Zij

• 1. Introduction

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  Zij is the name given to a genre of Islamic astronomical books that tabulated the parameters needed to calculate the positions of the sun, moon, stars, and planets. The word itself traces back to Middle Persian, derived from a term meaning "cord" -- a reference to the arrangement of threads in weaving, which transferred neatly to the rows and columns of tabulated data. That link between textile craft and celestial calculation captures something essential about what a zij was: a practical tool, organized with care, meant to be used. Over two hundred distinct zij works have been identified from Islamic astronomers working between the eighth and fifteenth centuries. What drove so many scholars across so many centuries to produce them, and what exactly did those tables contain? Those are the questions this documentary sets out to answer.

• 2. Roots and Borrowed Knowledge

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  The earliest zij works drew on a wide range of pre-Islamic scientific traditions. Some tabulated data from Indian planetary theory, known as the Sindhind, and from Sasanian models that predated the Islamic era. Most, however, adopted the framework of Ptolemy's geocentric model. Three foundational sources shaped the initial content of the genre: Ptolemy's "Handy Tables," known in Arabic as al-Qanun; the Zij-i Shah, compiled in Sasanian Persia; and the Indian siddhantas authored by Aryabhata and Brahmagupta. Muslim astronomers built on all of these inheritances but expanded the scope considerably. A typical zij covered chronology, geographical latitudes and longitudes, star tables, trigonometrical functions, spherical astronomy, the equation of time, planetary motions, eclipse computation, and tables for the first visibility of the lunar crescent. Some works went even further, explaining the theory behind the tables or reporting the direct observations that generated them. The principal contributions of most zij works lay not in new theory but in improved trigonometry, more refined computational methods, and sharper observational techniques.

• 3. Centers of Production

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  Baghdad under the Abbasid caliphs became the first great hub of zij production in the ninth century. The tradition then spread eastward and westward across the centuries. The Maragheh observatory carried the work forward in the thirteenth century, and the Samarkand observatory became a center of activity in the fifteenth century. The Constantinople observatory of Taqi ad-Din added another node in the sixteenth century. Each of these centers produced works shaped by the priorities of the ruling power. Zijes were updated by different empires to suit their various interests: the Mughal Empire, for instance, produced a simplified version of the Zij-i Sultani. Nearly a hundred more zij works were produced in India between the sixteenth and eighteenth centuries, a period when the tradition continued well past its classical peak in the Islamic heartlands. One of the most notable Indian examples was the Zij-i Muhammad Shahi, compiled at Sawai Jai Singh's Jantar Mantar observatories in the Kingdom of Amber. It is remarkable for employing telescopic observations, placing it at the intersection of the classical zij tradition and the tools of early modern astronomy.

• 4. Astrology and Resistance

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  Ibn al-Shatir's al-Zij al-jadid illustrates a tension that ran through the entire zij tradition. Religious conflicts with astrology led many astronomers to distance themselves explicitly from astrological use, intending their tables strictly for astronomical calculation. Yet many zij works were used for astrological purposes regardless of their authors' intentions. Ibn al-Shatir himself, who lived from 1304 to 1375, could not prevent his tables from being applied in ways he may not have sanctioned. This friction between the technical content of a zij and the uses to which readers put it was never fully resolved. Some authors stated their objections plainly; others structured their works to emphasize the astronomical at the expense of the astrological. The tables themselves, however, were general-purpose enough that the line between the two applications was easy to cross.

• 5. Landmark Works

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  Ulugh Beg published the Zij-i Sultani in 1438 or 1439. Ulugh Beg was both an astronomer and a sultan, and his work served as a reference zij throughout the Islamic world during the early modern era. Omar Khayyam, better known in the West as a poet, compiled the Zij-i Malik Shahi in 1079. That work was updated under various sultanates throughout the modern era, giving it a lifespan that stretched far beyond its original composition. Al-Khwarizmi, who lived roughly between 780 and 850, produced the Zij as-Sindhind, one of the early works based on Indian planetary theory. Muhammad ibn Jabir al-Battani, known in Latin as Albatenius, compiled the Az-Zij as-Sabi between 853 and 929. The list extends across centuries and geographies: Nasir al-Din al-Tusi's Zij-i Ilkhani, Jamshid al-Kashi's Khaqani Zij, and the Huihui Lifa, a Muslim calendrical astronomy work published in China multiple times until the early eighteenth century.

• 6. The Final Chapter

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  The last known zij treatise was the Zij-i Bahadurkhani, written in 1838 by the Indian astronomer Ghulam Hussain Jaunpuri and printed in 1855. Jaunpuri, who lived from 1760 to 1862, dedicated the work to Bahadur Khan. What makes the Zij-i Bahadurkhani particularly striking is that it incorporated the heliocentric system into the zij tradition -- a tradition that had, for the most part, built its calculations on geocentric models inherited from Ptolemy and the ancients. That a work produced in the nineteenth century could still operate within this centuries-old genre while absorbing the Copernican revolution says something about how durable the zij format proved to be. The genre that began with borrowed threads from Ptolemy, Aryabhata, and the Sasanian court ended with a text that folded the sun back to the center of its calculations.