Viewpoint No. 113 3 Islamic Astronomy from “Star Wars” to Star Tables Glen M. Cooper explores the cosmos as seen by Islamic scholars through history. Astronomy had a long and fruitful life in the and rulers in Islamic world, where ancient Greek astronomy terms of a grand was transformed into a fully institutionalised cosmological endeavour employing a comprehensive and scheme written predictive theory that was consistent with in the stars, physical principles as then understood. which both Astronomy in the ancient world was justified the motivated by different concerns than what current dynasty drives the science today. Its principal aim was and permitted to divine the future from planetary positions, knowledge of which eventually could be calculated using the political past data and theoretical models. Astrologers future. These have been associated with imperial courts interests in since ancient Mesopotamian times. There, in a political and his- kind of ancient “star wars”, they vied with each torical astrology other for the most accurate predictions. Meso- were inherited potamian stargazers accumulated centuries by the Muslim of observational data, and invented math- Abbasid dynasty ematical methods for predicting astrologically (750-1258 CE). significant planetary configurations. The most While the Mesopotamian cultures provided obvious differ- incentive and data for astronomy, the Greeks ence between were more concerned with integrating this modern and knowledge into a cosmology, with geometri- Islamic astron- cal models and a physics. The culmination of omy is that the these efforts was the Almagest, the work of latter is primarily the 2nd Century mathematical astronomer, mathematical Nasir al-Din al-Tusi at the observatory in Maragha, Persia. Ptolemy, who, using the Mesopotamian data, and predictive, Image courtesy of the British Library. produced the most powerful system of predic- and the former tive astronomy yet known, the Almagest. He has other obser- also developed a comprehensive astrology, vational goals, which, because of its mathematical preci- such as describing the physics of other worlds. ying speeds, Ptolemy had postulated that one sion, acquired the air of genuine science. The As noted earlier, the predictive character of of the spheres responsible for moving these Almagest showed how to derive mathemati- astronomy derived from its use in astrological planets rotated uniformly around a pole that cal models of the planets from observational forecasting. The Ptolemaic models were to an did not coincide with its own centre, which, data. Ptolemy’s methods were the foundation extent instrumentalist, namely, useful for gen- although it gives good mathematical results, of Islamic astronomy. erating planetary positions rather than being is physically impossible. Muslim astronomers Prior to Islam, the rulers of the Sasanian Per- strictly physically consistent. There were some invented new mathematical devices that sian Empire (224-651 CE) fostered a dynamic thinkers, however, such as al-Tusi, who desired produced the same effects without violating astrological tradition, which they employed to present a unified physics and cosmology of physical principles. for a variety of purposes. For example, the the heavens. Through his efforts and those of Observatories as institutions that housed state religion, Zoroastrianism, espoused a his followers, several of Ptolemy’s models that a collective effort to gather positional data chiliastic/millennialist view of history, and contained physically absurd elements were about the stars and planets were an Islamic thus invited astrological activity. Astrologi- replaced with physically consistent ones. For invention. Programs of observation began cal histories rationalised significant events example, in order to explain some planets’ var- under the 9th-century Abbasid rulers, but Viewpoint 113.indd 3 30/06/2017 08:26:39 4 Viewpoint No. 110 Above left: Ulugh Beg observatory, cour- tesy of Alaexis via Wikimedia Commons. Right: An Arabic translation of the astro- nomical tables of Ulugh Beg, courtesy of the Library of Congress. culminated in the grand observatories of Maragha (13th C.) under the Ilkhanids, and Samarkand (15th C.) under the Timurids. The main goal of these observatories was to improve the planetary tables (zijes; sing. zij) used to calculate planetary positions. Unlike modern observatories, their Islamic anteced- ents were useful only until all the data had been gathered over a period of decades at most. The main structural feature of the Islamic observatory was the meridian quadrant, which measured the planets’ elevations as they crossed the meridian. (See above). In addition, there were more portable instru- ments, including armillary spheres, quadrants, and