Holma Boat Club by the light of the moon

Moonlight consists of mostly

sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...

(with little

earthlight ''Earthlight'' is a science fiction novel by British writer Arthur C. Clarke, published in 1955. It is an expansion to novel length of a novella of the same name that he had published four years earlier. Overview ''Earthlight'' is a scie ...

) reflected from the parts of the Moon's surface where the Sun's light strikes.

History

The ancient Greek philosopher

Anaxagoras Anaxagoras (; , ''Anaxagóras'', 'lord of the assembly'; ) was a Pre-Socratic Greek philosopher. Born in Clazomenae at a time when Asia Minor was under the control of the Persian Empire, Anaxagoras came to Athens. In later life he was charged ...

was aware that "''the sun provides the moon with its brightness''".

Zhang Heng Zhang Heng (; AD 78–139), formerly romanization of Chinese, romanized Chang Heng, was a Chinese polymathic scientist and statesman who lived during the Han dynasty#Eastern Han (25–220 AD), Eastern Han dynasty. Educated in the capital citi ...

's treatise "''The Spiritual Constitution of the Universe''" concludes that the light of the moon comes from the Sun. He writes that the Sun and Moon are "like fire and water" where the Sun "gives out light" and the Moon "reflects it".

Illumination

The intensity of moonlight varies greatly depending on the

lunar phase A lunar phase or Moon phase is the apparent shape of the Moon's directly sunlit portion as viewed from the Earth. Because the Moon is tidally locked with the Earth, the same hemisphere is always facing the Earth. In common usage, the four maj ...

, but even the full moon typically provides only about 0.05–0.1

lux The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). It is equal to one lumen per square metre. In photometry, this is used as a measure of the irradiance, as perceived by ...

illumination. When a full Moon around

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

(a "

supermoon A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth. The te ...

") is viewed around upper

culmination In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events are also known as meridian tran ...

from the

tropics The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

, the

illuminance In photometry (optics), photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate ...

can reach up to 0.32 lux. From Earth, the

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of the full Moon is only about that of the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. The color of moonlight, particularly around full moon, appears bluish to the

human eye The human eye is a sensory organ in the visual system that reacts to light, visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and Balance (ability), keeping balance. The eye can be considered as a living ...

compared to other, brighter light sources due to the

Purkinje effect The Purkinje effect or Purkinje phenomenon (; sometimes called the Purkinje shift, often pronounced ) is the tendency for the peak luminance sensitivity of the eye to shift toward the blue end of the color spectrum at low illumination (lighting), ...

. The blue or silver appearance of the light is an

illusion An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people. Illusions may ...

. The Moon's

Bond albedo The Bond albedo (also called spheric albedo, planetary albedo, and bolometric albedo), named after the American astronomer George Phillips Bond (1825–1865), who originally proposed it, is the fraction of power in the total electromagnetic radi ...

averages 0.136, meaning only 13.6% of incident sunlight is reflected from the lunar surface. Moonlight takes approximately 1.26 seconds to reach Earth's surface. Scattered in

Earth's atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...

, moonlight generally increases the

brightness Brightness is an attribute of visual perception in which a source appears to be radiating/reflecting light. In other words, brightness is the perception dictated by the luminance of a visual target. The perception is not linear to luminance, and ...

of the

night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include moonlig ...

, reducing contrast between dimmer stars and the background. For this reason, many

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

s usually avoid observing sessions around a full moon.

Gallery

File:ISS-44 Moon - Goodnight Earth.jpg, Moonlight onto Earth's cloud cover from space File:Sunrise over the VLT.jpg, Moonlight shines on the

Very Large Telescope The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with ...

. File:Tonsvatnet, tåke og måne.JPG, Moonlight illuminates a lake and surroundings. File:Giftedtypist - red moon (by).jpg, During a

lunar eclipse A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, ...

, the Moon is colored red by indirect

, which

has scattered and

refracted In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenome ...

. File:Earthshine Moon.jpg,

Earthlight ''Earthlight'' is a science fiction novel by British writer Arthur C. Clarke, published in 1955. It is an expansion to novel length of a novella of the same name that he had published four years earlier. Overview ''Earthlight'' is a scie ...

