Shadow
- This article is about the optical phenomenon; for other meanings, see Shadow (disambiguation).
A shadow is a region of darkness where light is blocked. A shadow occupies all the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light.
Shadow is also an acoustical phenomenon caused by an object placed in front of a source of sound.
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Features
The closer to 90 degrees the angle between an elongated object and the direction of the light it blocks, the bigger its shadow. The smaller the angle between the direction of the light and the surface on which the shadow occurs, the longer the shadow is. If the object is close to the light source, the shadow is large. If the surface is curved there are further distortions.
For a non-point source of light, the shadow is divided into the umbra and penumbra. The wider the light source, the more blurred the shadow.
If there are multiple light sources there are multiple shadows, with overlapping parts darker, or a combination of colors. For a person or object touching the surface, like a person standing on the ground, or a pole in the ground, these converge at the point of touch.
Colored shadows
If white light is produced by separate colored light sources, the shadows are colored.
Illuminate a room with a red light, and the shadows are exclusively gray, or dark. Illuminate the shadows with a white light, and the shadows are green. Where both lights are blocked, or in other words where the shadows intersect, the shadows are gray. Away from the intersection, where the red light is blocked the shadows are green, and where the white light is blocked the shadows are red. In other words, light colors shadows or brightens them, according to the complementary color of the light blocked to cast the shadow. In the case of white and red lights, the complement of white is red; with white and green lights, the complement of white is green.
In the absence of multiple light sources, colored lights illuminate spaces where other lights are not blocked. In the above example, the red shadow cast by blocking white light is not a shadow with the white light off, but it is illuminated in red.
In the absence of white light, colored lights blocked by an opaque surface cast shadows in the colors complementary to the lights blocked. For green light, red shadows, and vice-versa; blue, orange; yellow, purple; intermediate light, intermediate shadows.
Faster than light
For objects moving at every-day speeds (much slower than the speed of light), the shadow cast by an object will move faster than the object which casts it. A cross-section of a shadow (a silhouette) is displaced by the motion of an object in front of a point source of light. The further the distance from the object blocking the light, the larger the silhouette and the greater the displacement by motion.
However, this simple relationship between speeds and distances becomes more complicated over vast distances for very fast moving objects due to the finite speed of light; the motion of an object may cut off the emission of light from a source to a surface, but the light that had already passed by the object will take some time before reaching the surface, and so there is some delay before the shadow on the surface reflects the updated position of the object. Thus while it is certainly possible to create shadows that move faster than light[1], this effect cannot be used to transmit information at superluminal speeds, because the motion of the shadow is being caused by the motion of the object in the past, not the present.
Other notes
A shadow cast by the Earth on the Moon is a lunar eclipse. Conversely, a shadow cast by the Moon on the Earth is a solar eclipse.
On satellite imagery and aerial 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.
A shadow shows, apart from distortion, the same image as the silhouette when looking at the object from the sun-side, hence the mirror image of the silhouette seen from the other side (see picture).
The term shadow is also used with regard to other things than light, for example rain: a rain shadow is a dry area, which, with respect to the prevailing wind direction, is beyond a mountain range; it is dry because air masses lose part of their water when they move over these mountains.
Furthermore, it is possible to see shadows by moonlight on clear evenings.
Fiction
- In Peter Pan the main character loses his shadow: it snaps off when he leaps out of the window, which is slammed closed behind him. It is put in a drawer and later sewed back on by Wendy.
- In the novel Starfish, by Peter Watts, Shadow is an "imaginary friend" of one of the rifters. Shadow likely represents one of many victims of that character's pathologies.
- In the MMORPG MapleStory, Hermits have the ability to make a copy of themselves with their shadow, and are also able to bind a monster with it.
- In many fantasy games, shadow is widely referred to as the source of dark arts and black magic. Shadows, mainly in this genre, are said to be the departed souls of people that have had their lives tragically cut short or did not receive acceptance in heaven or hell.
