Drohobych wrote a treatise about the solar eclipse that took place on July 29, 1478. He suggested that cosmic events of this nature may or may not have favorable effects on events on Earth but they certainly would not cause catastrophes. In the early 1480s, Italy was at the forefront of book printing. Initially all publications were of a religious nature, however books about astronomy, botany, and geography had been growing in popularity, too. In 1483 Drohobych published in Rome his first book in Latin ""Prognostic Estimation of the year 1483"" (Iudicium Pronosticon Anni MCCCCLXXXIII Currentis). It was a nineteen-page publication of astrological (zodiac) calendars, which were popular at that time, that helped its readers to make predictions about events on Earth depending on the planets' positions. This publication had several noteworthy elements: Drohobych gave accurate predictions for two lunar eclipses; he provided accurate calculations of the phases of the Moon; and he also touched upon the subject of planetary movement. Furthermore, he indicated that the geographic coordinates were an important factor in determining the sun's and planets' positions. Depending on the geographic location of the observer, the positions of cosmic objects would vary. His longitude calculations were not error-free, however. He deserves credit for being the first Eastern European scholar who in a printed publication indicated the exact geographic coordinates of several Ukrainian, Polish, and Lithuanian cities.