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
baryon-photon ratio
  وابر ِ باریون-فوتون   
vâbar-e bâriyon-foton

Fr.: rapport baryon-photon   

The → baryon number compared with the number of photons in the → Universe. The baryon-photon ratio can be estimated in a simple way. The → energy density associated with → blackbody radiation of → temperature  T is aT4, and the mean energy per photon is ~kT. Therefore, the number density of blackbody photons for T = 2.7 K is: nγ = aT4/kT = 3.7 x 102 photons cm-3, where a = 7.6 x 10-15 erg cm-3 K-4 (→ radiation density constant) and k = 1.38 x 10-16 erg K-1 (→ Boltzmann's constant). The number density of baryons can be expressed by ρm/mp, where ρm is the mass density of the Universe and mp is the mass of the → proton (1.66 x 10-24 g). → CMB measurements show that the baryonic mean density is ρm = 4.2 x 10-31 g cm-3 (roughly 5% of the → critical density). This leads to the value of ~ 2 x 10-7 for the number density of baryons. Thus, the baryon/photon ratio is approximately equal to η = nb/nγ = 2 x 10-7/3.7 x 102 ~ 5 x 10-10. In other words, for each baryon in the Universe there is 1010 photons. This estimate is in agreement with the precise value of the baryon-photon ratio 6.14 x 10-10 derived with the → WMAP. Since the photon number and the baryon number are conserved, the baryon-photon ratio stays constant as the Universe expands.

baryon; → photon; → ratio.

baryonic dark matter
  ماده‌ی ِ سیاه ِ باریونی   
mâde-ye siyâh-e bâriyoni

Fr.: matière noire baryonique   

Dark matter made up of → baryons that are not luminous enough to produce any detectable radiation. It is generally believed that most dark matter is → non-baryonic. The baryonic dark matter could reside in a number of forms, including cold gas and compact objects.

baryonic; → dark; → matter.

baryonic matter
  ماده‌ی ِ باریونی   
mâde-ye bâriyoni (#)

Fr.: matière baryonique   

Ordinary matter composed of → baryons, i.e. → protons and → neutrons, as distinct from → non-baryonic, exotic forms.

Adj. of → baryon; → matter.

basalt
  بازالت   
bâzâlt (#)

Fr.: basalte   

A dark fine-grained → igneous rock typically composed of → plagioclase with → pyroxene and → olivine and often displaying a columnar structure.

From L.L. basaltes, misspelling of L. basanites "very hard stone," from Gk. basanites, from basanos "touchstone," from Egyptian baban "a stone used by the Egyptians as a touchstone of gold."

base
  ۱، ۲، ۳، ۴) پایه، ۵) پایگاه، ۶) باز   
1, 2, 3, 4) pâyé (#), 5) pâygâh (#), 6) bâz (#)

Fr.: base   

1) The bottom support of anything; a fundamental principle or groundwork.
2) Geometry: The line or surface on which a figure is assumed to stand.
3) Arithmetic: The number which, raised to various powers, forms the main counting units of a system. Thus 10 is the base of the decimal system.
4) Logarithm: The number a in the equation N = ax. The base of common logarithm is 10.
5) A centre of operations or supply, such as a → database.
6) Chemistry: A substance that reacts with an acid to yield a salt and water.

M.E., from O.Fr. bas, from L. basis "foundation," from Gk. basis "step, pedestal," from bainein "to step."

Pâyé "base," from pâ, pây "foot," from Mid.Pers. pâd, pây; Av. pad-, cf. Skt. pat: Gk. pos, genitive podos; L. pes; PIE *pod-/*ped-.
Pâygâh, from pâyé + gâh "place" (O.Pers. gāθu-; Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come."
Bâz, loan from Fr., as above.

baseline
  پایه-خط   
pâye-xatt

Fr.: ligne de base   

1) In radio interferometry, the separation between the electrical, or phase centers of two interferometer elements.
2) In spectroscopy, the contribution to a spectrum from phenomena that are not of astronomical interest, such as frequency dependent properties of the receivers, or by astronomical sources other than those under study.

base; → line.

basic
  بازی   
bâzi (#)

Fr.: basique   

Chemistry: Of or denoting or of the nature of or containing a → base. Same as → alkaline.

base; → -ic.

basin
  حوضه   
howzé (#)

Fr.: bassin   

A large impact crater on a planet or moon, typically several hundred kilometers across, flooded with basaltic lava and surrounded by concentric rings of faulted cliffs.

From O.Fr. bacin, from V.L. *baccinum, from L. bacca "water vessel," perhaps originally Gaulish.

Howzé, from howz "pond, a large reservoir of water" (from Ar. hauz) + noun suffix.

battery
  باتری   
bâtri (#)

Fr.: batterie   

A combination of → cells connected together so as to produce useful electrical energy.

M.Fr. batterie "a grouping of artillery pieces for tactical purposes," from O.Fr. baterie "beatng, thrashing, assault," from battre "to beat," from L. battuere "to beat."

Bâtri, loanword from Fr., as above.

bay
  باهه   
bâhé

Fr.: baie   

A body of water forming an indentation of the shoreline, larger than a cove but smaller than a → gulf (Dictionary.com).

