RAINBOW IN THE DARK
A lunar rainbow, moonbow or night rainbow is a rainbow caused by moonlight, instead of sunlight.
Most photos of moonbows are what are called "false moonbows" that are caused by geographic features, not weather. Such are the moonbows people capture at Yosemite Falls in spring, for example. They're somewhat predictable moonbows, which means you're likely to also run into a huge crowd if you head to any of these locations when a moonbow may form.
What you see in this image is, however, a "true" moonbow, that is, a moonbow caused entirely by weather (rain). These "true moonbows" are not predictable at all, just like typical daylight rainbows, but much more rare.
The place is Papohaku Beach, in Moloka'i, a 5km long beach of undisturbed white sand. The Moon causing the night rainbow was directly behind me, still low and rising over the eastern horizon, a few days past its full phase. The lights in the horizon are from Honolulu and other cities from the island of O'ahu, about 30 miles away.