Overview of Rule-Based Lunar Calendars
Dear Calendar People,
While most lunar calendars are observation-based (especially the Islamic Calendar), I am curious about what rule-based lunar calendars are or have been in use. I know that such calendars can not predict the exact day of a new moon or an eclipse without becoming excessively complicated. This is because of eccentricity of the moon's orbit round the earth and the earth's orbit around the sun.
There are few rule-based lunar calendars around.
And invented recently:
- Hebrew Calendar
- Gregorian (for Easter) Calendar
- Julian (for Easter) Calendar
- Tabular Islamic Calendar with 30 year Cycle
- The Indonesian Caka Sunda Calendar
- Mayan Eclipse Cycle
- The Lunar Calendar in The Invisible Landscape
- The Week of Weeks Calendar of Full Moon Nights (Simon Cassidy)
- The Yerm Calendar (Karl Palmen)
- Goddess Lunar Calendar (Peter Meyer)
- The ONE DAY BEFORE calendar (Karl Palmen)
- The 17-Month Lunar Calendar (Karl Palmen)
Mario Hilgemeier produced a list of approximations for the lunar month good enough to give rise to the basic yerm calendar:
Assume a "reasonable" value for the synodic period of 29.53059 days (precision 7 digits).
approximation of the lunar month
by an integer numbers of days and lunar months:
lms = lunar months
len = approximated lunar month length, len = days/lms
relative error = (len - synodic)/synodicdays lms len relative error 29 1 29.0000000000 -1.7967e-02 30 1 30.0000000000 +1.5896e-02 59 2 29.5000000000 -1.0359e-03 simple approximation 266 9 29.5555555556 +8.4541e-04 short whole-week yerm (human gestation period) 325 11 29.5454545455 +5.0336e-04 eleven month system 384 13 29.5384615385 +2.6656e-04 the classical lunar year (The Invisible Landscape) 443 15 29.5333333333 +9.2898e-05 fifteen month yerm 502 17 29.5294117647 -3.9899e-05 seventeen month yerm 945 32 29.5312500000 +2.2350e-05 Simon Cassidy's basic Week of Weeks 1447 49 29.5306122449 +7.5328e-07 basic yerm calendar (17:17:15)Information about other rule-based lunar calendars is appreciated.
The above emails have been subject to editing refer to the CALNDR-L archive for full text
Last modified: 2001-02-01 CE
Copyright 2001 Karl Palmen
|Yerm Calendar||17-Month Lunar Calendar||Lunar Calendars|
|Lunar Calendar Links||Karl Palmen's Calendars||Calendar Studies|
|Hermetic Systems Home Page|