Commemorating the Great Scientist Abu Rayhan Berouni

Every year on Shahrivar 13, corresponding to September 4, the Islamic Republic of Iran, commemorates prominent Iranian Islamic scientist, Abu Rayhan Mohammad Ibn Ahmad al-Berouni, who was born in 973 AD in the ancient Iranian land of Khwarezm, a region adjoining the Aral Sea and presently divided among the three Central Asian republics of Turkmenistan, Uzbekistan and Kazakhstan.

His hometown was Kath, which today lies in the Karakalpakstan region of Uzbekistan and has been named Beruniy in honour of this multisided genius who authored some 180 books and treatises on a wide variety of subjects such as history, geography, astronomy, mathematics, mineralogy, etc.

Abu Rayhan Berouni began studies at a very early age under the famous astronomer and mathematician Abu Nasr Mansur, a prince of the local Banu Iraq rulers. By the age of seventeen he was engaged in serious scientific work and at this young age he computed the latitude of Kath by observing the maximum altitude of the sun. By the time he had reached 22 years, he had written several treatises, including one on cartography or map projections.

The comparatively quiet life that Berouni led up to this point was to come to a sudden end by the political events of the year 995. Khwarezm was part of the Iranian Samanid Empire with its capital at Bukhara. Other states in the region were the Iranian Ziyarid state with its capital at Gurgan on the Caspian Sea. Further west, was the third powerful Iranian state of the Buwayhid dynasty that ruled over the area between the Caspian Sea and the Persian Gulf as well as Iraq and Oman.
To the east in what is now Afghanistan a Turkic but thoroughly Persianized kingdom which was rapidly rising in influence was the Ghaznavids whose capital was at Ghazna, a kingdom which was to play a major role in Berouni's life.

In 995 Berouni had to flee his homeland at the outbreak of a civil war and settled for some time in Rayy near where modern Tehran stands today. Here he met the astronomer Abu Mahmoud al-Khujandi who was working with a very large instrument he had built on the mountain above Rayy to observe meridian transits of the sun near the solstices. The two discussed these observations, and the young Berouni pointed to the elderly Khujandi's errors. Berouni seemed to have spent part of this time in Gilan on the Caspian Sea, as is evident by the work he dedicated to the local ruler, Ibn Rustam, who was a vassal of the Ziyarid state.

In 997 Berouni returned to his native Kath, where he observed an eclipse, and at the same time arranged with fellow astronomer Abu'l-Wafa in Baghdad to observe it as well. Comparing their timings enabled the two to calculate the difference in longitude between the cities – a distance of some 1,600 km. It means, Berouni moved around frequently during this period, for by the year 1000 he was at Gorgan being supported by Qabous, the ruler of the Ziyarid state. He dedicated his work Chronology to Qabous around this time. Until 1017, he was busy in his scientific work in Jurjaniyya when Khwarezm was conquered by Sultan Mahmoud of Ghazna, where Berouni and several scholars were taken, perhaps as prisoners initially. Mahmoud provided patronage to Berouni’s scientific work. Berouni accompanied the sultan on his expeditions to beginning from 1022. In 1026 he reached the shores of the India Ocean. Berouni made keen observations of the northern parts including Punjab and Kashmir, and the result was the monumental work titled “Tahqiq ma lil-Hind”. This is a massive work covering many different aspects of the subcontinent. Berouni describes the religion and philosophy of India, its caste system and marriage customs. He then studies the Indian systems of writing and numbers before going on to examine the geography of the country. The book also examines Indian astronomy, astrology and the calendar. Berouni studied Indian literature in the original, translating several Sanskrit texts into Arabic. He was amazingly well read, having knowledge of Sanskrit literature.

In 1030 Mahmoud died and after a power struggle between his two sons, was succeeded by the elder, Ma’soud, to whom Berouni dedicated his encyclopedic work titled Qanoun al-Mas’oudi, in which he utilizes his observational data to disprove Ptolemy's immobile solar apogee. Here he also wrote an in-depth analysis and explanation of an astrolabe and how it should work. He drew many different depictions of various instruments that are considered to be the precursors of more modern objects such as clocks and the astrolabe. Berouni's eclipse data was used by British astronomer Richard Dunthorne in 1749 to determine the acceleration of the moon, and his observational data has entered the larger astronomical historical record and is still used today in geophysics and astronomy. The concept of the morning dawn and evening twilight were introduced by Berouni who described the scene at morning dawn and evening twilight in the book Qanoun al-Mas’oudi and concluded that the twilight occur when the position of the sun is at an altitude of -18°. The concept of Berouni is recognized by modern science, astronomy, and conform to the Islamic hadith. Besides, the discovery of Berouni on the height of the sun is so far used by several religious organizations in some countries to set the time for Isha or night and fajr and pre-dawn ritual prayers.

Another important work of Berouni is “Shadows”, the contents of which are an extremely important source for the history of mathematics, astronomy, and physics. It also contains important ideas such as the idea that acceleration is connected with non-uniform motion, using three rectangular coordinates to define a point in 3-space, and ideas that some see as anticipating the introduction of polar coordinates.

Berouni also made important contributions to geodesy and geography. 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 Europe until the 16th century. Berouni also wrote a treatise on time-keeping, wrote several treatises on the astrolabe and describes a mechanical calendar. He makes interesting observations on the velocity of light, stating that its velocity is immense compared with that of sound. He also describes the Milky Way as “a collection of countless fragments of the nature of nebulous stars.”

Topics in physics that were studied by Berouni included hydrostatics and made very accurate measurements of specific weights. He described the ratios between the densities of gold, mercury, lead, silver, bronze, copper, brass, iron, and tin. He displayed the results as combinations of integers and numbers of the form 1/n, n = 2, 3, 4, ... , 10.

Many of Berouni's ideas were worked out in discussions and arguments with other scholars. He had a long-standing collaboration with his teacher Abu Nasr Mansur, each asking the other to undertake specific pieces of work to support their own. He corresponded with his younger contemporary Abu Ali Ibn Sina, in a rather confrontational fashion, about the nature of heat and light. In eighteen letters which Ibn Sina had sent to Berouni, topics such as philosophy, astronomy and physics are discussed.

Berouni as a devout Muslim, was a follower of the Ahl al-Bayt or Blessed Household of Prophet Mohammad (SAWA). On the basis of hadith he scientifically proved the spherical shape of the Earth as it revolves around the Sun, half millennium before the Europeans Copernicus and Galileo publicized in the West by borrowing from the writings of this great Iranian Islamic scientist.