Worldbuilding Notes: Complicated Calenders

The skies of the world where my mountain and sea people live are bright and well populated and this had led to some very complicated calendars. The mountain and sea people are no exception.

• Eights and Threes are important to both the sea and mountain people. Three because of their three major heavenly bodies (Sun, Traveller’s Moon and Great Moon) and eight because of the orbits of the two moons being 8 and 32 days respectively. For this reason their weeks have 8 days and their months 32 days. There are almost exactly 13 lunations of the Great Moon in a year and planetary rotation is 21 Earth hours.
• The Traveller’s Moon and Great Moon’s cycles are so perfectly in synch (there exactly four lunations of the traveller’s moon during one lunation of the great moon) that it seems unlikely to be natural. (This is fantasy - the gods altered their positions to make it so).
• The first day of every month (and especially the new year) must be a: dark moon for both moons and b: the first day of the week.
• To avoid slippage an occasional intercalary day is inserted between years when the double dark moon would shift to the second day of the week. Because the lunar cycle is so well tied to the solar year on this world - there’s about two hours difference between a solar year and the time taken for 13 lunations - this doesn’t happen too often. Intercalary days are considered not to exist in a legal or religious sense. This has social and cultural implications - especially if you happen to be born on one.
• Aside from the lunar calender there are two other systems - 1 solar/seasonal and 1 sidereal - which are combined to give dates (see below).
• The seasonal system is zodiacal has eight signs based on the world’s quarter and cross quarter days and the eight directions. They are named for the 8 day gods who also protect the eight directions and who are believed to be children of the Traveller’s Moon. The seasonal year begins halfway between the winter solstice and the spring equinox at the cross-quarter day that marks the start of spring
• The sidereal system is based on the time of day “The Gatekeeper” rises. This star is so bright it can be seen even during daylight. The first point of this calender is its acronychal rising. That is the day it rises at sunset. Its midnight, heliacal and zenith risings mark other important days. This Calender has no signs but has 16 houses. The first house is the Gatekeeper’s house. A few of the other houses are named for bright stars within them but most are just numbered. Named houses are considered more important in the astrology of both peoples.
• There is a zodiacal calender which combines the two zodiacs. It begins when the acronychal rising of the Gatekeeper happens on the first day of Spring and proceeds through eight ages of roughly 3000 years apiece (ages change when the acronychal rising of the Gatekeeper is on a quarter or cross-quarter day). These ages are named for the appropriate seasonal sign (see above). In theory anyway, they are still in the first age and 24000 years is a long time.
• Since the zodiacal and lunar years gradually drift the dating system uses both. Since no one will even acknowledge that an intercalary day happened the best way to spot them in records is a jump in the zodiacal date compared to the calendar date.

I did warn you it was complicated, but lots of real world cultures had immensely complicated calendars as well.