Died  near Samarqand, (Uzbekistan), 27 October 1449

Ulugh Beg (Turkish for “great prince”) was governor of Transoxiana and Turkestan and, during the last 2 years of his life, Timurid Sultan. However, he is mostly remembered as a patron of mathematics and astronomy. In Samarqand, he founded a school and the famous astronomical observatory, where the most extensive observations of planets and fixed stars at any Islamic observatory were made. Ulugh Beg is associated with a Persian astronomical handbook (zīj) that stands out for the accuracy with which its tables were computed.

Ulugh Beg was the first‐born son of Shāhrukh (youngest son of the infamous conqueror Tīmūr or Tamerlane) and his first wife Gawharshād. He was raised at the court of his grandfather and, at the age of 10, was married to his cousin Agha Bīkī, whose mother was a direct descendent of Chingiz Khan. Thus Ulugh Beg could use the epithet Gūrgān, “royal son‐in‐law,” which had originally been used for Chingiz’s son‐in‐law.

In the years after Tīmūr’s death in 1405, Ulugh Beg became governor of Turkestan and Transoxiana, the most important cities of which were the cultural centers Samarqand and Bukhara. Although not completely divorced from affairs of state, he is better known for his interest in religion, architecture, arts, and sciences, which were fostered by the Mongols as well as by the Timurids. Ulugh Beg is said to have spoken Arabic, Persian, Turkish, Mongolian, and some Chinese. He had a thorough knowledge of Arabic syntax and also wrote poetry. Although he honored Turkic–Mongolian customs, he also knew the Quran by heart, including commentaries and citations. Ulugh Beg was also a passionate hunter.

By 1411, Ulugh Beg had developed a lively interest in mathematics and astronomy, which may have been aroused by a visit in his childhood to the remnants of the Marāgha Observatory that had been directed by Ṭūsī. In 1417, he founded in Samarqand a madrasa (religious school or college) that can still be seen on the Registan Square. At this institution, unlike other madrasas, mathematics and astronomy were among the most important subjects taught. The most prominent teacher was Qāḍīzāde al‐Rūmī, who was joined somewhat later by Kāshī.

Two extant letters by Kāshī to his father in Kāshān make clear that Ulugh Beg was personally involved in the appointment of scholars and that he was frequently present, and actively participated, in seminars, where he displayed a good knowledge of mathematical and astronomical topics. Kāshī relates how Ulugh Beg performed complicated astronomical calculations while riding on horseback. Anecdotes from other sources show that Ulugh Beg, like many other Muslim rulers, believed in astrology and fortune‐telling. He appears as a person who very much respected the scholars he appointed, and whose main objective was to reach scientific truth.

In 1420, Ulugh Beg founded his famous astronomical observatory on a rocky hill outside the city of Samarqand. Its circular main building, beautifully decorated with glazed tiles and marble plates, had a diameter of about 46 m and three stories reaching a height of approximately 30 m above ground level. The north–south axis of the main building was occupied by a huge sextant with a radius of 40 m (called Fakhrī sextant after that of Khujandī). On the scale of this instrument, which partially lay in an underground slit with a width of half a meter, 70 cm corresponded to 1° of arc, so that the solar position could be read off with a precision of 5″. On the flat roof of the main building various smaller instruments could be placed, such as an armillary sphere, a parallactic ruler, and a triquetrum. Among other instruments known to have been used in Samarqand are astrolabes, quadrants, and sine and versed sine instruments.

Although Ulugh Beg was the director of the Samarqand Observatory, Kāshī was in charge of observations until his death in 1429, after which he was succeeded by Qāḍīzāde, who died after 1440. The observational program was completed by Qūshjī, who had studied in Kirmān (southeastern Iran) before returning to Samarqand. The results of the observations made under Ulugh Beg include the measurement of the obliquity of the ecliptic as 23° 30’17” (the actual value at the time was 23° 30’48”) and that of the latitude of Samarqand as 39° 37’33” N. (modern value: 39° 40′). Furthermore, most of the planetary eccentricities and epicyclic radii were newly determined, and the longitudes and latitudes of the more than 1,000 stars in Ptolemy’s star catalogue were verified and corrected. Precession was found to amount to 51.4″ per year (corresponding to 1° in little more than 70 years; the actual value is 50.2″ per year).

The observatory of Ulugh Beg stayed in operation for little more than 30 years. It was finally destroyed in the 16th century and completely covered by earth in the course of time. In 1908, archaeologist V. L. Vyatkin recovered the underground part of the Fakhrī sextant, consisting of two parallel walls faced with marble and the section of the scale between 80° and 57° of solar altitude. Ulugh Beg’s observatory exerted a large influence on the huge masonry instruments built by Jai Singh in five Indian cities (most importantly Jaipur and Delhi) in the 18th century, more than 100 years after the invention of the telescope.

The main work with which Ulugh Beg is associated is an astronomical handbook with tables in Persian, variously called Zīj‐i Ulugh Beg, Zīj‐i Jadīd‐i Sulṭānī, or Zīj‐i Gūrgānī. In the introduction, Ulugh Beg acknowledges the collaboration of Qāḍīzāde, Kāshī, and Qūshjī, who were undoubtedly responsible for the underlying observations as well as the computation of the tables. The Zīj is in many respects a standard Ptolemaic work without any adjustments to the planetary models. It consists of four chapters dealing with chronology, trigonometry and spherical astronomy, planetary positions, and astrology, respectively. The instructions for the use of the tables, which were edited and translated into French by L. Sédillot in the middle of the 19th century, are clear but very brief and do not even include examples of the various calculations.

Thus, the most significant part of Ulugh Beg’s Zīj lies in the observations and computations underlying the tables. Most impressively, the sine table, covering 18 pages in the manuscript copies, displays the sine to five sexagesimal places (corresponding to nine decimals) for every arc minute from 0° to 87° and to six sexagesimal places (11 decimals) between 87° and 90°. All independently calculated values for multiples of 5′ are correct to the precision given, whereas the intermediate values, calculated by means of quadratic interpolation, contain incidental errors of at most two units. Also most of the planetary tables in the Zīj were calculated to a higher precision than before. New types of tables were added that simplified the calculation of planetary positions. Ulugh Beg’s star catalog for the year 1437 represents the only large‐scale observations of star coordinates made in the Islamic realm in the medieval period. (Most other catalogs simply adjusted Ptolemy’s ecliptic coordinates for precession or were limited to a relatively small number of stars.)

Ulugh Beg’s Zīj was highly influential and continued to be used in the Islamic world until the 19th century. It was soon translated into Arabic by Yaḥyā ibn ʿAlī al‐Rifāʿī and into Turkish by ʿAbd al‐Raḥmān ʿUthmān. Reworkings for various localities were made in Persian, Arabic, and Hebrew by scholars such as ʿImād al‐Dīn ibn Jamāl al‐Bukhārī (Bukhara), Ibn Abī al‐Fatḥ al‐Ṣūfī (Cairo), Mullā Chānd ibn Bahāʾ al‐Dīn and Farīd al‐Dīn al‐Dihlawī (both Delhi), and Sanjaq Dār and Husayn Qusʿa (Tunis). Commentaries to the Zīj were written by Qūshjī, Mīram Chelebī, Bīrjandī, and many others. Hundreds of manuscript copies of the Persian original of Ulugh Beg’s Zīj are extant in libraries all over the world. Already in 17th‐century England, various parts of the Zīj were published in edition and/or translation.

Little is known about other works of Ulugh Beg. A marginal note by him in the India Office manuscript of Kāshī’s Khāqānī Zīj presents a clever improvement of a spherical astronomical calculation. A Risāla fī istikhrāj jayb daraja wāḥida (Treatise on the extraction of the sine of 1°) has been attributed to Ulugh Beg on the basis of a citation in Bīrjandī, although most manuscripts of this work mention Qāḍīzāde as the author. Aligarh Muslim University Library lists a treatise Risāla‐yi Ulugh Beg that is yet to be inspected. Finally, an astrolabe now preserved in Copenhagen and made in 1426/1427 by Muḥammad ibn Jaʿfar al‐Kirmānī, who is known to have worked at the observatory in Samarqand, was originally dedicated to Ulugh Beg.

In 1447, Ulugh Beg succeeded his father Shāhrukh as sultan of the Timurid empire. However, he was killed on the order of his son ʿAbd al‐Laṭīf. An investigation of Tīmūr’s mausoleum by Soviet scholars in the 1940s showed that Ulugh Beg was buried as a martyr in accordance with Sharīʿa (Islamic law), i. e., fully clothed in a sarcophagus.

By Benno van Dalen, Ulugh Beg: Muḥammad Ṭaraghāy ibn Shāhrukh ibn Tīmūr, The Biographical Encyclopedia of Astronomers, pp 1157-1159.

Selected References

Bagheri, Mohammad (1997). “A Newly Found Letter of Al‐Kāshī on Scientific Life in Samarkand.” Historia Mathematica 24: 241–256.

Barthold, V. V. (1958). Four Studies on the History of Central Asia. Vol. 2, Ulugh‐Beg. Leiden: E. J. Brill.

Kary‐Niiazov, T. N. (1950). Astronomicheskaya shkola Ulugbeka (The astronomical school of Ulugh Beg) (in Russian). Moscow: Akademia Nauk SSSR. (Second enlarged edition in Kary‐Niiazov, Izbrannye trudy [Collected works]. Vol. 6. Tashkent: FAN, 1967.)

——— (1976). “Ulugh Beg.” In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 13, pp. 535–537. New York: Charles Scribner’s Sons.

Kennedy, E. S. (1956). “A Survey of Islamic Astronomical Tables.” Transactions of the American Philosophical Society, n.s., 46, pt. 2: 121–177, esp. 125–126 and 166–167. (Reprint, Philadelphia: American Philosophical Society, 1989.)

——— (1960). “A Letter of Jamshīd al‐Kāshī to His Father: Scientific Research and Personalities at a Fifteenth Century Court.” Orientalia 29: 191–213. (Reprinted in E. S. Kennedy, et al., Studies in the Islamic Exact Sciences, edited by David A. King and Mary Helen Kennedy. Beirut: American University of Beirut, 1983, pp. 722–744.)

——— (1998). “Ulugh Beg as Scientist.” Chapter 10 in Astronomy and Astrology in the Medieval Islamic World. Aldershot: Ashgate. (Describes the marginal note by Ulugh Beg in a manuscript of Kāshī’s Zīj.)

Knobel, Edward Ball (1917). Ulugh Beg’s Catalogue of Stars: Revised from All Persian Manuscripts Existing in Great Britain, with a Vocabulary of Persian and Arabic Words. Washington: Carnegie Institution of Washington.

Krisciunas, Kevin (1992). “The Legacy of Ulugh Beg.” In Central Asian Monuments, edited by H. P. Paksoy, pp. 95–103. Istanbul: Isis. (Includes a bibliography of all publications of parts of the Zīj of Ulugh Beg.)

——— (1993). “A More Complete Analysis of the Errors in Ulugh Beg’s Star Catalogue.” Journal for the History of Astronomy 24: 269–280.

Kunitzsch, Paul (1998). “The Astronomer al‐Ṣūfī as a Source for Uluġ Beg’s Star Catalogue.” In La science dans le monde iranien ā l’époque islamique, edited by Ž. Vesel, H. Beikbaghban, and B. Thierry de Crussol des Epesse, pp. 41–47. Tehran: Institut français de recherche en Iran.

Manz, Beatrice F. (2000). “Ulugh Beg.” In Encyclopaedia of Islam. 2nd ed. Vol. 10, pp. 812–814. Leiden: E. J. Brill.

Rosenfeld, B. A. and Jan P. Hogendijk (2002/2003). “A Mathematical Treatise Written in the Samarqand Observatory of Ulugh Beg.” Zeitschrift für Geschichte der Arabisch‐Islamischen Wissenschaften 15: 25–65.

Sayılı, Aydın (1960). The Observatory in Islam. Ankara: Turkish Historical Society, esp. pp. 260–289.

———(1960). Ghiyâth al‐Dîn al Kâshî’s Letter on Ulugh Beg and the Scientific Activity in Samarqand. Ankara: Turkish Historical Society.

Schoy, Carl (1927). Die trigonometrischen Lehren des persischen Astronomen Abū ʾl‐Rayḥān Muḥammed ibn Aḥmed al‐Bīrūnī dargestellt nach al‐Qānūn al‐Masʿūdī. Hanover: Lafaire. (Reprinted in Schoy, Beiträge zur arabisch‐islamischen Mathematik und Astronomie, edited by Fuat Sezgin, Vol. 2, pp. 629–746. Frankfurt am Main: Institute for the History of Arabic‐Islamic Science, 1988.) (Includes an edition of parts of Ulugh Beg’s sine and tangent tables.)

Sédillot, Louis P. E. Amélie (1847). Prolégomènes des tables astronomiques d’Oloug‐Beg. Publiés avec notes et variantes et précédés d’une introduction. Paris: Firmin Didot.

——— (1853). Prolégomènes des tables astronomiques d’Oloug‐Beg. Traduction et commentaire. Paris: Firmin Didot.

Shevchenko, Mikhail Yu (1990). “An Analysis of Errors in the Star Catalogues of Ptolemy and Ulugh Beg.” Journal for the History of Astronomy 21: 187–201.

Photo Credit

PHOTO YOKO AZIZ/ALAMY
The Ulugh Beg Observatory in Samarqand, Uzbekistan, completed in the fifteenth century, was used by several famous Islamic astronomers.

In the last few decades, a critical mass of excellent studies by competent historians of Islamic science has led to a qualitative shift in our understanding of this history. Yet despite this shift, an integrated approach to the study of the history of science in Muslim societies still needs to overcome some real hurdles. To start with, such an undertaking calls for an examination of wide-ranging cultural activities, in a vast geographical area, under different historical conditions, and for a period of at least seven centuries. Moreover, the sources for the study of this subject are daunting, and they include, in addition to material evidence, thousands of scientific manuscripts, most of which remain unexamined. The abundance of evidence also gives rise to a number of methodological difficulties: earlier surveys of the history of Islamic science were based on a handful of random studies of scientific treatises. Some of the actual studies were of a high quality; yet ironically, the paucity of hard evidence available to early scholars often enabled them to cover all the fields of science in all-inclusive, and often reductive, narratives. In the last few decades, many more scientific treatises have been critically examined, with the dual effect of providing detailed information about the various scientific disciplines, and highlighting the peculiarity of the history of each separate discipline or even fields within disciplines.

