Whispers in Tamris
The Lunar Calendar was devised by the elves millenia ago, and was adopted by humans for a time after the simple Agricultural Calendar was deemed less useful outside of planting/farming scenarios. This calendar is composed of 12 months or “cycles”, each 33 nights long, leaving 4 nights unaccounted for by a standard lunar cycle.
Though there is only one physical moon orbiting Tamris, each cycle bears a different color and traditional Elven name related to one of their ancient deities. The remaining 4 nights are collectively referred to as “no moon” or the “black moon”. These 4 nights are believed to be an evil and chaotic time. Though they always fall between the end phase of one moon’s cycle and the start of the next, these 4 nights randomly shift each year, except they will never repeat the same gap between cycles the next year. While it may fall between the 6th and 7th moon one year, the next year it may fall between the 1st and 2nd.
The Lunar Calendar is currently the least used of the calendars among humans. Elves and nocturnal races still utilize the Lunar Calendar among their own groups, and it is popular among seafarers for its navigational purposes. Even among these peoples, though, those who travel the world often learn the Solar Calendar as well.
To remove the issue behind these erratic 4 nights and to allay the fears behind the superstitions, human scholars devised a calendar which was inspired by the two calendars before it. This became the modern-day Solar Calendar.