Behind the scenes of al-Battānī Sive Albatenii Opus Astronomicum. The correspondence between the astronomer G.V. Schiaparelli and the arabist C.A. Nallino

Al- Battānī sive Albatenii Opus astronomicum is a three-volume work by Carlo Alfonso Nallino published between 1899 and 1907 on behalf of the Astronomical Observatory of Brera. The publication was so crucial that it consecrated Nallino as a scholar and an expert in astronomical sciences and Arab-Islamic studies, both in Italy and abroad. The masterful work resulted from a long period of study and research, which involved Nallino as well as Giovanni Virginio Schiaparelli, who was his mentor. A portion of the correspondence exchanged between the two during the years in which they collaborated is preserved at the Historical Archive of the Astronomical Observatory of Brera and is largely unpublished. In our contribution, we aim to present some original behind-the-scenes details about the edition, providing an excursus of the main stages of the work, through the written words of the scholars involved. The information included in the correspondence concerns not only private confidences and shared knowledge, but also significant exchanges of research-related material, such as astronomical calculations, observations on the solution of numerical equations, names of ancient and contemporary astronomers to be taken into account, and scientific works worth (or not worth) reading. We believe that the distribution of this kind of knowledge is precious in order to shed light both on the edition itself and on the modus operandi of these two great scholars, at a time when postal correspondence was an integral part of the transfer of scientific knowledge.