An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -sc Sag sam sat sca sca Sch sco sec sec sec sei sel sem sep sex Sha she sho sid sig sim sin Sir sky slo sno sod sol sol sol sol sou sou spa spe spe spe spe sph spi spo SS sta sta sta sta ste ste sto str str str sub sub suc sun sup sup sup sup sur swi syn Syr > >>

Number of Results: 1290
self-shadowed disk
  گرده‌ی ِ خود-پرده، دیسک ِ ~   
gerde-ye xod-pardé, disk-e ~

Fr.: disque auto-écranté   

A model of → accretion disk around a → pre-main sequence star or a → protostar in which the outer parts of the disk are geometrically flat, in contrast to a → flared disk. Inward of a certain radius (0.5-1 AU from the star) the dust in the disk evaporates. Because the dust is the main source of opacity and the gas in the disk is usually optically thin, the irradiation burns a hole in the disk. Moreover, the inner rim puffs up, similarly to the case of flared disks. The difference lies in the outer parts. The inner rim casts its shadow over the disk all the way out. Since the disk thickness is almost constant, no photons can reach the surface of the disk and the outer parts of the disk remain shadowed by the inner rim and the midplane temperatures decrease accordingly. This model explains the observed → spectral energy distribution of some pre-main sequence stars, such as HD 101412. It also accounts for the observed weak → far infraredexcess, weak or no → PAH emission, and weak or no [O I] emission.

self-; → shadow; → disk.

Gerdé, → disk; xod-, → self-; pardé, → screen.


Fr.: auto-écrantage   

The phenomenon whereby the → photodissociation transitions of a molecule in interstellar clouds become → optically thick, so that the molecule in question is "shielded" by other molecules against dissociating stellar → far-ultraviolet (FUV) photons. In the case of → molecular hydrogen (H2), when the → column density exceeds 1014 cm-2, the UV absorption bands become optically thick, and H2 undergoes self-shielding. More specifically, all of the photons that could lead to UV photodissociation are absorbed by H2 in the outer layers of the cloud, hence protecting the H2 within the cloud. Self-shielding occurs in → diffuse interstellar clouds exposed to the interstellar → radiation field or in → molecular clouds in proximity to sources of UV photons. Dust can also absorb UV photons, further limiting the photodissociation, but it dominates only when the local UV radiation field is unusually intense relative to the density of the cloud.

self-; → shield; → -ing.


Fr.: auto-similaire   

1) Of a geometric figure, having a structure analogous or identical to its overall structure. → fractal.
2) The quality of a variable entity in which the shape does not change with time, such as a → self-similar process.

self-; → similar.

self-similar process
  فراروند ِ خودهمانند   
farâravand-e xod-hamânad

Fr.: processus auto-similaire   

A process that is invariant in distribution under scaling of time. Schematically, images taken of such a process at different time scales will look similar.

self-; → similar; → process.


Fr.: auto-similarité   

The property of being → self-similar.

self-; → similarity.

Sellmeier's equation
  هموگش ِ زلمایر   
hamugeš-e Sellmeier

Fr.: équation de Sellmeier   

An empirical relation between the → refractive index of a medium and the wavelength of light passing through the medium: n2 - 1 = Σ (Aiλ2/(λ2 - λi2)), where n is the refractive index at wavelength λ, and Ai and λi are constants.

Named after Wolfgang Sellmeier who derived the equation in 1871; → equation.


Fr.: sémantique   

1) Of, pertaining to, or arising from the different meanings of words or other signs and symbols.
2) Of or pertaining to → semantics.

From Fr. sémantique, from Gk. semantikos "significant," from semainein "to show, signify, indicate by a sign," from sema "sign."

Cemârik, from cemâr, → meaning, + -ik, → -ic.


Fr.: sémantique   

The study of the → meaning of signs or symbols, as opposed to their formal relations (→ syntactics).

semantic; → -ics.

šosar (#)

Fr.: sperme, semence   

Biology: The male reproductive fluid, containing spermatozoa in suspension. → inseminate, → insemination; → fecundate, → fecundation.

M.E., from L. semen "seed;" akin to serere "to sow;" cf. O.C.S. seme, O.H.G. samo; E. sow.

From Mid.Pers. šusar "semen; liquid, fluid;" Av. xšudra- "semen; liquid, fluid;" related to Pers. šostan/šuy- "to → wash."

  نیم-، نیمه-   
nim- (#), nimé- (#)

Fr.: semi-, demi-   

A combining form meaning "half," freely prefixed to English words of any origin.

