Analysis of the New Moon Times on the Disk of the Astronomical Clock in Gdansk, Poland.

The calendar disk of the fifteenth century astronomical clock in the church of Saint Mary in Gdansk (Poland) contains a wealth of astronomical and calendrical data. We make a statistical analysis of the mean conjunction times of all the mean New Moons as represented on the disk for four Metonic 19-year cycles. We find that the conjunction times were generated using the Alfonsine value for the length of the synodic month and with a mean longitude correction from the Alfonsine meridian (Toledo in Spain) by 1 hour and 16 minutes. This indicates a location with a longitude of a little more than 19° east of Toledo but due to the uncertainty of the actual locations in longitude at the time it is not possible to point out a specific location. The method of calculating the conjunction times differs from other contemporary calendars and has considerably less quality than other contemporary conjunction lists.