a fortuitous offer by an occidentalist, if you wish, who simply managed to have his ideas incorporated by Renaissance scientists, also without producing fully translated texts from the original Arabic.

The occidentalist in question was a colorful character by the name of Ighnatius (Ignatius) Ni’matallah (Ni`meh), known variously as Ni`meh in the Eastern sources or Nehemias in the Latin ones. He was a patriarch of the Syriac Jacobite church and was raised to the see of the Antiochian patriarchate in the year 1557.[7]  While still in Diyar Bakr (modern Diyarbakir in South East Turkey), this patriarch seems to have earned the confidence of the local Ottoman governor of the district. The Ottoman rule itself was at that time still on the ascension. It had been barely one hundred years since the successful conquest of Constantinople, the capital of the Byzantine Empire. And with its fall the Ottoman conquest ushered in the defeat of the last vestiges of Byzantine presence in Asia Minor. One could safely say that at the time Christian Ottoman relations were not at their best. In addition, and even without the ascension of the Ottomans, the Christians in that area were living in a political turmoil that had been worsening visa vis their Muslim neighbors since the incursions of the crusaders between the 11th and 13th centuries, and reached an abyss amongst the Christians themselves when the fourth crusade 1204-1205 was redirected and finally launched against the capital city of Byzantium.

Thus by the middle of the sixteenth century, religious sensitivities and interfaith suspicions and intrigues had been ripening for centuries. It was not surprising, therefore, that the local Muslims were suspicious of a Christian patriarch like Ni’matallah gaining favor at the local governor’s court, ostensibly as the governor’s private physician on account of his expertise in Islamic medicine. Ni’matallah’s expertise was not totally off the mark. Other independent facts corroborate this expertise, and in a future study, devoted to this man, I will demonstrate that the first printing of Avicenna’s Arabic text of the Canon by the Medici’s Oriental Press, in 1593 in Florence, used one of the manuscripts which were brought along to Italy by this same Patriarch. His relatively advanced medical scholarship, however, could not protect him from jealousies and intrigues at the Diyar Bakr court. Thus in a gesture of reconciliation, and probably intending to protect his private physician, the local governor took off his own turban one evening and placed it on the head of the patriarch, while declaring that his own physician had by this gesture just converted to Islam. Conversion has a tremendous power, and many a sinful person was saved by the very act.

Historical reports tell us that the governor’s gesture went well with his Muslim audience. But they also tell us that the very act of a patriarch converting to a different religion, whether Islam or otherwise, infuriated his own Christian parishioners, who now clamored for his head. Sensing a danger for his life, the hapless patriarch managed to appoint his nephew to his patriarchal see (apparently still had some clout among his Christian followers for such an act of nepotism), and to escape with his life in the year 1576 AD. In addition, he apparently managed to haul along a relatively large collection of Arabic manuscripts. Concrete evidence of his escape still survives in a note appended to a manuscript, which is now kept, together with the rest of the patriarch’s manuscripts, at the Laurentiana Library in Florence, Italy. The note says that he, “the lost soul, by the name of Patriarch Ni`meh, finished resolving the problems in this manuscript while he was being tossed by the sea waves on his way to Venice, in the year 1888 of the Greeks (= 1577 AD).”[8]

Further background should at least partially explain the reasons why the Patriarch ventured on this dangerous trip in the first place, and should give us a clue as to what he expected to achieve with it. The decision taken by the Eastern Orthodox churches to split off from the Church of Rome in 1054 AD was unwelcome by the Vatican, and thus no effort was spared to re-integrate those churches back under the papal flag. The Syriac Antiochian church was one of those Eastern churches whose re-unification with the Church of Rome was at least promised by the Patriarch. That promise itself may have facilitated his reception at the papal see, when he finally arrived at Rome.

Thus far his motivation for taking the trip may be understandable. But what remains to be problematic is the reason why he decided to bring along a large number of Arabic manuscripts, mostly scientific ones, and what was he planning to do with those books. As we shall soon see, this problem remains unresolved unless we change our vision of the intellectual life during the Renaissance, and begin to appreciate the extent to which Islamic culture, and Islamic science in particular, had been sought after during that time. So what was the Patriarch hoping to do with those books?

In hindsight, we now know that there was a good market for them in northern Italy, along the corridor that stretched from Venice in the North East down to Florence and eventually to Rome. The sources report that sometime during the Patriarch’s trip from Venice to Rome, in the company of the converted Turk Paolo Orsini as his interpreter, the Patriarch made the acquaintance of the cardinal, and future Duke of Tuscany, Ferdinand de Medici, who was apparently considering the establishment of a press, later known as the Medici Oriental Press.[9] The Patriarch’s books were definitely useful for the enterprise. We are told that Ferdinand struck a deal with the Patriarch in which the Patriarch would receive a monthly stipend of 25 scudes, and a life-long free access to his books, if he consented to deliver those books to a governing board of the press that was then headed by Raimondi, and who later became the owner of the same press.

