An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

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Number of Results: 12955 Search : far
jansky (Jy)
  جنسکی   
jansky (#)

Fr.: jansky   

The unit of → radio flux density in → radio astronomy, equivalent to 10-26watts per square meter per → hertz.

Named in 1973 by the International Astronomical Union in honor of Karl Guthe Jansky (1905-1950), an American engineer of Czech descent who first identified radio waves from beyond the Solar System.

Janus
  یانوس   
Yânus (#)

Fr.: Janus   

The sixth of Saturn's known satellites. With a mean diameter of about 178 km it orbits Saturn at a distance of 150,000 km. Discovered by the French astronomer Audouin Dollfus (1924-) in 1966.

Janus was the god of gates and doorways in Roman mythology. He was also thought to represent beginnings, hence he lent his name to January, the first month of the year. He was depicted with two faces looking in opposite directions.

jasper
  یشم   
yašm (#)

Fr.: jaspe   

A colored form of natural silica, SiO2, which is a precious stone.

M.E. jaspe, jaspre, from M.Fr., O.Fr. jaspe, from L. iaspidem (nominative iaspis), from Gk. iaspis "jasper," via an Oriental language, probably an Eastern Iranian language, see below.

Yašm, variants, yasp, yasb, yašf "jasper;" Sogd. iešp "jasper," iešpênê "of jasper, crystalline."

Jeans
  جینز   
Jeans

Fr.: Jeans   

Named after Sir James Hopwood Jeans (1877-1946), English mathematical physicist, astrophysicist, and popularizer of science. He made important contributions to theoretical astrophysics, especially to the theory of stellar formation.

Jeans instability
  ناپایداری ِ جینز   
nâpâydâri-ye Jeans

Fr.: instabilité de Jeans   

An instability that occurs in a → self-gravitating  → interstellar cloud which is in → hydrostatic equilibrium. Density fluctuations caused by a perturbation may condense the material leading to the domination of gravitational force and the cloud collapse. The advent of instability involves a threshold called the → Jeans length or the → Jeans mass.

Jeans; → instability.

Jeans length
  درازای ِ جینز   
derâzâ-ye Jeans (#)

Fr.: longueur de Jeans   

The critical size of a homogeneous and isothermal interstellar cloud above which the cloud is unstable and must collapse under its own gravity. Below this size the cloud's internal pressure is sufficient to resist collapse. The Jeans length is defined by: λJ = (π cs2/Gρ)1/2 = 0.2 pc (T/10 K)1/2(nH2/104 cm-3)-1/2, where cs is the → sound speed, G is the → gravitational constant, ρ is the gas density, T is the gas temperature, and nH2 is the molecular hydrogen density.

Jeans; → length.

Jeans mass
  جرم ِ جینز   
jerm-e Jeans (#)

Fr.: masse de Jeans   

The → minimum mass for an → interstellar cloud below which the → thermal pressure of the gas prevents its → collapse under the force of its own → gravity. It is given by the formula MJ = (π5/2 / 6) G -3/2ρ0-1/2cs3, where G is the → gravitational constant, ρ0 the initial → density, and cs the isothermal → sound speed. It can be approximated to MJ ~ 45 (TK) 3/2 (ncm-3) -1/2 in units of solar masses, where TK is the temperature in → Kelvin, and ncm-3 the gas density per cm3. High density favors collapse, while high temperature favors larger Jeans mass. See also: → thermal Jeans mass, → turbulent Jeans mass.

Jeans; → mass.

Jeans scale
  مرپل ِ جینز   
marpel-e Jeans

Fr.: échelle de Jeans   

Same as → Jeans length.

Jeans; → scale.

jelly
  ژله   
želé (#)

Fr.: gelée   

1) A soft somewhat elastic food product made usually with gelatin or pectin; especially, a fruit product made by boiling sugar and the juice of fruit.
2) A substance resembling jelly in consistency (Merriam-Webster.com).

M.E. gely, from O.Fr. gelee "a jelly," from L. gelare "to freeze, congeal, stiffen," from PIE *gel- "cold; to freeze."

Želeh, loan from Fr., as above.

jellyfish
  مدوسا، عروس ِ دریایی   
medusâ, arus-e daryâyi

Fr.: méduse   

Any of various marine coelenterates of a soft, gelatinous structure, especially one with an umbrella like body and long, trailing tentacles; medusa (dictionary.com).

jelly; → fish.

