This is a photo of a moonbow, or lunar rainbow, in the mist of Lower Yosemite Falls in Yosemite National Park. Bob took this shot on the night of May 25th, 2021. The park was conducting prescribed burns in Yosemite Valley, so he was concerned that the smoke would diminish the moonlight enough that the moonbow wouldn't show up. Fortunately the smoke dispersed enough that it didn't interfere. In fact, Bob thinks this was one of the best moon bows he's ever seen, because it persisted through almost the entire predicted window and was a strong and, for the most part, broad arc of light. In our previous visits to see the moonbow in Lower Yosemite Falls, the moonbow has appeared and disappeared depending on which way the wind was blowing the mist.
Moonbows occur when moonlight strikes the mist of a waterfall or misty rain during a storm at a 42 degree angle from the observer and creates a rainbow just like sunlight can do. The difference is moonlight is much dimmer and is only bright enough two days before, the night of, and two days after the full moon to create a moonbow. Also, because moonlight is so much dimmer, the colors of the rainbow don't usually show up to the naked eye. The human eye sees color with retinal cells called cones, which require a brighter light intensity than the moon provides, in order to be stimulated enough for you to perceive color. To the naked eye, the moonbow appears as a ghostly white arc of light. The colors do show up in photos thanks to the longer exposures that cameras provide.
The Big Dipper and other stars are visible in the sky above Lower Yosemite Falls.
Remember, it's not just a picture, it's a story.
