From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 552-553

Courtesy of

Ibn o: Abū ʿAlī al‐usayn ibn Abī Jaʿfar Amad ibn Yūsuf ibn o

Emilia Calvo

DiedGranada, (Spain), 1316

Ibn Bāo was the head of the timekeepers (raʾīs al‐muwaqqitīn) in the Great Mosque of Granada. He was also a master of the science of calculation, highly skilled in astronomical observation, an inventor, and the author of several treatises.

Little is known about Ibn Bāo's life. He was probably one of the two Ibn Bāos mentioned by Ibn al‐Khaīb in his biographical work, al‐Iāa, although this author gives his name as Abū ʿAlī asan ibn Muammad ibn Bāo.

According to Ibn al‐Khaīb, Ibn Bāo was from the Sharq al‐Andalus, the eastern part of the Iberian Peninsula. The fact that he was the head of the timekeepers (raʾīs al‐muwaqqitīn) in the Great Mosque of Granada is extremely interesting, because it suggests that the mosque had an organized, institutionalized group devoted to timekeeping.

Two of Ibn Bāo's written texts are preserved. One of them is the Risālat al‐afīa al‐jāmiʿa li‐jamīʿ al‐ʿurū (Treatise on the universal plate for all latitudes). The other is the Risālat al‐afīa al‐mujayyaba dhāt al‐awtār (Treatise on the plate of sines provided with chords). In both texts the author is named as Abū ʿAlī al‐usayn ibn Abī Jaʿfar Amad ibn Yūsuf ibn Bāo and is described as amīn awqāt al‐alawāt (keeper of the times of prayers) and imām al‐muʾadhdhinīn (leader of the muezzins).

The differences in name between what one finds in Ibn al‐Khaīb's biography and in the treatises themselves have led some specialists (such as George Sarton) to suggest that there were two Ibn Bāos. However, later investigators—H. P. J. Renaud, among others—proposed that the treatises were the work of one and the same person, adducing that differences in the name were frequent in Arabic biographies.

The first treatise, the Risālat al‐afīa al‐jāmiʿa li‐jamīʿ al‐ʿurū, was compiled in the year 1273 and was devoted to the description of the use of a universal plate for all latitudes. The author states that he was the inventor of the instrument. The treatise suggests that the author was aware of the work of previous astronomers in the Muslim world, especially of the work carried out in the 11th century in Andalusia. There are also similarities with some treatises of mīqāt written in 13th‐century Egypt. The astrolabe plate is one in which the horizontal coordinates have been omitted, and the horizons have been multiplied in order to serve for different latitudes. It corresponds to the type of instrument usually called afīa āfāqiyya, “plate of horizons,” and it is similar to a conventional astrolabe plate. The fact that this plate does not have horizontal coordinates and is limited to the projection of a set of horizons has led specialists to think that it was used only for simple operations. However, a study of the treatise shows that the instrument was as versatile as any other astrolabe plate, although it is difficult to use because of the number of lines in its layout and because of the complicated procedures that the user would need to know. In this treatise the author is not seeking great precision: the values are clearly rounded. It was probably the didactic potential of the plate that the author was most interested in exploiting. Indeed, using the plate would have provided a very useful exercise for anybody who wanted to become familiar with the celestial spheres and their properties. This plate seems to have been designed to carry out all types of speculative calculation: its use in extreme northern latitudes or in latitudes south of the equator cannot be considered a practical application. Nevertheless, the possibility of using this plate as a southern astrolabe plate, in spite of the fact that it is designed for the Northern Hemisphere and is meant to fit in a northern astrolabe, is its most original characteristic and thus can be considered a forerunner of later instruments.

Ibn Bāo's work became well known. There are a number of summaries of the treatise, most of them of Maghribi origin, and the projection was included in several instruments still preserved in Andalusia, North Africa, and also in the Islamic East as is the case of instruments constructed by Mizzī in Damascus and Allāh‐Dād in Lahore. Although universal instruments of this type had already been described by earlier astronomers such as Sijzī or Bīrūnī, they do not seem to have been built until the time of Ibn Bāo, when, starting in the 14th century, they seem to have proliferated in North Africa and the Muslim East as well as in Europe.

