The shadow of a musician cast onto a brick wallPark fence shadow is distorted by an uneven snow surface.Shadows from cumulus clouds thick enough to block sunlight
Ashadow is a dark area on a surface wherelight from a light source is blocked by an object. In contrast,shade occupies the three-dimensional volume behind an object with light in front of it. Thecross section of a shadow is a two-dimensionalsilhouette, or a reverseprojection of the object blocking the light.
Apoint source of light casts only a simple shadow, called an "umbra". For a non-point or "extended" source of light, the shadow is divided into theumbra, penumbra, and antumbra. The wider the light source, the more blurred the shadow becomes. If two penumbras overlap, the shadows appear to attract and merge. This is known as theshadow blister effect.
The outlines of the shadow zones can be found by tracing the rays of light emitted by the outermost regions of the extended light source. The umbra region does not receive any direct light from any part of the light source and is the darkest. A viewer located in the umbra region cannot directly see any part of the light source.
By contrast, the penumbra is illuminated by some parts of the light source, giving it an intermediate level of light intensity. A viewer located in the penumbra region will see the light source, but it is partially blocked by the object casting the shadow.
If there is more than one light source, there will be several shadows, with the overlapping parts darker, and various combinations of brightnesses or even colors. The morediffuse the lighting is, the softer and more indistinct the shadow outlines become until they disappear. The lighting of an overcast sky produces few visible shadows.
The absence of diffusing atmospheric effects in thevacuum ofouter space produces shadows that are stark and sharply delineated by high-contrast boundaries between light and dark.
For a person or object touching the surface where the shadow is projected (e.g. a person standing on the ground, or a pole in the ground) the shadows converge at the point of contact.
A shadow shows, apart from distortion, the same image as the silhouette when looking at the object from the sun-side, hence themirror image of the silhouette seen from the other side.
The namesumbra, penumbra and antumbra are often used for the shadows cast byastronomical objects, though they are sometimes used to describe levels of darkness, such as in sunspots. An astronomical object casts human-visible shadows when itsapparent magnitude is equal or lower than -4.[2] The only astronomical objects able to project visible shadows onto Earth are theSun, theMoon, and in the right conditions,Venus orJupiter.[3][4]Night is caused by the hemisphere of a planetfacing its orbital star blocking its sunlight.
A shadow cast by the Earth onto the Moon is alunar eclipse. Conversely, a shadow cast by the Moon onto the Earth is asolar eclipse.[5]
The sun casts shadows that change dramatically through the day. The length of a shadow cast on the ground is proportional to thecotangent of the sun'selevation angle—its angleθ relative to the horizon. Near sunrise and sunset, whenθ = 0° andcot(θ) = ∞, shadows can be extremely long. If the sun passes directly overhead (only possible in locations between the Tropics of Cancer and Capricorn), thenθ = 90°,cot(θ) = 0, and shadows are cast directly underneath objects.[citation needed]
Such variations have long aided travellers during their travels, especially in barren regions such as theArabian Desert.[6]
The farther the distance from the object blocking the light to the surface of projection, the larger the silhouette (they are consideredproportional). Also, if the object is moving, the shadow cast by the object will project an image with dimensions (length) expanding proportionally faster than the object's own rate of movement. The increase of size and movement is also true if the distance between the object of interference and the light source are closer. Eventually, this speed may exceed the speed of light.;[7] however, this does not violate special relativity as shadows do not carry any information or momentum.[citation needed]
Although the edge of a shadow appears to "move" along a wall, in actuality the increase of a shadow's length is part of a new projection that propagates at the speed of light from the object of interference. Since there is no actual communication between points in a shadow (except for reflection or interference of light, at the speed of light), a shadow that projects over a surface of large distances (light years)cannot convey information between those distances with the shadow's edge.[8]
Visual artists are usually very aware of colored light emitted or reflected from several sources, which can generate complex multicolored shadows.Chiaroscuro,sfumato, andsilhouette are examples of artistic techniques which make deliberate use of shadow effects.[9]
During the daytime, a shadow cast by an opaque object illuminated by sunlight has a bluish tinge. This happens because ofRayleigh scattering, the same property that causes the sky to appear blue. The opaque object is able to block the light of the sun, but not the ambient light of the sky which is blue as the atmosphere molecules scatter blue light more effectively. As a result, the shadow appears bluish.[10]
A shadow occupies a three-dimensional volume of space, but this is usually not visible until it projects onto a reflective surface. A lightfog, mist, or dust cloud can reveal the 3D presence of volumetric patterns in light and shadow.
