An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 502
Bernoulli equation
  هموگش ِ برنویی   
hamugeš-e Bernoulli

Fr.: équation de Bernoulli   

The equation expressing → Bernoulli's theorem: P + (1/2)ρV2 + ρgz = constant, where P is the fluid → pressure, V is → velocity, ρ is → density, g is the acceleration due to → gravity, and z is the vertical reference → level. The theree terms are called → static pressure, → dynamic pressure, and → hydrostatic pressure, respectively. The Bernoulli equation states that the total pressure along a → streamline is → constant.

Bernoulli's theorem; → equation.

Bernoulli's theorem
  فربین ِ برنویی   
farbin-e Bernoulli

Fr.: théorème de Bernoulli   

A statement of the → conservation of energy in the → steady flow of an → incompressible, → inviscid fluid. Accordingly, the quantity (P/ρ) + gz + (V2/2) is → constant along any → streamline, where P is the fluid → pressure, V is the fluid → velocity, ρ is the mass → density of the fluid, g is the acceleration due to → gravity, and z is the vertical → height. This equation affirms that if the internal velocity of the flow goes up, the internal pressure must drop. Therefore, the flow becomes more constricted if the velocity field within it increases. Same as the → Bernoulli equation.

After Daniel Bernoulli (1700-1782), the Swiss physicist and mathematician who put forward the theorem in his book Hydrodynamica in 1738; → theorem.


Fr.: baie   

1) A small, round fruit on particular plants and trees.
2) Botany: Any of various small edible fruits such as the raspberry, blackberry, and strawberry.

M.E. berye, from O.E. berie "berry, grape," cf. M.Du. bere, Ger. Beere, O.Sax. winberi, Gothic weinabasi "grape," Norwegian and Danish bær, of unknown origin.

Pelâr, from Hamadâni, Malâyeri pellâr, pellâra "berry, grape berry;" cf. Laki, Xonsâri palâra "raisin grape," Aligudarzi pellâr "part of a raison grape," of unknown origin (related to berry, as above?).

beriliom (#)

Fr.: béryllium   

A grey, very hard metallic chemical element; symbol Be. → Atomic number 4; → atomic weight 9.01218; → melting point about 1,278°C; → boiling point 2,970°C (estimated); → specific gravity 1.85 at 20°C; → valence +2. Beryllium occurs as beryl, from which it is obtained by electrolysis. Used for light alloys which are corrosion resistant. Beryllium was discovered by Louis Nicolas Vauquelin (1763-1829) in 1798. First isolated by Friedrich Wöhler (1800-1882) in 1828.

From L. beryll(us), from beryl, a mineral, beryllium aluminum silicate, Be3Al2Si6O18, M.E. beril, from O.Fr., from L. berillus, from Gk. beryllos, + → -ium.


Fr.: Bessel   

From Friedrich Wilhelm Bessel (1784-1846), German astronomer and mathematicians, who made fundamental contributions to positional and spherical astronomy.

Bessel equation
  هموگش ِ بسل   
hamugeš-e Besel

Fr.: équation de Bessel   

A linear second-order differential equation, the solutions to which are called Bessel functions.

From → Bessel; → equation

Hamugeš, → equation.

Bessel's star
  ستاره‌ی ِ بسل   
setâre-ye Bessel

Fr.: étoile de Bessel   

Same as → 61 Cygni, the first star whose distance was measured, by Friedrich Bessel in 1838.

Bessel; → star.


Fr.: besselien, de Bessel   

Of or pertaining to Friedrich Wilhelm Bessel (1784-1846) or to his discoveries. → Besselian day number Bessel equation Besselian star constant Besselian year.


Besselian day number
  شماره‌ی ِ روز ِ بسلی   
šomâre-ye ruz-e Besseli


Any of the five quantities denoted by A, B, C, D, and E used in conjunction with → Besselian star constants for the reduction of a star's → mean catalog place to its → apparent place.

Besselian; → day; → number.

Besselian star constant
  پایای ِ اختری ِ بسلی   
pâyâ-ye axtari-ye Besseli

Fr.: constante stellaire besselienne   

Any of the eight quantities denoted by a, b, c, d (for → right ascension) and a', b', c', d' (for → declination) used in conjunction with → Besselian day numbers for the reduction of star's → mean catalog place.

Besselian; → star; → constant.

