An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < alp eff See > >>

Number of Results: 77 Search : effect
alpha effect
  اسکر ِ آلفا   
oskar-e Alfâ

Fr.: effet α   

In the → solar dynamo model, the process whereby the → azimuthal magnetic field transforms into a → meridional magnetic field due to the interaction of → convection and → differential rotation. See also → omega effect.

alpha; → effect.

anomalous luminosity effect
  اسکر ِ تابندگی ِ ناسان   
oskar-e tâbandegi-ye nâsân

Fr.: effet luminosité anormale   

Discrepant luminosity classes derived for the same → Am star when different criteria are used. Lore specifically, a luminosity criterion may indicate a → giant star, wheras another criterion indicates a → supergiant.

anomalous; → luminosity; → effect.

anomalous Zeeman effect
  اُسکر ِ زیمن ِ ناسان   
oskar-e Zeeman-e nâsân

Fr.: effet Zeeman anormal   

The splitting of a spectral line into several components in the → Zeeman effect when the magnetic field is weak. The splitting is much more complex than in the normal effect. The number of components of the lines often considerably exceeds their number in the normal effect. Contrarily to the normal Zeeman effect, the anomalous effect cannot be explained by classical theory. The historically "anomalous" effect is accounted for by the inclusion of electron spin in the total angular moment. In fact the idea of electron spin was put forward (Uhlenbeck and Goudsmit, 1926) to explain the anomalous Zeeman effect.

anomalous; → Zeeman effect.

backwarming effect
  ا ُسکر ِ فروگرمی   
oskar-e forugarmi

Fr.: effet de rétro-réchauffement   

A sort of → greenhouse effect in → stellar atmospheres where the deeper layers heat up due to overlying → opacity. The presence of numerous → bound-bound opacities of → metals amplifies the → scattering of → photons, in particular their → backscattering, forcing the → temperature to increase in order to conserve the radiation flux and the transport of energy from the interior to the outer parts of the atmosphere.

back; → warming; → effect.

blanketing effect
  ا ُسکر ِ پتومندی   
oskar-e patumandi

Fr.: effet de couverture   

line blanketing.

Blazhko effect
  اسکر ِ بلاژکو   
oskar-e Blazhko

Fr.: effet Blazhko   

A long term, generally irregular modulation of → light curves of a large subclass of → RR Lyrae stars. Most of the modulations occur on the time scale of some 60 periods, although the range extends from some tens to some hundreds of periods. Since its discovery over a hundred years ago, a number of explanations have been proposed for this effect, but its nature is still a matter of investigation. The explanations include: closely spaced pulsation modes, a modal 1 : 2 resonance, an oblique rotator model, a non-radial modal interaction, convective cycles, and nonlinear resonant mode coupling between the 9th overtone and the fundamental mode (see, e.g., R. Buchler and Z. Kolláth 2011, astro-ph/1101.1502).

Named after Sergei N. Blazhko (1870-1956), a Russian astronomer who discovered the effect for the star EW Dra (1907, Astron. Nachr. 175, 325); → effect.

boundary effect
  اسکر ِ کران   
oskar-e karân

Fr.: effet de bords   

An effect that forbids or invalidate locally the use of an idealized model of a system in which one or several of its dimensions are supposed to be infinite.

boundary; → effect.

Casimir effect
  اُسکر ِ کازیمیر   
oskar-e Casimir

Fr.: effet Casimir   

A small attractive force that appears between two close parallel uncharged plates in a vacuum. It is due to quantum vacuum fluctuations of the electromagnetic field. According to the quantum theory, the vacuum contains → virtual particles which are in a continuous state of fluctuation. Because the distance between the plates is very small, not every possible wavelength can exist in the space between the two plates, quite in contrast to the surrounding vacuum. The energy density decreases as the plates are moved closer, creating a negative pressure which pulls the plates together. The first successfully measurement of the effect was by Steve Lamoreaux in 1997. A more recent experiment in 2002 used a polystyrene sphere 200 μm in diameter coated in gold or aluminium. This was brought to within 0.1 μm of a flat disk coated with the same metals. The resulting attraction between them was monitored by the deviation of a laser beam. The Casimir force was measured to within 1% of the expected theoretical value.

After the Dutch physicist Hendrik Casimir (1909-2000), who predicted the phenomenon in 1948; → effect.

champagne effect
  اسکر ِ شامپانی   
oskar-e šâmpâyn

Fr.: effet champagne   

Blowing out of → ionized gas from a → molecular cloud when the → ionization front of an → H II region created by an → embedded  → massive star arrives at the molecular cloud edge. The large → pressure gradient set up between the H II region and the → interstellar medium ejects the ionized material with velocities larger than 30 km/s, in a way comparable to champagne flowing out of a bottle.

From a hydrodynamical model first proposed by Guillermo Tenorio-Tagle (1979). Champagne, Fr., short for vin de Champagne "wine from Champagne," a historical region at northeast France, from L.L. campania "flat open country," from L. campus "field;" → effect.

Compton effect
  اسکرِ کامپتون   
oskar-e Compton

Fr.: effet Compton   

Increase in the wavelength (reduction in the energy) of an → X-ray or → gamma ray  → photon when it collides a → free → electron.

Compton; → effect.

