The Astronomer Prince
"Another of Ulugh Beg Mirza's fine buildings is an observatory, that is, an instrument for writing astronomical tables. this stands three storeys high, on the skirt of the Kohik upland. By its means the Mirza worked out the Gurkhani Tables, now used all over the world instead of earlier such compilations...."
Babur, Moghul Emperor, 1483-1530
Samarqand, Uzbekistan, is situated at the crossroads between East and West. Its history as a significant urban settlement dates back to at least the Neolithic period making it one of the earliest in Central Asia. It prospered from its position on the network of routes known as the Silk Roads. It was a cultural, commercial, and political center that was a melting pot of Persian, Turkish, and Hellenistic influences. Under Islamic rule, medieval Samarqand flourished and was one of the important learning centers during the Golden Age of Islam of the 9th through 12th centuries. When Timur made the city the capital of his newly established empire in the late 14th century, Samarqand experienced a rebirth of art, culture, and science.
Timur, known in the West as Tamerlane, was a product of the Central Asian steppes. He was born to a petty chieftain of a Turko-Mongol tribe. This tribe had settled in the region of the Transoxiana, which encompasses areas of Uzbekistan, Tajikistan, Kazakhstan, and Kyrgyzstan. Since the death of Genghis Khan in 1227, the region was ruled by his second son Chagatai Khan and his successors. In 1370, Timur seized power over the province from the Khanate. He established Samarqand as his capital and used it as a base to begin expanding his territory. He shared ancestry with Genghis Khan on his paternal side, and Timur saw himself as a restorer of Genghis Khan's great empire. He conquered most of Central Asia, Iran, Iraq, southern Russia, and India within thirty-five. He defeated the Egyptian Mamluks as well as the Ottoman Turks. He died in 1405 as he attempted to invade China. Praised as a brilliant military commander and condemned as ruthless and unmerciful, Timur was a patron of the arts and brought artisans from all over his empire to Samarqand. He cultivated Persian literature and made Persian the official language. He initiated a flowering period of Islamic art whose influence would spread across the Muslim world. His successors would continue this patronage not only in the arts but also in the sciences and architecture.
Succession in many Asian empires was often a messy affair. Upon Timur's death, family members jockeyed for power resulting in several years of strife and civil war. In 1409, Timur's youngest son Shah-Rukh emerged as the victor. He transferred his capital to Herat in western Afghanistan. He set up his fifteen-year-old son Mohammed Taraghay as governor of Samarqand and the surrounding territories. Taraghay was subsequently given the moniker of Ulugh Beg - "Great Prince." As governor, Ulugh Beg wished to further cement Samarqand's reputation as the intellectual center of Islam. In 1417, he established a madrasa - an Islamic university- and brought many notable astronomers and mathematicians to the city, including his teacher Qadi Zada al-Rumi. Ulugh Beg's interest in astronomy came from his teacher, al-Rumi, and his travels on his grandfather's campaigns as a young child. In particular, he was inspired by a visit to the remains of the Persian observatory at Maragheh, now in present-day eastern Iran.
The observatory was established in 1259 by the Persian astronomer Nasir al-Din al-Tusi with the patronage of Hulagu Khan, Ghengis Khan's grandson and ruler of much of western Asia. The observatory contained several buildings that housed various astronomical instruments. The central tower had an instrument mounted upon the walls to measure angles, observe objects' positions, and was aligned to the meridian. This is known as a mural instrument. There was also an extensive library that was said to contain over 400,000 books. Al-Tusi had the observatory built to compile updated astronomical tables. His work attracted many other Islamic scientists and even students as far away as China came to study and learn at the observatory. With the death of Hulagu, al-Tusi lost his principal patron and financial backer. Financial problems and renewed Mongol invasions from the east ultimately led to disrepair and the loss of the great library.
Astronomy was more than a passing interest for Ulugh Beg. Muslim astronomers relied heavily on the works of ancient Greece and Rome. One of the critical concerns for these observers was ensuring the accuracy of the calendar and astrological readings. This required precise measurements and knowledge of the movement of heavenly bodies. For this reason, Ulugh Beg sponsored the construction of an observatory modeled after the one at Maragheh. Construction began sometime in the early 1420s but was not completed until 1429. It consisted of a three-story circular tower that commanded a hill north of Samarqand. From the top of the tower, a person viewed the distant desert and steppes toward the north and the white-capped Pamir Mountains to the south. The observatory housed one of the largest and most precise mural instruments ever constructed.
