An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 471
Boltzmann's constant
  پایای ِ بولتسمن   
pâyâ-ye Boltzmann

Fr.: constante de Boltzmann   

The physical constant, noted by k, relating the mean → kinetic energy of → molecules in an → ideal gas to their → absolute temperature. It is given by the ratio of the → gas constant to → Avogadro's number. Its value is about 1.380 x 10-16erg K-1.

Named after the Austrian physicist Ludwig Boltzmann (1844-1906), who made important contributions to the theory of statistical mechanics; → constant.

Boltzmann's entropy formula
  دیسول ِ درگاشت ِ بولتسمن   
disul-e dargâšt-e Boltzmann

Fr.: formule d'entropie de Boltzmann   

In → statistical thermodynamics, a probability equation relating the → entropy S of an → ideal gas to the quantity Ω, which is the number of → microstates corresponding to a given → macrostate: S = k. ln Ω. Same as → Boltzmann's relation.

Boltzmann's constant; → entropy; → formula.

Boltzmann's equation
  هموگش ِ بولتسمن   
hamugeš-e Boltzmann

Fr.: équation de Boltzmann   

1) An equation that expresses the relative number (per unit volume) of → excited atoms in different states as a function of the temperature for a gas in → thermal equilibrium: Nu/Nl = (gu/gl) exp (-ΔE/kTex), where Nu and Nl are the upper level and lower level populations respectively, gu and gl the → statistical weights, ΔE = hν the energy difference between the states, k is → Boltzmann's constant, and h  → Planck's constant.

Boltzmann's constant; → equation.

Boltzmann's relation
  باز‌آنش ِ بولتسمن   
bâzâneš-e Boltzmann

Fr.: relation de Boltzmann   

A relation between the → entropy of a given → state of a → thermodynamic system and the → probability of the state: S = k . ln Ω where S is the entropy of the system, k is → Boltzmann's constant, and Ω the thermodynamic probability of the state. Boltzmann's relation connects → statistical mechanics and → thermodynamics. Ω is the number of possible → microstates of the system, and it represents the → randomness of the system. The relation also describes the statistical meaning of the → second law of thermodynamics. This expression has been carved above Boltzmann's name on his tombstone in Zentralfreihof in Vienna. Same as → Boltzmann's entropy formula.

Boltzmann's constant; → relation.

band (#)

Fr.: lien   

The attractive force that holds together neighboring atoms in molecules.

Bond, variant of band, from M.E. bende, O.E. bend, from O.Fr. bande, bende, PIE *bendh- "to bind" (cf. Goth bandi "that which binds;" Av./O.Pers. band- "to bind, fetter," banda- "band, tie," Skt. bandh- "to bind, tie, fasten," bandhah "a tying, bandage").

Band "band, tie," from Mid.Pers., O.Pers./Av. band- "to bind," banda- "band, tie."

Bond albedo
  سپیدای ِ باند   
sepidâ-ye Bond

Fr.: albedo de Bond   

The fraction of the total amount of electromagnetic radiation falling upon a non-luminous spherical body that is reflected in all directions by that body. The bond albedo takes into account all wavelengths at all → phase angles. Compare with → geometric albedo.

Named after the American astronomer George Phillips Bond (1825-1865), who proposed it; → albedo.

Bondi-Hoyle accretion
  فربال ِ بوندی-هویل   
farbâl-e Bondi-Hoyle

Fr.: accrétion de Bondi-Hoyle   

The → accretion of mass by a star (assumed as point particle) moving at a steady speed through an infinite, uniform gas cloud. It is directly proportional to the star mass (M) and the medium density (ρ) and inversely proportional to the relative star/gas velocity (v). In its classical expression: 4πρ(G M)2 / v3, where G is the → gravitational constant. See Bondi & Hoyle (1944, MNRAS 104, 273) and Bondi (1952, MNRAS 112, 195). For a recent treatment of accretion in a turbulent medium see Krumholtz et al. 2006 (ApJ 638, 369).

Named after Hermann Bondi (1919-2005), an Anglo-Austrian mathematician and cosmologist and Fred Hoyle (1915-2001), British mathematician and astronomer best known as the foremost proponent and defender of the steady-state theory of the universe; → accretion.