All of these facts could not simply be happy circumstances. What is the likelihood of the convergence of such characters as a patriarch, traveling to Venice with a considerable load of Arabic books; a business/cleric/and future Duke from the banking family of the Medicis, interested in setting up an oriental press towards the end of the sixteenth century; and a Pope, interested in re-uniting the Eastern churches under the papal flag? The only explanation that could connect all those facts together is to assume that there was a lively intellectual and business environment in sixteenth century Italy that valued the sciences of, and possible business with, the Islamic world. A word of this interest must have already reached the Islamic lands so that the Patriarch could smell a commercial prospect for his books. The re-unification of the churches must have only been an excuse to facilitate the trip, for we know that nothing of the sort happened, and that a very small group of Eastern Christians had a long and checkered history with the Papacy who, at various stages of their history, all the way from the great schism of the eleventh century till the nineteenth century, split off and re-united themselves with the papal authority several times over.

At the Patriarch’s arrival in Rome the reigning Pope, Gregory XIII (1572-1585), had other reasons to rejoice at meeting him. Not only did the Pope want to test the grounds for a campaign against the Turks,[10] but he also wanted to revive the Catholic church from the debilitating attacks it had received at the hands of the protestants. A patriarch from the Turkish lands of Islam, ostensibly wishing to re-unite his flock with the Pope’s, would be very useful to the Pope, and a learned one to boot, who could be employed in the papal committee that was to achieve the single most famous act of this pope, namely, the Gregorian Reform of the Julian calendar, which eventually reestablished the Catholic church’s authority, at least symbolically, in protestant lands.[11] Eastern orthodox churches, in countries where the Gregorian calendar is accepted by political authorities for civic purposes, still refuse to follow the ecclesiastical injunctions of this calendar, differing with it most notably over the Easter cycle. One should not underestimate the symbolism of this rejection as a means to safeguard the independence of the Eastern churches from that of Rome.

For the moment, I wish to leave aside the incorporation of the Patriarch’s ideas into the production of the books at the Medici Oriental Press, for I would like to treat that issue at much greater length at a different occasion. But for now, let it be said that the first batch of printed Arabic books that this press issued from Florence, which were supposed to benefit the missionaries who were to proselytize in Arabic-speaking Islamic lands, included some four important scientific books, including Avicenna’s Canon and a hybrid text of the revised Elements of Euclid. The manuscript copies for both of these books came from the Patriarch’s library.[12] I note in passing that I find it hard to believe that anyone would deliberately use Euclid’s Elements in order to proselytize among Muslims who had been using this book for almost a full millennium at the time. My contention is that the press had a European market in mind, and used the missionary work to avoid being censored by the Inquisition for producing Arabic books in the very heart of Christendom.

Now that I lay the matter of the Patriarch’s role in the Medici Oriental Press aside, I wish to devote the rest of this paper to the Patriarch’s role in the Gregorian calendar reform itself. Not much is known about the details of the deliberations that led to the reform of the Julian calendar in 1582, under Gregory XIII. We do not know who proposed what, at what time, and for what reasons. We also do not know the particular expertise the Patriarch brought to the committee, other than his being well versed in the secular sciences of the Islamic world. But few tidbits have already come to light, and through them we can still trace the general theme of the embedding of the Islamic legacy into the intellectual environment of Renaissance Europe.

We are particularly fortunate that the Vatican had the wisdom to convene a conference at the 400th anniversary of the Gregorian reform, and that the proceedings of the conference are now in print for all to consult.[13] And although none of the conferees devoted a paper to the role of the patriarch in the making of the Gregorian reform, several of them have hinted to that role. I will only single out those who have made remarks that help us understand the phenomenon of embedding of scientific ideas or remarks that warrant further research. I only have the chance to highlight those remarks here and not to go into them in any great detail.

In the article, “Christoph Clavius and the Scientific Scene in Rome,” Ugo Baldini had occasion to refer to the report, Ratio Corrigendi[14] that was submitted by the calendar committee, on the 14th of September in the year 1580, to Pope Gregory XIII, regarding their proposed reform of the calendar. The important part of the report is that it included the names of the members of that committee.

Among the nine signatures we find the names of three prominent prelates. The first is Cadinal Guglielmo Sirleto who was the prefect of the congregation and co-ordinator of its works. Next comes Bishop Vincenzo Lauri of Mondovi who was perhaps the co-ordinator of the group before Sirleto. In the third place we find the name of the Patriarch Ignatius of Antioch. It is certain that the three of them were well acquainted with astronomy and we have direct evidence of this in the case of the Patriarch.” [15]

Notice that the name of the famous Christoph Clavius is not among the top three signatures of the report. By the direct evidence of the Patriarch’s knowledge of astronomy, Baldini means the existence of a correspondence between the Patriarch and Clavius in which, according to the Laurentiana manuscript OR. 301 where the original Arabic of this correspondence is kept, he says that

Patriarch Ignatius maintained that the idea of a variable tropical year was due to observational and instrumental errors, also adding that a whole series of near-eastern observations (708 A.D. to 1472) showed the length of the year to be constant. He alludes to these observations by listing, sometimes the authors, sometimes the places where they had been made.” [16]

Baldini goes on to say that “this series of observations does not seem to have been sufficiently researched in studies on Islamic astronomy.”[17]

What Baldini’s testimony really means is that the Patriarch was considered among the top three knowledgeable persons on the committee, that the committee was composed of a chosen few (nine members), and that the Patriarch contribution to this committee was that he was well grounded in Islamic astronomy and that he brought along with him from Diyar Bala very important information the committee needed to know. One can imagine what kind of information that could be when we know that any ecclesiastical calendar had to consider, at a minimum, the best values if could have for the lengths of the solar year and the lunar month, and the manner in which those values were determined. So the Patriarch’s list of observations which led to a fixed solar year was crucial for the calendar’s deliberation.

