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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 442
fingering instability
  ناپایداری ِ انگشتوار   
nâpâydâri-ye angoštvâr

Fr.: instabilité à traines   

A type of instability that often occurs in fluids which are thermally stably stratified, but have an inhomogeneous composition. A well-known example, found in upper layers of the Earth's oceans, is → salt fingers. Similar fingering instabilities can occur in any other thermally stably stratified solution, provided the concentration of the slower-diffusing solute increases with height. The saturated state of this instability, → fingering convection, takes the form of tightly-packed, vertically-elongated plumes of sinking dense fluid and rising light fluid, and significantly enhances the vertical transport of both heat and chemical composition. The fingering instability occurs in stars within radiation zones that have an unstable mean → molecular weight  → gradient (μ gradient). This situation is often found as a result of material accretion onto a star by anything from a single or multiple planets, to material from a dust-enriched or debris accretion disk, or material from a more evolved companion. It also naturally arises in the vicinity of the → hydrogen shell burning in → red giant branch (RGB) stars, and in thin element-rich layers near the surface of intermediate-mass stars. The fingering instability initially takes the form of thin tubes, hence the name "finger," within which the fluid moves vertically. The tubes rapidly break down, however, as a result of parasitic shear instabilities that develop inbetween them, and the fingering instability eventually saturates into a state of homogeneous fingering convection where the typical aspect ratio of the eddies is closer to one (P. Garaud et al., 2015, arXiv:1505.07759).

finger; → -ing; → instability.

fingers of God
  انگشتان ِ خدا   
angoštân-e Xodâ

Fr.: doigts de Dieu   

A → redshift space distortion which causes the dense central regions of → galaxy clusters to appear elongated along the → line of sight. This effect is attributed to random velocities in clusters of galaxies deviating from pure → Hubble flow. For an observer galaxies with peculiar velocity perpendicular to the line of sight do not change the redshift, which is given just by the normal Hubble expansion. On the contrary, galaxies with peculiar velocity along the line of sight appear with a different redshift, resulting from the Hubble expansion velocity plus the peculiar velocity. Since this affects only redshift and not position on the sky, the stretching occurs only radially, toward the observer. See also → Kaiser effect, → peculiar velocity.

finger; → God.

finite
  کرانمند   
karânmand (#)

Fr.: fini   

1) Math: The opposite of → infinite.
2) Physics: Either non-infinite or non-zero.

From L. finitus, p.p. of finire "to limit, set bounds, end."

Karânmand, from karân "boundary, side, end, coast" + -mand adjective suffix. Karân, variants karâné, kenâr, from Mid.Pers. karân, karânak, kenâr "edge, limit, boundary," Av. karana- "side, boundary, end."

finite population
  پرینش ِ کرانمند   
porineš-e karânmand

Fr.: population finie   

A → statistical population consisting of individuals or items which are finite in number.

finite; → population.

finite series
  سری ِ کرانمند   
seri-ye karânmand (#)

Fr.: série finie   

A sum a1 + a2 + a3 + · · · + aN, where the ai's are real numbers. In terms of Σ-notation, it is written as a1 + a2 + a3 + · · · + aN = Σ (n = 1 to N).  See also → infinite series.

finite; → series.

finite set
  هنگرد ِ کرانمند   
hangard-e karânmand

Fr.: ensemble fini   

A → set whose elements can be numbered from 1 to n, for some positive integer n.

finite; → set.

fire
  آتش، تش، آذر   
âtaš(#), taš (#), âzar (#)

Fr.: feu   

A state, process, or instance of combustion in which a substance combines with oxygen producing heat, light, and flame.

O..E. fyr, from P.Gmc. *fuir (cf. O.N. fürr, M.Du. vuur, Ger. Feuer), from PIE *paewr-; cf. Mod.Pers. Lori porpor "blazing charcoal," Gilaki bur, biur "smokeless red fire" (Lori perisk, periska "spark," Kurd. biriske "spark," Lârestâni pelita "spark"); Tokharian por, puwar "fire;" Gk. pyr "fire;" Hitt. pahhur "fire;" Skt. pū- "to cleanse."

Âtaš, variants âzar, taš, from Mid.Pers. âtaxš, âtur "fire;" Av. ātar-, āθr- "fire," singular nominative ātarš-; O.Pers. ātar- "fire;" Av. āθaurvan- "fire priest;" Skt. átharvan- "fire priest;" cf. L. ater "black" ("blackened by fire"); Arm. airem "burns;" Serb. vatra "fire;" PIE base *āter- "fire."

fireball
  تشگوی، آذرگوی   
tašguy (#), âzarguy (#)

Fr.: boule de feu   

A → meteor that is brighter than the brightest planets, i.e. with an apparent magnitude of -5 or greater. Fireballs are often followed by → meteorite falls. Also called → bolide.

From → fire + ball, from O.E., from O.N. bollr "ball," from P.Gmc. *balluz (cf. O.H.G. ballo, Ger. Ball), from PIE base *bhel- "to swell."

Tašguy, from taš "fire," variant of âtašfire + guy "ball, sphere," variants golulé, gullé, goruk, gulu, gudé (cf. Skt. guda- "ball, mouthful, lump, tumour," Pali gula- "ball," Gk. gloutos "rump," L. glomus "ball," globus "globe," Ger. Kugel, E. clot; PIE *gel- "to make into a ball").

first
  نخست، نخستین، یکم، آغاز   
naxost (#), naxostin (#), yekom (#), âqâz (#)

Fr.: premier   

Being before all others with respect to time, order, importance, etc., used as the ordinal number of one.

