Double moonbow over Victoria Falls! (photograph by Calvin Bradshaw)
Spectacular rainbows are an Instagram feed a dozen, but what about moonbows? These rainbows of the night, also known as “lunar rainbows” or “space rainbows,” are a rare weather phenomenon you can only catch in a few of our world’s locales.
The moonbows are created by moonlight refracting through moisture in the air, which is why they’re easiest to see on full moon nights over waterfalls that fill the air around them with water droplets. This particular occurrence, because there can never be enough names for something so spectacular, is a “lunar spraybow.”
The buoyant naturalist John Muir wrote of the one at Yosemite Falls:
“Lunar rainbows or spray-bows abound in the glorious affluence of dashing, rejoicing, hurrahing, enthusiastic spring floods, their colors are distinct as those of the sun and regularly and obviously banded, though less vivid. Fine specimens may be found any night at the foot of the Upper Yosemite Fall, glowing gloriously amid the gloomy shadows and thundering waters, whenever there is plenty of moonlight and spray.”
Many times the moonbows appear white as it’s hard for our human eyes to discern their colors at night, but through a timelapse photograph the whole spectrum comes through. When scouting the world’s waterfalls and rainy terrains, it’s important not to get tricked by the “false moonbows.” These are rainbow rings around the moon, which, as cool as that is, are a different kind of light refraction through a cloud.
Moonbows at Yosemite Falls are fairly reliable — you can even find moonbow predictions calculated by the University of Texas. They’re also a regular apparition at the Cumberland Falls in Kentucky, Victoria Falls in southern Africa, and in Costa Rica’s cloud forests. So mark your calendar for the next full moon and get to the nearest waterfall to see if you can spot this rare and wondrous spectacle.
Moonbow over Wallaman Falls, Australia (photograph by Thierry Legault)
Moonbow over Jerome, Arizona (photograph by Alan Stark)
Moonbow at Yosemite Falls (photograph by Brocken Inaglory)
Moonbow over the Canterbury Plains in New Zealand (photograph by Ben/Flickr user)