Furthermore, the concept of the solar year itself involves decisions whether this year was a sidereal or a tropical year, and the relationship between the two was governed by a third concept, namely, that of precession. What was well known by then was that the Ptolemaic value for precession was considerably off the mark, and that this very value was indeed corrected by the observations that were performed during Islamic times in more than one Islamic capital. So what did the calendar committee do with such parameters? Baldini goes on to say that the committee “almost completely abandoned … the Ptolemaic linear theory, according to which there was a constant rate of precession of 1° per century. It had proved unable to account for the observations made by Muslim astronomers in 9th century Baghdad…”[18] Of course, the variation in the value of precession had necessitated debates over a third concept, namely that of trepidation. And the models proposed for this trepidation had a long history that stretched all the way from ninth century Baghdad till the time of Copernicus and the time of the committee itself.

Here again the Patriarch had a crucial intervention brought to the committee’s attention, and later on to the Pope himself as we are told by Baldini when the subject of those trepidation models was discussed. In Baldini’s words:

Each one of these models led to a different theory of the tropical year. The linear precession of Ptolemy gave a constant value of the length of the year which was known to be wrong. This had become clear already to Muslim astronomers working from the 9th century onwards in Baghdad and elsewhere, as the Patriarch Ignatius explained to the Pope in a letter (1579) and in a later report on the Compendium (12 March 1580) in which he maintained that the year had a constant, although non-Ptolemaic value.”[19]

The Patriarch was therefore already involved in the minute technical details of the committee’s deliberations, and his position was apparently clearly expressed in letters as the one whose copy is still preserved at the Laurentiana, according to Baldini. More importantly, he was apparently instrumental in convincing the committee to abandon the obsolete values of Ptolemy and adopt instead the latest, up to date values that were determined in Islamic times. This in itself is the best illustration I can think of to elucidate the concept of embedding ideas as a means of science transmission.

Other participants in the commemorative conference also noted the interjections of Patriarch Ignatius Na’matallah in the committee’s deliberations and appreciated the full scope of his role in the calendar reform.

In his own article on the Papal Bull of 1582 that aimed to promulgate the reformed calendar, August Ziggelaar had occasion to address the persons who gave this Bull the authority it had and the calendar the shape it finally took. Of course, the lion’s share in promulgating the Bull had much to do with the very dynamic personality of Pope Gregory XIII himself, and with his power of persuasion. But the Calendar’s authority rested with the nine men who went through the minute technical deliberations. But more importantly, Ziggelaar reveals that not all the members were in one voice supporting the results that were reached and circulated by the Pope in his letter to all catholic princes.[20] Notable among the dissenting voice was that of Patriarch Ni’matallah and for very technical reasons. They are the same reasons contained in the Laurentiana manuscript, which has been repeatedly mentioned so far.

Because of the importance of that dissent, Ziggelaar devoted a whole section to describing it in his article, under the title “The Criticism by Patriarch Ingatius.”[21] In it he lists the substantial points that were raised by the Patriarch. For apparently the Patriarch, like Clavius, had studied the very details of the new calendar and on his own had come to the following conclusions:

(1) The anticipation of the equinoxes cannot be as much as one day in 134 years because at the time of the Council of Nicea it was on 21 or 20 March and it had not yet gone back to 10 March; (2) from many observations in the East one concludes that the sun anticipates one day in 132 years; (3) the idea of leaving out ten leap days during 40 years should be rejected; (4) adjustments at the turn of the centuries is too irregular; (5) the moon gains one day, not in 304, but in 276 years; (6) the 14th of the lunation, according to the calculation of the Compendium by mean motions, differs sometimes two to four days from the true motion so that we could sometimes celebrate Easter with and sometimes before the Jews; (7) for the same reason Easter may sometimes be celebrated a month late. Finally, the Patriarch promised to present within a very few days the result of the research in his books, according to the commission of his Holiness.”[22]

Ziggelaar tells us that the Patriarch kept his word, and his critique of the calendar is apparently still preserved, in Karshuni, in the Laurentiana manuscript, which has been referred to several times already. The present author had not yet seen this manuscript and thus has to depend on the reports about it summarized in Zigglaar’s and other articles in the proceedings of the Gregorian Reform conference. Apparently the critique of the Patriarch did not stop with the seven points listed above. He went on to discuss other defects in the proposed reform that was being circulated by the Pope. For example, he contended that

it is not the conjunction of the sun and moon which marks the beginning of the month but the day when the moon becomes visible minus 24 hours and this according to the horizon of Jerusalem and as calculated by mean motions. Thus the 14th day will be full moon but the Compendium makes full moon fall on the 16th day. The Compendium believes that the mean motion of the sun is irregular and hence the length of the year variable. But this has to be attributed to the instruments of observation. A long series of observations in the East, from 708 to 1472, establish that the length of the year is 365 days, 5 hours, 48 minutes, 53 5/12 seconds.”[23]

All this reveals the amount of scrutiny the Patriarch was able to bring to the effort of the reform. And more was to come.

