The Yosemite Moonbow

The rare Yosemite Moonbow captured in May, 2016, at Lower Yosemite Falls. Photo credit: Jonathan Irish

When all the elements come together — clear skies, heavy water flow, time of year, moon phase, etc. — there's an event at Lower Yosemite Falls called a "moonbow." We were thrilled to be able to witness it in May. It happens only a couple of times a year and can be witnessed in only a handful of places on Earth—the others being in Wiamea on the Big Island of Hawaii, Victoria Falls on the Zambia/Zimbabwe border, and at Plitvice Lakes National Park in Croatia.

John Muir called the nighttime event seen by the light of the full moon at Yosemite "lunar spraybows"... the folks at NASA might like to call them by their technical name, "lunar rainbows." They are also called "white rainbows," as they appear a ghostly white color to the naked eye. The refracted color is then brought out through long-exposure photography, which is what you will see in photos like the one Jonathan captured that is shown on this page. One thing that can be agreed upon is that they are rare and wonderful, and although they have been mentioned as far back as 350 BC by Aristotle, there is still little known about them. 

Moonbows are far rarer than rainbows because weather and astronomical conditions must be exactly right for them to be created. Earth's moon must be very low to the horizon and must be full, or near full. The sky must be very dark. And finally, water droplets must be present in the air in the opposite direction of the moon. The location at Lower Yosemite Falls and the mist that is naturally created there makes it a prime viewing location.

We ventured to the falls at 11pm during the new moon in May and met with a small group of photographers also hip to the phenomenon. Stefanie left her camera behind, opting to simply savor the experience while catching an unusually bright Saturn and Mars in the night sky. Jonathan photographed the moonbow for the second time at this location, and this was the result:

The Yosemite Moonbow, May, 2016. Credit: Jonathan Irish