Let’s look at multiple possible ways that would allow synchronization of a Luni-solar Calendar.
(1) If Calendar is purely Solar in nature, many possibilities exist..
– e.g. 11 months of 30 days each and 12th month of 35-36 days to match total duration of the sun’s travel through the ecliptic in 365-366 days.
– Gregorian Calendar – 12 months of varying duration (28-31) and leap year.
(2) If Calendar is purely Lunar in nature,
– Current Islamic calendar is purely lunar in nature. Since this calendar does not bother to synchronize with the solar calendar, the seasons for Islamic festivals change over a period of time (e.g. month of Ramadan).
(3) Luni-Solar Calendar, by definition, employs moon’s positions and phases for daily counting (of course fixed duration of a month can be used in a civil sense which does not have to depend on moon’s positions or phases..but then such a calendar is not Luni-Solar anyways) while sun’s travel through the ecliptic to keep seasons in check, at least in the short run.
Thus sole objective of synchronizing Luni-Solar calendar (Lunar with Solar) is to have daily reckoning via moon’s phases and positions (including moon’s positions at the time of full moon and amawasya) that also align with the same season (albeit approximately) every year.
Lunar calendar can be conceived of two kinds:
– Sidereal month – Each month would be about 27.3 days when moon travels a complete round around the ecliptic from a specific nakshatra to the same nakshatra. Some multiple of these sidereal months can be considered a ‘sidereal lunar year’.
– Synodic month – Each month would be about 29.5 days when moon with a specific phase (as seen from the earth) travel through the ecliptic until it attains the same phase. Twelve such rounds (lunations) constitutes a lunar year of ~354 days.
In next part we will explore various combinations that can be employed to synchronize Luni-Solar Calendar. Against these possibilities, we will begin to explore evidence for this synchronization, as employed, in ancient Indian literature.