An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 417
free expansion phase
  فاز ِ گسترش ِ آزاد   
fâz-e gostareš-e âzâd

Fr.: phase d'expansion libre   

The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy  ESN is transformed into → kinetic energy of the ejected gas, the ejection velocity ve can be estimated from ESN by using ESN = (1/2) Meve2, which leads to ve = (2ESN / Me)(1/2), where Me is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, RSW, is defined by Me = (4π/3) RSW3ρ0, that is RSW = (3Me / 4πρ0)(1/3), where ρ0 is the initial density of the ISM. This radius is reached at the sweep-up time tSW = RSW/ve. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.

free; → expansion; → phase.

free fall
  افت ِ آزاد   
oft-e âzâd (#)

Fr.: chute libre   

The motion of a body under the influence of → gravity alone. See also → free-fall time.

free; → fall.

free flow
  تچان ِ آزاد   
tacân-e âzâd

Fr.: écoulement libre   

A fluid flow which develops when density differences within the fluid are the only driving forces. See also → forced flow.

free; → flow.

free occurrence
  رخداد ِ آزاد   
roxdâd-e âzâd

Fr.: occurrence libre   

An → occurrence of a → variable in a → wff, → iff it is not a → bound occurrence.

bound; → occurrence.

free oscillation
  نَوِش ِ آزاد   
naveš-e âzâd

Fr.: oscillation libre   

Oscillation of any system in stable equilibrium under the influence of internal forces only, or of a constant force originating outside the system, or of both.

free; → oscillation.

free radical
  رادیکال ِ آزاد   
râdikâl-e âzâd

Fr.: radical libre   

A chemical radical that can exist independently from atoms or group of atoms.

free; → radical.

free system
  راژمان ِ آزاد   
râžmân-e âzâd

Fr.: système libre   

A → mechanical system if all of its constituent particles or bodies can occupy arbitrary points in space or have arbitrary velocities. Otherwise, it is called a → constrained system.

free; → system.

free-bound emission
  گسیل ِ آزاد-بندیده   
gosil-e âzâd-bandidé

Fr.: émission libre-liée   

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

free; → bound; → emission.

free-fall time
  زمان ِ افت ِ آزاد   
zamân-e oft-e âzâd

Fr.: temps de chute libre   

The characteristic time it would take a body to collapse under its own → gravitational attraction, if no other forces existed to oppose the collapse. It is given by: tff = (3π/32 ρ0 G)1/2, where ρ0 denotes the initial density and G the → gravitational constant. Free-fall time is independent of the starting radius. Also known as → dynamical time scale.

free fall; → time.

free-floating objects
  بر‌آخت‌های ِ شناور   
barâxthâ-ye šenâvar

Fr.: objets flottants   

A population of → substellar objects which are not bound to stars; they are detected in young star clusters. Their masses, estimated from their fluxes, is several Jupiter masses, lower than those of → brown dwarfs. Their formation is not yet explained. Among the envisaged possibilities: 1) These objects form like stars, from protostellar core collapse and subsequent accretion; 2) they form as low-mass members of small groups, and are ejected from the group; 3) they form like planets within circumstellar disks of higher-mass objects, but are ejected either due to internal dynamics or external interactions.

free; floating, from M.E. float, from O.E. flotian "to float" (cf. O.N. flota, M.Du. vloten); → object.

Barâxt, → object; šenâvar "that swims, floats," from šenâ "swimming;" Mid.Pers. šnâz "swim," šnâzidan "to swim;" Av. snā- "to wash, swim;" cf. Skt. snā- "to bathe, to wash;" L. nare, natare "to swim" (Fr. nage, nager, natation; Sp.nadar, natacion).

free-free emission
  گسیل ِ آزاد-آزاد   
gosil-e âzâd-âzâd (#)

Fr.: emission libre-libre   

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.

âzâdi (#)

Fr.: liberté   

The state of being free or at liberty.

From M.E. fredom, from O.E. freodom, from freo "free; noble, joyful," → free.

Âzâdi "freedom," noun from âzâd, → free.

Freeman's law
  قانون ِ فریمن   
qânun-e Freeman

Fr.: loi de Freeman   

A statistical finding about "normal" → spiral galaxies, whereby there is an upper limit on the mean central → surface brightness of disks. This value is constant for different spiral types, amounting to 21.65 ± 0.30 mag arcsec2 in the B band.

Named after K. C. Freeman (1970, Ap.J. 160, 811); → law.

