Moonlight

A photograph taken by moonlight with an exposure time of ten 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 0.05-0.1 lux illumination.[2] When the Moon is nearest to Earth and viewed at high altitude at tropical latitudes, the illuminance can reach 0.32 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. It takes approximately 1.26 seconds for the moonlight to hit the Earths 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. It is no longer thought to be caused by moonlight.

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. 1 2 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). "Celestial body irradiance determination from an underfilled satellite radiometer: application to albedo and thermal emission measurements of the Moon using CERES". Applied Optics. 47 (27): 4981–93. Bibcode:2008ApOpt..47.4981M. PMID 18806861. doi:10.1364/AO.47.004981.
  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.
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