On f. 22r Ignatius reveals the “greatest error” of the Compendium: “that it has not understood the first day of the month of the Jews.” It counts the 14th day from noon, whereas the day of the Jews begins at sunset. Also, if conjunction takes place shortly before sunset, the next day will invariably be the first day of the month. It thus results that the month always begins more than one day too early in the Compendium. If we also take the anomaly of the moon’s motion and the longitude difference between Rome and Jerusalem into account, the real full moon may occur up to five days later than calculated. Summarizing, Ignatius repeats that the Compendium makes the lunation begin one day too early and from noon, as astronomers do, but not as the Jews do. Ignatius joins a few tables to find Sunday letters according to several assumptions and he also adds thirty tables to find the new moons according to the opinion of the Holy Fathers and that of the Compendium.” [24]

Apparently the Patriarch’s reservations were taken very seriously, especially by the senior mathematician on the committee Clavius himself. For according to Ziggelaar

In his Explicatio Clavius asserts that the reform agrees completely with those rules of the Christians in the East which Patriarch Ignatius showed the commission in Rome, in particular that Easter may be celebrated immediately after the 14th day of the lunation. Ignatius is among the members who signed the report of the commission dated 14 September, 1580.” [25]

The final adoption of the reform was not a straightforward matter, and could not be assumed as finalized as soon as the Compendium was issued. It was in fact a long process, and some may even remember that as early as 1514 Copernicus himself was supposed to have participated in a proposed solution for the calendar reform.[26] The criticisms and the discussions that followed the first announcements of the Gregorian reform necessitated, several times, a return to the drawing table. At one point, the Paris faculty of theology’s response to the Compendium in 1577, judged that “astronomers are contemptible, dangerous and ignorant people.”[27]But particularly the Patriarch’s criticisms seem to have found a listening ear, for in the final formulation of the calendar reform, the commission

agreed on a few guide-lines, called “hypotheses”: if full moon occurs after six p.m., it is assigned to the next day. At new moon however, there is no need of so much precision. This seems to be the result of all the criticism by Ignatius.”[28]

And yet in the final reform formulation, as promulgated in 1582, the problem of the new moon falling after 6 pm being relegated to the next day was not formally accepted, but was found to be most correct if followed in practice. Ziggelaar concludes that “perhaps the criticism of Ignatius was accepted in practice, though never overtly.”[29]

Having a scientifically valid calendar, and accepting to keep within it the influence of the church tradition, like keeping Easter tagged to Passover, and the Vernal Equinox on March 21, as it was during the Nicean Council when Easter rules were established, instead of 25, which was being proposed at the time of the Gregorian reform, is one thing, and having it accepted universally by all churches East and West is another matter. Of all the committee members, Clavius was the most conscious of the political hoops the calendar had to go through after it was finally pronounced in the bull Inter gravissimas in 1582. He already anticipated that, especially in the Eastern churches, who incidentally never signed onto this reform at least as far as the date of Easter was concerned. In that respect, he must have known that the presence of the Patriarch on the committee would become a political asset. In fact, as early as 1581, he began to deploy that political asset as could be easily detected in his use of the name of the Patriarch in order to smooth the passage of the calendar in the Eastern churches. He must have been even worried about the Eastern Christians who were still affiliated with the Papal see, like the Maronites of Lebanon and the Melkites of Lebanon, Syria and Palestine, a sizeable number of whom did not participate in the boycott of the Roman church in 1054, just as much as he was worried about the Orthodox Christian churches who never fully adopted this reform as we just saw.

We have already said before that this particular pope, Gregory XIII, had his own ambitions visa vis the East, both in its Turkish face, against which he was trying to mount another crusade, and its Christian face as he was trying to re-unify the Eastern churches that had split off some five centuries before. After all, he welcomed Patriarch Ni’matallah in Rome, and assigned him a stipend from the papal treasury for the sole hope that the Patriarch would bring his Syrian church back under the papal flag as he promised he would do. It was also this Pope who had already sent several Jesuit emissaries during the 1570’s to Lebanon, Syria, Palestine and Egypt probably to attempt to proselytize among the Muslims, but most importantly to give aid to the few Eastern Christians who still swore allegiance to the Pope.

