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

Spectrum

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.

There are many specific meanings of spectrum:

Spectroscopy is the study of spectra.

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

• The Spectrum, now known as the Wachovia Spectrum, was the sports arena in Philadelphia where the Philadelphia Flyers Hockey team and the Philadelphia 76ers Basketball team played until the Wachovia Center was built; it is still located, used largely by the Philadelphia Phantoms and Philadelphia Soul, in the sports complex on Broad Street in Philadelphia.

In mathematics

• The frequency spectrum is the result of a Fourier-related transform of a mathematical function into the frequency domain.
• The spectrum of an operator has to do with the invertibility of an operator in function spaces.
• The spectrum of a matrix is basically the spectrum of an operator where the matrix is considered as operator. Precisely, it is the set of the matrix's eigenvalues.
• The spectrum of a ring is the set of prime ideals of a ring.
• A (strange) construction, similar to the frequency spectrum, is the cepstrum of the quefrency.
• Finding a spectrum is a method of cycles analysis.

In music

• See timbre. Spectra is one of the determinants of the timbre or quality of a sound. It is the relative strength of pitches called harmonics and partials (collectively overtones) at various frequencies usually above the fundamental frequency, which is the actual note named (eg. an A).

In physics

• The electromagnetic spectrum is the power spectrum of an electromagnetic signal. It can be measured by spectroscopy.
• The optical spectrum is the electromagnetic spectrum of visual light
• The power spectrum is the distribution of the energy of a function in the frequency domain, which is actually the same as the magnitude of the frequency spectrum. See spectroscopy, spectrum of gravity waves.

In pharmacology

• The spectrum of activity of an antibiotic evaluates how wide a range of infections can be treated.

In politics

• There is a political spectrum which is said to go from left to right.

In psychology

• There exists the concept of a bipolar spectrum.

In telecommunication

• The term spread spectrum is used for certain kinds of signal transmission.

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

• Spectrum is the name of the defence force of Earth in the science fiction television series Captain Scarlet.

• The ZX Spectrum was also the name of a 1980s personal computer see ZX Spectrum.

• IEEE Spectrum is a magazine edited by the Institute of Electrical and Electronics Engineers (IEEE Spectrum web site).

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