Mural instruments were used to measure the altitude of celestial objects in terms of angular degrees. Since ancient times, they have been used, and early forms were either drawn or constructed directly onto a wall. They usually measure angles from 0 to 90, and these are called mural quadrants. The arc is divided into fractions of degrees. An indicator would be at the center of the arc. An observer moves a second device until the line of sight of the two indicators aligns with the observed object. The instrument at Samarqand measured angles from 0 to 60, making it more of a sextant. It was over 200 feet (63 m) along its edge, and a radius was nearly 130 feet (40 m). The lower track of what is referred to as the Fakhri sextant was built into the rock of the hillside. Such a large instrument allowed the astronomers to calibrate the sextant more accurately. Light from an object would come in from an opening in the tower and would have illuminated part of the curved track, which would have been marked precisely with degrees, minutes, and seconds. Astronomer Kevin Krisciunas remarked that the observatory could achieve a resolution of several seconds of arc--on the order of a six-hundredth of a degree, or the diameter of an American penny at a distance of more than half a kilometer."
Such a precise instrument enabled Ulugh Beg to determine highly accurate positions and measurements of various celestial objects. He measured the obliquity of the ecliptic. This is the path of the sun and its angular relationship to the Earth's equator. It is a reflection of the Earth's tilt. Ulugh Beg obtained 23° 30' 17", which has an error of 32" from the modern calculation. He also determined the length of the year to be 365 days 6 hours 10 minutes 8 seconds. He was off by 58 seconds from the modern value. The most important contribution that Ulugh Beg and the astronomers at Samarqand made was the compilation of a star catalog and astronomical table. It was called the Zij-i Sultani, and it would be the most accurate work o its kind since Ptolemy and before Tycho Brahe's work in the 17th century.
The star catalog is organized based on Ptolemy's Almagest. Still, Ulugh Beg, who recognized errors in previous catalogs, decided to determine his own positions of the stars and planets based on his location in Samarqand. The catalog lists the names and positions of 992 fixed stars. Ulugh Beg added 27 stars from another source because these were too far south to be observed from Samarqand. The Zij is divided into four sections. The first is about timekeeping and chronology. The second reviews how the observations were made. The third provides tables of the apparent positions of the Sun, Moon, and Planets. In this section, Ulugh Beg gives the ascending and descending lunar nodes, the places where the moon crosses the ecliptic and talks about predicting eclipses using this information. The final section is about astrology. One of the byproducts of this work was the creation of trigonometric tables. These tables contained the calculation of sines and cosines to the ninth decimal place as accurate as modern calculators.
Unfortunately for Ulugh Beg, he was less capable of a ruler than a scientist. His father died in 1447, and he assumed the throne of the Timurid empire. He became beset by rival claimants, including his son. After suffering several defeats, he surrendered to his son Abd al Latif. Latif allowed Ulugh Beg to make a pilgrimage to Mecca as a self-imposed exile. But Ulugh Beg would not get far out of Samarqand before being killed by his son's assassins. Religious fundamentalists opposed Ulugh Beg's support of the sciences and gained control in Samarqand. They ultimately razed the great observatory and looted the library. Many scholars fled the city for other parts of the Islamic world. One of Ulugh Beg's students was able to smuggle out a copy of the Zij-I Sultani - the star catalog. He had it published and translated into Arabic, and for the next century, Islamic astronomers used the tables. In the mid-17th century, the catalog was translated into English, and the Western world was introduced to Ulugh Beg's works. It came too late as Tycho Brahe, the great Danish astronomer, had already constructed his own widely used star tables. Though not familiar in the west, Ulugh Beg's work influenced the sciences in the Moghul Empire of Southeast Asia. Russian archaeologists would discover the remains of the observatory in the early 20th century.
Astronomy and Astrology in the Islamic World: Stephen Blake
History of Arabic Astronomy: Planetary Theories During the Golden Age of Islam: George Saliba