Most empires remember their grandsons badly. Timur’s grandson is the exception: Mirza Muhammad Taraghay, known to history by his honorific Ulugh Beg (“great ruler”), governed Samarkand for four decades and spent most of that time doing something no other ruler of his century attempted at that scale — measuring the sky. The star catalogue his team produced in 1437 was the most substantial fresh survey of stellar positions made anywhere between Ptolemy in the second century and Tycho Brahe in the sixteenth.
It is a strange and slightly sad story. The same man who assembled the finest observatory in the Islamic world was an indifferent politician and a worse general, and he was beheaded in 1449 on the orders of his own son. His observatory was pulled down, its location forgotten for four and a half centuries, and rediscovered only in 1908 by a Russian archaeologist digging on a hill outside the city.
This guide covers the man and the science — who he was, what his astronomers actually measured, how accurate they were, and how his numbers ended up being printed at Oxford two centuries after his death. For the practical business of visiting the observatory site — tickets, opening times, how to get up the hill — see our separate Ulugh Beg Observatory guide.
The prince who preferred mathematics
Ulugh Beg was born on 22 March 1394 at Sultaniyya, in what is now northwestern Iran, while his grandfather Timur was on campaign. He was raised in the household of Timur’s senior wife, Saray Mulk Khanum, and travelled with the court as a child — including, by most accounts, on Timur’s campaigns into Anatolia. That upbringing gave him an education in the Persianate scholarly tradition that most Timurid princes received, and in his case it took unusually deep root.
When Timur died in 1405 the empire fractured, as Timurid empires reliably did. Ulugh Beg’s father, Shahrukh, emerged on top and ruled from Herat. In 1409 he installed his teenage son as governor of Samarkand and the province of Transoxiana. Ulugh Beg was about fifteen. He would hold that post for roughly forty years, and for most of it his father’s authority in Herat gave him something rare in the fifteenth century: a stable, wealthy province and very little obligation to fight for it.
He used it to build. To understand what Samarkand had already become before he inherited it, our guide to Silk Road history in Uzbekistan covers the century of conquest and construction that preceded him.
The Samarkand school
Ulugh Beg’s real achievement was institutional rather than personal. He recruited the best mathematicians and astronomers he could find and paid them to work together in one place for years — a research institute in everything but name.
Three names matter most:
- Qadi Zada al-Rumi — a mathematician from Bursa in Anatolia, the senior figure of the school and effectively its first director.
- Jamshid al-Kashi — arguably the finest computational mathematician of the age, who calculated pi to sixteen decimal places and whose letters home give us much of what we know about how the observatory actually worked day to day. He died around 1429, early in the observing programme.
- Ali Qushji — the youngest of the circle, who survived Ulugh Beg by decades, carried the completed tables westward and ended his career in Ottoman Istanbul. He is a large part of the reason the work was not lost entirely.
Ulugh Beg took part in the observations himself and was competent enough that his collaborators treated him as a colleague rather than a patron to be flattered. Al-Kashi’s correspondence, which is fairly blunt about the abilities of everyone else at court, is notably respectful about the prince’s mathematics.
The observatory and its great instrument
Construction of the observatory on Kuhak hill, north-east of the city, began in the 1420s. The building was a cylindrical structure of three storeys, richly tiled, holding a range of instruments — but everything was arranged around one enormous device.
The Fakhri sextant was a meridian arc with a radius of just over 40 metres, the largest instrument of its kind ever built. Rather than mount it above ground, where its own weight and the wind would have flexed it, the builders sank it into a trench roughly two metres wide cut into the bedrock of the hill, aligned precisely north–south along the meridian. Immobility was the entire point: a movable instrument accumulates errors every time it is repositioned, while a fixed arc cut into a hillside does not move at all.
Size bought precision in the graduations. On an arc that large, one degree of angle occupies about 70 centimetres of physical arc, which meant a single minute could be marked at roughly 12 millimetres and divisions down to a few seconds of arc were physically possible to inscribe and read. The instrument was used to pin down the solar constants — the obliquity of the ecliptic, the moment of the equinox, the length of the year.
