Astronomy · a Light

A prince measured a thousand stars and timed the year

Ulugh Beg was a grandson of Timur and governor of Samarkand, and he was more interested in the sky than in ruling. In the 1420s he built an observatory whose main instrument was a sextant arc about forty metres in radius, sunk into a trench in the rock so it could not shift. In 1437 his team completed the Zij-i Sultani, a catalogue of 1,018 stars measured fresh rather than copied from Ptolemy, along with a value for the length of the year that is within about a minute of the modern figure. He was killed in 1449. The buried arc of his instrument was rediscovered by excavation in 1908 and can be visited.

Ulugh Beg · Samarkand, 1437 CE