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
bistability
  دو-پایداری   
do-pâydâri

Fr.: bistabilité   

The condition in which a physical system is capable of assuming either of two stable states.

bi-; → stable.

bistability jump
  جهش ِ دو-پایداری   
jaheš-e do-pâydâri

Fr.: bistabilité par saut   

An abrupt discontinuity in the → stellar wind properties of → hot stars near → effective temperatures about 21,000 K and 10,000 K, corresponding to O9.5-B3 supergiants (Castor et al. 1975, ApJ 195, 157; Lamers et al., 1995, ApJ 455, 269). At these temperatures the → terminal velocity of the wind drops steeply by about a factor two and the → mass loss rate increases steeply by about a factor three to five, when going from high to low temperatures. Bistability jump is related to the degree of ionization in the wind. With a little drop in the temperature, the dominant driving element (Fe) will recombine to lower ionization stages which produces a lower terminal velocity and a relatively high density in the wind. → wind momentum. Additional bistability jumps may occur at higher temperatures where CNO may provide the dominant line driving, especially for low metallicity stars (Vink et al. 2001, A&A 369, 574). However, a recent study using a larger sample finds that there is a gradual decline in the wind terminal velocities of early B supergiants and not a "jump" (Crowther et al. 2006, A&A 446, 279).

bistability; → jump.

bistability mechanism
  سازوکار ِ دو-پایداری   
sâzokâr-e do-pâydâri

Fr.: mécanisme de bistabilité   

The mechanism that accounts for the → bistability jump.

bistability; → mechanism.

bit
  بیت، رقم ِ درین   
bit, raqam-e dorin

Fr.: bit   

A contraction of → binary digit, either 0 or 1.

Bit, from binary + digit

bivalent
  دو-ارز   
do-arz

Fr.: bivalent   

1) Chem.: Having a → valence of two or having two valences.
2) → bivalent logic.

bi-; → valence.

bivalent logic
  گوییک ِ دو-ارز   
guyik-e do-arz

Fr.: logique bivalente   

A logical system, such as → classical logic, in which every declarative sentence expressing a → proposition has exactly one → truth value, either → true or → false. Bivalent logic is just a sub-set of a more powerful type of logic known as → fuzzy logic. See also → polyvalent logic.

bivalent; → logic.

BL Lac object
  بر‌آخت ِ BL چلپاسه   
barâxt-e BL Calpâsé

Fr.: objet BL Lac   

A member of a family of → quasars, or extragalactic → Active Galactic Nuclei, which displays a high radio emission and/or important optical variability over a short period of time. BL Lac objects appear star-like but their spectrum is flat, and partially polarized. Also called → blazars.

BL Lac, from object BL in the constellation → Lacerta (BL Lacertae). The reason for this terminology is that it was originally thought to be an irregular variable star in our Galaxy; hence its variable star designation. In the 1970s the "star" was identified with a bright, variable → radio source and a very faint galaxy; → object.

Blaauw mechanism
  ساز-و-کار ِ بلاؤ   
sâzokâr-e Blaauw

Fr.: mécanisme de Blaauw   

A mechanism aimed at explaining the → disruption of a → binary system. As one component loses mass dramatically, the resulting loss of → gravitational attraction changes the orbit of, or ejects completely, the → companion star.

Adriaan Blaauw (1914-2010), 1961, Bull. Astron. Inst. Netherlands 15, 265; → mechanism.

black
  سیاه، سیه   
siyâh (#), siyah (#)

Fr.: noir   

Very dark in color; absorbing light without reflecting any of its various rays.

Black, from O.E. blæc "black," from P.Gmc. *blak-, from PIE *bhelg- "to shine, flash, burn" (cf. Gk. phlegein "to burn, scorch," L. flagrare "to blaze, glow, burn," fulgur "lightning").

