In 997 al-Biruni returned to Kath, where he observed a lunar eclipse that Abu al-Wafa observed in Baghdad; on the basis of the time difference they determined the longitudinal difference between the two cities, one of the few instances in which this method, the only secure one available in antiquity, is known to have been applied.
By 1004 al-Biruni was in Jurjaniya. He became a prominent figure at the Jurjaniya court, being often employed as a diplomat and as a spokesman for the throne. He continued, however, making his astronomical observations under the Shah's patronage.
Most of his extant works were written in the 1020s and 1030s and reflect his interest in, and growing knowledge of, the Sanskrit astronomical texts current in the Punjab. These include On Shadows (ca. 1021), Tahdid (1025), On Chords (1027), On Transits, India (1031), and Al-Qanun al-Masudi, as well as the Arabic translation of Vijayanandin's Sanskrit Karanatilaka. These are fundamental texts for the history of Islamic and Indian astronomy of the 8th-10th centuries because of al-Biruni's extensive citations of earlier texts; they are also full of reports of al-Biruni's own observations, which are among the best made in the medieval period. He was not always as successful in his calculations.
Till his death soon after 1050 in Afghanistan, al-Biruni continued to write, turning his attention to problems of specific gravity, gemology, pharmacology, and Indian philosophy (the Patanjali ), among other subjects. It is not clear when he wrote the Tafhim, his most important work on astrology. In all, the bibliography he himself drew up lists 113 titles, and this list can be expanded to 146; 22 are extant. He was, then, a most prolific author, and throughout his work, all of which is extremely technical, he maintained the highest standards of competence. He well deserved the epithet "Master" bestowed on him by his admiring contemporaries.
Further ReadingMany of al-Biruni's extant writings have not been published. He has been the object of many intensive studies, but the results are scattered among various scholarly journals. Some idea of the range of this scholarship can be gained from the volume issued by the Iran Society of Calcutta on the occasion of the thousandth lunar year since his birth, Al-Biruni Commemoration Volume (1951). See also George Sarton, Introduction to the History of Science, vol. 1 (1927); Eugene A. Myers, Arabic Thought and the Western World in the Golden Age of Islam (1964); and Seyyed Hossein Nasr, An Introduction to Islamic Cosmological Doctrines: Conceptions of Nature and Methods Used for Its Study by the Ikhwan al-Safa, al-Biruni, and Ibn Sina (1964).