What is a Moon Bow and how is it Formed

A moonbow (lunar rainbow) is the sight of spectral colors created by moonlight over a medium, for instance, a waterfall. A moonbow is caused by the sunlight which is reflected off the surface of the moon.  Moonbows are formed when light rays are diffracted off water droplets suspended in the atmosphere; the water vapor of a rain cloud or the mist of a waterfall. Moonbows always appear white because the reflected light from the moon is usually too faint to excite the cone color receptors of the human eye; however, the colors of the spectrum may appear in long exposure photographs. The following gives a description of a moonbow.

Moonbows are created by the indirect light of the sun which is reflected by the moon´s surface on a clear full moon night, as opposed to a rainbow which is created by the direct sunlight. Moonbows are caused by the interaction between moonlight and mist with the moon positioned at the proper angle. The light coming from the moon is a little decreased in intensity than that of the sun, creating moonbows which are almost imperceptible. This produces colorless moonbows; however, a camera can capture the colors of a moonbow, producing a colorful moonlight rainbow.

Moonbows are most commonly observed on a dark night within a few days of a full moon. A full moon is necessary so it can reflect sufficient sunlight required to produce this phenomenon. The moon must be in a 42° angle or closer to the horizon, as well. Moonbows always appear in the part of the sky opposite the moon with the moon behind the viewer.  It is necessary that a combination of a full moon, dark night and a moon situated at a middle angle or lower exist in order to produce the phenomenon.

Moonbows are interesting phenomena to watch.  Although, they´re not produced by the light coming from the sun, but the light reflected from the sun via the moon. Moonbows are more unusual than rainbows produced by the sun.  Moonbows only occur within a few days from a full moon. It is during this time that moonlight is refracted while interacting with the particles of rain or mist. The color of a moonbow varies from grayish white or simply plain white due to the low amount of sunlight reflected from the moon.

Other names by which a moonbow is known include lunar rainbow, white rainbow, lunar bow and space bow. The best location to watch a moonbow is in a place where the conditions for a moonbow to become visible are met, such as a waterfall; however, there are famous places in the world where moonbows have been seen, including, Yosemite National Park and Cumberland Falls in the U.S., Waimea Canyon, Hawaii and Victoria Falls, Africa.