(addition of photons to a beam of EMR)
The term emission is used in the study of
radiative transfer and spectroscopy
to mean the addition of photons to a beam of
electromagnetic radiation (e.g., light), from changes in atoms, and from scattering.
It is the inverse of absorption, the removal of photons
to the beam. The concept is used widely in astrophysics,
for explaining and modeling stars, for dealing with the effects of the
Earth's atmosphere, for explaining and modeling gas clouds, etc.
Each type of absorption has an emission inverse, or if it is
scattering, is both absorption and emission, thus the classification
of absorption processes also is a possible classification of emission
Spontaneous emission is the emission of a photon by an atom
not from any immediate interaction, e.g., the emission of a photon
when an atom a lower level of atomic excitation,
e.g., when an electron moves to a lower orbit.
Stimulated emission is the emission of a photon by a similar atom,
but specifically when a photon of the same wavelength approaches.
This is the effect used by masers and lasers.
Emission also includes photons which enter the beam through
scattering, e.g., Thomson scattering or Compton scattering.
advection dominated accretion flow (ADAF)
active galactic nucleus (AGN)
alpha CO (αCO)
anomalous microwave emission (AME)
broad emission line region
cosmic microwave background (CMB)
Cygnus A (3C 405)
Dwingeloo Obscured Galaxy Survey (DOGS)
Dickel-Wendker-Bieritz Catalog (DWB)
emission line galaxy (ELG)
emission coefficient (j)
star formation feedback
GALEX Arecibo SDSS Survey (GASS)
Galactic All-sky Survey (GASS)
luminous infrared galaxy (LIRG)
Massive Cluster Survey (MACS)
Mars Exploration Rover (MER)
obscured fraction-luminosity relation
radiative transfer (RT)
radio galaxy (RG)
radiative transfer code (RT code)
equation of radiative transfer (RTE)
radiative transfer model (RTM)
star formation rate (SFR)
spectral index (α)
state of excitation
Tully-Fisher relation (TFR)