An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The release of → alpha particles at high velocity from an atom's nucleus as it undergoes radioactive transformation.

→ alpha; → emission.

The emission of electromagnetic radiation from the atmosphere due to thermal and → non-thermal processes. → Thermal emission comes mainly from → water vapor. Non-thermal processes result in emission lines oxygen (optical) and OH (near-IR). Atmospheric emission is a very significant source of noise in astronomical observations. See also → airglow, → aurora.

→ atmospheric; → emission.

The → electromagnetic radiation emitted in planetary atmospheres involving the → aurora phenomenon.

→ auroral; → emission.

Emission undergone → Comptonization.

→ Comptonize; → emission.

A continuous radiation produced by three processes: radiative recombination due to transition between electron free-free states, two-photon decays of metastable levels, and thermal bremsstrahlung.

→ continuum; → emission.

Thermal emission in infrared from interstellar → dust grains receiving photons. Dust grains absorb ultraviolet and visible light emitted by nearby stars and re-radiate in the infrared wavelengths. Since the infrared light is of lower energy than the ultraviolet/visible light, the difference goes into heating the dust grain. Typical temperatures for interstellar grains are tens of degrees Kelvin.

→ dust; → emission.

In an atom, a characteristic amount of energy radiated (as line emission) when an electron moves from an outer orbit to an inner orbit around the nucleus, corresponding to the lost energy of the electron.

From L. emissionem "a sending out," from emiss-, stem of emittere "send forth," from → ex- "out" + mittere "to send."

Gosil, variant gosi "sending away, dismission;" Mid.Pers. wisé "to despatch" (Parthian Mid.Pers. wsys- "to despatch;" Buddhist Mid.Pers. wsydy "to despatch;" Sogdian 'ns'yd- "to exhort"), from Proto-Iranian *vi-sid- "to despatch, send off," from prefix vi- "apart, away, out," + *sid- "to call."

In a spectrum, a combination of several closely spaced, often unresolved, → emission lines occurring across a limited range of wavelengths.

→ emission; → band.

Electromagnetic flux emitted by a source per unit volume per unit time.

→ emission; → coefficient.

Any emission mark in the spectrum of a celestial object resulting from line formation or of unknown origin.

→ emission; → feature.

A bright line in the electromagnetic spectrum of a radiating substance caused by emission at a particular wavelength.

→ emission; → line.

The product of the square of the electron density times the linear size of the emitting region (in parsecs).

→ emission; → measure.

An ionized nebula whose spectrum consists of → emission lines. → planetary nebula; → H II region.

→ emission; → nebula.

A spectrum consisting of emission lines, produced when the light does not undergo absorption between the source and the spectrograph.

→ emission; → spectrum.

A → forbidden line in → emission.

→ forbidden; → emission; → line.

The radiation emitted when a → free electron is captured by an → ion. See also: → free-free emission; → bound-free transition.

→ free; → bound; → emission.

→ Electromagnetic radiation produced in a → plasma by → free electrons scattering off → ions without being captured. The electrons are free before the interaction and remain free afterward.

→ free; → emission.

The emission of radiation from an atom when it is bombarded by photons. The induced radiation has the same wavelength and direction as the bombarding radiation. Same as → stimulated emission.

→ induced; → emission.

The portion of → electromagnetic radiation from → astrophysical objects in → infrared frequencies.

→ infrared; → emission.

Same as → LINER.

→ low; → ionization; → nuclear; → emission; → line; → region.