Lunation Number
The Moon's continuous count · and where its sunrise has reached
The Moon keeps no clock, and that is the interesting part: a lunar solar day is about 29.5 Earth days, so twenty-four lunar hours would each run nearly thirty of ours. What lunar observers use instead is a count and an angle. The Brown Lunation Number runs continuously from the first new moon of 1923, numbering every lunation since. Selenographic colongitude gives the longitude of the morning terminator — the line of lunar sunrise creeping across the surface at about 12.2 degrees a day. It reads 270 degrees at new moon, 0 at first quarter, 90 at full and 180 at last quarter, which makes it the Moon’s own time of day, and it is what tells an observer which craters are catching the low light tonight.
In UTC at 02:02 on October 27, 2026, this calendar read Lunation 1,284 · day 16.4. The reading above is live, in your own time zone.
At a glance
- Type
- A continuous count of lunations
- Origin
- Ernest W. Brown’s lunar tables, numbering from 1923
- Months
- Each lunation is one month — about 29.53 days, new moon to new moon
- Day
- A lunar day lasts about 29.5 Earth days; the colongitude stands in for its time of day
- Counts from
- The first new moon of 1923 (Brown Lunation Number 1)
- Where it’s used
- Lunar observing — which craters the sunrise is lighting
- How it’s worked out here
- The average lunation from a reference new moon; the colongitude from the moon’s phase
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