Spectral energy distribution

A function describing how a source’s energy or flux varies with wavelength or frequency. Its shape records how the source emits or transmits radiation across the spectrum.

Electromagnetic spectrum: The full range of electromagnetic radiation, arranged by frequency or wavelength. A spectral energy distribution describes a source across a portion or all of this range.
Black-body radiation: Electromagnetic radiation emitted by an idealized body in thermal equilibrium. Its characteristic spectrum provides a baseline for interpreting thermal source distributions.
Stellar classification: The grouping of stars by observable properties, especially spectra and surface temperature. Stellar spectral shapes help assign stars to temperature-related classes.
Spectral energy distribution (frequency representation): A spectral energy distribution expressed per unit frequency rather than per unit wavelength. Changing the spectral variable changes the plotted density through a Jacobian factor.
Wavelength: The distance between successive corresponding points of a wave, such as crest to crest. Distributions often use wavelength as their horizontal variable.
Planck's law: A formula giving the spectral radiance of a black body as a function of temperature and wavelength or frequency. It predicts the form of a thermal spectral energy distribution.
Effective temperature: The temperature of a black body that would emit the same total flux as a given object. It compresses a star’s overall energy output into a single thermal comparison.
Bolometric luminosity: The total power emitted by an astronomical source across all wavelengths. It integrates the distribution rather than describing its variation across the spectrum.
Frequency: The number of wave cycles passing a point per unit time. Frequency is an alternative horizontal variable, inversely related to wavelength for light.
Wien's displacement law: The relation stating that a black body's peak wavelength is inversely proportional to its temperature. The peak location offers a compact clue to the temperature behind a thermal distribution.

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