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Ulugh Beg and His Observatory




Ulugh Beg was the oldest son of Shahrukh, born in the city of Sultaniyah during his grandfather Timur's (Tamerlane's) campaign in northern Iran in 1394. At age 4 he accompanied his grandfather as far as Kabul, on the campaign that went on to take Delhi; almost immediately after the Indian campaign, he joined Tamerlane's campaign to the west which resulted in the defeat of the Ottoman ruler Bayezid I at Ankara in 1402. As Tamerlane was preparing to invade China, he celebrated the marriages of several of his grandsons, among them Ulughbeg (then age 10), who also was designated to rule over a significant portion of Moghulistan (the region encompassing part of the Tien Shan Mountains and NW Xinjiang), which, of course, was yet to be conquered. It is likely that Ulugh Beg was one of the princes seen by the Spanish ambassador Clavijo when he visited Tamerlane's court in 1403-1404.

Tamerlane's death in early 1405 not only cancelled the invasion of China but ushered in a period of civil strife in which the young Ulugh Beg took an active part. When his father, Shahrukh, finally managed to regain control over Transoxiana, he appointed Ulugh Beg as the regent there. The latter assumed his full responsibilities in 1411, although he continued to be subordinate to his father, who ruled the empire from Herat. At Shahrukh's death in 1447, Ulugh Beg succeeded him, but survived only two years as an independent ruler before being overthrown and beheaded in 1449.

Although for a time in the mid-1420s Ulugh Beg's armies waged a successful war for control of parts of Moghulistan (including Kashgar), increasingly he seems to have devoted himself to scholarly pursuits and patronage of the arts. In 1417-1420 he had a large madrasa (school) built, which still stands on the Registan in the center of Samarkand. The Timurid founder of the Moghul Empire in the early sixteenth century, Babur, describes what this complex of buildings was like then (only the school has survived):

Amongst Ulugh Beg's buildings inside the town are a college and a hospice (khanaqah). The dome of the hospice is very large: few so large are known anywhere else in the world. Near these two buildings he constructed an excellent hot bath...; he had the pavements in this made of all sorts of stone. There is no bath like this in Khurasan or anywhere else in Samarkand....To the south of the college is his mosque, known as the "Carved Mosque" because its ceiling and walls are all covered with carved islimi and pictures made of inlaid woods...

Babur goes on to describe Ulugh Beg's observatory (see below) and some of the splendid gardens and pavilions that he had built, one of them apparently decorated with porcelain specially ordered from China. His conscious efforts to honor his grandfather included donation of the huge Koran stand that can still be seen in the Bibi Khanum Mosque and placement of of a striking jade cenotaph above Tamerlane's grave in the Gur-i Amir mausoleum. There is reason to believe that this huge block of jade came as booty from one of Ulugh Beg's campaigns in Moghulistan in the 1420s. Ulugh Beg was laid to rest in the Gur-i Mir at the feet of his grandfather (in the photo, Ulugh Beg's grave is in the foreground; Tamerlane's behind).

While the achievements of his reign were many, he is probably best remembered for his scientific contributions. The madrasa became a major center of learning in the Islamic world, whose influence spread widely and lasted beyond Ulugh Beg's death, at which time some of the scholars he had supported left Samarkand for capitals such as Istanbul which promised more stability. The first director of his observatory was Qazizadeh Rumi, who had in fact come to Central Asia from Anatolia and was one of Ulugh Beg's teachers. Tradition has it that he is buried the elegant double-domed tomb constructed for him in the Shah-i Zinde mausoleum complex at Ulugh Beg's behest.

The tradition of Islamic science upon which Ulugh Beg and his scholars drew had long been valued by the rulers of Inner Asia. For example, the famous Mongol Emperor Khubilai Khan, staffed his new observatory in Beijing (shown on the left) with Muslim scientists. Muslim scholars made important contributions in mathematics (as is well known, our word "algebra" and the mathematics it embodies come from Arabic treatises). In astronomy, they drew heavily on the legacy of Classical Greece and Rome. One concern of royal astronomers was with calendars and astrological readings of heavenly signs (the boundary between astronomy and astrology was not clearcut as it is today). Underlying such "practical" applications was serious measurement and study of the movement of heavenly bodies; it is in this area that Ulugh Beg made some of his most important contributions. The observatory built at Maragha in the late thirteenth century for the Mongol Ilkhanid rulers of Iran was probably the most important direct influence on the Samarkand observatory.