- In Roger Zelazny's novel Jack of Shadows, the main character has a unique ability to manipulate shadows magically.
- In the Chronicles of Amber series of novels (also by Zelazny), Shadow is a metaphysical substance in which all possible universes can exist, if a person who meets certain criteria desires to go to them.
- In Final Fantasy VI, Shadow is the name of a mysterious assassin (or ninja) who joins up with the protagonists at various locations and times during the game. Little is known about the character within the main course of the game, however much of his story-line is revealed when and if certain circumstances are met.
- In Final Fantasy Tactics Advance, Assassins can bind a target's shadow to the ground, paralyzing them in time and space.
- In Slayers and an episode of InuYasha, throwing a knife onto the ground in a person's shadow would paralyze them, aptly named "Shadow Bind".
- In The Lord of the Rings by J.R.R. Tolkien, Mordor is the land 'where shadows lie.'
- Victoria by Knut Hamsun and Hard-Boiled Wonderland and the End of the World by Haruki Murakami feature a character depriving people of their shadows when approaching the end of the world.
- In ninja fiction, ninjas are supposedly able to become "one with the shadows" or, "a living shadow." In the manga Naruto, a special shuriken is named "The Windmill of Shadows." Also in Naruto, Shikamaru Nara possesses the technique to control a person's body movements once his shadow touches theirs. He can also manipulate his shadow into several shapes. This is known as Kagemane no Jutsu (The Art of Me-and-My-Shadow). In the movie Ninja Scroll, Shijima, one of the eight devils of Kimon, is able to meld with and move around in the shadows. Also, in the game Samurai Warriors, Hanzo Hattori Can reach a level named the shadow.
- In DC Comics, both Obsidian and Shadow-Thief have abilities over shadow.
- In the Sonic the Hedgehog franchise, Shadow the Hedgehog is one of Sonic's main rivals.
- In American Gods, a novel by Neil Gaiman, Balder Moon (Shadow) is the main character and also thought to be the god Balder.
- In Kingdom Hearts the basic and most common heartless enemy are called Shadows.
- In Dungeons & Dragons, there is a class named "Shadowdancer" that supposedly draws on shadow powers to induce abnormal effects in combat.
- In many cartoons that are very loosely based in reality (such as Looney Tunes) or comedy movies with roughly equal disregard for reality (such as Dracula: Dead and Loving It), it is possible for shadows to act completely independently of the person who is supposed to be casting them. This often ranges from a person's shadow fighting with them (especially famous in the classic Peter Pan), or going the wrong way to shadow puppets running amok (usually a shadow puppet in the shape of a monster). It is also possible for people to make photorealistic shadow puppets (such as the Eiffel Tower or a horse galloping through a desert or jumping over recognizable obstacles) in these mediums.
- In the Bionicle universe, Makuta is master of shadows. He use a Kanohi mask called Kraahkan, to allows he the shadows powers. Others beings control Shadows in Bionicle, like Roodaka and the Dark Hunter Kraata-Kal.
- In The Seventh Tower book series, creatures from a spirit-world are bound to people and become free-willed shadows.
- In Magic: The Gathering, Shadow is a creature ability that results in the creature only being able to participate in combat with other creatures that also have Shadow.
- In Vampire: The Masquerade, the Lasombra are a species of vampire that can manipulate shadows and darkness in general.
- in tales of symphonia and the rest of the tales series, shadow is the summon spirit of darkness
- in Legend of Zelda, Shadow Link is a recurring enemy the real Link must overcome.
- in Tales of Symphonia, Shadow is the summon spirit of darkness and when summoned it prevents physical allignments for party members in a given area
- In the WoWRadio IRC Channel pointing at everyone.
Heraldry
In heraldry, when a charge is supposedly shown in shadow (the appearance is of the charge merely being outlined in a neutral tint rather than being of one or more tinctures different from the field on which it is placed), it is called umbrated. Supposedly only a limited number of specific charges can be so depicted.
See also
Categories
Optical phenomena