other devices for measuring celestial posi- tions by hand. The way to improve upon data from earlier observatories was to build a larger plished. However, the most famous observa- sciences. meridian quadrant in order to obtain more tory was established at Maragha in northwest- The majority of those who used astronomi- precise observations, which in turn improved ern Iran by the Mongol Ilkhanid ruler Hulegu cal information did so in the form of tables, the accuracy of the zij tables. This basic design (d.1265) in 1259, under the direction of Nasir and so did not require advanced mathematics. persisted for centuries, and even found its way al-Din al-Tusi (d.1374). The first observatory Along with planetary models, Ptolemy had into Tycho Brahe’s 16th Century Uraniborg. to be supported by a religious endowment also shown how to use tables for the relatively (The main difference there was that, whereas (waqf), it not only produced an improved zij easy calculation of planetary positions. Only the Ptolemaic tradition had astronomers (Zij-i Ilkhani), but also began a major reform of basic arithmetic was needed, since the tables taking observations at major conjunctions Ptolemaic astronomy. This resulted in a new of various functions already had complex or at other significant times of the planetary tradition of planetary theory that culminated trigonometry built into them. cycles in order to extrapolate the rest using in the models of Ibn al-Shatir (d.1375), ele- In the Islamic tradition, such tables were the model, Tycho observed the planets on the ments of whose contributions Copernicus called “zijes”, from a Persian word that means days between, and thus had a far more precise incorporated in his own revolutionary treatise, “thread”, because their cross-hatched appear- set of data). On the Revolutions (1543). The Samarkand ance, with numbers in the spaces, resembles The Abbasid Caliph al-Ma’mun (r.813-833) observatory, established and supervised by a woven cloth (see illustration, above). Zijes founded two observatories at Baghdad and the Timurid ruler and astronomer Ulugh Begh were typically a collection of such tables along Damascus, respectively, where some of the (d.1449), produced a new zij (Zij-i Sultani), and with instructions for their use, including tables initial updates to the Almagest were accom- supported a flowering of the mathematical for converting between calendars, for Islamic Viewpoint 113.indd 4 30/06/2017 08:26:42 Viewpoint No. 113 5 prayer times, and for determining planetary longitudes, based on the number of elapsed days and hours since a known position, or “epoch”. Zijes were calculated using math- Cocktail parties ematical models of the planetary motions, which in turn were based on observational parameters that were determined at the observatories. So, advances in astronomy under starlight were expressed in new zijes, which were the result of more accurate parameters or better Pedro Ruiz-Castell highlights the role of amateur astronomy as a models, or both. form of sociability under Franco’s dictatorship. To simplify the process further for the eve- ryday practitioner, yearly almanacks were pro- duced, which used the zijes to determine all of the celestial data for the upcoming year on a daily basis, much like a modern ephemeris. Islamic astronomy was interconnected with all of the other sciences, in a comprehensive cosmology inherited from Aristotle. Through their unrelenting critique of ancient astron- omy and natural philosophy, Islamic astrono- mers laid the groundwork for the scientific advances of both the European Late Middle Ages and the Scientific Revolution. Coper- nicus, Brahe, Kepler and many others used methods developed in Islamic astronomy to critique and eventually replace the ancient cosmology. The opening of Aster’s new premises, 3 June 1949. Source: Aster, 1 (1949), p. 49. Glen M. Cooper The Spanish Civil War (1936-1939) was a by academics and senior amateurs. Despite Claremont McKenna College devastating conflict that marked the begin- encouraging and promoting systematic ama- [email protected] ning of one of the longest European dictato- teur work –such as the methodical observa- rial regimes of the twentieth century. Franco’s tion of variable stars–, SADEYA seemed to dictatorship signified a break with the past in have problems accommodating the enthusi- many political, ideological, and social aspects, asm of young people. This situation led to the including cultural expressions and intellectual creation of new amateur astronomical associa- traditions. It also brought important changes tions in Spain during the central decades of from an institutional perspective and meant the twentieth century. the purge and forced exile of many Spanish The foundation of