The Science of Moonbows

Dumgoyach, via Wikimedia Commons

With National Moon Day approaching on July 20th and the Anniversary of the Apollo 11’s first landing on the Moon, we felt it appropriate to feature the science of moonbows in this month’s newsletter.

A moonbow is also commonly referred to as a lunar rainbow. A moonbow is a rare natural atmospheric phenomena that occurs when the Moon’s light is reflected and refracted off water droplets in the air.

Moonbows are much fainter than rainbows made by the sun and often appear to be white. This is due to the smaller amount of light reflected from the surface of the moon. The light from the moon is usually too faint to be perceived by the receptors in the human eye, it is difficult for the human eye to discern colors in a moonbow. However, the colors in a moonbow do appear in long exposure photographs.

A bright moon near to its brightest phase known as a full moon is needed in order to have a chance at seeing a moonbow. It must be also be raining opposite the moon, the sky must be dark and the moon must be very low in the sky (about 42º above the horizon). All these put together makes seeing a moonbow very special and rare!

There are some locations around the world where moonbows occur more frequently. Most of these locations tend to have waterfalls, which create layers of mist in the air. Some of these locations include Yosemite National Park in California and Cumberland Falls State Resort Park in Kentucky. Victoria Falls on the border of Zambia and Zimbabwe and Waimea in Hawaii.

Moonbow at Victoria Falls; By Scolopendra33 via Wikimedia Commons

Moonbow at Lower Yosemite Falls; By Brocken Inaglory via Wikimedia Commons

Moonbow over Kula, Hawaii; By Arne-kaiser via Wikimedia Commons