Lunar Phases in the Moon Calendar

Nowadays the Hijri calendar is amongst the most widespread moon calendars. It is based on the classic moon year system, which splits it into twelve lunar months. The calendar’s time frame is not aligned to the solar year, making difference as much as twelve days per year. However, periodicity of the Hijri lunar calendar implies that it enters the same phase with the Sun once in thirty-three years according to Islamic time counting.

The religious foundation of Hijri calendar made things that way. As for now, this calendar is treated as merely canonical and used for reference, but religious influence faded out.

Comparing Hijri calendar to other calendars of similar type, it is noticeable that other calendars use lunisolar system. The effect of such combined system is that lunar cycles are aligned on the frames of the Sun’s year. With the notion of 12 synodic intervals (also recognized by name “lunations”) within 1 Sun’s year, the resulting day count of precisely 354.37 solar days is referred to as “lunatic year”. Among famous lunisolar calendars are the following: Hindu, Hebrew, Chinese, and numerous ancient ones. Those calendars as a rule incorporated an odd month count (11, 13, 15...) and the actual Sun year’s seasons could not be tracked because of time slips.

Apart from calendars having theoretical and astronomical origin, there exist ones that reflect and are aligned to annual natural phenomena. The chosen phenomena were usually ones depending on the moon’s and Sun’s cycles. An apparent example of such calendar is the calendar developed at the Banks Islands. Surprisingly it is not a full year calendar, as it has only 3 months in it. And this period is nothing but the interval when local palolo worms populate the beaches to come through their reproductive cycle. As it was noticed, those cycles occur accurately at the final interval of the moon’s month. Different calendars with moon phases also happen to deviate in terms of the day that comes first in a month, or adjusts it on periodical basis. For example, the Chinese proprietary calendar is anchored to the date when the phase of new moon is initiated, making it the month’s first day. Duration of a month is also variable, being adjusted with the course of time and reflecting further observations.