  ۱) یخ بستن؛ ۲) رچیدن   
1) yax bastan; 2) rocidan

Fr.: geler   

1) To change from the liquid to the solid state by loss of heat; become hardened into ice.
2) Become hardened into a solid body. → coagulate.

Freeze, from O.E. freosan "turn to ice," from P.Gmc. *freusanan (cf. O.H.G. friosan, Ger. frieren "to freeze"), from *freus-, from PIE base *preus- "to freeze" also "to burn" (cf. Skt. pruśva- "hoar-frost, ice;" L. pruina "hoar-frost," Skt. pruśta- "burnt;" Albanian prus "burning coals;" L. pruna "a live coal").

1) Yax bastan, from yax "ice" + bastan "to bind, shut; to congeal, coagulate." The first component yax, from Av. aexa- "ice, frost," isav-, isu- "icy, chilly," cf. Sarikoli (Pamir dialect) īš "cold," P.Gmc. *isa- (O.N. iss, O.Fris. is, Du. ijs, Ger. Eis). The second component bastan, from Mid.Pers. bastan/vastan "to bind, shut;" Av./O.Pers. band- "to bind, fetter," banda- "band, tie" (cf. Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind;" Ger. binden; E. bind). 2) Rocidan, → coagulate.

  ۱) یخ‌بست؛ ۲) رچش   
1) yaxbast; 2) roceš

Fr.: gel, congélation   

1) The phase transition of a substance passing from the liquid to the solid state; the opposite of → fusion. In meteorology, the freezing of water.
2) Solidification.

Verbal noun from → freeze.

freezing point
  نقطه‌ی ِ یخ‌بست   
noqte-ye yaxbast

Fr.: point de congélation   

1) The temperature at which a liquid of specified composition changes into a solid under a specified pressure.
2) The temperature at which the liquid and solid phases of a substance of specified composition coexist in equilibrium.

freezing; → point.

French Republican Calendar
  گاهشمار ِ جمهوری ِ فرانسه   
gâhšomâr-e jomhuri-ye Farâncé

Fr.: Calendrier républicain, Calendrier révolutionnaire français   

A calendar composed by Fabre d'Eglantine and others during the French Revolution which divided the year into 12 months of 30 days each, with five odd days called → Sansculottides. The year started at → autumnal equinox and the months were: Vendémiaire (Vintage), Brumaire (Fog), Frimaire (Frost), Nivôse (Snow), Pluviôse (Rain), Ventôse (Wind), Germinal (Buds), Floréal (Flowers), Prairial (Meadows), Messidor (Harvest), Termidor (Heat), Fructidor (Fruits). The week consisted of 10 days, and was called a Décade; each 10th day of Décade (called Décadi) was a day of rest. The calendar was used by the French government for about 12 years, from late 1793 to 1805, when it was suppressed by Napoleon.

M.E. Frensh, French, O.E. Frencisc "of the Franks," from Frank; republican, from republic, from Fr. république, from L. respublica, from res publica "public interest, the state," from res "affair, matter, thing" + publica, feminine of publicus "public;" → calendar.

  بسامد، فرگی   
basâmad (#), feregi (#)

Fr.: fréquence   

The number of complete oscillations per unit time of a vibrating system. The reciprocal of the → period, T.

From L. frequentia "assembly, multitude, crowd."

Basâmad, from bas "many, much" (Mid.Pers. vas "many, much;" O.Pers. vasiy "at will, greatly, utterly;" Av. varəmi "I wish," vasô, vasə "at one's pleasure or will," from vas- "to will, desire, wish") + âmad past stem of âmadan "to occur, to come, to become" (Mid.Pers. âmatan; O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes;" Proto-Iranian *āgmatani; Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").
Feregi, from feré "much, more; increase; priority," farâ(vân) "abundant," Mid.Pers. frêh "more, much;" O.Pers. fra- "before, forth;" Av. frā, fərrā "forth, forward;" PIE base *pro-; cf. L. pro "on behalf of, in place of, before, for;" Gk. pro- "before, in front of."

frequency band
  باند ِ بسامد   
bând-e basâmad

Fr.: bande de fréquence   

A range of frequencies that is continuous between two specified limits, selected from a more extended range of frequencies.

frequency; → band.

frequency drift
  دلک ِ بسامد   
delek-e basâmad

Fr.: dérive de fréquence   

An undesired progressive change in an oscillator's frequency with time.

frequency; → drift.

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