1429
Ghiyath al-Din Jamshid al-Kashi
Mathematician and astronomer
A mathematician and astronomer from Kashan and one of the first directors of Ulugh Beg's observatory. In Samarkand he calculated π to 16 decimal places — a record that stood for nearly 170 years.
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From Kashan to Samarkand
Ghiyath al-Din Jamshid ibn Mas'ud al-Kashi was born around 1380 in Kashan, in central Iran. He took up astronomy young: in 1407 he wrote The Stairway of Heaven, on the sizes and distances of celestial bodies, and in 1416 treatises on astronomical instruments. His Khaqani Zij, an improvement on Nasir al-Din Tusi's tables, was dedicated to Ulugh Beg.
Around 1420 he moved to Samarkand at Ulugh Beg's invitation. His letters home to his father in Kashan survive, describing the building of the observatory, the debates in the madrasa and Ulugh Beg's own mathematical gifts — a rare eyewitness view of Samarkand's scientific life in the 15th century. Together with Qadi Zada al-Rumi he directed the construction of the observatory and its instruments.
A master of calculation
In his Treatise on the Circumference (1424) al-Kashi computed 2π to nine sexagesimal places — sixteen decimal digits. Nobody surpassed it until the Dutchman Ludolph van Ceulen in 1596, nearly 170 years later.
The Key to Arithmetic, finished in 1427, is a vast manual of arithmetic, algebra and practical measurement that sets out decimal fractions systematically. In his Treatise on the Chord and Sine he devised an iterative method for finding the sine of one degree with great precision, and he also invented an instrument that determined planetary positions graphically.
Death
Al-Kashi died in Samarkand on 22 June 1429, just as work on the Zij-i Sultani was getting under way. Various theories have been put forward about his death, but nothing is certain. Ulugh Beg remembered him as one of the most famous scholars in the world, a perfect master of the science of the ancients who could solve the most difficult problems.
