ʿAlī ibn ʿĪsā al-Asṭurlābī (Arabic: علي بن عيسى, fl. 832) was a 9th century Arab geographer and astronomer. 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.^[1] Differing reports state that they obtained a result of 56 miles (90 km), 56 and two-thirds, or 56 and one-quarter miles per degree.^[2]