Did you know?

Click any word in a definition or example to find the entry for that word


noun [countable]

a rainbow produced when water droplets in the air reflect light from the moon rather than the sun

'Whitman was absolutely awestruck after seeing a moonbow that was formed over Dartmoor and he captured the stunning sight in his camera, The Herald reported. Photographing a moonbow is extremely rare …'

Science World Report 6th December 2016

Spring is becoming a welcome reality in the northern hemisphere, the happy prospect of saying a temporary goodbye to short days and chilly temperatures and a pleasant respite for any dog owners who don't relish exercising their canine chums on cold, dark evenings. It does however reduce their chances of being as lucky as Plymouth dog owner Lewis Whitman, who in the company of his red Labrador Nellie, was fortunate enough in late 2016 to witness what's often considered to be one of earth's most elusive natural wonders – the moonbow.

To the naked eye, moonbows often look white … but slow-exposure photography can reveal their colours

A moonbow, also often described as a lunar rainbow, is formed when moonlight, rather than sunlight, is reflected and refracted off water droplets in the air. To the naked eye, moonbows often look white (and so are sometimes dubbed 'white rainbows'), but slow-exposure photography can reveal their colours, as this example of a moonbow photographed in the UK in recent months impressively shows. Moonbows are far rarer than rainbows because they need a very specific set of meteorological and astronomical conditions: a full moon which is very low, a particularly dark night sky (because any bright light obscures them), and water droplets of rain or mist falling opposite the moon.

Moonbows are more frequent in locations such as Iceland and Yosemite Park in California, where spectacular-scale waterfalls create layers of mist in the air, but in late 2016 night skies in the UK also exhibited more than one example of this unusual phenomenon, partly courtesy of a rare spike in the incidence of supermoons, full or new moons which appear much larger than normal because they are closer to the earth.

Background – moonbow

In scientific circles, the word moonbow appears to date back at least as far as the mid 19th century, though has only begun to pop up in mainstream usage relatively recently. With three supermoons in October, November and December last year (there's only one anticipated in 2017), 2016 was a year in which moon-related terminology seemed to drop more firmly into the popular consciousness, media coverage of the phenomenon perhaps offering a little light relief against headlines dominated by the presidential election and Brexit. Other variations on the theme include micromoon, a full moon which appears much smaller than normal because its orbit is at the farthest point from earth (the opposite of a supermoon), blue moon, so-called because atmospheric dust or smoke particles scatter red light to make it appear blue (and indeed so very rare an occurrence it spawned the well-known idiomatic phrase once in a blue moon), halo moon, formed when moonlight reflects off ice crystals in the atmosphere and produces a ring of light around the moon, Harvest/Hunter's moon, a full moon occurring in late summer or autumn, characteristically orange due to its closeness to the horizon (and sometimes described as a blood or sanguine moon if coinciding with a lunar eclipse), and the rare strawberry moon, a full moon which occurs in June, named by native Americans not for its amber hue, but because it marks the beginning of the strawberry-picking season.

by Kerry Maxwell, author of Brave New Words

Last month …

Read last month's BuzzWord. Hamdog.

This article was first published 8th March 2017.

Open Dictionary

Dunning-Kruger effect

the phenomenon by which an incompetent person is too incompetent to understand his own incompetence

add a word


A must for anyone with an interest in the changing face of language. The Macmillan Dictionary blog explores English as it is spoken around the world today.

global English and language change from our blog