Lunar rainbows.

A moonbow (lunar rainbow, white rainbow, lunar bow, or space rainbow), it looks rather like something from fantasy art or a background scene for the Hobbit. It’s a rainbow that reflects light off the surface of the moon rather than direct sunlight. A very rare occurance, very specific lunar and weather conditions are necessary to be able to even catch a glimpse of these. Because the light is usually too faint to excite the cone color receptors in human eyes, it is difficult for the human eye to discern colors in a moonbow. As a result, they often appear to be white. However, the colors in a moonbow do appear in long exposure photographs.

Moonbows are most easily viewed when the moon is near to full. For true moonbows, other than those produced by waterfalls or sprays, the moon must be low in the sky, about 42 degrees, and the sky must be very dark. Since the sky is still light on a rising full moon, this means they can only be observed 2 to 3 hours before sunrise, a time with few observers. And, of course, there must be rain falling opposite the moon. This combination of requirements makes moonbows much rarer than rainbows produced by the sun. Moonbows may also be visible when rain falls during full moonrise at extreme latitudes during the winter months, when the prevalence of the hours of darkness give more opportunity for the phenomenon to be observed.

Moonbows can only be seen in a few different locations on the planet, mainly in the Scottland highlands, souther England and wales, most of Ireland and Hawaii.