In the absence of thorough and exhaustive accounts for developments in the various scientific disciplines as well as accounts for the epistemological foundations of these sciences, it only stands to reason that attempts to provide general characterizations of science in Muslim societies and its relation to religion can only be provisional and subject to scrutiny. Even such seemingly straight forward characterizations of the scientific activity in Muslim societies as Islamic or Arabic cannot be taken for granted, and the same applies to the assertion that Islam has either a positive or a negative attitude towards science. I do not mean here to deny the validity of using terms such as “Islamic science”, but simply to stress the importance of addressing the question of methodology before venturing such general characterizations.

Due to the extent of the scientific enterprise in classical Muslim societies, the question of the relationship between science and religion in Islam can be approached from many different perspectives, and may vary according to, and within, the region, period, or discipline under consideration. For example, one may look at standard discussions among religious scholars and theologians. Alternatively, the classifications of the sciences provide an epistemological perspective which pertains to theories of knowledge. One can also examine and attempt to classify the manifold views of scientists as well as religious scholars on the relationship between science and religion. In this essay, I will restrict myself to the field of astronomy; in particular, I will compare two important trends of research in theoretical astronomy. Astronomy, I should add, is especially relevant to the question of the relationship between science and religion because of its cosmological dimension and the relative ease with which it can be invoked in connection with metaphysical questions. The main focus in this paper is on the way communities of scientific knowledge conceived of their profession and research within the larger context of religion. However, I will first say a few words about religious scholars who discussed science and proposed “Islamic” assessments of the various sciences.

Almost invariably, discussions of the Islamic attitude toward science invoke the works of al-Ghazali (d. 505/111). I will not attempt to summarize Ghazali¹s views on the various sciences; these views have received more scholarly attention than those of any other Muslim scholar who had written on the subject. It is important to note, however, that the debate regarding Ghazali¹s true attitudes and views continues among contemporary scholars, and there seems to be no consensus even over the interpretation of his most obvious work, Tahafut al-Falasifa (The Incoherence of the Philosophers), let alone an integrated assessment of his whole oeuvre, including such relevant works to our subject as al-Iqtisad fi al-IŒtqad, MiŒyar al-ŒIlm, al-Qustas al-Mustaqim, Maqasid al-Falasifa, and al-Mustasfa min ŒIlm al-Usul.

Aside from al-Ghazali and whether he actually condoned, neglected, or opposed the sciences, there are, to be sure, some radical and credible traditionalists, such as Ibn Taymiyya (d. 1328), who attacked some of the fields of knowledge that Ghazali condoned, but in the face of these there are equally radical and popular traditionalists, such as Ibn Hazm (11th century), who defended logic and argued for the interconnection between the various sciences. What is more important about the provocative writings of Ibn Taymiyya with such titles as “The Rebuttal of Logic” and “The attack on Logicians” is that Ibn Taymiyya employed the discourse of formal logic, and rather than deny the validity of logic, he only denies the claim by a professional group of logicians to have an exclusive monopoly over methods of arriving at Truth. Moreover, Ibn Taymiyya questioned the validity of some of the propositions and syllogisms of certain kinds of formal logic, and not all kinds of logic. Furthermore, Ibn Taymiyya criticized Ghazali¹s denial of causality and was a strong believer in physics and the natural laws. Again, the purpose of citing these authors here is not to provide an exhaustive analysis of their views, but simply to point out the diversity as well as complexity of the views of traditional Muslim scholars on science and scientific knowledge.

The differences between these traditional religious scholars highlight the difficulty of identifying a unified, traditional Islamic attitude toward science. It is clear, however, that the overall outcome of the religious debates over scientific knowledge was to naturalize some of the exact sciences and to provide Islamic justifications for certain kinds of scientific knowledge. Such was the assessment of the famous 14th century historian Ibn Khaldun who remarks in his Muqaddima that after Ghazali all religious scholars studied logic, but they studied it from new sources, such as the works of Ibn al-Khatib and al-Khunji (13th century), and that people stopped using the books of the ancients; “the books and the methods of the ancients”, says Ibn Khaldun, “are avoided, as if they had never been”. Later, he adds (p. 143) “It should be known that the early Muslims and the early speculative theologians greatly disapproved of the study of this discipline [logic]. They vehemently attacked it and warned against it… Later on, ever since al-Ghazzali and the imam Ibn al-Khatib, scholars have been somewhat more lenient in this respect. Since that time, they have gone on studying (logic)…”

Generally speaking, therefore, religious assessments of the epistemic value of various kinds of scientific knowledge were nuanced and diverse. And although one cannot adduce a direct and mechanical correlation between the religious arguments and the ways in which scientists perceived of and theorized their own scientific disciplines, it is abundantly clear that the views of scientists were also manifold. Furthermore, since they were inspired by a variety of cultural factors, these articulations by scientists are obvious and tangible expressions of what “Islamic” science meant in actual history, and are as indicative of the Islamic dimension as the views expressed by religious scholars. In what follows, I will approach the question of the relationshipbetween science and religion by focusing on two particular traditions of astronomical research, one in the Muslim east and the other in the Muslim west. My interest is in charting out the peculiar modes of thinking that provided the epistemological and methodological conditions for the formation of these two traditions, and the diverse conceptual frameworks that informed the different planetary theories proposed in each.

Ever since Sarton¹s attempt to write a universal history of science, the Islamic sciences have had a considerable presence in various accounts of this history. Despite their large quantitative presence, however, Islamic sciences are all too often absent from grand, integrative narratives of the history of science. When historians offer conceptual analysis of epochal changes in the history of science (which is something they often do), the cumulative legacy of the Islamic sciences is simply overlooked. Conceptually, the Islamic scientific legacy is seen as a rather mechanical continuation of the Greek one: the Islamic sciences expanded and refined the Greek sciences without departing from them conceptually. A justification of this oversight is seldom provided, but when it is, it usually has to do with the role of philosophy or theory in science. In the field of astronomy in particular, theoretical considerations were often overlooked on the basis of a widely held assumption that Islamic science was practical and hence theoretically or philosophically shallow. The decline of Islamic science, according to this view, was a result of the lack of theoretical rigor. In the last few decades, however, an alternative view has been proposed, often by competent historians of science. In contrast to the notion that the Islamic sciences declined because of their feeble philosophical foundations, historians of astronomy now argued that the motivation for the most important tradition of astronomical reform in the Muslim world was philosophical. Despite its different understanding of the role of philosophy in connection with the science of astronomy, this thesis often served to undermine the “scientific” value of these astronomical reforms.

In a sense, the two different views regarding the role of philosophy in Islamic science echo a fundamental debate over the function of scientific theory. Simply put, scientist and philosophers (as well as historians of science) differ over whether the primary role of scientific theory is to explain nature as it exists in reality or simply describe and predict its appearance as we perceive it. In the latter case (description and prediction), the quest of science is to “save the phenomena,” whereas in the former case, science goes beyond appearance to explore causal connections or, in the language of philosophers, “first causes.” This philosophical controversy, and many variations of it, is at the roots of the emergence of what is commonly called “modern science”, and it continues to inform modern and postmodern debates on the relationship between scientific knowledge and others forms of knowledge. This controversy has also influenced readings of the history of “non-western” science. Before examining the question of the role of theory in science as reflected in the two Islamic traditions of astronomical reform, a few words on the early developments in Islamic astronomy that provided the background for the latter reform traditions.

Astronomy was one of the oldest, most developed and most esteemed exact sciences of antiquity. (Many of the mathematical sciences were originally developed to facilitate astronomical research. Various disciplines and belief systems intersected and interacted in astronomy, including physics and metaphysics, as well as mathematics and religion. Islamic/Arabic astronomy was also culturally hybrid (Babylonian, Indian, Persian, and Greek), and intimately connected to politics (astrology, dynastic legitimization). Finally, practical considerations such as finding one’s direction during night travel, and the correlation between the seasons of the year and the positions of the planets provided additional incentives for the study of astronomy. For all of these reasons, astronomical research was hybrid and spirited, and the field of astronomy provided fertile grounds for questioning old conceptions and developing and testing new ones.

The first astronomical texts that were translated into Arabic in the eighth century were of Indian and Persian origin. The real emergence of Arabic astronomy, however, occurred in the ninth century at which time the major Greek astronomical texts were translated. Right from its very beginnings in the ninth and all the way till the sixteenth century, astronomical activity was wide-spread and intensive. This activity is reflected in the large number of scientists working in practical and theoretical astronomy, the number of books written, the active observatories, and the new observations.

Arabic astronomy was first exposed to Persian and Indian astronomy, and it continued to use some of the parameters and methods of these two traditions, yet the greatest formative influence on Arabic astronomy is undoubtedly Greek. Early in the ninth century, astronomers realized that the Greek astronomical tradition was far superior to the other two, both in its comprehensiveness and its use of effective geometrical representations. One particular Greek author, and more specifically one work by this author, exerted a disproportionate influence on all of medieval astronomy through the whole of the Arabic period and until the eventual demise of the geocentric astronomical system. This is the Almagest of Ptolemy (second century AD). That this text should exert so much influence is neither accidental nor surprising, for it is the highest achievement in Hellenistic mathematical astronomy, and one of the greatest achievements of all of Hellenistic science.

The Almagest was rightly considered the main authoritative work of antiquity on Astronomy. In this book, Ptolemy synthesizes the earlier knowledge of Hellenistic astronomy in light of his own new observations. The main purpose of the book is to establish the geometric models which would accurately account for observational phenomena. A large part of the book is dedicated to the methods for constructing various models and for calculating the parameters of these models. Ptolemy also provides tables for planetary motions to be used in conjunction with his models. Of all the books of antiquity, the Almagest represents the most successful work of mathematical astronomy: its geometric representations of the universe provided the most accurate and best predictive accounts for the celestial phenomena. A Greek tradition of physical astronomy is also reflected in the Almagest and in Ptolemy’s other influential work, the Planetary Hypothesis. According to this predominantly Aristotelian tradition, the universe is organized into a set of concentric spheres, each carrying a star and rotating around the stationary earth at the center of the universe. In contrast to sublunary rectilinear motion, the heavenly bodies move in perfect uniform circular motions. Ptolemy adopted, at least in theory, the two basic Aristotelian principles: that the earth is stationary at the center of the universe, and that the motion of heavenly bodies ought to be represented by a set of uniform circular motions. In practice, mathematical considerations often forced Ptolemy to disregard the second of these principles. However, against his better “mathematical” judgement, the only physical theory or cosmology available to Ptolemy was that of Aristotle. Ptolemy thus had no other option but to profess his adherence to this cosmology, an adherence which gave rise, in the Islamic period and later in Europe, to a long and fruitful tradition of astronomical reform.

Astronomical reform in the Islamic period took different forms. Under the Caliph al-Ma¹mun, a program of astronomical observations was organized in Baghdad and Damascus. Like any organized research project, this program endowed astronomical activity in the Islamic world with formal prestige. The professed purpose of this program was to verify the Ptolemaic observations by comparing the results derived by calculation, based on the Ptolemaic models, with actual observations conducted in Baghdad and Damascus some 700 years after Ptolemy. The results were compiled in al-Zij al-Mumtahan (The verified tables), which is no longer extant in its entirety, but is widely quoted by later astronomers. The most important correction introduced was to show that the apogee of the solar orb moves with the precession of the fixed stars. On a more general note, this program stressed the need for continuing verification of astronomical observations, and for the use of more precise instruments.

Thus, right from its beginnings, Arabic astronomy set out to rectify and complement Ptolemaic astronomy. Having noted several discrepancies between new observations and Ptolemaic calculations, astronomers then proceeded to reexamine the theoretical basis of Ptolemy’s results. This critical reexamination took several forms. Although the general astronomical research of this period (ninth century) is conducted within the framework of Ptolemaic astronomy, this research reworked and critically examined the observations and the computational methods of this astronomy and, in a limited way, was able to explore problems outside its set frame. The application of diverse mathematical disciplines to each other also had the immediate effect of expanding the frontiers of disciplines and introducing new scientific concepts and ideas. The use of systematic mathematization transformed the methods of reasoning and enabled, in turn, further creative developments in the branches of science.

In the tenth and eleventh centuries, the earlier examinations of Ptolemaic astronomy led to systematic projects which, rather than addressing the field in its totality, focused on specific aspects of astronomy. One of the main characteristics of this period was the tendency to provide exhaustive synthesizing works on particular astronomical topics, culminating in Biruni¹s (973-c. 1048) al-Qanun al-MasŒudi, a synthesis of the Greek, Indian, and Arabic astronomical traditions. It is with Biruni that we have the first systematic discussion, by a scientist (astronomer), of the relationship between science and philosophy. A book entitled al-As¹ila wal-Ajwiba (questions and answers) preserves an exchange between Biruni and his contemporary Ibn Sina, the most celebrated Muslim philosopher of all time. Biruni presents Ibn Sina with a set of questions in which he criticizes Aristotle’s physical theory, especially as it pertains to astronomy. Ibn Sina then responds, and a lively debate ensues. In the course of this exchange, Biruni questions almost all of the fundamental Aristotelian physical axioms: he rejects the notion that heavenly bodies have an inherent nature, and asserts that their motion could very well be compulsory; he maintains that there is no observable evidence that rules out the possibility of vacuum; he further asserts that, although observation corroborates Aristotle’s claim that the motion of heavenly bodies is circular, there is no inherent “natural” reason why this motion cannot be, among other things, elliptical. What is more significant than the actual objections raised by Biruni is the argument he employs in the course of the debate. Biruni draws a distinction between his vocation and that of Aristotle and Ibn Sina. He seems to argues that the metaphysical axioms on which philosophers build their physical theories do not constitute valid evidence for the mathematical astronomer. In other words, Biruni clearly distinguishes between the philosopher and the mathematician, the metaphysician and the scientist. He conceives of himself as a mathematical astronomer for whom the only valid evidence is observational or mathematical. Biruni’s example illustrates how the systematic application of rigorous mathematical reasoning led to the mathematization of astronomy and, by extension, to the mathematization of nature. Rather than subsuming the various sciences under the all-encompassing umbrella of philosophy, many scientists considered their professions as autonomous mathematical enterprises, separate from, and on par with philosophy.

As I noted earlier, Ptolemy had taken the liberty to propose models that did not conform to Aristotelian cosmology; so how does Biruni¹s example differ from that of Ptolemy? Put differently, can we think of both Ptolemy and Biruni as prototypes for scientists that are interested in the descriptive functions of science, in “saving the phenomena,” as opposed to scientists seeking to explain and not just describe? I will try to answer this question by comparing two traditions of astronomical reform in the Muslim east and west.

