Archive for History of Exact Sciences 73 (2019): 551–617 Andalò di Negro’s De compositione astrolabii. A Critical Edition with English Translation and Notes Dominique Raynaud 1 , Samuel Gessner and Bernardo Mota Abstract In this article, we publish the critical edition of Andalò di Negro’s De compositione astro- labii, with English translation and commentary. The mathematician and astronomer Andalò di Negro (Genoa ca. 1260–Naples 1334) presumably redacted this treatise on the astrolabe in the 1330s, while residing at the court of King Robert of Naples. The present edition has three purposes: first, to make available a text missing from the previous compilations of works by Andalò di Negro (ed. Bonus 1475; Bertolotto 1892; Fornaciari and Faracovi 2005); second, to revise a privately-circulated edition of the text (Cesari 1984); third, to help disseminating one of the rare Latin texts presenting the princi- ples of the stereographic projection which underlie the construction of the astrolabe. Keywords astrolabe · stereographic projection · critical edition · Latin Europe 1 Introduction The astronomer Andalò di Negro (Genoa ca. 1260–Naples 1334) came from an important Genoese merchant and ambassador family who had seigneurial rights in Liguria, but also on Cyprus, in the kingdom of Armenia and in Syria (Acre). Andalò was befriended by Hugues IV of Lusignan, king of Cyprus and Jerusalem, and had conversations with him about astronomy (De Simoni 1874: 318). Andalò acted as ambassador of the Republic of Genoa in the Orient when he was entrusted the peace negotiations with the Emperor of Trebizond in 1314. Nothing is known about his whereabouts from that time on for over twenty years. On 9 th June 1334 his name resurfaces in a diploma by king Robert of Anjou, in Naples, indicating that Andalò was receiving a yearly pension of six ounces and that he had died a little earlier (De Blasiis 1908: 182). We are led to believe that Andalò was called to the court of king Robert in the final stage of his life as a physician and astronomy professor. Boccaccio who lived in Naples from 1327 to 1341 praises Andalò di Negro for the lessons he had taught some time before 1334 (Libri 1828: 200–2; Mojon 1846: 110–15; Poggendorff 1863: 265; De Simoni 1874: 313–39; * Dominique Raynaud: dominique.raynaud@univ-grenoble-alpes.fr Université Grenoble Alpes, Grenoble, France S. Gessner CIUHCT, Universidade de Lisboa, Lisbon, Portugal B. Mota Centro de Estudos Clássicos, Universidade de Lisboa, Lisbon, Portugal