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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

   Homepage   
   


A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

<< < R A rad rad rad rad rad rad Ram Ran rat rea rea rec rec red red ref ref reg rei rel rel rem rep res res res ret rev rhy rif Rin rob Rom rot rot rum > >>

Number of Results: 736
Rankine-Hugoniot conditions
  بوتارهای ِ رانکین-هوگونیو   
butârhâ-ye Rankine-Hugoniot

Fr.: conditions de Rankine-Hugoniot   

Hydrodynamics → conservation laws (which can be extended to → magnetohydrodynamics, MHD) which describe the physical conditions of material across a → shock front. A fluid is completely described by its velocity, density, pressure, specific heat ratio, and magnetic field (in the MHD case). Mass, momentum, and energy fluxes are conserved in the shock, leading to the Rankine-Hugoniot relations. Also called Rankine-Hugoniot jump conditions. See also → jump condition.

Named after William John Rankine, → Rankine scale, and Pierre Henri Hugoniot, → Hugoniot curve; → condition.

Raoult's law
  قانون ِ رایءول   
qânun-e Raoult (#)

Fr.: loi de Raoult   

The → vapor pressure of an ideal → solution is dependent on the vapor pressure of each chemical component and the → mole fraction of the component present in the solution. This means that the addition of → solute to a liquid lessens the tendency for the liquid to become a → solid or a → gas. For example, the addition of → salt to water causes the water to freeze below its normal → freezing point (0°C) and to boil above its normal → boiling point (100°C).

After François-Marie Raoult (1830-1901), the French chemist who studied the physical properties of chemical solutions; → law.

rapid
  تند   
tond (#)

Fr.: rapide   

Occurring within a short time; happening speedily; moving or acting with great speed; swift (Dictionary.com).

From L. rapidus "tearing away, seizing, swift," from rapere "to hurry away, seize, plunder;"

Tond "swift, rapid, brisk; fierce, severe" (Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through;" PIE base *(s)teud- "to thrust, to beat").

Rapid Burster
  بلکور ِ تند   
belkvar-e tond

Fr.: source à sursaut rapide   

An object with technical designation MXB 17302335 which is characterized by erratic and extremely intense → X-ray emissions. The Rapid Burster is a → binary system comprising a → low-mass star as its → primary and a → secondary  → neutron star. The → gravitational attraction of the neutron star strips its → companion of some of its gas, which then forms an → accretion disk and spirals toward the neutron star. The Rapid Burster is located at a distance of 110 kpc in the highly reddened → globular cluster Liller 1. It is a → low-mass X-ray binary (LMXB) and a recurrent → X-ray transient. So far less than 200 LMXBs have been detected in the → Galaxy and the → Magellanic Clouds. All produce a persistent flux of X-rays, the result of a release of → gravitational potential energy. Approximately 40 of them also exhibit → Type I bursts which are due to → thermonuclear flashes on the surface of a neutron star. The Rapid Burster is unique among the LMXBs in that it produces X-ray bursts in quick succession. These are called → Type II bursts, and they result from a spasmodic release of gravitational potential energy, which is due to some unknown → accretion disk instability (Lewin et al., 1996, ApJ 462, L39).

rapid; → burster.

rapidly oscillating Ap star
  ستاره‌ی Apی ِ تند نونده   

Fr.: étoile Ap à oscillation rapide   

A chemically peculiar star characterized by the presence of high-frequency non-radial oscillations, with periods that range between about 4 and 16 min. These variations have periods from about 5 to 20 minutes and low amplitudes (B < 10 mmag). They are consistent with acoustic (→ p mode) pulsations of low degree and high radial overtone.

rapid; → -ly; → oscillate; → -ing; → Ap star.

rapids
  تنداب   
tondâb (#)

Fr.: rapides   

A part of a river where the current runs very swiftly. See also → torrent.

rapid.

Tondâb, from tond, → rapid, + âb, → water.

rare
  پرز، کمیاب   
perz, kamyâb (#)

Fr.: rare   

Not occurring very often; not found in large numbers.

M.E., from O.Fr. rere "sparse" from L. rarus "thinly sown; not thick; having intervals between."

