What is a Moonbow?
Sunlight Reflected Off the Surface of the Moon
A moonbow (lunar rainbow) is an interesting phenomena that occurs when the light from the Sun gets reflected off the surface of the Moon. A moonbow forms when the reflected light from the Moon is diffracted when interacting with water droplets suspended in a rain cloud or the mist of a waterfall. Unlike the colorful rainbows produced by the sun´s light in a rainy day, moonbows appear white due to the loss of brightness which is not able to activate the cone color receptors in the eyes.
Moonbows are most easily observed on a dark night, preferably far away from any source of city lights. A moonbow is created by the indirect light from the Sun via Sun-Moon-moonbow. This produces a decrease in light intensity, producing moonbows which are almost imperceptible. In addition, the loss of intensity could be further eclipsed by added light luminosity, depriving the possibility of witnessing a moonbow.
The best time to observe a moonbow is on a full moon night. A full moon is essential in order to reflect plenty of light necessary to create the phenomenon. The Moon must be positioned in a 42° angle, or less from the horizon. Moonbows usually appear in the part of the sky opposing the Moon with the viewer behind the Moon. It is essential that a dark night, full Moon and the Moon situated at a suitable angle be present for a moonbow to be appreciated.
Moonbow Created by the Rising Mist from the Waterfall
How is a Moonbow Formed?
The light reflected from the Moon creates a faint moonbow when interacting with the mist rising from the waterfall. Sometimes, a colorful arc moonbow can be witnessed when the full Moon is shining above in the sky on a clear cloudless night, allowing a considerable amount of moonlight to be diffracted off the droplets in the air.
The waterfall provides the medium against which the light reflected off the moon will interact in order to produce a moonbow. The best way to observe a moonbow is to situate yourself between the medium (mist) and the Moon with the full Moon behind you.
Moonbow and Aurora Borealis
Moonbow in the Northern Latitudes
If you happen to be in the northern latitudes contemplating a moonbow with clear skies and a bright full Moon, the phenomenon may be accompanied by other natural phenomena, such as the glowing lights of the aurora borealis curtains with their characteristic green color in the background sky, such as in the photograph taken in Iceland.
A moonbow is produced by reflection, refraction and dispersion of the light coming from the Moon and interacting with the mist or falling rain. A moonbow contains the colors of the spectrum; however, in not too intense full moon nights, only a white moonbow will be perceived. Its color varies from plain white to grayish white. Other names with which a moonbow is known include moonrainbow, nightrainbow, lunar rainbow and white rainbow.
Moonbow at Yosemite National Park
Famous Places to Watch a Moonbow
Moonbows are fascinating phenomena to watch. Moonbows are more rare than rainbows created by the Sun, as they depend on more factors other than just sunlight. The most usual places to witness a moonbow are the ones that meet the required conditions for them to be seen, such as a waterfall. There are famous places in which mooonbows are known to become visible, including Cumberland Falls and Yosemite National Park in the U.S. Victoria Falls in Africa and Waimea Canyon in Hawaii.
Cumberlands Falls, Kentucky claims to be the only place in the Western Hemisphere where a moonbow can be predicted for observation.
Additional Data about Moonbows
Other names with which a moonbow is known include: lunar rainbow, white rainbow and space rainbow.
For a moonbow to occur there must be good weather conditions with clear skiesand a full Moon; however, a clear moonlit night can be good enough to reflect enough sunlight to show a moonbow.
A colorful moonbow is most commonly seen during the fall and winter season when the air in the atmosphere is drier.
Long exposure cameras can capture the colors of a moonbow
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