Medusâ, from Gk. Medousa, literally "guardian," from medein "to protect, rule over."

jellyfish galaxy
  کهکشان ِ مدوسا   
kahkešên-e medusâ

Fr.: galaxie méduse   

A type of galaxy exhibiting "tentacles" (tails) of material that appear to be stripped from the main body of the galaxy, making it resemble a jellyfish. Such type of galaxies occur in → galaxy clusters and are produced by a process called → ram pressure stripping. The mutual → gravitational attraction between galaxies causes them to fall at high speed into the clusters, where they encounter a hot → intracluster medium (ICM) with dense gas. The falling galaxy feels a powerful wind, forcing tails of gas out of the galaxy's disk and triggering → starbursts within it. Jellyfish galaxies have mainly been observed in nearby clusters (e.g., Virgo, Coma, A1367, A3627, Shapley). A few examples have been identified in clusters at → redshifts z ~ 0.2-0.4, and there is accumulating evidence for a correlation between the efficiency of the stripping phenomenon and the presence of shocks and strong gradients in the X-ray → intergalactic medium (Poggianti et al., 2016, AJ 151, 78).

jellyfish; → galaxy.

jet
  ۱، ۲، ۳) اِشان، شان؛ ۴) جت   
1, 2, 3) ešân, šân; 4) jet

Fr.: jet   

1) A stream of a liquid, gas, or small solid particles forcefully shooting forth from a nozzle, orifice, etc.
2) Fountain-like formations of gas and/or dust gushing out from compact regions of some astronomical objects. → astrophysical jets.
3) Meteo.: A common abbreviation for → jet stream.
4) Shortened of → jet plane.

Jet, from M.Fr. jeter "to throw," from V.L. *jectare, alter. of L. jactare, from jac- "throw" + -t- frequentative suffix + -are infinitive suffix; PIE base *ye- "to do" (cf. Gk. hienai "to send, throw;" Hittite ijami "I make").

Ešân, from ešândan, → eject; šân contraction of ešân.

jet engine
  موتور ِ شانی   
motor-e šâni

Fr.: turboréacteur   

An → engine that works by taking in air at the front and expelling exhaust gases at the rear so that the reaction to this exhaust propels the vehicle forward.

jet; → engine.

jet launching
  پرتاب ِ شان   
partâb-e šân

Fr.: lancement de jet   

The mechanism whereby → astrophysical jets are thrown out of → accretion disks . Observed correlations between emission from the accretion disk and from the jet provide evidence that the jets are launched from the disks directly. As the energy emitted from the jets is a → synchrotron radiation, the presence of a → magnetic field is deduced for the ejection. The most promising model for such "accretion-ejection" structures is based on a scenario where a large-scale magnetic field threads an accretion disk. This model, using a → magnetohydrodynamic (MHD) approach, shows that the magnetic field can azimuthally brake the matter inside the disk (carrying off → angular momentum allowing accretion) and accelerate matter above the disk surface. The → collimation of the flow is achieved via → magnetic tension due to the presence of a → toroidal component of the magnetic field. The magnetic field provides an effective alternative to the radially outward transport of disk angular momentum by → viscosity. The interaction of the magnetic structure with the disk plasma can create a MHD → Poynting flux leaving the disk along the magnetic surface. This energy flux can then be converted into → kinetic energy of the matter within the jet. Because the → mass density in the jet is smaller than in the disk, it is thereby possible to reach high → terminal velocities for a given amount of angular momentum removed from the disk (Casse & Keppens, 2002, ApJ 581, 988, and references therein).

jet; → launch; → -ing.

jet plane
  جت، هواپیما‌ی ِ ~   
jet (#), havâpeymâ-ye ~ (#)

Fr.: avion à réaction   

An airplane moved by → jet propulsion.

jet; plane, short for airplane, from Fr. aeroplane, from aero-, → air, + plane feminine of plan "flat, level," from L. planus, perhaps by association with forme plane; apparently coined and first used by Fr. sculptor and inventor Joseph Pline in 1855.

jet; havâpeymâ "airplane," from havâ, → air, + peymâ "travelling; traveller," from peymudan, peymâyidan "to travel, traverse, pass over," from Mid.Pers. patmudan, paymudan "to measure (against)," from *pati-māya-. The first element *pati- "against, back" (cf. Mod.Pers. pâd- "against, contrary to;" Mid.Pers. pât-; O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Av. paiti; Skt. práti "toward, against, again, back, in return, opposite;" Pali pati-; Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti). The second element from *mā- "to measure;" O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure." Apart from peymâ, several other terms in Mod.Pers. are related to this second element, which occurs also as mun, mân, man, mâ, mu, and mây: pirâmun "perimeter," âzmun, âzmây- "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," man "a measure weighing forty seers)," nemudan, ne- "to show, display," âdan, âmây- "to prepare."

jet propulsion
  پیشرانش ِ شانی   
pišrâneš-e šâni

Fr.: propulsion par réaction   

Powerful, forward thrust that results from the rearward expulsion of a jet of fluid, especially propulsion by jet engines.

jet; → propulsion.

jet stream
  رابه‌ی ِ شانی   
râbe-ye šâni

Fr.: jet stream   

Meteo.: An area of relatively strong winds that are concentrated in a narrow band in the upper troposphere of the middle latitudes and subtropical regions of the Northern and Southern Hemispheres.

jet; → stream.