Coriolis effect
  اسکر ِ کوریولیس   
oskar-e Koriolis

Fr.: effet Coriolis   

The apparent → deflection of a body in motion with respect to the Earth, as seen by an → observer on the Earth, caused by the → Earth's rotation. Thus, a projectile fired due north from any point on the northern hemisphere will land slightly east of its target (deflection to the right). This involves two factors: 1) the eastward velocity of Earth's surface decreases from the → equator to the → poles, and 2) when an object starts to move north or south without being firmly connected to the ground it maintains its initial eastward speed (conservation of → angular momentum). Hence, an object travelling away from the equator will be heading east faster than the ground and will seem to be forced east. On the other hand, a ball fired in the northern hemisphere toward the equator deflects to the west. As for the southern hemisphere, a ball fired southward will deflect East. The projectile is not subject to this effect only on the equator, when it is thrown in an east-west direction. The Coriolis effect is therefore greater at higher → latitudes and smaller near the equator. This effect is of paramount importance to the large-scale → atmospheric circulation, the development of storms, and the sea-breeze circulation. In low pressure systems, i.e. zones where air ascends, the air is less dense than its surroundings and this creates a center of low atmospheric pressure. Winds blow from areas of high pressure to areas of low pressure, and so the surface winds would tend to blow toward a low pressure center. But, because of the Coriolis effect, they are deflected. In the northern hemisphere they are deflected toward the right, and fail to arrive at the low pressure center, but instead circulate around it → counterclockwise. In the southern hemisphere the circulation around a low pressure center would be → clockwise. Regarding high pressure systems in the northern hemisphere, a general clockwise rotation is created around the center. Same as the → Coriolis force. See also → geostrophic wind, → geostrophic flow.

Named after Gaspard Gustave Coriolis (1792-1843), French engineer and mathematician who first described this effect; → effect.

diamond ring effect
  اسکر ِ انگشتر ِ الماس   
oskar-e angoštar-e almâs

Fr.: effet anneau de diamant   

An intense flash of light that happens a few seconds before and after totality during a solar eclipse. The effect is caused by the last rays of sunlight before totality (or the first rays of sunlight after totality) shining through valleys on the edge of the Moon.

diamond; → ring; → effect.

Oskar, → effect; angoštar "a ring worn on the finger," from angošt "finger," Mid.Pers. angušt "finger, toe," Av. angušta- "toe," from ank- "curved, crooked," cf. Skt. angustha- "thumb," ankah "hook, bent," Gk. angkon "elbow," angkura "anchor," L. angulum "corner" (E. angle), Lith. anka "loop," O.E. ancleo "ankle," O.H.G. ango "hook," PIE base *ang-/*ank- "to bend"; → diamond.

Doppler effect
  اسکر ِ دوپلر   
oskar-e Doppler

Fr.: effet Doppler   

Change in frequency of a wave (light, sound) due to the relative motion of source and receiver. Approaching objects have their wavelengths shortened. Receding objects have emitted wavelengths lengthened.

Doppler, after Christian Andreas Doppler (1803-1853), Austrian physicist who first described how the observed frequency of sound and light waves is affected by the relative motion of the source and the detector; → effect.

dynamo effect
  اسکر ِ دینامو   
oskar-e dinâmo

Fr.: effet dynamo   

The generation of magnetic fields by movements within a → plasma, such as the → convective cores and → convective envelopes of stars. The magnetic field is intensified by the motion of the plasma in much the same way as in a dynamo. The generated magnetic field is not static, but evolves over time.

dynamo; → effect.

  ا ُسکر   

Fr.: effet   

1) Something brought about by a → cause or agent; a result.
2) A scientific law, hypothesis, or phenomenon, such as the → Compton effect, → Coriolis effect, → Doppler effect, → diamond ring effect, → photoelectric effect, and so on.

From O.Fr. effect, from L. effectus "accomplishment, performance," from stem of efficere "to work out, accomplish," from → ex- "out" + facere "to do, to make," from PIE base *dhe- "to put, to do;" cf. Mod.Pers. dâdan "to give," Mid.Pers. dâdan "to give," O.Pers./Av. dā- "to give, grant, yield," dadāiti "he gives;" Skt. dadáti "he gives," Gk. didomi "I give," tithenai "to put, set, place;" L. dare "to give, offer;" Rus. delat "to do;" O.H.G. tuon, Ger. tun, O.E. don "to do."

Oskar, from os-, → ex-, + kar-, kardan "to do, make;" Mid.Pers. kardan; O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "he makes;" cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base kwer- "to do, to make."

  ا ُسکرمند   

Fr.: effectif   

Actually in operation or in force; concrete; real.

M.E., from L. effectivus "practical," from effect(us), p.p. of efficere, → effect + -ivus "-ive."

Oskarmand, from oskar, → effect + -mand possession suffix.

effective aperture
  دهانه‌ی ِ ا ُسکرمند   
dahâne-ye oskarmand

Fr.: ouverture effective   

Of an antenna, the ratio of the extracted power by the antenna to the power per unit area (power density) in the incident wave.

effective; → aperture.

effective Eddington parameter
  پارامون ِ ادینگتون ِ اسکرمند   
pârâmun-e Eddington-e oskarmand

Fr.: paramètre d'Eddington effectif   

The effective value of the → Eddington parameter in a non-homogeneous system (porous opacity).

effective; → Eddington limit; → parameter.

effective focal length
  درازا‌ی ِ کانونی ِ ا ُسکرمند   
derâzâ-ye kânuni-ye oskarmand

Fr.: longueur focale effective   

The focal length of an imaging system, which consists of several lenses or mirrors.

effective; → focal length.

effective gravity
  گرانی ِ اُسکرمند   
gerâni-ye oskarmand

Fr.: gravité effective   

In a → rotating star, the sum of the → gravity and the → centrifugal acceleration. The effective gravity is a function of the rotation velocity (Ω) and the → colatitude (θ). At the pole (θ = 0°) and the equator (θ = 90°) the effective gravity is radial. See also → total gravity.

effective; → gravity.

<< < alp eff See > >>