There’re probably not a whole lot of people in the world who don’t know, much less haven’t seen, a rainbow. And most everybody is sure to appreciate the sight of that bright and multicolored arch in the sky before or after some rain. It’s through the rainbow that many students get their first in-depth lesson in colors and how they come from seemingly white light. But not so many are aware that the scientific principles which give form to a rainbow during the day when the sun is up are also repeatable during the evenings, in certain places of the world, with the moon taking the sun’s place.
As BBC tells the story, on the night of October 18 a most spectacular sight lit up the night sky over the countryside of Coquet Valley in Northumberland, England. As lightning split the sky a grand arch of brilliant lights streaked across the clouds as if framing the lightning bolts and the fields down below. Quick-acting shutterbugs in both Northumberland and Yorkshire have managed to capture the magnificent occurrence of a lunar rainbow, or moon-bow, and these pictures quickly earned viral status on social media due to the crisp images they encapsulated.
A moon-bow is produced very much like its sun-powered cousin, through the refraction of light in through a large amount of water droplets in the atmosphere. As a rule, both rainbows and moon- bows always appear in the opposite direction of the sky from the source of light relative to whoever is looking. That’s why the moon isn’t anywhere around those moon-bow pictures in the UK, but one can see the beginnings of the rain shower from which the water droplets that refracted the moonlight originated.
Since the moon is a fainter source of light than the sun, a moon-bow is a lot less clear than a rainbow. In fact, the Northumberland and Yorkshire pictures aside, usually the lunar light is so faint that the individual color bands tend not to be so distinct, making it appear most of the rare times it shows as wholly white. Furthermore, the chances of a moon-bow being formed are greater on nights when the moon is closest to becoming full, and often only in the two to three-hour periods following sunset and before sunrise.
When no light rain is evident in the sky, there’s a chance that mist from large rushing waterfalls can produce the moon-bow effect, like in the lower Yosemite Falls in Yosemite Park, California or Victoria Falls between Zambia and Zimbabwe. The recent moon-bow, formed during an evening rain on a moonlit night, was similar to a much earlier event reported in a November 1799 issue of The Norfolk Chronicle, and referenced by minor English poet William Cole in one of his poems.
Photo Credit to http://www.bbc.com/news/uk-england-37689358