spectrum

Dictionary: spec·trum   (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.]

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.

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.

For more information on spectrum, visit Britannica.com.

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

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.

Modern meaning in the physical sciences

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.

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.

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

• 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).

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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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