Islamic Astronomy

Scholars in the Islamic world were responsible for providing a vital bridge connecting ancient Babylonian and Greek astronomy to modern scientific astronomy. But for this bridge, the traditions of thought that had led to the development of mathematical astronomy in Hellenistic Greece (after the conquests of Alexander the Great in the fourth century B.C.E. had brought the Babylonian and Greek traditions into direct contact) would have been all but severed. In any case, several centuries had passed by the time (in the ninth century C.E.) that serious quantities of old astronomical treatises written in Greek began to be retrieved, translated into Arabic, and thence communicated around the Muslim world. There they helped give birth to one of the world's richest and most sophisticated astronomical traditions. Early elements of this tradition (including translations and re-translations of the ancient Greek texts) subsequently passed into Christian Europe, where they contributed to the development of ideas within the European Renaissance. (This legacy is most obvious today in the fact that a number of modern star names, such as Aldebaran, Alnilam, Alnitak, and Altair—as well as techni-

Muslims bow their heads toward Mecca in prayer. Mecca, in present-day Saudi Arabia, is the birthplace of Muhammad, the prophet upon whose teachings Islam is based. (PhotoDisc/Getty Images)

cal terms, such as azimuth, zenith and nadir—are Arabic in origin.) However, Islamic astronomy continued to develop in its own right until around the beginning of the sixteenth century, and Europeans remained largely ignorant of it. In fact, developments in Europe and the Muslim world remained largely independent until the nineteenth century.

Astronomy and astronomers generally thrived in the Islamic world. The distinctive nature of the astronomy that they studied and practiced derived from a particular mixture of traditions: indigenous folk astronomies, Babylonian and Greek ideas drawn from ancient texts, and elements of Persian and Indian astronomy absorbed as the Muslim world stretched eastwards. An example of this mixed intellectual heritage is the set of stars and aster-isms known as anwa' that identified twenty-eight lunar stations or "mansions"; these helped identify the position of the moon on successive nights and hence to track its monthly course through the stars. The general concept may well have been adopted from Hindu astronomy, while the chosen reference stars derived from Bedouin knowledge of heliacal and acronical events. Muslim astronomers advanced mathematical astronomy in various ways, including studies of the motions of the sun, moon, and planets, and catalogues of stars and their positions, tabulated in substantial documents known as zijes. They were also responsible for the construction of many fine portable astronomical instruments and made a number of important technical advances in the design of the astrolabe and the quadrant.

Coexisting alongside what we would recognize as scientific astronomy was a tradition of folk astronomy that did not involve any attempt to make systematic observations or predictions based on mathematical models. What it did do was to regulate both agricultural activities and religious ones using straightforward observations of the skies. While mathematical astronomy could achieve the same ends, and indeed do so with a great deal more precision, it was the preserve of just a few specialists; folk astronomy, on the other hand, was accessible to all, and thus had far wider social implications since it determined everyday practice for ordinary people.

Prior to the widespread adoption of the Muslim faith, different cultural traditions within what became the Islamic world would have tended to produce a mish-mash of local seasonal calendars and/or astronomical rules of thumb molded by the particular subsistence requirements of a given community. The rapid exchange of ideas within the Islamic world itself brought about a degree of rationalization: thus a broadly consistent set of anwa' became widely used for divination and were increasingly adopted as a means of time keeping. Nonetheless, what makes it possible to speak meaningfully of "Islamic folk astronomy" is the fact that very particular requirements would have been imposed upon all practicing Muslims by sacred Islamic law. Folk astronomies all over the Muslim world adapted to satisfy these common needs.

The first essential was to observe religious festivals on the right days, and particularly to correctly define such critical dates as the beginning and end of the month-long fast in the holy month of Ramadan. The formal Islamic calendar is lunar, and consists of only twelve synodic (phase-cycle) months, since intercalary months are forbidden by the Quran: this means that it is eleven days shorter than the seasonal year. Whatever calendars were in local use for seasonal reckoning, it was necessary for liturgical purposes to determine the start of each new month by direct observations of the new crescent moon. People with good eyesight might be sent to watch the western sky on the critical evenings, and various solutions had to be found when the critical part of the sky was obscured by cloud. It is scarcely surprising that the star and crescent symbol, depicting the crescent moon, has become a global symbol of the Islamic faith.

