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: 12948 Search : far
ultrasound
  اولتر-صدا، اولتر-سدا   
ultar-sedâ

Fr.: ultra-son   

Sound with a frequency lying above the audition frequency range, usually taken to be about 20 kHz. → sound wave.

ultra- + → sound.

ultraviolet (UV)
  فرابنفش، اولتر-بنفش   
farâ-banafš, ultar-banafš

Fr.: ultraviolet   

The part of the electromagnetic radiation beyond the violet end of the visible spectrum with wavelengths approximately in the range 50 Å to 4,000 Å. → extreme ultraviolet; → far ultraviolet.

ultra-; → violet.

ultraviolet astronomy
  اخترشناسی ِ فرابنفش، ~ اولتر-بنفش   
axtaršenâsi-ye farâ-banafš, ~ ultar-banafš

Fr.: astronomie ultraviolette   

The study of astronomical objects in the ultraviolet portions of the electromagnetic spectrum, in the waveband 3000 Å to about 10 Å. At these wavelengths, the atmosphere prevents ultraviolet radiation from reaching the Earth surface. Therefore ground-based observatories cannot observe in the ultraviolet. Only with the advent of space-based telescopes has this area of astronomy become available for research.

ultraviolet; → astronomy.

ultraviolet catastrophe
  نگونزار ِ فرابنفش   
negunzâr-e farâbanafš

Fr.: catastrophe ultraviolette   

A → paradox encountered in the classical theory of → thermal radiation (→ Rayleigh-Jeans law), whereby a → blackbody should radiate an infinite amount of energy at infinitely short wavelengths, in contradiction with what is observed. The problem was solved by Max Planck in 1900, who suggested that, rather than being continuous, the energy comes in discrete parcels called → quanta. The avoidance of the ultraviolet catastrophe was one of the first great achievements of → quantum mechanics.

This problem was first raised by Lord Rayleigh (1842-1919), whereas the term ultraviolet catastrophe was first used by Paul Ehrenfest (1880-1933); → ultraviolet; → catastrophe.

ultraviolet excess
  فزونی ِ فرابنفش، فرهبود ِ اولتر-بنفش   
fozuni-ye farâbanafš, ferehbud-e ultar-banafš

Fr.: excès ultraviolet   

Ultraviolet emission from an object in excess of that expected for a reference. For example, → subdwarf stars show ultraviolet excess with respect to that expected from a star with → solar metallicity at a given → effective temperature. In this case, UV excess results from smaller → line blanketing in → population II stars.

ultraviolet; → excess.

ultraviolet star
  ستاره‌ی ِ فرابنفش، ~ ِ اولتر-بنفش   
setâre-ye farâbanafš, ~ ultar-banafš

Fr.: étoile ultraviolette   

A star, such as O types or hot central stars of planetary nebulae, which radiates essentially in the ultraviolet part of the electromagnetic spectrum.

ultraviolet; → star.

umbra
  سایه   
sâyé (#)

Fr.:ombre   

1) Optics: A dark area, especially the blackest part of a shadow from which all light is cut off. → penumbra.
2) Sun: The central darkest part of a → sunspot, which is also the coolest part (~ 4,200 K).

From L. umbra "shade, shadow."

Sâyé "shadow," from Mid.Pers. sâyak "shadow;" Av. a-saya- "throwing no shadow;" Skt. chāya- "shadow;" Gk. skia "shade;" Rus. sijat' "to shine;" M.H.G. schinen, O.H.G. skinan, Ger. Schein "glow, shine;" PIE base *skai- "bright."

Umbriel
  اومبریل   
Umbriel (#)

Fr.: Umbriel   

The thirteenth of Uranus's known satellites and the third largest. It has a diameter of 1170 km and orbits Uranus every 4.144 days at a mean distance of about 265,980 km. Umbriel is very dark, with an albedo of 0.18. It has a heavily cratered surface. Umbriel was discovered by William Lassell (1799-1880) in 1851.

Umbriel named for an evil spirit in Alexander Pope's (1688-1744) poem The Rape of the Lock. Moreover, Umbriel derives from L. → umbra "shadow," which fits the satellite's appearance.

un-
  نا-   
nâ- (#)

Fr.: in-, non-   

A prefix meaning "not."

M.E., O.E. un- (cf. O.Fris., O.H.G., Ger. un-, Goth. un-, Du. on-), cognate with Pers. nâ-, as below.

Nâ- "not," variants na "no, not," ma- "not" (prohitive); Mid.Pers. nê, ma "no, not;" O.Pers. naiy, nai "not;" Av. nôit, naē "not;" cf. Skt. "not;" L. ne-, in-, un-; Gk. ni; Lith. ; O.C.S. ne "not;" E. un-, as above; PIE *ne-.

unaided eye
  چشم ِ بی‌یاور، ~ ِ برهنه   
cašm-e biyâvar, ~ berehné

Fr.: œil nu   

The eye unassisted by an optical instrument, except for eyeglasses. Same as → naked eye.

un- + aided, from aid, M.E. ayde, from O.Fr. aidier, from L. adjutare, frequentative of adjuvare "to give help to," from → ad- "to" + juvare "to help;" → eye.

