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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Denebola (β Leonis)
  شیردم، ذنب الاسد   
Širdom, Zanab-ol-asad (#)

Fr.: Denebola   

The second brightest star, of magnitude V = 2.14, in the constellation → Leo. A → main sequence star of → spectral type A3 V.

Denebola, from Ar. dhanab al-asad (ذنب الاسد) "tail of the lion," referring to the lion in Gk. mythology.

Širdom "tail of the lion," from šir "lion" → Leo + dom "tail," → comet. Zanab-ol-asad from Ar., as above.

denial
  نیارش   
niyâreš

Fr.: dénégation, démenti   

1) An assertion that something said, believed, alleged, etc., is false.
2) Refusal to believe a doctrine, theory, or the like.
3) Disbelief in the existence or reality of a thing (Dictionary.com).

deny; → -al.

denominate
  آنامنیدن   
ânâmenidan

Fr.: dénommer   

1) To give a specific name to.
2) To express in a multiple of a unit of measurement.

de-; → nominate.

denomination
  آنامنش   
ânâmeneš

Fr.: groupe, catégorie, unité; dénomination   

1) A name or designation.
2) The action of naming or classifying something. 3) One of the grades or degrees in a series of designations of quantity, value, measure, weight, etc. (Dictionary.com).

Verbal noun of → denominate.

denominator
  آنامنگر   
ânâmengar

Fr.: dénominateur   

The quantity y in a fraction x/y. The quantity x is the → numerator.

denominate; → -or.

denounce
  واژاییدن   
vâžâyidan

Fr.: dénoncer   

1) To condemn or censure openly or publicly.
2) To make a formal accusation against, as to the police or in a court (Dictionary.com).

de-; → announce.

dense
  چگال   
cagâl (#)

Fr.: dense   

Having relatively high → density.
Math.: The quality of a subset A of a topological space X, indicating that any point in X can be well approximated by points in A.

From L. densus "thick, crowded," cognate with Gk. dasys "hairy, bushy, thick grown."

Cagâl "dense, thick," related to ceqer "stiff, hard, tough, firm" (dialectal Kermâni ceqel, Šândizi caqal), caqâlé "stiff, unripe fruit."

dense core
  مغزه‌ی ِ چگال   
maqze-ye xagâl

Fr.: coeur dense   

An opaque region of a → molecular cloud (AV  10 mag) which is considered to be the progenitor of → star formation. Dense cores have temperatures of about 10 K and masses of roughly 1 to 10Msun each and in which the → molecular hydrogen density is roughly 104-105 cm-3 and size 0.1 pc. The → self-gravity of a dense core plays a central part in star formation. See also → hot molecular core.

dense; → core.

dense core mass function
  کریای ِ جرم ِ مغزه‌ی ِ چگال   
karyâ-ye jerm-e maqze-ye cagâl

Fr.: fonction de masse des cœurs denses   

core mass function.

dense; → core; → mass; → function.

dense molecular cloud
  ابر ِ مولکولی ِ چگال   
abr-e molekuli-ye cagâl

Fr.: nuage moléculaire dense   

A type of → interstellar medium cloud in which → carbon (C) becomes almost completely molecular due to relatively high → extinction. The chemistry is qualitatively different from that of → diffuse molecular clouds, as the → electron abundance is very low (→ cosmic-ray ionization being the dominant source) and the reactive C is replaced by the very stable → carbon monoxide (CO). This regime is found only in → sightlines with AV > 5-10 mag; not all such sightlines will contain dense cloud material and if dense cloud material is present it is likely to be surrounded by → translucent material. These clouds are typically → self-gravitating, and are most often observed by → infrared absorption and → millimeter wave emission methods. Their densities are typically at least 104 cm-3, and their → kinetic temperatures are typically on the order of 10-50 K in the quiescent regions. Most of the more than 140 currently known → interstellar molecules were found through observations of → microwaverotational transitions in such clouds, starting with the discovery of OH, followed by a host of other new detections such as CO, NH3, H2O, and H2CO (Snow & McCall, 2006, ARA&A 44, 367).

dense; → molecular; → cloud.

density
  چگالی   
cagâli (#)

Fr.: densité   

The amount of any quantity per unit volume. The mass density is the mass per unit volume. The energy density is the energy per unit volume; particle density is the number of particles per unit volume.
See also:
charge density, → column density, → critical density, → current density, → density fluctuation, → density parameter, → density profile, → density wave, → density-bounded H II region, → density-wave theory, → electron density, → energy density, → flux density, → magnetic flux density, → maximum density of water, → neutral density filter, → nuclear density, → number density, → optical density, → period-mean density relation, → Planck density, → potential density, → power spectral density, → probability density function, → radio flux density, → relative density, → specific density, → spectral density, → surface density.

