An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 27 Search : old
sard (#)

Fr.: froid   

Having a relatively low temperature.

M.E., from O.E. cald, ceald "cold, cool" (cf. O.Fr. and O.Sax. kald, O.H.G. and Ger. kalt, Goth. kalds "cold"), from PIE root *gel-/*gol- "cold;" cf. L. gelare "to freeze," gelu "frost," glacies "ice;" Kurd. girsân, girsiân "to coagulate" (Cheung 2007).

Sard "cold, cool," afsordan, afsârdan "to congeal;" Mid.Pers. sard/sart "cold;" Av. sarəta- "cold;" cf. Skt. śiśira- "cold;" L. calidus "warm;" Lith. šaltas "cold;" Welsh clyd "warm;" PIE *keltos- "cool."

cold absorber
  درشمگر ِ سرد   
daršamgar-e sard

Fr.: absorbeur froid   

A broad → absorption feature observed in → X-ray spectra of → active galactic nuclei (AGN). It is caused by material associated with the → interstellar medium in our → Galaxy and/or the host galaxy of the AGN or cold material near the AGN. → Quasars commonly have their X-ray spectrum absorbed by cold gas between us and the quasar X-ray source (along our → line of sight). This is particularly common in less luminous quasars. See also → warm absorber.

cold; → absorber.

cold accretion flow
  تچان ِ فربال ِ سرد   
tacân-e farbâl-e sard

Fr.: écoulement d'accrétion froid   

1) A type of → accretion flow by a → compact object such as a → black hole that consists of cool → optically thick gas and has a relatively high mass → accretion rate, in contrast to → hot accretion flows.
2) Gas accreting from the → intergalactic medium (IGM) onto → galactic haloes with sufficiently low velocities so that it will not be shocked to the → virial temperature of the halo, but will instead flow at a relatively low temperature (T ~ 104 K). Galaxies grow by accreting gas from → cosmic filaments. Feedback from star formation and → active galactic nuclei returns a significant fraction of the → interstellar medium (ISM) to the halo and may even blow it out of the halo into the IGM. This "cold accretion" will happen if the cooling time of → virialized gas is too short to maintain a hot, → hydrostatic halo. The existence of such a cold accretion mode has been confirmed by simulations, which have furthermore demonstrated that cold mode accretion can also be important for halos sufficiently massive to contain hot, hydrostatic gas. Because gas accretes preferentially along the filaments of the cosmic web, the streams of infalling gas have relatively high gas densities and correspondingly low cooling times. This allows the cold streams to penetrate the hot, hydrostatic halos surrounding massive galaxies, particularly at → high redshifts (F. van de Voort et al., 2012, MNRAS 421, 2809).

cold; → accretion; → flow.

cold dark matter (CDM)
  ماده‌ی ِ سرد ِ تاریک   
mâdde-ye sard-e târik (#)

Fr.: matière noire froide   

Any → hypothetical → non-baryonic  → dark matter that is → non-relativistic at the point of → decoupling in the → early Universe. CDM plays a key role in → cosmic structure formation. See also → CDM model, → lambda cold dark matter, → Meszaros effect, → missing satellites problem.

cold; → dark; → matter.

cold disk accretion
  گرده‌ی ِ فربال ِ سرد   
gerde-ye farbâl-e sard

Fr.: disque d'accrétion froid   

An accretion process whereby material coming from an → accretion disk settles onto the → protostellar surface through a geometrically thin layer or thin accretion columns. Heat brought into the protostar in the accretion flow radiates freely into space until the temperature attains the photospheric value. Most of the stellar surface is unaffected by the accretion flow (see, e.g., Hosokawa et al. 2010, ApJ 721, 478).

cold; → disk; → accretion.

e-folding time
  زمان ِ e-تایی   
zamân-e e-tâyi


The time within which the amplitude of an oscillation increases or decreases by a factor e (= 2.71828...).

From e the base of the natural, or Napierian, system of logarithms; folding, from -fold suffix meaning "of so many parts," or denoting multiplication by the number indicated by the stem or word to which the suffix is attached (as in twofold; manifold), from O.E. -feald, related to Ger. -falt; Gk. altos, -plos, -plus; → time.

