9th Ali ibn Isa al-Asturlabi

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Alī ibn ʿĪsā al-Asṭurlābī (Arabic: علي بن عيسى‎) was an Afro-Arab^{[citation needed]} astronomer and geographer of the 9th century. He wrote a treatise on the astrolabe and was an opponent of astrology. During the reign of al-Ma'mun, and together with Khālid ibn ʿAbd al‐Malik al‐Marwarrūdhī, he participated in an expedition to the Plain of Sinjar to measure the length of a degree, or the circumference of the Earth.^[1] He measured the Earth's circumference, getting a result of 40,248 km (or, according to other sources, 41,436 km).^{[citation needed]}

ʿAlī ibn ʿĪsā al-Asṭurlābī, author of an early Arabic treatise on the astrolabe and an opponent of astrology, enjoyed renown as an astronomical instrument maker and contributed to observations initiated by the ʿAbbāsid caliph Maʾmūn. He took part with Khālid ibn ʿAbd al-Malik al-Marwarrūdhī and others in an expedition to the Plain of Sinjār to measure 1° of latitude and, thus, the size of the Earth. ʿAlī ibn ʿĪsā made astronomical observations at Baghdad in 829/830 and at Damascus in 832–833. He divided the mural quadrant used for the Damascus observations to confirm results of the earlier missions.

Alī ibn ʿĪsā al-Asṭurlābī (Arabic: علي بن عيسى‎) was an Afro-Arab astronomer and geographer of the 9th century. He wrote a treatise on theastrolabe and was an opponent of astrology. During the reign of al-Ma'mun, and together with Khālid ibn ʿAbd al‐Malik al‐Marwarrūdhī, he participated in an expedition to the Plain of Sinjar to measure the length of a degree, or the circumference of the Earth. He measured the Earth's circumference, getting a result of 40,248 km (or, according to other sources, 41,436 km).  more from Wikipedia