Moonbows
Just about everybody has seen a rainbow. They are truly one of nature's most lovely natural phenomena. Now imagine a rainbow that occurs at night, lit by the moon rather than the sun. Such things exist, and they are called moonbows. They are very rare, of course, and very difficult to photograph. NASA has a picture here, but it required such a long exposure time that it appears as just another garden-variety rainbow.

I believe they are most often seen under a full moon at the base of waterfalls. Here is one at Cumberland Falls in Kentucky. They've also been spotted at certain falls in Yosemite National Park. - served up by Oven @ 12:56 PM