Traditions of astronomical reform in the Islamic period

Building on the cumulative achievements of Arabic astronomy, the eleventh century witnessed the emergence of a new tradition of astronomical research. After the eleventh century, the efforts of most theoretical astronomers were directed towards providing a thorough evaluation of the physical and philosophical underpinnings of Ptolemaic astronomy, and proposing alternatives to it. It should be noted here that the emergence of this tendency in astronomical research does not represent a move away from the thorough mathematical examination of astronomy, but is an outcome of this increasing mathematization. This line of research was pursued by several eleventh-century scientists. In a book entitled Tarkib al-Aflak, Abu ŒUbayd al-Juzjani (d. c. 1070) indicates that both he and his teacher, Ibn Sina, were aware of the o-called equant problem of the Ptolemaic model. Juzjani even proposes a solution for this problem. The author of an anonymous Andalusian astronomical manuscript refers to another work which he composed under the title al-Istidrak Œala Batlamyus (recapitulation regarding Ptolemy), and indicates that he included in this book a list of objections to Ptolemaic astronomy. The most important work of this genre, however, was written in the same period by Ibn al-Haytham (d. 1039). In his celebrated work Al-Shukuk Œala Batlamyus (doubts on Ptolemy), Ibn al-Haytham sums up the physical and philosophical problems inherent in the Greek astronomical system, and provides an inventory of the theoretical inconsistencies of the Ptolemaic models. The tradition of astronomical reform thrived in the thirteenth century, climaxed in the fourteenth, and continued well into the fifteenth and sixteenth centuries. Most astronomers of this period took up the theoretical challenge outlined by Ibn al-Haytham, attempted to rework the models of Ptolemaic astronomy and to provide, with varying degrees of success, alternatives to these models. The list of astronomers working within this tradition comprises some of the greatest and most original Muslim scientists. The astronomers who have received modern scholarly attention include: Mu¹ayyad al-Din al-ŒUrdi (d. 1266), Nasir al-Din al-Tusi (d. 1274), Qutb al-Din al-Shirazi (d. 1311), Sadr al-ShariŒa al-Bukhari (d. 1347), Ibn al-Shatir (d. 1375), and ŒAla¹ al-Din al-Qushji (d. 1474).

To appreciate the technical aspects of these astronomical reforms, a quick overview of some aspects of Ptolemaic astronomy is in order. In his Almagest, Ptolemy used the results of earlier Hellenistic astronomy and incorporated them into one great synthesis. Of particular geometrical utility was the concept of eccentrics and epicycles developed by Hipparchus (second century BC) and adopted by Ptolemy. In an astronomical representation employing the eccentric model (Figure 1), a planet is carried on the circumference of an eccentric circle which rotates uniformly around its own center G. This center, however, does not coincide with the location O of an observer on the earth. As a result, the speed of the planet appears to vary with respect to the observer at O. In an epicyclic model, the planet P is carried on the circumference of an epicycle, whose center is in turn carried on a circle called the deferent, which rotates uniformly around the center of the universe, the earth. Viewed by an observer at point O, the combination of the two uniform motions of the deferent and the epicycle produces a non-uniform motion which is mathematically equivalent to the motion of the eccentric model.

(Not Shown)
Figure 1

The Ptolemaic model for the motion of the sun utilized either a simple eccentric or the equivalent combination of a deferent and an epicycle. All the other Ptolemaic models for planetary motions were considerably more complex. For example, in the model for the longitudinal motion of the upper planets Mars, Jupiter and Saturn (Figure 2), the center G of the deferent circle no longer coincides with the earth O; moreover, the uniform motion of the center of the epicycle on the circumference of the deferent is measured around the point E, called the equant center, rather than the center G of the deferent. Ptolemy proposed this model because it allowed for fairly accurate predictions of planetary positions. However, circle G in this model is made to rotate uniformly around the equant E which is not its center. This represented a violation of the Aristotelian principle, adopted by Ptolemy, of uniform circular motion around the Earth, the stationary center of the universe. In other words, for the sake of observation, Ptolemy was forced to breach the physical and philosophical principles on which he built his astronomical theory. Other Ptolemaic models were even more complex, and with each additional level of complexity new objections were raised against Ptolemaic astronomy.

(Not Shown)
Figure 2

Other objections raised by Ibn al-Haytham and taken up by later astronomers include the problem of the prosneusis point in the model for the longitudinal motion of the moon; the problem of the inclination and deviation of the spheres of Mercury and Venus; the problem of planetary distances, and so on. In the case of the moon, additional difficulties arise because Ptolemy’s model has a deferent center which is itself moving; moreover, the motion of the center of the epicycle on this deferent is not uniform around the deferent’s center; rather, it rotates uniformly around the center of the world. To complicate matters further, the anomalistic motion on the epicycle is measured away from the mean epicyclic apogee, that is aligned with a movable point called the prosneusis point, rather than being measured from the true apogee, that is aligned with the center of the world. This prosneusis point is the point diametrically opposite to the center of the deferent on the other side of the center of the world. The model for the longitudinal motion of Mercury contained complex mechanisms that were equally objectionable. Additional complications also resulted from the motion of the planets in latitude: the motion in longitude is measured on the plane of the ecliptic which is the great circle of the celestial sphere that traces the apparent yearly path of the sun as seen from the earth. The deferents of the Ptolemaic models, however, did not coincide with this plane. The least problematic is the case of the lunar model, where the deferent has a fixed inclination with respect to the ecliptic, and the epicycle lies in the plane of the deferent. However, the epicycles of the upper planets do not lie in the plane of the deferent, and they have a variable deviation with respect to it. In the case of the lower planets, both the inclination of the deferent with respect to the ecliptic and that of the epicycle with respect to the deferent are variable. Without getting into details, one can easily imagine the complexity and potential problems of the Ptolemaic models which attempted to account for these see-saw and oscillation motions.

The astronomers who attempted to solve the above problems can be classified into two general schools: a mathematically oriented school which was predominantly in the eastern parts of the Muslim world, and a philosophically oriented school based in the western regions of the empire. The name “Maragha school” is often given to the eastern reformers in recognition of the achievements of a number of astronomers working in an observatory established at Maragha. Whereas the contributions of these astronomers are no doubt monumental, it should be noted that the reform of Ptolemaic astronomy started before the establishment of the Maragha observatory in the thirteenth century, and reached its highest point in the fourteenth. In fact, some of the astronomers of the Maragha group seem to have started their reform projects even before they joined this observatory; they were perhaps invited to join the observatory team because they were already engaged in such research. The eastern reform tradition, then, was too diffused to be associated with any one geographical area or period; rather, it characterizes several centuries of Arabic astronomical research throughout the Eastern domains of the Muslim world.

Astronomers of the eastern reform tradition adopted several mathematical strategies in their attempts to solve the theoretical problems of the Ptolemaic models. One of their main objectives was to come up with models in which the motions of the planets could be generated as a result of combinations of uniform circular motions, while at the same time conforming to the accurate Ptolemaic observations. Two useful and extremely influential mathematical tools were invented by Tusi and ŒUrdi. The first tool, known in modern scholarship as the Tusi couple, in effect produces linear oscillation as a result of a combination of two uniform circular motions. The tool was used in various ways by many astronomers including Copernicus. The ŒUrdi lemma is an equally versatile mathematical tool used by ŒUrdi and his successors. To produce optimal representations that are physically and mathematically sound, other astronomers used various combinations of these two tools, and devised additional tools of their own invention. In addition, other mathematical solutions were proposed to resolve the contradictions inherent in the Ptolemaic models. For example, ŒUrdi reversed the direction and tripled the magnitude of motion of the inclined sphere in the Ptolemaic lunar model; he was thus able to produce uniform motion around the geometric center of the sphere, while at the same time reproducing the uniform motion around the old Ptolemaic center. The most comprehensive and successful models were introduced in the fourteenth century by the Damascene astronomer Ibn al-Shatir; his models for all the planets utilize combinations of perfect circular motions where each circle rotates uniformly around its center. Ibn al-Shatir was also able to solve problems of planetary distances, and to provide more accurate accounts for observations.

The development of Arabic astronomy in al-Andalus and North Africa followed different routes. The beginnings of significant scientific activity in al-Andalus started in the ninth century; yet this activity was almost completely dependent upon and lagging behind the sciences of the eastern part of the Muslim world. Between the ninth and eleventh centuries, however, a full-fledged scientific tradition emerged. Many scientists traveled east to study science; scientific books were systematically acquired and large private and public libraries were established. A solid familiarity with the eastern astronomical tradition led, in the eleventh century, to an intensive and at times original astronomical activity. The emphasis of the activity of these and other astronomers was focused on the compilation of tables and on spherical astronomy. Their primary original contributions were limited to some new observations, but mostly to the mathematics of the trepidation movement of the stars, as well as to the invention of highly sophisticated astronomical instruments. During this entire period, however, little work of significance was devoted to planetary theory.

In contrast to the earlier period, the focus of astronomical research in al-Andalus and North Africa in the twelfth century shifted to planetary theory. The names associated with this research tradition include Ibn Baja (d. 1138), Jabir Ibn Aflah (fl. 1120), Ibn Tufayl (d. 1185), Averroes (d. 1198), and Al-Bitruji (fl. 1200). Of these, Al-Bitruji was the only one to formulate an alternative to Ptolemaic astronomy, while the others produced philosophical discussions of this astronomy. Both the discourses on Ptolemaic astronomy, as well as the actual proposed model of al-Bitruji, conceived of astronomical reform in reactionary terms-that is, in terms of adopting older and mathematically inferior models in place of the ones used since Ptolemy. The aim of the western school was to reinstate Aristotelian homocentric spheres, and to completely eliminate any use of eccentrics and epicycles. In accordance with the most stringent and literal interpretations of Aristotelian principles, the western researchers demanded that the heavens be represented exclusively by nested homocentric spheres and perfect uniform circular motions. Even epicycles and deferents that rotated uniformly around their centers were not tolerated, because their use entailed an attribution of compoundednesss to heavenly phenomena; according to Aristotelian principles, the heavens are perfectly simple. However, since the predictive power of the Ptolemaic models and their ability to account for the observed phenomena relied on the use of epicycles and eccentrics, the western models were strictly qualitative and philosophical, and were completely useless from a mathematical point of view. These models were neither numerically verifiable, nor could they be used for predicting planetary positions. It is no wonder, therefore, that all but one of the western philosophers did not bother to produce actual geometrical models.

The significance of the difference between the eastern and western reform traditions of Arabic astronomy cannot be overemphasized. The prevalent view in contemporary scholarship attributes the steady decline of the intellectual sciences in al-Andalus and North Africa to the rise of the so-called “fundamentalist” states of the Almoravids (1091-1144) and Almohads (1147-1232). It was precisely during this period, however, that the greatest Andalusian philosophers worked under the patronage of the rulers of these two states. What we have, therefore, is not a steady decline of the intellectual disciplines, but the rise of some at the expense of others. The decline of mathematical astronomy has nothing to do with the Almoravids or the Almohads, nor with an alleged theological counter-revolution. Rather, the decline is a result of the adoption of a specific research program of astronomical research, a program which is driven by the untenable, and by then outdated, Aristotelian philosophical concerns that proved incompatible with the advanced mathematical and scientific aspects of astronomy.

In sharp contrast with the western school, the eastern school of Arabic astronomy did not favor philosophy at the expense of mathematics. The objections of this school were mathematical and physical and, as the comparison with their western counterpart clearly illustrates, these objections were certainly not philosophical. A common view which is prevalent in earlier studies maintains that the eastern reform tradition of Arabic astronomy was driven by philosophical considerations, a notion which is often used to undermine the mathematical and scientific significance of this tradition. Given the overwhelming evidence of detailed research on this tradition, such a view is no longer tenable. The alternative solar model proposed by Ibn al-Shatir is an example in which reform was motivated by purely observational considerations, even though the Ptolemaic model was completely unobjectionable from a physical or philosophical point of view. More generally, the eastern tradition of astronomical reform has its roots in the systematic mathematization of astronomy and, to some extent, even of nature itself. A recent study of the al-Takmila fi Sharh al-Tadhkira of al-Khafri (d. 1525) clearly illustrates one of the main characteristics of this tradition. Al-Khafri was primarily a religious scholar who wrote a highly sophisticated commentary on the Tadhkira of Nasir al-Din al-Tusi, one of the classics of the eastern reform tradition. Al-Khafri presents in this work thorough accounts for the various alternative models proposed by arlier astronomers. The purpose of this presentation, however, is not to look for a correct model, nor to decide which one conforms with an ideal or preferred cosmology, but to establish the mathematical equivalence of all of these models.

Now to go back to the question I raised earlier, namely whether we can think of this tradition of astronomical research as an expansion of the descriptive tendency started by Ptolemy himself. The answer, in my view, is no. To start with, it would be inaccurate to talk of a mathematical school and a philosophical school in Greek astronomy, since the astronomers who provided mathematical models in violation of Aristotelian physics did not theorize the superiority of mathematical principles over philosophical ones. Moreover, this supposed school of mathematical astronomy culminated in Ptolemy, who considered his models defective because they did not conform fully with Aristotelian cosmology. In contrast, in the case of the eastern Islamic astronomical tradition, the proposed mathematical models were deliberate theoretical and epistemological choices that were conceived as alternatives to the philosophical choice. This reform tradition thus shifted the understanding of physics from metaphysics to mathematics. In turn, this shift laid the foundation for the demise of Aristotelian physics and for the emergence of the new sciences. Despite the diversity of their proposed solutions, a shared, fundamental change introduced by the astronomers of the Muslim east is in the understanding of what constitutes a principle. The principles employed by these astronomers did not derive from philosophical speculation about the nature of heavenly bodies (as in the case of the principles adopted by Ptolemy), but from mathematics. Such is, for example, the principle that the uniform motion of a sphere can only be around an axis passing through its center, since any other rotation is, by definition, non-uniform. At the same time, ŒUrdi, for example, does not hesitate to reverse the direction of the motion in his proposed model, simply because he can reproduce the Ptolemaic observations while employing spheres that rotate uniformly around their own centers; ŒUrdi could not have possibly conceived of this reversed motion as one that corresponds to reality, but only as one that allows accurate predictions of planetary positions. Likewise, Tusi¹s couple and ŒUrdi¹s lemma were pure mathematical tools that had no physical counterpart. While the objective of the western Islamic astronomical tradition was to save the (meta)-physical theory, that of the eastern tradition was to save the phenomena as well as the newly constituted physics. In this physics, mathematical principles were not just tools or a vehicles for studying nature but also for conceptualizing it.

Philosophy, the overarching discipline in the Greek classifications, was gradually relegated in the Islamic hierarchy of knowledge to one subdivision among many other sciences. Having isolated philosophy, Muslims could then single it out as a potential source of conflict with religion without jeopardizing the other demonstrable sciences. The western (Islamic) tradition of astronomical research subscribed to the older Greek metaphysics, whereas the eastern tradition did not. It is thus legitimate to think of this latter tradition of astronomical reform as a specific Islamic development, and of the views espoused in the formulations of members of this tradition as indications of what is “Islamic” about Islamic science. A notable characteristic of this tradition of astronomical reform is the development of mathematical principles to replace the older physical, or rather metaphysical principles of astronomy. Thus conceived, the areas in which science and religion overlap are reduced, and scientific knowledge is separated from religious knowledge. In other words, one of the consequences of the separation of science and philosophy was the separation of religion and science. To a certain extent, therefore, the Islamization of science in the practice of medieval Muslim astronomers actually meant its secularization.

