Spectrum has since been applied by analogy to topics outside optics. Thus, one might talk about the " spectrum of political opinion ", or the "spectrum of activity" of a drug, or the " autism spectrum ".
Getting on the 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. Nonscientific uses of the term spectrum are sometimes misleading.
For instance, a single left—right spectrum of political opinion does not capture the full range of people's political beliefs. Political scientists use a variety of biaxial and multiaxial systems to more accurately characterize political opinion. In most modern usages of spectrum there is a unifying theme between the extremes at either end. This was not always true in older usage. 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.
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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.
The prefix "spectro-" is used to form words relating to spectra. For example, a spectrometer is a device used to record spectra and spectroscopy is the use of a spectrometer for chemical analysis. In the 17th century, the word spectrum was introduced into optics by Isaac Newton , referring to the range of colors observed when white light was dispersed through a prism.
The term spectrum was expanded to apply to other waves , such as sound waves that could also be measured as a function of frequency, frequency spectrum and power spectrum of a signal.
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 signal as a function of the dependent variable. Electromagnetic spectrum refers to the full range of all frequencies of electromagnetic radiation  and also to the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object. Devices used to measure an electromagnetic spectrum are called spectrograph or spectrometer.
The visible spectrum is the part of the electromagnetic spectrum that can be seen by the human eye. The emission spectrum refers to the spectrum of radiation emitted by the compound due to electron transitions from a higher to a lower energy state. Light from many different sources contains various colors, each with its own brightness or intensity. A rainbow, or prism , sends these component colors in different directions, making them individually visible at different angles. A graph of the intensity plotted against the frequency showing the brightness of each color is the frequency spectrum of the light.
When all the visible frequencies are present equally, the perceived color of the light is white, and the spectrum is a flat line. Therefore, flat-line spectra in general are often referred to as white , whether they represent light or another type of wave phenomenon sound, for example, or vibration in a structure. In radio and telecommunications, the frequency spectrum can be shared among many different broadcasters.
When many broadcasters are present, the radio spectrum consists of the sum of all the individual channels, each carrying separate information, spread across a wide frequency spectrum.
Any particular radio receiver will detect a single function of amplitude voltage vs. The radio then uses a tuned circuit or tuner to select a single channel or frequency band and demodulate or decode the information from that broadcaster. If we made a graph of the strength of each channel vs. In astronomical spectroscopy , the strength, shape, and position of absorption and emission lines, as well as the overall spectral energy distribution of the continuum, reveal many properties of astronomical objects. Stellar classification is the categorisation of stars based on their characteristic electromagnetic spectra.
The spectral flux density is used to represent the spectrum of a light-source, such as a star. In radiometry and colorimetry or color science more generally , the spectral power distribution SPD of a light source is a measure of the power contributed by each frequency or color in a light source. The light spectrum is usually measured at points often 31 along the visible spectrum , in wavelength space instead of frequency space, which makes it not strictly a spectral density.
Some spectrophotometers can measure increments as fine as one to two nanometers. This can be helpful in analyzing the color characteristics of a particular source.
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A plot of ion abundance as a function of mass-to-charge ratio is called a mass spectrum. It can be produced by a mass spectrometer instrument.
Tandem mass spectrometry is used to determine molecular structure. In physics, the energy spectrum of a particle is the number of particles or intensity of a particle beam as a function of particle energy. Examples of techniques that produce an energy spectrum are alpha-particle spectroscopy , electron energy loss spectroscopy , and mass-analyzed ion-kinetic-energy spectrometry.
In physics, particularly in quantum mechanics , some differential operators have discrete spectra, with gaps between values. Common cases include the Hamiltonian and the angular momentum operator. In acoustics , a spectrogram is a visual representation of the frequency spectrum of sound as a function of time or another variable.
A source of sound can have many different frequencies mixed. A Musical tone 's timbre is characterized by its harmonic spectrum.
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