Difference between revisions of "Spectrum"

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==Origin==
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A '''spectrum''' (plural ''spectra'' or ''spectrums''[http://dictionary.reference.com/browse/spectrum Dictionary.com] is a condition that is not limited to a specific set of values but can vary infinitely within a [[continuum]]. The word saw its first scientific use within the field of [[optics]] to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by analogy to many fields. Thus one might talk about the ''spectrum of political opinion'', or the ''spectrum of activity'' of a drug, or the ''autism spectrum''. In these uses, values within a spectrum are not necessarily precisely defined numbers as in optics; exact values within the spectrum are not precisely quantifiable.  Such use implies a broad range of conditions or behaviors grouped together and studied under a single title for ease of discussion.
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New Latin, from [[Latin]], [[appearance]] — more at specter
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In [[Latin]] ''spectrum'' means "image" or "[[apparition]]", including the [[meaning]] "[[spectre]]". Spectral [[evidence]] is [[testimony]] about what was done by spectres of persons not present physically, or hearsay evidence about what [[ghosts]] or apparitions of [[Satan]] said. It was used to convict a number of persons of witchcraft at Salem, Massachusetts in the late 17th century. The word "spectrum" [Spektrum] was strictly used to designate a ghostly optical afterimage by [http://en.wikipedia.org/wiki/Goethe Goethe] in his ''[http://en.wikipedia.org/wiki/Theory_of_Colours_(book) Theory of Colors]'' and [http://en.wikipedia.org/wiki/Arthur_Schopenhauer Schopenhauer] in ''[http://en.wikipedia.org/wiki/On_Vision_and_Colors On Vision and Colors]''.
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*[http://en.wikipedia.org/wiki/17th_century 1671]
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==Definitions==
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*1a :  a [[continuum]] of [[color]] formed when a beam of white [[light]] is dispersed (as by passage through a prism) so that its component [[wavelengths]] are arranged in order
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:b :  any of various continua that resemble a color spectrum in consisting of an ordered arrangement by a particular characteristic (as [[frequency]] or [[energy]]): as (1) : [[electromagnetic]] spectrum (2) : [[radio]] spectrum (3) :  the range of frequencies of [[sound]] [[waves]] (4) :  mass spectrum
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:c :  the representation (as a plot) of a spectrum
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*2a :  a continuous [[sequence]] or range <a wide spectrum of interests> <opposite ends of the political spectrum>
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:b :  kinds of [[organisms]] associated with a particular situation (as an environment)
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:c :  a range of effectiveness against pathogenic organisms <an antibiotic with a broad spectrum>
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==Description==
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A '''spectrum''' (plural spectra or spectrums) is a condition that is not limited to a specific set of [[values]] but can vary infinitely within a [[continuum]]. The word was first used scientifically within the field of [[optics]] to describe the [[rainbow]] of [[colors]] in visible light when separated using a prism. As scientific understanding of light advanced, it came to apply to the entire [http://en.wikipedia.org/wiki/Electromagnetic_spectrum electromagnetic spectrum].
  
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In most modern usages of ''spectrum'' there is a unifying theme between extremes at either end.  Some older usages of the word did not have a unifying theme, but they led to modern ones through a sequence of events set out below. Modern usages in mathematics did evolve from a unifying theme, but this may be difficult to recognize.
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Spectrum has since been applied by [[analogy]] to topics outside of optics. Thus, one might talk about the spectrum of political [[opinion]], or the spectrum of activity of a [[drug]], or the [[autism]] spectrum. In these uses, values within a spectrum may not be associated with precisely quantifiable numbers or [[definitions]]. Such uses imply a broad range of conditions or [[behaviors]] grouped together and studied under a single title for ease of [[discussion]].
  
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==Origins==
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In most modern usages of spectrum there is a unifying theme between [[extremes]] at either end. Some older usages of the word did not have a unifying theme, but they led to [[modern]] ones. Modern usages in [[mathematics]] did evolve from a unifying theme, but this may be difficult to recognize.
  
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In [[Latin]] ''spectrum'' means "image" or "[[apparition]]", including the meaning "[[spectre]]". Spectral evidence is testimony about what was done by spectres of persons not present physically, or hearsay evidence about what ghosts or apparitions of Satan said. It was used to convict a number of persons of witchcraft at Salem, Massachusetts in the late 17th century.
 
