Moon · 8 of 8

The Moon's 18.6-Year Swing

Why does the Moon swing five degrees past the Sun’s limits in some years?

Why the Moon swings five degrees past the Sun's limits in some years and stops five short of them in others: its path's tilt turning round, once in 18.6 years.

You’ll be able to say why the Moon rides higher in some years than in others.

7 steps · about 5 min

Before this: Celestial Coordinates (8 min), The Ecliptic (8 min), Eclipse Seasons (9 min)

Where and which night

Working out when this is best placed from where you are…

Where

Which night

Date

Time

Kept for this guide only, until you change it here — your map settings, and every other guide, stay as they are.

Print, play outside or present

Present on a big screen

Scan with a phone's camera, or open

Sources

Meeus, Astronomical Algorithms, 2nd ed. (1998), ch. 47 — the Moon's position, and its node
US Naval Observatory — dates of the equinoxes and solstices
Wikipedia, "Lunar standstill" — Callanish, Chimney Rock, and the next major standstill in 2043

← GUIDES

More below ↓

With a keyboard, focus the sky, aim it with the up and down arrow keys, and press Enter to drop the pin at the centre of the view; or press Show me.

You are here

Settings

Screen

Night mode Turns every page red, to keep your eyes adjusted to the dark.

High contrast Bolder constellation lines, larger and brighter names on the sky, and stronger text and edges everywhere. Starts on if your device asks for more contrast.

Reduce motion The camera cuts to where it is going instead of flying there, and panels and sheets appear without sliding. Starts on if your device asks for less motion.

Battery saver Draws the sky thirty times a second at most: smoothness traded for battery.

Night brightness Dims the screen below your phone’s lowest setting, down to a fifth, while night mode is on.

Clock and voice

Clock How every time is written. Until you choose, your language’s own clock decides.

D describes What D says about the view on the sky: one sentence, or in full with the field, the constellation and five names.

Sounds Quiet tones as you use the map: a tick as you drag the clock past a mark or dusk, a chime for the star you pick — higher for hotter stars — and a low swell while a figure is out of the dome. Made in your browser, and off until you turn them on.

All settings and your progress

In early 2025 the Moon rode higher over London than the midsummer Sun ever does. In 2034 it won't come close. Same Moon, on the same dashed path among the stars — so what changed?

The ecliptic, the Sun's road, peaks 23.44° north of the celestial equator: the midsummer Sun's height. The Moon's path is tilted 5.15° to the ecliptic, so here it runs a little above that peak or a little below it.

The cross is a node, where the Moon's path crosses the ecliptic. The nodes slide west, once round in 18.6 years — the turn that brings eclipse seasons 19 days sooner each year — so the Moon's tilt keeps its size but turns its direction.

↺ The nodes' 18.6-year slide, from Eclipse Seasons

Run 18.6 years over the ecliptic's peak. When the two tilts point the same way the dashed path reaches 28.6° from the equator, as in 2025; when they oppose, only 18.3°, as in 2034.

Forty years of the Moon's farthest north, month by month. The peaks are the major standstills, the troughs the minor ones. At a major standstill it swings five degrees past the Sun's limit, and rises and sets far further north.

Face east: the Moon rises where the dashed path meets the horizon, and over a month that point swings north and south. At a major standstill the swing is widest. Callanish in Scotland and Chimney Rock in Colorado mark it; the next is 2043. This month, note where the Moon rises over your skyline.

The farthest the Moon's path reaches from the equator. Mark where the full Moon rises: its swing narrows until 2034.

The Moon's path tilts 5° to the Sun's road
Its nodes turn once in 18.6 years
Next major standstill: 2043