The Mongol Who Built a Mural Sextant

بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ

Shaykh Abu Mahmud Hamid ibn al-Khidhr al-Khujandi (r.a.) was a mathematician and astronomer from Khurasan, a kingdom covering what is now Afghanistan, Turkmenistan, and Uzbekistan.  He was of Mongol origin and lived in the late 10^th century.  He was born in Khujand.  There is a bronze bust of him in a park in modern Khujand, now part of the Republic of Tajikistan. 

What little we know from his life come from his surviving writings as well as from comments made by Imam Naswr ad-Din Muhammad ibn Muhammad ath-Thusi (q.s.).  We are fairly certain that Shaykh al-Khujandi (r.a.) was one of the rulers of the Mongol tribe in the Khudzhand region. 

However, we do know that he was responsible for building one of the largest astronomical instruments of the era, the mural sextant near Rayy, in modern Iran.  The mural was done on a 60-degree arc between two interior walls of a building.  It measures about 43 metres in diameter, and the arc was sliced into degrees.  Each degree was further divided into 360 parts.  This made the mural incredibly precise for a solar calendar and also the first device capable of accurate measurement on such a small scale. 

Between the summer and winter solstices, the Sun moves 47 degrees in the sky.  The arc room was topped with a domed ceiling with a hole to allow the Sun’s rays to strike the arc.  Shaykh al-Khujandi’s (r.a.) calculations allowed him to trace the movement of the Sun and to determine his latitude.  Shaykh al-Khujandi’s (r.a.) pioneering work led to the development of other instruments like the astrolabe.