Astrophysics (index)

Spectral Index

(power by which an object's flux depends on frequency)

The Spectral Index of a source of Electromagnetic Radiation (EMR) is a scalar measure describing its spectrum, assuming the spectrum forms a Power Law. It is specifically the exponent of the Frequency that produces a term proportional to the Radiant Flux at the same frequency, i.e.,

S ∝ να
  • S - radiant Flux.
  • ν - frequency.
  • α - Spectral Index.

Confusingly, sometimes the term is used to mean the negative of this exponent, or equivalently, the analogous exponent of the Wavelength.

In cases where the radiant flux by frequency is not a power law, it can be said that the spectral index varies by frequency. The concept seems less useful in this case.


Referenced by:
Lambda-CDM model (ΛCDM)
USS Sources