A pagan money changer from Harran who measured the year to within seconds
Thābit ibn Qurra, a 9th-century scholar in Baghdad, is credited with putting the sidereal year at 365 days, 6 hours, 9 minutes and 12 seconds, which Copernicus judged only 2 seconds off. He also translated Euclid and Archimedes, helped found statics, and wrote 150 works, of which fewer than a dozen survive.
Thābit was born in Harran in Upper Mesopotamia and spoke Syriac as his first language. He belonged to the Sabians of Harran, a Hellenized star-worshipping religion that still survived there in his time. One medieval source says he was working as a money changer in the market when Muḥammad ibn Mūsā, one of three scholarly brothers known as the Banū Mūsā, noticed his remarkable gift for languages and brought him to Baghdad to train in mathematics, astronomy and philosophy. A modern historian doubts the money-changer story, arguing his mastery of Greek science implies serious schooling beforehand.
Fluent in Syriac, Greek and Arabic, he became a key figure in the movement that carried Greek learning into Arabic. He translated Apollonius, Archimedes, Euclid and Ptolemy, revised an existing Arabic Elements, and his version of an Archimedes work on building a regular heptagon turned up in the 20th century after the Greek original had been lost. He also founded a school of translation and, it was said, secured lasting standing for the pagan community at the caliph's court, proudly defending his ancestral faith.
His own mathematics was inventive. He derived a rule for finding amicable numbers, extended number theory to describe ratios between geometric quantities in a way the Greeks never had, and produced a generalized proof of the Pythagorean theorem. He approximated the volume of a paraboloid, worked on combinatorial chessboard problems, and proved the law of the lever. In physics he rejected Aristotle's idea that each element has a natural place, proposing instead that weight causes both upward and downward motion.
Late in life he served as court astronomer and personal friend to Caliph al-Mu'tadid. He was also a respected physician, writing on smallpox, measles, eye conditions and even the anatomy of birds, and one chronicle credits him with saving a butcher everyone expected to die. He died in Baghdad in 901, and his son and grandson carried on the family's scientific work.
Source: Thābit ibn Qurra