His observatory was built beginning around 1420 on a hill to the north of Samarkand. Since it was destroyed within a few generations of his death, by the twentieth century no one knew its exact location. All that remains of the building, now excavated by archaeologists, are the foundations and the lower part of the largest of its scientific instruments, a huge "sextant." There is a small museum with exhibits about Ulugh Beg and his scientific achievements; one can contemplate there a bust sculpted on the basis of the study of his remains.

Babur described the building as it still stood in the early sixteenth century:

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....


One modern reconstruction of the building's appearance is shown here.

The so-called "sextant" obviously would have extended well above the ground (as the drawing shows) and likely was closer to being a quadrant. As Krisciunas points out in his interesting discussion of the instrument, it "was by far the largest meridian instrument ever built." Fragments of the curved measuring track have survived with markings for around 20 degrees; this is about the highest point that observations likely would have been made. The "sextant" would have been used to measure the angle of elevation of major heavenly bodies, especially at the time of the winter and summer solstices. Light from the given body, passing through a controlled opening, would have shone on the curved track, which is marked very precisely with degrees and minutes. "It 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" (Krisciunas). It is not clear whether more than the sun and moon could have been measured in this fashion, since planets, for example, would not have cast sufficient light. The observatory was equipped with a variety of other instruments, which probably accounted for the largest part of its scientific measurement. While only written lists (not the actual instruments) have survived, one can at least get a feel for what some might have been like (among them armillary spheres) from those to be seen today atop Khubilai Khan's observatory in Beijing.


One of the most important measurements carried out by Ulugh Beg's astronomers was the obliquity of the ecliptic. The ecliptic is the circular path described by the the sun in the course of a year, and its obliquity is the angle at which it cuts the equator. Establishing this precisely is important for a variety of other astronomical measurements and calendrical calculations. The astronomers in the classical world had errors on the order of 7'-10'. Arab astronomers achieved for the most part much greater precision; in the case of Ulugh Beg, the error was only -0'32". His results for the calculation of the movement of the planets are also impressively close to those obtained by modern means. Some consider his most significant achievement to be the compilation of a catalogue of the stars and their locations. This was the first such catalogue based on new, direct observation since that complied some 1600 years earlier by the important Greek astronomer Hipparchus. Our appreciation for Ulugh Beg's work increases when we remember that he was working nearly two centuries prior to the invention of the telescope.

His work eventually became known in Europe, with the publication in London in 1650 of a Latin translation of his "Chronology," and fifteen years later the first of many European editions of his star tables. As Krisciunas points out, the impact on European astronomy was slight though, given the advances that had been made prior to the time when Ulugh Beg's work became known. The Samarkand observatory was much more important for its influence on astronomy in Mughal India. That said, Ulugh Beg

was certainly the most important observational astronomer of the 15th century. He was one of the first to advocate and build permanently mounted astronomical instruments. His catalogue of 1018 stars (some sources count 1022) was the only such undertaking carried out between the times of Cladius Ptolemy (ca. 170 A.D.) and Tycho Brahe (ca. 1600). And...his attitude towards scientific endeavors was surprisingly modern. (Krisciunas)

-- Daniel C. Waugh



1) Aydin Sayili, The Observatory in Islam and Its Place in the General History of the Observatory (Ankara, 1960), Ch. VIII, pp. 260-289.

2)Kevin Krisciunas, "Ulugh Beg's Zij," in H. B. Paksoy, ed., Central Asian Monuments (Istanbul, 1992). A professional astronomer's assessment, with extensive bibliography.

3) Iz istorii epokhi Ulugbeka (Tashkent, 1965).

4) Bernhard du Mont, "Ulugh Beg: Astronom und Herrscher in Samarkand," Sterne und Weltraum, 2002, Nos. 9-10, pp. 38-46. The first of two beautifully illustrated articles on Ulugh Beg by German astronomers; published in a high-quality popular astronomy journal.

5) Heiner Schwan, "Die Tabellen von Ulugh Beg: Die Sternkataloge des Ptolemäus, Ulugh Beg und Tycho Brahe im Vergleich," Sterne und Weltraum, 2002, Nos. 9-10, pp. 48-51.

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© 2002 Silk Road Seattle   Silk Road Seattle is a project of the Walter Chapin Simpson Center for the Humanities at the University of Washington. Additional funding has been provided by the Silkroad Foundation of Saratoga California.