By Ahmad Dallal

The House of Wisdom

The foundations of Islamic science in general and of astronomy in particular were laid two centuries after the emigration of the prophet Muhammad from Mecca to Medina in A.D. 622. This event, called the Hegira, marks the beginning of the Islamic calendar. The first centuries of Islam were characterized by a rapid and turbulent expansion. Not until the late second century and early third century of the Hegira era was there a sufficiently stable and cosmopolitan atmosphere in which the sciences could flourish. Then the new Abbasid dynasty, which had taken over the caliphate (the leadership of Islam) in 750 and founded Baghdad as the capital in 762, began to sponsor translations of Greek texts. In just a few decades the major scientific works of antiquity–including those of Galen, Aristotle, Euclid, Ptolemy, Archimedes and Apollonius–were translated into Arabic. The work was done by christian and pagan scholars as well as by Muslims. The most vigorous patron of this effort was Caliph al-Ma’mun, who acceded to power in 813. Al-Ma’mun founded an academy called the House of Wisdom and placed Hunayn ibn Ishaq al-’Ibadi, a Nestorian Christian with an excellent command of Greek, in charge. Hunayn became the most celebrated of all translators of Greek texts. He produced Arabic versions of Plato, Aristotle and their commentators, and he translated the works of the three founders of Greek medicine, Hippocrates, Galen and Dioscorides. The academy’s principal translator of mathematical and astronomical works was a pagan named Thabit ibn Qurra. Thabit was originally a money changer in the marketplace of Harran, a town in northern Mesopotamia that was the center of an astral cult. He stoutly maintained that the adherents of this cult had first farmed the land, built cities and ports and discovered science, but he was tolerated in the Islamic capital. There he wrote more than 100 scientific treatises, including a commentary on the Almagest. Another mathematical astronomer at the House of Wisdom was al-Khwarizmi, whose Algebra, dedicated to al-Ma’mun, may well have been the first book on the topic in Arabic. Although it was not particularly impressive as a scientific achievement, it did help to introduce Hindu as well as Greek methods into the Islamic world. Sometime after 1100 it was translated into Latin by an Englishman, Robert of Chester, who had gone to Spain to study mathematics. The translation, beginning with the words “Dicit Algoritmi” (hence the modern word algorithm), had a powerful influence on medieval Western algebra. Moreover, its influence is still felt in all mathematics and science: it marked the introduction into Europe of “Arabic numerals.” Along with certain trigonometric procedures, the Arabs had borrowed from India a system of numbers that included the zero. The Indian numerals existed in two forms in the Islamic world, and it was the Western form that was transmitted through Spain into medieval Europe. These numerals, with the explicit zero, are far more efficient than Roman numerals for making calculations. Yet another astronomer in ninth-century Baghdad was Ahmad al-Farghani. His most important astronomical work was his Jawami, or Elements, which helped to spread the more elementary and nonmathematical parts of Ptolemy’s earth-centered astronomy. The Elements had a considerable influence in the West. It was twice translated into Latin in Toledo, once by John of Seville (Johannes Hispalensis) in the first half of the 12th century, and more completely by Gerard of Cremona a few decades later. Gerard’s translation of al-Farghani provided Dante with his principal knowledge of Ptolemaic astronomy. (In the Divine Comedy the poet ascends through the spheres of the planets, which are centered on the earth.) It was John of Seville’s earlier version, however, that became better known in the West. It served as the foundation for the Sphere of Sacrobosco, a still further watered-down account of spherical astronomy written in the early 13th century by John of Holywood (Johannes de Sacrobosco). In universities throughout Western Christendom the Sphere of Sacrobosco became a long-term best seller. In the age of printing it went through more than 200 editions before it was superseded by other textbooks in the early 17th century. With the exception of Euclid’s Elements no scientific textbook can claim a longer period of supremacy. Thus from the House of Wisdom in ancient Baghdad, with its congenial tolerance and its unique blending of cultures, there streamed not only an impressive sequence of translations of Greek scientific and philosophical works but also commentaries and original treatises. By A.D. 900 the foundation had been laid for the full flowering of an international science, with one language–Arabic–as its vehicle.

Religious Impetus

A major impetus for the flowering of astronomy in Islam came from religious observances, which presented an assortment of problems in mathematical astronomy, specifically in spherical geometry. At the time of Muhammad both Chistians and Jews observed holy days, such as Easter and Passover, whose timing was determined by the phases of the moon. Both communities had confronted the fact that the approximately 29.5-day lunar months are not commensurable with the 365-day solar year: 12 lunar months add up to only 354 days. To solve the problem Christians and Jews had adopted a scheme based on a discovery made in about 430 B.C. by the Athenian astronomer Meton. In the 19-year Metonic cycle there were 12 years of 12 lunar months and seven years of 13 lunar months. The periodic insertion of a 13th month kept calendar dates in step with the seasons. Apparently, however, not every jurisdiction followed the standard pattern; unscrupulous rulers occasionally added the 13th month when it suited their own interests. To Muhammad this was the work of the devil. In the Koran (chapter 9, verse 36) he decreed that “the number of months in the sight of God is 12 [in a year]–so ordained by Him the day He created the heavens and the earth; of them four are sacred: that is the straight usage.” Caliph ’Umar I (634-44) interpreted this decree as requiring a strictly lunar calendar, which to this day is followed in most Islamic countries. Because the Hegira year is about 11 days shorter than the solar year, holidays such as Ramadan, the month of fasting, slowly cycle through the seasons, making their rounds in about 30 solar years. Furthermore, Ramadan and the other Islamic months do not begin at the astronomical new moon, defined as the time when the moon has the same celestial longitude as the sun and is therefore invisible; instead they begin when the thin crescent moon is first sighted in the western evening sky. Predicting just when the crescent moon would become visible was a special challenge to Islamic mathematical astronomers. Although Ptolemy’s theory of the complex lunar motion was tolerably accurate near the time of the new moon, it specified the moon’s path only with respect to the ecliptic (the sun’s path on the celestial sphere). To predict the first visibility of the moon it was necessary to describe its motion with respect to the horizon, and this problem demanded fairly sophisticated spherical geometry. Two other religious customs presented problems requiring the application of spherical geometry. One problem, given the requirement for Muslims to pray toward Mecca and to orient their mosques in that direction, was to determine the direction of the holy city from a given location. Another problem was to determine from celestial bodies the proper times for the prayers at sunrise, at midday, in the afternoon, at sunset and in the evening. Solving any of these problems involves finding the unknown sides or angles of a triangle on the celestial sphere from the known sides and angles way of finding the time of day, for example, is to construct a triangle whose vertexes are the zenith, the north celestial pole and the sun’s position. The observer must know the altitude of the sun and that of the pole; the former can be observed, and the latter is equal to the observer’s latitude. The time is then given by the angle at the intersection of the meridian (the arc through the zenith and the pole) and the sun’s hour circle (the arc through the sun and the pole). The method Ptolemy used to solve spherical triangles was a clumsy one devised late in the first century by Menelaus of Alexandria. It involved setting up two intersecting right triangles; by applying the Menelaus theorem it was possible to solve for one of the six sides, but only if the other five sides were known. To tell the time from the sun’s altitude, for instance, repeated applications of the Menelaus theorem were required. For medieval Islamic astronomers there was an obvious challenge to find a simpler trigonometric method. By the ninth century the six modern trigonometric functions–sine and cosine, tangent and cotangent, secant and cosecant–had been identified, whereas Ptolemy knew only a single chord function. Of the six, five seem to be essentially Arabic in origin; only the sine function was introduced into Islam from India. (The etymology of the word sine is an interesting tale. The Sanskrit word was ardhajya, meaning “half chord,” which in Arabic was shortened and transliterated as jyb. In Arabic vowels are not spelled out, and so the word was read as jayb, meaning “pocket” or “gulf.” In medieval Europe it was then translated as sinus, the Latin word for gulf.) From the ninth century onward the development of spherical trigonometry was rapid. Islamic astronomers discovered simple trigonometric identities, such as the law of sines, that made solving spherical triangles a much simpler and quicker process.

Stars and Astrolabes

One of the most conspicuous examples of modern astronomy’s Islamic heritage is the names of stars. Betelgeuse, Rigel, Vega, Aldebaran and Fomalhaut are among the names that are directly Arabic in origin or are Arabic translations of Ptolemy’s Greek descriptions. In the Almagest Ptolemy had provided a catalogue of more than 1,000 stars. The first critical revision of the catalogue was compiled by ’Abd al-Rahman al-Sufi, a 10th-century Persian astronomer who worked in both Iran and Baghdad. Al-Sufi’s Kitab su-war al-kawakib (“Book on the Constellations of Fixed Stars”) did not add or subtract stars from the Almagest list, nor did it remeasure their often faulty positions, but it did give improved magnitudes as well as Arabic identifications. The latter were mostly just translations of Ptolemy. For many years it was assumed that al-Sufi’s Arabic had established the stellar nomenclature in the West. It now seems that his 14th- and 15th-century Latin translators went to a Latin version of the Arabic edition of Ptolemy himself for the star descriptions, which they combined with al-Sufi’s splendid pictorial representations of the constellations. Meanwhile the Arabic star nomenclature trickled into the West by another route: the making of astrolabes. The astrolabe was a Greek invention. Essentially it is a two-dimensional model of the sky, an analog computer for solving the problems of spherical astronomy [see “The Astrolabe,” by J. D. North; SCIENTIFIC AMERICAN, January, 1974]. A typical astrolabe consists of a series of brass plates nested in a brass matrix known in Arabic as the umm (meaning “womb”). The uppermost plate, called the ’ankabut (meaning “spider”) or in Latin the rete, is an open network of two or three dozen pointers indicating the position of specific stars. Under the rete are one or more solid plates, each engraved with a celestial coordinate system appropriate for observations at a particular latitude: circles of equal altitude above the horizon (analogous to terrestrial latitude lines) and circles of equal azimuth around the horizon (analogous to longitude lines). By rotating the rete about a central pin, which represents the north celestial pole, the daily motions of the stars on the celestial sphere can be reproduced. Although the astrolabe was known in antiquity, the earliest dated instrument that has been preserved comes from the Islamic period [see cover of this issue]. It was made by one Nastulus in 315 of the Hegira era (A.D. 927-28), and it is now one of the treasures of the Kuwait National Museum. Only a handful of 10th-century Arabic astrolabes exist, whereas nearly 40 have survived from the 11th and 12th centuries. Several of these were made in Spain in the mid-11th century and have a distinctly Moorish style. The earliest extant Arabic treatise on the astrolabe was written in Baghdad by one of Caliph al-Ma’mun’s astronomers, ’Ali ibn ’Isa. Later members of the Baghdad school, notably al-Farghani, also wrote on the astrolabe. Al-Farghani’s treatise was impressive for the mathematical way he applied the instrument to problems in astrology, astronomy and timekeeping. Many of these treatises found their way to Spain, where they were translated into Latin in the 12th and 13th centuries. The most popular work, which exists today in about 200 Latin manuscript copies, was long mistakenly attributed to Masha’allah, a Jewish astronomer of the eighth century who participated in the decision to found Baghdad; it probably is a later pastiche from a variety of sources. In about 1390 this treatise was the basis for an essay on the astrolabe by the English poet Geoffrey Chaucer. Indeed, England seems to have been the gateway for the introduction of the astrolabe from Spain into Western Christendom in the late 13th and 14th centuries. It is possible that scientific activity centered at Oxford at the time contributed to the surge of interest in the device. Merton and Oriel colleges of the University of Oxford still own fine 14th-century astrolabes. On them one finds typical sets of Arabic star names written in Gothic Latin letters. Included on the Merton College astrolabe, for example, are Arabic names that have evolved into standard modern nomenclature: Wega, Altahir, Algeuze, Rigil, Elfeta, Alferaz and Mirac. Thus as a result of the astrolabe tradition of Eastern Islam, transmitted through Spain to England, most navigational stars today have Arabic names, either indigenous ones or Arabic translations of Ptolemy’s Greek descriptions.

Refining Ptolemy

It would be wrong to conclude from the preponderance of Arabic star names that Islamic astronomers made exhaustive studies of the sky. On the contrary, their observations were quite limited. For instance, the spectacular supernova (stellar explosion) of 1054, which produced the Crab Nebula, went virtually unrecorded in Islamic texts even though it was widely noted in China. Modern astronomers struck by this glaring gap often do not realize that Islamic astronomers failed to document most specific astronomical phenomena. They had little incentive to do so. Their astrology, unlike that of the Chinese, depended not so much on unusual heavenly omens as on planetary positions, and these were quite well described by the Ptolemaic procedures. The planetary models that Ptolemy devised in the second century A.D. had the sun, the moon and the planets moving around the earth. A simple circular orbit, however, could not account for the fact that a planet periodically seems to reverse its direction of motion across the sky. (According to the modern heliocentric viewpoint, this apparent retrograde motion occurs when the earth is passing or being passed by another planet on its way around the sun.) Hence Ptolemy had each planet moving on an epicycle, a rotating circle whose center moved about the earth on a larger circle called the deferent. The epicycle, together with other geometric devices invented by Ptolemy, gave a fairly good first approximation to the apparent motion of the planets. As a great theoretician, Ptolemy must have been fairly confident of the particular geometry of his models, since he never described how he settled on it. On the other hand, the idea of applying mathematics to a specific numerical description of the physical world was something rather novel for the Hellenistic Greeks, quite different from the pure mathematics of Euclid and Apollonius. In this part of his program Ptolemy must have realized that improved values for the numerical parameters of his models were both desirable and inevitable, and so he gave careful instructions on how to establish the parameters from a limited number of selected observations. The Islamic astronomers learned this lesson all too well. They limited their observations, or at least the few they chose to record, primarily to measurements that could be used for rederiving key parameters. These included the orientation and eccentricity of the solar orbit and the inclination of the ecliptic plane. An impressive example of an Islamic astronomer working strictly within a Ptolemaic framework but establishing new values for Ptolemy’s parameters was Muhammad al-Battani, a younger contemporary of Thabit ibn Qurra. Al-Battani’s Zij (“Astronomical Tables”) is still admired as one of the most important astronomical works between the time of Ptolemy and that of Copernicus. Among other things, al-Battani was able to establish the position of the solar orbit (equivalent in modern terms to finding the position of the earth’s orbit) with better success than Ptolemy had achieved. Because al-Battani does not describe his observations in detail, it is not clear whether he adopted an observational strategy different from that of Ptolemy. In any case his results were good, and centuries later his parameters for the solar orbit were widely known in Europe. His Zij first made its way to Spain. There it was translated into Latin early in the 12th century and into Castilian a little more than 100 years later. The fact that only a single Arabic manuscript copy survives (in the Escorial Library near Madrid) suggests that al-Battani’s astronomy was not as highly regarded in Islam as it was in Europe, where the advent of printing ensured its survival and in particular made it available to Copernicus and his contemporaries. In De revolutionibus orbium coelestium (“On the Revolutions of the Heavenly Spheres”) the Polish astronomer mentions his ninth-century Muslim predecessor no fewer than 23 times. In contrast, one of the greatest astronomers of medieval Islam, ’Ali ibn ’Abd al-Rahman ibn Yunus, remained completely unknown to European astronomers of the Renaissance. Working in Cairo a century after al-Battani, Ibn Yunus wrote a major astronomical handbook called the Hakimi Zij. Unlike other Arabic astronomers, he prefaced his Zij with a series of more than 100 observations, mostly of eclipses and planetary conjunctions. Although Ibn Yunus’ handbook was widely used in Islam, and his timekeeping tables survived in use in Cairo into the 19th century, his work became known in the West less than 200 years ago. Throughout the entire Islamic period astronomers stayed securely within the geocentric framework. For this one should not criticize them too harshly. Until Galileo’s telescopic observations of the phases of Venus in 1610, no observational evidence could be brought against the Ptolemaic system. Even Galileo’s observations could not distinguish between the geo-heliocentric system of Tycho Brahe (in which the other planets revolved about the sun but the sun revolved about the earth) and the purely heliocentric system of Copernicus [see “The Galileo Affair,” by Owen Gingerich; SCIENTIFIC AMERICAN, August, 1982]. Furthermore, although Islamic astronomers followed Ptolemy’s injunction to test his results, they did not limit themselves simply to improving his parameters. The technical details of his models were not immune from criticism. These attacks, however, were invariably launched on philosophical rather than on observational grounds.