Perz, in several Iranian languages and dialects "little, few, small, minute part of any thing" (Khonsâri: perz, Qatrâni: perzema, Birjandi: porzu, Farâmarzâni: pesk, Kurd petik, Tabari: perik "minute quantity, particle"); maybe ultimately from Proto-Ir. *paraka- "small part," → part.
Kamyâb "rare, difficult to find," from kam "little, few; deficient, wanting; scarce" (Mid.Pers. kam "little, small, few," O.Pers./Av. kamna- "small, few"); + yâb present stem of yâftan, yâbidan "to find, discover; to obtain, acquire" (Mid.Pers. ayâftan, ayâpênitan "to reach, attain;" Manichean Mid.Pers. 'y'b "to attain;" Parthian, Sogdian (+ *pati-) pty'b "to reach, obtain;" Av. ap- "to reach, overtake," apayeiti "achieved, reached;" Skt. âp- "to reach, gain," âpnoti "reaches, gains;" Gk. hapto, haptomai "to touch, cling to, adhere to;" L. apiscor "touch, reach;" PIE base *ap- "to take, reach").

rare earth element
  بن‌پار ِ خاکی ِ کمیاب، خاک ِ کمیاب   
bonpâr-e xâki-ye kamyâb, xâk-e kamyâb

Fr.: terre rare   

Any of the group of metallic → chemical elements with → atomic numbers between 57 and 71 inclusive. The name is an inappropriate terminology, since they are neither rare nor earth; preferred name → lanthanide.

rare; → earth; → element.

rare gas
  گاز ِ کمیاب   
gâz-e kamyâb (#)

Fr.: gaz rare   

Another name for → inert gas.

M.E., from O.Fr. rere "sparse," from L. rarus "loose, wide apart, thin, infrequent;" &rar; gas.

Kamyâb "rare, difficult to find," from kam "little, few; deficient, wanting; scarce" (Mid.Pers. kam "little, small, few," O.Pers./Av. kamna- "small, few"); + yâb present stem of yâftanyâftan, yâbidan "to find, discover; to obtain, acquire" (Mid.Pers. ayâftan, ayâpênitan "to reach, attain;" Manichean Mid.Pers. 'y'b "to attain;" Parthian, Sogdian (+ *pati-) pty'b "to reach, obtain;" Av. ap- "to reach, overtake," apayeiti "achieved, reached;" Skt. âp- "to reach, gain," âpnoti "reaches, gains;" Gk. hapto, haptomai "to touch, cling to, adhere to;" L. apiscor "touch, reach;" PIE base *ap- "to take, reach").

rarefaction
  آلرش   
âlareš

Fr.: raréfaction   

The state of being rarefied, less dense.
An instantaneous reduction in density of a gas resulting from passage a sound wave; opposite of → compression.

M.E. rarefien, from M.Fr. rarefier, from L. rarefacere "make rare," from rarus "loose, wide apart, thin, infrequent."

Verbal noun from âlar present stem of âlaridanrarefy + , a suffix.

rarefaction wave
  موج ِ آلرش   
mowj-e âlareš

Fr.: onde de raréfaction   

A pressure wave in a fluid generated by rarefaction. It travels in the opposite direction to that of a shock wave in the medium.

rarefaction; → wave.

rarefied gas
  گاز ِ آلریده   
gâz-e âlaridé

Fr.: gaz raréfié   

A gas whose pressure is much less than a reference pressure.

Past participle of → rarefy; → gas.

rarefy
  آلریدن   
âlaridan

Fr.: raréfier   

1) To make less dense.
2) To become less dense; become thinned.
Related concepts: → attenuate, → dilute, → decompress.

M.E. rarefien, from M.Fr. rarefier, from rare, combining form of rarus "loose, wide apart, thin, infrequent."

Alaridan, infinitive of âlar, from intensive/nuance prefix â- + lar "thin, meagre" (Dehxodâ), Lori, Laki larr, larrek "thin cow or sheep," Kurd. lerr "thin, lean," variants of laqar (Torbat-Heydariyé), lâqar "lean, meagre, slender; weak."

Rasalgethi (α Herculis)
  رأس‌الجاثی   
Ra's-el-jâsi (#)

Fr.: Rasalgethi   

The brightest star in the constellation → Hercules. It is a → red supergiant of type M5 (surface temperature about 3300 K) lying at a distance of 380 light-years. Rasalgethi is a variable star with a mean magnitude of V = 3.48. It has a fifth magnitude companion 5'' away. This secondary is itself a double that consists of a 4 solar-mass class G5 giant star with a temperature about that of the Sun and a 2.5 solar-mass F2 dwarf star (somewhat hotter than the Sun) in orbit around each other separated by 0.4 AU with a 52 day period.

