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Shadow - Wikipedia, the Free Encyclopedia Shadow - Wikipedia, the free encyclopedia Create account Log in Article Talk Read Edit View history Shadow From Wikipedia, the free encyclopedia Main page For other uses, see Shadow (disambiguation). Contents A shadow is an area where direct light from a light Featured content source cannot reach due to obstruction by an object. It Current events occupies all of the space behind an opaque object with Random article light in front of it. The cross section of a shadow is a Donate to Wikipedia two-dimensional silhouette, or reverse projection of the Interaction object blocking the light. The sun causes many objects to Help have shadows and at certain times of the day, when the About Wikipedia sun is at certain heights, the lengths of shadows change. Community portal An astronomical object casts human-visible shadows when Recent changes its apparent magnitude is equal or lower than −4.[1] Contact Wikipedia Currently the only astronomical objects able to produce Toolbox visible shadows on Earth are the sun, the moon and, in the right conditions, the planet Venus. Print/export Contents [hide] Languages 1 Variation with time 2 Non-point source 3 Shadow propagation speed Avañe'ẽ 4 Color of shadow on Earth Български 5 In photography Català 6 Fog shadows Česky Shadow cast by an old street lamp at 7 Other notes ChiShona sunset 8 Mythological connotations Dansk 9 Heraldry Deutsch 10 See also Ελληνικά 11 References Español 12 External links Esperanto Euskara Variation with time [edit] Français Shadow length when caused by the sun changes Galego dramatically throughout the day. The length of a shadow 한국어 cast on the ground is proportional to the cotangent of the sun's elevation angle—its angle θ relative to the horizon. Park grid on the snow surface Ido Near sunrise and sunset, when θ = 0° and cot(θ) is infinite, Bahasa Indonesia shadows can be extremely long. If the sun passes directly overhead, then θ = 90°, cot(θ)=0, and Italiano shadows are cast directly underneath objects. עברית Non-point source [edit] Latina http://en.wikipedia.org/wiki/Shadow[2013-03-07 09:22:23] Shadow - Wikipedia, the free encyclopedia Latviešu For a non-point source of light, the shadow is divided into Lietuvių the umbra and penumbra. The wider the light source, the Magyar more blurred the shadow. If two penumbras overlap, the shadows appear to attract and merge. This is known as Монгол the Shadow Blister Effect. Nederlands If there are multiple light sources there are multiple shadows, with overlapping parts darker, or a combination 日本語 of colors. For a person or object touching the surface, like Umbra, penumbra and antumbra Norsk bokmål a person standing on the ground, or a pole in the ground, Norsk nynorsk these converge at the point of touch. Polski Português Shadow propagation speed [edit] Română Runa Simi The farther the distance Русский from the object blocking Sicilianu the light to the surface of projection, the larger the silhouette (they are Simple English considered Slovenčina proportional). Also, if Српски / srpski the object is moving, Suomi Steam phase eruption of Castle the shadow cast by the Svenska Geyser in Yellowstone National Park cast a shadow on its own steam. object will project an Crepuscular rays are also seen. image with dimensions Türkçe (length) expanding Українська Shadow cast by vapour trail of proportionally faster passing aircraft Tiếng Việt than the object's own rate of movement. The increase of size Žemaitėška and movement is also true if the distance between the object 中文 of interference and the light source are closer. This, however, Edit links does not mean the shadow may move faster than light, even when projected at vast distances, such as light years. The loss of light, which projects the shadow, will move towards the surface of projection at light speed. The misconception is that the edge of a shadow "moves" along a wall, when in actuality the increase of a shadow's length is part of a new projection, which will propagate at the Fog shadow of the South Tower of speed of light from the object of interference. the Golden Gate Bridge 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 give information between those distances with the shadow's edge.[2] Color of shadow on Earth [edit] During the daytime, a shadow cast by an opaque object illuminated by sunlight has a bluish tinge. This happens Clouds and shadows over the because of Rayleigh scattering, the same property that causes Mediterranean 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 http://en.wikipedia.org/wiki/Shadow[2013-03-07 09:22:23] Shadow - Wikipedia, the free encyclopedia molecules scatter blue light more effectively. As a result, the shadow appears bluish.[3] In photography [edit] In photography, which is Reversed text in shadow essentially recording patterns of light, shade, and colour, "highlights" and "shadows" are the brightest and darkest parts of a Fog Shadow of Sutro scene or image. Photographic exposure must be adjusted (unless Tower special effects are wanted) to allow the film or sensor, which has limited dynamic range, to record detail in the highlights without them being washed out, and in the shadows without their becoming undifferentiated black areas. Fog shadows [edit] Fog shadows look odd since humans are not used to seeing shadows in three dimensions. The 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 shadow through the "fog" appears darkened. In a sense, these shadow lanes are similar to crepuscular rays, which are caused by cloud shadows, but here, they are caused by the shadows of solid objects. Other notes [edit] 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). Shadow as a term is often used for any occlusion, not just those with respect to light. For example, a rain shadow is a dry area, which, with respect to the prevailing wind direction, is beyond a mountain range; the range is "blocking" water from crossing the area. An acoustic shadow can be created by terrain as well that will leave spots that can't easily hear sounds from a distance. Sciophobia, or sciaphobia, is the fear of shadows. Mythological connotations [edit] Main article: Ghost An unattended shadow or shade was thought by some cultures to be similar to that of a ghost. It is also believed as an alternative construct that shadows are in fact a representation of God's presence around an object; like a halo. Early eastern beliefs also play to this theory. Heraldry [edit] 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 umbra-ted. Supposedly only a limited number of specific charges can http://en.wikipedia.org/wiki/Shadow[2013-03-07 09:22:23] Shadow - Wikipedia, the free encyclopedia be so depicted. Shadows can be colored by a colored transparent source of the shadow. See also [edit] Black drop effect Wikimedia Commons has media Convolution applications, for more physical and related to: Shadow mathematical discussion about shadows Gnomon Shade Shadow Cabinet Shadow mapping, in computer 3D graphics Shadow people Shadow play References [edit] 1. ^ NASA Science Question of the Week, April 7, 2006 2. ^ Is Faster-Than-Light Travel or Communication Possible? by Philip Gibbs 3. ^ Question Board -- Questions about Light External links [edit] http://www.schoolsobservatory.org.uk/astro/esm/shadows How sun casts shadows over day hours Categories: Optical phenomena Shading This page was last modified on 6 March 2013 at 15:19. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of Use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. Contact us Privacy policy About Wikipedia Disclaimers Mobile view http://en.wikipedia.org/wiki/Shadow[2013-03-07 09:22:23].
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