Fog shadows may look odd to viewers who are not used to seeing shadows in three dimensions. A thin fog is just dense enough to be illuminated by the light that passes through the gaps in a structure or in a tree. As a result, the path of an object's shadow through the fog becomes visible as a darkened volume. In a sense, these shadow lanes are the inverse ofcrepuscular rays caused by beams of light, they're caused by the shadows of solid objects.
Theatrical fog and strong beams of light are sometimes used by lighting designers and visual artists who seek to highlight three-dimensional aspects of their work.
Oftentimes shadows of chain-linked fences and other such objects become inverted (light and dark areas are swapped) as they get farther from the object. A chain-link fence shadow will start with light diamonds and shadow outlines when it is touching the fence, but it will gradually blur. Eventually, if the fence is tall enough, the light pattern will go to shadow diamonds and light outlines.
In photography, which is essentially recording patterns of light, shade, and color, "highlights" and "shadows" are the brightest and darkest parts, respectively, of a scene or image.Photographic exposure must be adjusted (unless special effects are wanted) to allow thefilm orsensor, which has limiteddynamic range, to record detail in the highlights without them being washed out, and in the shadows without their becoming undifferentiated black areas.
Onsatellite imagery andaerial photographs, taken vertically, tall buildings can be recognized as such by their long shadows (if the photographs are not taken in the tropics around noon), while these also show more of the shape of these buildings.
Shadow as a term is often used for any occlusion or blockage, not just those with respect to light. For example, arain shadow is a dry area, which with respect to the prevailingwind direction, is beyond amountain range; the elevated terrain impedes rainclouds from entering the dry zone. Anacoustic shadow occurs when a direct sound has been blocked or diverted around a given area.
Shadows often appear in mythical or cultural contexts. Sometimes in a malevolent light, other times not.An unattendedshade was thought by some cultures to be similar to that of a ghost. The name for the fear of shadows is "sciophobia" or "sciaphobia".[citation needed]
Inheraldry, when a charge is supposedly shown "in the shadow" (the appearance is of the charge merely being outlined in a neutral tint rather than being of one or moretinctures different from the field on which it is placed), it is technically described as "umbrated". Supposedly, only a limited number of specific charges can be so depicted.[citation needed]
Shadows are often linked with darkness and evil; in common folklore, like shadows who come to life, are often evil beings trying to control the people they reflect. The filmUpside-Down Magic features an antagonistic shadow spirit who possesses people.[citation needed]
Ancient Egyptians surmised that a shadow, which they calledšwt (shut), contains something of the person it represents because it is always present. Through this association, statues of people and deities were sometimes referred to as shadows.[citation needed]
InIslam, shadows are a sign of submission toGod. TheQuran emphasizes that everything in the heavens and the earth, including shadows, prostrates to the Almighty in awe and obedience: "Do they not see how everything that Allah has created casts its shadow, inclining to the right and to the left, prostrating to Allah while they are humble?" (Quran 16:48). Similarly, the Quran states, "And to Allah prostrates whoever is within the heavens and the earth, willingly or by compulsion, and their shadows [as well] in the mornings and the afternoons" (Quran 13:15). Shadows, in this context, are a testament to the divine order and unity of creation.[citation needed]
In a commentary to The Egyptian Book of the Dead (BD), Egyptologist Ogden Goelet, Jr. discusses the forms of the shadow: "In many BD papyri and tombs the deceased is depicted emerging from the tomb by day in shadow form, a thin, black, featureless silhouette of a person. The person in this form is, as we would put it, a mere shadow of his former existence, yet nonetheless still existing. Another form the shadow assumes in the BD, especially in connection with gods, is an ostrich-feather sun-shade, an object which would create a shadow."[11]
Scientists from theNational University of Singapore presented a shadow-effect energy generator (SEG), which consists of cells ofgold deposited on asilicon wafer attached on a plastic film. The generator has apower density of 0.14 μW cm−2 under indoor conditions (0.001 sun).[12]
^Goelet, Ogden Jr. (1994).The Egyptian Book of the dead: the Book of going forth by day: being the Papyrus of Ani (royal scribe of the divine offerings), written and illustrated circa 1250 B.C.E., by scribes and artists unknown, including the balance of chapters of the books of the dead known as the Theban recension, compiled from ancient texts, dating back to the roots of Egyptian civilization (1st ed.). Chronicle Books. p. 152.ISBN0811807673.
^Qian Zhang; et al. (2020). "Energy harvesting from shadow-effect". Energy & Environmental Science.doi:10.1039/D0EE00825G.
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