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: 13048 Search : far
Oort cloud
  ابرِ اورت   
abr-e Ort (#)

Fr.: nuage de Oort   

A huge theoretical cloud of → comets surrounding the Sun between about 50,000 and 100,000 → astronomical units and thought to be the reservoir of → long-period comets entering the inner solar system.

Named after Jan Hendrik Oort (1900-1992), a Dutch astronomer who proposed its existence in 1950. He also made major contributions to our knowledge of the structure and rotation of the Milky Way Galaxy; → cloud.

Oort limit
  حدِ اورت   
hadd-e Oort

Fr.: limite de Oort   

1) The upper limit for the density of all matter in the plane of the Galaxy near the Sun's locality, as calculated from the velocities and distribution of stars in relation to the gravitational field of the Galactic disk. The value is 0.14 solar masses per cubic parsec, or 9.5 x 10-24 g cm3.
2) The outer boundary of the → Oort cloud. The current estimate is about 100,000 → astronomical units from the Sun, which is approximately one third of the distance to the nearest star → Alpha Centauri.

Oort cloud; → limit.

Oort minimum
  کمینه‌ی ِ اورت   
kamine-ye Oort

Fr.: minimum de Oort   

A 40-year period of unusually low → solar activity, from about 1010 to 1050. See also the → Maunder minimum.

Oort cloud; → minimum.

Oort's constants
  پایاهایِ اورت   
pâyâhâ-ye Oort

Fr.: constantes de Oort   

Two parameters, denoted A and B, that describe the major features of our Galaxy's differential rotation in the Sun's neighbourhood. A is one-half of the shear and equal to +14.4 ± 1.2 km s-1 kpc-1, and B, one-half of the vorticity, equal to -12.0 ± 2.8 km s-1 pc-1.

Oort cloud; → constant.

opacity
  کدری   
kederi (#)

Fr.: opacité   

1) General: The state or quality of being opaque.
2) A measure of the absorption of photons on their way from the stellar center to the surface. Opacity depends upon the frequency of the radiation, the density, the chemical composition, and the thermodynamic state of the gas. For a given density, the hotter the gas the lower the opacity, since the gas absorbs less readily, as described by → Kramers' law. Conversely, the cooler the gas the higher the opacity. See also → stellar pulsation, → kappa mechanism, → valve mechanism, → partial ionization zone.

From Fr. opacité, from L. opacitatem (nom. opacitas) "shade, shadiness," from opacus "shaded, dark, opaque."

Kederi, from keder "opaque," from Ar. kader + -i suffix forming nouns from adjectives.

opal
  اپال   
opâl (#)

Fr.: opale   

A → mineral, an amorphous form of → silica, SiO2 with some → water of → hydration, found in many varieties and colors, including a form that is milky white.

M.E., from M.Fr. opalle, from L. opalus, from Gk. opallios "opal, gem;" probably from a source akin to Skt. upala "jewel, precious stone."

Loan from E., as above.

opalescence
  اپالستی   
opâlesti

Fr.: opalescence   

1) The state of being → opalescent, or emitting an → iridescence like that of an opal.
2) Physics: The milky → iridescent appearance of a dense transparent medium when it is illuminated by → polychromatic visible radiation (such as sunlight) due to local → fluctuations in its density and therefore in its → refractive index. → critical opalescence.

opal; → -escence.

opalescent
  اپالست   
opâlest

Fr.: opalescent   

Exhibiting a play of colors like that of the opal.

opal; → -escent.

opaque
  کدر   
keder (#)

Fr.: opaque   

General: Not permitting a radiation to pass through.
Meteo.: A condition where a material, such as a cloud, blocks the passage of radiant energy, especially light.

Adj. form of → opacity.

open
  باز   
bâz (#)

Fr.: ouvert   

Not closed.
Math.: → open interval; → open set.

O.E. open "not closed down, raised up," also "uncovered, bare; plain, evident," related to up; from P.Gmc. *upana (cf. O.N. opinn, Swed. öppen, Dan. aaben, O.Fris. epen, O.H.G. offan "open"), from PIE *upo "up from under, over;" cf. L. sub; Gk. hypo; O.Pers. upā (prep.) "under, with;" Av. upā, upa (prep.; prevb) "toward, with, on, in;" Mod.Pers. "with," from abâ; Skt. úpa (adv., prevb., prep.) "toward, with, under, on."