Doubting Ptolemy

Ptolemy’s models were essentially a mathematical system for predicting the positions of the planets. Yet in the Planetary Hypotheses he did try to fit the models into a cosmological system, the Aristotelian scheme of tightly nested spheres centered on the earth. He placed the nearest point of Mercury’s path immediately beyond the most distant point of the moon’s path; immediately beyond the farthest excursion of Mercury lay the nearest approach of Venus, and so on through the spheres for the sun, Mars, Jupiter and Saturn. To reproduce the observed nonuniform motions of the planets, however, Ptolemy adopted two purely geometric devices in addition to the epicycle. First, he placed the deferent circles off-center with respect to the earth. Second, he made the ingenious assumption that the motion of celestial bodies was uniform not around the earth, nor around the centers of their deferents, but instead around a point called the equant that was opposite the earth from the deferent center and at an equal distance. Eccentric deferents and equants did a good job of representing the varying speeds with which planets are seen to move across the sky, but to some minds they were philosophically offensive. The equant in particular was objectionable to philosophers who thought of planetary spheres as real physical objects, each sphere driven by the one outside it (and the outermost driven by the prime mover), and who wanted to be able to construct a mechanical model of the system. For example, as was pointed out by Maimonides, a Jewish scholar of the 12th century who worked in Spain and Cairo, the equant point for Saturn fell right on the spheres for Mercury. This was clearly awkward from a mechanical point of view. Furthermore, the equant violated the philosophical notion that heavenly bodies should be moved by a system of perfect circles, each of which rotated with uniform angular velocity about its center. To some purists even Ptolemy’s eccentric deferents, which moved the earth away from the center of things, were philosophically unsatisfactory. The Islamic astronomers adopted the Ptolemaic-Aristotelian cosmology, but eventually criticism emerged. One of the first critics was Ibn al-Haytham (Alhazen), a leading physicist of 11th-century Cairo. In his Doubts on Ptolemy he complained that the equant failed to satisfy the requirement of uniform circular motion, and he went so far as to declare the planetary models of the Almagest false. Only one of Ibn al-Haytham’s astronomical works, a book called On the Configuration of the World, penetrated into Latin Europe in the Middle Ages. In it he attempted to discover the physical reality underlying Ptolemy’s mathematical models. Conceiving of the heavens in terms of concentric spheres and shells, he tried to assign a single spherical body to each of the Almagest’s simple motions. The work was translated into Castilian in the court of Alfonso the Wise, and early in the 14th century from Castilian into Latin. Either this version or a Latin translation of one of Ibn al-Haytham’s popularizers had a major influence in early Renaissance Europe. The concept of separate celestial spheres for each component of Ptolemy’s planetary motions gained wide currency through a textbook, Theorica novae planetarum, written by the Viennese Georg Peurbach in about 1454. Meanwhile, in the 12th century in the western Islamic region of Andalusia, the astronomer and philosopher Ibn Rushd (Averroes) gradually developed a somewhat more extreme criticism of Ptolemy. “To assert the existence of an eccentric sphere or an epicyclic sphere is contrary to nature…,” he wrote. “The astronomy of our time offers no truth, but only agrees with the calculations and not with what exists.” Averroes rejected Ptolemy’s eccentric deferents and argued for a strictly concentric model of the universe. An Andalusian comtemporary, Abu Ishaq al-Bitruji, actually tried to formulate such a strictly geocentric model. The results were disastrous. For example, in al-Bitruji’s system Saturn could on occasion deviate from the ecliptic by as much as 26 degrees (instead of the required three degrees). As for the observed motions that led Ptolemy to propose the equant, they were completely ignored. In the words of one modern commentator, al-Bitruji “heaps chaos on confusion.” Nevertheless, early in the 13th century his work was translated into Latin under the name Alpetragius, and from about 1230 on his ideas were widely discussed throughout Europe. Even Copernicus cited his order of the planets, which placed Venus beyond the sun. At the other end of the Islamic world a fresh critique of the Ptolemaic mechanisms was undertaken in the 13th century by Nasir al-Din al-Tusi. One of the most prolific Islamic polymaths, with 150 known treatises and letters to his credit, al-Tusi also constructed a major observatory at Maragha (the present-day Maragheh in Iran). Al-Tusi found the equant particularly dissatisfactory. In his Tadhkira (“Memorandum”) he replaced it by adding two more small epicycles to the model of each planet’s orbit. Through this ingenious device al-Tusi was able to achieve his goal of generating the nonuniform motions of the planets by combinations of uniformly rotating circles. The centers of the deferents, however, were still displaced from the earth. Two other astronomers at the Maragha observatory, Mu’ayyad al-Din al-’Urdi and Qutb al-Din al-Shirazi, offered an alternative arrangement, but this system too retained the philosophically objectionable eccentricity. Finally a completely concentric rearrangement of the planetary mechanisms was achieved by Ibn al-Shatir, who worked in Damascus in about 1350. By using a scheme related to that of al-Tusi, Ibn al-Shatir succeeded in eliminating not only the equant but also certain other objectionable circles from Ptolemy’s constructions. He thereby cleared the way for a perfectly nested and mechanically acceptable set of celestial spheres. (He described his work thus: “I found that the most distinguished of the later astronomers had adduced indisputable doubts concerning the well-known astronomy of the spheres according to Ptolemy. I therefore asked Almighty God to give me inspiration and help me to invent models that would achieve what was required, and God–may He be praised and exalted–did enable me to devise universal models for the planetary motions in longitude and latitude and all other observable features of their motions, models that were free from the doubts surrounding previous ones.”) Yet Ibn al-Shatir’s solution, along with the work of the Maragha astronomers, remained generally unknown in medieval Europe.

Influence on Copernicus?

Ibn al-Shatir’s forgotten model was rediscovered in the late 1950’s by E. S. Kennedy and his students at the American University of Beirut. The discovery raised an intriguing question. It was quickly recognized that the Ibn al-Shatir and Maragha inventions were the same type of mechanism used by Copernicus a few centuries later to eliminate the equant and to generate the intricate changes in the position of the earth’s orbit. Copernicus, of course, adopted a heliocentric arrangement, but the problem of accounting for the slow but regular changes in a planet’s orbital speed remained exactly the same. Since Copernicus agreed with the philosophical objections to the equant–like some of his Islamic predecessors, he apparently believed celestial motions were driven by physical, crystalline spheres–he too sought to replace Ptolemy’s device. In a preliminary work, the Commentariolus, he employed an arrangement equivalent to Ibn al-Shatir’s. Later, in De revolutionibus, he reverted to the use of eccentric orbits, adopting a model that was the sun-centered equivalent of the one developed at Maragha. Could Copernicus have been influenced by the Maragha astronomers or by Ibn al-Shatir? No Latin translation has been found of any of their works or indeed of any work describing their models. It is conceivable that Copernicus saw an Arabic manuscript while he was studying in Italy (from 1496 to 1503) and had it translated, but this seems highly improbable. A Greek translation of some of the al-Tusi material is known to have reached Rome in the 15th century (many Greek manuscripts were carried west after the fall of Constantinople in 1453), but there is no evidence that Copernicus ever saw it. Scholars are currently divided over whether Copernicus got his method for replacing the equant by some unknown route from the Islamic world or whether he found it on his own. I personally believe he could have invented the method independently. Nevertheless, the whole idea of criticizing Ptolemy and eliminating the equant is part of the climate of opinion inherited by the Latin West from Islam. The Islamic astronomers would probably have been astonished and even horrified by the revolution started by Copernicus. Yet his motives were not completely different from theirs. In eliminating the equant, and even in placing the planets in orbit around the sun, Copernicus was in part trying to formulate a mechanically functional system, one that offered not only a mathematical representation but also a physical explanation of planetary motions. In a profound sense he was simply working out the implications of an astronomy founded by Ptolemy but transformed by the Islamic astronomers. Today that heritage belongs to the entire world of science.

By Owen Gingerich, Scientific American, April 1986 v254 p74(10).

Science and Islam are intimately linked. This sounds odd. First, because we normally think of religion as harmfully hostile to science. Wasn’t there a long and protracted war between science and Christianity? Did the Church not prosecute Galileo? But this “war” between science and religion was purely a western affair. There is no counterpart in Islam of such mutual hostilities. Second, science and technology are conspicuous in Muslim societies largely by their absence. It is this state of affairs that has led many – including at a recent seminar in Rome, George Carey, the former archbishop of Canterbury – to conclude that Islam is anti-science.

But nothing could be further from the truth. Islam not only places a high premium on science, but positively encourages its pursuit. Indeed, Islam considers it as essential for human survival.

The Koran devotes almost one-third of its contents to singing the praises of scientific knowledge, objective inquiry and serious study of the material world. The first Koranic word revealed to the Prophet Muhammad is: “Read.” It refers to reading the “signs of God” or the systematic study of nature. It is a basic tenet of Muslim belief that the material world is full of signs of God; and these signs can be deciphered only through rational and objective inquiry. “Acquire the knowledge of all things,” the Koran advises its readers; “. . . say: ‘O my Lord! increase me in knowledge”. One of the most frequently cited verses of the Koran reads:

Surely in the heavens and earth, there are signs for the believers;

And in your creation, and the crawling things He has scattered abroad, there are signs for a people having sure faith;

And in the alternation of night and day, and the provision God sends down from heaven, and therewith revives the earth after it is dead, and the turning about of the winds, there are signs for a people who understand. (45:3-5)

The sayings of the Prophet Muhammad reinforce these teachings. Islamic culture, he insisted, was a knowledge-based culture. He valued science over extensive worship and declared: “An hour’s study of nature is better than a year’s prayer.” This is why he directed his followers to “listen to the words of the scientist and instil unto others the lessons of science”.

The religious impulse propelled science in Muslim civilisation during the classical period, from the eighth to the 15th centuries. The need to determine accurate times for daily prayers and the direction of Mecca from anywhere in the Muslim world, and to establish the correct date for the start of the fasting month of Ramadan as well as the demands of the lunar Islamic calendar (which required seeing the new moon clearly), led to intense interest in celestial mechanics, optical and atmospheric physics, and spherical trigonometry. Muslim inheritance laws led to the development of algebra. The religious requirement of the annual pilgrimage to Mecca generated intense interest in geography, map-making and navigational tools.

Given the special emphasis that Islam placed on learning and inquiry, and the great responsibility that Muslim states took on themselves to assist in this endeavour, it was natural for Muslims to master ancient knowledge. At the instigation of powerful patrons, teams of translators lovingly translated Greek thought and learning into Arabic. But Muslims were not content with slavishly copying Greek knowledge; they tried to assimilate Greek teachings and applied Greek principles to their own problems, discovering new principles and methods. Scholars such as al-Kindi, al-Farabi, Ibn Sina, Ibn Tufayl and Ibn Rushd subjected Greek philosophy to detailed critical scrutiny.

At the same time, serious attention was given to the empirical study of nature. Experimental science, as we understand it today, began in the Muslim civilisation. “Scientific method” evolved out of the work of such scientists as Jabir Ibn Hayyan, who laid the foundations of chemistry in the late eighth century, and Ibn al-Haytham, who established optics as an experimental science in the tenth century. Medicine and surgery, as we know them today, evolved in the Muslim civilisation. Ibn Sina’s Canons of Medicine was a standard text in Europe until the 19th century. Many surgical instruments, such as scalpels, midwifery hooks for pulling out foetuses and instruments for eye surgery, were first developed by Muslims. From astronomy to zoology, there was hardly a field of study that Muslim scientists did not pursue vigorously or make an original contribution to.

The nature and extent of this scientific enterprise can be illustrated with four institutions considered typical of “the Golden Age of Islam”: scientific libraries, universities, hospitals and instruments for scientific observation (particularly astronomical instruments such as celestial globes, astrolabes, sundials and observatories). The most famous library was the “House of Science”, founded in Baghdad by the Abbasid ruler Caliph al-Mamun, which played a decisive role in spreading scientific knowledge throughout the Islamic empire. In Spain, the library of Caliph Hakam II of Cordoba had a stock of 400,000 volumes. Similar libraries existed from Cairo and Damascus to places as far off as Samarkand and Bukhara.

The first university in the world was established at al-Azhar Mosque in Cairo in 970. It was followed by a host of other universities in such cities as Fez and Timbuktu. Like universities, hospitals – where treatment was mostly provided free of charge – were institutions for training and for theoretical and empirical research. The Abodi hospital in Baghdad and the al-Kabir al-Nuri hospital in Damascus acquired worldwide reputations for their research output.

Similarly, there was a string of observatories dotted throughout the Muslim world; the most influential one was established by the celebrated astronomer Nasir al-Din al-Tusi, who developed the “Tusi couple”- a mathematical device that helped Copernicus to formulate his theory that the earth moved around the sun – at Maragha in Azerbaijan.

