What is a moonbow?

A moonbow forms exactly like a rainbow: light is refracted, reflected and dispersed by water droplets in the air. Because moonlight is far fainter than sunlight, the colours are too dim for the eye's colour-sensing cells, so most moonbows look white or silvery. Long-exposure photographs, however, reveal the full spectrum of colours. Moonbows are best seen around a full moon, when the moon is low in the sky and the sky is dark, opposite a source of spray or rain. Cumberland Falls in Kentucky and Victoria Falls in southern Africa are famous for regular moonbows.