---
title: Moon rules
description: The full MOON() syntax for scheduling by lunar phase, illumination percentage or a range.
order: 3
---

# Moon rules

`MOON(...)` is a rule expression you can use in a Calendite recurrence rule to schedule an event
by lunar phase. See the [rule reference](/docs/rules-reference.html) for the surrounding syntax.

Format:

```text
MOON({phaseOrNumberOrRange})
MOON({phaseOrNumberOrRange}, {half})
```

## Supported phase values

```text
NEW
WAXING_CRESCENT
FIRST_QUARTER
WAXING_GIBBOUS
FULL
WANING_GIBBOUS
LAST_QUARTER
WANING_CRESCENT
```

Named phases represent the exact date of that moon phase.

Examples:

```text
MOON(FULL)
MOON(NEW)
MOON(FIRST_QUARTER)
MOON(LAST_QUARTER)
```

## Number values

A number represents moon illumination as a percentage.

```text
MOON(0)
MOON(50)
MOON(100)
```

Examples:

```text
MOON(0)    = new moon
MOON(100)  = full moon
MOON(50)   = 50% illumination, waxing or waning
```

For numbers between `1` and `99`, the rule may match twice in a lunar cycle: once while the moon is waxing and once while it is waning.

## Range values

A range represents an illumination range.

```text
MOON({start}..{end})
```

Examples:

```text
MOON(95..100)
MOON(25..50)
MOON(0..10)
```

Meaning:

```text
MOON(95..100)
```

matches dates where the moon illumination is between `95%` and `100%`.

## Half values

The optional second argument controls which half of the lunar cycle should be matched.

Supported values:

```text
WAXING
WANING
BOTH
FIRST_HALF
SECOND_HALF
```

Aliases:

```text
WAXING      = FIRST_HALF
WANING      = SECOND_HALF
BOTH        = default
```

Examples:

```text
MOON(50, WAXING)
MOON(50, WANING)
MOON(50, BOTH)

MOON(95..100, WAXING)
MOON(95..100, WANING)
MOON(95..100, BOTH)
```

Meaning:

```text
MOON(50, WAXING)
```

matches the 50% illuminated moon during the first half of the lunar cycle.

```text
MOON(50, WANING)
```

matches the 50% illuminated moon during the second half of the lunar cycle.

```text
MOON(95..100, WAXING)
```

matches dates where the moon is between `95%` and `100%` illuminated while waxing.

```text
MOON(95..100, WANING)
```

matches dates where the moon is between `95%` and `100%` illuminated while waning.

## Behaviour with named phases and half values

When using a named phase, the half value is allowed but not needed.

These are equivalent:

```text
MOON(FULL)
MOON(FULL, BOTH)
MOON(FULL, WAXING)
MOON(FULL, WANING)
```

They all mean:

```text
the exact full moon date
```

The half argument only affects number and range rules.

## Examples

```text
MOON(FULL)
```

The exact full moon date.

```text
MOON(100)
```

The exact full moon date.

```text
MOON(95..100)
```

Any date where the moon is between `95%` and `100%` illuminated, either waxing or waning.

```text
MOON(95..100, WAXING)
```

Any date where the moon is between `95%` and `100%` illuminated during the waxing half of the lunar cycle.

```text
MOON(95..100, WANING)
```

Any date where the moon is between `95%` and `100%` illuminated during the waning half of the lunar cycle.

```text
MOON(50)
```

Any date where the moon is `50%` illuminated, either waxing or waning.

```text
MOON(50, WAXING)
```

The waxing 50% moon.

```text
MOON(50, WANING)
```

The waning 50% moon.