All this is, sadly, in stark contrast to the standing of science and technology in the Muslim world today. Apart from the notable exceptions of Abdus Salam, the Pakistani Nobel laureate, and Ahmed Zewail, the Egyptian scientist who won the Nobel prize in chemistry in 1999, modern Muslim societies have produced hardly any scientists of international repute. Scientific research has a very low priority in most Muslim states. The little that is undertaken is usually associated with defence and confined to developing nuclear or other weapons. Not a single university of international renown can be found in any Muslim country.

But things are about to change. A new movement is emerging dedicated to bringing science back to Islam. And these efforts begin with a frank admission: we cannot blame everything on colonialism and the west. As Building a Knowledge Society, the UN’s 2003 Arab Human Development Report, makes clear, a great deal of responsibility for the lack of science and technology in contemporary Islamic societies lies with Muslims themselves. The ground-breaking report blames authoritarian thinking, lack of autonomy in universities, the sorry state of libraries and laboratories, and underfunding in the Arab world. “The time has come,” it declares, “to proclaim those positive religious texts that cope with current realities.” In particular, the report calls for “reviving ijtihad and the protection of the right to differ”.

Ijtihad, or systematic original thinking, is a fundamental concept of Islam. It was the driving force behind the scientific spirit of Muslim civilisation. But the religious scholars, a dominant class in Muslim society, feared that continuous and perpetual ijtihad would undermine their power. They were also concerned that scientists and philosophers enjoyed a higher prestige in society than religious scholars. So they banded together – around the 14th and 15th centuries – and closed “the gates of ijtihad“. The way forward, they suggested, was taqlid, or imitation of the thought and work of earlier generations of scholars. Ostensibly, this was a religious move. But given that, in Islam, everything is connected to everything else, it had a hugely damaging impact on all forms of inquiry. The religious scholars thus buried scientific inquiry to preserve their hold on society.

It is now widely thought that science itself can play an important role in reopening the gates of ijtihad. So the revival of science in Muslim societies and the reform of Islam itself can proceed hand in hand. Similar thoughts are being echoed by the Organisation of the Islamic Conference’s standing commission on scientific and technological co-operation. The commission has argued that substantial increases in scientific expenditure and original work would not only improve Muslim societies, but would have a catalytic effect on Islamic thought. “Science played a key role in transforming Muslim societies in history; it can play the same role in transforming Islamic thought today,” says Dr Anwar Nasim, an adviser to the commission.

Dr Gamal Serour, professor and consultant in obstetrics and gynaecology at al-Azhar University in Cairo, agrees. “It was the neglect of science that plunged the contemporary Muslim world into poverty and underdevelopment,” he says.

During a recent visit to al-Azhar to make a Radio 4 documentary, I spoke to several scientists who expressed similar sentiments. Traditionally, the university concentrated on religious subjects. But now science is emphasised as much as religion. And the atmosphere of scientific inquiry and criticism in its classes and laboratories is bound to find its way into religious discourse.

Muslim societies have an emotional attachment to Islamic history. But their grasp of the true achievements of Muslim scientists is rather limited. Efforts are now under way in Turkey, Malaysia and Pakistan, as well as in some Arab countries, to introduce the history of Islamic science into school and university textbooks. In Britain, similar efforts are being made by the recently formed Foundation for Science, Technology and Civilisation. The foundation, which aims to popularise, disseminate and promote an accurate account of Islamic scientific heritage, has generated tremendous interest in the subject among Muslim students. Based in Manchester, and managed by a volunteer force of young Muslims, it maintains the popular website www.muslimheritage.com. The website, which claims to present a thousand years of missing history of science and technology, has become an invaluable educational forum for the Muslim community.

The wide-ranging Science and Religion in Schools Project (www.srsp.net), based at the Ian Ramsey Centre at Oxford University, aims to produce educational materials on Islam and science for GCSE and A-level students. The initial output of the project, which is led by John Hedley Brooke, professor of science and religion at Oxford, is being tested in a number of schools in Britain. Once its initial phase is over, the project will spread to other countries.

To be faithful to their scientific heritage, Muslims need to do much more than simply preserve the ashes of its fire; they need to transmit its flame. “The best way to appreciate the scientific heritage of Islam,” says Nasim, “is by building the scientific capacity of Muslim societies.” Muslims are now moving in the right direction. “We are beginning to realise that conscious efforts to reopen the gates of ijtihad and return to systematic, original thinking mean placing science where it belongs: at the very centre of Islamic culture,” Nasim declares.

By Ziauddin Sardar, published in NewStatesman, April 5th 2004.

Review – 1001 Inventions: Muslim heritage in our world: an exhibition at the Museum of Science and Industry, Manchester, UK, to 4 June 2006

IT still comes as a surprise to discover how many children (and their parents) think that modern science is a European event, starting with the Enlightenment. Perhaps those inclined to such Eurocentrism should be packed off to the north of England to see an ambitious exhibition. Teasingly called 1001 Inventions, it may go some way towards filling in what the curators call “1000 years of missing history” by showing the role of Islamic-era science in shaping the modern world.

It might also help see off easy talk of “civilisations in collision”. The fact is that by the 12th century the Islamic empire covered a swathe of the world from Spain to Indonesia and, as with all civilisations, expansion drove scientific excellence. The exhibition captures a time when states governed by sharia law no less produced world-class innovation by scientists and translators who were Christian, Jewish, Muslim and Zoroastrian.

As with modern science, much of their research was dictated by practical need. One catalyst for developing clocks, for example, was the need for mosques to announce accurate times for the five daily prayers. Similarly, administering a large empire required postal systems, good maps and surveying techniques, research into common diseases, intensive farming and irrigation – not to mention more effective weapons of war. It also drove serious amounts of fundamental research into astronomy, chemistry and mathematics.

There were also breakthroughs that were, just as they are today, pure serendipity. One of my favourites is the story of coffee. Discovered accidentally by a livestock farmer from Ethiopia, it was embraced by the Sufis of Yemen to help them stay awake at night, and brought to London in the 17th century by a Turkish merchant. Even the word derives from the Arabic kahwa. Arabic was very much the language of culture, administration and research. Most strikingly, as the exhibition shows, some scientific English words have Arabic roots: chemistry (kimia), algebra (al-gabr), and alkali (al-qaly).

This is all excellent. But what 1001 Inventions doesn’t do is explain what happened next, and why there is so little highquality science and learning in Muslim countries today. Indices of patents and research publications make it clear that countries with mostly Muslim populations rate poorly for generating new knowledge. They have produced just two science Nobelists: Egypt’s Ahmed Zewail for chemistry and Pakistan’s Abdus Salam in physics, and even they won their honours at western universities.

Today, Islam has a record number of followers: one-fifth of humanity is Muslim. Moreover the Koran is rare among religious texts in explicitly telling readers to go learn, study and think about the nature of the world around them. If Islam inspired great learning in the past, why not now?

Perhaps one answer is crudely financial. Science needs money, but today’s Muslim states spend on average 0.2 per cent of GDP on research and development, compared with a developed-world average of more than 2 per cent.

A second answer lies in the fact that Islam’s scientists of old were aware that science is a process. They understood that innovation is underpinned by knowledge of what happened before, and were voracious consumers of knowledge from ancient Greece, for example. Today, knowledge of the latest research is found in Europeanlanguage scientific journals. In Muslim countries, only a few elite universities have good access to the top journals, and translations from European languages into Arabic are pitifully rare.

Lack of encouragement for critical thinking is also a big factor. Scholarly debate and criticism flourished in the old Muslim world: it was possible to publish many things which today would result in an appointment with the censor – or even prison or exile. High-quality research needs a level of freedom to think, speak and publish that does not exist in many Muslim countries.

Commitment to a faith can be a strong catalyst for scientific excellence, but perhaps the overriding message of 1001 Inventions is that the freedom to push boundaries and to challenge dogma is an irreplaceable ingredient.

By Ehsan Masood, published in New Scientist

Ehsan Masood is a writer specialising in science in developing countries. See www.1001inventions.com for further information on the exhibition

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Ibn al-Haytham (10 to 11th century A.D.)

The turn of the first millennium was a time of intense research in mathematics, physics, and astronomy. One scientist active and productive in all of these fields was Ibn al-Haytham, called by his successors of the 12th century “Ptolemy the Second.”

Ibn al-Haytham, also known as Alhazen (the Latin transliteration of his first name al-Hasan), was born in Iraq, most likely in Bassorah, in the second half of the 10th century. He arrived in Cairo under the reign of Fatimid Caliph al-Hakim, a patron of the sciences who was particularly interested in astronomy. Ibn al-Haytham proposed to the Caliph a hydraulic project to control the flow of the Nile—an early Aswan dam. The Caliph refused, but al-Haytham continued to live in Cairo, in the neighborhood of the famous University of al-Azhar, until his death after 1040.

Ibn al-Haytham was born after a century and a half of intense research in mathematics, astronomy, optics, and other physical sciences. Scholars such as Banu Musa, Thabit ibn Qurra, Ibrahim ibn Sinan, al-Quhi (1), and Ibn Sahl measured curved surfaces and solids, invented new geometrical methods, and rediscovered the method of integral sums. They combined mathematical and observational astronomy and formulated the first rigorous geometrical theory of lenses.

Beyond the biographic details above, little is known about Ibn al-Haytham’s life. But his contribution to science is not in doubt. His work on optics, which includes a theory of vision and a theory of light, is considered by many to be his most important contribution, setting the scene for developments well into the 17th century. His contributions to geometry and number theory go well beyond the archimedean tradition. And by promoting the use of experiments in scientific research, al-Haytham played an important part in setting the scene for modern science.

The ancient bibliographers cite at least 96 scientific titles under al-Haytham’s name; more than 50 survive. Half of his writings are on pure mathematics; 14 on optics, including the authoritative and voluminous Kitab al-Manazir (Book on Optics) (2–4); and 23 on astronomy. He also wrote about philosophy of mathematics, statics, hydrostatics, and various other topics, grappling with all mathematical sciences of his time except algebra.

Few mathematical and scientific writings in the Middle Ages have been as influential as those of Ibn al-Haytham, whose works were translated into Latin, Italian, and Hebrew. The Latin translation of his Book on Optics and On Parabolic Burning Mirror provided a basis for centuries of research in optics. His mathematical works influenced Roger Bacon, Frederick of Fribourg, Kepler, Snell, Descartes, and Huygens and many others.

In one of his many geometrical studies, al-Haytham calculated the volume of solids such as the paraboloid and the sphere. He used the method of integral sums and generalized one of the propositions in Euclid’s Elements. In another study, he set out to prove that among planar figures with the same perimeter, the disk has the greatest area, and among solids with the same total surface the sphere has the greatest volume. To study these problems, Ibn al-Haytham formulated the first known theory on solid angle, which leads to double integrals (1, 3). It was the most advanced mathematical work of his time, combining a projective method and an infinitesimal method.

Some of Ibn al-Haytham’s most important geometrical writings deal with the theory of conic sections. Apollonius’ Conics, written in the 3rd century B.C.E., were translated into Arabic in the 9th century A.D., but the last (the eighth) book had long been lost in the original Greek. Ibn al-Haytham devoted a substantial treatise to the reconstruction of this lost book. He also used conic sections to construct solid figures known since antiquity, such as the regular heptagon, as well as new ones (1).

Earlier mathematicians had concentrated on isolated problems of geometrical construction. Ibn al-Haytham showed that geometrical figures could be built systematically with the help of intersections of conic curves, and that these curves could be constructed from in a pointwise fashion and could also be drawn continuously. His studies of pointwise geometrical transformations led him to introduce the notion of continuous movement into geometry. He went on to develop the first concept of space based on geometry (1).

Ibn al-Haytham redirected geometrical research and obtained many results attributed by historians to his successors of the 17th century. But his work in optics was no less revolutionary. He changed the meaning of the term optics, and established experiments as the norm of proof in the field. The revolution entailed his division of optics into two parts: a theory of vision and the associated physiology of the eye and psychology of perception, and a theory of light that includes geometric and physical optics.

There had been a doctrinal contest between “extramissionists,” who postulated a visual ray produced by the eye, and “intromissionists,” who held that objects sent off forms or totalities that emanated from the visible under the effect of light. Ibn al-Haytham proposed instead that rays emanate toward the eye from every point of a visible object. Looked at thus, the eye becomes a simple optical instrument. Ibn al-Haytham then explained how the eye perceives the visible with the help of the rays emitted from all points.

His optical theories rested on qualitative laws and quantitative rules derived from experiments, which he performed with an instrument that he designed and built himself. On the basis of these experiments, al-Haytham was the first to propose a camera obscura. He also discovered spherical aberration, and gave the correct explanation of the moon’s light. Henceforth, experimental control was viewed not only as a general practice of investigation but as the norm of proof in optics, and more generally in physics.

By Roshdi Rashed, published in Science  02 Aug 2002: Vol. 297, Issue 5582, pp. 773 DOI: 10.1126/science.1074591

References

1. R. Rashed, Les Mathématiques infinitésimales du IXe au XIe siècle (al-Furqan Islamic Heritage Foundation, London, 1993 to 2002), vol. 4.
2. M. Nazif, Al-Hasan ibn al-Haytham, Buhuthuhu wa kushufuhu al-basariyya (Nuri Press, Cairo, 1942 to 1943), vol. 2.
3. R. Rashed, Ed. Encyclopedia of the History of Arabic Science, 3 vols (Routledge, London/New, 1996).
4. A. I. Sabra, The Optics of Ibn al-Haytham: Books I-III on Direct Vision (Warburg Institute, London, 1989).

Ibn Rushd (1126—1198), was a native of Cordoba, in Andalusian Spain, and his work covered a broad range of topics in medicine, science and philosophy. He would be known to Thomas Aquinas and other European scholars in the next century as Averroes. And Ibn Rushd was—thanks to Aquinas—destined to have a much greater impact on the European mind than he ever did on Islamic culture.

First, a little context:

The wanderers who came to Spain and Sicily from Italy, France, the British Isles in the 11th and 12th centuries, did not know it at the time, but their rediscovery of scientific and medical treatises, would, long before Gutenberg and the printing press, lead to Europe’s first information revolution.

This revolution was triggered in no small part by a simple demand: for better technology. Or more precisely, a demand for better instructions on how to use technology.

Especially the tools of astronomy.

These tools included carefully written tables with precise recordings of celestial movements, and books of planetary theory—the most important of which was the great work of Claudius Ptolemy: The Almagest.

If you were a monk in France or Italy, intent on projecting the most accurate dates of each year that Easter and other holy days should fall, the only way to get your hands on the most reliable copies of these texts, meant finding a good translation from Arabic (or Greek).

