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A spectral energy distribution (SED) is a plot of energy versus
frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
or
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of light (not to be confused with a 'spectrum' of
flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phe ...
density vs frequency or wavelength). It is used in many branches of astronomy to characterize astronomical sources. For example, in
radio astronomy Radio astronomy is a subfield of astronomy that studies Astronomical object, celestial objects using radio waves. It started in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observat ...
they are used to show the emission from
synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in some types ...
, free-free emission and other emission mechanisms. In
infrared astronomy Infrared astronomy is a sub-discipline of astronomy which specializes in the astronomical observation, observation and analysis of astronomical objects using infrared (IR) radiation. The wavelength of infrared light ranges from 0.75 to 300 microm ...
, SEDs can be used to classify young stellar objects.


Detector for spectral energy distribution

The count rates observed from a given astronomical radiation source have no simple relationship to the flux from that source, such as might be incident at the top of the
Earth's atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...
. This lack of a simple relationship is due in no small part to the complex properties of radiation detectors. These detector properties can be divided into *those that merely attenuate the beam, including *#residual atmosphere between source and detector, *#absorption in the detector window when present, *#quantum efficiency of the detecting medium, *those that redistribute the beam in detected energy, such as *#fluorescent photon escape phenomena, *#inherent energy resolution of the detector.


See also

*
Astronomical radio source An astronomical radio source is an object in outer space that emits strong radio waves. Radio emission comes from a wide variety of sources. Such objects are among the most extreme and energetic physical processes in the universe. History In 1932 ...
*
Astronomical X-ray sources Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays. Several types of astrophysical objects emit X-rays. They include galaxy clusters, black holes in active galactic nucleus, acti ...
* Background radiation *
Bremsstrahlung In particle physics, bremsstrahlung (; ; ) is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic ...
* Cosmic microwave background spectral distortions * Cyclotron radiation *
Electromagnetic radiation In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength ...
*
Synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in some types ...
*
Wavelength dispersive X-ray spectroscopy Wavelength-dispersive X-ray spectroscopy (WDXS or WDS) is a non-destructive analysis technique used to obtain elemental information about a range of materials by measuring characteristic x-rays within a small wavelength range. The technique gener ...


References


Further reading

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External links


The High Energy Astrophysics Science Archive Research Center (HEASARC) at NASAThe Science of Spectroscopy
Applied and interdisciplinary physics Observational astronomy Optical phenomena Radiation Scattering Spectroscopy {{spectroscopy-stub