Ulugh Beg, Timur's grandson, measured the year with a 36-metre sextant
Without any telescope, a fifteenth-century prince in Samarkand built a sextant with a radius of about 36 metres and timed the sidereal year within a minute. Ulugh Beg was a brilliant astronomer and a weak ruler, and his own eldest son ended his reign in 1449.
Born on 22 March 1394 in Sultaniyeh while his grandfather Timur was invading Persia, he was named Muhammad Taraghay; Ulugh Beg, roughly great ruler, was a title rather than a name. As a boy he travelled across much of the Middle East and India with Timur's campaigns, and a youthful visit to the Maragheh Observatory, where Nasir al-Din al-Tusi had worked, sparked his love of astronomy. He reportedly spoke five languages, including a little Chinese.
After Timur died, his father Shah Rukh moved the capital to Herat, and in 1409 the sixteen-year-old became governor of Samarkand, later ruling all of Transoxiana. He built a madrasa on Registan Square between 1417 and 1420, still standing, and invited astronomers and mathematicians to teach there. Around 1428 he raised a vast observatory. Using the giant Fakhri sextant, his team produced the 1437 Zij-i-Sultani, often ranked the finest star catalogue between those of Ptolemy and Tycho Brahe.
That year he put the sidereal year at 365 days, 6 hours, 10 minutes and 8 seconds, just 58 seconds too long, using a 50-metre gnomon. Copernicus improved on it by 28 seconds in 1525. He also computed sine and tangent tables accurate to at least eight decimal places. His court traded envoys and gifts with Ming emperors, including a horse the Zhengtong emperor had painted in 1439.
Governing proved harder. When Shah Rukh died in 1447, a nephew claimed the throne in Herat; Ulugh Beg defeated him but then faced a rebellion by his eldest son Abdal-Latif, governor of Balkh, who overthrew him and had him killed around 1449. Another nephew later restored his reputation and reburied him at Timur's feet in the Gur-e-Amir, where Soviet archaeologists found his remains in 1941.
Source: Ulugh Beg
