The Book of Fixed Stars ( , literally The Book of the Shapes of Stars) is an astronomical text written by Abd al-Rahman al-Sufi (Azophi) around 964. Following the translation movement in the 9th century AD, the book was written in Arabic, the common language for scholars across the vast Islamic territories, although the author himself was Persian. It was an attempt to create a synthesis of the comprehensive star catalogue in Ptolemy’s Almagest (books VII and VIII) with the indigenous Arabic astronomical traditions on the constellations (notably the Arabic constellation system of the Anwā’). The original manuscript no longer survives as an autograph, however, the importance of tradition and the practice of diligence central to Islamic manuscript tradition have ensured the survival of the Book of Stars in later-made copies.
Historical context
The treatise was written in the Persian city of Shiraz, for the patron and Buyid emir ‘Adud al-Dawla. Although al-Sufi made his longitudinal calculations correct for the year 964 only, the work remained highly influential, functioning as the standard text on Arabic astronomy to be consulted in all Islamic territories and faithfully copied for many centuries after its production. Since it was only correct for the single year of 964, the Book of Fixed Stars was intended to serve a broader educational purpose, rather than being concerned with the mathematical technicalities of astronomy.
The Book of Fixed Stars is representative of the concerns of Islamic scholars during the late-9th to 11th centuries, where following the translation of Hellenistic texts from Greek to Arabic, "Islamic astronomers and astrologers concentrated on analyzing, criticizing, and perfecting the geometrical models of Ptolemy". Medieval Islamic astronomers also drew from Sanskrit and Middle Persian sources to learn "methods for calculating the position of heavenly bodies, and for creating tables recording the movement of the sun, the moon, and the five known planets." In the context of this shift to observational and theoretical astronomy set in motion by the translation movement, and with al-Sufi himself being an observational astronomer, the Book of Fixed Stars comprises an important organisation and revision of classical knowledge from antiquity (the first of its kind), and some of the earliest surviving examples of visual documentation of celestial bodies observable by the naked eye.
The interest in cataloging the stars also stems from the nature of worship in Islam. The religion requires that its members are able to locate Mecca so that they may pray in the right direction, and to also be able to determine the correct times for prayer. In addition to the daily requirements, during the festival of Ramadan they must also know the moments of sunrise and sunset for fasting, and the location of the moon for the start of each month.
The Book of Fixed Stars also follows a trend of increased production of illustrated manuscripts, as it is one of the oldest surviving treatises of its kind. This is not to say that this text was the first illustrated manuscript ever created, as there are many illustrated fragments that have been found and studied, most notably the Fustat fragments. The Fustat fragments are illustrated scraps of parchment that were found during excavations in Fustat, or Old Cairo. These fragments can be stylistically attributed to the Fatimid period (969-1171), therefore dating the existence of astronomical illustrations to many years before the creation of the Book of Fixed Stars. The increase in illustrated manuscripts is also related to the advent of paper in the Islamic world in the tenth century. The increased availability of paper, which was much cheaper than parchment, drove the production of books in the Islamic world.
Contents
The book was thoroughly illustrated along with observations and descriptions of the stars, their positions (copied from Ptolemy's Almagest with the longitudes increased by 12° 42' to account for the precession), their magnitudes (brightness) and their color. Notably, al-Sufi improved upon Ptolemy's system for measuring star brightness. Instead of two brightness categories (‘more bright’ and ‘less bright’), al-Sufi employed three: AṢghareh (‘less’), Akbareh (‘greater’), and A’ẓameh (‘much-greater’). Ihsan Hafez has recorded 132 stars in al-Sufi's work not mentioned by Ptolemy.