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Encyclopedia > Spectrum
The spectrum in a rainbow
The spectrum in a rainbow

A spectrum (plural spectra or spectrums[1]) 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. The word spectrum (plural, spectra) has many uses: // Common nouns The Spectrum article explains why so many things are called by this name The spectrum of activity of a drug The political spectrum of opinion The economic spectrum The bipolar spectrum, in psychology The autistic spectrum, in psychology In the... For other uses, see Rainbow (disambiguation). ... In mathematics, the word continuum sometimes denotes the real line. ... For the book by Sir Isaac Newton, see Opticks. ... For other uses, see Rainbow (disambiguation). ... Diagram of a triangular prism, dispersing light Lamps as seen through a prism. ... Political parties Part of the Politics series Politics Portal This box:      A political spectrum is a way of visualizing different political positions. ... The autism spectrum, also called autism spectrum disorders (ASD) or autism spectrum conditions (ASC), with the word autistic sometimes replacing autism, is a spectrum of psychological conditions characterized by widespread abnormalities of social interactions and communication, as well as severely restricted interests and highly repetitive behavior. ...


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.

Contents

Origins

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. For other uses, see Latins and Latin (disambiguation). ... Generally, an apparition is act or instance of appearing. ... Spectre, taken from the Battle for Wesnoth computer game. ... One of the great injustices of the Salem Witchcraft Trials was the admission of spectral evidence. ... Hearsay may refer to: Hearsay in English Law and Hearsay in United States law, a legal principle concerning the admission of evidence through repetition of out-of-court statements HearSay, a British pop group Category: ... Witch redirects here. ... Nickname: Location in Essex County in Massachusetts Coordinates: , Country State County Essex Settled 1626 Incorporated 1626 A City 1836 Government  - Type Mayor-council city  - Mayor Kimberley Driscoll Area  - Total 18. ... (16th century - 17th century - 18th century - more centuries) As a means of recording the passage of time, the 17th century was that century which lasted from 1601-1700. ...


Modern meaning in the physical sciences

The spectrum of a star of spectral type K4III
The spectrum of a star of spectral type K4III

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. This article is about the astronomical object. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... (16th century - 17th century - 18th century - more centuries) As a means of recording the passage of time, the 17th century was that century which lasted from 1601-1700. ... For the book by Sir Isaac Newton, see Opticks. ... Color is an important part of the visual arts. ... Dispersion of a light beam in a prism. ... If a shaft of light entering a prism is sufficiently narrow, a spectrum results. ... In physics, intensity is a measure of the time-averaged energy flux. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time. ... For other uses, see Frequency (disambiguation). ... For other uses, see Wavelength (disambiguation). ... In applied mathematics and physics, the spectral density is a general concept applied to a signal which may have any physical dimensions or none at all. ...


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. A WAVES Photographer 3rd Class The WAVES were a World War II era division of the U.S. Navy that consisted entirely of women. ... This article is about compression waves. ... 2-dimensional renderings (ie. ... Visible light redirects here. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... Surface waves in water This article is about waves in the most general scientific sense. ... In psychology, visual perception is the ability to interpret visible light information reaching the eyes which is then made available for planning and action. ... This article is about modern humans. ... For other uses, see Eye (disambiguation). ...


See also

Wikimedia Commons has media related to:

Image File history File links Commons-logo. ... Although some radiations are marked as N for no in the diagram, some waves do in fact penetrate the atmosphere, although extremely minimally compared to the other radiations The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. ... It has been suggested that this article or section be merged with periodogram. ... Spectrometer A spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. ...

References

  1. ^ Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. (accessed: January 25, 2008).

External links


  Results from FactBites:
 
Visible spectrum - Wikipedia, the free encyclopedia (898 words)
The visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye.
There are no exact bounds to the visible spectrum; a typical human eye will respond to wavelengths from 400 to 700 nm, although some people may be able to perceive wavelengths from 380 to 780 nm.
Helium was first detected through an analysis of the spectrum of the Sun; chemical elements can be detected in astronomical objects by emission lines and absorption lines; the shifting of spectral lines can be used to measure the redshift or blueshift of distant or fast-moving objects.
Spectrum - Wikipedia, the free encyclopedia (456 words)
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.
Thus 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.
  More results at FactBites »

 
 

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