al Biruni
The Uzbek Abu Rayhan Muhammad ibn Ahmad al Biruni (973 - after 1050), usually referred to as Al-Biruni, was a scholar and polymath.
He studied almost all the sciences of his day. At age 25 he went to Persia. Of his 146 books, 95 are devoted to astronomy, mathematics, and mathematical geography.
By means of the observation of the height of a mountain he determined the Earth's radius to be 6339.6 km, which is about 0.6% smaller than the true value.
He first subdivided the hour sexagesimally into minutes, seconds, thirds and fourths. This is where the word second comes from.
See also
Last modified:10 January 2026 2.51 p.m.