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
graviton
  گراویتون   
gerâviton (#)

Fr.: graviton   

A hypothetical elementary particle associated with the gravitational interactions. This quantum of gravitational radiation is a stable particle, which travels with the speed of light, and has zero rest mass, zero charge, and a spin of ± 2.

From gravit(y), → gravity + → -on a suffix used in the names of subatomic particles.

gravity
  گرانی   
gerâni (#)

Fr.: gravité   

1) The apparent force of → gravitation on an object at or near the surface of a star, planet, satellite, etc.
2) Same as → gravitation and → gravitational interaction.

From L. gravitatem (nom. gravitas) "weight, heaviness," from gravis "heavy," from PIE base *gwrə- "heavy" (cf. Mod.Pers. gerân "heavy;" Av. gouru- "heavy;" Skt. guru- "heavy, weighty, venerable;" Gk. baros "weight," barys "heavy;" Goth. kaurus "heavy").

Gerâni, noun of gerân "heavy, ponderous, valuable," from Mid.Pers. garân "heavy, hard, difficult;" Av. gouru- "heavy" (in compounds), from Proto-Iranian *garu-; cognate with gravity, as above.

gravity assist
  یاری ِ گرانشی   
yâri-ye gerâneši

Fr.: gravidéviation   

An important astronautical technique whereby a → spacecraft takes up a tiny fraction of the → orbital energy of a planet it is flying by, allowing it to change → trajectory and → speed. Since the planet is not at rest but gravitating around the Sun, the spacecraft uses both the orbital energy and the gravitational pull of the planet. Also known as the slingshot effect or → gravitational slingshot. More specifically, as the spacecraft approaches the planet, it is accelerated by the planet's gravity. If the spacecraft's velocity is too low, or if it is heading too close to the planet, then the planet's → gravitational force will pull it down to the planet. But if its speed is large enough, and its orbit does not bring it too close to the planet, then the gravitational attraction will just bend the spacecraft's trajectory around, and the accelerated spacecraft will pass rapidly by the planet and start to move away. In the absence of other gravitational forces, the planet's gravity would start to slow down the spacecraft as it moves away. If the planet were stationary, the slow-down effect would be equal to the initial acceleration, so there would be no net gain in speed. But the planets are themselves moving through space at high speeds, and this is what gives the "slingshot" effect. Provided the spacecraft is traveling through space in the same direction as the planet, the spacecraft will emerge from the gravity assist maneuver moving faster than before.

gravity; assist, from M.Fr. assister "to stand by, help, assist," from L. assistere "assist, stand by," from → ad- "to" + sistere "to cause to stand," from PIE *siste-, from *sta- "to stand" (cognate with Pers. istâdan "to stand").

Yâri "assistance, help; friendship," from yâr "assistant, helper, friend," from Mid.Pers. hayyâr "helper," hayyârêh "help, aid, assistance," Proto-Iranian *adyāva-bara-, cf. Av. aidū- "helpful, useful."

gravity brightening
  روشنش ِ گرانشی   
rowšaneš-e gerâneši

Fr.: embrillancement gravitationnel   

gravity darkening.

gravity; → brightening.

gravity darkening
  تاریکش ِ گرانشی   
târikeš-e gerâneši

Fr.: assombrissement gravitationnel   

The darkening, or brightening, of a region on a star due to localized decrease, or increase, in the → effective gravity. Gravity darkening is explained by the → von Zeipel theorem, whereby on stellar surface the → radiative flux is proportional to the effective gravity. This means that in → rotating stars regions close to the pole are brighter (and have higher temperature) than regions close to the equator. Gravity darkening occurs also in corotating → binary systems, where the → tidal force leads to both gravity darkening and gravity brightening. The effects are often seen in binary star → light curves. See also → gravity darkening exponent. Recent theoretical work (Espinosa Lara & Rieutord, 2011, A&A 533, A43) has shown that gravity darkening is not well represented by the von Zeipel theorem. This is supported by new interferometric observations of some rapidly rotating stars indicating that the von Zeipel theorem seems to overestimate the temperature difference between the poles and equator.

gravity; → darkening

gravity darkening coefficient
  همگر ِ تاریکش ِ گرانشی   
hamgar-e târikeš-e gerâneši

Fr.: coefficient de l'assombrissement gravitationnel   

According to the → von Zeipel theorem, the emergent flux, F, of total radiation at any point over the surface of a rotationally or tidally distorted star in → hydrostatic equilibrium varies proportionally to the local gravity acceleration: F ∝ geffα, where geff is the → effective gravity and α is the gravity darkening coefficient. See also the → gravity darkening exponent.

gravity; → darkening; → coefficient.

gravity darkening exponent
  نمای ِ تاریکش ِ گرانشی   
nemâ-ye târikeš-e gerâneši