Siyâh or siyah, from Mid.Pers. siyâ, siyâk, siyâvah "black," Av. sâma-, sayâva- "black, dark," cf. Skt. syama-, syava- "black, brown," Gk. skia "shadow."

black drop
  چکه‌ی ِ سیاه   
cekke-ye siyâh

Fr.: goutte noire   

The appearance of a band linking the solar limb to the disk of a transiting planet (Venus or Mercury) near the point of internal tangency. This effect increases the uncertainty in measuring the period from when the planet fully enters the solar disk to when it begins to depart. Historically, the black drop phenomenon limited the accuracy of the determination of the Astronomical Unit and the scale of the Solar System in the 18th and 19th centuries. While there have been many proposed theories over the years, the true cause of the effect was revealed during a transit of Mercury in 1999, which was observed by the NASA's TRACE satellite. Two effects could fully explain the black drop: the inherent blurriness of the image caused by the finite size of the telescope (→ point spread function), and an extreme dimming of the Sun's surface just inside the apparent outer edge (→ limb darkening). See Schneider et al. 2004, Icarus 168, 249.

black; → drop.

black hole
  سیه‌چال، ~ سوراخ   
siyah câl (#), ~ surâx (#)

Fr.: trou noir   

A fantastically → compact object, predicted by the theory of → general relativity, whose → gravity is so powerful that not even light can escape from it. A black hole forms when matter → collapses to → infinite  → density, producing a → singularity of infinite → curvature in the fabric of → space-time. Each black hole is surrounded by an → event horizon, at which the → escape velocity is the → speed of light. The → Schwarzschild radius for the Sun is about 3 km and for the Earth about 1 cm. There is observational evidence for black holes on a remarkable range of scales in the Universe: → stellar black hole, → intermediate-mass black hole, → primordial black hole, → mini black hole, → supermassive black hole, → Schwarzschild black hole, → Kerr black hole.

Historically, the Newtonian concept of such a celestial body appeared at the end of the 18th century when light was shown to have particle characteristics. In fact the English geologist John Mitchell (1724-1793) and French mathematician and astronomer Pierre Simon Laplace (1749-1827), independently, suggested that regions of space, where gravitational attraction was so strong that not even light could escape, may exist in the Universe. However, the term black hole was coined in 1967 by the Princeton physicist John A. Wheeler (1911-2008); → black; → hole.

black hole binary
  سیه‌چال ِ درین   
siyah câl-e dorin

Fr.: trou noir binaire   

A → binary system in which each component is a → black hole. The binary's evolution can be divided into three stages: → inspiral, → merger, and → ringdown.

black; → hole; → binary.

black hole candidate
  نامزد ِ سیه‌چال   
nâmzad-e siyah câl (#)

Fr.: candidat trou noir   

An object that seems likely to be a → black hole, but waits for more observational confirmations.

black; → hole; → candidate.

black hole corona
  تاج ِ سیه‌چال   
tâj-e siyah câl

Fr.: couronne du trou noir   

A spherical volume of hot plasma over a broader → accretion disk around a → black hole. The observation of energetic X-ray emission from black holes, which is inconsistent with → thermal emission from an accretion disk, is attributed to the presence of a putative hot corona. It has been widely postulated that the → hard X-rays are the product of → inverse Compton scattering of seed photons from accretion disks by hot ccoronae (See, e.g., F.L. Vieyro et al., 2010, arXiv:1005.5398 and R. C. Reis & J. M. Miller, 2013, arXiv:1304.4947).

black; → hole; → corona.

black hole merger
  تشک ِ سیه‌چالها   
tašk-e siyah-câlhâ

Fr.: fusion de trous noirs   

The collision of two → black holes in a → binary black hole system once they come so close that they cannot escape each other's gravity. They will merge in an extremely violent event to become one more massive black hole. The merger would produce tremendous energy and send massive ripples, called → gravitational waves, through the → space-time fabric of the Universe. Such an event (called GW150914) was first detected by the → Laser Interferometer Gravitational-Wave Observatory (LIGO) on September 14, 2015. The initial black hole masses were 36 and 29 Msun which gave a final black hole mass of 62 Msun, with 3 Msun radiated in gravitational waves. The event happened at a distance of 1.3 billion → light-years from Earth (Abbott et al., 2016, Phys. Rev. Lett. 116, 061102). Black hole merger is preceded by → inspiral and followed by → ringdown.