One of those emissaries who came to Lebanon several times in 1578 and throughout the 1580’s was a Jesuit by the name of Giambattista Eliano, who did indeed investigate the conditions of the Eastern Christians who were still in union with the Pope, and particularly the Maronites of Lebanon who had their own liturgy, different from that of Rome, and who never saw eye to eye with the Orthodox Christians who persecuted them as heretics when Orthodoxy was declared the religion of the Byzantine Empire during and after the schism of 1054. It was this fellow Jesuit, Eliano, who was the correspondent of Clavius, and to whom Clavius wrote in regard to the calendar:

About the calendar, which is already finished, you should not be anxious, because the Pope plans to let two very able men come from there, and the patriarch has also subscribed to our calendar and admitted that it is very good. I hope that it will soon be published, because the Pope is quite eager.”[30]

Clavius continued to defend the Calendar Reform well after it was announced in the bull of 1582. He did so, for example, in his voluminous Explicatio,[31] which was published in 1603. And in his correspondence with cardinal Vincenzo di Lauro, who was himself involved in the calendar reform and at one point appointed by the Pope to participate in and later head the committee that considered the proposal of Luigi Giglio for the reform,

Clavius also told [Lauro] how Patriarch Ignatius of Antioch appeared at the meeting of the commission with books from the East and it was verified that the measures planned by the commission were in full agreement with these texts.”[32]

This is as close as I have been able to get to the inner working of that committee, and to the role played by Na`matallah in the Gregorian reform. I will return to this point below when I assess this role and connect it with the general theme of this paper, namely the various modes of transmission of science from East to West. For now, it should have become clear how crucial that role was, and how intimate the relationship between the Patriarch and Clavius had become during the time when they both worked on the reform committee.

Before I conclude this paper I wish to use this information that we have already gathered about the Patriarch and Clavius in order to answer a question that was raised by my dear friend and colleague Eberhard Knobloch in his admirable work on Clavius and his knowledge of Arabic sources. I am referring here to Knobloch’s article with the same title that was published as part of the proceedings of a conference that took place in 2001.[33] In this splendid article, Knobloch reviews in the most masterly fashion the intricate relationship Clavius had with a dozen authors of Arabic mathematical texts, and examines very carefully Clavius’s interaction with those authors, texts, and the ideas contained in those texts. While discussing the relationship between Clavius’s work on Euclid’s Elements, and Tusi’s work on the same, Knobloch quotes Clavius’s preface of his 1589 edition of Euclid’s Elements as saying:

We learned long ago that the Arabs demonstrated the same principle. Though I diligently looked for the demonstration a long time, I could not see it, because it is not yet translated from the Arab [sic] into Latin. Hence I am obliged to imagine it by myself.” [34]

Knobloch goes on to say:

In the edition of his works Clavius replaced this section by the remark: “I never got the permission to read it though I continuously asked for it the owner of the Arabic Euclid.” We do not know anything about this person who must have been able to read Arabic and who did not give the book to Clavius.” [35]

After admitting that he did not know of the person who could read Arabic and who was an acquaintance of Clavius, Knobloch continues to identify the Euclidian text that Clavius was talking about. In that instance he says:

The Arabic Euclid must have been Pseudo-at-Iasi which appeared in Rome in 1594. But Clavius’s remark in his edition of 1589 proves that he knew this fact by hearsay already many years before the printed publication of the Arabic text appeared.” [36]

Knowing what we now know of the life and works of Patriarch Ni’matallah, you can say that this whole article was written just to answer my friend Knobloch’s puzzles. I think we now know who was the person intended by Clavius who could read Arabic but did not give Clavius the permission to see the book. I think that he was none other than the Patriarch. And the Eucledian text that Clavius had heard about was none other than the text that Ni’matallah brought along, which is now still preserved at the Laurentiana, and which was itself used as the base for the 1594 edition that was published by the Medici Oriental Press. We only need to remember that the Patriarch arrived in Rome in 1577, and was immediately appointed by the Pope to work on the committee for the Gregorian Reform. The Medici Oriental Press did not begin to publish the Arabic works that the Patriarch brought along until the early 1590’s, some ten years or so after the work on the Gregorian Reform was finished and promulgated with the Bull Inter gravissimas. Between the time when Clavius came to know of the Patriarch, in the late 1570’s, and the time the Press began to function, the Patriarch had, in all likelihood, not yet reached the deal with the Medici’s to join the board of the press under the leadership of Raimondi, and had not yet secured his livelihood of the 25 monthly scudes and life-time access to his books that he was promised if accepted to give his books to be used by the press. During that period of anxiety, and knowing how valuable those books were, otherwise he wouldn’t have taken them along in his perilous journey, the Patriarch was probably a little stingy with strangers wishing to consult them. That could explain his refusal to give Clavius the permission he needed.


In light of this multilayered evidence, I hope we can now safely say that Renaissance Europe was in fact in need of the sciences that were already relatively well developed in the Islamic world. The Patriarch knew that, and thus brought his scientific books along, and Clavius and the Pope knew that as well, and thus immediately made use of this learned man who offered his services at the right time. Clavius had already heard of the various Arabic sources that he used, and were elegantly gathered by Knobloch, through their Arabic translations. He was apparently eager to learn more, as was also concluded by Knobloch when he collected all the Arabic material that Clavius had heard about, and wished to pursue. In some instances he had to come up with solutions of his own which were already found in the Arabic sources, as Knobloch says. But in all instances, Clavius was a living example of a very competent scientist, a younger contemporary with Copernicus, like his French colleague Guillaume Postel, of the kind of fertile cross breeding that was taking place between the worlds of Islam and Renaissance Europe.

