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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

   Homepage   
   


A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

<< < "no abe acc act aff ama ani ant aps ast atm aut bar bif Boh bou cal car Cen chi Cla col com com Com con con con con con con con con con con con con cor cor Cou cur dec def Den det dif dim dis dis dou E-t edi ele ell ene ero exa exp ext fer Fla fra FU Gam geo gra gra had har hig Hub Hyp imp ind inf ins int int ion iro ite Kep lar lep lin lon lun mag mas mer mig mol Moo mut neg new New non non non nuc obs on- opt Ori oxi par per per phl pho Pla ple pol pos pre Pro pro pub qua rad rad rec red reg rem res rev rot Sak Sco sec seg sha sim sol sou sph sta ste Str sub sup T a the Tho tra tre tum uni vel vis wav wor > >>

Number of Results: 3079 Search : on
accreting neutron star
  ستاره‌ی ِ نوترونی ِ فربالنده   
setâre-ye notroni-ye farbâlandé

Fr.: étoile à neutron accrétrice   

A → neutron star in a → binary system that accretes matter from the → campion star, either from the → stellar wind or from an → accretion disk that forms if the companion overflows its → Roche lobe. The → gravitational energy from the infalling matter provides at least part of the energy for the observed radiation and the accretion torques dominate the spin evolution. Despite these common properties, accreting → neutron stars display a wide variety of behaviors, depending on the neutron star → magnetic field strength, mass of the companion and properties of → accretion (A. K. Harding, 2013, Front. Phys. 8, 679).

accreting; → neutron; → star.

accretion
  فربال، فربالش   
farbâl, farbâleš

Fr.: accrétion   

1) The process by which an object increases its mass under the influence of its → gravitational attraction. Accretion plays a key role in a wide range of astrophysical phenomena. In particular stars result from the accretion of material by a → protostar from a surrounding → molecular cloud. The accumulation of mass on the protostar involves the formation of an → accretion disk. Theoretical and observational investigations of protostars and newborn stars indicate the important role of → magnetic fields in this process. They favor the magnetospheric accretion model for mass transfer from the circumstellar disk onto the newborn star. In this model, the stellar magnetosphere → truncates the disk at a few stellar radii. Gas from the disk accretes onto the star along the magnetic field lines and hits the stellar surface at approximately the → free fall velocity, causing a strong accretion shock. Various → emission lines, such as the hydrogen → Balmer series, He I 5876 Å, Brγ 2.17 μm, and so forth are formed in the infalling magnetospheric flow. Moreover, optical/ultraviolet excess continuum emission is produced in the → accretion shocks. The accretion is accompanied by mass ejection through collimated → bipolar jets.
2) Accumulation of dust and gas onto larger bodies by → coalescence under the influence of their mutual → gravitational attraction or as a result of chance collisions.
See also:
accretion column, → accretion disk, → accretion flow, → accretion rate, → accretion shock, → accretion time.

L. accretionem (nom. accretio, gen. accretionis) "a growing larger," from stem of accrescere, from ad- "to" + crescere "to grow".

Farbâl from prefix → far- which conveys "increase, abundance" + bâl, from bâlidan "to grow, to wax great," Mid.Pers. vâlitan, Av. varəd-, varədait- "to increase, augment, strengthen, cause to prosper," Skt. vrdh-, vardhati.

accretion column
  ستون ِ فربال   
sotun-e farbâl

Fr.: colonne d'accrétion   

The channel through which matter is accreted onto a body such as a → protostar, → white dwarf, → neutron star, or → black hole. The accreting body possesses magnetic fields strong enough to disrupt the → accretion flow and carry the material through column-shaped channels directly on to a small fraction of the stellar surface near the magnetic poles.

accretion; → column.

accretion disk
  گرده‌ی ِ فربال   
gerde-ye farbâl

Fr.: disque d'accrétion   

A rotating disk of gas and dust formed around a center of strong gravity that pulls material off a surrounding or near-by gaseous object. Accretion disks are associated with several astrophysical objects such as → binary stars, → protostars, → white dwarfs, → neutron stars, and → black holes. Accretion disk forms because the infalling gas does not directly crash the accreting object due to its too high → angular momentum. The individual particles go into a circular orbit around the accretor because the circular orbit has the lowest energy for a given angular momentum. A spread in angular momentum values will give a population of particles moving on different orbits, so that a rotating disk of matter forms around the object. The matter in the disk becomes very hot due to internal friction and → viscosity as well as the tug of the accreting object. Since this hot gas is being accelerated it radiates energy and loses angular momentum and falls onto the accretor. Theoretical and observational pieces of evidence point to the importance of → magnetic fields in the accretion process. According to current models, the stellar magnetosphere → truncates the disk at a few stellar radii. Gas from the disk accretes onto the star along the magnetic field lines and hits the stellar surface at approximately the → free fall velocity, causing a strong accretion shock. See also → flared disk, → self-shadowed disk, → protoplanetary disk, → alpha disk model.

