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
Richardson criterion
  سنجیدار ِ ریچاردسون   
sanjidâr-e Richardson

Fr.: critère de Richardson   

A condition for the onset of → instability in multilayer fluids which compares the balance between the restoring force of → buoyancy and the destabilizing effect of the → shear.

Named after the British meteorologist Lewis Fry Richardson (1881-1953), who first arrived in 1920 to the dimensionless ratio now called → Richardson number. The first formal proof of the criterion, however, came four decades later for → incompressible flows (Miles, J. W. 1961, J. Fluid Mech., 10, 496; Howard, L. N., 1961, J. Fluid Mech., 10, 509). Its extension to → compressible flows was demonstrated subsequently (Chimonas 1970, J. Fluid Mech., 43, 833); → criterion.

Richardson number
  عدد ِ ریچاردسون   
adad-e Richardson

Fr.: nombre de Richardson   

A dimensionless number which is used according to the → Richardson criterion to describe the condition for the → stability of a flow in the presence of vertical density stratification. If the → shear flow is characterized by linear variation of velocity and density, with velocities and densities ranging from U1 to U2 and ρ1 to ρ2 (ρ2>ρ1), respectively, over a depth H, then the Richardson number is expressed as: Ri = (ρ2 - ρ1) gH / ρ0 (U1 - U2)2. If Ri < 0.25, somewhere in the flow turbulence is likely to occur. For Ri > 0.25 the flow is stable.

Richardson criterion; → number.

richness
  پرداری   
pordâri

Fr.: richesse   

The property of being very abundant.

rich; → -ness.

richness class
  رده‌ی ِ پرداری   
rade-ye pordâri

Fr.: classe de richesse   

A classification of → galaxy clusters into six groups (0 to 5), as in the → Abell catalog. It depends on the number of galaxies in a given cluster that lie within a → magnitude range m3 to m3+2, where m3 is the magnitude of the 3rd brightest member of the cluster. The first group contains 30-49 galaxies and the last group more than 299 galaxies.

richness; → group.

riddle
  کروس   
kervas (#)

Fr.: énigme, devinette   

1) A question or statement so framed as to exercise one's ingenuity in answering it or discovering its meaning; conundrum.
2) A puzzling question, problem, or matter (Dictionary.com).

M.E. redel, redels, from O.E. rædels "riddle; counsel; conjecture; imagination;" cf. O.Fr. riedsal "riddle," O.Sax. radisli, M.Du. raetsel, Du. raadsel, O.H.G. radisle, Ger. Rätsel "riddle."

Kervas "riddle, puzzle" [Dehxodâ], Kurd. karvâs "riddle," of unknown origin.

ridge
  روک   
ruk

Fr.: faîte, dorsale   

A long, narrow elevation of the Earth's surface, generally sharp crested with steep sides, either independently or as part of a larger mountain or hill. See also: → submarine ridge, → wrinkle ridge, → mid-Atlantic ridge.

M.E. rigge; O.E. hrycg "spine, back of a man or beast" (cf. O.Fris. hregg, Du. rug, O.H.G. hrukki, Ger. Rücken "the back").

Ruk, from dialectal Tabari ruk "mountain, ridge;" cf. (Dehxodâ) raš "hill."

Riemann curvature tensor
  تانسور ِ خمیدگی ِ ریمان   
tânsor-e xamidegi-ye Riemann

Fr.: tenseur de courbure de Riemann   

A 4th → rank tensor that characterizes the deviation of the geometry of space from the Euclidean type. The curvature tensor Rλμνκ is defined through the → Christoffel symbols Γλμν as follows: Rλμνκ = (∂Γλμκ)/(∂xν) - (∂Γλμν)/(∂xκ) + ΓημκΓλην - ΓημνΓληκ.

Riemannian geometry; → curvature; → tensor.

Riemann problem
  پراسه‌ی ِ ریمان   
parâse-ye Riemann

Fr.: problème de Riemann   

The combination of a → partial differential equation and a → piecewise constant → initial condition. The Riemann problem is a basic tool in a number of numerical methods for wave propagation problems. The canonical form of the Riemann problem is: ∂u/∂t + ∂f(u)/∂x = 0, x ∈ R, t > 0, u(x,0) = ul if x < 0, and u(x,0) = ur if x > 0 .

Riemann's geometry; → problem.

Riemann's geometry
  هندسه‌ی ِ ریمان   
hendese-ye Riemann

Fr.: géométrie de Riemann   

Same as → Riemannian geometry.

Riemannian; → geometry.

Riemannian
  ریمانی   
Riemanni (#)

Fr.: riemannien   

Of or pertaining to Georg Friedrich Bernhard Riemann (1826-1866) or his mathematics findings. → Riemannian geometry, → Riemannian manifold, → Riemannian metric, → Riemann problem, → Riemann curvature tensor.

After the German mathematician Georg Friedrich Bernhard Riemann (1826-1866), the inventor of the elliptic form of → non-Euclidean geometry, who made important contributions to analysis and differential geometry, some of them paving the way for the later development of → general relativity.

Riemannian geometry
  هندسه‌ی ِ ریمانی   
hendese-ye Riemanni

Fr.: géométrie riemannienne   

A → non-Euclidean geometry in which there are no → parallel lines, and the sum of the → angles of a → triangle is always greater than 180°. Riemannian figures can be thought of as figures constructed on a curved surface. The geometry is called elliptic because the section formed by a plane that cuts the curved surface is an ellipse.

Riemannian; → geometry.

