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

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 process that transforms data into another format in such a way that only specific individual(s) can reverse the transformation. Encryption is for maintaining data confidentiality. See also → decryption and → encoding.

→ encrypt; → -tion.

Of a stellar → nuclear fusion, the equation describing the → energy generation rate as a function of → density and → temperature.

→ energy; → generation; → equation.

Of a stellar → nuclear fusion, the energy produced per unit mass per unit time, usually denoted ε (erg g^-1s^-1). The general form of the energy generation equation is: ε = ε₀ρ^λT^ν, where ε₀, ρ, and λ are constants over some efficiently restricted range of → temperature T, → density ρ, and → chemical composition. The temperature exponent ν is about 4, 15, and 40 for → proton-proton chain, → CNO cycle, and → triple alpha process, respectively.

→ energy; → generation; → rate.

A rare kind of → meteorite containing the → enstatite mineral. These meteorites are thought to comprise only about 2% of the chondrites that fall on Earth. Also called → E-type chondrite.

→ enstatite; → chondrite.

1) An aggregate of surrounding → circumstances, → conditions, or → influences in which a thing is situated or is developed.
2) Computers: The entire set of conditions under which one operates a → computer, as it relates to the hardware, operating platform, or operating system.
3) Ecology: The totality of circumstances surrounding an → organism or group of organisms. More specifically, the combination of external physical conditions that affect and influence the growth, development, and survival of organisms.

From environ + -ment; the first component from Fr. environs, plural of O.Fr. environ "compass, circuit," from environ (adv.) "around," from en- "in" + viron "circle, circuit," from virer "to turn."

Pargir, from par- "around, surrounding," variant pirâ-→ circum- + gir agent noun and present stem of gereftan "to take, seize; to make prisoner; to intercept" (Mid.Pers. griftan; Av./O.Pers. grab- "to take, seize;" cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving;" M.L.G. grabben "to grab," from P.Gmc. *grab; E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").
Zistbum, from zist "life, existence," → bio-, + bum "region, land, place," → eco-.

The length of a tropical second (1/31,556,925.97474 of the tropical year) on 1900 January 0.5 → ephemeris time.

→ ephemeris; → second.

In a → disk galaxy, the motion of a star about the orbital → guiding center when it is displaced radially. See also → epicyclic frequency, → epicyclic theory.

→ epicyclic; → oscillation.

→ reionization epoch.

→ epoch; → reionization.

The period during the → early Universe before the → recombination era when the photons were hot enough to ionize hydrogen. The density was so high that the interactions between → matter and → radiation were very numerous. Therefore, matter and photons were in constant contact and their → temperatures were the same. As a result, the radiation became → thermalized, i.e. the → electromagnetic spectrum of the radiation became that of a → blackbody, a process called → thermalization. Since the time of recombination the photons of → cosmic background radiation have been free to travel uninhibited by interactions with matter. Thus, their distribution of energy is a perfect → blackbody curve, as predicted by the → Big Bang theory and shown by several observations, such as → Cosmic Background Explorer (COBE), → Wilkinson Microwave Anisotropy Probe (WMAP), and → Planck Satellite.

→ epoch; → thermalization.

The act of making equal or uniform.
Electronics: The reduction of frequency or phase distortion by introducing networks which compensate for the particular type of distortion over the required frequency band.

Noun of equalize.

A statement asserting the equality of two numbers or two expressions. It consists of two parts, called sides or members of the equation, separated by the Same as → equality sign.

From L. æquation- "an equalizing," noun of → equate.

Verbal noun of hamugidan, → equate.

1) Any equation that describes the motion of objects, i.e., variation of velocity, distance covered, acceleration, etc., as a function of time; e.g., V = V₀ + at, S = Vt + (1/2)at².
2) For a fluid, a relation, in its most fundamental form, equating the rate of change of momentum of a selected portion of fluid and the sum of all forces acting on that portion of fluid.
3) In quantum mechanics, an equation that governs the time variation of the → state of the system. → Schrodinger equation. However, in the Heisenberg formulation of quantum mechanics the equation of motion does not involve the states, which in this case is time independent, but rather the → observables of the system.

→ equation; → motion.