From L. semi- "half," from PIE *semi-; cf. Skt. sāmi "half," sāmi-krita- "half-done;" Gk. hemi- "half;" O.E. sam-; Goth. sami- "half."

Nim, nimé "half," from Mid.Pers. nêm, nêmag "half;" Av. naēma- "half;" cf. Skt. néma- "half."

semi-forbidden line
  خط ِ نیمه-بژکم   
xatt-e nime-bažkam

Fr.: raie semi-interdite   

A → spectral line for which the upper and lower → energy levels have different values of S, the total → spin angular momentum. These lines violate the quantum mechanical → selection rule under → LS coupling, ΔS = 0. For example, the Ca I λ6573 line results from transition between the upper → triplet state (3P1) with a total spin angular momentum S = 1 and the → ground state, a → singlet state (1S0, total spin angular momentum S = 0). A semi-forbidden line is marked by a right bracket following the atom name, i.e. Ca I], in the above-mentioned case. Same as → interconnection line and → intersystem line.

semi-; → forbidden; → line.

semi-forbidden transition
  گذرش ِ نیمه-بژکم   
gozareš-e nime-bažkam

Fr.: transition semi-interdite   

An → atomic transition whose probability is reduced by a factor of the order of 106 because of → selection rules. Same as → interconnection line.

semi-; → forbidden; → transition.

semi-major axis
  آسه‌ی ِ نیمه‌مهین   
âse-ye nimeh-mehin

Fr.: demi grand axe   

Half the length of the major axis of an ellipse; a standard element used to describe an elliptical orbit. see orbital elements

semi-; → major; → axis.

  نیم-هازا، نیمه-رسانا   
nim-hâzâ, nime-rasânâ

Fr.: semi-conducteur   

Any of various solid crystalline substances, such as germanium or silicon, which has conducting properties intermediate between metals and insulators.

semi-; → conductor.

semiconductor junction
  جوهه‌ی ِ نیم-هازا   
juhe-ye nim-hâzâ

Fr.: jonction semi-conducteur   

In a semiconductor device, a region of transition between semiconducting regions of different electrical properties.

semiconductor; → junction.


Fr.: semi-convection   

An instability occurring in the region just outside the → convective core of a → massive star. The instability occurs when a → superadiabatic layer is stabilized by a chemical gradient. In fact, semiconvection takes place if → Schwarzschild's criterion for convection is fulfilled but at the same time → Ledoux's criterion is not fulfilled. The time-scale of semiconvection is the thermal time-scale, which is short compared to the nuclear time-scale in → main sequence stars but long compared to the time-scale of convection. However, semiconvection has a profound influence on the → post-main sequence star evolution. It affects the convective mixing above the hydrogen shell source, determines the appearance and extent of → blue loops in the → Hertzsprung-Russell diagram during core → helium burning, and is essential for defining the extent of the convective cores during core helium burning (See, e.g., N. Langer, 2012, Ann. Rev. Astron. Astrophys. 50, 107).

semi-; → convection.

semidetached binary
  دُرین ِ نیم-جدا   
dorin-e nim-jodâ

Fr.: bianire semi-détachée   

A binary system whose secondary member fills its Roche lobe but whose primary member does not.

semi-; detached, p.p. of detach, from O.Fr. destachier (Fr. détacher), from des- "apart," + -tachier (as in atachier "to attach"); → binary.

Dorin, → binary; nim-jodâ, from nim-semi- + jodâ "separate," from Mid.Pers. yut "separate, different;" Av. yuta- "separate, apart."

semidetached system
  راژمان ِ نیم-جدا   
râšmân-e nim-jodâ

Fr.: système semi-détaché   

Same as → semidetached binary.

semi-; detached, p.p. of detach, from O.Fr. destachier (Fr. détacher), from des- "apart," + -tachier (as in atachier "to attach"); → system.

Râžmân, → system; nim-jodâ, from nim-semi- + jodâ "separate," from Mid.Pers. yut "separate, different;" Av. yuta- "separate, apart."


Fr.: demi-diamètre   

The angle at the observer subtended by the equatorial radius of the Sun, Moon, or a planet.

semi-; → diameter.


Fr.: semi-empirique   

Describing an → equation or → formula that results from a → combination of → experiment and → theory.

semi-; → empirical.

<< < -sc Sag sam sat sca sca Sch sco sec sec sec sei sel sem sep sex Sha she sho sid sig sim sin Sir sky slo sno sod sol sol sol sol sou sou spa spe spe spe spe sph spi spo SS sta sta sta sta ste ste sto str str str sub sub suc sun sup sup sup sup sur swi syn Syr > >>