An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13009 Search : far
Rhea
  ریءا   
Reâ (#)

Fr.: Rhéa   

The second largest satellite of Saturn, also known as Saturn V. It has a diameter of 1530 km and orbits Saturn at a mean distance of 527,040 km in 4.518 days. Rhea is composed primarily of water ice with rock making up less than 1/3 of its mass. It was discovered by Cassini in 1672.

In Gk. mythology Rhea was the sister and wife of Cronus (Saturn) and the mother of Demeter, Hades (Pluto), Hera, Hestia, Poseidon (Neptune), and Zeus (Jupiter).

rhenium
  رنیوم   
reniom (#)

Fr.: rhénium   

A metallic chemical element; symbol Re. Atomic number 75; atomic weight 186.207; melting point about 3,180°C; boiling point about 5,625°C. Rhenium is a very dense, high-melting, silver-white metal; specific gravity 21.02 at 20°C. Of the elements, only carbon and tungsten have higher melting points and only iridium, osmium, and platinum are more dense. It was discovered by x-ray spectroscopy in 1925 by the German chemists, Walter Noddack, Ida Tacke and Otto Berg.

The name derives from L. rhenus for "the Rhine river in Germany".

rheology
  روانه‌شناسی   
ravâné šenâsi (#)

Fr.: rhéologie   

A branch of physics dealing with the way matter flows and deforms.

From rheo- "flow, current, stream," from Gk. rheos "stream," cognate with Pers. rud "river," → Eridanus, + → -logy.

Ravâné, from ravân "flowing, running," pr.p. of raftan "to go, walk; to flow;" (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack") + šenâsi, → -logy.

rheonomous
  روانداتیک   
ravândâtik

Fr.: rhéonome   

Relating to a constraint or system that contains time explicitly. For example, a pendulum with an extensible string of length l rheonomous, the condition of constraint is: x2 + y2 = l2(t), where l(t) is the length of the string at time t.

From Gk. rheo-, from rheos "a flowing, stream, current," → rheology, + -nomous, → -nomy.

Rho Cassiopeiae
  رو-کاسیوپه   
ρ Kâsiopé

Fr.: Rho Cassiopée   

A → yellow hypergiant in the constellation Cassiopeia, classified as F8-G2 Ia0pe. Rho Cas is about 11,650 light-years away from Earth, yet can still be seen by the naked eye, as it is 550,000 times as luminous as the Sun. It is in fact one of the most luminous stars in our Galaxy. ρ Cas is also one of the only seven currently known yellow hypergiants in the Milky Way. It is variable and fluctuates around magnitude 5 but dimmed to 6th magnitude on 1946. Its last eruption happened in 2000-2001, during which the star ejected about 10 percent of a solar mass, dimmed by more than a full magnitude, and changed its spectral type from late F to early M. During this outburst, the star surface cooled from 7,000 to 4,000 K.

Rho, a Gk. letter of alphabet used in → Bayer designation; Cassiopeiae, genitive of → Cassiopeia.

Rho Ophiuchi Cloud
  ابر ِ رو-مارافسا   
abr-e rho Mâr-afsâ

Fr.: Nuage de rho Ophiuchi   

A complex region of molecular and dust clouds containing emission and reflection nebulae near the star ρ Oph in the constellation → Ophiuchus. It is one of the closest star forming regions, some 400 light-years distant. Recent studies using the latest X-ray and infrared observations reveal more than 300 young stellar objects within the large central cloud. Their median age is only 300,000 years.

Rho, Gk. letter; → Ophiuchus; → cloud.

rhodium
  رودیوم   
rodiom (#)

Fr.: rhodium   

A metallic chemical element; symbol Rh. Atomic number 45; atomic weight 102.9055; melting point about 1,966°C; boiling point 3,727±100°C; specific gravity 12.41 at 20°C. Rhodium was discovered in 1803 by the English chemist and physicist William Hyde Wollaston during experiments on crude platinum ore.

The name derives from Gk. rhodon "rose" because of the "rose color of dilute solutions of its salts."

rhombic
  لوزیک   
lowzik

Fr.: rhombique   

Shaped like a rhombus.

From rhomb, → rhombus, + → -ic.

rhombus
  لوزی   
lowzi (#)

Fr.: losange   

A quadrilateral having all sides equal and all angles oblique.

L.L. rhombus, from Gk. rhombos "rhombus, spinning top," from rhembesthai "to spin, whirl."

Lowzi, resembling a lowz "almond."

rhythm
  ریتم   
ritm (#)

Fr.: rythme   

1) An ordered recurrent alternation of strong and weak elements in the flow of sound and silence in speech; a particular example or form of rhythm.
2) The aspect of music comprising all the elements (as accent, meter, and tempo) that relate to forward movement.
3) A regularly recurrent quantitative change in a variable biological process (Merriam-Webster.com).

From L. rhythmus "movement in time," from Gk. rhythmos "measured flow or movement, rhythm; proportion, symmetry; arrangement," related to rhein "to flow," from PIE root *sreu- "to flow"

Ritm, loan from Fr.