Fr.: exposant de l'assombrissement gravitationnel   

The exponent appearing in the power law that describes the → effective temperature of a → rotating star as a function of the → effective gravity, as deduced from the → von Zeipel theorem or law. Generalizing this law, the effective temperature is usually expressed as Teff∝ geffβ, where β is the gravity darkening exponent with a value of 0.25. It has, however, been shown that the relation between the effective temperature and gravity is not exactly a power law. Moreover, the value of β = 0.25 is appropriate only in the limit of slow rotators and is smaller for fast rotating stars (Espinosa Lara & Rieutord, 2011, A&A 533, A43).

gravity; → darkening; → exponent.

gravity mode
  ترز ِ گرانی، مد ِ ~   
tarz-e gerâni, mod-e ~

Fr.: mode gravité   

Same as → g mode

gravity; → mode.

gravity wake
  کل ِ گرانی   
kel-e gerâni

Fr.: sillage de gravité   

Transient → streamers which form when → clumps of particles begin to collapse under their own → self-gravity but are sheared out by → differential rotation. This phenomenon is believed to be the source of → azimuthal asymmetry in → Saturn's → A ring (Ellis et al., 2007, Planetary Ring Systems, Springer).

gravity; → wake.

gravity wave
  موج ِ گرانی   
mowj-e gerâni

Fr.: onde de gravité   

1) A wave that forms and propagates at the free → surface of a body of → fluid after that surface has been disturbed and the fluid particles have been displaced from their original positions. The motion of such waves is controlled by the restoring force of gravity rather than by the surface tension of the fluid.
2) Not to be confounded with → gravitational wave.

gravity; → wave.

gravo-turbulence
  گرانی-آشوبناکی   
gerâni-âšubnâki

Fr.: gravo-turbulence   

The interplay between supersonic turbulence and self-gravity in star forming gas.

Gravo-, from grav-, from → gravity + epenthetic vowel -o- + → turbulence.

gray
  خاکستری   
xâkestari (#)

Fr.: gris   

(n.) A color between white and black. (adj.) Having a neutral hue.

M.E., O.E. græg, from P.Gmc. *græwyaz; cf. O.N. grar, O.Fris. gre, Du. graw, Ger. grau; Frank. *gris, Fr. gris.

Xâkestari, "ash-colored," from xâkestar "ashes," from Mid.Pers. *xâkâtur, from xâk "earth, dust" + âtur "fire," varaint âtaxš (Mod.Pers. âtaš, âzar, taš), from Av. ātar-, āθr- "fire," singular nominative ātarš-; O.Pers. ātar- "fire;" Av. āθaurvan- "fire priest;" Skt. átharvan- "fire priest;" cf. L. ater "black" ("blackened by fire"); Arm. airem "burns;" Serb. vatra "fire;" PIE base *āter- "fire."

gray (Gy)
  گری   
gray

Fr.: gray   

An SI unit of absorbed radiation dose. One gray is equivalent to an energy absorption of 1 → joule/kg. It has replaced the → rad (rd), an older standard. One gray is equivalent to 100 rad.

Named for Louis Harold Gray (1905-1965), British radiologist and the pioneer of use of radiation in cancer treatment.

gray atmosphere
  جّو ِ خاکستری، هواسپهر ِ ~   
javv-e xâkestari, havâsepher-e ~

Fr.: atmosphère grise   

A simplifying assumption in the models of stellar atmosphere, according to which the absorption coefficient has the same value at all wavelengths.

gray; → atmosphere.

gray body
  جسم ِ خاکستری   
jesm-e xâkestari (#)

Fr.: corps gris   

A hypothetical body which emits radiation at each wavelength in a constant ratio, less than unity, to that emitted by a black body at the same temperature.

gray; → body.

graze
  برمژیدن   
barmažidan (#)

Fr.: raser, frôler, effleurer   

To touch or rub lightly in passing.

Perhaps special use of graze "to feed on grass," from M.E. grasen, O.E. grasian.

Barmažidan, from Choresmian parmž "to touch, to rub," variants barmajidan, majidan, parmâsidan, Mid.Pers. pahrmâh- "to touch, to feel;" ultimately from Proto-Ir. *pari-mars-, from *Hmars-, *Hmarz- "to touch, rub, wipe;" probably related to marz "border, frontier," mâlidan "to rub, polish."

grazer
  برمژنده   
barmžandé

Fr.: rasant   

A thing that grazes.

Agent noun of → graze.

grazing
  ۱) برمژنده؛ ۲) برمژ   
1) barmažandé; 2) barmaž

Fr.: 1) rasant; 2) rasage, frôlement, effleurement   

1) Describing something that grazes. → grazing angle, → grazing occultation.
2) The act of touching or rubbing lightly in passing.

graze; → -ing.

grazing incidence
  فتاد ِ برمژنده   
fotâd-e barmažandé

Fr.: incidence rasante   

Light striking a surface at an angle almost perpendicular to the normal. → grazing-incidence telescope.

grazing; → incidence.

grazing occultation
  فروپوشانش ِ برمژنده   
forupušâneš-e barmažandé

Fr.: occultation rasante   

A special type of occultation that occurs when the star appears to pass tangentially on the → edge of the → Moon.

grazing; → occultation.

<< < -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 > >>