An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 487
Bohr's first postulate
  فراوس ِ نخست ِ بؤر   
farâvas-e naxost-e Bohr

Fr.: premier postulat de Bohr   

One of the postulates used in the → Bohr model, whereby there are certain steady states of the atom in which electrons can only travel in stable orbits. In spite of their acceleration, the electrons do not radiate electromagnetic waves when they move along stationary orbits.

Bohr; → first; → postulate.

Bohr's postulate
  فراوس ِ بؤر   
farâvas-e Bohr

Fr.: postulat de Bohr   

One of the three postulates advanced in the → Bohr model which led to the correct prediction of the observed line spectrum of hydrogen atom. See also → Bohr's first postulate, → Bohr's second postulate, → Bohr's third postulate,

Bohr; → postulate.

Bohr's second postulate
  فراوس ِ دوم ِ بؤر   
farâvas-e dovom-e Bohr

Fr.: deuxième postulat de Bohr   

One of the postulates used in the → Bohr model, whereby when an atom is in the steady state an electron travelling in a circular orbit should have → quantized values of the → angular momentum which comply with the condition p = n(h/2π), where p is the angular momentum of the electron, h is → Planck's constant, and n is a positive integer called → quantum number.

Bohr; → second; → postulate.

Bohr's third postulate
  فراوس ِ سوم ِ بؤر   
farâvas-e sevom-e Bohr

Fr.: troisième postulat de Bohr   

One of the postulates used in the → Bohr model, whereby the atom emits (absorbs) a quantum of electromagnetic energy (→ photon) when the electron passes from an orbit with a greater (lesser) n value to one with a lesser (greater) value. The energy of the quantum is equal to the difference between the energies of the electron on its orbits before and after the transition or "jump": hν = ε1 - ε2, where h is the → Planck's constant and ν the frequency of the transition.

Bohr; → third; → postulate.

boiling point
  نقطه‌ی ِ جوش   
noqte-ye juš (#)

Fr.: point d'ébullition   

The temperature at which a liquid changes to a gas (vapor) at normal atmospheric pressure. In other words, the temperature at which the vapor pressure of a liquid is equal to the external pressure.

M.E. boillen; O.Fr. boillir, from L. bullire "to bubble, seethe," from bulla "a bubble, knob;" → point.

Noqté, → point; juš "boiling," present stem of jušidan "to boil;" Khotanese jis- "to boil;" Av. yaēšiiant- "boiling;" cf. Skt. yas- "to boil, become hot," yasyati "boils, seethes;" Gk. zein "to bubble, boil, cook;" O.H.G. jesan "to ferment, foam;" Ger. Gischt "foam, froth," gären "to ferment;" O.E. gist; E. yeast.

Bok globule
  گویچه‌ی ِ بوک   
guyce-ye Bok

Fr.: globule de Bok   

A small, roughly spherical cloud of → interstellar dust and gas that appears as a dark compact globule when viewed against the background of an → H II region. Bok globules range in mass from about 1 to 1,000 or more → solar masses, and in size from about 10,000 → astronomical units to 3 → light-years. They typically have temperatures of around 10 → Kelvin. Bok globules are thought to represent a stage in the collapse of a dense fragment of → molecular clouds that are in the process of forming new stars. → elephant trunk.

In honor of Bart Jan Bok (1906-1983), the Dutch-American astronomer, who first observed these objects. In 1947, in collaboration with Edith F. Reilly, he put forward the hypothesis that these globules were undergoing → gravitational collapse to form new stars (Bok & Reilly, 1947, ApJ 105, 255); → globule.


Fr.: bolide   

A → meteor which is extremely bright, particularly one that breaks up during its passage through the → atmosphere. Also called → fireball.

Bolide, Fr., from L. bolis, bolidis, from Gk. bolis, bolidos "missile, flash of lightning," from ballein "to throw;" PIE *gwelH1- "to throw;" → ballistics.

Garzin "arrow;" cf. Tâleši ger "meteor" (from Proto-Iranian *garH- "to throw"), cognate with Gk. ballein, as above; → ballistics.


Fr.: bolomètre   

1) An instrument for measuring the intensity of radiant energy in amounts as small as one millionth of an erg. It uses the change in resistance of a thin conductor caused by the heating effect of the radiation. → actinometer, → photometer, → pyrheliometer, → pyrometer, radiometer.
2) In astronomy, an instrument that measures the amount of radiant energy received from a celestial object.

From Gk. bole "stroke, beam of light," from ballein "to throw" + middle suffix -o- + → -meter..

Tâvsanj, from tâv "light, brightness, heat, warmth" (from tâbidan "to radiate") + sanj, → -meter.

  تاوسنجی، تاوسنجیک   
tâvsanji, tâvsanjik

Fr.: bolométrique   

Of or relating to or measured by a → bolometer.

bolometer; → -ic.

bolometric correction
  ارشایش ِ تاوسنجی، ~ تاوسنجیک   
aršâyeš-e tâvsanji, ~ tâvsanjik

Fr.: correction bolométrique   

The difference between the → visual magnitude and → bolometric magnitude.

bolometric; → correction.

bolometric luminosity
  تابندگی ِ تاوسنجی، ~ تاوسنجیک   
tâbandegi-ye tâvsanji, ~ tâvsanjik

Fr.: luminosité bolométrique   

The total rate of energy output of an object integrated over all wavelengths.

bolometric; → luminosity.

bolometric magnitude
  برز ِ تاوسنجی، ~ تاوسنجیک   
borz-e tâvsanji, ~ tâvsanjik

Fr.: magnitude bolométrique   

The magnitude of an astronomical object for the entire range of its electromagnetic spectrum.

bolometric; → magnitude.

Boltzmann constant
  پایای ِ بولتسمن   
pâyâ-ye Boltzmann

Fr.: constante de Boltzmann   

Boltzmann's constant.

Boltzmann's constant.

Boltzmann factor
  کروند ِ بولتسمن   
karvand-e Boltzmannn

Fr.: facteur de Boltzmann   

The factor e-E/kT involved in the probability for atoms having an excitation energy E and temperature T, where k is Boltzmann's constant.

Boltzmann's constant; → factor.

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" (see below); 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," also present stem of bastan "to bind, shut," → shutter.

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.

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