He inherited Tamerlane's empire and would rather have had the exact length of the year. He got the year.
On a hill north-east of Samarkand, a grandson of Tamerlane sank a marble arc into the bedrock — a curve so vast that its radius ran past forty metres, its lower run cut down into the rock — and aimed it at the meridian. Around it he raised a cylinder of brick and glazed tile three storeys high, and into it he moved the best mathematicians he could find anywhere between Anatolia and China. Ulugh Beg was a prince of the largest empire in Asia. What he wanted was a sky measured properly.
He got it. By 1437 his observatory had fixed the positions of 1,018 stars by fresh observation — the first great catalogue compiled from scratch since Ptolemy, thirteen centuries earlier — and pinned the length of the sidereal year to within a minute of the value we use today. Twelve years later his eldest son had him beheaded on the road to Mecca, and the observatory was stripped for its bricks until even its location was forgotten.
Prince, teacher, astronomer, casualty
The lifeline
1394
Born at Sultaniyya in Persia, in the marching camp of his grandfather Timur
1409
Not yet sixteen, he is given Samarkand and all Transoxiana to govern
1420
His madrasa opens on the Registan — and he lectures in it himself
1424
Begins the great observatory, built around a meridian arc of 40.4 m radius
1437
Completes the Zij-i Sultani — 1,018 stars, newly measured
1449
Deposed and beheaded at 55 on his own son's order; the observatory is razed
By the numbers
The measure of him
40.4 m
Radius of the marble meridian arc — the largest astronomical instrument of its age
1,018
Stars whose positions he and his astronomers fixed anew from Samarkand
58 sec
His whole error in the sidereal year: 365d 6h 10m 8s, against 6h 9m 10s
459
Years his observatory lay lost — razed in 1449, dug up again in 1908
What Samarkand produced
The work
1417–1420
The madrasa on the Registan. He built it, staffed it with mathematicians rather than courtiers, and taught in it. It is still standing, and still the oldest building on the square.
1424–1429
The Samarkand observatory. A three-storey drum some 46 m across, wrapped around the great meridian arc — the most ambitious instrument built anywhere before the telescope.
c. 1429
sin 1° to sixteen decimal places, computed at Samarkand by his colleague Jamshid al-Kashi — a precision no one in Europe would approach for nearly two hundred years.
1437
The Zij-i Sultani. Star catalogue, planetary tables, and tables of sines and tangents at one-minute intervals: the most accurate astronomical work produced anywhere in the pre-telescopic world.
1648 · 1665
Oxford prints him. John Greaves publishes part of the catalogue, then Thomas Hyde the whole of it in Latin — two centuries after his death, European astronomers are still checking their stars against Samarkand.
A poor king and a great astronomer
Recognition
In his lifetime
A middling soldier and a worse politician — he held the sultanate barely two years
Deposed by his eldest son, Abd al-Latif, and beheaded in October 1449
The observatory was pulled apart for building stone within a generation
Its site was so thoroughly lost that scholars argued over where it had stood
Today
His star positions were printed and consulted in Europe into the 1600s
The excavated arc, found in 1908, sits in a UNESCO World Heritage site
The lunar crater Ulugh Beigh and asteroid 2439 Ulugbek carry his name
Uzbekistan's national astronomical institute is named for him
Where the sky was measured
Samarkand
Timur had made Samarkand the capital of an empire reaching from Delhi to Anatolia, and filled it with plundered craftsmen and blue tile. His grandson filled it with astronomers. The observatory stood on Kuhak hill outside the walls; the madrasa still faces the Registan. In 1449 the first was destroyed and the second survived — which is roughly the wrong way round, and the reason it took the world four and a half centuries to work out what he had done.
46 m
Across the observatory drum, three storeys high, on Kuhak hill
1908
Year the archaeologist V. L. Vyatkin uncovered the buried arc
3
Madrasas on the Registan today — his was the first of them
"The pursuit of knowledge is the duty of every Muslim, man and woman."
— Inscribed over the gate of the Ulugh Beg Madrasa, Samarkand, 1420
