An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13048 Search : far
ultra-high-energy neutrino
  نوترینو‌ی ِ اولتر-مه‌کاروژ   
notrino-ye ultar-meh-kâruž

Fr.: neutrino ultra haute énergie   

A neutrino particle accelerated to energies above 1018 → electron-volts. They are produced by the interaction of → ultra-high-energy cosmic ray (UHECR)s with the → cosmic microwave background radiation. Also called → cosmogenic neutrinos. See also → Greisen-Zatsepin-Kuzmin limit.

ultra-; → high; → energy; → neutrino.

ultracompact
  اولتر-همپک   
ultar-hampak

Fr.: ultracompact   

Extremely compact with respect to a comparison value. → ultracompact H II region, → ultracompact dwarf galaxy.

ultra-; → compact.

ultracompact dwarf galaxy (UCD)
  کهکشان ِ کوتوله‌ی ِ اولتر-همپک   
kahkešân-e kutule-ye ultar-hampak

Fr.: galaxie naine ultracompacte   

A type of very bright compact → stellar system (-14 ≤ MV≥ -12) that is intermediate between → globular clusters (GCs) and → compact elliptical galaxies (cEs). With masses of M > 2 × 106 Msun and radii > 10 → parsecs (pc), UCDs are among the densest stellar systems in the Universe. Nevertheless, the nature and origin of these objects is still widely debated. Early interpretations suggested that UCDs could be the most massive GCs or possibly the → tidally stripped remnants of → dwarf galaxies. However, there is evidence that both formation mechanisms could contribute to the UCD population. → Supermassive black holes (SMBHs) have been confirmed in most UCDs with masses M > 107 Msun. The most massive UCD discovered to date, M59-UCD3 (M* ~ 2 × 108 Msun, radius ~ 25 pc), hosts a SMBH (Ahn et al., 2018, arxiv/1804.02399, and references therein).

ultracompact; → dwarf; → galaxy.

ultracompact H II region
  ناحیه‌ی ِ H IIی ِ اولتر-همپک   
nâhiye-ye H II-ye ultar hampak

Fr.: région H II ultracompacte   

A very young → H II region fully embedded in its natal molecular cloud. Ultracompact H II regions are distinguished from classical H II regions by their small sizes (diameter ≥ 0.1 pc), high densities (Ne ≥ 105 cm-3), and high emission measures (EM ≥ 107 pc cm-6). Their typical ionized gas content is about 10-2  → solar masses, in contrast to classical H II regions with a mass of about 105 solar masses. Due to very important extinction, ultracompact H II regions are not accessible to visible wavelengths.

ultra-; → compact; → H II region.

ultracool dwarf
  کوتوله‌ی ِ اولترسرد   
kutule-ye ultarsard

Fr.: naine ultrafroide   

A star-like objects with an → effective temperature of less than 2,700 K. Ultracool dwarfs constitute a heterogeneous group including stars of extremely low mass as well as → brown dwarfs, and represent about 15% of the population of astronomical objects near the Sun.

ultra-; → cool; → dwarf.

ultraluminous
  اولتر-تابان   
ultar-tâbân

Fr.: ultralumineux   

The quality of an object whose → luminosity exceeds a certain value.

ultra-; → luminous.

ultraluminous infrared galaxy (ULIRG)
  کهکشانِ فروسرخ ِ اولتر-تابان   
kahkešân-e forusorx-e ultar-tâbân

Fr.: galaxie ultralumineuse en infrarouge   

A galaxy that emits more than 90% of its energy in the infrared (8-1000 µm) and whose infrared luminosity exceeds 1012 solar luminosities. → luminous infrared galaxy (LIRG). Quasars can also have such high or even higher bolometric luminosities. However LIRGs and ULIRGs emit the bulk of their energy in the infrared. Most of ULIRGs are found in merging and interacting galaxy systems. It is thought that their luminosity results from galactic collisions, which increase the rate of star formation.

ultraluminous; → infrared; → galaxy.

ultraluminous X-ray source (ULX)
  خن ِ پرتو ِ ایکس ِ اولتر-تابان   
xan-e partow-e iks-e ultar-tâbân

