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: 13116 Search : far
dwarf galaxy
  کهکشان ِ کوتوله   
kahkešân-e kutulé (#)

Fr.: galaxie naine   

A small, low luminosity galaxy that is associated with a larger spiral galaxy and may make up part of a galactic halo. There are many of them in the Local Group, and often orbit around larger galaxies such as the Milky Way and the Andromeda Galaxy. There are three main types of them: → dwarf elliptical galaxy (dE), → dwarf irregular galaxy (dI), and → dwarf spiral galaxy (dSA).

dwarf; → galaxy.

dwarf irregular galaxy
  کهکشان ِ بی‌سامان ِ کوتوله   
kahkašân-e bisâmân-e kutulé

Fr.: galaxie irrégulière naine   

An irregular galaxy that is much smaller than other irregulars. Dwarf irregulars are generally metal poor and have relatively high fractions of gas. They are thought to be similar to the earliest galaxies that populated the Universe, and are therefore important to understand the overall evolution of galaxies.

dwarf; → irregular; → galaxy.

dwarf nova
  نووای ِ کوتوله، نو‌اختر ِ ~   
novâ-ye kutulé, nowaxtar-e ~

Fr.: nova naine   

A class of → novae and → cataclysmic variables that have multiple observed → eruptions. Their prototype is → U Geminorum star. Optically, dwarf nova eruptions have amplitudes of 2-6 mag in V, a duration of a few to 20 days and a recurrence time-scale of weeks to years. Dwarf novae are thought to be → semidetached binary stars consisting of a → white dwarf  → primary accreting via → Roche lobe overflow from a → companion which is usually a → late-type, generally → main-sequence star. DN outbursts are usually attributed to the release of gravitational energy resulting from an → instability in the → accretion disk or by sudden mass transfers through the disk.

dwarf; → nova.

dwarf planet
  سیاره‌ی ِ کوتوله   
sayyâre-ye kutulé (#)

Fr.: planète naine   

A new category of → astronomical objects in the → solar system introduced in a resolution by the 26th General Assembly of the → International Astronomical Union (IAU) on August 24, 2006. The characterizing properties are as follows: 1) It is in orbit around the Sun; 2) It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a → hydrostatic equilibrium (nearly round) shape; 3) It has not "cleared the neighbourhood" around its orbit; and 4) It is not a → satellite of a → planet, or other non-stellar body. The property 3 reclassified → Pluto from a planet to a dwarf planet because it has not cleared the neighborhood of its orbit (the → Kuiper Belt). The largest known dwarf planets are: → Eris, → Pluto, → Ceres, → Makemake, and → 2015 RR245.

dwarf; → planet.

dwarf spheroidal galaxy (dSph)
  کهکشان ِ کره‌وار ِ کوتوله   
kahkašân-e korevâr-e kutulé (#)

Fr.: galaxie sphéroïdale naine   

A subtype of dwarf ellipticals (→ dwarf elliptical galaxy), which are companion to the → Milky Way and other similar galaxies. The first example of such objects was discovered by Harlow Shapley (1938) in the constellation → Sculptor. 22 such galaxies are known currently to orbit the Milky Way and at least 36 exist in the → Local Group of galaxies. Nearby → galaxy clusters such as the → Virgo, → Fornax, → Centaurus, and → Coma clusters contain hundreds to thousands of individual dSph galaxies. These galaxies have very low → surface brightnesses, as low as only 1% that of the → sky background. They are also among the smallest, least luminous galaxies known. Most of the radiation from dSph galaxies is emitted by stars in the optical portion of the → electromagnetic spectrum. The lack of strong → emission lines, → infrared, or → radio emission suggests that these galaxies are generally devoid of → interstellar medium. The velocities of stars within dSph galaxies are so high that them must be disrupting. However, the bulk of mass in these galaxies might be undetected. Dynamical models that include → dark matter do adequately explain the → velocity dispersion of the stars in all dSph systems. In the most extreme cases, only 1% of the mass of the galaxy is visible. Many of the Local Group dSph galaxies show evidence for → star formation more recent than 10 Gyr.

