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

The act of permitting. Authorization granted to do something.

verbal noun of → permit; → -tion.

The emission of electrons as a result of incident radiation in the → photoelectric effect. Also called → external photoelectric effect.

→ photo- + → emissive; → effect.

A → continuum emission with frequencies in the radio range of the electromagnetic spectrum.

→ radio; → continuum; → emission.

→ Electromagnetic radiation carried by → radio waves.

→ radio; → emission.

The emission of → secondary electrons from the surface of a material when an incident particle (often, charged particle such as electron or ion) impacts the material with sufficient energy.

→ secondary; → emission.

A manned or unmanned space flight outside the Earth's atmosphere.

→ space; mission, from L. missionem (nominative missio) "act of sending," from mittere "to send," of unknown origin.

Gosilân, from 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" + -ân nuance suffix; fazâyi adj. of fazâ, → space.

The emission of electromagnetic radiation from an atom or molecule that does not depend on the presence of external fields.

→ spontaneous; → emission.

The process by which an electron, which is already in an excited state (an upper energy level, in contrast to its lowest possible level or "ground state"), can "stimulate" a transition to a lower level, producing a second photon of the same energy. The quantum energy of the incoming photon should be equal to the energy difference between its present level and the lower level. This process forms the basis of both the → laser and → maser. Same as → induced emission.

Stimulated, p.p. of → stimulate; → emission.

An act or instance of submitting. The condition of having submitted. → submit

Verbal noun of → submit.

→ thermal radiation.

→ thermal; → emission.

Electrons gaining enough thermal energy to escape spontaneously from the cathode or dynodes and mimic photoelectrons.

thermion; → emission.

1) The act or process of transmitting. The fact of being transmitted.
2) The broadcasting of electromagnetic waves from one location to another, as from a transmitter to a receiver.

Verbal noun of → transmit.

The frequency range above the cutoff frequency in a waveguide or transmission line.

→ transmission; → band.

The ratio given by the → amplitude (or energy) of a transmitted wave divided by the amplitude (or energy) of the incident wave.

→ transmission; → coefficient.

A diffraction grating that has grooves ruled onto a transparent material so that a beam of light passed through the grating is partly split into spectral orders.

→ transmission; → grating.

A decrease in power in transmission from one point to another.

→ transmission; → loss.

An assembly of elements which are capable of functioning together to transmit power or signals.

→ transmission; → system.

The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.

→ two; → photon; → emission.

A member of a class of cntral stars of planetary nebula, → CSPN, which have weaker and narrower emission lines than → Wolf-Rayet-like CSPNe (Tylenda et al. 1993, A&AS 102, 595).

→ weak; → emission; → line.