The planet which you call Faerum has two natural satelites. The largest is called Luna after the goddess, Selune. It has a natural cycle of 28 days which it completes 13 times a year. The smaller moon is known as Selune's Hand maiden or often Celene. It completes 4 orbits of the planet in one year.

The calender is divided into 12 three week months. Each week has 10 days. The days that Celene is full are typically marked as holidays and are in fact not included in any month. These four days are known as Midsummer, Harvestide, Sunsbirth(midwinter) and Greengrass. By some fluke, Luna and Celene are both full on Midsummer night. As one might imagine this is not a good time to be abroad in werebeast infested areas.