A prince's scientific ambition
In the 1420s, the Timurid ruler Ulugh Beg, grandson of the conqueror Timur, shifted his focus from empire-building to the cosmos. Near his capital of Samarkand, he commissioned a monumental observatory, a three-story circular building about 46 meters in diameter and 30 meters high. Unlike a typical ruler, Ulugh Beg was a skilled astronomer and mathematician who actively participated in the observatory's work alongside dozens of the era's leading scientists, including Jamshid al-Kashi and Ali Qushji.
The centerpiece of the institution was a colossal instrument called the Fakhri sextant. To ensure its stability and precision, the main arc of the sextant was built into the earth itself. A deep trench, two meters wide, was dug along the meridian line, housing a massive marble arc with a radius of 40.04 meters. This design made it the largest meridian instrument of its time and allowed for exceptionally precise measurements. The scale was so large that a single degree of arc spanned over 70 centimeters of marble, allowing for gradations fine enough to measure angles with high accuracy.
The Sultan of Stars' catalog
The primary mission of the Samarkand observatory was to create a new, comprehensive star catalog based on fresh observations, and updated the classical works of Ptolemy. The result, published around 1437, was the Zij-i-Sultani ("The Sultan's Astronomical Tables"). This work listed the positions of 1,018 stars, with 992 of them being newly measured from Samarkand.
The accuracy achieved without telescopes was remarkable. The team made several fundamental astronomical calculations. They determined the length of the tropical year (the time from one spring equinox to the next) to be 365 days, 5 hours, 49 minutes, and 15 seconds. This figure was only 25 seconds longer than the modern value and more accurate than the calculation Nicolaus Copernicus would make nearly a century later. They also measured the Earth's axial tilt with extraordinary precision, calculating it as 23.5047 degrees (23° 30' 17"). This is a historically accurate value, superior to later measurements by both Copernicus and Tycho Brahe.
Ulugh Beg's reign was short. Following his assassination in 1449, ordered by his own son, the observatory was abandoned and eventually destroyed. For centuries, its exact location was lost. In 1908, Russian archaeologist V.L. Vyatkin, guided by historical land deeds, rediscovered the foundations and the buried portion of the great marble sextant.