Ricci scalar
  مرپلی ِ ریتچی   
marpeli-ye Ricci

Fr.: scalaire de Ricci   

The simplest curvature invariant for a → Riemannian manifold. It is derived from the → Ricci tensor Rμν ≡  Rαμαν by contracting indices. Taking the trace of the Ricci tensor gives the Ricci scalar: R ≡ Rμνgμnu; = Rμν = Rαμαμ. Also called → scalar curvature.

Ricci tensor; → scalar.

Ricci tensor
  تانسور ِ ریتچی   
tânsor-e Ricci

Fr.: tenseur de Ricci   

A → rank 2, → symmetric tensor Rμν that is a contraction of the → Riemann curvature tensor Rλμνλ. More specifically, Rμν ≡ Σ (λ) Rλμνκ = Rλμνκ. Closely related to the Ricci tensor is the → Einstein tensor, which plays an important role in the theory of → general relativity.

Named after the Italian mathematician Gregorio Ricci-Curbastro (1853-1925); → tensor.

rich
  پر-، پردار   
por-, pordâr

Fr.: riche   

Having large amounts of something specified. → metal-rich environment, → rich cluster; → enrich, → enrichment, → richness, → poor.

M.E., from O.E. rice "wealthy, powerful" (cf. Du. rijk, Ger. reich "rich"), from PIE base *reg- "move in a straight line," hence, "to direct, rule" (cf. Mod.Pers./Mid.Pers. râst "right, straight;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" 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).

Por "full, much, very, too much" (Mid.Pers. purr "full;" O.Pers. paru- "much, many;" Av. parav-, pauru-, pouru-, from par- "to fill;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full); pordâr, literally "having much possession," from por + dâr "having, possessor," from dâštan "to have, to possess," → property.

rich cluster
  خوشه‌ی ِ پُردار   
xuše-ye pordâr

Fr.: amas riche   

A → galaxy cluster with a particularly large number of galaxies.

rich; → cluster.

Richardson cascade
  پی‌شار ِ ریچاردسون   
peyšâr-e Richardson

Fr.: cascade de Richarson   

Same as → energy cascade

Named after L. F. Richardson (1922), Weather Prediction by Numerical Process (Cambridge Univ. Press); → cascade.

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.

<< < -es -iv -ti 21- a p abe abs abs acc acc acc act act ada adi ads aes Age Alb Alf ali all alp alt ama amp ana ang ang ann ano ant ant ape apo app app arb are ari art ass ast ast ast Atl ato ato Aug aut awa azi bac bal Bar Bar Bay bea Bep Bet BIC bij bin bio bir bla bla blu blu bol Boo bou Bq bre bri bub B[e cal cal can car car Cas cat cau cel cen Cer cha cha cha che chi CI cir cir cla cle clo clu co- cob 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 coo cor cor cor cos cos cos cou cov cra cri cro cry cum cur cyc d'A dar dat DC dea dec dec dec def def deh Del den dep des det deu dia dif dif dif dim dip Dir dis dis dis dis dis div dom dos dou dri Dum dus dyn dyn ear eas ecl Edd eff Ein eje ele ele ele ele eli emb emi Enc ene ens eph epo equ equ eru eth Eul eve evo exc exc exi exo exp exp ext ext Fab fai Fan fea fem fer fie fil fir fir fla flo flu foc For for fos fra fre fre fro fun g m Gal gal gal gas gau gel gen geo geo geo gho gla gno gra gra gra gra Gre Gre gro gyr had hal har Har HD hea hel hel Her Her Hic hig hip hol hor hos hov Hub hun hyd hyd Hyd hyp IC ide ill ima imp imp inc inc ind ind inf inf inf inf inj ins ins int int int int int int int int inv inv ion iro Isl iso iso Jac jet jud jur kel Kep kil Kle 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 Mei Mer Mer met met Met mic mid Mil min Mir mix mod mod mol mon Mor mou mul muo mys nan nat nav nec Nep neu New New NGC nob nom non non nor not nuc nuc num Nyq obj obs obs oce oen OH omn opa ope opt opt opt orb ord Ori ort osc out ove oxi pai pan par par par par pas pea pen per per per per Per pet pha Pho pho pho pho Pic Pis Pla pla pla pla Ple poa pol pol pol pol pop pos pos pow pra pre pre pre pri pri pri pro pro pro pro pro pro pro Pto pul puz qua qua qua qua qui rad rad rad rad rad rad rai ran rar Ray rea Rea rec rec red red ref ref reg rel rel rel rep res res res res ret Rhe rid rig ris Roe Ros rot rub rut Sag sam sat sca sca Sch sci sea sec sec see sel sem sen ser Sgr sha shi sho sid sig sim sin Sir ske sli smo soc sol sol sol sol sol sou sou spa spe spe spe spe sph spi spl spu sta sta sta sta sta ste ste sti sto str Str sub sub sub sul sup sup sup sup sur sus sym syn sys Tam Tay tel ten Ter Tha the the the thi thr tib tid tim tok Tor tot tra tra tra tra Tri tri tro tru tur twi Typ ufo ult unc uni uni uni upl ura uti val var vec vel ver ver vil vir vis voc von wak Was wav wax wea wei whi Wie win WN6 wom X-r yea You zer zod > >>