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Friday, 04 September 2015 10:51

Tributes to Abu Rayhan Birouni

Tributes to Abu Rayhan Birouni

Today, the 13th of the Iranian month of Shahrivar, corresponding to September 4, is the birth anniversary of the Iranian-Islamic multi-sided genius, Abu Rayhan Mohammad ibn Ahmad Birouni, who several centuries before Copernicus and Galileo, inspired by the teachings of Islam, scientifically proved the spherical shape of the Planet Earth and its orbit around the Sun as it revolves on its axis.


Born in 933 AD in the ancient Iranian region of Khwarazm, adjoining the Aral Sea, near the city of Kath, in a family following the jurisprudential school of the Ahl al-Bayt or Blessed Household of Prophet Mohammad (blessings of God upon him and his progeny), he started learning the holy Qur’an and memorizing it at an early age. He acquired the epithet “Birouni” since his childhood was spent outside the city. He lived both in Kath and in Jurjaniyya as he grew up and began studies at a very early age under the famous astronomer and mathematician Abu Nasr Mansur. By the age of seventeen, he was engaged in serious scientific work, for it was in 990 that he computed the latitude of Kath by observing the maximum altitude of the sun. Other works which he undertook were more theoretical. Before 995 (when he was 22 years old) he had written a number of short works. One which has survived is his “Cartography” which is a work on map projections. The comparatively quiet life that he led up to this point was to come to a sudden end, because of political events of 995. The end of the 10th century and beginning of the 11th century was a period of great unrest in the Islamic world and there were civil wars in the region in which Birouni was living. Khwarazm was at this time part of the Iranian Samanid Empire which ruled from Bukhara. Other states in the region were the Ziyarid state of northern Iran with its capital at Gorgan on the Caspian Sea. Further west, the Iranian Buwayhid dynasty ruled over the area between the Caspian Sea and the Persian Gulf, and over Iraq. Another kingdom which was rapidly rising in influence was the Turkic Ghaznavids whose capital was at Ghazna in Afghanistan.

In 995 when the local rulers of Khwarazm, who were patrons of Birouni were overthrown in a coup, he fled his homeland and went to Rayy – which today is a southern suburb of Tehran. In Rayy, he met the astronomer Khujandi who was working with a very large instrument he had built on the mountain above the city to observe meridian transits of the sun near the solstices. He made observations on 16 and 17 June 994 for the summer solstice and 14 and 17 December 994 for the winter solstice. From these values he calculated the obliquity of the ecliptic, and the latitude of Rayy but neither are particularly accurate. Khujandi discussed these observations, and his large sextant, with Birouni who later reported on them in his “Tahdid” where he notes that the aperture of the sextant settled by about one span in the course of Khujandi's observations due to the weight of the instrument. Birouni is almost certainly correct in pinpointing the cause of Khujandi's errors. His description of an eclipse of the moon on 24 May 997 which he observed at Kath means that he had returned to his hometown by this time. The eclipse was an event that was also visible in Baghdad and Birouni had arranged with Abu'l-Wafa in Iraq to observe it there. Comparing their timings enabled them to calculate the difference in longitude between the two cities that were far apart. Birouni next travelled to Gorgan where his scientific endeavours were supported by Shah Qabous, the Ziyarid ruler, to whom he dedicated his famous work on Chronology, titled “Asaar al-Baqiya an Qoroun al-Khaliya”.  During this time he wrote seven other works: one on the decimal system, one on the astrolabe, one on astronomical observations, three on astrology, and two on history.

Wars in the region disrupted the scientific work of Birouni and eventually he left Khwarazm and forcibly taken to Ghazna by Sultan Mahmoud. It is likely that he was kept under surveillance at the court of Mahmoud and was not free to leave. However Mahmoud's military excursions into India meant that Birouni was taken to that land, where he made quite a few scientific observations that enabled him to determine the latitudes of eleven towns around the Punjab and the borders of Kashmir. His most famous work India was written as a direct result of the studies he made while in that country, and is titled “Tahqiq ma lil-Hind.” This is a massive work covering many different aspects of the subcontinent. Birouni describes the religion and philosophy of India, its rigid caste system and marriage customs. He then studies the Indian systems of writing and numbers before going on to examine the geography of the land. The book also examines Indian astronomy, astrology and the calendar. He studied Indian literature in the original, translating several Sanskrit texts into Arabic. He also wrote several treatises devoted to certain aspects of Indian astronomy and mathematics which were of particular interest to him. Birouni was amazingly well read, having knowledge of Sanskrit literature on topics such as astrology, astronomy, chronology, geography, grammar, mathematics, medicine, philosophy, religion, and weights and measures. One of the most important works of Birouni is “The Shadows” ,which he wrote around 1021. The contents of the work include the Arabic nomenclature of shade and shadows, strange phenomena involving shadows, gnomonics, the history of the tangent and secant functions, applications of the shadow functions to the astrolabe and to other instruments, shadow observations for the solution of various astronomical problems, and the shadow-determined times of Muslim prayers. Biroun’s bood “The Shadows” is an extremely important source for our knowledge of the history of mathematics, astronomy, and physics.

The book details the mathematical contributions of Birouni. These include: theoretical and practical arithmetic, summation of series, combinatorial analysis, the rule of three, irrational numbers, ratio theory, algebraic definitions, method of solving algebraic equations, geometry, Archimedes' theorems, trisection of the angle and other problems which cannot be solved with ruler and compass alone, conic sections, stereometry, stereographic projection, trigonometry, the sine theorem in the plane, and solving spherical triangles. Important contributions to geodesy and geography were also made by Birouni. He introduced techniques to measure the earth and distances on it using triangulation. He found the radius of the earth to be 6339.6 km, a value not obtained in the West until the 16th century. His book “Qanoun al-Masoudi” dedicated to Sultan Mahmoud’s son and successor, Sultan Mas’oud, contains a table giving the coordinates of six hundred places, almost all of which he had direct knowledge. “At-Tafhim” is the only Persian book which has been authored by Birouni in his native language. According to historical quotes, Birouni wrote the book in Ghazna at the request of Rayhana the daughter of Hussain Khawarzmi . In this book, Birouni has attempted to express the introductory to mathematics and astronomy in a simple language. His audiences are the teen agers who are not much familiar with these sciences. Abu Rayhan Birouni died at the age of around 80.


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