Thabit ibn Qurra abu' l'Hasan ibn Marwan al-Sabi al'Harrani, (826 – February 18, 901) was an Arab astronomer and mathematician. In Latin he was known as Thebit.
Thabit was born in Harran (antique Carrhae), Mesopotamia (now Turkey). Upon the proposal of Muhammad ibn Musa ibn Shakir Thabit went to study in Baghdad to Shakir's brothers the Bani Mussa. He led a group of translators, who came from the pagan pseudo Sabeans from Harran. Arabic writters confound the Babylonian Sabeans from the Harrarian Sabeans. Harrarian Sabeans respected stars and for this reason they have very soon showed a great interests for astronomy and mathematics. In the times of Muslim supremacy they have accepted the name Sabean to get benefits from privileges that were allowed by the Ko'ran. This name later ramained and this strange sect have lived in vicinity of the main center of the Caliphate till the half of the 13th century, when the Mongols have destroyed their last shrine. Their merits in the spiritual and scientifical fields have with no doubt helped them to get a protection from the Muslims. In the times of al-Mutawakkil reign their city became a center of the philosophical and medical school, which was transferred from Alexandria to Antioch. Very soon they have taken over a huge part of the Greek culture and science. In the beginnings they have spoken Greek.
Thabit and his pupils lived in this midst. He worked in Baghdad and he occupied himself with mathematics, astronomy, mechanics, medicine and philosophy. His native language was Syriac, which was the eastern Aramaic dialect from Edessa, and he knew well also Greek. He translated from Greek Apollonius, Archimedes, Euclid and Ptolemy. Thabit had revised translation of Euclid Elements of Hunayn ibn Ishaq. He had also rewritten the Hunayn's translation of Ptolemy's Almagest and he translated Ptolemy's Geography, which later became very known. Later Thabit's patron was the Abbasid Caliph al-Mu'tadid (reigned 892–902) and Thabit very soon became his personal friend and the visitor of his court. There are just a few original Thabit's works that were preserved.
Thabit has developed a theory about the trepidation and oscilation of the equinoctial points, of which many scolars debated in the Middle Ages. According to Copernicus Thabit has determined the length of the sidereal year 365d 6h 9m 12s (an error of 2s). He published his observations of the Sun. In mathematics Thabit discovered an equation for determining the amicable numbers.
Thabit died in Baghdad. After him the greatest Sabean name was Al-Batani. Thabit and his grandson Ibrahim ibn Sinan have studied the curves which are needed for making of sundials. Abu'l-Wafa has also written a book about the geometrical methods, which were required by craftsmen.