Noun form of → dense.

density cusp
  تیزه‌ی ِ چگالی   
tize-ye cagâli

Fr.: cuspide de densité   

A localized increase in number of → stellar black holes near a → supermassive black hole predicted by models of galactic → stellar dynamics (Bahcall, Wolf, 1976, ApJ, 209, 214). Same as → stellar cusp.

density; → cusp.

density fluctuation
  افتاخیز ِ چگالی   
oftâxizhâ-ye cagâli

Fr.: fluctuations de densité   

In the early Universe, localized enhancements in the density of either matter alone or matter and radiation. According to models, very small initial fluctuations (less than 1 percent) can lead to subsequent formation of galaxies.

density; → fluctuation.

density of an element
  چگالی ِ بن‌پار   
cagâli-ye bonpâr

Fr.: densité d'élément   

The number of units of mass of the → chemical element that are present in a certain volume of a medium. The density of an element depends on temperature and pressure. The element Osmium has the highest known density: 22.61 g/cc; in comparison gold is 19.32 g/cc and lead 11.35 g/cc.

density; → element.

density parameter
  پارامون ِ چگالی   
pârâmun-e cagâli

Fr.: paramètre de densité   

One of the four terms that describe an arranged version of the → Friedmann equations. They are all time dependent.
1) For matter: Ωm = 8πGρm/(3H2), where G is the → gravitational constant, ρm is the mean matter density, and H the → Hubble parameter. The matter density parameter is also expressed as Ωm = ρmcrit, where ρcrit is the → critical density.
2) For radiation: Ωr = 8πGρr/(3H2), where ρr is the radiation equivalent of matter density. This parameter is also expressed as Ωr = ρrcrit.
3) For the → cosmological constant: ΩΛ = Λc2/(3H2). Similarly, ΩΛ = ρΛcrit, where &rhoΛ = Λc2/(8πG) is sometimes referred to as the density of → dark energy.
4) For the → curvature of space-timeΩk = -kc2/(R2H2), where k is the → curvature constant and R the → cosmic scale factor.
Note that: Ωm + Ωr + ΩΛ + Ωk = 1, and Ωtotal = Ωm + Ωr + ΩΛ = 1 - Ωk.

density; → parameter.

density profile
  فراپال ِ چگالی   
farâpâl-e cagâli

Fr.: profile de densité   

1) A → profile representing the → density of a quantity.
2) A → profile representing the distribution of stars as a function of their number in a region.

density; → profile.

density wave
  موج ِ چگالی   
mowj-e cagâli (#)

Fr.: onde de densité   

A wave phenomenon in which the density fluctuations of a physical quantity propagates in a compressible medium. For example, the → spiral arms of a → galaxy are believed to be due to a density wave which results from the natural instability of the → galactic disk caused by its own gravitational force. A common example of a density wave concerns traffic flow. A slow-moving vehicle on a narrow two-lane road causes a high density of cars to pile up behind it. As it moves down the highway the "traffic density wave" moves slowly too. But the density wave of cars does not keep the same cars in it. Instead, the first cars leave the density wave when they pass the slow vehicle and continue on at a more normal speed and new ones are added as they approach the density wave from behind. Moreover, the speed with which the density wave moves is lower than the average speed of the traffic and that the density wave can persist well after its original cause is gone. See → density wave theory.

density; → wave.

density wave theory
  نگره‌ی ِ موج ِ چگالی   
negare-ye mowj-e cagâli

Fr.: théorie des ondes de densité   

One possible explanation for → spiral arms, first put forward by B. Lindblad in about 1925 and developed later by C.C. Lin and F. H. Shu. According to this theory, spiral arms are not material structures, but regions of somewhat enhanced density, created by → density waves. Density waves are perturbations amplified by the self-gravity of the → galactic disk. The perturbation results from natural non-asymmetry in the disk and enhanced by environmental processes, such as galaxy encounters. Density waves rotate around the → galactic center and periodically compress the disk material upon their passage. If the spiral arms were rigid structures rotating like a pinwheel, the → differential rotation of the galaxy would wind up the arms completely in a relatively short time (with respect to the age of the galaxy), → winding problem. Inside the region defined by the → corotation radius, density waves rotate more slowly than the galaxy's stars and gas; outside that region they rotate faster.
As the density waves rotate, they are overtaken by the individual stars and nebulae/molecular clouds that are rotating around the galaxy at a higher rate. The molecular clouds passing through the density wave are subjected to compression because it is a region of higher density. This triggers the formation of clusters of new stars, which continue to move through the density wave.
The short-lived stars die, most likely as supernovae, before they can leave the spiral density wave. But the longer-lived stars that are formed pass through the density wave and eventually emerge on its front side and continue on their way as a slowly dissipating cluster of stars. Density wave theory explains much of the spiral structure that we see, but there are some problems. First, computer simulations with density waves tend to produce very orderly "grand design" spirals with a well-defined, wrapped 2-arm structure. But there are many spiral galaxies that have a more complex structure than this (→ flocculent spiral galaxy). Second, density wave theory assumes the existence of spiral density waves and then explores the consequences.
See also: → stochastic self-propagating star formation.

