- noun a range of different but related things or stages
- The distribution of energy from a body in terms of its frequency, in any part of the electromagnetic spectrum or the whole of it. Spectra in visible light were the first to be observed and are the most informative for most kinds of celestial objects. Spectra of astronomical objects are interpreted in the light of measurements made in Earthly laboratories. Their role in astronomy and astrophysics is fundamental because the spectrum of an object provides most of the information obtainable on most astronomical objects, with rare exceptions like the few stars with substantial proper motions. Normally, almost everything we can find out about the composition, distance, velocity and other characteristics of a celestial body is derived in some way from its spectrum.
- A distribution, display, plot, or other output which is based on an order of increasing or decreasing magnitude of a property, such as mass, energy, wavelength, or ionization potential. For example, a mass spectrum is a distribution, display, plot, or other visual output of the charge-to-mass ratios of ions within a given sample.
- A range of energies arranged in order of increasing or decreasing wavelengths or frequencies. For example, an absorption spectrum, an emission spectrum, or a sound spectrum. Also, a distribution, display, plot, or other output depicting such a range.
- A spectrum (1) or spectrum (2) based on a property of light. For example, the energy emitted by a light source as a function of wavelength. Also, a distribution, display, plot, or other output depicting such a range.
- A frequency band utilized for a given purpose or which identifies a given region. For example, the infrared, visible, ultraviolet, or radio spectrums.
- The range of frequencies of electromagnetic radiation. This encompasses frequencies from just above 0 Hz to beyond 1024 Hz, corresponding to wavelengths of over 108 meters, to less than 10-16 meters, respectively. These include, in order of ascending frequency: subsonic frequencies, audio frequencies, radio frequencies, infrared light, visible light, ultraviolet light, X-rays, gamma rays, and cosmic rays. These intervals have been arbitrarily established, may be labeled with alternate names associated with specific applications, and may have subdivisions. Also called electromagnetic spectrum.
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