Abū’l-'Abbās al-Faḍl ibn Ḥātim al-Nairīzī (Arabic: أبو العباس الفضل بن حاتم النيريزي; Persian: ابوالعباس فضل بن حاتم نیریزی; Latin: Anaritius, Nazirius, c. 865 – c. 922) was a Persian mathematician and astronomer from Nayriz, now in Fars province, Iran.
He mentioned al-Mu'tadid, the Abbasid caliph, in his works, and so scholars have assumed that al-Nairīzī flourished in Baghdad during this period.
[1] Al-Nairīzī used the umbra (versa), the equivalent to the tangent, as a genuine trigonometric line, as did the Persian astronomer al-Marwazi before him.
He wrote a treatise on an exact method for the numerical determination of the kibla and a text about a device for measuring the heights, widths, and depths.
[citation needed] Al-Nayrizi's most important astronomical works, his commentary on Ptolemy's Almagest and both his zijes, are lost.