The section that survives today is the underground portion of that trench, with its two parallel marble-faced rails running down into the hill. It is the only part that was below ground level, which is exactly why it is the only part that outlasted the building’s destruction.
The Zij-i Sultani and how good it actually was
The observatory’s output was the Zij-i Sultani, completed around 1437 and revised until shortly before Ulugh Beg’s death. A zij is a handbook of astronomical tables — the reference work a working astronomer or astrologer would actually consult — and this one had two parts that mattered.
The star catalogue
The catalogue lists 1,018 stars. Crucially, 992 of those positions were freshly observed from Samarkand rather than copied forward from Ptolemy with a correction applied — which is what most intervening catalogues had done. The remaining 27 stars sit too far south to be seen from Samarkand’s latitude, and for those Ulugh Beg’s team openly took the values from al-Sufi’s tenth-century Book of Fixed Stars. That honesty about the limits of their own data is one reason historians of science take the catalogue seriously.
The constants
The solar measurements are where the observatory’s scale paid off.
| Quantity | Ulugh Beg’s value (1437) | Best modern comparison | Error |
|---|---|---|---|
| Length of the sidereal year | 365d 6h 10m 8s | 365d 6h 9m 10s | about +58 seconds |
| Refined sidereal year (later working) | 365d 6h 9m 35s | as above | about +25 seconds |
| Obliquity of the ecliptic | 23° 30′ 17″ | 23° 30′ 48″ (the true value in 1437) | about 31 arcseconds |
An error of half an arcminute on the Earth’s axial tilt, measured with no optics whatsoever, is a genuinely remarkable result for the fifteenth century.
One claim worth correcting
You will often read online that Ulugh Beg measured the axial tilt as “23.52 degrees, exactly matching the modern value.” This is wrong twice over, and it is worth flagging because it appears on a great many travel pages and even some observatory websites. His figure of 23° 30′ 17″ is 23.505 degrees, not 23.52. And it does not match the modern value, because the obliquity is not a fixed number — it drifts slowly, and today it stands at roughly 23.44 degrees. What Ulugh Beg got remarkably close to was the true obliquity of his own era, which is the meaningful comparison and impressive enough without embellishment.
The madrasahs
Ulugh Beg founded three madrasahs — at Samarkand, Bukhara and Gijduvan — and staffed them to teach mathematics and astronomy alongside the standard religious curriculum. The Samarkand madrasah, built between about 1417 and 1420 on the western side of the Registan, is the oldest surviving building on that square and the only one dating from the fifteenth century; the two facing it are seventeenth-century additions. Its façade is decorated with star patterns, which is not a coincidence.
The Bukhara madrasah of 1417 still stands near the Kalyan complex and is generally reckoned the oldest madrasah of its type in Central Asia — worth seeking out if you are working through our Bukhara travel guide.
A poor ruler and a violent end
Shahrukh died in 1447 and Ulugh Beg finally inherited the wider Timurid throne he had spent forty years not preparing for. It went badly almost immediately. He lost territory, lost battles, and lost the confidence of the religious establishment and the military aristocracy, neither of which had much use for a sultan whose priority was tabulating stars.
His eldest son, Abdal-Latif, defeated him in the field in 1449. Ulugh Beg was permitted to set out on pilgrimage to Mecca and was beheaded just outside Samarkand on 27 October 1449 by an assassin acting on his son’s orders. Abdal-Latif was himself killed some six months later. The observatory was abandoned and eventually demolished; the astronomers scattered.
There is a grim postscript. When Soviet anthropologist Mikhail Gerasimov opened the Timurid tombs in the Gur-e-Amir in 1941, the remains identified as Ulugh Beg’s showed cervical vertebrae severed by a clean blade cut — physical confirmation of the manner of his death.