accretion; → disk.

accretion flow
  تچان ِ فربال   
tacân-e farbâl

Fr.: flot d'accrétion   

1) Flow of matter during an accretion process.
2) In a → binary system, flow of matter from the losing-mass → companion toward the compact one. The flow can be from a → stellar wind or through the → inner Lagrangian point.
3) → cold accretion flow, → hot accretion flow.

accretion; → flow.

accretion rate
  نرخ ِ فربال   
nerx-e farbâl

Fr.: taux d'accrétion   

The amount of mass → accreted during unit time. The accretion rate for the → collapse of a singular → isothermal sphere is expressed by: dM/dt = 0.975 cs3/G, where cs is the isothermal → sound speed (Shu 1977, ApJ 214, 488). This relation can be written as: dM/dt = 4.36 x 10-6 (T / 20 K)3/2 in units of solar masses per year, where T is the temperature. Observed temperatures of 10-20 K in regions of → low-mass star formation imply accretion rates of about 10-6 to 10-5 solar masses per year. Accretion rates for → massive stars amount to values of 10-4 to 10-3 solar masses per year.

accretion; → rate.

accretion shock
  تش ِ فربال   
toš-e farbâl

Fr.: choc d'accrétion   

A → shock wave occurring at the surface of a compact object or dense region that is accreting matter with a → supersonic velocity from its environment. In the case of → young stellar objects the process is believed to take place by funneled streams in the form of → accretion columns that originate in the surrounding → accretion disk and flow along the → field lines of the → protostar → magnetosphere. The gas falls supersonically onto the surface of the central body and its impact produces strong shocks of a few million → kelvin, a phenomenon that is observable in → X-rays.

accretion; → shock.

accretion time
  زمان ِ فربال، دیرش ِ ~   
zamân-e farbâl, direš-e ~

Fr.: temps d'accrétion   

The time necessary for the → accretion of a definite amount of mass with a fixed → accretion rate.

accretion; → time.

accusation
  مارزش   
mârzeš

Fr.: accusation   

A charge or claim that someone has done something illegal or wrong; the action or process of accusing someone (OxfordDictionaries.com).

accuse; → -tion.

achondrite
  اکوندریت   
akondrit

Fr.: achondrite   

A class of → stony meteorites that lack → chondrules. They are made of rock that has crystallized from a molten state. Achondrites are relatively rare, accounting for about 8% of all meteorite falls.

Achondrite, from Gk. prefix a- (an- before stems beginning with a vowel or h) "not, without, lacking" + Gk. chondrite, from chondr-, from chondros "grain," + affix -ite.

acoustic wave equation
  هموگش ِ موج ِ صدایی   
hamugeš-e mowj-e sedâyi

Fr.: équation de l'onde acoustique   

A → differential equation that describes the time evolution of the → scalar potential of the field φ. It is expressed by: ∇2φ = (1/c2)∂2φ/∂t2, where c is → velocity of → longitudinal waves and ∇2 is the → Laplacian operator.

acoustic; → wave; → equation.

acronical
  شامگاهی   
šâmgâhi

Fr.: acronyque   

Relating to or occurring at sunset. → heliacal

Acronical, from Gk. akronukos, from akros "tip, end," cf. Av. aγra- "top, first," Skt. agra- "first, foremost, climax" + nuks, nuktos "night," → night.