Zamân, → time; e, as above; tâyi noun of multiplicative suffix, also "fold, plait, wrinkle; like, resembling."

flat manifold
  بسلای ِ تخت   
baslâ-ye taxt

Fr.: variété plate   

A manifold with a → Riemannian metric that has → zero → curvature.

flat; → manifold.

  تلا، طلا، زر   
talâ (#), zarr (#)

Fr.: or   

A yellow, → ductile  → metal which occurs naturally in veins and alluvial deposits associated with → quartz or → pyrite; symbol Au (L. aurum "shining dawn"). → Atomic number 79; → atomic weight 196.9665; → melting point 1,064.43 °C; → boiling point 2,808 °C; → specific gravity 19.32 at 20 °C. Like other → chemical elements the gold found on Earth has an → interstellar origin. However, the new-born Earth was too hot and most of the molten gold, mixed with → iron, sank to its center to make the core during the first tens of millions of years. The removal of gold to the → Earth's core should have left the Earth's crust depleted of gold. Nevertheless, the precious metal is tens to thousands of times more abundant in the → Earth's mantle than predicted. One explanation for this over-abundance is the → Late Heavy Bombardment. Several hundred million years after the core formation a flux of → meteorites enriched the → Earth's crust with gold (Willbold et al., 2011, Nature 477, 195).

M.E., from O.E. gold, from P.Gmc. *gulth- (cf. O.H.G. gold, Ger. Gold, Du. goud, Dan. guld, Goth. gulþ), from PIE base *ghel-/*ghol- "yellow, green;" cf. Mod.Pers. zarr "gold," see below.

Talâ "gold," variants tala, tali.
Zarr "gold;" Mid.Pers. zarr; Av. zaranya-, zarənu- "gold;" O.Pers. daraniya- "gold;" cf. Skt. hiranya- "gold;" also Av. zaray-, zairi- "yellow, green;" Mod.Pers. zard "yellow;" Skt. hari- "yellow, green;" Gk. khloe literally "young green shoot;" L. helvus "yellowish, bay;" Rus. zeltyj "yellow;" P.Gmc. *gelwaz; Du. geel; Ger. gelb; E. yellow.

Goldbach's conjecture
  هاشن ِ گلدباخ   
hâšan-e Goldbach

Fr.: conjecture de Goldbach   

Every number greater than 2 is the sum of two → prime numbers. Goldbach's number remains one of the most famous unsolved mathematical problems of today.

Named after the German mathematician Christian Goldbach (1690-1764); → conjecture.

golden number
  عدد ِ زرّین   
adad-e zarrin (#)

Fr.: nombre d'or   

1) The number giving the position of any year in the lunar or → Metonic cycle of about 19 years. Each year has a golden number between 1 and 19. It is found by adding 1 to the given year and dividing by 19; the remainder in the division is the golden number. If there is no remainder the golden number is 19 (e.g., the golden number of 2007 is 13).
2) Same as → golden ratio.

Golden, adj. of → gold; → number.

golden ratio
  وابر ِ زرین   
vâbar-e zarrin

Fr.: nombre d'or   

If a line segment is divided into a larger subsegment (a) and a smaller subsegment (b), when the larger subsegment is related to the smaller exactly as the whole segment is related to the larger segment, i.e. a/b = (a + b)/a. The golden ratio, a/b is usually represented by the Greek letter φ. It is also known as the divine ratio, the golden mean, the → golden number, and the golden section. Its numerical value, given by the positive solution of the equation φ2 - φ - 1 = 0, is approximately 1.618033989. The golden ratio is closely related to the → Fibonacci sequence.

golden; → ratio.

Goldschmidt classification
  رده‌بندی ِ گولدسمیت   
radebandi-ye Goldschmidt

Fr.: classification de Goldschmidt   

A → geochemical classification scheme in which → chemical elements on the → periodic table are divided into groups based on their → affinity to form various types of compounds: → lithophile, → chalcophile, → siderophile, and → atmophile. The classification takes into account the positions of the elements in the periodic table, the types of electronic structures of atoms and ions, the specifics of the appearance of an affinity for a particular → anion, and the position of a particular element on the → atomic volume curve.

