Moonbows are mostly reported in places such as the Scottish Highlands and Hawaiian Islands.
Although moonbows are rare, they do tend to happen more frequently in certain locations.
The moonbows created near waterfalls are often called spray moonbows.
Earlier this month a spectacular rare moonbow was photographed over Northumberland.
Just like the rays of the sun can create a rainbow during the day, reflected light from the moon can create a moonbow if the conditions are just right.
The moonbow is no different with the exception that the light source is replaced by the moon itself.
John Muir, the naturalist largely responsible for the creation of Yosemite National Park, eloquently described moonbows in waterfalls:
Inspired by Muir's dramatic accounts, we decided to write a computer program to predict dates and precise times when moonbows would appear in the Yosemite waterfalls.
The best moonbows at Yosemite occur during the snowmelt runoff season of April, May, June, and sometimes early July.
edu/~do01, contains more detailed descriptions of the position of the Moon and appearance of the moonbows in 2007, along with links to moonbow photographs from 2006.
Our program typically predicts moonbows on four or five nights near each full Moon during the snowmelt run-off period.
At night the geometry is the same except that the antilunar point (opposite the Moon) is the center for this display--known as a lunar rainbow, moon rainbow, or moonbow.