Medieval astronomical clocks in the Baltic region and the mysterious golden numbers in Gdansk

Large medieval clocks were built in a number of Hanseatic towns in the Baltic region from the end of the fourteenth century to the middle of the fifteenth century. Several factors contributed to their building: there was a need for public display of time in the rapidly growing medieval towns, the technique of constructing mechanical clocks became available with the invention of the verge escapement in Italy in the second half of the of the thirteenth century, and wealthy Hanseatic towns had the means to pay for their construction. The layout of the clock dial and calendar disk of a number of these clocks in the region is studied. There are two main types of clocks, an older one for clocks constructed around the beginning of the fourteenth century, and a second one for clocks constructed around the middle and end of this century. The older clocks are characterised by having a dial with a stereographic projection of the sky not used in the later clocks. Most clocks also have a calendar disk to display specific information about the days of the year like Sunday letters, golden numbers, and calendar date. The only original calendar disk extant is the one on the Saint Mary cathedral in Gdansk giving times of the mean New Moons for the years 1463 to 1538. The times indicate an origin in the Alfonsine Tables modified for the longitude of Nuremberg in Germany