spectrum

(spĕk'trəm)

1. Physics. The distribution of a characteristic of a physical system or phenomenon, especially:
   1. The distribution of energy emitted by a radiant source, as by an incandescent body, arranged in order of wavelengths.
   2. The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses.
2. A graphic or photographic representation of such a distribution.
3. 1. A range of values of a quantity or set of related quantities.
   2. A broad sequence or range of related qualities, ideas, or activities: the whole spectrum of 20th-century thought.

[Latin, appearance, from specere, to look at.]

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For more information on spectrum, visit Britannica.com.

The term spectrum is applied to any class of similar entities or properties strictly arrayed in order of increasing or decreasing magnitude. In general, a spectrum is a display or plot of intensity of radiation (particles, photons, or acoustic radiation) as a function of mass, momentum, wavelength, frequency, or some other related quantity. For example, a β-ray spectrum represents the distribution in energy or momentum of negative electrons emitted spontaneously by certain radioactive nuclides, and when radionuclides emit α-particles, they produce an α-particle spectrum of one or more characteristic energies. A mass spectrum is produced when charged particles (ionized atoms or molecules) are passed through a mass spectrograph in which electric and magnetic fields deflect the particles according to their charge-to-mass ratios. The distribution of sound-wave energy over a given range of frequencies is also called a spectrum. See also Mass spectroscope; Sound.

In the domain of electromagnetic radiation, a spectrum is a series of radiant energies arranged in order of wavelength or of frequency. The entire range of frequencies is subdivided into wide intervals in which the waves have some common characteristic of generation or detection, such as the radio-frequency spectrum, infrared spectrum, visible spectrum, ultraviolet spectrum, and x-ray spectrum.

Spectra are also classified according to their origin or mechanism of excitation, as emission, absorption, continuous, line, and band spectra. An emission spectrum is produced whenever the radiations from an excited light source are dispersed. An absorption spectrum is produced against a background of continuous radiation by interposing matter that reduces the intensity of radiation at certain wavelengths or spectral regions. The energies removed from the continuous spectrum by the interposed absorbing medium are precisely those that would be emitted by the medium if properly excited. A continuous spectrum contains an unbroken sequence of waves or frequencies over a long range. Line spectra are discontinuous spectra characteristic of excited atoms and ions, whereas band spectra are characteristic of molecular gases or chemical compounds. See also Atomic structure and spectra; Band spectrum; Electromagnetic radiation; Line spectrum; Molecular structure and spectra; Spectroscopy.

The range of electromagnetic radiation (electromagnetic waves) in our known universe, which includes visible light. The radio spectrum, which includes both licensed and unlicensed frequencies up to 300 GHz has been defined worldwide in three regions: Europe and Northern Asia (Region 1); North and South America (Region 2), and Southern Asia and Australia (Region 3). Some frequency bands are used for the same purpose in all three regions while others differ. See satellite bands and optical bands.

Higher Frequencies

Frequencies above 40 GHz have not been licensed, but are expected to be made available in the future as the technology is developed to transmit at these smaller wavelengths (higher frequencies). The spectrum can be viewed in meticulous detail from the Federal Communications Commission (FCC) and National Telecommunications and Information Administration (NTIA) by visiting www.fcc.gov/oet/spectrum and www.ntia.doc.gov/osmhome/osmhome.html. See electromagnetic radiation and wave.

Should Airwaves Be Licensed?

There is a great deal of controversy over the licensing of frequencies. In Kevin Werbach's very educational white paper, "Radio Revolution," the author says an artificial scarcity has been created because policy makers do not understand the technology. He states that many believe the traditional policy of dividing the airwaves into licensed bands now impedes progress because today's radio technologies allow for much more sharing of the spectrum than ever before. The old notion that radio waves interfere with and cancel each other is a false one. Waves just mix together and become more difficult to differentiate, but modern electronics can, in fact, separate them.

