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Moonlight

The Moon illuminates a boat club in Holma, Sweden.

Moonlight consists of mostly sunlight (with little earthlight) reflected from the parts of the Moon's surface where the Sun's light strikes.[1]

Illumination

The intensity of moonlight varies greatly depending on its phase, but even the full Moon typically provides only about 0.05–0.1 lux illumination.[2] When the full Moon is at perigee and viewed around upper culmination from the tropics, the illuminance can reach up to 0.32 lux.[2] From Earth, the apparent magnitude of the full Moon is only about ​1380,000 that of the Sun.[citation needed]

The color of moonlight, particularly around full moon, appears bluish to the human eye compared to most artificial light sources due to the Purkinje effect. Moonlight 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 incident sunlight is reflected from the lunar surface. Moonlight generally hampers astronomical viewing, so astronomers usually avoid observing sessions around full Moon. It takes approximately 1.26 seconds for moonlight to reach Earth's surface.

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.

"Moon blindness" is a name for equine recurrent uveitis. Moonlight is no longer thought of as the cause.

In the 16th century, moonmilk, a soft white limestone precipitate found in caves, was thought to be caused by the rays of the moon.[5]

Moonlight in art

See also

References

  1. ^ Toomer, G. J. (December 1964). "Review: Ibn al-Haythams Weg zur Physik by Matthias Schramm". Isis. 55 (4): 463–465 [463–4]. doi:10.1086/349914.
  2. ^ a b Kyba, Christopher C M; Mohar, Andrej; Posch, Thomas (1 February 2017). "How bright is moonlight?". Astronomy & Geophysics. 58 (1): 1.31–1.32. doi:10.1093/astrogeo/atx025. Retrieved 14 February 2017.
  3. ^ Matthews, Grant (2008). "CERES". Applied Optics. 47 (27): 4981–93. Bibcode:2008ApOpt..47.4981M. doi:10.1364/AO.47.004981. PMID 18806861.
  4. ^ A Dictionary of English folklore, Oxford University Press, 2000
  5. ^ Gessner, Conrad (1555). Descriptio Montis Fracti sive Montis Pilati [Description of Mount Fractus, or Mount Pilatus] (in Latin). p. 54. Retrieved March 12, 2016.

External links