And the only way to acquire these … was to hit the road.

Such was the origin of the medieval ‘translation movement’, an enterprise that largely took place in Spain and in Sicily between the years 1130 and 1275.

But what started out as a search for better translations of astronomical and astrological guides, led first to the discovery of Arabic treatises on the astrolabe and the astronomical tables of the great Muslim astronomer al-Kwarzimi who worked in Baghdad in the ninth century.

This led in turn to the discovery of other Arabic textbooks on medicine, philosophy and science by figures such as Ibn al-Haythem and al-Biruni.

As Arab philosophers and doctors had long adopted the ancient works of Aristotle, scholars from Europe found themselves rediscovering the Greek philosopher’s source texts as well, source texts that for centuries they had only known from references in other works that merely summarized them—and often not accurately.

Back to our hero: Ibn Rushd was writing at the height of this translation movement, although he never came in contact with the scholars in the northern cities of Spain, lately recaptured by Christian dukes.

Born in 1126, Ibn Rushd came from a prominent family of judges in Cordoba. He was educated as a physician, but felt strongly drawn to the study of pure philosophy.
A fortuitous meeting with the Caliph of Cordoba, Abu Ya’qub Yusuf, led to a full time position for the young doctor. Yusuf also enjoyed the study of philosophy in spite of the more conservative attitude that the Almohad dynasty had toward the subject, and he employed Ibn Rushd to write new commentaries on Aristotle to clarify all the major works. Many had been previously translated into Arabic from earlier Syriac versions, but Yusuf found them difficult to understand.

This period, the last quarter of the twelfth century, was the time in which Ibn Rushd wrote his most influential treatises, adopting a rationalist point of view—not unlike the view (I discussed recently here) propounded by Adelard of Bath and William of Conches—that would have such profound influence on the pursuit of science in the later Middle Ages–namely, that nature operated according to its own autonomous laws, and that these laws could be fruitfully explored in their own right.

After the death of Abu Ya’qub Yusuf, the Caliph’s son al-Mansur continued to support Ibn Rushd for a few years, but by the 1190s, more conservative members of the Islamic schools began to attack the philosopher, and on the excuse of some questionable charges made against him, Ibn Rushd was, at the age of 69, banished from Cordoba to the nearby village of Lucena.

Though he did not suffer execution, his books were banned, and indeed most were eventually burned—though not all. He was allowed to return to Cordoba, one year before he died in 1199 when he was 73. But he was not destined to have anything like the influence on Islamic thought that earlier masters such as Ibn Sina and al-Ghazali had.

Ibn Rushd was never to know the honor and esteem in which his works would be held by his country’s enemies to the north of the Pyrenees. When Aquinas wrote his Summa Theologica in the latter half of the thirteenth century, he referred to Ibn Rushd as “The Commentator.” When it came to any discussion of Aristotle, Aquinas rarely failed to reference Ibn Rushd’s assessment of any question—even when he disagreed with it.

The Latin Christians, for example, believed Ibn Rushd espoused a doctrine of ‘double-truths’, whereby philosophy and theology allow one to adopt two contradictory positions, for example about the eternity of the universe. This was roundly condemned.

But as it turns out, the source of this assessment of Ibn Rushd was based on a faulty understanding, due to a lack of access to his complete works.

One of the main reasons that led to such a deep misunderstanding, Nidhal Guessoum writes in the introduction to his book Islam’s Quantum Question, is the simple fact that two of the three books that contained Ibn Rushd’s essential views were never translated into Latin or later to European languages until the twentieth century. “Only his commentaries on Aristotle’s and other great Hellenistic works were known to the West until recently.”

There’s another twist to this tale as well.

As historian Diarmaid MacCulloch notes in his book Christianity: the First Three Thousand Years:

Scholasticism was disputatious, skeptical, analytical, and that remained characteristic of Western intellectual exploration long after most Western intellectuals had parted company with scholasticism itself. And it had its precedent in the method used in Islamic higher education. It is a happy irony that one of the great expressions of the cultural unity of the Latin West, evolved at the age of the Crusades, had its roots in the culture which the West was trying to destroy.” [p. 399]

For an excellent short biography of Ibn Rushd, check out Averroes, written in 2001 by Majid Fakhry, Emeritus Professor of Philosophy at the American University of Beirut.

By John Farrell, published in Forbes, June 30^th 2014.

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The first heritage regrouped the savoir-faire, often ingenious, that were practised and transmitted, orally and on initiation in the world of corporations, particular professions or activities. This was the case of the knowledgeable who dealt with generally, by commodity, to be classed in the following groups: military or civil technology (water based systems, automations), chemistry (treatment of glass and colours, cosmetics, metal works), administration and calculations for transactions, geometry, land surveying and decoration etc. The comparative study of these methods and techniques reveals the diversity of their origins and their links with different cultures in which they occurred.

The second heritage comprises of the theories or applications of knowledge which have been preserved and circulated in writings. They were produced generally in Greece, India, Persia, Mesopotamia and to a lesser extent the Iberian peninsula. The results of their enquiries have not been the same all over: a great part of Greek sciences were hypothetically deduced, those of India, Persia and Mesopotamia were due to algorithmic and experimental methods.

This diversity had the same goal, that of establishing the results and making tools, characteristic of the first scientific footsteps in Islamic countries were disparate elements of knowledge coming from diverse cultural horizons, having firstly been juxtaposed before making the object arising from a prolific amount of suggestions and giving a unified expression across the Arab world. It is also from the IX century, that a network of scientific establishments were set up, in towns such as Baghdad and Damascus at the centre of the Empire, Samark and in central Asia, Kairouan au Maghreb abd Cordoba in the Iberian peninsular. From the end of the X century, its centres would come together with others, all just as dynamic, such as Rayy in Iran, Cairo in Egypt and, a little later, Toledo, Saragossa and Marrakech in the Muslim East. It is important to remember that, in all these centres, science was practised in the same fashion, according to a norm that you could describe as “universal”, that is to say did not depend on any specific denomination, ethnic or cultural identity, apart from the unity of the language of expression, that we have already evoked, and that is the only justification for the mode of expression of “Arabic science” to design this together in practice.

After a period of more than a century where this was known, from the first heritage, which was to work in different sectors of activity in the Islamic city, the need to access the contents of the second heritage, starting by formulating and improving some of the first translations, which were financed by the caliphs and other high persons of the State. But, from the end of the IX century, these initiatives experienced a great amplification –right through to the middle of the X century- carried by civil members of the society not necessarily belonging to the courts of caliphs and princes. As this society was cosmopolitan, multi-denominational and multi-cultural, it is not surprising that this long-time activity of translation reflecting its diversity (even if the Arabic libraries note the strong participation of the Christian communities increasingly in the activity of translation). It must, finally, be added, about this phenomenon, that its duration is explained by the development, in certain groups of society, of a real demand. The member of these groups were generally less well off than the patron caliphs but relatively more numerous. Amongst them, it is interesting to note the presence of eminent scientists such as al-Kindi (died circa 873) and the brothers Banû Mûsâ (IX century).

These translations concern all the scientific and technical domains as were practised in the previous civilisations: astronomy and Indian medicine written in Sanskrit or Persian writings in pehlevi, texts in Latin dealing with astrology and medicine, treatises of nabatéen agriculture. . . To this modest amount, you must add, much more importantly, produced within the framework of Greek scientific and philosophical tradition since the V century B.C. It is this material, which after translation, has added to or impregnated all the disciplines practised in Islamic countries, even those who have originated contributions to the new civilisation. There was, in the first place, mathematicians, with their different orientations, which were designed from the end of the III century: numerical theories with Pythagoras and Nikomacheia, plane and cubic geometry of Euclid, conic geometry with Apollonius, and geometry of measurement with Archimedes. In close relation with his disciples, he also studied astronomy, (models of planets, astronomical tables, instruments for measuring) and physics (statics, hydrodynamics, optics). At the time there was all the sciences as one considered them as not Arts; Greek heritage: medicine (physiology, anatomy, pharmacopaeia), mechanics (ludic or utilitory) chemistry (experimental or esoteric), botany, zoology, agriculture, etc.

As the discoveries and innovations in this book unfold themselves, they are divided into six categories, it seems practical to describe them, briefly, the development of each one is placed in order to show its original contribution which is the object of this book to show the general development of the science to which they refer.

Mathematics started off in Islamic countries, from its practical aspects, which refer to the different economic needs (accounting, commercial transactions), justice (division of inheritances) and arts (architecture, decorations). Some ancient chapters have been reactivated, such as the procedures for mental calculation, the Indian arithmetical procedure based on the system of positional numbers (with the zero), geometry tools to make the architectural shapes and to copy the figures in two dimensional decorations. It is within this frame-work that they have valued and perfected the geometric steps and techniques (symmetry, rotations, calligraphy, and that of the mosaic).

The second great orientation of mathematics is purely theoretic in the sense where the researchers wanted to solve problems that their Greek predecessors had stumbled on or new problems that they had been set, or other sciences had asked them to solve. Sharing the results and the steps that were inherited from the Ancients, they started off by commenting on them, sometimes criticising them, then reflecting on the foundations of their discipline, to elaborate on the thesis, before developing them in new ways. Certain ones, as algebra and trigonometry, were extensions and enrichments of old practices. Others, as combination analysis and magic squares were suggested then favoured by a cultural context.

From the start, astronomy had the attention of the State. Certain caliphs not only financed the translations but also made certain orders to the leading astronomers: the compiling of calendars and geographical maps, the determination of the direction of Mecca, calculation of the times for everyday prayers. Always in response to the needs, this time in response to particular people (merchants, pilgrims, men of science), interest in ancient instruments (planispheric astrolabes, solar bodies) which were redressed and perfected, such as was described in the chapter “ from al-Khwârizmî to al-Zarqâlî, the astrolabe became the king of instruments”. Later, and in the scope of optimisation (lightening instruments) new instruments were invented (the universal astrolabe, sines).

But astronomy had had an important theoretical wing that one knew less and had perhaps constituted a decisive stage in the development of this discipline, even across some of its checks. In this domain, the work concerned the realisation of numerous astrological tables for all uses, the conception of models of new planets to replace those of Ptolemy which, which having reigned for centuries in astronomy were no longer considered as satisfactory. They even had, at the beginning of the XI century, in central Asia, discussions on the theory of the Earth’s rotation on its axis and that of its rotation around the sun. These hypothesises were finally abandoned, not for theological or philosophical reasons, but for reasons judged as scientific in their time.

In physics, and in an extension of Greek traditions, four disciplines were particularly developed: statics, dynamics, hydro-dynamics and optical. Three of the contributions as presented in this book illustrate the vitality of these domains: the scales of wisdom of al-Khâzinî (XII century), the theory of light of Ibn al-Haytham (died 1041) and the rainbow theory of al-Fârisî (died 1319). It is important to state that the contributions were not the end of the investigations that had started, for certain among them, at the start of the IX century. To take for example optics, the sources we learn first researched concerned mirrors, which interested first of all the military, because they could be used to start fires and so burn the fleets and fortresses of the enemy. Then there were the theoretical preoccupations on the technical aspects. Led by al-Kindî, Ibn Sahl (X century) and their two successors; these studies concerned the physiology of optics, the laws of reflection and refraction and certain light phenomena that can be seen in the sky.

Arab medicine, solidly anchored in the galénic medical tradition, seems to have had trouble to free itself from its ancient conceptions and convictions. But this did not impede the innovation in certain other domains. Its most significant contribution, by amplitude and duration, has been the setting up of a medical hospital, financed firstly by State representatives then by members of the society with the help of waqf (Assets belonging to the state that can’t be sold). Certain of these hospitals even had sections for the mentally ill. They also had advances in anatomy (knowledge of certain bones in the human body), in the diagnosis of certain illnesses, in the practice of surgical instrumentalisation, in particular with the contribution of Andalusian az-Zahrâwî (XI century), and in the elaboration of great medical synthesis, such as those of Ibn Sîna (Avicenne, died 1037) and of ar-Râzî (Rhazes, died 935), who directed medical teaching in Europe until XVIIth century. But it was in physiology, with the discovery of the small circulation of blood, which is described in the chapter “the discovery of pulmonary circulation by Ibn al-Nafîs”, that a new road was followed. Unfortunately, this was abandoned by the medical community of the era (XIII century) which stayed faithful to the Galien theory, confirmed by Avicenne.

In mechanics, it was in response to civil and military needs that the works of Héron of Alexandria, Archimedes, and Philon de Byzance were translated into Arabic. After having adapted and perhaps bettered their contents the Islamic countries’ mechanics set out to innovate, in particular automations and hydraulic systems. It is in this last domain that they updated and applied the conical valve, the camshaft, the piston and the crankshaft. Certain original ideas were already thought up in the book of the brothers Banû Mûsâ. But it was with al-Jazarî (died in 1206) that you hear the most numerous and significant innovations, as those that we presented here, in the chapter “the al-Jazari (hydraulic) water pump”.

Chemistry with medicine is the discipline, which, it appears, the best to survive the decline of the ancient civilisations of the eastern Mediterranean. This explains its precocious reactivation in the sphere of the new civilisation. in effect, from the start of the VIII century, it has assisted with the constitution of a solid tradition in this domain with, as the undisputable animator, the famous Jâbir Ibn Hayyân (Geber), whose works together with those of his disciples, abound in original results. after them, different chemical practices were developed, such as calcination, sublimation, purification, and above all distillation, which had substantial progress, as is shown in the chapter “Introduction to Arab alchemy”. Always in the framework of the theory of the four elements inherited from the Greeks and refined by Jâbir, these works added to the description of substances not previously known about, the setting up of mineral acids and the elaboration of new classifications of analysed products. Among the scientists who have taken part in these advances are al-Kindî and Abû Bakr ar-Râzî.

One part of the contributions that we are going to present briefly has started to circulate, relatively quickly, outside the borders of Islamic countries, in particular towards Europe. The figures called “Arabic” and the astrolabe arrived in the south of Europe at the end of the X century. Some works of medicine published in Baghdad and at Kairouan have been transcribed in Latin by Constantine the African in the second half of the XI century. But you have to wait until the start of the XII century for this activity of translation (from Arabic to Latin and Hebrew) to grow. At Toledo and Palermo, where this phenomenon had its seat, dozens of young Europeans freshly ‘arabised’ were engaged in this with a passion, supported and financed by enlightened men of the church and, later, by the Castilian king Alphonse X the wise. Their work allowed access for men of science and practitioners to the rich inheritance in origin Greek, Indian and Arab cultivated and elaborated on in the Muslim world since the IX century. The assimilation of these rich contents opened the way to new investigations which were, in their turn, contributions to modern day science.