But most important for us is the manner in which Arabic scientific ideas were embedded into the Latin scientific tradition of the time. Ideas seem to have seeped in, as if by osmosis, without much fanfare and without the traditional modality of transmission of science where we can easily detect the routes between original Arabic books and their Latin translations. Aren’t we slightly better prepared now to understand how Copernicus could have known about the earlier Islamic astronomical works? And aren’t we better equipped to understand the intellectual climate of the Renaissance and the desperate need Renaissance scientists must have had for scientific texts from the Islamic world.


[1] The first version of this paper was delivered at a conference A Shared Legacy: Islamic Science East and West, which was hosted by the University of Barcelona in April 2007, for whose support and facilities to attend this conference is here gratefully acknowledged. See my most recent book Islamic Science and the Making of the European Renaissance, MIT Press, 2007.

[2] See Edward Said, Orientalism, Pantheon, 1978.

[3] See Anthony Grafton, “Michael Maestlin’s Account of Copernican Planetary Theory.” Proceedings of the American Philosophical Society 117, no. 6 (1973): 523-550.

[4]  Nowel Swerdlow, “The Derivation and First Draft of Copernicus’s Planetary Theory: A Translation of the Commentariolus with Commentary.” Proceedings of the American Philosophical Society 117, no. 6 (1973): 423-512, esp. p. 504

[5] Ibid.

[6] George Saliba, “Whose Science is Arabic Science in Renaissance Europe?,” http://www.columbia.eduf-gas 1 /proj ectivisions/case 1 /sci.1.html

[7] The information on this Patriarch derives from several sources, most important among them is a note written by Yubanna ‘Azzo, the secretary of the Antiochian Syriac Patriarchate. This biographical note was used as an introduction to `Azzo’s Arabic translation of the Syriac autobiographical letter that was sent by patriarch Ighnatius Ni`meh (short for Ni’matallah) to his parishioners in Diyar Bakr (probably from Rome towards the end of the sixteenth century). See Yiiharma `Azzo, “Ristilat al-batriyark Ighnatius Ni`meh,” al-Mashriq, vol 31 (1933) pp. 613-623, 730-737, 831-838. A less reliable biographical note was added by Louis Cheikho, in a previous issue of the same journal to his article “al-Tdifa al-mitruniya wa-l-ruhbaniya al-yastriya ft 1-qarnayn ‘ashar wa-l-scibi` ‘ashar“, al-Masriq, vol. 19 (1921), p. 139.

[8] Much of the information regarding the life of the Patriarch in Italy comes from the excellent work of John Robert Jones, Learning Arabic in Renaissance Europe (1505-1624), Ph.D. dissertation, London University, 1988. This particular note is appended to the Laurentiana manuscript OR 177, fol. 79r. Several other Arabic manuscripts in the Laurentiana collection are clearly marked as having been owned by this Patriarch Ignatius.

[9] The information regarding the relationship between the Patriarch and Ferdinand de Medici and the matter of the press comes from, among others, John Robert Jones, Learning Arabic, op. cit, John Robert Jones, The Arabic and Persian Studies of Giovan Battista Raimondi (c. 1536-1614), M. Phil dissertation, Warburg, London, 1981, and [John] Robert Jones, “The Medici Oriental Press (Rome 1584-1614) and the Impact of its Arabic Publications on Northern Europe,” in The Arabick’ Interest of the Natural Philosophers in Seventeenth-Century England, ed. G. A. Russell, Brill, Leiden, 1994, pp. 88-108. More information on this press and the role played by Ignatius Ni`meh, can be found in G. J. Toomer, Eastern Wisedome and Learning, Oxford University Press, Oxford, 1996.

[10] For Gregory’s interest in a Turkish campaign, see the Catholic Encyclopedia, s.v. Gregory XIII.

[11] See, for example Jones, Learning Arabic, p. 42, where he says: Ignatius “Ni`matallah brought more than political influence to Europe. He was educated in the lingua franca of the Middle East, Arabic, and he was familiar with the medicine, mathematics and astronomy of the region. Joseph Scaliger referred appreciatively several times in his great Chronology, De Emendatione Temporum to a learned correspondence he had entered into with Ni`matallah; and the Pope appointed him to the commission for calendrical reform.”

[12] Jones, ”The Medici Oriental Press” op.cit.

[13] Gregorian Reform of the Calendar: Proceedings of the Vatican’s Conference to Commemorate its 400th Anniversary (1582-1982), edited by G. V. Coyne, S. J., M. A. Hoskins, and 0. Pedersen, Vatican, 1983.

[14] Ratio corrigendi fastos confirmata, et nomne omnium, qui ad Calendarii Correctionem delecti sunt oblate D.N. Gregorio XIII. According to Baldini this report exists only in two Latin manuscripts: one at the Vatican Library Cod. Vat. Lat. 3685, 1-10, and the other at the Biblioteca Casanatense, Rome, 649, 164-167. See Baldini’s remarks about these manuscripts in Ibid, p. 155, n.1.

[15] Ibid, p. 137.

[16] Ibid., p. 162, n. 55.

[17] Ibid.

[18] Ibid, p. 148.

[19] Ibid.

[20] Ibid. p. 201.

[21] Ibid. p. 215.

[22] Ibid. p. 216.

[23] Ibid. p. 216-7.

[24] Ibid. p. 217.

[25] Ibid. p. 217-8.