(indirect sunlight reflected from Earth) illuminates the dim side of the Moon, while direct sunlight the bright side. File:High ISO with long exposure.jpg, With manual exposure settings, photographs taken in moonlight do not appear much different from those taken in

daylight Daylight is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected by Earth and terrestrial objects, like landforms and buildings. Sunlig ...

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 In folklore, a werewolf (), or occasionally lycanthrope (from Ancient Greek ), is an individual who can shapeshifting, shapeshift into a wolf, or especially in modern film, a Shapeshifting, therianthropic Hybrid beasts in folklore, hybrid wol ...

. The light of the Moon was thought to worsen the symptoms of lunatics, and to sleep in moonlight could make one blind, or mad.''A Dictionary of English Folklore'', Oxford University Press, 2000

Nyctalopia Nyctalopia (; ), also called night blindness, 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. " Moon blindness" is a name for equine recurrent uveitis. Moonlight is no longer thought of as the cause. In the 16th century,

moonmilk Moonmilk (sometimes called mondmilch, also known as bergmilch, montmilch, or cave milk) is a white, creamy substance found inside limestone, dolomite, and possibly other types of caves. It is a precipitate from limestone comprising aggregates o ...

, a soft white limestone precipitate found in caves, was thought to be caused by the rays of the Moon. Selenoplexia was a supposed medical condition caused by the rays of the moon.''Lippincott's Medical dictionary'' (Lippincott, 1906), p. 920.

Art

File:Joseph Vernet - Night - Seaport by Moonlight - WGA24731.jpg, ''Seaport by Moonlight'' (1771) by Claude Joseph Vernet Image:Joseph Wright of Derby - Dovedale by Moonlight - Google Art Project.jpg, '' Dovedale by Moonlight'' (1784) by

Joseph Wright of Derby Joseph Wright (3 September 1734 – 29 August 1797), styled Joseph Wright of Derby, was an English landscape and portrait painter. He has been acclaimed as "the first professional painter to express the spirit of the Industrial Revolution". Wr ...

File:Philippe-Jacques de Loutherbourg - A Philosopher in a Moonlit Churchyard.jpg, '' Visitor to a Moonlit Churchyard'' (1790) by

Philip James de Loutherbourg Philip James de Loutherbourg, RA (born Philippe Jacques de Loutherbourg; 31 October 174011 March 1812) was a French-born British painter who became known for his large naval works, his elaborate set designs for London theatres, and his invent ...

File:Ed. Manet. Clair de lune sur le port de Boulogne.jpg, '' The Port of Boulogne by Moonlight'' (1869) by

Édouard Manet Édouard Manet (, ; ; 23 January 1832 – 30 April 1883) was a French Modernism, modernist painter. He was one of the first 19th-century artists to paint modern life, as well as a pivotal figure in the transition from Realism (art movement), R ...

File:Van Gogh - Starry Night - Google Art Project.jpg, ''

The Starry Night ''The Starry Night'', often called simply ''Starry Night'', is an oil-on-canvas painting by the Dutch Post-Impressionist painter Vincent van Gogh. Painted in June 1889, it depicts the view from the east-facing window of his asylum room at Sain ...

'' (1889) by

Vincent van Gogh Vincent Willem van Gogh (; 30 March 185329 July 1890) was a Dutch Post-Impressionist painter who is among the most famous and influential figures in the history of Western art. In just over a decade, he created approximately 2,100 artworks ...

File:Stanisław_Witkiewicz_-_Wiatr_halny_1895.jpg, ''Halny'' (1895) by Stanisław Witkiewicz In 2008

Katie Paterson Katie Paterson (born 1981) is a Fife-based visual artist from Glasgow, Scotland, having previously lived and worked in Berlin whose artworks concern translation, distance, and scale. Paterson holds a BA from Edinburgh College of Art (2004) and a ...

produced an artwork titled ''Light bulb to Simulate Moonlight''. It consists of 289 lightbulbs coated to produce a similar spectrum to the light of the full Moon.

References

External links

Phases of the Moon
at

USNO The United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the ...

Strange Moonlight
a
Science@NASA

a

{{Parts of a day Lunar observation Light Light sources