Rasalgethi, from Ar. Ra's al-Jathi (رأس‌الجاثی) "the Kneeler's Head," in reference to an early name for the constellation, the figure of the man seen upside down, his head toward the south, from ra's "head" + jathi "kneeling."

Rasalhague (α Ophiuchi)
  رأس‌الحیه   
ra's-el-hayyé (#)

Fr.: Rasalhague   

The brightest star (V = 2.08) in the constellation → Ophiuchus. Rasalhague is a → giant star of type A5 lying 47 light-years from Earth. It has a faint, very close companion only 0''.5 away, 7 A.U., that orbits with a period of 8.7 years.

Rasalhague, from Ar. Ra's al-Hayyah (رأس‌الحیه), literally the "head of the snake," from ra's "head" + Hayyah "snake," referring to the creature in Gk. mythology.

rat
  گرز   
gerz (#)

Fr.: rat   

Any of various long-tailed rodents resembling mice but larger, especially one of the genus Rattus (TheFreeDictionary.com).

From M.E. rat, rotte, from O.E. ræt, of unknown origin.

Gerz, from (Lori, Laki) gerza "rat, big mouse," Gilaki (Lâhijân, Gâleš, Bandar-Anzali, etc.) gerze "rat; mouse," variant (Mâzandarân) gal "mouse," of unknown origin.

rate
  نرخ   
nerx(#)

Fr.: taux   

The amount of change of some quantity during a time interval divided by the length of the time interval.

M.E. rate "monetary value," M.Fr. rate "price, value," from M.L. rata (pars) "fixed (amount)," from L. rata "fixed, settled," p.p. of reri "to reckon, think," → reason.

Nerx "rate, price, tariff."

ratio
  وابَر   
vâbar

Fr.: rapport   

Math.: The quotient of two quantities arrived at by dividing one by the other.

From L. ratio "reckoning, calculation," also "reason," from rat-, p.p. stem of reri "to reckon, calculate," also "think," → reason.
Fr. rapport, back-formation from rapporter "bring back," from → re- "back, again" + apporter "to bring," from L. apportare "to bring," from → ad- "to" + portare "to carry."

Vâbar, on the model of Fr. rapport "bringing back," as above, from vâ- prefix meaning "back to the original place, again," → re-, + bar present stem of bordan "to carry, lead" (Mid.Pers. burdan, O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive)," Skt. bharati "he carries," Gk. pherein, L. fero "to carry;" PIE base *bher- "to carry").

rational
  ۱) راینی، راینوار؛ ۲) خردانه، خردمندانه؛ ۳) وابری   
1) râyani, râyanvâr; 2) xeradâné, xeradmandâné; 3) vâbari

Fr.: rationnel   

1) Having or exercising the ability to → reason.
2) Consistent with or based on reason; logical; in accordance with sound reasoning.
3) Math.: Capable of being expressed as a quotient of integers.

M.E. racional, from O.Fr. racionel, from L. rationalis "of or belonging to reason, reasonable," from ratio (genitive rationis) "reckoning, calculation, reason," from rat-, pp. stem of reri "to reckon, calculate; consider, think."

1) Râyani, of or pertaining to râyan, → reason.
2) Xeradâné, xeradmandâné, of or pertaining to xerad "understanding, judgement, intellect, wisdom;" Mid.Pers. xrad "reason, intellect, intelligence, wisdom, understanding;" O.Pers. xraθu- "wisdom;" Av. xratu- "intelligence, undestanding, wisdom; will, purpose, council;" cf. Skt. krátu- "power, will-power;" Gk. kratos "power, strength."
3) vâbari, of or pertaining to vâbar, → ratio.

rational number
  عدد ِ وابری   
'adad-e vâbari

Fr.: nombre rationnel   

Any number that can be expressed as a ratio of two integers, providing the second number is not zero.

rational; → number.

<< < R A rad rad rad rad rad rad Ram Ran rat rea rea rec rec red red ref ref reg rei rel rel rem rep res res res ret rev rhy rif Rin rob Rom rot rot rum > >>