Šâmgâhi, adj. of šâmgâh "evening," from šâm "evening, evening meal" + gâh "time." The first component, šâm, from Mid.Pers. šâm "evening meal, supper," from Av. xšāfnya- "evening meal," from Av. xšap-, xšapā-, xšapan-, xšafn- "night" (O.Pers. xšap- "night," Mid.Pers. šap, Mod.Pers. šab "night"); cf. Skt. ksap- "nigh, darkness;" Hittite ispant- "night." The second component gâh "time," Mid.Pers. gâh, gâs "time," O.Pers. gāθu-, Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come."

acronical rising
  بر‌آیش ِ شامگاهی   
barâyeš-e šâmgâhi

Fr.: lever acronyque   

The rising of a star in the sky at or just after sunset. → heliacal rising.

acronical; → rising.

acronical setting
  فروشد ِ شامگاهی   
forušod-e šâmgâhi

Fr.: coucher acronyque   

The setting of a star at nightfall. → heliacal setting.

acronical; → setting.

action
  ژیرش، کنش   
žireš, koneš (#)

Fr.: action   

1) The process or state of acting or of being active.
2) According to → Newton's third law of motion, an external force that is applied to a body and that is counteracted by an equal force in the opposite direction ( → reaction).
3) A quantity whose → dimension (ML2T-1) coincides with that of → angular momentum, the → impulse of a force, or → energy x → time. The action plays an important part in → analytical mechanics, → quantum mechanics, and in a number of other fields of physics. Initially introduced in analytical mechanics, the concept of action has become a basic ingredient of modern physics, due to the role it has played in the generalization of → variational principle.
4) A scalar quantity computed as a function of the path followed by a system during its evolution between an initial instant ti and a final instant tf. It is defined by the → integral of the → Lagrangian between the two instants:
S = ∫L dt
In the framework of the → field theory, the action is expressed by the integral of the → Lagrangian density over the corresponding space-time volume:
S = ∫Ld d4x.
In classical physics, the path actually followed by the system is the one for which S is stationary (→ least action problem).
5) → quantum of action.
6) Math.: The action is a → functional, a mathematical relationship which takes an entire path and produces a single number.

Action, from O.Fr. action, from L. actionem, from agere "to do," → act.

Žireš, verbal noun from žir stem of žiridan "to act;" → act. Koneš, noun from kardan "to do, to make," Mid.Pers. kardan, O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "makes," cf. Skt. kr- "to do, to make," krnoti "makes," karma "act, deed;" PIE base kwer- "to do, to make."

action at a distance
  ژیرش از دور   
žireš az dur

Fr.: action à distance   

The instantaneous action of a body on another body independently of the distance separating them. The description of → gravity by → Newton's law and → electrostatics by → Coulomb's law are examples of action at a distance. According to Newton, → gravitation acts directly and instantaneously between two objects. For example, if the Sun should suddenly break apart, the Earth's orbit would be affected instantaneously. However, action at a distance violates the → principle of relativistic causality. According to → general relativity, gravitational effects travel at the → speed of light. For modern physics there is no instantaneous action at a distance.

action; → distance.

action variable
  ورتنده‌ی ِ ژیرش   
vartande-ye žireš

Fr.: variable d'action   

The time integral associated with the evolution of a physical system in the phase space.

action; → variable.

activation
  ژیرانش   
žirâneš

Fr.: activation   

1) The process of inducing or creating a state of → activity.
2) The process of producing a → radioactive isotope by bombarding a → stable → nuclide with → nuclear particles (such as → protons, → neutrons, → alpha particles, heavy ions, etc.).

Verbal noun of → activate; → -tion.

activation energy
  کاروژ ِ ژیرانش   
kâruž-e žirâneš

Fr.: énergie d'activation   

Chemistry: The minimum amount of energy that is required to activate → atoms or → molecules to a condition in which they can undergo a → chemical reaction. Most reactions involving neutral molecules cannot take place at all until they have acquired the energy needed to stretch, bend, or otherwise distort one or more → bonds. In most cases, the activation energy is supplied by → thermal energy.

activation; → energy.

active region
  ناحیه‌ی ِ ژیرا   
nâhiye-ye žirâ

Fr.: région active   

An area of the Sun exhibiting → solar activity with the presence of → sunspots, → flares, → faculae, → prominences, and other phenomena associated with intense magnetic fields.

active; → region.

<< < "no abe acc act aff ama ani ant aps ast atm aut bar bif Boh bou cal car Cen chi Cla col com com Com con con con con con con con con con con con con cor cor Cou cur dec def Den det dif dim dis dis dou E-t edi ele ell ene ero exa exp ext fer Fla fra FU Gam geo gra gra had har hig Hub Hyp imp ind inf ins int int ion iro ite Kep lar lep lin lon lun mag mas mer mig mol Moo mut neg new New non non non nuc obs on- opt Ori oxi par per per phl pho Pla ple pol pos pre Pro pro pub qua rad rad rec red reg rem res rev rot Sak Sco sec seg sha sim sol sou sph sta ste Str sub sup T a the Tho tra tre tum uni vel vis wav wor > >>