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Astronomic Soli-Lunar Calendar

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The Astronomic Soli-Lunar Calendar or Astronomical Blue Moon Calendar was developped by Walter Ziobro, who posted a description to the CALNDR-L mailing list on 22 August 2013[1]. Karl Palmen suggested alternative month names early / mid / blue / late per quarter.

This lunisolar calendar is based on the seasonal blue-moon rule: If four full moons occur between two seasonal points (equinoxes and solstices), the third is a seasonal blue moon. It becomes the leap month here.

The year is divided into a notos half, where the full moon will occur south of the celestial equator, and a arctos half, when it will appear north. Months within these halves are labeled by Greek letter names sequentially, but leap months use ancient letters Qoppa and Digamma respectively.

Season Ordinal number Months Approximate Hebrew Approximate Gregorian
North Spring, South Fall/Autumn, Southward / Southither / Paschal /  East 01 01 01 01 01 α Notos Alpha Early Nisan March–April
02  02 02 02 02 β Notos Beta Mid Iyar April–May
 03 ϟ Notos Koppa Blue blue leap
03 04 03 03 03 γ Notos Gamma Late Sivan May–June
North Summer, South Winter, Southback / Southence / Post-Paschal / South 04  05 04 04 04 δ Notos Delta Early Tammuz  June–July
05 06 05 05 05 ε Notos Epsilon Mid Av July–August
06 ϝ Notos Digamma Blue blue leap
06  07 07 06 06 ζ Notos Zeta Late Elul August—September
North Fall/Autumn, South Spring, Northward / Northither / Anti-Paschal / West 07  08 08 07 07 Α Arctos Alpha Early Tishrei September–October
08  09 09 08 08 Β Arctos Beta Mid Cheshvan October–November
09 Ϟ Arctos Koppa Blue blue leap
09 10 10 10 09 Γ Arctos Gamma Late Kislev November–December
North Winter, South Summer, Northback / Northence / Pre-Paschal / North 10 11 11 11 10 Δ Arctos Delta Early Tevet December–January
11 12 12 12 11 Ε Arctos Epsilon Mid Shevat  January–February
12 Ϝ Arctos Digamma Blue blue leap
12 13 13 13 13 Ζ Arctos Zeta Late  Adar February–March

Months start with the new moon per UT, therefore their lengths are variable.

In the 19 year period between 2014-03-31 and 2033-03-30, there will be seven leap months:

Notos Koppa
Notos Digamma
Arctos Koppa
Arctos Digamma

This uneven distribution exemplifies that northern spring and summer are longer than the southern ones, i.e. northern fall/autumn and winter, currently.


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