O.E. fyrst "foremost," superlative of fore, from P.Gmc. *furisto (cf. O.H.G. furist, O.N. fyrstr, Dan. første, M.Du. vorste "first," Ger. Fürst "prince"), superlative of *fur-/*for-, from PIE *pro- (cf. Av. pouruua- "first," fra- "forward, forth;" Skt. pūrva- "first," pra- "before, formerly," Gk. pro; L. pro; E. fore).

Naxost, from Mid.Pers. naxust "the first," Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx "beginning" + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost; naxostin, from naxost + suffix -in.
Yekom, from yek, → one, + -om suffix of ordinal numbers.
Âqâz "beginning," from Proto-Iranian *āgāza-, from prefix ā- + *gāz- "to take, receive," cf. Sogdian āγāz "beginning, start," pcγz "reception, taking."

first approximation
  نزدین ِ نخست   
nazdin-e naxost

Fr.: première approximation   

1) Generally, an expression to indicate that a comment or result is only approximate.
2) Math.: In calculus, limiting a differential equation to its → first derivative, for example: ex≅ 1 + x. Also called → linear approximation.

first; → approximation.

first collapse
  رمبش ِ نخست   
rombeš-e naxost

Fr.: premier effondrement   

An early phase in the process of star formation which begins when the mass of a → molecular cloud → clump exceeds the → Jeans mass. The collapse is initially → optically thin to the thermal emission from → dust grains, and the compressional heating rate is much smaller than the cooling rate by the → thermal radiation. The collapse proceeds → isothermally. The isothermal condition is broken when the central density reaches about 10-13 g cm-3 and a small region at the center of the cloud starts to become → opaque. The heat generated by the collapse in this region is no longer freely radiated away, and the compression becomes approximately → adiabatic. The central temperature and pressure then begin to rise rapidly, soon becoming sufficient to decelerate and stop the collapse at the center. There then arises a small central core, called the → first core, in which the material has stopped collapsing and is approaching → hydrostatic equilibrium. Outside this core, the material is still nearly isothermal and continues to fall inward almost in → free fall. Consequently a shock front arises at the boundary of the core, where the infalling material is suddenly stopped. The initial mass and radius of the core are about 1031 g and 6 x 1013 cm, respectively, and the central density and temperature are about 2 x 10-10 g cm-3 and 170 K, respectively. As the collapse proceeds, the core grows in mass due to the infall of the surrounding material; at the same time, however, the core radius decreases because of radiative energy losses from the outer layers of the core. The process leads to the → second collapse (R. B. Larson, 1969, MNRAS 145, 271).

first; → collapse.

first contact
  پرماس ِ نخست   
parmâs-e naxost

Fr.: premier contact   

1) The beginning of a → solar eclipse when the eastern part of the lunar limb touches the western limb of the Sun, marking the beginning of an eclipse.
2) For a → lunar eclipse, the moment when the eastern limb of the Moon is the first to enter the Earth's shadow.

first; → contact.

first core
  مغزه‌ی ِ نخست   
maqze-ye naxost

Fr.: premier cœur   

A first object in → hydrostatic equilibrium predicted to form during early dynamical contraction of a → molecular cloud → clump in the course of the → first collapse.

first; → core.

first degree equation
  هموگش ِ درجه‌ی ِ یکم   
hamugeš-e daraje-ye yekom

Fr.: équiation du premier degré   

A equation in which the highest → exponent of the → variable is 1. Same as → linear equation.

first; → degree; → equation.

first derivative
  واخنه‌ی ِ نخست   
vâxane-ye naxost

Fr.: dérivée première   

The simplest mathematical → differentiation of one quantity relative to another; df(x)/dx. It is the same as → derivative, contrasted with the → second derivative or the nth derivative.

first; → derivative.

first derivative test
  آزمون ِ واخنه‌ی ِ نخست   
âzmun-e vâxane-ye naxost

Fr.: teste de la dérivée première   

In → calculus, a method for determining whether an → inflection point is a → local minimum, → local maximum, or neither.

first; → derivative; → test.

first dredge-up
  برونکشید ِ نخست   
borunkašid-e naxost

Fr.: premier dragage   

The → dredge-up occurring after core hydrogen burning as the core contracts before helium burning ignites (on the ascending giant branch). The hydrogen envelope becomes convective and this convective zone penetrates deep into the core dredging up material that has been processed by the central nuclear reactions. As a result the abundances of helium and nitrogen are boosted.

first; → dredge-up.

first law of thermodynamics
  قانون ِ نخست ِ گرماتوانیک   
qânun-e naxost-e garâtavânik

Fr.: première loi de la thermodynamique   

The total energy of a → closed system is constant. This means that energy can be changed from one form to another, or transferred from one system to another, but it cannot be created or destroyed. A mathematical formulation of the first law is: δQ = δU + δW, where δQ is the heat transferred to the system, δU the change in internal energy (resulting in a rise or fall of temperature), and δW is the work done by the system.

first; → law; → thermodynamics.

first light
  نخستین فروغ، ~ نور   
naxostin foruq, ~ nur

Fr.: première lumière   

The first astronomical observation done with a major newly built telescope.

first; → light.

First Point of Aries
  نقطه‌ی ِ آغاز ِ برّه   
noqte-ye âqâz-e barré (#)

Fr.: premier point de Bélier   

One of the two points on the celestial sphere where the ecliptic and the celestial equator crossed one another at → vernal equinox several thousands years ago.

first; → point; → Aries.

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