Dva astronomické dopisy papeže Silvestra II.
Two Astronomical Letters by Pope Sylvester II

Summary/Abstract: The paper focuses on the astronomical interests of one of most well-known figures of the end of the tenth century Gerbert of Reims (ca. 940/50–1003; a monk in Aurillac, scholasticus in Reims, abbot in Bobbio, illegitimate archbishop of Reims, archbishop of Ravenna and Pope Sylvester II). The paper analyses two of Gerbert’s letters. The first of them (De sphaera addressed to Constantine of Fleury) was probably written around the year 980 and presents the construction and setting of the unique observation hemisphere. The second letter (to brother Adam) was written during the spring of 989. It deals with timekeeping and includes practical instructions for determining the longest presence of sunshine in a particular location. Both letters were addressed to highly educated readers and an analysis of their content allows for an illustrative understanding of certain aspects of medieval geocentric astronomy of the late tenth century.

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