Bâz "open," from Mid.Pers. abâz-, apâc-, O.Pers. apa- [pref.] "away, from;" Av. apa- [pref.] "away, from," apaš [adv.] "toward the back;" cf. Skt. ápāñc "situated behind."

open cluster
  خوشه‌یِ باز   
xuše-ye bâz (#)

Fr.: amas ouvert   

A loose grouping of dozens or hundreds of young stars distributed in a region a few light-years across. Open clusters are relatively young, typically containing many hot, highly luminous stars. They are located within the disk of the Galaxy, whence their older name Galactic clusters.

open; → cluster.

open interval
  اندروارِ باز   
andarvâr-e bâz

Fr.: intervalle ouvert   

An interval that does not include its two endpoints.

open; → interval.

open magnetic field line
  خط ِ باز ِ میدان ِ مغناتیسی   
xatt-e bâz-e meydân-e meqnâtisi-ye

Fr.: ligne ouverte de champ magnétique   

In the context of solar physics, a → magnetic field line when it crosses the solar surface only once, i.e., when it goes from surface to infinity. This is the case at a sufficiently large scale in → coronal holes. This is mostly not the case in → active regions.

open; → magnetic; → field; → line.

open set
  هنگردِ باز   
hangard-e bâz

Fr.: ensemble ouvert   

A → set consisting of points having → neighborhoods wholly contained in the set, as the set of points within a circle.

open; → set.

open space
  فضایِ باز   
fazâ-ye bâz (#)

Fr.: espace ouvert   

A space of infinite volume without any boundary. Triangles which lie on the surface of an open space will have a sum of angles which is less than 180°. An open space has a negative → curvature. See also → open Universe, → closed space.

open; → space.

open system
  راژمان ِ باز   
râžmân-e bâz

Fr.: système ouvert   

Thermodynamics: A system which can exchange both energy and matter with the surroundings. → closed system; → isolated system.

open; → system.

open Universe
  گیتیِ باز   
giti-ye bâz (#)

Fr.: Univers ouvert   

A → Freidmann-Lemaitre  → cosmological model in which → space is → infinite and of → negative  → curvature or → Euclidean, and which expands forever.

open; → universe.

open wff
   wff باز   
wff bâz

Fr.: FBF ouverte   

In → predicate logic, a → well-formed formula with one or more → free occurrences of → variables.

open; → wff.

operability
  آپاریدنیگی، آپارش‌پذیری   
âpâridanigi, âpârešpaziri

Fr.: opérabilité   

The capability of being put into use, operation, or practice.

operable; → -ity.

operable
  آپاریدنی، آپارش‌پذیر   
âpâridani, âpârešpazir

Fr.: opérable   

Capable of operating or of being operated.

operate; → -able.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer AGB air Alf Alg all alp alt AM amo ana And ang ani ano Ant Ant apa apo app app Ara Arc ari Arr ash ass ast ast asy atm ato att aut ave axi Bab bal Bal bar bar bea Bek Bes bia Big bin bin bip biv bla bli blu Boh Bol Bos bou bra bri bro buo cal cal can cap car Car cat cat CCD Cen cen CH cha cha che Che chr cir cir cit cla clo clo clu 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 Cop Cor cor cor cos cos cou cou Cow cre cri cro cry cur cya Cyg dan dar dat de- deb dec dec ded def deg del dem den dep des det dev dia dif dif dih dio Dir dis dis dis dis dis dis DO don dou dow dro dur dwa dyn Dys ear ebb ecl edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ esc eth Eur Eve exa exc exe exi exp exp ext ext ext fac fal far fed Fer fer fie fin fir fis fla flo flu fol for for fou fra fre Fre fro fut G-t gal gal gam gas Gau Gem gen geo geo geo gia Gli Gol gra gra gra gra gre gri gui H I Hag hal har hat He- hea hel Hel her Hes hie hig his hom hor hot Hub Hug hur hyd hyd hyg 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 Io ion iro isl iso iso Jac jet jud jur Kel Kep kil Klo Kui Lag lam Lap Lar lat law lea len lep Lib lig lim lin lin Lio lit loc LOF lon Lor low lum lun Lup Lyo mac mag mag mag mag mag mai man Mar mas mas mat Max mea mec Meg Mer Mer met met Met mic Mid Mil min Mir mit mod mod mol mon Mor mou mul mul mys nan Nat nau nec neo neu nev New NGC no nom non non nor not nuc nuc num nut obj obs obs occ ocu oft ome Oor ope opp opt opt orb ord ori ort osc out ove oxi pai pan par par par par pas pea pen per per per per Per per pha phi pho pho pho phy pio Pla pla pla pla Pla plu Poi pol pol pol poo pos pos pot pra pre pre pre pre pri pri pro pro pro pro pro Pro pro pse pul pur qua qua qua qua que rac rad rad rad rad rad rad 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 Rus Sac sal sat sca sca Sch sci Scu sec sec Sed sel Sel sen ser Sex Sha she sho sid sig sil sim sin siz sla Sma sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spi spr squ sta sta sta sta ste ste ste Sto Str str str sub sub suc sun sup sup sup sup sur swa syn syn tab tar tek tem ter tes the the the the Tho thr tid tim Tis Too Tor tra tra Tra tra tra tri tri tru Tul tur two Typ ult un- und uni uni unk upp Urc utt val var vec vel ver vib vio vir vis voi vor wan wat wav wax wea Wei whi Wil win WN9 wor X-r yel you zer zod > >>