An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 12948 Search : far
angle of incidence
  زاویه‌ی ِ فتاد   
zâviye-ye fotâd

Fr.: angle d'incidence   

The angle formed between a ray of light striking a surface and the normal to that surface at the point of incidence. Also called → incidence angle.

angle; → incidence.

angle of inclination
  زاویه‌ی ِ درکیل   
zâviye-ye darkil

Fr.: angle d'inclinaison   

1) General: The angle between one plane and another, or the angle formed by a reference axis and a given line.
2) Binary systems: The angle between the plane of the orbit and the → plane of the sky.
3) Rotating stars: The angle between the → equatorial plane and the → plane of the sky.

angle; → inclination.

angle of minimum deviation
  زاویه‌ی ِ کژرفت ِ کمینه   
zâviye-ye kažraft kaminé

Fr.: angle de déviation minimale   

The angle between the light entering and exiting the prism when the light passing through the prism is parallel to the prism's base. Angle of minimum deviation (D) is used to measure the → index of refraction (n) of the prism glass, because: n = sin [(A + D)/2]/sin (A/2), where A is the → prism angle.

angle; → minimum; → deviation.

angle of prism
  زاویه‌ی ِ منشور   
zâviye-ye manšur

Fr.: angle de prisme   

prism angle.

angle; → prism.

angle of reflection
  زاویه‌ی ِ بازتاب   
zâviye-ye bâztâb (#)

Fr.: angle de réflexion   

The angle between the reflected ray and the normal to the reflecting surface.

angle; → reflection.

angle of refraction
  زاویه‌ی ِ شکست   
zâviye-yé šekast (#)

Fr.: angle de réfraction   

The angle between the direction in which a ray is refracted and the normal to the refracting surface.

angle; → refraction.

Angstrom unit (Å)
  یکا‌ی ِ آنگستروم   
yekâ-ye Ângštrom

Fr.: unité d'Ångström   

Unit of length used to describe wavelengths and interatomic distances. 1 Å = 10-10 m.

Named after Anders Jonas Ångström, Swedish physicist and astronomer who founded the science of spectroscopy and discovered by studying the solar spectrum that there is hydrogen in the Sun's atmosphere; → unit.

angular
  زاویه‌ای   
zâviye-yi (#)

Fr.: angulaire   

Having, forming, or consisting of an → angle or angles.

From L. angularis "having corners or angles," from angulusangle.

Zâviye-yi, adj. from zâviyé, → angle.

angular acceleration
  شتاب ِ زاویه‌ای   
šetâb-e zâviye-yi

Fr.: accélération angulaire   

The rate of change of → angular velocity. It is equal to the → first derivative of the → angular velocity: α = dω/dt =d2θ/dt2 = at/r, where θ is the angle rotated, at is the linear tangential acceleration, and r is the radius of circular path.

angular; → acceleration.

angular diameter
  ترامون ِ زاویه‌ای، قطر ِ ~   
tarâmun-e zâviye-yi, qotr-e ~

Fr.: diamètre angulaire   

The apparent diameter of an object in angular measure.

angular; → diameter.

angular diameter distance
  اپست ِ زاویه‌ای   
apest-e zâviye-yi

Fr.: distance angulaire   

1) The ratio of an object's → linear size (l) to its → angular size (δθ, in → radians), that is DA = l/δθ. It is used to convert observed angular separations into proper separations at the source.

