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Created page with 'File:lighterstill.jpgright|frame ==Etymology== [http://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD...'
[[File:lighterstill.jpg]][[File:Gamma-ray-burst.jpg|right|frame]]

==Etymology==
[http://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], from Anglo-French rai, from Latin radius rod, ray
*Date: [http://www.wikipedia.org/wiki/14th_Century 14th century]
==Definitions==
*1 a : any of the lines of [[light]] that [[appear]] to radiate from a bright object
:b : a beam of radiant [[energy]] (as light) of small cross section
:c (1) : a stream of [[material]] [[particles]] traveling in the same line (as in radioactive [[phenomena]]) (2) : a single [[particle]] of such a stream
*2 a : [[light]] cast by rays : radiance
:b : a [[moral]] or [[intellectual]] [[light]]
*3 : a thin line suggesting a ray: as a : any of a [[group]] of lines diverging from a common center
:b : half line
*4 a : one of the bony rods that extend and support the membrane in the fin of a fish
:b : one of the radiating divisions of the [[body]] of a radiate animal (as a starfish)
*5 a : a branch or flower stalk of an umbel
:b (1) : medullary ray (2) : vascular ray
:c : ray flower
*6 : [[particle]], trace <a ray of [[hope]]>
==Description==
In [[optics]], a '''ray''' is an [[idealized]] narrow beam of [[light]]. Rays are used to [[model]] the propagation of light through an optical [[system]], by dividing the real light field up into discrete rays that can be [[computationally]] propagated through the system by the [[techniques]] of ray tracing. This allows even very [[complex]] [[optical]] [[systems]] to be [[analyzed]] [[mathematically]] or [[simulated]] by computer. Ray tracing uses approximate solutions to [http://en.wikipedia.org/wiki/Maxwell%27s_equations Maxwell's equations] that are valid as long as the [http://en.wikipedia.org/wiki/Light_wave light waves] propagate through and around objects whose [[dimensions]] are much greater than the light's wavelength. Ray [[theory]] does not describe [[phenomena]] such as [[interference]] and [[diffraction]], which require wave theory (involving the [[phase]] of the [[wave]]).[http://en.wikipedia.org/wiki/Ray_(optics)]

[[Category: Physics]]

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