1. Chronological remarks. The main source for our knowledge of ancient astronomy is Ptolemy. His Mathematical composition, commonly known as the Almagest, quotes observations of his own ranging from 127 to 142 A.D. [35; 36; 37]. This work seems to be the earliest of a whole series of fundamental works, such as his Geography [41 ], the Tetrabiblos [39; 40], and so on, whose influence on mediaeva...