Developed by Victor Goldschmidt (1888-1947); → classification.

Humboldt current
  جریان ِ هومبولت   
jarayân-e Humboldt (#)

Fr.: courant de Humboldt   

A cold ocean current that flows northward along the western side of South America, offshore Chile and Peru. Dominate weather in this area includes coastal fog and low clouds. The presence or lack of this current is a vital part of the weather pattern known as El Niño.

Named after the German naturalist and explorer Alexander von Humboldt (1769-1859). → current.

lambda cold dark matter model
  مدل ِ لامبدا-ماده‌ی-سرد ِ- تاریک   
model-e lâmbdâ-mâde-ye-sard-e-târik

Fr.: modèle ΛCDM   

The → standard model of → Big Bang that incorporates both → dark matter and → dark energy. See also → cold dark matter (CDM).

lambda, → cosmological constant; → cold; → dark; → matter; → model.

large Reynolds number flow
  تچان با عدد ِ بزرگ ِ رینولدز   
tacân bâ adad-e bozorg-e Reynolds

Fr.: écoulement à grand nombre de Reynolds   

A turbulent flow in which viscous forces are negligible compared to nonlinear advection terms, which characterize the variation of fluid quantities. The dynamics becomes generally turbulent when the Reynolds number is high enough. However, the critical Reynolds number for that is not universal, and depends in particular on boundary conditions.

large; → Reynolds number; → flow.

magnetic Reynolds number
  عدد ِ رینولدز ِ مغناتیسی   
adad-e Reynolds-e meqnâtisi

Fr.: nombre de Reynolds magnétique   

A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → magnetic advection to → magnetic diffusion. It is given by: Rm = σμ0νLU0, where σ is the → conductivity of the fluid, μ0 is the → magnetic permeability of the fluid, L is he characteristic length scale of the fluid flow, and U0 the characteristic velocity of the flow. A typical value for the Earth is Rm ~ 200.

magnetic; → Reynolds number.

baslâ (#)

Fr.: variété   

A → topological space in which every point has a → neighborhood which resembles → Euclidean space (Rn), but in which the global structure may be different. An example of a one-dimensional manifold would be a circle; if you zoom around a point the circle looks locally like a line (R1). An example of a two-dimensional manifold would be a sphere; a small portion looks locally like a plane (R2). See also → flat manifold.

O.E. monigfald (Anglian), manigfeald (W.Saxon) "varied in appearance," from manig "many" + -feald "fold."

Baslâ, from bas "many, much" (Mid.Pers. vas "many, much;" O.Pers. vasiy "at will, greatly, utterly;" Av. varəmi "I wish," vasô, vasə "at one's pleasure or will," from vas- "to will, desire, wish") + "fold."

  کهن، پیر   
kohan (#), pir (#)

Fr.: vieux   

Of an astronomical object, having existed as specified with relation to younger or newer objects of the same category; e.g. → old star.

From M.E., from O.E. eald, ald; cf. Du. old, Ger. alt, Goth. altheis; akin to O.N. ala "to nourish."

Kohan "old, ancient," kohné "worn;" Mid.Pers. kahwan "old, aged, worn."
Pir, from Mid.Pers. pir "old, aged, ancient;" Av. parô (adv.) "before, before (of time), in front (of space);" cf. Skt. puáh, combining form of puras "before (of time and place), in front, in advance."

old star
  ستاره‌یِ کهن، کهن‌ستاره، ستاره‌ی پیر   
setâre-ye kohan (#), kohan-setâré (#), setâre-ye pir (#)

Fr.: vielle étoile   

A member of a population of stars that, according to stellar evolution theories, are almost as aged as the galaxy in which it resides.

old; → star.

old stellar population
  پرینش ِ ستاره‌ای ِ کهن   
porineš-e setâre-yi-ye kohan

Fr.: population stellaire vielle   

A population of stars in a stellar system that have definitely left the → main sequence.

old; → stellar; → population.

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