A moonbow (also known as a moon rainbow or lunar rainbow) is a rainbow (concentric arcs of colors produced on a screen of water droplets) produced by moonlight rather than direct sunlight. Other than the difference in the light source, its formation is the same as for a solar rainbow: It is caused by the refraction and reflection of light in many water droplets, such as a rain shower or a waterfall, and is always positioned in the opposite part of the sky from the Moon relative to the observer.

A moon bow over the town of Kihei, seen from Kula, on Maui, Hawaii, in February 2016. Source: Wikicommons, Author: Arne-kaiser.