Cašm, → eye; biyâvar "without help," from bi- "without" + yâvar, variant yâr "helper; companion" (Mid.Pers. hayyâr "helper," hayyârêh "help, aid, assistance," Proto-Iranian *adyāva-bara-, cf. Av. aidū- "helpful, useful"); berehné, → naked.

unbiased
  بی‌وَرَک   
bi-varak

Fr.: non biaisé   

Not biased or prejudiced.
Statistics: With an expected value that is equal to the parameter being estimated.

un- + → biased.

Bi- "without" + varak, → bias.

unbiased estimator
  بر‌آور ِ بی‌وَرَک   
barâvar-e bi-varak

Fr.: estimateur non biaisé   

A sample statistics when the mean of the sampling distribution of that statistic can be shown to be equal to the parameter being estimated.

unbiased; → estimator.

unbiased sample
  نمونان ِ بی‌وَرَک   
nemunân-e a bi-varak

Fr.: échantillon non biaisé   

A sample in which every individual element in the population has an equal chance of being selected.

unbiased; → sample.

unblanketed model
  مدل ِ ناپتومند   
model-e nâpatumand

Fr.: modèle non blanketé   

A stellar atmosphere model which ignores metals and their physical effects. → line-blanketed model; → line blanketing.

un-; → blanketed model.

unbound
  نابندیده   
nâbandidé

Fr.: non lié   

1) Not bound or tied up.
2) Not held by a → chemical bond, → gravity, or other physical force (OxfordDictionaries.com).
See: → unbound charge, → unbound cluster, → unbound system.

un-; → bound.

unbound charge
  بار ِ نابندیده   
bâr-e nâbandidé

Fr.: charge non liée   

Same as → free charge.

unbound; → charge.

unbound cluster
  خوشه‌ی ِ نابندیده   
xuše-ye nâbandidé

Fr.: amas non lié   

A cluster of objects, such as stars or galaxies, in which the members are not tied together gravitationally. In such a cluster the members scatter through space following different directions. → bound cluster.

unbound; → cluster.

unbound system
  راژمان ِ نابندیده   
râžân-e nâbandidé

Fr.: système non lié   

An association of bodies which are not gravitationally tied together.

unbound; → system.

unbound young stellar system (UYSS)
  راژمان ِ ستاره‌ای ِ جوان ِ نابندیده   
râžmân-e setâre-yi-ye javân-e nâbandidé

Fr.: système stellaire jeune non lié   

A class of gravitationally loose stellar conglomerate with a notable apparent shape making it different from typical → bound  → star clusters. The UYSS class includes a large range of objects, which extend at various size scales and at various degrees of self-binding; from small (semi-)compact → unbound systems named → stellar associations, to huge extended superstructures of → massive stars that make up whole parts of Galactic → spiral arms, known as → stellar complexes (Gouliermis, D. A., 2018, PASP 130:072001; arXiv:1806.11541).

unbound; → young; → stellar; → system.

unbounded function
  کریای ِ بیکران   
karyâ-ye bikarân

Fr.: fonction non bornée   

The function y = f(x) in a given range of the argument x if there is no number M such that for all values of x in the range under consideration the inequality | f(x) | ≤ M will be fulfilled. → bounded function.

unbound; → function.

<< < -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 div dog Dop dou dra dua dus dwa dyn e-m ear ecl eco eff ein Ein elb ele ele ele ele Els emi emp ene enr env epi equ equ Eri est Euc eva evo exc exc exh exo exp exp ext ext f-n Fah fam fau fee Fer fib fil fin fir fix fle flu foc for for for fra fre fre fri fun fuz gal gal gal Gan gau GCN gen geo geo geo geo Gl glo gra gra gra gra gra gre gro GW1 hab hal han HAR haz hea hel hel Hen Her heu Hig Hil hol hop hor hou Hub Hum Hyd hyd hyd hyp hys ide ign ima imp imp inc inc ind ine inf inf inf inh INP ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jos Jun K2 Kep key kin Kol lag lam Lan lar las lav lea leg len lev lig lim lin lin lin lis lob loc log lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal mar mas mas mat max mea mea mee Men mer met met met mic mid Mil min Mir mix mod mod mol mon Mor mou mul muo mys nan nat nav nec Nep neu New New NGC nob nom non non nor not nuc nuc num Nyq obj obs obs oce oen OH omn opa ope opt opt opt orb ord Ori ort osc out ove oxy pal pan par Par par par pas pea Pen per per per per per pet pha pho pho pho phy pie Pit Pla pla pla pla ple Poi pol pol pol pol pop pos pos pow pre pre pre Pre pri pri pri pro pro pro pro pro pro Pro pub pul pyr qua qua qua qua Qui rad rad rad rad rad rad ram ran rat rea rec rec rec red ref ref reg reg rel rel rem rep res res res ret rev rho Rie rim riv rol Ros rot rul S a Sah san Sat sca Sch Sch scr sec sec sec sei sel sem sep set sha she sho sid sig sil sim sin sit sky slu sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spl spr sta sta sta sta sta ste ste sti sto str str sub sub sub sug sun sup sup sup sup sur syl syn sys tal Tay tel ten ter tex the the the thi tho thu tid tim tod top tot tra tra tra tra tri tri tro tru tur twi Typ UFO ult unc uni uni uni upg ura uti val var vec vel ver ver vig vir vis voc von wak Was wav wax wea wei whi Wie win WN6 wom X-r yel you zer zod > >>