2) In cosmology, a distance defined as the ratio of an object's physical transverse size (l) to its angular size (δθ). It is used to convert angular separations in telescope images into proper separations at the source. The angular diameter distance is defined by: DA = l / δθ. Consider a light source of size l at r = r1 and t = t1 subtending an angle δθ at the origin (r = 0, t = t0). The proper distance between the two ends of the object is related to δθ by: δθ = l / [a(t1). r1], where a(t1) is the → scale factor at the present epoch. Therefore, DA = r1 / (1 + z). The angular diameter distance has the particularity that it does not increase infinitely with z→ ∞. It gets its maximum value at a → redshift of ~ 1 and then decreases for higher z. Therefore, more distant objects appear larger in angular size. This is explained by considering the size of the Universe when the light of the object was emitted. At that time the Universe was smaller and therefore the object occupied a larger fraction of the size of the Universe. In other words, objects appear larger because the entire Universe acts as a → gravitational lense.

angular; → diameter; → distance.

angular differential imaging (ADI)
  تصویرگری ِ دگرسانه‌ای ِ زاویه‌ای   
tasvigari-ye degarsâne-yi-ye zâviye-yi

Fr.: imagerie différentielle angulaire   

A high-contrast imaging technique that reduces minute temporal and spatial → seeing fluctuations and facilitates the detection of faint point sources, in close separation from their stars. It consists of the acquisition of a sequence of images with an → altazimuth mounting telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference → point spread function (PSF) is constructed from other appropriately selected images of the same sequence and subtracted to remove quasistatic PSF structure (Marois et al. 2006, ApJ 641, 556).

angular; → differential; → imaging.

angular dispersion
  پاشش ِ زاویه‌ای   
pâšeš-e zâvie-yi

Fr.: dispersion angulaire   

The rate of change of the angles of emergence θ of various wavelengths from a dispersing prism: dθ/dλ.

angular; → dispersion.

angular distance
  اپست ِ زاویه‌ای   
apest-e zâviye-yi

Fr.: distance angulaire   

Between two points A and B, the angle → subtended by lines drawn from an observing point O to A and B. Same as → angular separation.

angular; → distance.

angular frequency
  بسامد ِ زاویه‌ای   
basâmad-e zaviye-yi (#)

Fr.: fréquence angulaire   

The number of complete rotations per unit time, expressed in radian per second: ω = 2πν, where ν is the frequency (cycles per second).

angular; → frequency.

angular kinetic energy
  کاروژ ِ جنبشی ِ زاویه‌ای   
kâruž-e jonbeši-ye zâviye-yi

Fr.: énergie cinétique angulaier   

Same as → rotational energy.

angular; → kinetic; → energy.

angular momentum
  جنباک ِ زاویه‌ای   
jonbâk-e zâviye-yi

Fr.: moment angulaire, moment cinétique   

The product of → moment of inertia and → angular velocity; synonymous with moment of momentum about an axis. Angular momentum is a vector quantity; it is conserved in an isolated system.

angular; → momentum.

angular momentum catastrophe
  نگونزار ِ جنباک ِ زاویه‌ای   
negunzâr-e jonbâk-e zâviye-yi

Fr.: catastrophe du moment angulaire   

A problem encountered by the → cold dark matter model of galaxy formation. The model predicts too small systems lacking → angular momentum, in contrast to real, observed galaxies. → cusp problem; → missing dwarfs.

angular; → momentum; → catastrophe

angular momentum parameter
  پارامون ِ جنباک ِ زاویه‌ای   
pârâmun-e jonbâk-e zâviye-yi

Fr.: paramètre de moment angulaire   

The ratio J/M, where J is the → angular momentum of a → rotating black hole and M the mass of the black hole.

angular; → momentum; → parameter.

angular momentum problem
  پراسه‌ی ِ جنباک ِ زاویه‌ای   
parâse-ye jonbâk-e zâviye-yi