black; → hole; → merger.

black hole surface gravity
  گرانی ِ رویه‌ی ِ سیه‌چال   
gerâni-ye ruye-ye siyah câl

Fr.: gravité de surface de trou noir   

The acceleration of gravity at the → event horizon of a → black hole. For a → Schwarzschild back hole it is given by κ = GM/RSch2 = c4/(4GM).

black; → hole; → surface; → gravity.

black hole's shadow
  سایه‌ی ِ سیه‌چال   
sâye-ye siyah-câl

Fr.: ombre de trou noir   

A gravitationally lensed image of a → black hole as seen by a distant observer if the black hole is in front of a bright background. According to → general relativity, photons circling the black hole slightly inside the boundary of the → photon sphere will fall down into the → event horizon, while photons circling just outside will escape to infinity. The shadow appears therefore as a rather sharp boundary between bright and dark regions and arises from a deficit of those photons that are captured by the event horizon. Because of this, the diameter of the shadow does not depend on the photons energy, but uniquely on the → angular momentum of the black hole. In a pioneering study, Bardeen (1973) calculated the shape of a dark area of a → Kerr black hole, that is, its "shadow" over a bright background appearing, for instance, in the image of a bright star behind the black hole.

black; → hole; → shadow.

black string
  ریسمان ِ سیاه   
rismân-e siyâh

Fr.: corde noire   

The extension of the → black hole concept in a → space-time with → dimensions higher than 4. Theoretically, it is possible to extend the 4D black hole with S2 horizon into the fifth dimension producing a hypercylindrical black hole S2× R. Black strings are unstable; it is not yet well understood whether they end up as black holes or different objects.

black; → string.

black-widow pulsars
  تپارها‌ی ِ سیاه-بیوه، پولسارها‌ی ~   
tapârhâ-ye siyâh-bivé, pulsârhâ-ye ~

Fr.:   

A class of binary millisecond pulsars in which the pulsar is eclipsed by its stellar companion, and the companion is being gradually ablated by the relativistic wind of the pulsar. The first system discovered in 1988 was PSR 1957+20, a 1.6074 millisecond in a near circular 9 hr orbit around a low-mass companion star.

Black widow, a venomous spider (Latrodectus mactans), shiny, coal black in color, that lives in North and South America. The female averages 8-10 mm in length and has long slender legs and a round abdomen. → black; widow, from O..E. widewe, widuwe, from P.Gmc. *widewo (cf. Du. weduwe, weeuw, Ger. Witwe), from PIE *widhewo (cf. Av. viδavâ-, Mid.Pers. wêwag, Mod.Pers. bivé, Skt. vidhava-, L. vidua, Rus. vdova,); → pulsar.

Tapâr , → pulsar; siyâh-bivé "black widow," from siyâh, → black + bivé, akin to E. widow, as explained above.

blackbody
  سیه‌جسم   
siyah-jesm (#)

Fr.: corps noir   

A theoretical object that is simultaneously a perfect → absorber (it does not reflect any radiation) and a perfect → emitter of → radiation in all → wavelengths and whose radiation is governed solely by its → temperature. Blackbody radiation cannot be explained by → classical physics. The study of its characteristics has, therefore, played an important role in the development of → quantum mechanics. A blackbody can be realized in the form of a cavity with highly absorbing internal walls and a small aperture. Any ray entering through the aperture can leave the cavity only after repeated reflection from the walls. When the aperture is sufficiently small, therefore, the cavity will absorb practically all the radiation incident on the aperture, and so the surface of the aperture will be a black body. The light within the cavity will always interact and exchange energy with the material particles of the walls and any other material particles present. This interaction will eventually → thermalize the radiation within the cavity, producing a → blackbody spectrum, represented by a → blackbody curve.
See also → blackbody photosphere; → blackbody radiation; → Planck's blackbody formula; → Planck's radiation law; → Rayleigh-Jeans law; → Stefan-Boltzmann law; → thermalization; → Wien's displacement law.

black; → body.

<< < -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 > >>