Moon Night Notation

Moon-Night Notation

The notation Μx·y (p/z) describes a position within the current lunar cycle.

It uses nights rather than civil days because a night provides a useful observational unit for the Moon. This is a presentation choice, not a statement that the Moon is only a night-time object; the Moon is of course also visible during daylight.

Μx – lunar cycle number

Μx identifies the lunar cycle assigned to the selected reference year.

The reference can be either the Gregorian year or the Light Year. The cycle itself is astronomical and does not follow civil calendar months.

The normal sequence is M1–M13. The boundary markers M0 and, occasionally, M14 are explained on Lunar Structure.

·y – night within the cycle

The number after the dot gives the current night of the lunar cycle.

For example:

• Μ3·1 – first night of the third lunar cycle;
• Μ3·12 – twelfth night of the same cycle.

For the displayed notation, a night ends at sunrise. This keeps an event that occurs after civil midnight but before sunrise within the same observational night.

(p/z) – full moon and cycle length

The values in parentheses describe two properties of the current cycle.

p is the night on which the full moon occurs.

z is the total number of nights in the lunar cycle, normally 29 or 30.

For example:

Μ5·12 (16/30)

means that the current night is:

• in lunar cycle Μ5;
• night 12 of that cycle;
• the full moon is on night 16;
• the cycle contains 30 nights.

New-moon boundary

The astronomical new moon is an instant and does not necessarily occur at a civil-day boundary.

For assigning the first calendar night of a lunar cycle, the implementation uses the rule described on Lunar Structure: a new moon before 12:00 UTC is assigned to the preceding day/night; a new moon at or after 12:00 UTC is assigned to the same day/night.

This rule defines the cycle for the notation. The real-time night counter can still change at sunrise.

What the notation is for

The notation is intended to answer four simple questions at once:

• Which lunar cycle of the year is this?
• Which night of that cycle is it?
• On which night is the full moon?
• How long is this cycle?

It is an optional companion to the solar Light Calendar rather than a separate calendar system.

Calendar Representation >

Light Calendar >