Fr.: source ultralumineuse en rayons X   

An X-ray source that is not in the nucleus of a galaxy, and is more luminous than 1039 ergs s-1, brighter than the → Eddington luminosity of a 10 → solar mass → black hole. In general, there is about one ULX per galaxy in galaxies which host ULXs. The Milky Way contains no such objects. ULXs are thought to be powered by → accretion onto a → compact object. Possible explanations include accretion onto → neutron stars with strong → magnetic fields, onto → stellar black holes (of up to 20 → solar masses) at or in excess of the classical Eddington limit, or onto → intermediate-mass black holes (103-105 solar masses). NGC 1313X-1, NGC 5408X-1, and NGC 6946X-1 are three ULXs with X-ray luminosities up to ~ 1040 erg s-1 (Ciro Pinto et al., 2016, Nature 533, N) 7601).

ultraluminous; → X-ray source.

ultrarelativistic
  اولتر-بازانیگی‌مند   
ultar-bazânigimand

Fr.: ultrarelativiste   

Describing a system or situation for which the → Lorentz factor, γ, is much larger than 1. See also → subrelativistic.

ultra- + → relativistic

ultrarelativistic gas
  گاز ِ اولتر-بازانیگی‌مند   
gâz-e ultar-bazânigimand

Fr.: gaz ultrarelativiste   

A gas composed of ultrarelativistic particles.

ultrarelativistic; → gas.

ultrashort-period Cepheid
  کفیءوسی ِ اولتر-کوتاه-دوره   
Kefeid-e ultar-kutâh-dowré

Fr.: céphéide à très courte période   

A → Cepheid star of → spectral type A-F with regular pulsation period of 1-3 hours and with small variations in amplitude. This group is also known as δ Scuti stars.

ultra-; → short; → period; → Cepheid.

ultrasonics
  اولتر-صداییک، اولتر-سداییک   
ultar-sedâyik

Fr.: physique des ultra-sons   

The branch of physics dealing with elastic waves of frequencies above 20 kHz to 1010 kHz propagated in solids, liquids, and gases.

ultra-; sonic from L. sonussound + → -ics.

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.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer AGB air Alf Alg all alp alt AM amo ana And ang ani ano Ant Ant apa apo app app Ara Arc ari Arr ash ass ast ast asy atm ato att aut ave axi Bab bal Bal bar bar bea Bek Bes bia Big bin bin bip biv bla bli blu Boh Bol Bos bou bra bri bro buo cal cal can cap car Car cat cat CCD Cen cen CH cha cha che Che chr cir cir cit 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 con Cop Cor cor cor cos cos cou cou Cow cre cri cro cry cur cya Cyg dan dar dat de- deb dec dec ded def deg del dem den dep des det dev dia dif dif dih dio Dir dis dis dis dis dis dis DO don dou dow dro dur dwa dyn Dys ear ebb ecl edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ esc eth Eur Eve exa exc exe exi exp exp ext ext ext fac fal far fed Fer fer fie fin fir fis fla flo flu fol for for fou fra fre Fre fro fut G-t gal gal gam gas Gau Gem gen geo geo geo gia Gli Gol gra gra gra gra gre gri gui H I Hag hal har hat He- hea hel Hel her Hes hie hig his hom hor hot Hub Hug hur hyd hyd hyg hyp ice ide ima Ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv Io ion iro isl iso iso Jac jet jud jur Kel Kep kil Klo Kui Lag lam Lap Lar lat law lea len lep Lib lig lim lin lin Lio lit loc LOF lon Lor low lum lun Lup Lyo mac mag mag mag mag mag mai man Mar mas mas mat Max mea mec Meg Mer Mer met met Met mic Mid Mil min Mir mit mod mod mol mon Mor mou mul mul mys nan Nat nau nec neo neu nev New NGC no nom non non nor not nuc nuc num nut obj obs obs occ ocu oft ome Oor ope opp opt opt orb ord ori ort osc out ove oxi pai pan par par par par pas pea pen per per per per Per per pha phi pho pho pho phy pio Pla pla pla pla Pla plu Poi pol pol pol poo pos pos pot pra pre pre pre pre pri pri pro pro pro pro pro Pro pro pse pul pur qua qua qua qua que rac rad rad rad rad rad rad ran rar ray rea rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot Rus Sac sal sat sca sca Sch sci Scu sec sec Sed sel Sel sen ser Sex Sha she sho sid sig sil sim sin siz sla Sma sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spi spr 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 tek tem ter tes the the the the Tho thr tid tim Tis Too Tor tra tra Tra tra tra tri tri tru Tul tur two Typ ult un- und uni uni unk upp Urc utt val var vec vel ver vib vio vir vis voi vor wan wat wav wax wea Wei whi Wil win WN9 wor X-r yel you zer zod > >>