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: 31 Search : dust
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.

gas-to-dust ratio
  وابر ِ گاز به غبار   
vâbar-e gâz bé qobâr

Fr.: rapport gaz/poussière   

The mass ratio of gas to dust. It amounts to approximately 100 in the → interstellar medium, but may vary in → molecular clouds and → circumstellar disks due to dust → grain evaporation, → dust settling, → condensation of gas, etc. The gas-to-dust ratio depends on the → metallicity. It is larger in galaxies with lower metallicity.

gas; → dust; → ratio.

hot dust-obscured galaxy (HDOG)
  کهکشان ِ تیره با غبار ِ داغ   
kahkešân-e tiré bâ qobâr-e dâq

Fr.: galaxie obscure à poussière chaude   

A member of the most extreme galaxies in terms of their luminosities and unusual hot → dust temperatures. The → infrared emission from HDOGs is dominated by obscured accretion onto a central → supermassive black hole (SMBH), in most cases without significant contribution from → star formation. The large contrast between the underlying → host galaxy and the hyper-luminous emission from the → active galactic nucleus (AGN) implies that either the SMBH is much more massive than expected for the stellar mass of its host, or is radiating well above its → Eddington limit. The most extreme of these remarkable systems known is → W2246-0526.

hot; → dust; → obscure; → galaxy.

interplanetary dust
  غبار ِ اندرسیاره‌ای   
qobâr-e andarsayyâreyi

Fr.: poussière interplanétaire   

Particles of dust in the → interplanetary medium. They are left-overs from the beginning of the solar system or from other sources such as sublimating comets. Their existence was first deduced from observations of → zodiacal light.

interplanetary; → dust.

interstellar dust
  غبار ِ اندر-اختری   
qobâr-e andaraxtari

Fr.: poussière interstellaire   

An aggregation of → dust grains in the space between stars. Interstellar dust absorbs, scatters, and polarizes the light from distant stars, causing the → interstellar extinction. Large dark regions in the plane of the Milky Way and other galaxies are caused by → intervening clouds of dust. The conclusive proof for the presence of a general and selective interstellar absorption is due to R. J. Trumpler (1930). See also → reddening; → very small grain; → big grain; → PAH.

interstellar; → dust.

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

Fr.: grain de poussière interstellaire   

dust grain.

interstellar; → dust; → grain.

intervening dust
  غبار ِ اندرگمنده   
qobâr-e andargamandé

Fr.: poussière intervenante   

A cloud of dust particles that happens to lie on the → line of sight between the → observer and the → object.

intervening; → dust.

lunar dust
  غبار ِ ماه   
qobâr-e mâh

Fr.: poussière lunaire   

A fine, powder-like dust covering the Moon's surface. → regolith. It is formed when meteoroids crash on the Moon's surface, heating and pulverizing rocks, which contain silica and metals. Since there is no wind or water to smooth rough edges, the tiny grains are sharp and jagged, and cling to nearly everything. Their main chemical compositions are SiO2 (about 45%) and Al2O3 (about 15%). The dust grains have an average size of 19 microns (40% smaller than hair).

lunar; → dust.

MRN dust model
  مدل ِ MRN   
model-e MRN

Fr.: modèle MRN   

A model concerned with the distribution in size of → interstellar grains to account for observations of → interstellar extinction from 0.11 μm to 1.0 μm. The → distribution has the form N(a)da ∝ a-3.5da, where a is the grain radius. It extends from 5 nm to 1 μm for → graphite and over a narrower range for other materials.

MNR, the initials of authors J. S. Mathis, W. Rumpl, and K. H. Nordsiek (1977, ApJ 217, 425), who introduced the mode; → dust; → model.

nanodust
  نانو-غبار   
nâno-qobâr

Fr.: nano-poussière   

Dust grains at → nanoscale sizes found in various astrophysical environments, such as → interstellar medium and → interplanetary space of our Solar System.

nano-; → dust.

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.

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