Tamerlane's grandson got the length of the year wrong by just 58 seconds.

1424 · 1437 · apart: 13 years

In 1437 Ulugh Beg in Samarkand calculated the sidereal year as 365 days, 6 hours, 10 minutes and 8 seconds.

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The event

• Ulugh Beg's observatoryc. 1424 · Samarkand (Uzbekistan). Timur's grandson Ulugh Beg, ruler of Samarkand, built an observatory on Kuhak hill in the 1420s, with a giant sextant about 40 metres in radius. His astronomers compiled the Zij-i Sultani, tables giving the positions of more than a thousand stars and a length of the year within about a minute of the true value. After Ulugh Beg was murdered in 1449 the observatory was destroyed; archaeologist Vasily Vyatkin unearthed its remains in 1908.

15th century

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