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. A rainbow is an optical and meteorological phenomenon that causes a spectrum of Light to appear in the Sky when the Sun In Mathematics, the word continuum has at least two distinct meanings outlined in the sections below 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. A rainbow is an optical and meteorological phenomenon that causes a spectrum of Light to appear in the Sky when the Sun In Optics, a dispersive prism is a type of optical prism, normally having the shape of a geometrical triangular prism. Thus one might talk about the spectrum of political opinion, or the spectrum of activity of a drug, or the autism spectrum. A political spectrum (plural Spectra) is a way of modeling different political positions by placing them upon one or more geometric axes The autism spectrum, also called autism spectrum disorders (ASD or autism spectrum conditions (ASC with the word autistic sometimes replacing autism 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.

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.

Origins

In Latin spectrum means "image" or "apparition", including the meaning "spectre". Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. A spectre or specter is a (usually terrifying phantom, Apparition, or Ghost, or an unreal appearance 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. Spectral evidence was a form of evidence accepted in court during the Salem Witch Trials that was based upon dreams and visions. Not to be confused with Heresy. Hearsay is a legal term referring to the use of out of court statements as evidence It was used to convict a number of persons of witchcraft at Salem, Massachusetts in the late 17th century. Witchcraft, in various historical anthropological religious and mythological contexts is the use of certain kinds of Supernatural or magical powers Salem is a city in Essex County, Massachusetts, United States. As a means of recording the passage of Time, the 17th Century was that Century which lasted from 1601 - 1700 in the Gregorian calendar

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. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics As a means of recording the passage of Time, the 17th Century was that Century which lasted from 1601 - 1700 in the Gregorian calendar In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency In Optics, a prism is a transparent optical element with flat polished surfaces that refract Light. 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. 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 Frequency is a measure of the number of occurrences of a repeating event per unit Time. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. In Statistical signal processing and Physics, the spectral density, power spectral density ( PSD) or energy 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 wave is a disturbance that propagates through Space and Time, usually with transference of Energy. An acoustic wave is a weak compression wave (meaning a small pressure change that moves at the Speed of sound. A spectrum is a usually 2-dimensional plot, of a compound signal, depicting the components by another measure. In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it 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. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain 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

• Electromagnetic spectrum
• Spectrogram
• Spectrometer

References

External links

• Emission Spectrum Photos of Various Light Sources
• NIST Physical Reference Data - Atomic Spectroscopy Data