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Lunar Structure
The Light Calendar uses a simple lunar index. Each lunar cycle has a home year: it is the year in which its full moon occurs. Now, here you have to decide whether you want your moons being indexed to the Gregorian year or the Light Year. Both works well.
The “normal” moons of a (Light/Gregorian) Year are numbered M1–M13. In addition, there can be an M0 (and in rare cases an M14) to show spill-over cycles at the year boundaries.
- Home-year numbering: M1–M13
- A lunar cycle belongs to the (Light/Gregorian) Year in which its full moon occurs.
- Start of a lunar cycle:
- The cycle starts at the astronomical new moon, rounded by a natural rule:
- New moon before 12:00 UTC → previous day/night (start date = previous day/night)
- New moon at/after 12:00 UTC → same day/night
- The cycle starts at the astronomical new moon, rounded by a natural rule:
- Cycle length is 29 or 30 nights.
To avoid gaps at the (Light/Gregorian) Year boundary, neighbouring cycles are still shown:
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M0
- Represents the last moon of the previous (Light/Gregorian) Year, whose cycle still extends into the first nights of the new year.
- Its full moon lies before the (Solar/Gregorian) New Year (before 1 Jan/1 New February), but its tail is still visible in the new year, so it is displayed as M0·x.
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M14 (very rare)
- In some years, a first moon of the next (Light/Gregorian) Year can already start in the last nights of the current year.
- In that case, the implementation may display it as M14·x as a forward spill-over.
- Conceptually, you can still think in terms of M0–M13; M14 is just a rare edge case.
In practice, this ensures that every date shows a moon index (even on the first and last nights of the year), and no cycle is visually “cut off”.
Μ11·19 (16/30)
Meaning:
- Μ11 → 11th moon of the (Light/Gregorian) Year
- 19 → tonight is night 19 of this lunar cycle
- 16 → the full moon occurred on night 16 of this cycle
- 30 → total length of this cycle (29 or 30 days)
When displaying real-time information, the notation of “moon nights” switches at 06:00 local time (instead of 12:00) to better reflect the usual end of the night and provide clearer orientation.
The lunar index (M1–M13, plus edge moons M0 and rarely M14) provides full lunar orientation without a separate lunar calendar, while remaining astronomically precise and continuous at year boundaries.