Monday, October 27, 2014

A Sultan's Observatory

The Ulugh Beg Observatory Museum, built in 1970
Ulugh Beg is the more familiar name of Mīrzā Muhammad Tāraghay bin Shāhrukh (22 March 1394 - 27 October 1449). "Ulugh Beg" is more of a nickname, meaning "Great Ruler."

He was a grandson of Tamerlane who became sultan in Samarkand while still a teenager. He decided to turn Samarkand into an intellectual center, building a university and inviting scholars to take up residence.

He also built the Ulugh Beg Observatory in 1420, where some of the finest Islamic astronomers worked and studied, but only those whom Ulugh personally approved. The picture here is a modern structure on the site of the original, which was destroyed by religious fanatics in 1449. An excavation uncovered its primary feature—a giant sextant:
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. [link]
Building a giant permanent astronomical instrument was a unique idea at the time—remember that this was 200 years prior to the invention of a telescope. He created a catalog of over 1018 stars, discovering and correcting many inaccuracies in the star tables created by Ptolemy. Copies of these star charts are on display at the Ulugh Beg Observatory Museum; the originals are in the Bodleian Library in Oxford.

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