ASTRONOMY

Before Islam, Arab knowledge of the stars was limited to the division of the year into precise periods on the basis of star risings and settings. This area of astronomical knowledge was known as anwa?, and it was largely overshadowed by the traditions of Arabic mathematical astronomy that emerged in the Islamic period. From its beginnings in the ninth and through the sixteenth centuries, astronomical activity in the Muslim world was widespread and intensive. The first astronomical texts that were translated into Arabic in the eighth century were of Indian and Persian origin. The earliest extant Arabic astronomical texts date to the second half of the eighth century and were influenced by the Indian and Persian traditions. However, the greatest formative influence on Arabic astronomy is undoubtedly Greek, on account of the use in Greek astronomy of effective geometrical representations. The Almagest of Ptolemy (second century c.e.), in particular, 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. However, at the same time the first Arabic translation of this text were prepared, original work of Arabic astronomy was also produced. Thus, original astronomical research went hand in hand with translation and, from its very beginnings in the ninth century, Arabic astronomy attempted to revise, refine, and complement Ptolemaic astronomy, rather than simply reproduce it.

In its earlier stages, Arabic astronomy reworked and critically examined the observations and the computational methods of Greek astronomy and, in a limited way, was able to explore problems outside its set frame. Arabic astronomy witnessed further developments in the tenth and eleventh centuries as a result of systematic astronomical research as well as developments in other branches of the mathematical sciences. In this period, steps were also taken toward the establishment of large-scale observatories. Subsequently, several programs of astronomical observations involved the establishment of observatories in institutional setups where collective programs of astronomical research were executed. Advances in trigonometry resulting from the full integration of the Indian achievements in the field, as well as from new discoveries in the tenth and eleventh centuries, played a central role in the further development of Arabic astronomy. As a great synthesis of the Greek, Indian, and Arabic astronomical traditions, the al-Qanun al-Mas?udi of the illustrious astronomer al-Biruni (973–c. 1048) represents the culmination of this first stage in the development of Arabic astronomy.

Following its systematic mathematization, the rethinking of the theoretical framework of astronomy was further developed after the eleventh century, leading to a thorough evaluation of its physical and philosophical underpinnings. One of the main objectives of this reform tradition 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. The Ptolemaic models were considered defective because they posited physically impossible models in which spheres rotate uniformly around axes that do not pass through their centers. The reform tradition continued well into the fifteenth and sixteenth centuries, and the list of astronomers working within it comprises some of the greatest and most original Muslim scientists. The work produced within this tradition had a formative influence on the work of Copernicus.

In addition to theoretical astronomy, practical astronomical problems occupied a great many astronomers who were responsible for significant advances in the field. Some of these problems had a specific Islamic character, whereas others had to do with the general practical needs of society. The general kind includes such problems as finding the direction of one locality with respect to another, a problem that requires determining the longitudes and latitudes of these localities as well as other aspects of mathematical geography. The "Islamic" problems, on the other hand, were problems related to Islamic worship such as determining the times of prayer, the time of sunrise and sunset in relation to fasting, the direction of the qibla (the direction of the Ka?ba in Mecca, which Muslims have to face during prayer), crescent visibility in connection with the determination of the beginning of the lunar month, and calendar computations. The methods employed to solve these problems varied from simple approximative techniques to complex mathematical ones.

Problems like the determination of the direction of the qibla and the times of prayer also gave a great impetus to the science and art of instrument building. Astrolabes, quadrants, compass boxes, and cartographic grids of varying degrees of sophistication were designed and introduced to solve some of these problems. Many of these same instruments were also used for other astronomical observations and computations; the most important of these is the astrolabe, which was a versatile medieval observational instrument and calculator. Extensive tables were also compiled in connection with time keeping, finding the direction of the qibla, and other astronomical functions.

See alsoAstrology ; Biruni, al- ; Hijri Calendar ; Science, Islam and ; Translation .

BIBLIOGRAPHY

King, David. Astronomy in the Service of Islam. Aldershot, Hampshire, U.K.: Variorum, 1993.

Rashed, Roshdi, ed., in collaboration with Morelon, Régis. Encyclopedia of the History of Arabic Science, Vol. 1: Astronomy—Theoretical and Applied. London and New York: Routledge, 1996.

Saliba, George. A History of Arabic Astronomy: Planetary Theories During the Golden Age of Islam. New York: New York University Press, 1994.

Samso, Julio. Islamic Astronomy and Medieval Spain. Aldershot, Hampshire, U.K.: Variorum Reprints, 1994.

Ahmad S. Dallal