dwarf; → spheroidal; → galaxy.

dwarf spiral galaxy
  کهکشان ِ مارپیچ ِ کوتوله   
kahkašân-e mârpic-e kutulé (#)

Fr.: galaxie spirale naine   

A galaxy that belongs to the spiral class but is significantly smaller.

dwarf; → spiral; → galaxy.

dwarf star
  ستاره‌ی ِ کوتوله   
setâre-ye kutulé (#)

Fr.: étoile naine   

A star that burns its hydrogen content to produce its energy and therefore belongs to the main-sequence luminosity class.

dwarf; → star.

dwarf starburst galaxy
  کهکشان ِ کوتوله‌ی ِ ستاره-بلک   
kahkešân-e kutule-ye setâre-belk

Fr.: galaxie naine à flambée d'étoiless   

A → starburst galaxy that is a → dwarf galaxy. Examples include: the → dwarf irregular galaxy IC 10, the compact dwarf irregular Henize 2-10, and the dwarf irregular galaxy NGC 5253.

dwarf; → starburst; → galaxy.

dynamic
  توانیک   
tavânik

Fr.: dynamique   

1) Involving or relating to force related to motion.
2) Pertaining to the science of → dynamics.

From Fr. dynamique, from Ger. dynamisch, introduced by Leibnitz in 1691, from Gk. dynamikos "powerful," from dynamis "power," from dynasthai "be able to have power" + → -ic.

Tavânik, from tavân "power, strength," tavânestan "to be powerful, able," + Pers. suffix -ik; → -ics. The first component from Mid.Pers. tuwan "power, might," from O.Pers./Av. base tav- "to have power, to be strong, to be able," Av. tavah- "power," təviši- "strength," Mod.Pers. tuš, tâb "power, ability," O.Pers. tauman- "power, strength," tunuvant- "powerful," Skt. tu- "to be strong, to have authority," tavas-, tavisa- "strong, energetic," tavisi- "power, strength" + -ik-ic.

dynamic equilibrium
  ترازمندی ِ توانیک   
tarâzmandi-ye tavânik

Fr.: équilibre dynamique   

Mechanics: The condition of a moving mechanical system when the accelerating force is balanced by an imaginary kinetic reaction according to → d'Alembert's principle. See also → static equilibrium; → thermodynamic equilibrium.

Dynamic, adj. from → dynamics; → equilibrium.

dynamic oblateness
  پخی ِ توانیک   
paxi-ye tavânik

Fr.: aplatissement dynamique   

A measure of the extent to which mass has been shifted from the polar regions of a (spinning) body toward its equator (Ellis et al., 2007, Planetary Ring Systems, Springer).

dynamic; → oblateness.

dynamic pressure
  فشار ِ توانیک   
fešâr-e tavânik

Fr.: pression dynamique   

A property of a moving → fluid defined by (1/2)ρv2 in → Bernoulli's law, where ρ is → density of fluid and v is → velocity. Dynamic pressure is the difference between → total pressure and → static pressure. Also called → velocity pressure. → ram pressure.

dynamic; → pressure.

dynamic range
  برد ِ توانیک   
bord-e tavânik

Fr.: dynamique   

The ratio of the maximum to minimum signal levels present in an image. For instance, a true 12-bit digital camera is capable of providing a dynamic range of 4096 to 1.

Adj. of → dynamics; → range.

dynamic viscosity
  وشکسانی ِ توانیک   
vošksâni-y tavânik

Fr.: viscosité dynamique   

Same as → viscosity and → absolute viscosity.

dynamic; → viscosity.

dynamical
  توانیک   
tavânik

Fr.: dynamique   

Of or pertaining to force or power; of or pertaining to force related to motion.
Pertaining to the science of dynamics. Same as dynamic.

