moonbow
noun

- a rainbow produced by moonlight rather than direct sunlight; formed by the refraction of moonlight in water droplets, much fainter than a solar rainbow and often appearing white to the naked eye.

- a rare optical phenomenon in which moonlight is refracted, reflected, and dispersed through water droplets in the air, creating an arc of colour visible on dark, clear nights near a full moon.

Merriam-Webster, Collins English Dictionary

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WORD ORIGIN

Moonbow is a compound word built from two of the oldest elements in English.

Moon goes back to Old English mōna, which is closely related to Old High German māno, Old Norse máni, and Gothic mena. All derive from the Proto-Germanic root mēnōn, which itself traces to Proto-Indo-European mēnsis — the root also behind the Latin mensis (month) and the Greek mēnē (moon).

The connection between moon and the measurement of time is ancient and direct: people counted months by watching the lunar cycle long before they had written language.

Bow in the sense of an arc or curve comes from Old English boga, related to Old High German bogo and Old Norse bogi. Its PIE root bheug- means "to bend." The same root gives us "elbow" and the archery bow.

The word rainbow — Old English renboga — has existed since at least the 10th century. Moonbow is a natural, logical parallel formation. The OED traces the written word to 1871.

The phenomenon itself was described long before the word existed in English. Aristotle wrote about it in his Meteorology around 350 BC — making moonbow one of those curious cases where the observation preceded the vocabulary by more than two thousand years.

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MOONBOWS

A moonbow is technically a rainbow. It has all seven colours — red, orange, yellow, green, blue, indigo, violet — in exactly the right order. The human eye just can't usually see them.

The colour-detecting cells in our eyes, called cones, need a certain minimum level of light to switch on. Moonlight — which is only reflected sunlight, at roughly 400,000 times less intensity — doesn't reach that threshold. So we see a pale arc instead of a colourful one.

Cameras have no such limitation. A long-exposure photograph of a moonbow reveals the full spectrum in vivid detail. What the eye misses, the sensor catches.

Cumberland Falls in Kentucky and Victoria Falls on the Zambia-Zimbabwe border are the two most reliable spots on earth for consistent moonbow sightings.

Aristotle first wrote about moonbows in 350 BC. The phenomenon waited until 1871 for an English word to describe it.

Helga & Paul Smith

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SYNONYMS

arc of moonlight, celestial night arc, ghost rainbow, ghost-arc, grey rainbow, grey-white arc in the night, lunar arc (bow, light bow, rainbow), lunar refraction arc, midnight rainbow, mist bow (related), moon arc, MOONBOW, moon rainbow, moonlit arc, moonlit bow, night arc, night bow (rainbow), nighttime rainbow, pale arc, pale bow, pale night arch, white arc, white bow (rainbow), white-light rainbow

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“Aristotle observed and wrote about MOONBOWS over two thousand years ago, he just didn't have a word to dscribe it.”

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