The other treatise written by Ibn Bāo that is still preserved, the Risālat al‐afīa al‐mujayyaba dhāt al‐awtār, is contained in manuscript 5550 of the National Library of Tunisia. The introduction of this treatise presents abundant similarities to that of the previous one. In this treatise, the author describes the use of a trigonometric plate of his invention that can perform all kinds of calculations of spherical astronomy.

Selected References

Brockelmann, Carl (1937). Geschichte der arabischen Litteratur. Suppl. 1, p. 860. Leiden: E. J. Brill.

Calvo, Emilia (1991). “Les échos de l'oeuvre d'Ibn Bāṣo en Afrique du Nord.” In Le Patrimoine Andalous dans la Culture Arabe et Espagnole, pp. 65–79. Tunis.

——— (1992). Ibn Bāṣo's Universal Plate and Its Influence in European Astronomy.” Scientiarum historia 18: 61–70.

——— (1992). “La ciencia en la Granada nazarí (Ciencias exactas y tecnología).” In El legado científico andalusí, edited by Juan G. Vernet and Julio Samsó, pp. 117–126. Madrid.

——— (1993). Abū ʿAlī al‐usayn Ibn Bāṣo (m. 716/1316): Risālat al‐ṣafīḥa al‐jāmiʿa li‐jamīʿ al‐ʿurū. Edición crítica, traducción y estudio. Madrid.

——— (1994). “On the Construction of Ibn Bāṣo's Universal Astrolabe (14th C.) According to a Moroccan Astronomer of the 18th Century.” Journal for the History of Arabic Science 10: 53–67.

——— (1996). Ibn Bāṣo's Astrolabe in the Maghrib and East.” In From Baghdad to Barcelona: Studies in the Islamic Exact Sciences in Honour of Prof. Juan Vernet, edited by Joseph Casulleras and Julio Samsó, vol. 2, pp. 755–767. Barcelona: Instituto “Millás Vallicrosa” de Historia de la Ciencia árabe.

——— (2000). “A Study of the Use of Ibn Bāṣo's Universal Astrolabe Plate.” Archives internationales d'histoire des sciences 50: 264–295.

——— (2001). “Transformation of Coordinates in Ibn Bāṣo's al‐Risāla ʾl‐ṣafīḥa al‐mujayyaba dhāt al‐awtār.” Journal for the History of Arabic Science 12: 3–21.

Ibn al‐Khatīb, Lisān al‐Dīn (1973). al‐Iāa akhbār Gharnāta, edited by Muammad ʿAbd Allāh ʿInān. Vol. 1, p. 468. Cairo.

Renaud, H. P. J. (1932). “Additions et Corrections à Suter.” Isis 18: 166–183, n. 381b.

——— (1937). “Notes critiques d'histoire des sciences chez les musulmans. I. Les Ibn Bāṣo.” Hesperis 24: 1–12.

——— (1942). “Quelques constructeurs d'astrolabes en occident musulman.” Isis 34: 20–23.

Samsó, Julio (1966). “Nota acerca de cinco manuscritos sobre astrolabio.” Al‐Andalus 31: 385–392.

——— (1973). “À propos de quelques manuscrits astronomiques des bibliothèques de Tunis: Contribution à une étude de l'astrolabe dans l'Espagne musulmane.” In Actas del II Coloquio Hispano‐Tunecino, pp. 171–190. Madrid.

Sarton, George (1947). Introduction to the History of Science. Vol. 3, pt. 1, p. 696. Baltimore: Published for the Carnegie Institution of Washington by Williams and Wilkins.

Suter, Heinrich (1900). “Die Mathematiker und Astronomen der Araber und ihre Werke.” Abhandlungen zur Geschichte der mathematischen Wissenschaften 10: 157, n. 381b.