[26] Noel Swerdlow and Otto Neugebauer, Mathematical Astronomy In Copernicus’s De Revolutionibus, Springer, NY, 1984, p. 8.

[27] Gregorian Reform of the Calendar, op. cit. p. 234, note 25.

[28] Ibid. p. 218.

[29] Ibid. p. 221.

[30] Letter quoted in part by Ziggelaar in ibid. p. 231.

[31] Chrisotopher Clavius, Romani calendarii a Gregorio XIII restituti explication, Roma, 1603.

[32] Quoted by Ziggelaar, in Gregorian Reformop. cit. p. 232.

[33] Knobloch Eberhard, “Christoph Clavius (1538-1612) and his knowledge of Arabic sources”. In: Gesuiti e university in Europa (secoli XVI — XVIII) Atti del Convegno di studi Parma, 13-15 dicembre 2001, a cura di Gian Paolo Brizzi e Roberto Greci. Bologna 2002, pp. 403-420.

[34] Ibid. p. 419.

[35] Ibid. p. 420.

[36] Ibid.

Khudsatai Apni Tareef Aik Tabah Kun Amar


As-salamu alaikum wa Rahmatullahi wa Barakatohu

Start your Day by reading Quran: (521) 🍁

*بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ*

*أَلَمْ تَرَ إِلَى الَّذِينَ يُزَكُّونَ أَنْفُسَهُمْ ۚ بَلِ اللَّهُ يُزَكِّي مَنْ يَشَاءُ وَلَا يُظْلَمُونَ فَتِيلًا * انْظُرْ كَيْفَ يَفْتَرُونَ عَلَى اللَّهِ الْكَذِبَ ۖ وَكَفَىٰ بِهِ إِثْمًا مُبِينًا*

_”Kiya aap ne un logon ko nahi dekha jo apne Nafs ki Pakeezgi ka Ailan karte hain halanke Allah jisko chahta hai Pakeezgi ata karta hai aur bando par zarrah barabar bhi zulm nahi kiya jayega.”_
_”Aap dekhen woh kis tarah se Khuda par jhoot tarash rahe hain unke Gunahgar hone ke liye yehi wazeh (clear) Gunah Kafi hai.”_
(Surah Nisa: 49 – 50)

📚📖 🍁
👉 _*�Tafseer:*_
Ye Khud satai (Self Praise) ka tazkarah hai. Ayat to Yahood o Nasara ko mukhatib hai lekin ye nasihat sab ke liye hai. 
Ya aam zaban mein yun kahen ke inke bol bachan zyada par kam mein zero hote hain. Sirf woh lambi lambi hankna jante hain.
Khud Satai ka source hai Khud bini, ghuroor, ghamand. Bahut si qaumo ki bad hali, ladai jhagde isi ka natija hain. Means har insaan ye samjhta hai ke mein hi Nek Pak o Pakeeza hun, baqi sab log usse kamtar hain. Lekin ye sab Fazilat Allah ata karta hai jo zara bhi zulm nahi karta, unka khud ka kuchh nahi hota. فتيلا _’Fateelah’_ Means usko kahte hain jo khajoor ki ghuthli par jo bareek si jhilli hoti hai. Means Allah itna bhi Zulm nahi karta

Islamic Astronomy from “Star Wars” to Star Tables

Astronomy had a long and fruitful life in the Islamic world, where ancient Greek astronomy was transformed into a fully institutionalized endeavor employing a comprehensive and predictive theory that was consistent with physical principles as then understood. Astronomy in the ancient world was motivated by different concerns than what drives the science today. Its principal aim was to divine the future from planetary positions, which eventually could be calculated using past data and theoretical models. Astrologers have been associated with imperial courts since ancient Mesopotamian times. There, in a kind of ancient “star wars”, they vied with each other for the most accurate predictions. Mesopotamian stargazers accumulated centuries of observational data, and invented mathematical methods for predicting astrologically significant planetary configurations.

Left: Babylonian tablet recording Halley’s comet in 164 BCE, the comet was last witnessed in 1986 (Source), Right: Map showing the extent of Mesopotamia (Source) 

While the Mesopotamian cultures provided incentive and data for astronomy, the Greeks were more concerned with integrating this knowledge into a cosmology, with geometrical models and a physics. The culmination of these efforts was the work of the 2nd Century mathematical astronomer, Ptolemy, who, using the Mesopotamian data, produced the most powerful system of predictive astronomy yet known, the Almagest. He also developed a comprehensive astrology, which, because of its being firmly grounded in Aristotelian natural philosophy, and because of the mathematical precision of the Almagest, acquired the air of genuine science. The Almagest showed how to derive mathematical models of the planets from observational data.

Ptolemy’s methods were the foundation of Islamic astronomy. Prior to Islam, the rulers of the Sasanian Persian Empire (224-651 CE) fostered a dynamic astrological tradition, which they employed for a variety of purposes. For example, the state religion, Zoroastrianism, espoused a chiliastic/millennialist view of history, and thus invited astrological activity. Astrological histories rationalized significant events and rulers in terms of a grand cosmological scheme written in the stars, which both justified the current dynasty and permitted knowledge of the political future. These interests in political and historical astrology were inherited by the Muslim Abbasid dynasty (750-1258 CE).

