An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 18 Search : grain
big grain
  دانه‌ی ِ بزرگ   
dâne-ye bozorg

Fr.: gros grain   

A type of → interstellar dust grains with a size ranging from 150 to 1000 Å. Big grains consist of graphite and silicates. They are in → thermal equilibrium with the radiation field and their emission can be described by a modified → blackbody radiation following from → Kirchhoff's law.

big; → grain.

Cassegrain focus
  کانون ِ کسگرن   
kânun-e Cassegrain (#)

Fr.: foyer Cassegrain   

The main focus in → Cassegrain telescope.

Cassegrain telescope; → focus.

Cassegrain telescope
  دوربین ِ کسگرن، تلسکوپ ~   
durbin Cassegrain, teleskop-e ~ (#)

Fr.: Télecope Cassegrain   

A reflecting telescope whose primary mirror has a hole bored through the center to allow the reflected light from the convex secondary mirror be focused beyond the back end of the tube.

Cassegrain, named after the French priest and school teacher Laurent Cassegrain (1629-1693), who invented this system in 1672; → telescope.

dust grain
  دانه‌ی ِ غبار   
dâne-ye qobâr (#)

Fr.: grains de poussière   

A small, solid flake of → graphite and/or → silicates coated with water ice, found in the → interstellar medium or the → interplanetary medium. Dust grains are irregularly shaped with sizes from microns to Angstroms (→ very small grain; → big grain; → PAH). It is believed that the dust is mainly formed in the cool outer layers of → red giants and dispersed in the interstellar medium. In dense environments, such as → molecular clouds and around → protostars, dust grains grow due to collisions (→ grain growth). Therefore, dust grains in → protostellar disks should be larger than interstellar grains. Dust grains absorb and scatter optical and ultraviolet light and re-radiate in infrared (→ dust emission). Dust acts as a catalyst in the interstellar medium, because molecules form via reactions on the surface of dust grains.

dust; → grain.

fluffy dust grain
  دانه‌ی ِ غبار ِ کرکوار   
dâne-ye qobâr-e korkvâr

Fr.: grain de poussière duveteux   

An aggregate of small particles loosely stuck together. Same as → porous dust grain.

fluffy; → dust; → grain.

dâné (#)

Fr.: grain   

1) A small, hard seed of plants, especially the seed of cereals.
2) A tiny portion or particle of something such as sand or salt; → dust grain.

M.E. grain, grein, from O.Fr. grein, from L. granum "seed;" akin to corn.

Dâné "grain, seed;" Mid.Pers. dân, dânag "seed, corn;" Av. dānô- in dānô.karš- "carrying grains; an ant;" cf. Skt. dhânâ- "corn, grain;" Tokharian B tāno "grain;" Lith. duona "corn, bread."

grain coagulation
  ماسش ِ دانه   
mâseš-e dâné

Fr.: coagulation des grains   

Sticking together of micron- to centimetre-sized grains occurring in the interstellar and protoplanetary environments to form larger grain agglomerates.

grain; → coagulation.

grain evaporation
  بخارش ِ دانه   
boxâreš-e dâné

Fr.: évaporation des grains   

Conversion of dust grains into smaller grains due to high environmental temperatures.

grain; → evaporation.

grain formation
  دیسش ِ دانه   
diseš-e dâné

Fr.: formation des grains   

The process by which dust grains are assembled or produced.

grain; → formation.

grain growth
  رویش ِ دانه   
ruyeš-e dâné (#)

Fr.: croissance des grains   

The increase of dust grains to micron sizes in the interstellar environments due to various physical processes, for example mutual collisions and accumulation of ice mantles.

grain; → growth.

grain mantle
  روپوش ِ دانه   
rupuš-e dâné (#)

Fr.: manteau de grain   

A layer of icy molecules covering interstellar dust grains.

grain; mantle, from O.E. mentel "loose, sleeveless cloak," from L. mantellum "cloak," perhaps from a Celtic source.

