Ulugh Beg

Mīrzā Muhammad Tāraghay bin Shāhrukh, known as Ulugh Beg ("Great Ruler"), was a Timurid sultan, astronomer, and mathematician. The grandson of the conqueror Timur (Tamerlane), he ruled the Timurid Empire from Samarkand. Unlike most rulers of his era, Ulugh Beg was primarily a scientist and scholar. In the 1420s he built the great Samarkand Observatory, one of the finest in the Islamic world and among the largest astronomical observatories of the medieval period. The observatory's main instrument was a massive sextant with a radius of about 36 meters, built into a hillside trench, which allowed extraordinarily precise measurements of stellar and planetary positions. His monumental work, the Zīj-i Sultānī (1437), was a star catalog containing the positions of over 1,000 stars — the first comprehensive original star catalog since Hipparchus. His measurements were remarkably accurate, with positional errors often less than a few arcminutes, making it the most precise star catalog produced before the invention of the telescope. Ulugh Beg also calculated the length of the sidereal year as 365 days, 6 hours, 10 minutes, and 8 seconds — only about 58 seconds longer than the modern accepted value. His determination of the axial tilt of the Earth was similarly precise. He was tragically murdered in 1449 by his own son, and the observatory was destroyed shortly after. However, his star catalog was preserved and later brought to Europe, where it influenced Renaissance astronomers including Tycho Brahe.

Zīj-i Sultānī star catalog (1437) with positions of 1,018 stars — the most accurate pre-telescopic star catalog; Precise measurement of the sidereal year (365d 6h 10m 8s); Accurate determination of Earth's axial tilt (23.52°); Trigonometric tables of sine and tangent values to eight decimal places; Built the Samarkand Observatory with a 36-meter radius sextant