Adj. from → dynamics.

dynamical age
  سن ِ توانیک   
senn-e tavânik

Fr.: âge dynamique   

Age based on dynamical properties of a system. For example, the time derived for a system to evolve from an initial state to its present state, based on velocity and dimension (size) measurements.

dynamical; → age.

dynamical disruption
  گسیخت ِ توانیک   
gosixt-e tavânik

Fr.: rupture dynamique   

The process whereby a → bound system, such as a → binary system or a → globular cluster, is broken apart.

dynamical; → disruption.

dynamical equilibrium
  ترازمندی ِ توانیک   
tarâzmandi-ye tavânik

Fr.: équilibre dynamique   

Of a physical system, a condition in which the parts of the system are in continuous motion, but they move in opposing directions at equal rates so that the system as a whole remains in equilibrium.

dynamical; → equilibrium.

dynamical friction
  مالش ِ توانیک   
mâleš-e tavânik

Fr.: frottement dynamique   

The gravitational interaction between a relatively massive body and a field of much less massive bodies through which the massive body travels. As a result, the moving body loses → momentum and → kinetic energy. An example of dynamical friction is the sinking of massive stars to the center of a → star cluster, a process called → mass segregation. Dynamical friction plays an important role in → stellar dynamics. It was first quantified by Chandrasekhar (1943).

dynamical; → friction.

dynamical law
  قانون ِ توانیک   
qânun-e tavânik

Fr.: loi dynamique   

A law that describes the motion of individual particles in a system, in contrast to → statistical laws.

dynamical; → law.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer aga air Alf Alg alk Alp alt alu amm ana And ang ani ano ant ant Ap apo app app Aqu Arc arg arr asc ass ast ast asy atm ato att aur aut axi B-m bad Bal bar bar Bay Bed ber Bet bif bim bin bio bis bla ble blu Bod Bol bor bou Bra Bre bro bul C-t Cal Cam can car Car Cas cat cav cel cen cer Cha cha Cha che chl Cir cir cir Cla cli clo clu co- coc 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 cou Cra Cre cri cro cub cur cyc cyl Dan dat Dav de- Deb dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dod Dop dou Dra dua dus dwa dyn DZ Ear ecc eco edi EHB Ein ela ele ele ele ele ell eme emp end Eng ent epi equ equ era ESP eth Eur evi exa exc exe exi exp exp ext ext ext fac fal far fec Fer fer fie fin fir fis fla Flo flu fog for for Fou fra fre fre Fro fun G s Gal gal gal Gar gau geg gen geo geo geo ger gla gly gra gra gra gra gra Gre gro GYR Had Hal hap Har HD hea hel hel Hen Her hex hig Hil hol Hoo hor hou Hub hum hyb hyd hyd hyp hys ide ign ima imp imp in- inc Ind ind ine inf inf inf ini ins ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jor jum K c Kep Ker kin kno lab Lam Lan Lap las lat Le lef len lev lig lig lin lin lin liq Lit loc log lon lou LS lun lun Lym M s Mag mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil Min Mir mix mod mod mol mon mor mov mul mur mys nan nat nav nec Nep neu New New NGC nob nom non non nor nos nuc nuc num nut obj obl obs occ oct off oli oni ope opp opt opt orb ord org orp osc out ove oxi P-w pal par par par par Pas pat pej per per per per per per pha Phe pho pho pho phy pin pla Pla pla pla pla plu poi pol pol Pol pol por pos pot Poy pre pre pre pre pri pri pri pro pro pro pro pro pro Psa pul pum Q i qua qua qua qua 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 Rho Rie ril riv rog Ros rot rul S A Sag sam sat sca sca Sch Sco Sec sec sec seg sel sem sen set Sha sha shi sho sid sig sim sin Sir ske sli Smo soc sof sol sol sol sol sou sou spa spe spe Spe spe sph spi Spi spr sta sta sta sta sta ste ste ste Sto str str sub sub sub suc sun sup sup sup sup sur swa syn syn tac tas tel tem ter tes the the the the thi thr tid til tip ton tor tou tra tra tra tra Tri tri tru tsu tur two Typ UHE ult unc uni uni uni upg ura uti val var vec Vel ver Ver vie Vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>