Spectral energy distribution

A spectral energy distribution (SED) is a plot of brightness or flux density versus frequency or wavelength of light. It is used in many branches of astronomy to characterize astronomical sources. For example, in radio astronomy, an SED with a negative spectral index around −0.7 would indicate a synchrotron radiation source. In infrared astronomy, SEDs can be used to classify young stellar objects.

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. 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

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