Rupuš "overgarment, cloak," from ru "surface, face; aspect; appearance" (Mid.Pers. rôy, rôdh "face;" Av. raoδa- "growth," in plural form "appearance," from raod- "to grow, sprout, shoot;" cf. Skt. róha- "rising, height") + puš "covering, mantle," from pušidan "to cover; to put on" (Mid.Pers. pôšidan, pôš- "to cover; to wear;" cf. Mid.Pers. pôst; Mod.Pers. pust "skin, hide;" O.Pers. pavastā- "thin clay envelope used to protect unbaked clay tablets;" Skt. pavásta- "cover," Proto-Indo-Iranian *pauastā- "cloth").

grain sputtering
  ا ُسپرانی ِ دانه   
osparâni-ye dâné

Fr.: érosion des grains par pulvérisation   

The ejection of atoms from interstellar dust grains due to impact by gas ions, which leads to grain destruction.

grain; sputtering, from sputter "to spit with explosive sounds," cognate with Du. sputteren.

Osparâni, verbal noun of osparândan, from os- "out of, outside," → ex- + parândan "to eject," transitive of paridan "to fly" (from Mid./Mod.Pers. par(r) "feather, wing," Av. parəna- "feather, wing;" cp. Skt. parna "feather," E. fern; PIE *porno- "feather").

interstellar dust grain
  دانه‌ی ِ غبار ِ اندر‌اختری   
dâne-ye qobâr-e andaraxtari

Fr.: grain de poussière interstellaire   

dust grain.

interstellar; → dust; → grain.

interstellar grain
  دانه‌ی ِ اندر-اختری   
dâne-ye andaraxtari

Fr.: grain interstellaire   

Irregularly shaped → dust grains that occur in the → interstellar medium. They are mostly composed of carbon and/or silicates and measure a fraction of micron across.

interstellar; → grains.

porous dust grain
  دانه‌ی ِ غبار ِ پرلیک   
dâne-ye qobâr-e porlik

Fr.: grain de poussière poreux   

A type of → interstellar dust grain made up of an aggregate of components with a hollow structure. Various processes operating in interstellar and → circumstellar media are believed to produce inhomogeneous and porous dust grains. Porous grains can produce more → extinction per unit mass than their combined individual dust components. They are generally cooler than compact grains (see, e.g., Iati et al. 2001, MNRAS 322, 749).

porous; → dust; → grain.

presolar grain
  دانه‌ی ِ پیش-خورشیدی   
dâne-ye piš-xoršidi

Fr.: grain pré-solaire   

A → refractory → nanoparticle embedded in → meteorites and → interplanetary dust particles whose → isotopic ratios suggest formation earlier than the Solar System.

presolar; → grain.

Schmidt-Cassegrain telescope
  تلسکوپ ِ اشمیت-کاسگرن، دوربین ِ ~   
teleskop-e Schmidt-Cassegrain, durbin-e ~ (#)

Fr.: télescope Schmidt-Cassegrain   

A mixture of the → Cassegrain telescope with a very short → focal length and of a Schmidt design (due to the presence of the → corrective plate), used mainly in → amateur astronomy. The main advantage of this telescope is its compact design. However, Schmidt-Cassegrain telescopes produce fainter images with less contrast than other telescope designs with similar → aperture sizes. This is due to the comparatively large → secondary mirror required to reflect the light back the → eyepiece.

Schmidt telescope; → Cassegrain telescope.

very small grain (VSG)
  دانه‌ی ِ بسیار کوچک   
dâne-ye besyâr kucak

Fr.: très petit grain   

A special type of carbonaceous → interstellar dust grains with a size ranging from 10 to 150 Å and consisting of tens to hundreds of atoms. In contrast to → big grains, VSGs are not in → thermal equilibrium. They can be heated to very high temperatures (~ 1000 K) by the absorption of a single photon. It is thought that VSGs are clusters of → PAH.

very; → small; → grain.