Bondi-Hoyle accretion radius
  شعاع ِ فربال ِ بوندی-هویل   
šo'â'-e farbâl-e Bondi-Hoyle

Fr.: rayon de l'accrétion de Bondi-Hoyle   

In the → Bondi-Hoyle accretion process, the radius where the gravitational energy owing to star is larger than the kinetic energy and, therefore, at which material is bound to star. The Bondi-Hoyle accretion radius is given by RBH = 2 GM / (v2 + cs2) where G is the gravitational constant, M is the stellar mass, v the gas/star relative velocity, and cs is the sound speed.

Bondi-Hoyle accretion; → radius.

Bonner Durchmusterung (BD)
Bonner Durchmusterung

Fr.: Bonner Durchmusterung   

A catalog of 324,188 stars in the → declination zones +89 to -01 degrees. The goal of the survey was to obtain a → position and estimated → visual magnitude for every star visible with the 78 mm → refracting telescope at Bonn. Actual → magnitude estimates were made and reported to 0.1 mag for all stars down to 9.5 mag. Positions are given to the nearest 0.1 sec in → right ascension and 0.1 arcmin in declination. The survey was carried out by Friedrich W. Argelander (1799-1875) and his assistants in the years 1852-1861.

The Ger. name means Bonn Survey.

Bonnor-Ebert mass
  جرم ِ بونور-ابرت   
jerm-e Bonnor-Ebert

Fr.: masse de Bonnor-Ebert   

The largest gravitationally stable mass of the → Bonnor-Ebert sphere.

After W.B. Bonnor (1956) and R. Ebert (1955); → mass.

Bonnor-Ebert sphere
  سپهر ِ بونور-ابرت، کره‌ی ِ ~   
epehr-e Bonnor-Ebert, kore-ye ~

Fr.: sphère de Bonnor-Ebert   

A sphere of interstellar gas at uniform temperature in equilibrium under its own gravitation and an external pressure. The pressure of a hotter surrounding medium causes the sphere to collapse. → Bonnor-Ebert mass.

Bonnor-Ebert mass; → sphere.

  کتاب، نامه، نسک   
ketâb (#), nâmé (#), nask (#)

Fr.: livre   

A bound set of printed or manuscript pages.

M.E., from O.E. boc "book, written document;" cf. Ger. Buch "book;" Du. boek; O.N. bôk; Gothic boka.

Ketâb, loanword from Ar.
Nâmé "book, letter;" Mid.Pers. nâmag "book, letter, inscription;" O.Pers./Av. nāman- "name;" cf. Skt. nama-; Gk. onoma, onuma; L. nomen; PIE *nomen-.
Nask; Mid.Pers. nask "one of the book comprising Avesta;" Av. naska-, literally "bundle, bunch," naskô.frasa- "one who devotes himself to the study of nasks;" cf. Skt. nah- "to tie, bind," nahyati "he ties, binds;" L. nectere "to tie, bind," nodus "node;" O.Ir. nasc "a tie, bond, ring," nascim "I bind."

Booli (#)

Fr.: de Boole   

A → variable or → function which takes the value → true or → false. → Boolean algebra.

After the English mathematician George Boole (1815-1864), the founder of mathematical, or symbolic, logic.

Boolean algebra
  جبر ِ بولی   
jabr-e Booli (#)

Fr.: algèbre de Boole   

Any of a number of possible systems of mathematics that deals with → binary digits instead of numbers. In Boolean algebra, a binary value of 1 is interpreted to mean → true and a binary value of 0 means → false. Boolean algebra can equivalently be thought of as a particular type of mathematics that deals with → truth values instead of numbers.

Boolean; → algebra. The term Boolean algebra was first suggested by Sheffer in 1913.

Boomerang Nebula
  میغ ِ بومرانگ   
miq-e bumerâng

Fr.: nébuleuse du Boomerang   

A → nebula displaying two nearly symmetric lobes of matter that are being ejected from a central star at a speed of about 600,000 km per hour (each lobe nearly one light-year in length). The Boomerang Nebula resides 5,000 → light-years from Earth in the direction of the Southern constellation → Centaurus.

Boomerang, adapted from wo-mur-rang, boo-mer-rit, in the language of Australian aborigines; → nebula.

  گاوران، گایار   
Gâvrân, Gâyâr

Fr.: Bouvier   

The Herdsman, the Ox Driver. A constellation in the northern hemisphere, at right ascension about 14h 30m, north declination about 30°. Its brightest star is → Arcturus. Abbreviation: Boo; genitive form: Boötis.