Lost, then found in 1908
The observatory’s location passed out of memory entirely. It was recovered in 1908 by Vasily Vyatkin, a Russian archaeologist working from a seventeenth-century property deed that referenced the site, who dug on Kuhak hill and found the buried arc of the sextant still in place. Everything visible at the site today descends from that excavation.
How the numbers reached Europe
Ali Qushji’s journey west carried manuscript copies of the Zij into the Ottoman world, and from there copies eventually reached European libraries. The English route runs through Oxford. In 1648 the positions of 98 stars appeared in print in a volume published at Oxford, drawn from work by the astronomer John Greaves, who had compiled the tables from Persian manuscripts. In 1665 Thomas Hyde, then a young orientalist, published the catalogue in full with a parallel Latin translation and commentary, edited from Bodleian manuscripts.
That is how a set of measurements made on a Samarkand hillside in the 1430s became a working reference for seventeenth-century European astronomers, Johannes Hevelius among them, more than two hundred years after the man who commissioned them was killed.
Where to see his legacy today
| Site | City | What it shows you |
|---|---|---|
| Observatory site and museum | Samarkand | The surviving underground arc of the sextant, plus a small museum |
| Ulugh Beg Madrasah, Registan | Samarkand | His teaching institution; the oldest building on the square |
| Gur-e-Amir | Samarkand | His grave, alongside Timur and Shahrukh |
| Ulugh Beg Madrasah | Bukhara | His 1417 foundation, the earliest of the three |
All four sit comfortably within a standard Uzbekistan route — see our Samarkand travel guide for how to sequence the Samarkand three in a day.
Frequently Asked Questions
Was Ulugh Beg really an astronomer, or just a patron?
He was a genuine working astronomer and a capable mathematician, not merely a funder. He observed alongside his team and contributed to the analysis, and his collaborators — including al-Kashi, who was sparing with praise — treated his technical judgement as sound. The Zij-i Sultani is nonetheless a collective product of the Samarkand school rather than one man’s work.
How accurate was his star catalogue by modern standards?
Typical positional errors run to a fraction of a degree — far coarser than anything a modern instrument produces, but the best available anywhere until Tycho Brahe’s naked-eye observations over a century later. The more important point is that the positions were newly measured rather than inherited from Ptolemy, which made the catalogue an independent check on a thousand years of accumulated assumption.
Why was the observatory destroyed?
It was abandoned after Ulugh Beg’s assassination in 1449 and demolished in the decades that followed. The usual explanation points to hostility from a conservative religious faction that regarded the work as suspect, though the simpler factor is that its patron was dead and no successor had any interest in paying for it.
Is the observatory worth visiting if I’ve seen the Registan?
It is architecturally modest — a trench and a small museum, not a monument on the scale of the Registan — so manage expectations. Visit it for what it represents rather than for spectacle; knowing what the arc was for makes the difference between five minutes and an hour. Practical details are in our observatory guide.
Where is Ulugh Beg buried?
In the Gur-e-Amir mausoleum in Samarkand, in the Timurid family crypt alongside his grandfather Timur and his father Shahrukh. His remains were examined during the 1941 Soviet exhumation, which confirmed he had been beheaded.
Did his work influence European astronomy?
Yes, though indirectly and late. His tables travelled west through Ali Qushji into the Ottoman world, and reached print at Oxford in 1648 and in full in 1665. Seventeenth-century European astronomers used the catalogue as a comparison set, by which time the observations were more than two centuries old.
Ulugh Beg is the rare ruler remembered for what he measured rather than what he took. Standing at the top of that trench on Kuhak hill, with the marble rails disappearing into the hillside, it is worth remembering that the numbers produced there were still being consulted in Oxford when Newton was a student. Further reading: the Britannica entry on Ulugh Beg, the UNESCO Portal to the Heritage of Astronomy record for the observatory, and the Linda Hall Library’s Scientist of the Day profile.
Featured image: Bobyrr (CC BY-SA 4.0) via Wikimedia Commons.