Fr.: problème de moment angulaire   

1) The fact that the Sun, which contains 99.9% of the mass of the → solar system, accounts for about 2% of the total → angular momentum of the solar system. The problem of outward → angular momentum transfer has been a main topic of interest for models attempting to explain the origin of the solar system.
2) More generally, in star formation studies, the question of the origin of the angular momentum of a star and the evolution of its distribution during the early history of a star. Consider a filamentary molecular cloud with a length of 10 pc and a radius of 0.2 pc, rotating about its long axis with a typical → angular velocity of Ω = 10-15 s-1. At a matter density of 20 cm-3, the cloud is about 1 → solar mass. The cloud collapses to form a star with radius of 6 x 1010 cm. The conservation of angular momentum (∝ ΩR2) requires that as the radius decreases from 0.2 pc to the stellar value, a factor of 107, the value of Ω must increase by 14 orders of magnitude to 10-1 s-1. The star's rotational velocity will be 20% the speed of light and the ratio of → centrifugal force to gravity at the equator will be about 104. Observational data, however, indicate that the youngest stars are in fact rotating quite slowly, with rotational velocities of 10% of the → break-up velocity. The angular momentum problem was first studied in the context of single stars forming in isolation (L. Mestel, 1965, Quart. J. R. Astron. Soc. 6, 161). For more information see, e.g., P. Bodenheimer, 1995, ARAA 33, 199; H. Zinnecker, 2004, RevMexAA 22, 77; R. B. Larson, 2010, Rep. Prog. Phys. 73, 014901, and references therein.

angular; → momentum; → problem.

<< < -es -iv -ti 21- A r abe abs abs acc acc acc act act ada adi adu aff age alc Alf ali all alp alt ama amp ana ang ang ann ano ant ant ape apo app aps arc Arg ari art ass ast ast ast atm ato att aur aut axi B r bac Bal Bar Bar Bay bec Ber Bet Bie bij bin bio bis bla bla blu blu bol Bor bou Bra bre bro Bug C-s cal Cam can car Car Cas cat cav cel cen cer Cha cha cha che cho cir cir cir cla clo clo clu coa coe coh col col col com com com com com com com com com con con con con con con con con con con con coo cor cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl dar dat daw de- Deb dec dec dee def deg del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis div dog Dop dou dra dua dus dwa dyn e-m ear ecl eco eff ein Ein elb ele ele ele ele Els emi emp ene enr env epi equ equ Eri est Euc eva evo exc exc exh exo exp exp ext ext f-n Fah fam fau fee Fer fib fil fin fir fix fle flu foc for for for fra fre fre fri fun fuz gal gal gal Gan gau GCN gen geo geo geo geo Gl glo gra gra gra gra gra gre gro GW1 hab hal han HAR haz hea hel hel Hen Her heu Hig Hil hol hop hor hou Hub Hum Hyd hyd hyd hyp hys ide ign ima imp imp inc inc ind ine inf inf inf inh INP ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jos Jun K2 Kep key kin Kol lag lam Lan lar las lav lea leg len lev lig lim lin lin lin lis lob loc log lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal mar mas mas mat max mea mea mee Men mer met met met mic mid Mil min Mir mix mod mod mol mon Mor mou mul muo mys nan nat nav nec Nep neu New New NGC nob nom non non nor not nuc nuc num Nyq obj obs obs oce oen OH omn opa ope opt opt opt orb ord Ori ort osc out ove oxy pal pan par Par par par pas pea Pen per per per per per pet pha pho pho pho phy pie Pit Pla pla pla pla ple Poi pol pol pol pol pop pos pos pow pre pre pre Pre pri pri pri pro pro pro pro pro pro Pro pub pul pyr qua qua qua qua Qui rad rad rad rad rad rad ram ran rat rea rec rec rec red ref ref reg reg rel rel rem rep res res res ret rev rho Rie rim riv rol Ros rot rul S a Sah san Sat sca Sch Sch scr sec sec sec sei sel sem sep set sha she sho sid sig sil sim sin sit sky slu sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spl spr sta sta sta sta sta ste ste sti sto str str sub sub sub sug sun sup sup sup sup sur syl syn sys tal Tay tel ten ter tex the the the thi tho thu tid tim tod top tot tra tra tra tra tri tri tro tru tur twi Typ UFO ult unc uni uni uni upg ura uti val var vec vel ver ver vig vir vis voc von wak Was wav wax wea wei whi Wie win WN6 wom X-r yel you zer zod > >>