The 18.6-year lunar standstill, measured rather than asserted
The Moon's declination range swings between ±18.5° and ±28.7° over 18.6 years. Here is the cycle, computed year by year, and why it is not a solstice.
The Sun’s declination cycles once a year, between +23.44° and −23.44°, and that range is fixed. The Moon’s does not have a fixed range at all: it swings between roughly ±18.5° and ±28.7° on an 18.6-year period.
The reason is that the Moon’s orbit is inclined 5.14° to the ecliptic, and the line where the two planes cross — the node line — rotates backwards, completing a circuit in 18.6 years. When the ascending node points toward the vernal equinox, the inclination adds to the obliquity: 23.44 + 5.14 = 28.58°. Half a cycle later it subtracts: 23.44 − 5.14 = 18.30°.
Computed maximum declination by year, from this site’s lunar engine:
| Year | Max |declination| | Year | Max |declination| | |
|---|---|---|---|---|
| 2022 | 27.50° | 2030 | 23.56° | |
| 2023 | 28.30° | 2032 | 20.27° | |
| 2024 | 28.70° | 2033 | 18.96° | |
| 2025 | 28.70° | 2034 | 18.54° | |
| 2026 | 28.41° | 2035 | 19.32° | |
| 2027 | 27.69° | 2038 | 23.89° | |
| 2028 | 26.62° | 2040 | 26.77° | |
| 2029 | 25.19° | 2042 | 28.51° |
Two things in that table are worth reading carefully.
The peak is broad, not sharp. 2024 and 2025 both reach 28.70°, because the Moon’s declination maximum is smoothed by the orbit’s eccentricity — it is not a single instant but a plateau of a year or two. That is why published accounts say “the major standstill of 2024–2025” rather than naming a date.
The minimum is deeper than the simple sum predicts. 18.54° against a predicted 18.30°, because the Moon’s declination also carries a small oscillation from the eccentricity of its orbit. The computed number is the one to trust; the arithmetic explains it, not the other way round.
What a standstill actually looks like
The visible consequence is where the Moon rises and sets on the horizon. At a major standstill, seen from 50°N, the Moon can rise up to about 10° further north or south than the Sun ever does at the solstices. It also climbs higher at upper transit — up to 28.7° + 50° = 78.7° at 50°N, close to overhead.
At a minor standstill the Moon stays inside the Sun’s range entirely: it never rises or sets outside the solstice limits, and never climbs higher than the Sun does in June.
That difference is large enough to be obvious over a few years of casual observing — the full Moon’s rising point in winter walks noticeably along the horizon — and it is the basis of a whole class of archaeological claims about stone circles and standing stones aligned on lunar extremes.
What it is not
A standstill is not an eclipse season, not a solstice, and not a “moon event” in the popular sense. Nothing happens on the day. The Moon looks exactly like a full moon; it is simply rising in a different place from where it rose a few years ago.
It is also not rare. A major standstill comes every 18.6 years, and a minor one in between, which means roughly every nine years something happens that is worth pointing out — just not worth a headline.
If what you want is the immediate, visible version of this geometry, the fifty-minutes-later page shows how the Moon’s path angle changes the rise interval night by night, and the moonrise table gives the numbers for a real city.
Declinations computed from the truncated ELP-2000/82 theory and checked against JPL Horizons. The 18.6-year period is the mean regression of the node; individual years vary within the range shown.
Frequently asked questions
- What is a lunar standstill?
- The point in an 18.6-year cycle when the Moon's declination reaches its maximum or minimum range. At a major standstill the Moon swings between +28.7° and −28.7°, rising and setting further north and south than the Sun ever does. At a minor standstill the range is only ±18.5°, and the Moon stays within the Sun's range.
- When was the last one?
- The most recent major standstill peaked in 2024–2025, when the computed maximum declination reached 28.70° in both years. The next minor standstill is in 2034, at 18.54°, and the following major standstill falls around 2042–2043.
- Is a standstill the same as a solstice?
- No, though the idea is similar. A solstice is when the Sun reaches its extreme declination, which happens every year because the Sun's declination cycle is annual. A lunar standstill is when the Moon's extreme declination is at its largest or smallest, which happens every 18.6 years because the Moon's orbital plane rotates against the ecliptic on that period.
- Does it have any effect on Earth?
- It changes where the Moon rises and sets on the horizon, by up to 10° either way compared with a minor standstill, and it slightly changes the maximum altitude the Moon reaches. That is all. Claims connecting standstills to weather, earthquakes or human behavior are not supported by measurement.
Sources
Each source is a primary or official reference, checked before publication. Links open the original.
- NASA Science — Moon: the 5.1° inclination of the lunar orbit to the ecliptic and the 18.6-year regression of the nodes that produces the standstill cycle (science.nasa.gov/moon/)
- Meeus, Astronomical Algorithms, 2nd edition, chapters 47 and 22 — the lunar theory and the obliquity conversion that give the Moon's declination used in the table on this page
- JPL Horizons (DE441) — the ephemeris against which this site's lunar declination is checked to within 30 arcseconds over 2026–2027 test dates (ssd.jpl.nasa.gov/horizons/)
- Royal Astronomical Society and archaeoastronomy literature on major lunar standstill alignments, including the 2024–2025 observing campaign at stone circles and recumbent stone settings