Solar Calendars

Solar calendars are based on the local year, or the amount of time it takes for the planet [Earth] to orbit its star [Sun]. Such a calendar makes sense especially in non-equatorial regions of planets with a significant axial tilt, such that the local climate changes in a predicatable cycle with a length equal to that of the planets orbit. However, even a planet or region of a planet in which the climate does not vary over the cycle of the planets orbit could develop a solar calender because the stars would move across the sky in a predictable cycle with a length equal to that of the planets orbit. On the Earth the year takes approximately 365.26 local days. For some reason several solar calendars developed on the Earth are essentially 360 day calendars have been made 365/366 day calenders by adding extra days at the end. The mayan civil calendar [haab] of 18 months of 20 days each followed by 5 or 6 unlucky days is one of this type.

Lunar Calendars

Lunar calendars are based on the local month, or the amount of time it takes for a natural sattellite [Moon] of the planet to complete an orbit. On the Earth, because the orbit of the moon around the Earth [29.93 days] and the orbit of the Earth around the Sun [365.26 days] do not match up,the months of a purely lunar calendar will occur at a different time each year until enough time passes to bring the two back into alignment.

Non-Solar Non-Lunar Calendars

These calendars are not associated with the cycles of the solar year or the lunar month. The two most famous calendars of this type are the divine calendar of the Maya [Tzolkin] and the local calender of Bali [Pawukon]. The Tzolkin calender consists of a day cycle of 13 days and a month cycle of 20 days which evolve concurrently making the Tzolkin calendar a 260 day cycle. The Pawukon consists of 10 different concurrent week cycles of 1,2,3,4,5,6,7,8,9, and 10 days each, as well as 6 months of 35 days each, making the Pawukon a 210 day cycle. For each of the 3, 5, 6, and 7 day weeks the days of that week cycle normally, giving 70, 42 and 30 cycles per Pawukon respectively. Each of the 30 cycles of the seven day week is also named. The 4 and 8 day weeks also cycle normally except that two extra days of each is inserted at the middle of the Pawukon since 210 mod 4 is not zero. Since 210 mod 9 is also not zero, 3 days must be added to the cycle of 9 day weeks as well, but these 3 days are inserted at the beginning of the year. The occurance of the days of the 1, 2, and 10 day weeks is irregular and derived from special calculations. Each of the days of the 5 and 7 day weeks has a urip, or ritual value. For any particular day of the Pawukon, add the urip of the day of the 5 day week to the day or the seven day week and then add one. This ritual value or urip determines which day of the week it is in the 1, 2, and 10 day weeks. Why do such non-Lunar non-Solar calendars exist ? Unless you believe that the Mayans and the Balinese brought a calendar from another planet, it is likely that something in their environment had an observable cycle of the same duration as their special non-solar, non-lunar calendar. For the people of Bali that cycle seems likely to have been the 210 day cycle of the rice crop. For the Mayans it seems likely that the cycle was in some way astronomical, since they are known to have placed religous importance on the movements of venus and other celestial bodies.