An imperative for any Muslim is to observe the five daily prayers, which must take place within set intervals during the day and night. The intervals in question are specified according to the daily motions of the sun: in relation to the lengths of shadows when the sun is up; in relation to certain visible phenomena (such as the redness of the sky) at twilight; and in rela tion to set time intervals during the night (the evening prayer, specifically, should preferably be completed before a third of the night has passed). This means that the actual prayer times vary both according to latitude and longitude, and at any given place they change from day to day with the varying length of daylight. This makes the problem of determining the correct prayer times nontrivial, and before tables based on scientific data became available, the use of sundials and gnomons was common, with anwa' used to estimate the time of night.

Folk astronomy had a third and rather different application, though to something no less vital in the practice of the Muslim faith. This was to help determine the sacred direction, or qibla. One of the most basic necessities for any Muslim is to know the direction of Mecca, in order to determine the correct bodily orientation during prayers and other activities. Formally this has nothing to do with astronomy, but (again, before Muslim mathematicians had produced tabulations of the qibla for different latitudes and longitudes) astronomical observations were extensively used to provide the best available approximations, some of which were rather better than others. Typically they used the horizon rising or setting point of a particular bright star or the rising or setting arc of the sun. This seemed only natural as the base of the Kaaba itself—the cube-shaped stone structure at the center of the Great Mosque in Mecca that forms the sacred center of the Muslim world— had been known as far back as the seventh century to have its longer axis oriented upon the rising of the star Canopus and its minor axis aligned (roughly) in line with midsummer sunrise and midwinter sunset.

Historically, the assumed qibla is most evident in the orientation of mosques and in the layouts of some cities. In some cases, historical accounts attest to how the sacred direction was actually determined. Thus, we know that the earliest mosques in Iraq were built with their prayer walls facing midwinter sunset in order to face the northeastern wall of the Kaaba, while Egyptian ones were built with their prayer walls facing midwinter sunrise in an attempt to be parallel with the Kaaba's northwestern wall. However, in many cases we can only speculate about the methods used to determine the qibla. Since the errors were sometimes considerable, anyone trying to reconstruct the motivation behind mosque orientations in the absence of anything but the orientations themselves would have a hard time fathoming that the intention was always to orient them toward Mecca.

See also:

Lunar and Luni-Solar Calendars; Orientation; Star and Crescent Symbol.

Heliacal Rise; Lunar Phase Cycle; Solstitial Directions.

References and further reading

Belmonte Avilés, Juan Antonio. Tiempo y Religión: Una Historia Sagrada del Calendario, ch. 6. Madrid: Ediciones del Orto, 2005. [In Spanish.]

Chamberlain, Von Del, John Carlson, and Jane Young, eds. Songs from the Sky: Indigenous Astronomical and Cosmological Traditions of the World, 26-31. Bognor Regis: Ocarina Books, and College Park, MD: Center for Archaeoastronomy, 2005.

Hoskin, Michael, ed. Cambridge Illustrated History of Astronomy, 50-63. Cambridge: Cambridge University Press, 1997.

McCluskey, Stephen C. Astronomies and Cultures in Early Medieval Europe, 165-187. Cambridge: Cambridge University Press, 1998.

Ruggles, Clive, and Nicholas Saunders, eds. Astronomies and Cultures, 124-138. Niwot: University Press of Colorado, 1993.

Schaefer, Bradley E. "Lunar Crescent Visibility." Quarterly Journal of the Royal Astronomical Society 37 (1996), 759-768.

Selin, Helaine, ed. Astronomy across Cultures, 468-471, 585-650. Dordrecht, Neth.: Kluwer, 2000.

Walker, Christopher, ed. Astronomy before the Telescope, 143-174. London: British Museum Press, 1996.

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