The Spectrum reference article from the English Wikipedia on 24-Jul-2004
(provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Spectrum

Videos show Africa through the eyes of children

A spectrum is a usually 2-dimensional plot, of a compound signal, depicting the components by another measure. Sometimes, it is used to refer 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.

The spectrogram is the result of calculating the frequency spectrum of windowed frames of the signal.

Spectroscopy is the study of spectra. (Spectra is the plural of spectrum.)

There are many specific meanings of spectrum:

Table of contents
1 In sports
2 In mathematics
3 In music
4 In physics
5 In pharmacology
6 In politics
7 In psychology
8 In telecommunication
9 History
10 Other meanings

In sports

In mathematics

In music

In physics

In pharmacology

In politics

In psychology

In telecommunication

History

Originally a spectrum was a phantom or apparition. Spectral evidence is hearsay concerning 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.

In the 17th century the term was introduced into optics, referring to what was observed when white light was dispersed through a prism. Soon the term referred to a plot of light intensity as a function of frequency or wavelength. Max Planck later realized that frequency represents electromagnetic energy:

where E is the energy of a photon, h is Planck's Constant, and ν is the frequency of the light.

Other meanings