An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 412
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.

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.

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.


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.


Fr.: opalescent   

Exhibiting a play of colors like that of the opal.

opal; → -escent.

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.

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.

  آپاریدنیگی، آپارش‌پذیری   
âpâridanigi, âpârešpaziri

Fr.: opérabilité   

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

operable; → -ity.

  آپاریدنی، آپارش‌پذیر   
âpâridani, âpârešpazir

Fr.: opérable   

Capable of operating or of being operated.

operate; → -able.


Fr.: opérer   

To function or work; to make something function or work.

From L. operari "to work, labor," L. opus "a work, labor, exertion," Av. *āpah-, *apah- "to do, operate," see below, Skt. ápas- "work, action, religious act;" O.H.G. uoben "to start work, to practice, to honor;" Ger. üben "to exercise, practice;" Du. oefenen; O.E. æfnan "to perform, work, do," afol "power"); PIE base *op- "to work, perform."

Âpâridan, from âpâr-, from Av. *āp(ah)- "to do, operate," as above, + suffix -ar (as in vadar- "weapon," zafar- "jaw," baēvar- "thousand," and so on), shifted to -âr, + -idan suffix of infinitives. The Av. *āpah- "to do, operate," is extant in Mod.Pers. xub "good;" Mid.Pers. hwp, xub "good;" from Av. huuāpah- "doing good work, masterly," from huu-, hv- "good" → eu- + āpah- "work, deed," hauuapanha- "creativity;" cf. Skt. sv-ápas- "doing good work, skillful;" PIE base *op-, as above.

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