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The eminent Iranian astronomer and mathematician, Ghiyaseddin Jamshid Kashani

Compiled by: Syed Ali Shahbaz
On 19th of the Islamic month of Ramadhan in 832 AH, the eminent Iranian astronomer and mathematician, Ghiyaseddin Jamshid Kashani, died under suspicious circumstances in Samarqand at the age of around 50 years. He was born in Kashan and went to Samarqand at the invitation of the Timurid scientist-ruler, Ologh Beg, to set up the famous observatory. He produced a Zij entitled the “Khaqani Zij”, which was based on Khwaja Naseereddin Tusi's “Zij-e Ilkhani”.
He also produced tables on transformations between coordinate systems on the celestial sphere, such as the transformation from the ecliptic coordinate system to the equatorial coordinate system. He wrote the book “Sullam as-Sama” on the resolution of difficulties met by predecessors in the determination of distances and sizes of heavenly bodies such as the Earth, the Moon, the Sun and the Stars. He also invented a mechanical planetary computer which he called the Plate of Zones, which could graphically solve a number of planetary problems, including the prediction of the true positions in longitude of the Sun and Moon, and the planets in terms of elliptical orbits; the latitudes of the Sun, Moon, and planets; and the ecliptic of the Sun. In one of his numerical approximations of "P" (pronounced pie), he correctly computed 2 P to 9 sexagesimal digits. This approximation of 2 P is equivalent to 16 decimal places of accuracy.
This was far more accurate than the estimates earlier given in Greek mathematics of 3 decimal places by Archimedes, Chinese mathematics of 7 decimal places by Zu Chongzhi and Indian mathematics of 11 decimal places by Madhava of Sangamagrama. The accuracy of Jamshid Kashani's estimate was not surpassed until Ludolph van Ceulen computed 20 decimal places of "P" nearly 200 years later.

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