In conclusion, it remains for us to make a few remarks on the nature of the scientific activities of Islamic countries, in the sphere of which the discoveries presented here have been realised, and on the actual gateway of these discoveries.

It should be first of all stated that as the scientific practices which are going to be briefly described here, during each of their phases, in a context of intercultural exchanges, which are never contradicted. The scientific historians have even observed the totally non religious character of these practices, which may be at the level of their contents, of their formation, of their approach, or discussion which has been produced on the scientific production itself. This aspect only serves to reinforce the universality of the science produced in Islamic countries, favouring, just the same, their circulation in Muslim cultures and in Christian cultures of medieval Europe, and this in spite of the religious antagonisms that are sometimes expressed from the advent of Islam and which are deepened from time to time, particularly, at the time of the crusades (end XI – end XII centuries).

As to the discoveries presented here, they are certainly constituted on a time, largely well passed, in the elaboration of science. But they are more than that. In effect, by the motivations which have animated their authors, by their approaches and their goals that they have met, they witness, further than the specificity of each of them, from what appears to men of science from different eras and cultures: an instant curiosity, patient observation of studied phenomenon, taking things into account, with a critical attitude, in relation to your predecessors, obstinate research of the truth, comforted by the unbreakable faith in the capacities of science to surpass all obstacles. It is this lesson, finally very modern and universal, that the authors of this book have read in the contributions of some of these Islamic savants, and that they want to render it accessible to the teachers and their pupils.

Ahmed Djebbar

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Dallal is a historian of science who has specialized in Arab-Islamic heritage. He is currently provost of the American University of Beirut (AUB), having gone there in 2009 from Georgetown University in Washington, DC, where he served as the chair of the Department of Arabic and Islamic Studies. He had previously held academic appointments at Stanford University (2000-03), Yale University (1994-2000), and Smith College (1990-94).

The AUB short biographical sketch of Dallal (dead link) describes this new important book, which is based on the Dwight H. Terry lectures that he delivered at Yale University in February 2008, as “trac[ing] the historical delineations between scientific knowledge and religious authority in Muslim societies.”

I cannot reproduce here my long review of the book, for copyright reasons, and the full text is only available for subscribers on the JIS website; the journal makes an “extract” available here, but it is only two paragraphs long.

The first paragraph is the opening of my review:

I often describe the field of ‘Islam and Science’ as a cultural and intellectual space in three dimensions: a) the historical developments of science during the Islamic civilization; b) the conceptual discussions of conflict, harmony, or separation between Islam and modern science; c) the issues of practical application of science in Islamic life (ranging from the calculation of prayer times to in vitro fertilization and euthanasia). Ahmad Dallal’s book, though rather concise, manages to encompass all three dimensions in a grand narrative and with a bold thesis. Indeed, while surveying the major trends of scientific activity from its emergence in the early Islamic civilization to the present time, he takes special interest in at least one specific case of application of science and intersection with religious rules (the direction of the qibla), and by the last chapter he dabbles in the conceptual issues raised by Darwinism and ‘the new astronomy’ (i.e. the heliocentric revolution).

But for the benefit of the readers of Irtiqa, let me add a couple of paragraphs (as a bonus) to help give an idea of the book’s thesis and the extent to which Professor Dallal has been successful in convincing his readers about it.

The thesis he is attempting to prove, however, is never stated clearly, but any careful reader will figure it out, especially since Dallal attempts to draw conclusions toward it at the end of each chapter. What he tries to show is that science in the Islamic civilization slowly but successfully was extricating itself from the double embrace of (Aristotelian) philosophy and religion. Dallal clearly believes that any link, whether strong or weak, made between science and religion or philosophy is counterproductive and regressive. He writes: “Yet while religion dominated the moral sphere and claimed a higher rank there […], it did not exercise an epistemological hegemony over science” (p. 147); “[w]hen Muslims were the main producers of science in the world, they did not advocate wedding science and religion” (p. 170).

…

In summary, this is an important book, with a grand narrative and a bold thesis. It is very well written, though one can find weaknesses, biases, or short-cuts here and there. It is an important book precisely because it proposes a viewpoint: separation between science and religion, and even philosophy, is not only the correct course to follow but also the historical path that Muslim thinkers took over the global Islamic history. This thesis needs to be discussed and examined in light of the historical record, a fuller treatment which looks at many more viewpoints and avoids any swift generalizations. Dallal is still to be applauded for having produced an essay which forces us to think and argue the merits of his views.

By Nidhal Guessoum, published in Irtiqa, August 1st 2011.

By Ehsan Masood

As we celebrate Darwin, let’s not forget the unsung champions of evolution from the Muslim world

Last month, scientists from around the world partied into the small hours on the 200th anniversary of the birth of Darwin.

But as we celebrate the work of one of the most influential scientists ever, let’s take a moment or two to remember others who contributed ideas in the history of evolutionary thought. Many came from Britain as well as other countries in Europe. Others came from further afield, and their writings are increasingly coming to light thanks to the painstaking work of historians of science, and historians of ideas.

One of them is an East African writer based in Baghdad in the 9th century called al-Jahiz. In a book describing the characteristics of animals, he remarked:

“Animals engage in a struggle for existence, and for resources, to avoid being eaten, and to breed.” He added, “Environmental factors influence organisms to develop new characteristics to ensure survival, thus transforming them into new species. Animals that survive to breed can pass on their successful characteristics to their offspring.”

Or there’s Muhammad al-Nakhshabi, a scholar from 10th century central Asia. He wrote: “While man has sprung from sentient creatures [animals], these have sprung from vegetal beings [plants], and these in turn from combined substances; these from elementary qualities, and these [in turn] from celestial bodies.”

In their excellent Darwin’s Sacred Cause: Race, Slavery and the Quest for Human Origins, Adrian Desmond and James Moore describe how Darwin and his family were influenced by the anti-slavery movement, and they explore the extent to which these ideas, in turn, influenced his own thinking – especially on the idea of the connectedness of humanity.

A parallel line of argument can also be found from a Spanish philosopher from the 12th century. His name is Muhammad ibn Arabi and he developed an idea that his translators called the “unity of existence”. He believed that all living matter is connected. And many commentators now think that this was his way of showing that within humanity, there can be no outsiders or “others”.

These ideas were later taken up in the writings of Indian-born philosopher-poet Muhammad Iqbal in the early 20th century. We also know that Iqbal had been reading Darwin and wanted to find a way of synthesising the latest ideas from biological science with earlier Islamic-era philosophy. Iqbal today is revered throughout South Asia and also happens to be Pakistan’s national poet.

Why is it important to emphasise links between Darwin, and thinking on evolution in other cultures?

One reason is that in many developing countries today, Darwin – and by extension evolution – are seen as being in the service of imperialism. This is partly because of the period in which Darwin lived and worked, but also because of a perception that Darwin’s ideas were used by colonialists to provide “scientific” justification for empire.

Another reason comes from the rise of creationism. I’ve just finished work on a new documentary series for BBC radio 4 on science and Islam in the modern world. One thing I didn’t expect to find was the extent to which creationism poses a risk to what is otherwise more encouraging news: that after decades of neglect, interest and investment in science and learning in Islamic countries is on an upward trajectory.

Many countries are building more universities and opening doors for young people to embark on PhDs. Progress, however, will be slower if more start believing that scientific knowledge can be found in the pages of sacred texts; or if they devote time and energy getting sucked into anti-evolution campaigns.

Instead, if today’s young scientists could just take a peek into the history of science in Islamic cultures, they would see a respectable tradition of thinking, debate and argument on the origins of life and the evolution of species.

The irony in all this is that creationism did not exist as a significant movement during the heyday of Islamic civilisation. Back when Baghdad was a centre for advanced learning, scientists did not spend hours examining passages of revelation to see if they compare with observed knowledge of the natural world.

Instead, they went out and tried to discover things for themselves.

Islam and Science is on BBC Radio 4 at 9pm on Monday 2 March. It is also available to download on BBC i-player.

By Ehsan Masood, published in The Guardian, March 1st 2009.

Interest in optics began in antiquity. The Babylonians, Egyptians and Assyrians all used polished quartz lenses. The basic principles of geometric optics were laid down by Plato and Euclid. They included ideas such as the propagation of light in straight lines, and simple laws of reflection from plain mirrors. The earliest serious contribution from the Islamic world came from ninth-century Arab scholar Ya’qub ibn Ishaq al-Kindi.

As a young man, Ibn al-Haytham received an excellent education and was widely noted as a mathematical and scientific prodigy. Frustrated by his administrative duties working in a government post in the vast Islamic Empire — which at the time stretched from India to Spain — he was sacked owing to real or, as some speculate, faked mental illness.

Sometime during the first decade of the new millennium, he proposed an ambitious project to dam the Nile. He was invited to Egypt by the Fatimid caliph al-Hakim bi’amr Illah. However, on seeing the scale of the task, Ibn al-Haytham quickly realized that it was beyond him. He was promptly imprisoned in Cairo for wasting the caliph’s time.

Far from cowing him, the decade of imprisonment granted Ibn al-Haytham the seclusion to think and write, particularly on optics. After his release around the year 1020, he began working at a prolific rate, carrying out a series of famous experiments on the nature of light. For example, using a camera obscura, he proved that light travels in straight lines; he also mathematized the fields of catoptrics (reflection of light by mirrors) and dioptrics (refraction of light through lenses). This huge body of experiment and theory culminated in his Book of Optics.

This treatise can be regarded as a science textbook. In it, Ibn al-Haytham gives detailed descriptions of his experiments, such as exploring how light rays are reflected off plain and curved surfaces. He includes the apparatus he used, the way he set it up, the measurements and his results. He then uses these observations to justify his theories, which he develops with geometrical models. He even urges others to repeat his experiments to verify his conclusions. Many historians of science consider Ibn al-Haytham to be the first true proponent of the modern scientific method.

The work can be roughly divided into Books I, II and III, devoted to the theory of vision and the associated physiology of the eye and the psychology of perception; and Books IV to VII, covering traditional physical optics. The work’s most celebrated contribution to science is its explanation of vision.

At that time, scholars’ understanding of the phenomenon was a mess. The Greeks had several theories. In the fifth century bc, Empedocles had argued that a special light shone out of the eye until it hit an object, thereby making it visible. This became known as the emission theory of vision. It was ‘refined’ by Plato, who explained that you also need external light to see. Plato’s student Aristotle suggested that rather than the eye emitting light, objects would ‘perturb’ the air between them and the eye, triggering sight. Other philosophers around this time, including Epicurus, attempted a form of ‘intromission theory’ of vision (light entering the eye from outside), but it was Plato’s theory that was given a mathematical basis by Euclid, who described light rays emerging in a cone from the eye. Several centuries later, Ptolemy expanded on this idea.

Early Islamic scholars such as al-Kindi and Hunayn ibn Ishaq favoured a combined emission–intromission theory. They posited that the eye sends out light to the observed object, which then reflects the light back into the eye.

It took the genius of Ibn al-Haytham to finally resolve the issue. He argued that if we see because rays of light are emitted from the eye onto an object (Plato and Euclid’s ‘sight rays’), then either the object sends back a signal to the eye or it does not. If it does not, how can the eye perceive what its rays have fallen on? Light must be coming back to the eye, and this is how we see. But if so, what use is there for the original rays emitted by the eye? The light could come directly from the object if it is luminous or, if it is not, could be reflected from the object after being emitted by another source. Rays from the eye, decided Ibn al-Haytham, are an unnecessary complication.

He also went further than anyone before in trying to understand the underlying physics of refraction. He argued that the speed of light was finite and varied in different media, and he used the idea of resolving the path of a light ray into its vertical and horizontal components of velocities. He carried out all his work geometrically, and introduced many new ideas, such as the study of how the atmosphere refracts light from celestial bodies.

Later Islamic scholars, including the thirteenth-century Persians Qutb al-Din al-Shirazi and Kamal al-Din al-Farisi, extended the Optics. Al-Farisi, who wrote The Revision of the Optics (Tanqih al-Manazir), used geometry to arrive at the first correct mathematical explanation of the rainbow (at the same time as, but independently of, the German scholar Theodoric of Freiberg).

“Many historians of science consider Ibn al-Haytham to be the first true proponent of the modern scientific method.”

The Book of Optics was first translated into Latin in the late twelfth or early thirteenth century, as De Aspectibus. The English philosopher and empiricist Roger Bacon then wrote a summary of it, as did his Polish contemporary Witelo. It was soon being cited across Europe. Among the many ideas taken up by Ibn al-Haytham’s Latin-reading disciples was that pure light was not visible, and that its job was simply to allow us to see colour. Even Kepler, who studied Ibn al-Haytham’s work, thought this; it took Newton to describe light as itself being made up of different colours. (Other erroneous ideas in Optics include a repetition of Ptolemy’s mistaken law of refraction, and an incorrect understanding of reflection as a more intense form of refraction.)

Ibn al-Haytham’s work decisively influenced the theory of perspective that flowered in Renaissance European science and art. De Aspectibus was translated into Italian in the fourteenth century, making it accessible to practitioners such as the Florentine art theorist and architect Leon Battista Alberti, author of the 1435 treatise On Painting (Della pittura), the sculptor Lorenzo Ghiberti and the geometer-artist Piero della Francesca. They harnessed Ibn al-Haytham’s discussions on perspective to help to create the illusion of three-dimensional depth on canvas and in friezes. These revolutionary artists strove to understand both the objective world and the visual system that determined its appearance.

Today, as we use laser beams to manipulate atoms, stimulate neurons with light or convey information in entangled photons, it is worth recalling that the foundations of this field were laid down around 1,000 years ago by Ibn al-Haytham.

By Jim Al-Khalili, published in Nature, February 11th 2015.

I review first the main similarities and differences between the planetary model of Ibn al-Shatir (14^th-Century Muslim astronomer) and of Copernicus. I show that important similarities reside in the technical aspects of the orbits constructed by the two astronomers but that fundamental differences are:

(a) Copernicus adopted a heliocentric model while Ibn al-Shatir (and all Muslim astronomers) assumed a geocentric model, as strictly as possible;

(b) Copernicus followed a clear inductive method while Ibn al-Shatir remained within the Zij (astronomical tables) tradition.

On the question of the extent to which Copernicus had benefitted from the ‘transmission’ of thos models and critiques of Ptolemy, I insist that neither Ibn al-Shatir nor any Muslim astronomer accepted, let alone proposed, a heliocentric model. I then briefly discuss the Copernican Revolution and try to assess the extent to which the Polish astronomer might have been influenced by earlier Muslim discussions on the centrality (or not) and immobility (or possible motion) of Earth.

Nidhal Guessoum is associate dean at the American University of Sharjah. He can be followed on Twitter at: www.twitter.com/@NidhalGuessoum

Source: http://adsabs.harvard.edu/full/2008Obs…128..231G

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