Short answers, pulled from the story.
A zij is an Islamic astronomical book that tabulates parameters used to calculate the positions of the sun, moon, stars, and planets. Over 200 distinct zij works were produced by Islamic astronomers between the eighth and fifteenth centuries. The name derives from a Middle Persian term for "cord," referring to the arrangement of threads in weaving.
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 also explained the underlying theory or reported the direct observations that generated the tables.
The Zij-i Sultani was published by the astronomer and sultan Ulugh Beg in 1438 or 1439. It served as a reference zij throughout the Islamic world during the early modern era. The Mughal Empire later produced a simplified version of it.
The greatest centers were Baghdad under the Abbasid caliphs in the ninth century, the Maragheh observatory in the thirteenth century, the Samarkand observatory in the fifteenth century, and the Constantinople observatory of Taqi ad-Din in the sixteenth century. Nearly 100 more zij works were also produced in India between the sixteenth and eighteenth centuries.
The last known zij treatise was the Zij-i Bahadurkhani, written in 1838 by the Indian astronomer Ghulam Hussain Jaunpuri and printed in 1855. It was dedicated to Bahadur Khan and was notable for incorporating the heliocentric system into the traditional zij framework.
Many zij works were used for astrological purposes despite some authors explicitly intending their tables only for astronomical calculation. Religious conflicts with astrology led astronomers like the compiler of al-Zij al-jadid to distance themselves from astrological use, but the tables were general-purpose enough that they were frequently applied that way regardless.