Riemannian manifold
  بسلای ِ ریمانی   
baslâ-ye Riemanni

Fr.: variété riemannienne   

A → manifold on which there is a defined → Riemannian metric (Douglas N. Clark, 2000, Dictionary of Analysis, Calculus, and Differential Equations).

Riemannian; → metric.

Riemannian metric
  متریک ِ ریمانی   
metrik-e Riemanni

Fr.: métrique riemannienne   

A positive-definite inner product, (.,.)x, on Tx(M), the tangent space to a manifold M at x, for each x  ∈ M, which varies continually with x (Douglas N. Clark, Dictionary of Analysis, Calculus, and Differential Equations).

Riemannian; → metric.

rift
  چاک، گسل‌دره   
câk, gosal-darré

Fr.: rift; fissure, crevasse   

1) General: a gap or break made by splitting, cleaving, etc.; fissure; cleft.
2) Geology: A narrow cleft, fissure, or other opening in rock, made by cracking or splitting.
3) Geology: An elongated trough in the Earth's crust bounded by → faults.

M.E., from a Scandinavian source; cf. Dan., Norw. rift "a cleft."

1) Câk "fissure, rupture, cleft, crack," related to caqidan "to drive a nail, strike together, fix a spike;" caxidan "to quarrel, strive;" diatectal Shughni cuγ, Roshani coγ "breaking, tearing, ripping up;" Malâyeri ceqidan "cracking of a cold porcelain bowl when receiving hot water;" Yazghulami cok-, coxt "to pound, to stamp;" Wakhi cuk-, cukt "to strike;" Ossetic cædyn "to shake, strike iron;" Lori cok "a mark fixed to separate two grounds;" Sogd. cax "to battel, fight;" Mid.Pers. (prefixed) pacên "copy" (see also Cheung 2007). Gosal-darré, from gosal, → fault, + darré, → valley.

rift valley
  گسل‌دره   
gosal-darré

Fr.: fossé d'effondrement, ~ tectonique   

A long, narrow valley formed by the lowering of land between two → faults. Also called → graben.

rift; → valley.

Rigel (β Ori)
  رجل   
Rejl (#)

Fr.: Rigel   

The brightest star in the constellation → Orion (visual magnitude 0.18). A → blue supergiant of type B8 Iab with an initial mass of 17 solar masses, Rigel is 773 light-years away, and actually shines with the light of 40,000 Suns. It is accompanied by a fairly bright, seventh magnitude companion nine seconds of arc apart. The companion is itself double, the components much fainter and much less massive → main sequence stars of type B.

Rigel "foot," short for Ar. rijl al-jauza' (رجل‌الجوزاء) "the foot of jauza'." The latter word means "the manifest one," initially "black sheep with white middle." The Gk. figure was translated as such because of its conspicuousness among other constellations.

Rejl, from Ar., as above.

Rigel Kentaurus
  پای ِ کنتاؤروس   
Pâ-ye Kentawros

Fr.: Rigil Kentaurus   

Same as the star → Alpha Centauri.

From Ar. Rijl al-Qanturis "foot of Centaurus," from rijl "foot," + Qanturis Arabicized → Centaurus.

Pâ-ye Kantawros, "foot of Centaurus," from , → foot, + Kentawros, → Centaurus.

right
  ۱) راست؛ ۲) درست؛ ۳) راشن   
1) râst (#); 2) dorost; 3) râšan

Fr.: droit   

1a) Straight, free from curves, angles, or irregularities. → right ascension.
1b) Opposite of → left. → right-hand rule, → right-hand screw rule.
2) In accordance with fact, reason, or truth; correct or true.
3) Something that a person is or should be morally or legally allowed to have, get, or do (Merriam-Webster).

M.E.; O.E. reht, riht; cf. O.H.G. reht, Ger. recht, O.N. rettr, Goth. raihts; P.Gmc. *rekhtaz, cognate with Pers. râst, as below.

1) Râst "right, true; just, upright, straight;" Mid.Pers. râst "true, straight, direct;" Soghdian rəšt "right;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" related to Mid.Pers. rây-, râyênitan "to arrange;" Mod.Pers. raj "line, row," variants raž, rak, râk, rezg (Lori), radé, râdé "line, rule, row," rasté, râsté "row, a market with regular ranges of shops;" ris, risé "straight;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" PIE base *reg- "move in a straight line," hence, "to direct, rule;"
2) Dorost "correct, whole, complete, healthy," → integral.
3) Râšan, related to râst, as above; cf. Mid.Pers. Rašn "Justice deity; calendar 18th day;" Av. rašnu- "the Zoroastrian Justice deity, orientation."

right angle
  زاویه‌ی ِ راست   
zâviye-ye râst

Fr.: angle droit   

An angle of 90°.

right; → angle.

right ascension
  راست‌افراز   
râst afrâz (#)

Fr.: ascension droite   

A coordinate in the → equatorial system measured from the → vernal equinox eastward to the point where the object → hour circle intersects the → celestial equator. Right ascension (symbol α) is expressed in hours, minutes, and seconds. See also: → declination.

right; ascension, M.E. ascencioun, from O.Fr., from L. ascendere "to climb up," from → ad- "to" + scandere "to climb."

Râst, → right; afrâz present stem of afrâzidan, afrâštan "to raise, exalt, extole," from Mid.Pers. abrâstan, abrâz- "to lift, raise," from ab-, from O.Pers./Av. abiy-/aiwi- "to, upon, against;" cf. Skt. abhi-, Gk. amphi- + râst "straight, direct, true;" from O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right; PIE base *reg- "move in a straight line," hence, "to direct, rule."

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