# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 Alfvénic   آلفونیک   AlfvenikFr.: alfvénicité   Involving → Alfvén waves.→ Alfvénic; → -ity. Alfvénic fluctuation   افتاخیز ِ آلفونیک   oftâxiz-e AlfvenikFr.: fluctuation alfvénique   Large amplitude fluctuations in the → solar wind with properties resembling those of → Alfvén waves. A fluctuation is said to be Alfvénic if the following relationship between the velocity fluctuations (Δv) and magnetic field fluctuations (ΔB) is satisfied: Δv = ± ΔB/(μ0ρ)1/2. Also called Alfvénicity.→ Alfvénic; → fluctuation. Alfvénicity   آلفونیکی   AlfvenikiFr.: alfvénicité   → Alfvénic; → -ity. Alfven Mach number   عدد ِ ماخ ِ آلفونی   adad-e Mach-e AlfvéniFr.: nombre de Mach alfvénique   The ratio of the flow velocity to the → Alfvén speed in a medium.→ Alfvén wave; → number. Alfven point   نقطه‌ی ِ آلفون   noqte-ye AlfvénFr.: point d'Alfvén   In magnetized disk models, the point where the → poloidal velocity equals the → Alfven speed. Within this point, the magnetic energy density dominates, and the gas is forced to flow along the field lines. Well beyond this point, the kinetic energy acquired by the flowing gas prevails and the field is forced to follow the flow.→ Alfven wave; → point. Alfven radius   شعاع ِ آلفون   šo'â'-e AlfvénFr.: rayon d'Alfvén   1) In theories of magnetized → accretion disks, the distance from a non-rotating star where the → free fall of a spherical accretion flow is stopped, which occurs where the → ram pressure of the infalling matter equals the → magnetic pressure of the star. 2) More generally, the distance from an accreting or wind-blowing star where the → Alfvén Mach number of the flow (→ inflow or → outflow) is unity.→ Alfvén wave; → radius. Alfven speed   تندا‌ی ِ آلفون   tondâ-ye AlfvénFr.: vitesse d'Alfvén   The speed at which → Alfven waves are propagated along the magnetic field. It is a characteristic velocity at which perturbations of the lines of force travel. Alfvén speed is given by: vA = B/(μ0.ρ)1/2, where B is the → magnetic field strength, μ0 is the → magnetic permeability, and ρ is the density of the plasma. Alfvén speed plays a role analogous to the sound speed in non-magnetized fluid dynamics. Same as Alfvén velocity.→ Alfvén wave; → speed. Alfven surface   رویه‌ی ِ آلفون   ruye-ye AlfvénFr.: surface d'Alfvén   In a magnetized wind, the geometric loci of the points where the magnetic pressure equals the flow pressure. See also → Alfven point.→ Alfven wave; → surface. Alfven velocity   تندای ِ آلفون   tondâ-ye AlfvénFr.: vitesse d'Alfvén   same as → Alfven speed.→ Alfven wave; → velocity. Alfven wave   موج ِ آلفون   mowj-e AlfvénFr.: onde d'Alfvén   A → magnetohydrodynamic wave in a → magnetized plasma, arising as a result of restoring forces associated with the magnetic field. It is a → transverse wave which propagates in the direction of the magnetic field. Also called magnetohydrodynamic wave.Named after Hannes Alfvén (1908-1995), Swedish physicist, who developed the theory of → magnetohydrodynamics, and was awarded the Nobel Prize in Physics in 1970; → wave. Alfvenic   آلفونیک   AlfvenikFr.: alfvénicité   Involving → Alfvén waves.→ Alfvénic; → -ity. Alfvenic fluctuation   افتاخیز ِ آلفونیک   oftâxiz-e AlfvenikFr.: fluctuation alfvénique   Large amplitude fluctuations in the → solar wind with properties resembling those of → Alfvén waves. A fluctuation is said to be Alfvénic if the following relationship between the velocity fluctuations (Δv) and magnetic field fluctuations (ΔB) is satisfied: Δv = ± ΔB/(μ0ρ)1/2. Also called Alfvénicity. Alfvenicity   آلفونیکی   AlfvenikiFr.: alfvénicité   → Alfvénic; → -ity. alga   جلبک   jolbak (#)Fr.: algues   A single-celled or multicellular plant living in water or moist conditions, which contain chlorophyll and other pigments but has no true root, stem, or leaf. Algae include seaweeds and pond scum.From alga (singular), from L. alga "seaweed," of uncertain origin.Jolbak "alga." algebra   جبر   jabr (#)Fr.: Algèbre   The branch of mathematics which deals with the properties and relations of numbers using symbols (usually letters of the alphabet) to represent numbers or members of a specified set; the generalization and extension of arithmetic.Algebra, from M.L., from Ar. al jabr "reunion of broken bones," the first known use in the title of a book by the Persian mathematician and astronomer Abu Ja'far Mohammad ibn Musa al-Khwarizmi (c780-c850), who worked in Baghdad under the patronage of Caliph Al-Mamun. The full title of the tratise was Hisab al-Jabr w'al-Muqabala "Arithmetic of Completion and Balancing." → algorithm.Jabr, from Ar. al jabr, as above. algebraic   جبری   jabri (#)Fr.: algébrique   Relating to, involving, or according to the laws of algebra.→ algebra + → -ic. algebraic equation   هموگش ِ جبری   hamugeš-e jabriFr.: équation algébrique   An equation in the form of P = 0, where P is a → polynomial having a finite number of terms.→ algebra; → equation. algebraic function   کریای ِ جبری   karyâ-ye jabriFr.: fonction algébrique   A function expressed in terms of → polynomials and/or roots of polynomials. In other words, any function y = f(x) which satisfies an equation of the form P0(x)yn + P1(x)yn - 1 + ... + Pn(x) = 0, where P0(x), P1(x), ..., Pn(x) are polynomials in x.→ algebraic + → function. algebraic number   عدد ِ جبری   adad-e jabri (#)Fr.: nombre algébrique   A number, → real or → complex, that is a → root of a → non-zero polynomial equation whose → coefficients are all → rational. For example, the root x of the polynomial x2 - 2x + 1 = 0 is an algebraic number, because the polynomial is non-zero and the coefficients are rational numbers. The imaginary number i is algebraic, because it is the solution to x2 + 1 = 0.→ algebraic; → number. Algenib (γ Pegasi)   الجنب   Aljanb (#)Fr.: Algenib   A star which lies at the lower left-hand corner of → Pegasus. Its apparent magnitude varies between +2.80 and +2.86 over a period of 3.6 hours; → spectral type B2 IV.Algenib, from Ar. Aljanb al-Faras "the horse's flank," from al "the" + janb "flank" + faras "horse".