Astrophysics (Index)About

thermal emission

(thermal radiation)
(EMR due to a body's heat)

Thermal emission (or thermal radiation) is electromagnetic radiation (EMR) emitted by something because of its heat, such as from the activity at the molecular level creating photons. The well-known type of thermal emission, black-body radiation results when the source is in thermodynamic equilibrium, and often the terms thermal emission and thermal radiation presuming that case. Thermodynamic equilibrium and implies the source is at a defined, constant temperature, and if a gas, implies the particle velocity is described by the Maxwell-Boltzmann distribution, The Planck function describes the resulting spectrum (black-body spectrum), and the resulting EMR is termed Planckian.

Thermal emission from a source not in thermodynamic equilibrium diverges from the black-body spectrum (thus is non-Planckian, NP), but if it is close to equilibrium, the divergence may be small, and the black-body spectrum is often taken to be a good approximation. Kirchhoff's laws characterize the results of some situations. Thermal emission from an optically thin plasma can result in thermal bremsstrahlung, another case where the spectrum is non-Planckian.

Further reading:

Referenced by pages:
black-body radiation
brightness temperature (TB)
continuum emission
core collapse
infrared (IR)
Mars Exploration Rover (MER)
neutron star (NS)
protoplanetary disk (PPD)
star formation rate (SFR)
thermal bremsstrahlung
James Webb Space Telescope (JWST)