Moonlight

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File:2011-08-11 22-12-47-moonlight.jpg
A photograph taken by moonlight with an exposure time of fifty minutes.

Moonlight is the light that reaches Earth from the Moon, consisting mostly of sunlight, with some starlight and earthlight reflected from those portions of its surface which the Sun's light strikes.[1]

Illumination

The intensity of moonlight varies greatly depending on the lunar cycle but even the full Moon typically provides only about 0.1 lux illumination. When the Moon is viewed at high altitude at tropical latitudes, the illuminance can reach 0.26 lux.[2] The full Moon is about 1,000,000 times fainter than the Sun.

The color of moonlight, particularly near full Moon, appears bluish to the human eye compared to most artificial light sources. This is because of the Purkinje effect - the light is not actually tinted blue, and although moonlight is often referred to as "silvery" it has no inherent silvery quality. The Moon's albedo is 0.136,[3] meaning only 13.6% of sunlight incident on the Moon is reflected. Moonlight generally hampers astronomical viewing, so astronomers usually avoid making observations near full Moon.

Folklore

In folklore, moonlight sometimes has a harmful influence. For example, sleeping in the light of a full Moon on certain nights was said to transform a person into a werewolf. The light of the Moon was thought to worsen the symptoms of lunatics, and to sleep in moonlight could make one blind, or mad.[4] Nyctalopia (night blindness caused by a lack of vitamin A) was thought to be caused by sleeping in moonlight in the tropics.

In popular literature, The fictional short story "The Trade Wind", by Morgan Robertson, a popular author of sea stories, describes the adventures of an entire crew of sailors afflicted by "Moon Blindness" (a disease of horses now known as equine recurrent uveitis). It presumes that the reader is familiar with this condition and accepts the premise that it is a known painful but temporary result of sleeping in bright moonlight. In this case it occurred as the aftermath of passing-out drunk on deck following a party, and explores how such a group might deal with the handling of a sailing vessel on the open sea without eyesight.

The story first appeared in Collier's Weekly in the late 1800s and was later included in the 1899 collection "Where Angles Fear To Tread, and other Tales of the Sea" (available on-line).

Moonlight in art

See also

References

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  4. A Dictionary of English folklore, Oxford University Press, 2000

External links