L. Boötes, from Gk. bootes "plowman," literally "ox-driver," from bootein "to plow," from bous "ox," from PIE *gwou- "ox, bull, cow;" compare with Av. gao-, gâuš "bull, cow, ox," Mod.Pers. gâv, Skt. gaus, Armenian kov, O.E. cu.

Gâvrân "ox-driver," from gâv "ox, cow" + rân "driver," from rândan "to drive."
Gâyâr, from Lori "bull driver, plower, plow man" (Tabari goyâr), from "bull, cow," variant of gâv, explained above, + -âr, either "driver", Av. ar- "to set in motion" (Skt. ir-, IER *er-), or IER *are- "to plow" (L. arare, Gk. aroun, O.C.S. orja, Lith. ariu, Goth. arjan, O.E. erian, Tokharian AB âre). Compare also with Gilaki urân " to plow," Qâeni ordu "plow".

Borda circle
  دایره‌ی ِ بُردا   
dâyere-ye Borda

Fr.: cercle de Borda   

An instrument which was an improved form of the → reflecting circle, used for measuring angular distances. In Borda's version the arm carrying the telescope was extended right across the circle. The telescope and a clamp and tangent screw were at one end, and the half-silvered horizon glass at the far end from the eye. In practice, with the index arm clamped, the observer first aims directly at the right hand object and by reflection on the left, moving the telescope arm until this is achieved. He then frees the index arm, sights directly on the left hand object with the telescope arm clamped, and moves the index arm until the two coincide again. The difference in the readings of the index arm is twice the angle required, so that the final sum reading must be divided by twice the number of double operations. Borda's instrument greatly contributed to the French success in measuring the length of the meridional arc of the Earth's surface between Dunkirk and Barcelona (1792-1798). The operation carried out by Jean Baptiste Delambre (1749-1822) and Pierre Méchain (1744-1804) was essential for establishing the meter as the length unit.

After the French physicist and naval officer Jean-Charles de Borda (1733-1799), who made several contributions to hydrodynamics and nautical astronomy. Borda was also one of the most important metrological pioneers; → circle.

zâdé (#)

Fr.: né   

Brought forth by → birth. Past participle of bear. → born-again AGB star.

M.E., from O.E. boren, p.p. of beran "to bear, bring, wear", from P.Gmc. *beranan (O.H.G. beran, Goth. bairan "to carry"), from PIE root *bher- "to bear; to carry" (cf. Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother," Mod.Pers. bordan "to carry," bâr "charge, load", bârdâr "pregnant," Skt. bharati "he carries," Gk. pherein).

Zâdé "born," p.p. of zâdan "give birth" (Av. zan- "to bear, give birth to a child, be born," infinitive zizâite, zâta- "born," cf. Skt. janati "begets, bears," Gk. gignesthai "to become, happen," L. gignere "to beget," gnasci "to be born," PIE base *gen- "to give birth, beget").

born-again AGB star
  ستاره‌یِ AGBیِ باز‌زاده   
setâre-ye AGB-ye bâzzâdé

Fr.: étoile AGB recyclée   

A → post-AGB star that undergoes a last → thermal pulse when it is already on the → white dwarf  → cooling track. The thermal pulse will expand the hot central star, whereby hydrogen will be ingested into the → helium burning shell. This will temporarily return the star to the → AGB phase it has previously left.

born; → again; → asymptotic giant branch; → star.

born-again planetary nebula
  میغ ِ سیاره‌ای ِ باز‌زاد   
miq-e sayâreyi-ye bâzzâd

Fr.: nébuleuse planétaire recyclée   

A → planetary nebula which is thought to have experienced a → very late thermal pulse (VLTP) when the central star (→ CSPN) was on the → white dwarf cooling track. The VLTP event occurs when the thermonuclear → hydrogen shell burning has built up a → shell of helium with the critical mass to ignite its → fusion into carbon and oxygen (→ helium shell burning). Since the → white dwarf envelope is shallow, the increase of pressure from this last helium shell flash leads to the ejection of newly processed material inside the old planetary nebula, leaving the stellar core intact. As the stellar envelope expands, its → effective temperature decreases and the star goes back to the → asymptotic giant branch (AGB) region in the → H-R diagram. The subsequent stellar evolution is fast and will return the star back to the → Post-AGB track in the H-R diagram: the envelope of the star contracts, its effective temperature and ionizing photon flux increase, and a new fast stellar wind develops (see, e.g. J. A. Toalá et al. 2015, ApJ 799, 67).

born; → again; → planetary; → nebula.

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