**Thabit Ibn Qurra Ibn Marwan al-Sabi al-Harrani**was born in the year 836 C.E. at Harran (present Turkey). As the name indicates he was basically a member of the Sabian sect, but the great Muslim mathematician Muhammad Ibn Musa Ibn Shakir, impressed by his knowledge of languages, and realising his potential for a scientific career, selected him to join the scientific group at Baghdad that was being patronised by the Abbasid Caliphs. There, he studied under the famous Banu Musa brothers. It was in this setting that Thabit contributed to several branches of science, notably mathematics, astronomy and mechanics, in addition to translating a large number of works from Greek to Arabic. Later, he was patronised by the Abbasid Caliph al-M'utadid. After a long career of scholarship, Thabit died at Baghdad in 901 C.E. Thabit's major contribution lies in mathematics and astronomy. He was instrumental in extending the concept of traditional geometry to geometrical algebra and proposed several theories that led to the development of non-Euclidean geometry, spherical trigonometry, integral calculus and real numbers. He criticized a number of theorems of Euclid's elements and proposed important improvements. He applied arithmetical terminology to geometrical quantities, and studied several aspects of conic sections, notably those of parabola and ellipse.

A number of his computations aimed at determining the surfaces and volumes of different types of bodies and constitute, in fact, the processes of integral calculus, as developed later. In astronomy he was one of the early reformers of Ptolemaic views. He analyzed several problems related to the movements of sun and moon and wrote treatises on sun-dials.

**Works**

Only a few of Thabit's works are preserved in their original form.

The medieval astronomical theory of the trepidation of the equinoxes is often attributed to Thabit. But it had already been described by Theon of Alexandria in his comments of the Handy Tables of Ptolemaeus. According to Copernicus Thabit determined the length of the sidereal year as 365 days, 6 hours, 9 minutes and 12 seconds (an error of 2 seconds). Copernicus based his claim on the Latin text attributed to Thabit. Thabit published his observations of the Sun.

In mathematics, Thabit discovered an equation for determining the amicable numbers. He also wrote on the theory of numbers, and extended their use to describe the ratios between geometrical quantities, a step which the Greeks never took. Another important contribution Thabit made to geometry was his generalization of the Pythagorean theorem, which he extended from special right triangles to all triangles in general, along with a general proof.

In physics, Thabit rejected the Peripatetic and Aristotelian notions of a "natural place" for each element. He instead proposed a theory of motion in which both the upward and downward motions are caused by weight, and that the order of the universe is a result of two competing attractions : one of these being "between the sublunar and celestial elements", and the other being "between all parts of each element separately".

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