  
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==Modern meaning in the physical sciences==
 
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[[Image:Light dispersion conceptual.gif|right|frame|<center>dispersion of [[light]]</center>]]
 
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In the 17th century the word ''spectrum'' was introduced into [[optics]], referring to the range of colors observed when white light was dispersed through a prism. Soon the term referred to a plot of light intensity or power as a function of [[frequency]] or [[wavelength]], also known as a [[spectral density]].
 
  
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The term ''spectrum'' was soon applied to other waves, such as sound waves, and now applies to any signal that can be decomposed into frequency components. A spectrum is a usually 2-dimensional plot, of a compound signal, depicting the components by another measure.  Sometimes, the word ''spectrum'' refers to the compound signal itself, such as the "spectrum of visible light", a reference to those electromagnetic waves which are visible to the [[human]] eye.  Looking at light through a prism separates visible light into its colors according to wavelength. It separates them according to its dispersion relation and a grating separates according to the grating equation and if massive particles are measured often their speed is measured. To get a spectrum, the measured function has to be transformed in their independent variable to frequencies and the dependent variable has to be reduced in regions, where the independent variable is stretched. For this imagine that the spectrum of pulse with a finite number of particles is measured on a film or a CCD. Assuming no particles are lost, any nonlinearity (compared to frequency) on the spectral separation concentrates particles at some points of the film. The same is true for taking a spectrum by scanning a monochromator with a fixed slit width. Violet at one end has the shortest wavelength and red at the other end has the longest wavelength of visible light.  The colors in order are violet, blue, green, yellow, orange, red.  As the wavelengths get bigger below the red visible light they become infrared, microwave, and radio.  As the wavelengths get smaller above violet light, they become ultra-violet, x-ray, and gamma ray.
 
  
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== See also ==
 
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* [http://en.wikipedia.org/wiki/Electromagnetic_spectrum Electromagnetic spectrum]
 
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* [http://en.wikipedia.org/wiki/Spectrogram Spectrogram]
 
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*[http://en.wikipedia.org/wiki/Spectrometer Spectrometer]
 
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*[http://en.wikipedia.org/wiki/Spectrometry Spectroscopy]
 
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==References==
 
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#Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004.
 
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== External links ==
 
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* [http://ioannis.virtualcomposer2000.com/spectroscope/amici.html#colorphotos Emission Spectrum Photos of Various Light Sources]
 
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* [http://physics.nist.gov/PhysRefData/contents-atomic.html NIST Physical Reference Data - Atomic Spectroscopy Data]
 
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[[Category: General Reference]]
 
 
[[Category: Physics]]
 
[[Category: Physics]]

Revision as of 16:07, 5 June 2014

Lighterstill.jpg

Spectre 2.jpg

Origin

New Latin, from Latin, appearance — more at specter In Latin spectrum means "image" or "apparition", including the meaning "spectre". Spectral evidence is testimony about what was done by spectres of persons not present physically, or hearsay evidence about what ghosts or apparitions of Satan said. It was used to convict a number of persons of witchcraft at Salem, Massachusetts in the late 17th century. The word "spectrum" [Spektrum] was strictly used to designate a ghostly optical afterimage by Goethe in his Theory of Colors and Schopenhauer in On Vision and Colors.

Definitions

  • 1a : a continuum of color formed when a beam of white light is dispersed (as by passage through a prism) so that its component wavelengths are arranged in order
b : any of various continua that resemble a color spectrum in consisting of an ordered arrangement by a particular characteristic (as frequency or energy): as (1) : electromagnetic spectrum (2) : radio spectrum (3) : the range of frequencies of sound waves (4) : mass spectrum
c : the representation (as a plot) of a spectrum
  • 2a : a continuous sequence or range <a wide spectrum of interests> <opposite ends of the political spectrum>
b : kinds of organisms associated with a particular situation (as an environment)
c : a range of effectiveness against pathogenic organisms <an antibiotic with a broad spectrum>

Description

A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word was first used scientifically within the field of optics to describe the rainbow of colors in visible light when separated using a prism. As scientific understanding of light advanced, it came to apply to the entire electromagnetic spectrum.

Spectrum has since been applied by analogy to topics outside of optics. Thus, one might talk about the spectrum of political opinion, or the spectrum of activity of a drug, or the autism spectrum. In these uses, values within a spectrum may not be associated with precisely quantifiable numbers or definitions. Such uses imply a broad range of conditions or behaviors grouped together and studied under a single title for ease of discussion.

In most modern usages of spectrum there is a unifying theme between extremes at either end. Some older usages of the word did not have a unifying theme, but they led to modern ones. Modern usages in mathematics did evolve from a unifying theme, but this may be difficult to recognize.

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