Al-Biruni

Abu Raihan Muhammad ibn Ahmad al-Biruni (973 - around 1050) was a scholar from Khwarazm and one of the central figures of the Islamic Golden Age. A mathematician, astronomer, geographer, historian, philosopher and linguist, he is also regarded as a founding figure in comparative religion and in the study of India. What makes him stand out is the way he joined careful observation, calculation and a serious study of languages and cultures foreign to his own.

He was born in Kath, in what is now Uzbekistan, and his name is often linked to the outlying district where he grew up. His mother tongue was Khwarezmian, and he mastered Persian and Arabic, as well as Sanskrit, Greek, Hebrew and Syriac. His interest in the sky appeared early: at seventeen he estimated the latitude of his home town from the highest point the Sun reached, and by twenty-two he had written short works on cartography. After the fall of the Afrighids in 995 he left his homeland and moved between the courts of Bukhara, Tabaristan and Gurganj. In Gurganj he worked again with his former teacher Abu Nasr Mansur, and around the year 1000 he completed his first major book, on historical and scientific chronology, known in English as The Remaining Signs of Past Centuries.

Around 1017, after Mahmud of Ghazni captured Kath, he was taken to Ghazni, in present-day Afghanistan, together with other scholars, and spent much of the rest of his life there as court astrologer. He accompanied the ruler on several campaigns across the Indian subcontinent, which gave him the chance to learn Sanskrit, study Hindu religion and philosophy, and write his History of India, finished around 1030. That work is the main reason he is remembered as an Indologist. Life at court did not stop his research: during the journeys he used a makeshift quadrant to measure the height of the Sun.

He is credited with some 146 books, 95 of them on astronomy, mathematics and mathematical geography, although only a fraction survives. To estimate the radius of the Earth he used a method based on the height of a hill and the dip of the horizon, and the accuracy of his figure depends on how the old unit of the cubit is converted. In his Mas'ud Canon, named after the sultan, he recorded observations that challenged Ptolemy, such as the fact that the Sun's apogee moves. He also wrote on the astrolabe and discussed the rotation of the Earth, which he thought fit the astronomical evidence well, while doubting it on physical grounds.

His correspondence with Avicenna is a remarkable record of debate: the two discussed the void, elliptical orbits, and the nature of light and heat, and in his letters Biruni argued that the universe had a beginning. He separated astronomy, which he supported, from astrology, which he criticised in a dedicated treatise, even though he had long studied its mathematical side. His method relied on observation and experiment more than on original theories, which is why he is remembered as a great encyclopaedist rather than a radical innovator.

His influence reached Islamic astronomy, geodesy and the study of India. Today he is recognised as a precursor of comparative anthropology because of his fair treatment of the beliefs of other peoples, and his work remains an essential source for historians of science.