Lunar Rainbows

A moonbow is the nighttime version of a rainbow. Where a rainbow is caused by the deflection of the sun’s direct light through water droplets, a moonbow is created by the light provided by the moons reflection as seen through these same droplets of water. The effect of the moon’s reflected light, which creates a moonbow, is normally not as strong as a rainbow because there is less light reflected off of the moon’s surface than is provided by the sun during the day. A moonbow often looks like a white arch to the naked eye because of the weaker amounts of light reflected at night. Additional names given for a moonbow are a lunar bow, lunar rainbow and a white rainbow.

Moonbows are created from the same phenomenon as with rainbows. The conditions required for a moonbow to occur are a full moon or a night in which the moon is strongly lit. As light enters a droplet of water, it is refracted. It is then reflected off of the back of the water droplet and refracted once again. While observing a daytime rainbow this refraction and reflection of white light from the sun causes the entire spectrum of light to become visible. The white light is reflected into separate spectrums of light based on their individual frequencies. Additionally, for a moonbow to appear the weather must be clear and this source of water droplets must be present. This source of water must also be positioned in the opposite side of the sky from the moon.

Unlike daytime rainbows, moonbows have only been seen in regular frequency at a few locations throughout the world. Within the United States moonbows can be seen at Cumberland Falls, Kentucky, Yosemite National Park, California and at Waimea in the Hawaiian Islands. Outside of the United States, Victoria Falls in Africa is also very well known for having frequent moonbow sightings from the mist created near the bottom of their great water fall.

Rainbows have folklore surrounding them of bringing luck. Their rare occurrences make for a wonderful surprise to those that witness them. Much more unique than rainbows, nighttime moonbows only form regularly in several locations throughout the entire world. They only appear under specific circumstances and on certain days during the moons lunar cycle. Their appearance is truly a marvel of nature’s beauty.

For more information on moonbows see