Thābit ibn Qurra

Thābit ibn Qurra (full name: , , ; 826 or 836 – February 19, 901), was a pagan Sabian scholar known for his work in mathematics, medicine, astronomy, and translation. He lived in Baghdad in the second half of the ninth century during the time of the Abbasid Caliphate.

Thābit ibn Qurra made important discoveries in algebra, geometry, and astronomy. In astronomy, Thābit is considered one of the first reformers of the Ptolemaic system, and in mechanics he was a founder of statics. Thābit also wrote extensively on medicine and produced philosophical treatises. The ʿAbbāsid court employed many non-Arab scholars learned both in Arabic and the language of their communities such as Aramaic, Persian and Greek.

According to Ibn al-Nadim, Thābit worked as a money changer in a marketplace in Harran before meeting Muḥammad ibn Mūsā, the oldest of three mathematicians and astronomers known as the Banū Mūsā; Tamara Green has questioned this detail, arguing that the breadth of Thābit's later command of Greek science points to extensive prior academic training rather than a background in trade. Muslim sources report that Thābit had quarreled with his fellow Sabians in Harran over matters of doctrine. Under the patronage of Muḥammad ibn Mūsā, and at the invitation of the caliph, he relocated to Baghdad, where he founded a school staffed by fellow Harranians. Thābit displayed such exceptional linguistic skills that ibn Mūsā chose him to come to Baghdad to be trained in mathematics, astronomy, and philosophy under the tutelage of the Banū Mūsā. Here, Thābit was introduced to not only a community of scholars but also to those who had significant power and influence in Baghdad.

In Baghdad, Thābit is credited by Ibn al-Nadim's Fihrist with having "founded the leadership" (ri'āsa) of the pagans in the city and in the presence of the caliphs, after which the community achieved lasting recognition, standing, and prestige at court. He is reported to have continued to regard himself as protector of his coreligionists at Harran, interceding with the caliph on their behalf. According to the Syriac historian Bar Hebraeus, Thābit defended his ancestral religion in explicitly proud terms, declaring, "We are the heirs and transmitters of ḥanpūthā." Green suggests Thābit may have chosen this Syriac term, cognate with the Arabic ḥanīf, deliberately for its Qur'anic association with Abraham, linking the Harranian Sabians to the same original monotheistic faith the Qur'an attributes to the first ḥanīf.

Thābit and his pupils lived in the midst of the most intellectually vibrant, and probably the largest, city of the time, Baghdad. Thābit came to Baghdad in the first place to work for the Banū Mūsā becoming a part of their circle and helping them translate Greek mathematical texts. What is unknown is how Banū Mūsā and Thābit occupied himself with mathematics, astronomy, astrology, magic, mechanics, medicine, and philosophy. Later in his life, Thābit's patron was the Abbasid Caliph al-Mu'tadid (reigned 892–902), whom he became a court astronomer for. By the end of his life, Thābit had managed to write 150 works on mathematics, astronomy, and medicine. With all the work done by Thābit, most of his work has not lasted time. There are less than a dozen works by him that have survived. which was the Middle Aramaic variety from Edessa, and he was fluent in both Medieval Greek and Arabic. He was the author to multiple treaties. Due to him being trilingual, Thābit was able to have a major role during the Graeco-Arabic translation movement.

Astronomy Thābit is believed to have been an astronomer of Caliph al-Mu'tadid. Thābit was able to use his mathematical work on the examination of Ptolemaic astronomy.

Thābit was also an author and wrote De Anno Solis. This book contained and recorded facts about the evolution in astronomy in the ninth century.

Thābit described a generalized proof of the Pythagorean theorem. He provided a strengthened extension of Pythagoras' proof which included the knowledge of Euclid's fifth postulate. This postulate states that the intersection between two straight line segments combine to create two interior angles which are less than 180 degrees. The method of reduction and composition used by Thābit resulted in a combination and extension of contemporary and ancient knowledge on this famous proof. Thābit believed that geometry was tied with the equality and differences of magnitudes of lines and angles, as well as that ideas of motion (and ideas taken from physics more widely) should be integrated in geometry.

The continued work done on geometric relations and the resulting exponential series allowed Thābit to calculate multiple solutions to chessboard problems. This problem was less to do with the game itself, and more to do with the number of solutions or the nature of solutions possible. In Thābit's case, he worked with combinatorics to work on the permutations needed to win a game of chess.

In addition to Thābit's work on Euclidean geometry there is evidence that he was familiar with the geometry of Archimedes as well. His work with conic sections and the calculation of a paraboloid shape (cupola) show his proficiency as an Archimedean geometer. This is further embossed by Thābit's use of the Archimedean property in order to produce a rudimentary approximation of the volume of a paraboloid. The use of uneven sections, while relatively simple, does show a critical understanding of both Euclidean and Archimedean geometry. Thābit was also responsible for a commentary on Archimedes' .

Physics In physics, Thābit 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 (jadhb): one of these being "between the sublunar and celestial elements", and the other being "between all parts of each element separately". and in mechanics he was a founder of statics. In addition, Thābit's Liber Karatonis contained proof of the law of the lever. This work was the result of combining Aristotelian and Archimedean ideas of dynamics and mechanics. Another piece of important text is Kitab fi sifat alwazn, which discussed concepts of equal-armed balance. Qurra was reportedly one of the first to write about the concept of equal-armed balance or at least to systematize the treatment.

Qurra sought to establish a relationship between forces of motion and the distance traveled by the mobile.

One account of Thābit's work as a physician is given in Ibn al-Qiftī's Ta'rikh al-hukamā, where Thābit is credited with healing a butcher who was presumed to be certain to die. On the Composition of Ratios

In his epitome of al-Qifṭī's Kitāb ikhbār al-'ulamā' bi akhbār al-ḥukamā, al-Zawzanī lists seven religious works in Syriac by Thābit and says that he also wrote in Syriac on music and geometry. According to Bar Hebraeus, the 13th-century Syriac historian, Thābit wrote some 150 works in Arabic and 16 in Syriac. He claims to have seen most of the Syriac works himself and lists them. The list of Bar Hebraeus is consistent with that of al-Zawzanī. Most of the works concern pagan religion, but there is a work on music and two on geometry as well as a "book of the chronicle of the ancient Syrian kings, who are Chaldeans" and a "book on the renown of his race and his forefathers, from whom they descend".

Eponyms Thabit number Thebit (crater)