Al-Khujandi's mural sextant (Fakhri sextant)

What it is

Wall-built meridian arc of 60° and about 20 m radius, with which he measured the obliquity of the ecliptic to a precision of arcseconds. It inaugurated the great fixed observatory instruments.

Al-Khujandi recognised that the pinhole aperture had shifted as the wall settled, introducing an error of about 2 arcminutes.

What it led to

• monumental instruments at Maragheh and Samarkand
• precise measurements of the obliquity of the ecliptic
• the sextant as an astronomical instrument

Built on

• Astronomical quadrantc. 850

Made possible

• Maragheh observatory and the Tusi couple1259
• Ulugh Beg observatory and star catalogue1420-1437

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