Moon · 4 of 8

Supermoon Seasons

Why do supermoons nearly always come in threes?

Why some full Moons come closer: two months that don't match, a 411.8-day beat, and supermoons that nearly always come in threes.

You’ll be able to say when the next run of supermoons comes, and why they arrive in threes.

6 steps · about 5 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

Espenak, AstroPixels — Moon at Perigee and Apogee, 2001 to 2100, and the mean 27.55455-day anomalistic month
Espenak, AstroPixels — Full Moon at Perigee (Full Supermoon), 2001 to 2100: the distance and apparent size of every close full Moon
Meeus, Astronomical Algorithms, 2nd ed. (1998), ch. 47, 49 and 50 — the Moon's distance, the 29.530589-day synodic month, and perigee and apogee
NASA Moon Fact Sheet — the Moon's 1737.4 km radius, from which its apparent width follows

← 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

A supermoon is a full Moon nearer than 360,000 km — two or three most years. This is the coming year's nearest, close to perigee, the near end of the Moon's oval orbit. The ring is a fixed size; the disc nearly fills it.

The farthest full Moon of the year, near apogee, the oval's far end: in the same ring it sits loose. Compare the tags. Months apart, with nothing to measure against, hardly anyone can tell.

The Moon's oval orbit from outside, the line to the Sun. Run 412 days.

The Moon's distance swings in and out every 27.55 days, perigee to perigee. The dots are full Moons, every 29.53 days. Out of step, each lands two days later in the swing.

Joined, the full Moons make a slow wave: one pass through perigee every 411.8 days, a year and a month and a half. Each trough is a run of supermoons, usually three, now and then two. Not rare, just bunched.

The coming year's nearest full Moon, on the date in the readout. By eye, the gap is hard to judge.

A full Moon at the near end of the oval
About a seventh wider than the farthest
They come in runs, every 412 days