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
Lamb shift
  کیب ِ لمب   
kib-e Lamb

Fr.: décalage de Lamb   

A tiny change in the → energy levels of the → hydrogen atom between the states 2S1/2 and 2P1/2, which creates a shift in the corresponding → spectral lines. The 2P1/2 state is slightly lower than the 2S1/2 state, contrarily to the Schrodinger's solution. The difference is explained by the interaction between → vacuum energy fluctuations and the hydrogen electron in different orbitals.

Named after Willis Eugene Lamb, Jr. (1913-2008), an American physicist who discovered this effect in 1951, and won the Nobel Prize in physics in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum;" → shift.

lambda
  لامبدا   
lâmbdâ

Fr.: lambda   

The eleventh letter of the Greek alphabet. In lower case, λ, it denotes → wavelength. It is also used in the → Bayer designation system to identify a specific star in a → constellation. See also → lambda point.
In upper case, Λ, it represents the → cosmological constant or → dark energy.

From Phoenician lamedh.

Lambda Bootis star
  ستاره‌ی ِ لامبدا گاوران   
setâre-ye lâmbda Gâvrân

Fr.: étoile lambda du Bouvier   

The prototype of a small class of stars (A-F types) which have weak metallic lines (indicating that they are depleted in metals heavier than Si, but with solar abundances of C, N, O, and S). Moreover, they have moderately large rotational velocities and small space velocities. Lambda Boo stars may be pre-main-sequence objects, or they may be main sequence stars that formed from gas whose metal atoms had been absorbed by interstellar dust.

Named after the prototype, the star → Lambda (λ) of constellation → Bootes; → star.

lambda cold dark matter model
  مدل ِ لامبدا-ماده‌ی-سرد ِ- تاریک   
model-e lâmbdâ-mâde-ye-sard-e-târik

Fr.: modèle ΛCDM   

The → standard model of → Big Bang that incorporates both → dark matter and → dark energy. See also → cold dark matter (CDM).

lambda, → cosmological constant; → cold; → dark; → matter; → model.

Lambda Orionis
  لامبدا-شکارگر، ~-اریون   
Lâmbdâ-Šekârgar, ~-Oryon

Fr.: Lambda (λ) Orionis   

Same as → Meissa.

Lambda (λ), a Greek letter used in the → Bayer designation of star names.

lambda point
  نقطه‌ی ِ لامبدا   
noqte-ye lâmbdâ

Fr.: point lambda   

The temperature (roughly 2.17 K) at which → liquid helium (→ helium I) becomes → superfluid (→ helium II).

The name was given by the Dutch physicist Willem Hendrik Keesom (1876-1956), who discovered the behavior of helium near this transition point and successfully solidified helium in 1926 (under an external pressure of 25 atmospheres). The name was originally suggested by Paul Ehrenfest (1880-1933), who was inspired by the shape of the → specific heat curve, which resembles the Gk. letter → lambda; → point.

lambert
  لامبرت   
lambert

Fr.: lambert   

A centimeter-gram-second (cgs) unit of luminance (or brightness) equal to 1/π candle per square centimeter. Physically, the lambert is the luminance of a perfectly diffusing white surface receiving an illuminance of 1 lumen per square centimeter.

Johann Heinrich Lambert (1728-1777), German scientist and mathematician; → law.

Lambert's cosine law
  قانون ِ کوسینوس ِ لامبرت   
qânun-e cosinus-e Lambert

Fr.: loi en cosinus de Lambert   

The intensity of the light emanating in any given direction from a perfectly diffusing surface is proportional to the cosine of the angle between the direction and the normal to the surface. Also called → Lambert's law.

lambert; → cosine; → law.

Lambert's law
  قانون ِ لامبرت   
qânun-e Lambert

Fr.: loi de Lambert   

Same as → Lambert's cosine law.

lambert; → law.

Lambertian disk
  گرده‌ی ِ لامبرتی، دیسک ِ ~   
gerde-ye Lamberti, disk-e ~

Fr.: disque lambertien   

A → planetary or → satellite disk with → Lambertian surface. Such a disk has the same → surface brightness at all angles.

lambert; → disk.

Lambertian surface
  رویه‌ی ِ لامبرتی   
ruye-ye Lamberti

Fr.: surface lambertienne   

A surface whose → luminous intensity obeys → Lambert's cosine law. Such a source has a → reflectance that is uniform across its surface and uniformly emits in all directions from all its points. It appears equally bright from all viewing directions. Lambertian surface is a very useful concept for the approximation of radiant power transfer.

lambert; → surface.

lament
  ۱) شکوه؛ ۲) شکویدن   
1) šekvé (#); šekvidan

Fr.: 1) lamentation, grief; 2) se lamenter   

1a) A real or imagined cause for → complaint, especially unfair treatment.
1b) A feeling of resentment over something believed to be wrong or unfair.
2) To feel or express sorrow or regret for; to mourn for or over (OxfordDictionaries.com).

