Moonlight
Overview
 
Moonlight is the light that reaches Earth from the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. This light does not originate from the Moon, but from sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

. The Moon does not, however, reflect sunlight like a mirror
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...

, but it reflects light from those portions of its surface which the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's light strikes. See diffuse reflection
Diffuse reflection
Diffuse reflection is the reflection of light from a surface such that an incident ray is reflected at many angles rather than at just one angle as in the case of specular reflection...

.

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
Werewolf
A werewolf, also known as a lycanthrope , is a mythological or folkloric human with the ability to shapeshift into a wolf or an anthropomorphic wolf-like creature, either purposely or after being placed under a curse...

.
Encyclopedia
Moonlight is the light that reaches Earth from the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. This light does not originate from the Moon, but from sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

. The Moon does not, however, reflect sunlight like a mirror
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...

, but it reflects light from those portions of its surface which the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's light strikes. See diffuse reflection
Diffuse reflection
Diffuse reflection is the reflection of light from a surface such that an incident ray is reflected at many angles rather than at just one angle as in the case of specular reflection...

.

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
Werewolf
A werewolf, also known as a lycanthrope , is a mythological or folkloric human with the ability to shapeshift into a wolf or an anthropomorphic wolf-like creature, either purposely or after being placed under a curse...

. The light of the moon was thought to worsen the symptoms of lunatics, and to sleep in moonlight could make one blind, or mad. Nyctalopia
Nyctalopia
Nyctalopia is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition...

 (night blindness caused by a lack of vitamin A) was thought to be caused by sleeping in moonlight in the tropics.

Illumination

The intensity of moonlight varies greatly depending on the lunar cycle but even the full moon typically provides only about 0.2 lux
Lux
The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface...

 illumination, so the full moon is about 500,000 times fainter than the sun. When the moon is viewed at high altitude at tropical latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s, the illuminance
Illuminance
In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of the intensity of the incident light, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per...

 can reach 1 lux. 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
Purkinje effect
The Purkinje effect is the tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.This effect introduces a difference in color contrast under different levels of...

 - 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
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 is 0.136, meaning only 13.6% of sunlight incident on the Moon is reflected.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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