Mural Sextants
Mural sextants are a special case of a mural instrument. Many were made that were quadrants rather than sextants. They were a kind of speciality of medieval Muslim astronomers to whom the credit of building the first mural sextants is attributed.
The first known mural sextant was constructed in Ray, Iran, by Abu-Mahmud al-Khujandi in 994. To measure the obliquity of the ecliptic, al-Khujandī invented a device that he called al-Fakhri sextant (al-suds al Fakhrī), a reference to his patron; Buwayhid ruler, Fakhr al Dawla (976-997). This instrument was a sixty-degree arc on a wall aligned along a meridian arc (north-south line). Al Khujandi’s instrument was larger than previous such instruments; it had a radius of about twenty meters. The main improvement incorporated in al-Fakhri sextant over earlier instruments was bringing the precision of reading to seconds while older instruments could only be read in degrees and minutes. This fact was confirmed by al-Birūni, al-Marrākushī and al-Kāshī. Al-Khujandī used his device to measure the sun's angle above the horizon at the summer and winter solstices; these two measurements allow to compute the latitude of the sextant's location and the obliquity of the ecliptic.
Ulugh Beg constructed a Fakhri Sextant that had a radius of 40.4 meters, the largest instrument of its type in the 16th century. Seen in the image on the right, the arc was finely constructed with a staircase on either side to provide access for the assistants who performed the measurements.
Read more about this topic: Sextant (astronomical)
Famous quotes containing the word mural:
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