M.E., from M.Fr. lament and directly from L. lamentum "a wailing, moaning, weeping" from lamentum "a wailing," from PIE root *la- "to shout, cry."

Šekvé, Pers. construction from Ar. šakvâ "complaint."

lamina
  ورقه   
varaqé (#)

Fr.: lame, lamina   

A thin plate, layer, or flake.

From L. lamina "thin plate or layer, leaf."

Varaqé "sheet, plate," from varaq "a leaf of tree or of paper," from Ar. waraq, from Pers. barg "leaf" (Tabari, Gilaki valg, balg; Kurd. belg, balk, Semnâni valg); Mid.Pers. warg "leaf;" Av. varəka- "leaf;" cf. Skt. valká- "bark, bast, rind;" Russ. volokno "fibre, fine combed flax."

laminar
  ورقه‌ای   
varaqe-yi

Fr.: laminaire   

Composed of, or arranged in, laminae, sheets.

lamina + → -ar.

laminar boundary layer
  لایه‌ی ِ کرانی ِ ورقه‌ای   
lâye-ye karâni-ye varaqe-yi

Fr.: Couche limite laminaire   

In a fluid flow, layer next to a fixed boundary. The fluid velocity is zero at the boundary but the molecular viscous stress is large because the velocity gradient normal to the wall is large. → turbulent boundary layer.

laminar; → boundary; → layer.

laminar flow
  تچان ِ ورقه‌ای   
tacân-e varaqe-yi

Fr.: écoulement laminaire   

A flow in which the particles of fluid are moving orderly, and in which adjacent layers or laminas glide smoothly over another with little mixing between them. A laminar flow may rapidly transform into a → turbulent flow for large → Reynolds numbers.

laminar; → flow.

laminar sublayer
  زیرلایه‌ی ِ ورقه‌ای   
zirlâye-ye varaqe-yi

Fr.: sous-couche laminaire   

A layer in which the fluid undergoes smooth, nonturbulent flow. It is found between any surface and a turbulent layer above.

laminar; sublayer, from → sub- + → layer.

lamp
  لامپ، چراغ   
lâmp (#), cerâq (#)

Fr.: lampe   

Any of various devices producing artificial light, as by electricity, gas, or oil.

From O.Fr. lampe, from L. lampas, from Gk. lampas "torch, lamp, beacon, meteor, light," from lampein "to shine," from PIE base *lap- "to shine" (cf. Lith. lope "light," O.Ir. lassar "flame").

Lâmp, loanword from Fr., as above.
Cerâq "lamp" (variants Kurd. cira, cerâh, Laki cerâx, Zâzâ cərâ, cərâx "lamp, candle," Shughni cirow, cirâw, cərêγ "candle, lamp"); Mid.Pers. cirâq "lamp," related to foruq "light," afruxtan "to light, kindle," rowšan "bright, clear," rowzan "window, aperture;" ruz "day;" Mid.Pers. rôšn "light; bright, luminous," rôc "day;" O.Pers. raucah-rocânak "window;" O.Pers. raocah- "light, luminous; daylight;" Av. raocana- "bright, shining, radiant;" akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" L. lux "light" (also lumen, luna); Fr. lumière; E. light; O.E. leoht, leht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- "light, brightness."

land
  خشکی، زمین   
xoški (#), zamin (#)

Fr.: terre   

Any part of the earth's surface not covered by a body of water.

M.E., from O.E. land, lond, "ground, soil, territory;" PIE base *lendh- "land, heath" (cf. O.N., O.Fris. Du., Ger., Goth. land; O.Ir. land; Welsh llan "enclosure, church," Breton lann "heath," source of Fr. lande; O.C.S. ledina "waste land, heath," Czech lada "fallow land").

Xoški, from xošk, → dry, + noun suffix -i; zamin "land, → earth."

land breeze
  نسیم ِ خشکی   
nasim-e xoški (#)

Fr.: brise de terre   

A coastal breeze blowing from land to sea after sunset, caused by the temperature difference when the sea surface is warmer than the adjacent land. The warmer air above the water continues to rise, and cooler air from over the land replaces it, creating a breeze.

Land, → lander; → breeze.

Xoški "land," from xošk "dry;" Mid.Pers. xušk "dry;" O.Pers. uška- "mainland;" Av. huška- "dry;" cf. Skt. śuska- "dry, dried out;" Gk. auos "dry, dried up;" O.E. sēar "dried up, withered;" Lith. sausas "dry, barren."

<< < -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 > >>