Jewish calendar
  گاهشمار ِ یهود   
gâhšomâr-e yahud (#)

Fr.: calendrier juif   

Same as → Hebrew calendar

Jewish, adj. of jew, from M.E. jewe, giu, gyu, ju, from O.Fr. juiu, juieu, gyu, from L.L. judeus, from L. juaeus, from Gk. ioudaios, from Aramaic yehudhai, from Heb. yəhudhi "Jew," from Yəhudah "Judah," literally "celebrated," name of Jacob's fourth son and of the tribe descended from him; → calendar.

Gâhšomârcalendar; yahud, from Ar., from Heb., as above.

JHK system
  راژمان ِ JHK   
râžmân-e JHK

Fr.: système JHK   

1) Three → atmospheric windows in the → near infrared portion of the → electromagnetic spectrum at 1.25 (J), 1.65 (H), and 2.20 (K) μm.
2) An extension of Johnson's → photometric system into near infrared using filters corresponding to the atmospheric windows J (1.25 μm), H (1.65 μm), and K (2.20 μm), with → bandwidths 0.3 μm, 0.4 μm, and 0.6 μm respectively.

Letters of alphabet, used conventionally; → system.

Jilin meteorite
  شهاب‌سنگ ِ جیلین   
šahâbsang-e jilin (#)

Fr.: météorite de Jilin   

The biggest meteorite ever witnessed falling and the largest stone meteorite known. It happened near Jilin, an industrial port city located northeastern China, on March 8, 1976. Of the four tons of fragments of the type H5 chondrite recovered, one piece weighs 1.774 tons and measures about 100 x 80 x 50 cm. The meteorite exploded in the sky and produced a shower covering an area of more than 500 square kilometers.

Jilin, from the name of the Chinese city, known also as Chi-lin City or Kirin City. → meteorite.

<< < -es -iv -ti 21- A r abe abs abs acc acc acc act act ada adi adu aff age alc Alf ali all alp alt ama amp ana ang ang ann ano ant ant ape apo app aps arc Arg ari art ass ast ast ast atm ato att aur aut axi B r bac Bal Bar Bar Bay bec Ber Bet Bie bij bin bio bis bla bla blu blu bol Bor bou Bra bre bro Bug C-s cal Cam can car Car Cas cat cav cel cen cer Cha cha cha che cho cir cir cir cla clo clo clu coa coe coh col col col com com com com com com com com com con con con con con con con con con con con coo cor cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl dar dat daw de- Deb dec dec dee def deg del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis diu dog Dop dou Dra dua dus dwa dyn e-f Ear ecl eco edu eig Ein ela ele ele ele Ele elo emi emp ene Enl env epi equ equ Eri est Euc eva evo exc exc exh Exo exp exp ext ext f(R fac fam fat fee Fer Fib fig fin fir fix fle flu foc for for for fra fre Fre fri fun fuz Gal gal gal Gam gau Gay gen Geo geo geo geo gim glo gov gra gra gra gra gre gro Gun hab hal han Har haz hea hel hel Hen Her het Hig hil hol Hoo hor hou Hub hum hyd hyd hyd hyp hys ide ign ima imp imp inc inc ind Ind inf inf inf inf inn ins ins int int int int int int int int inv ion ion Irr iso iso iso jan jit Jul jus Kel ker kin kni La lam lan Lap las lat Lay Led Len let lif lig lin lin lin liq Lit loc log lon lou low lum lun Lym M d Mag mag mag mag mag mag maj man mar mas mas mat mea mea mec mem mer Mes met met mho mic Mie Mil min mis MKS MOd mol Mon moo mot mul mul myo nak Nas nat neb neg neu neu New New nit noi non non nor nor nuc nuc nul nut obj obl obs occ oct off oli oni ope opp opt opt orb ord org orp osc out ove oxi pai Pan par par Par par pas Pav Pel per per per per Per per pha phi pho pho pho phy Pip Pla pla PLA pla ple plu pol pol pol pol pop pos pos pot Pra pre pre pre Pri pri pri pro pro pro pro pro pro pro Pto pul pur 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 RHB rid rig ris roc Ros rot rub Rut Sag sam sat sca sca Sch sci Sea sec sec see sel sem sen set Sha sha shi shu sid sil sim sin SIS ski Slo smo Soc sol sol sol sol son sou spa spa spe spe spe sph spi spi Spo squ sta sta sta sta Ste ste ste sto str str str sub sub suc sun sup sup sup sup sur Swa syn syn tab tar tel tem ter tes the the the the Tho thr tid tim Tit top tot tra tra TRA tra tre tri tri tru Tun Tus tym Typ ult unb und uni uni uns upp Urs vac van var Vei Ven ver vic Vir vir vis vol W 4 war wat wav wea wed wet wid win WN2 Wol wri xen yok zen zin > >>