Gars al-Din ibn Ahmad ibn Khalil al-Halabi

Gars al-Din ibn Ahmad ibn Khalil al-Halabi was a Syrian astronomer who died in 971 AH (1563) according to Suter, as Heinen reports. ¹

He wrote Tanbih al-naqqad ala ma fi al-hay'a al-mashhura min al-fasad, dated by its colophon to 958 AH (1551), a title showing his dissatisfaction with the prevailing astronomy. ¹ In a chapter on the accidental motion of the celestial bodies and spheres he defended the older view against a newer one, using the ship analogy. ^{1 2}

In the book he rejects basic Ptolemaic notions such as the equant and the eccentric deferent, citing Ibn al-Shatir and Mu'ayyad al-Din al-Urdi while finding difficulties in their theories too. ² He notes that the observed diameters of Venus and Mars do not fit the accepted theory, and in geography draws on navigators' experience that the inhabited north extends to 72 degrees. ²