M.E. baye, from M.Fr. baie, from L.L. bâia, perhaps ultimately from Iberian bahia.

Bâhé, loan from Sp. bahia.

Bayer designation
  نامگزینی ِ بایر   
nâmgozini-ye bayer

Fr.: designation de Bayer   

A stellar designation system in which a specific star is identified by a Greek letter, followed by the genitive form of its hosting → constellation's Latin name. For example, Alpha Eridani, Delta Cephei, Lambda Bootis. The Greek alphabet has only 24 letters. In case a single constellation contained a larger number of stars, Bayer amended with Latin letters: upper case A, followed by lower case b through z (omitting j and v), for a total of another 24 letters. Bayer did not go beyond z, but later astronomers added more designations using both upper and lower case Latin letters, the upper case letters following the lower case ones in general. Examples include, for Vela: a Vel (Velorum), z Vel, A Vel, Q Vel; for Scorpius: d Sco (Scorpii), A Sco; for Leo: b Leo (Leonis), o Leo, A Leo, → c Orionis. Compare with the → Flamsteed designation.

First introduced by Johann Bayer (1572-1625) in his atlas Uranometria, published in 1603 at Augsburg, Germany; → designation.

Bayes' theorem
  فربین ِ بیز   
farbin-e Bayes

Fr.: théorème de Bayes   

A theorem in probability theory concerned with determining the → conditional probability of an event when another event has occurred. Bayes' theorem allows revision of the original probability with new information. Its simplest form is: P(A|B) = P(B|A) P(A)/P(B), where P(A): independent probability of A, also called prior probability; P(B): independent probability of B; P(B|A): conditional probability of B given A has occurred; P(A|B): conditional probability of A given B has occurred, also called posterior probability. Same as Bayes' rule.

Named after its proponent, the British mathematician Reverend Thomas Bayes (1702-1761). However, Bayes did not publish the theorem during his lifetime; instead, it was presented two years after his death to the Royal Society of London.

Bayesian
  بیزی   
Bayesi

Fr.: bayésien   

Being, relating to, or denoting statistical methods based on → Bayes' theorem.

Referring to → Bayes' theorem.

Bayesian inference
  دربرد ِ بیزی   
darbord-e Bayesi

Fr.: inférence bayésienne   

An approach to → statistical analysis in which → unknowns to be estimated have a prior → probability distribution which combined with the information from data produces a posterior probability distribution for the target quantities.

Bayesian; → inference.

Bayesian model
  مدل ِ بیزی   
model-e Bayesi

Fr.: modèle bayésien   

A mathematical framework described by the prior distribution of a random parameter and by the likelihood of the observations. In this framework, all information on the random parameter based on the observations is included in the posterior distribution which can be obtained using → Bayes' theorem (see, e.g., Andrieu et al., 2001, "An Introduction to Monte Carlo Methods for Bayesian Data Analysis," in Nonlinear Dynamics and Statistics, ed. A. I. Mees, Boston: Birkhäuser).

Bayesian; → model.

Bayesian model averaging (BMA)
  میانگین-گیری ِ بیزی ِمدل   
miyângin-giri-ye Bayesi-e model

Fr.:   

An approach to model selection in which one bases inference on an average of all possible models instead of a single best model. The BMA is largely used in various branches of knowledge to properly account for model uncertainty in performing predictions.

Bayesian; → model; → average.

Be phenomenon
  پدیده‌ی ِ Be   
padide-ye Be

Fr.: phénomène Be   

The episodic occurrence of abrupt → mass loss in → Be stars resulting in → Balmer lines in emission and → infrared excess. The Be phenomenon results from a combination of a long-term secular effect and short-term instabilities, such as pulsation. The secular evolution brings the star close enough to the critical → break-up velocity, so that the additional velocity field due to the instability may allow some mass ejection (Maeder 2011).

Be star; → phenomenon.

Be star
  ستاره‌یِ Be   
setâre-ye Be

Fr.: étoile Be   

A hot star of → spectral type B showing → Balmer lines in emission. Be stars are fast rotators (spinning at about 200 km/sec) and have strong → stellar winds with important → mass loss.

B, referring to the spectral type; e for emission lines; → star.

beam
  تابه   
tâbé (#)

Fr.: 1) faisceau, 2) lobe, 3) tache de diffraction   

1) A collection of nearly parallel → light  → rays or a concentrated stream of → particles. See also → beam of light.
2) The area of the sky being observed at any one time by a → radio telescope.
3) The size of the → diffraction pattern; synonymous with point spread function.

M.E. beem, from O.E. beam "tree;" akin to O.H.G boum "tree," Ger. Baum.

Tâbé, from tâb; tâbidan "light; to shine" + noun suffix.

beam efficiency
  کار‌آیی ِ تابه   
kârâi-ye tâbé

Fr.: efficacité de lobe   

A parameter indicating the quality of an antenna as a direction measuring device. It is given by the ratio of the total received power contained in the main beam of an antenna to the total power (including the sidelobes); the same as main beam efficiency. See also → beamwidth.

beam; → efficiency.

<< < -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 > >>