An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 94 Search : low
subsonic flow
  تچان ِ زیر-صدایی   
tacân-e zir-sedâyi

Fr.: écoulement subsonique   

A flow in which the velocity of the constituting particles never exceeds that of sound in the same fluid. Also called subcritical flow.

subsonic; → flow.

Taylor-Couette flow
  تچان ِ تیلر-کویءت   
tacân-e Taylor-Couette

Fr.: écoulement de Taylor-Couette   

The → Couette flow between two concentric cylinders with fluid filling the annular region. The flow is generated by the relative rotation of the two cylinders. Under some physical conditions the flow may undergo the → Taylor-Couette instability.

Taylor number; → flow.

three-dimensional flow
  تچان ِ سه-وامونی   
tacân-e sé-vâmuni

Fr.: écoulement tri-dimensionnel   

A flow whose parameters (velocity, pressure, and so on) vary in all three coordinate directions. Considerable simplification in analysis may often be achieved, however, by selecting the coordinate directions so that appreciable variation of the parameters occurs in only two directions, or even only one (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

three; → dimensional; → flow.

transitional flow
  تچان ِ گذرشی   
tacan-e gozareši

Fr.: flux de transition   

In fluid mechanics, a flow composed of → laminar and → turbulent flows, for which the → Reynolds number is between 2300 and 4000.

transition; → flow.

tube of flow
  لوله‌ی ِ تچان   
lule-ye tacân

Fr.: tube d'écoulement   

Same as → flow tube.

tube; → tube.

turbulent flow
  تچان ِ آشوبناک   
tacân-e âšybnâk

Fr.: écoulement turbulent   

A → flow characterized by → turbulence. In other words, a flow in which the motion at any point varies unpredictably in direction and magnitude. See also → laminar flow; → transitional flow.

turbulent; → flow.

two-dimensional flow
  تچان ِ دو-وامونی   
tacân-e do-vâmuni

Fr.: écoulement bi-dimensionnel   

A flow whose parameters are functions of time and two space coordinates (x and y) only. There is no variation in the z direction and therefore the same → streamline pattern could at any instant be found in all planes in the fluid perpendicular to the z direction (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

two; → dimensional; → flow.

very low-mass star
  ستاره‌ی ِ بسیار کم‌جرم   
setâre-ye besyâr kamjerm

Fr.: étoile de très faible masse   

A star with a typical mass of one-hundredth of the mass of the Sun (→ solar mass) and a luminosity of about one-millionth that of the Sun (→ solar luminosity). Same as → brown dwarf.

very; → low; → mass; → star.

zard (#)

Fr.: jaune   

The primary color between green and orange in the visible spectrum; an effect of light with a wavelength between 5700 and 5900 Å. → yellow giant; → yellow supergiant.

M.E. yelou; O.E. geolo, geolu; P.Gmc. *gelwaz (cf. O.S., O.H.G. gelo, M.Du. ghele, Du. geel, Ger. gelb, Swed. gul "yellow"); cognate with Pers. zar "yellow," as below.

Zard "yellow," related to zarr "gold;" Mid.Pers. zard "yellow," zarr "gold;" O.Pers. daraniya- "gold;" Av. zaray-, zairi- "yellow, green," zaranya-, zarənu- "gold;" cf. Skt. hari- "yellow, green," hiranya- "gold;" Gk. chloros "light green," chloe "green shoot;" L. helvus "yellowish, bay;" Rus. zeltyj "yellow;" P.Gmc. *gelwaz, as above.

yellow giant
  غول ِ زرد، غولپیکر ِ ~   
qul-e zard (#), qulpeykar-e ~ (#)

Fr.: géante jaune   

A star that appears in the upper-middle part of the → H-R diagram, to the left of the → red giants. Yellow giants are low-mass evolved stars that are burning their helium, on their path to the → planetary nebula stage. Most yellow giants behave as variable stars, usually because their outer layers pulsate. Periods of these pulsations are usually days or weeks. The Sun after leaving the red giant stage will become a pulsating yellow giant for some 100 million years.

yellow; → giant.

yellow hypergiant (YHG)
  هیپرغول ِ زرد   
hiperqul-e zard

Fr.: hypergéante jaune   

An evolved, → very massive star of spectral type F or G with a very high luminosity (~105 times solar) lying near the empirical upper luminosity boundary in the → H-R diagram (→ Humphreys-Davidson limit). Yellow hypergiants have high → mass loss rates (10-5-10-3 solar masses per year) and are in a short, transitional evolutionary stage. Their evolutionary state is thought to correspond to post-red supergiants rapidly evolving in blueward loops in the H-R diagram. In their post-RSG blueward evolution these stars enter a temperature range (6000-9000 K), called → yellow void, with increased dynamical instability. Their link to other advanced evolutionary phases of massive stars such as → Luminous Blue Variables and → Wolf-Rayet stars is still an open issue in stellar evolution theory. The most famous yellow hypergiant is → Rho Cassiopeiae.

yellow; → hypergiant.

yellow supergiant (YSG)
  اَبَر-غول ِ زرد   
abarqul-e zard (#)

Fr.: supergéante jaune   

A supergiant star of type F and G whose effective temperature is between 4800 and 7500 K. Yellow supergiants are extremely rare, because they represent a very short-lived phase, typically a few tens of thousands of year, in the evolution of → massive stars.

yellow; → supergiant.

yellow void
  تهی ِ زرد   
tohi-ye zard

Fr.: lacune jaune   

A temperature range (6000-9000 K) in the → H-R diagram occupied by → yellow hypergiants in their post-RSG blueward evolution, where high → mass loss episodes occur.

yellow; → void.

  کیک ِ زرد   
keyk-e zard

Fr.: yellow cake, "gâteau jaune"   

The final product obtained from the processing of uranium ores. It is a coarse powder, a mixture of uranium oxides, with about 80% U3O8. It has a pungent odor and melts at approximately 2878 °C. The yellowcake produced by most modern mills is actually brown or black, not yellow; the name comes from the color of the concentrates produced by early mining operations due to impurities from ammonium diuranate. Yellowcake must be converted into → uranium hexafluoride (UF6) before it can be enriched, the process that makes the sort of uranium used by nuclear power plants or bomb-makers (→ uranium enrichment). The uranium hexafluoride is heated to become a gas and loaded into cylinders. When it cools, it condenses into a solid.

yellow; cake, M.E., from O.Norse kaka "cake," from which also derive M.Du. koke, Du. koek, Ger. Kuchen.

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