The Common Year (CY) is the most widely used calendar system in Flanaess. It was created by the Great Kingdom Aerdy with the Declaration of Universal Peace, and that year has henceforth been known as 1 CY.
According to the scholars, the sun travels once around Oerth in 364 days, visiting the 12 Lairs of the Zodiac in an appointed round that never varies. The Great Moon, called Luna, waxes and wanes in fixed cycles of 28 days (Luna’s cycle governs lycanthropy). Each lunar cycle marks the passage of one month, which is further subdivided into four weeks of seven days each.
The Lesser Moon, Celene, follows a path that reveals her full beauty but four times each year, thus showing the times of the Festivals.
Dozenmonth of Luna and the Four Festivals