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Lunar Structure
The Light Calendar uses a simple and continuous lunar index. Each lunar cycle is assigned a home year, defined as the year in which its full moon occurs. For this purpose, you can choose whether lunar cycles are indexed relative to the Gregorian year or to the Light Year. Both approaches are internally consistent and work equally well.
The regular moons of a year are numbered M1–M13. In addition, an M0 (and in rare cases an M14) may appear to represent lunar cycles that overlap the year boundaries.
The lunar index is not a lunar calendar. It is a notation layer within the Light Calendar: lunar cycles are observed and numbered relative to the Light Year, but the calendar's structure, rhythm, and meaning remain entirely solar. The full moon serves as the indexing anchor, because it represents the light maximum of the lunar cycle – consistent with the Light Calendar's central theme of light as an experiential and measurable phenomenon.
Each lunar cycle begins at the astronomical new moon (with the 12:00 UTC rounding rule for calendar display, see below). For year assignment and numbering (M1–M13), however, a cycle is assigned to the year in which its full moon occurs – analogous to ISO 8601 calendar weeks, where the week belongs to the year containing its midpoint.
If the new moon occurs before 12:00 UTC, the cycle is assigned to the previous day and night. If it occurs at or after 12:00 UTC, the cycle begins on the same day and night. Each lunar cycle spans 29 or 30 nights, following the natural synodic rhythm.
To maintain continuity at the transition between years, neighbouring lunar cycles are still shown even if their full moon lies outside the current year.
M0 represents the final lunar cycle of the previous year whose tail extends into the first nights of the new year. Its full moon occurred before the start of the current (Gregorian or Light) Year, but because part of the cycle is still visible, it is displayed as M0·x.
In rare cases, the opposite situation occurs: the first lunar cycle of the next year may already begin during the final nights of the current year. In such cases, the implementation may display this cycle as M14·x. Conceptually, however, the system remains centred on M1–M13; M14 is merely a forward spill-over marker.
This approach ensures that every date is associated with a lunar index and that no cycle is visually or conceptually cut off at the year boundary.
Μ11·19 (16/30)
This notation indicates that the current night belongs to the 11th lunar cycle of the year. It is night 19 of that cycle. The full moon occurred on night 16, and the total length of the cycle is 30 nights.
For real-time display, the transition between lunar nights occurs at sunrise, or alternatively at 06:00 local time instead of the calculated 12:00 UTC threshold. This reflects the practical end of the night more intuitively and improves everyday orientation.
The lunar index (M1–M13, with edge moons M0 and occasionally M14) provides complete lunar orientation without requiring a separate lunar calendar. It remains astronomically precise, continuous across year boundaries, and simple enough to be used intuitively in daily life.