density; → wave; → theory.

density-bounded H II region
  ناحیه‌ی ِ H IIی ِ چگالی‌کرانمند   
nâhiye-ye H II-ye cagâli karânmand

Fr.: bornée par la densité   

An → H II region which lacks enough matter to absorb all → Lyman continuum photons of the → exciting star(s). In such an H II region a part of the ionizing photons escape into the → interstellar medium. See also → ionization-bounded H II region.

density; → bounded; → region.

deny
  نیاردن   
niyârdan

Fr.: nier   

To state that (something declared or believed to be true) is not true (Dictionary.com).

M.E. denien, from O.Fr. denoiir "deny, repudiate, withhold," from L. denegare "to deny, reject, refuse," from → de- "away" + negare "refuse, say no," from Old L. nec "not," from PIE root *ne- "no, not."

Niyârdan, literally "to bring (say) no," from ni-, variant of nanot, → non-, → un-, + ârdan contraction of âvardan "to bring; to cause or produce," → production.

<< < -es -it -sc 201 951 abe abs abs aca acc acc aco act ada adh ado aer aft air Alf alg alk alp Alt alt amb ana And ang ani ann ant ant ant apo app app Apu arc arg Arn art ass ast ast ast atm ato att aur aut avo azi bac bal bar bar bat Bea Bel bet bia big bin bio Bir bla bla blo Blu bol Boo bou box bre Bri bro bur cal cal Can cap car Car cat cau cel cen cen cha Cha cha che Chi chr cir cir civ cla clo clo CMB 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 con coo cor cor cor Cos cos cos cou cou cra cri cro cry cul cur cyc D l dar dat day dea dec dec dec def def deg Del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis diu dog Dop dou Dra Dsc dus dwa dyn Dys Ear ecc eco edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ eru eth Eur eve exa exc exe exi exo exp ext ext ext fab fai Fan fea fem fer fie fil fir fir fla fli flu foc for for for fra fre fre fri fun fuz gal gal gal Gam gau Gau gen geo geo geo geo Gib glo gov gra gra gra gra gre gro Gui H-a hal Ham har Hay hea hei hel Hel her het hie hig hoa hom hor hot Hub Hug hur hyd hyd hyl hyp ice ide ima ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv inv ion iro Isl iso iso Jab jet Jov Jup Kar Kep kil Kip Kra Lag Lam Lan Lar las law lea Leg Leo lev lig lim lin lin lin lit loc loc log Lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal map mas mas mat Mau mea mea med Men mer Mes Met met mic mic Mie mil min Mir mix mod mol mom Moo mor mov mul mur n-b nan nat nea neg Ner neu new New NGC noc nom non non nor nor nuc nuc nul nut obj obl obs occ oct off old one ope opp opt opt orb ord org Ori osc oth ove Owl P-s Pal par par par par Pas pat pec pen per per per per per Pha pha pho pho pho phy pie pix Pla pla pla pla Pli Poi pol pol pol pol por pos pos pow pre pre pre pre pri pri pri pro pro pro pro pro pro pro pub pul pyc qua qua qua qua qui rad rad rad rad rad rad rai ran rar Ray rea Rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot rur S5- Sal sat sca sca Sch sci Scu sec sec sed sel sel sem seq set sha she sho sid sie sil sim sin sit sky slo sno sod sol sol sol sol son sou spa spa spe spe spe spe sph spi spo squ sta sta sta sta ste ste ste Sti sto str str sub sub sub sul sup sup sup sup sur sur syl syn sys tal Tay tel ten ter tex the the the the Tho thr tid tim Tit too Tor tra tra Tra tra Tra tri Tri tru tub tur two Typ ult ult unc uni uni uni upl ura uti val var vec vel ver Ver vie vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>