The most obvious difference between modern and Islamic astronomy is that the latter is primarily mathematical and predictive, and the former has other observational goals, such as describing the physics of other worlds. As noted earlier, the predictive character of astronomy derived from its use in astrological forecasting. The Ptolemaic models were to an extent instrumentalist, namely, useful for generating planetary positions rather than being strictly physically consistent.

Nasir al-Din al-Tusi at the observatory in Maragha, Persia. Image courtesy of the British Library.

There were some thinkers, however, such as Nasir al-Din al-Tusi, who desired to present a unified physics and cosmology of the heavens. Through his efforts and those of his followers, several of Ptolemy’s models that contained physically absurd elements were replaced with physically consistent ones. For example, in order to explain some planets’ varying speeds, Ptolemy had postulated that one of the spheres responsible for moving these planets rotated uniformly around a pole that did not coincide with its own centre, which, although this model gives good mathematical results, is physically impossible. Muslim astronomers invented new mathematical devices that produced the same effects without violating physical principles.

Observatories as institutions that housed a collective effort to gather positional data about the stars and planets were an Islamic invention. Programs of observation began under the 9th-century Abbasid rulers, but culminated in the grand observatories of Maragha (13th C.) under the Ilkhanids, and Samarkand (15th C.) under the Timurids. The main goal of these observatories was to improve the planetary tables (zijes; sing. zij) used to calculate planetary positions.

Unlike modern observatories, their Islamic antecedents were useful only until all the data had been gathered over a period of decades at most. The main structural feature of the Islamic observatory was the meridian quadrant, which measured the planets’ elevations as they crossed the meridian. (See above). In addition, there were more portable instruments, including armillary spheres, quadrants, and other devices for measuring celestial positions by hand. The way to improve upon data from earlier observatories was to build a larger meridian quadrant in order to obtain more precise observations, which in turn improved the accuracy of the zij tables. For example, the meridian quadrant of Ulugh Begh’s Samarkand observatory was significantly larger than that of Maragha.

This basic design persisted for centuries, and even found its way into Tycho Brahe’s 16th Century Uraniborg. (The main difference there was that, whereas the Ptolemaic tradition had astronomers taking observations at major conjunctions or at other significant times of the planetary cycles in order to extrapolate the rest using the model, Tycho observed the planets on the days between, and thus had a far more precise set of data). The Abbasid Caliph al-Ma’mun (r.813-833) founded two observatories at Baghdad and Damascus, respectively, where some of the initial updates to the Almagest were accomplished. However, the most famous observatory was established at Maragha in northwestern Iran by the Mongol Ilkhanid ruler Hulegu (d.1265) in 1259, under the direction of Nasir al-Din al-Tusi (d.1274). The first observatory to be supported by a religious endowment (waqf), it not only produced an improved zij (Zij-i Ilkhani), but also began a major reform of Ptolemaic astronomy. This resulted in a new tradition of planetary theory that culminated in the models of Ibn al-Shatir (d.1375), elements of whose contributions Copernicus incorporated in his own revolutionary treatise, On the Revolutions (1543). The Samarkand observatory, established and supervised by the Timurid ruler and astronomer Ulugh Begh (d.1449), produced a new zij (Zij-i Sultani), and supported a flowering of the mathematical sciences.

Left: An Arabic translation of the astronomical tables of Ulugh Beg. (Library of Congress). Right: Ulugh Beg observatory. This trech was lined with marble in Ulugh Beg’s time (Source) 

The majority of those who used astronomical information did so in the form of tables, and so did not require advanced mathematics. Along with planetary models, Ptolemy had also shown how to use tables for the relatively easy calculation of planetary positions. Only basic arithmetic was needed, since the tables of various functions already had complex trigonometry built into them. In the Islamic tradition, such tables were called “zijes”, from a Persian word that means “thread”, because their crosshatched appearance, with numbers in the spaces, resembles a woven cloth (see illustration, above). Zijes were typically a collection of such tables along with instructions for their use, including tables for converting between calendars, for Islamic  prayer times, and for determining planetary longitudes, based on the number of elapsed days and hours since a known position, or “epoch”. Zijes were calculated using mathematical models of the planetary motions, which in turn were based on observational parameters that were determined at the observatories. So, advances in astronomy were expressed in new zijes, which were the result of more accurate parameters or better models, or both. To simplify the process further for the everyday practitioner, yearly almanacks were produced, which used the zijes to determine all of the celestial data for the upcoming year on a daily basis, much like a modern ephemeris. Islamic astronomy was interconnected with all of the other sciences, in a comprehensive cosmology inherited from Aristotle. Through their unrelenting critique of ancient astronomy and natural philosophy, Islamic astronomers laid the groundwork for the scientific advances of both the European Late Middle Ages the Scientific Revolution. Copernicus, Brahe, Kepler and many others used methods developed in Islamic astronomy to critique and eventually replace the ancient cosmology. 

Illustration by al-Bīrūnī of different phases of the moon, from Kitab al-tafhim. Source: Seyyed Hossein Nasr,Islamic Science: An Illustrated Study, London: World of Islam Festival, 1976. (Source)