Moonlight (orMoonshine) is light from the surface of theMoon, consisting mostly of reflectedsunlight, and someearthlight.[1]
The ancient Greek philosopherAnaxagoras noted that "the sun provides the moon with its brightness".[2] Ancient Chinese polymathZhang Heng concluded that the light of the moon comes from the Sun. He writes in his treatise,The Spiritual Constitution of the Universe, that the Sun and Moon are "like fire and water", where the Sun "gives out light", and the Moon "reflects it".[3]
Nyctalopia was called "moonblink" and thought to be caused by sleeping in moonlight in the tropics as late as the 19th century,[4] but is actually caused by a deficiency inVitamin A. Moonlight was historically thought to causeequine recurrent uveitis, which was called "moon blindness".[citation needed]Moonmilk, a soft white limestone precipitate found in caves, was thought to be caused by the rays of the Moon.[5]Selenoplexia was a supposed medical condition caused by the rays of the moon.[6]
The color of moonlight appears bluish or silvery to thehuman eye compared to other, brighter light sources, however this is an illusion, due to thePurkinje effect.[citation needed] The intensity of moonlight varies greatly depending on thelunar phase, with thefull moon typically providing about 0.05–0.1 lux illumination.[7] When a full Moon atperigee (a "supermoon") is viewed around upperculmination from thetropics, theilluminance can reach up to 0.32 lux.[7] From Earth, theapparent magnitude of the full Moon is only about1⁄380,000 that of theSun.[citation needed] The Moon'sBond albedo averages 0.136,[8] meaning only 13.6% of incident sunlight is reflected from the lunar surface. Moonlight takes approximately 1.26 seconds to reach Earth's surface. Moonlight isscattered by particles in theatmosphere of Earth, which increases thebrightness of thenight sky, and decreasescontrast between dimmer stars and the background. For this reason, manyastronomers usually avoidobserving the sky around a full moon.[citation needed]
Alunar eclipse is anastronomical event that occurs when theMoon moves into theEarth's shadow, causing the moonlight to be darkened.[9] Such an alignment occurs during aneclipse season, approximately every six months, during thefull moon phase, when the Moon's orbital plane is closest tothe plane of the Earth's orbit.
When the Moon is totally eclipsed by the Earth (a "deep eclipse"),[10][11] it takes on a reddish color that is caused by the planet when it completely blocks directsunlight from reaching the Moon's surface, as the only light that isreflected from the lunar surface is what has beenrefracted by theEarth's atmosphere. This light appears reddish due to theRayleigh scattering of blue light, the same reason sunrises and sunsets are more orange than during the day.
Moonlight sometimes thought to have a harmful influence in folklore. For example, sleeping in the light of a full moon was believed to transform a person into awerewolf. The light of the Moon was thought to worsen the symptoms oflunatics, and to sleep in moonlight could make one blind, or mad.[12]
Katie Paterson produced a display atThe Guggenheim in 2008, entitledLight bulb to Simulate Moonlight, which consisted of 289 lightbulbs coated to produce a similar spectrum to the light of the full Moon.[13]
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