To obtain a copy of this insightful report written in 2003, as well as other related articles, visit Werbach's Web site at www.werbach.com. See smart radio.

Visible Light

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Range of radiant energy (light) wavelengths. Within the visible spectrum, various light wavelengths are perceived as colors ranging from red to blue, depending upon the length of the wave. White light is a combination of all visible colors mixed in equal proportions. This characteristic of light, which enables it to be combined, so that the resultant light is equal to the sum of its constituent wavelengths, is called additive color mixing. See also cold color; subtractive primaries; warm color.

The range of wavelengths characteristic of a specific type of radiation.

• Optics - spectrum: array of various wavelengths that compose light
• Celestial Phenomena and Points - spectrum: light emitted by star or other source, dispersed according to wavelength
• Painting Tools and Techniques - spectrum: series of colored bands arranged in order of respective wavelength from infrared to ultraviolet
• Order, Hierarchy, and Systems - spectrum: continuous sequence or range

This article deals with the general meaning of "spectrum" and the history of its use. For other meanings and specific uses, see Spectrum (disambiguation).

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 other than 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 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 1 Origins 2 Modern meaning in the physical sciences 3 See also 3.1 Physical science 3.2 Social and medical sciences 3.3 Mathematics 4 References

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. 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.

Modern meaning in the physical sciences

The spectrum of a uniform light source rendered into the sRGB color space.

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.

Mass spectrum of a peptide showing the isotopic distribution

The term spectrum was expanded to apply to other waves, such as sound waves that could also be measured as a function of frequency. The term now applies to any signal that can be measured or decomposed along a continuous variable such as energy in electron spectroscopy or mass to charge ratio in mass spectrometry. Spectrum is also used to refer to a graphical representation of the as a function of the dependent variable.

See also

Wikimedia Commons has media related to: Spectrum

Physical science

• Electromagnetic spectrum
  • Visible spectrum or optical spectrum, a subset of the electromagnetic spectrum
  • Emission spectrum observed in light
  • Absorption spectrum observed in light
• Energy spectrum of a collection of particles (particle physics)
• Frequency spectrum of a signal
• Mass spectrum chemical analysis of atoms and molecules
• Power spectrum of a signal
• Spectrogram
• Spectrometer

Social and medical sciences

• Antibiotic classification
• Economic spectrum
• Political spectrum of opinion
• Spectrum disorder, in psychiatry

Mathematics

• Spectrum (homotopy theory)
• Spectrum of a matrix, in linear algebra
• Spectrum of an operator, in functional analysis (a generalisation of the spectrum of a matrix)
• Spectrum of a ring, in commutative algebra
• Spectrum of a C*-algebra
• Spectrum of a theory, in mathematical logic
• Stone space of Boolean algebra

References

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

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - spektrum

Nederlands (Dutch)
spectrum

Français (French)
n. - (Phys) spectre, gamme

Deutsch (German)
n. - Spektrum

Ελληνική (Greek)
n. - (χρωματικό) φάσμα, μετείκασμα, (φυσ.) ηλιακό φάσμα, γκάμα

Italiano (Italian)
spettro

Português (Portuguese)
n. - espectro (m)

Русский (Russian)
спектр, диапазон, разнообразие, широкий диапазон, изображение, призрак, образ

Español (Spanish)
n. - gama, espectro

Svenska (Swedish)
n. - spektrum, skala

中文（简体）(Chinese (Simplified))
谱, 频谱, 光谱, 射频频谱

中文（繁體）(Chinese (Traditional))
n. - 譜, 頻譜, 光譜, 射頻頻譜

한국어 (Korean)
n. - 스펙트럼, 잔상, 분포 범위

日本語 (Japanese)
n. - スペクトル, 分光, 残像, 範囲, 周波数域

العربيه (Arabic)
‏(الاسم) الطيف ( الضوئي)‏

עברית (Hebrew)
n. - ‮תחזית, ספקטרום, צבעי הקשת, טווח כולל של דרגות מסווגות‬

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