Galileo's Telescope Reconstruction "Reconstrucion of the optical caracteristics of the telescope used by Galileo during the observations reported in the Sidereus Nuncius". ROMA TRE University, Graduated Iacopo Vigilante, Supervisor Dr. Enrico Bernieri. In this thesis were analyzed quantitatively the observations reported by Galileo Galilei in the Starry Messenger in order to reconstruct the optical characteristics of the instrument he used. In the first chapter we are briefly introduced the figure of Galileo Galilei. The highlights of his life are recounted together the description of the historical context in which he carried out his scientific activity. Special reference is given to the Starry Messenger, the first astronomical publication of Galileo, as it is an integral part of the tools that were used by me to understand his methods and reconstruct the features of his telescope. They are finally introduced the methods used by Galileo for his astronomical observations, or, more precisely, what have been understood up to now on them and which investigations were carried out on the manuscripts and instruments that have survived. The second chapter displays some basics on the functioning of refractor telescopes, needed to build a suitable environment for the optical analysis. The third chapter contains a detailed description of the original work done for this thesis: the reconstruction process, with the Skychart v3.0 planetarium software, of the astronomical measurements conducted from Jan 7, 1610 to March 2 of that year, during the observation of "medicean" satellites. Is briefly explained the operation of the planetarium software and how the measures relating to the mutual angular distances between Jupiter and its satellites were collected. Next, are present the data collected (more than 180 angular separations) and is discussed how these relate to those noted by Galileo. Once reached a thorough understanding of the methods of measurement of the pisan astronomer studying a small group of unusual measures, i have calculated the resolution of the telescope used. Statistical analysis of the mistakes made at that time was then used to identify the distorting effects of its lenses. It is finally mapped its representation of the Pleiades, recognizing each of the 36 stars drawn, using the astronomical program Aladin v8.040, in order to derive the limit magnitude of the Galilean telescope and consequently the opening of its objective lens. In conclusion, are presented some final reflections and are summarized the optical characteristics obtained during the analysis: the resolution, openness, and possible aberrations. Two appendices complete the work. The first one describes a method of measurement likely used by Galileo. The second one is a comprehensive table which includes all numeric data initially collected by the Sidereus.