His teaching at Bologna did not interfere with his experiments in astronomy. In a letter which he sent in early 1478 to his friend Mykola Chepel in Poznań, Drohobych mentioned his calculations of planetary positions during a year. According to his observations and calculations, he estimated the exact time for two lunar eclipses; he also included a chart of the phases of the Moon for a year. In the letter, Drohobych described how he had calculated the geographic locations of major cities in what is now Poland and Ukraine. He also gave predictions concerning political events that had been taking place in Europe, Egypt, Turkey, Arabia, and India. Mykola Chepel shared these notes with his colleagues at Poznań University. The news about Drohobych's findings quickly spread among many learned people in Europe. One of the first German Humanists and book collector, Hartmann Schedel, copied these letters. In part thanks to his efforts, they were preserved for posterity.