Besselian year
  سال ِ بسلی   
sâl-e Beseli

Fr.: année besselienne   

The period taken for the right ascension of the mean Sun to increase by 24 hours. The starting point is when the mean Sun's longitude is 280°, corresponding roughly to January 1. It is virtually the same as the tropical year.

Besselian; → year.

best fit
  بهترین سز   
behtarin saz

Fr.: meilleur ajustement   

In a scatter plot, a mathematical line or curve that passes as near to as many of the data points as possible.

Best, M.E., from O.E. betst, akin toi O.E. bot "remedy." Fit, from M.E. fitten "to marchal troops," from or akin to M.Dutch vitten "to be suitable."

Behtarin supperlative of beh "good, fine" (Mid.Pers. veh "better, good," O.Pers. vahav-, vahu-, Av. vah-, vohu- "good," cf. Skt. vasu- "good," Hittite wasu-, Gaulish vesus "good") + saz, from sazidan "to be fit, proper," from Mid.Pers. saz, sazistan "to be fitting, proper."

Beta Andromedae

Fr.: Beta Andromedae   

The brightest star in the constellation → Andromeda with an average → apparent visual magnitude of 2.05. It is a red (B - V = +1.57), → giant star of → spectral type M0 III. Beta And lies at a distance of 197 ± 7 → light-years (61 ± 2 → parsecs). It has a mass of 3-4 Msun (→ solar mass), a → luminosity of ~ 2,000 Lsun (→ solar luminosity), and a radius of 100 Rsun (→ solar radius). Its other designations include: Mirach, Merach, Mirac, Mizar, 43 Andromedae, BD+34°198, HD 6860, HIP 5447, HR 337, LTT 10420, and SAO 54471. Beta And happens to lie nearly along the → line of sight to the galaxy → NGC 404. This galaxy, known as → Mirach's Ghost, is visible seven arc-minutes away.

Beta, a Greek letter of alphabet used in the → Bayer designation; → Andromeda

Beta Cephei

Fr.: bêta Céphée   

The second brightest star in the constellation → Cepheus and the prototype of → Beta Cephei variables. It is a variable B2 type → giant star with a visual magnitude of 3.23 varying with a period of 4.57 hours. Its mass is a dozen times that of the Sun. Beta Cephei is a → triple system lying at a distance of about 600 → light-years. The inner → spectroscopic companion, → spectral type A, is only about 45 AU away, and takes around 90 years to orbit. The third visual companion is at least 2400 AU away, with an orbital period of at least 30,000 years.

Beta (β), the second letter of the Gk. alphabet; → Cepheus.

Beta Cephei variable
  ورتنده‌ی ِ بتا-کفؤسی   
vartande-ye betâ Kefeusi

Fr.: variables bêta Céphée   

A variable star, of early B or late O types, undergoing radial pulsations with short periods (< 1 day). Beta Cephei stars are confined within a narrow band of the → H-R diagram above the upper → main sequence. They are believed to be near the end of core hydrogen-burning stars of approximately 10 to 20 solar masses. The famous bright stars → Spica and → Mirzam belong to this family.

Beta Cephei; → variable.

beta decay
  تباهی ِ بتا   
tabâhi-ye betâ (#)

Fr.: désintegration bêta   

The transformation of a → radioactive nuclide in which a → beta particle is emitted. In beta minus decay, a → neutron changes into a → proton, → antineutrino, and → electron: n → p + e + ν-. Beta plus decay involves the conversion of a proton to a neutron, → positron, and → neutrino: p → n + e+ + ν.

Beta (β), from → beta particle; → decay.

beta minus decay
  تباهی ِ بتا کمن   
tabâhi-ye betâ kaman

Fr.: désintegration bêta moins   

beta particle.

beta particle; → minus; → decay.

beta particle
  ذره‌ی ِ بتا   
zarre-ye betâ (#)

Fr.: particule bêta   

An → electron or a → positron emitted from an unstable nucleus during a → radioactive process known as → beta decay.

The term "beta particle" relates to the early history of the → radioactivity studies when the nature of the emergent particles was not elucidated; → particle.

Beta Pictoris (β Pic)
betâ Negârgar

Fr.: bêta Pictoris   

The second brightest star, with an apparent magnitude of 3.86, in the southern constellation → Pictor. Beta Pic is a young star of spectral type A lying 63 → light-years away. It has a luminosity 8.6 times that of the Sun and its surface temperature is 8250 K. Beta Pic is surrounded by a dust and gas disk stretching 400 A.U. away from the star in each direction, 10 times the average distance of Pluto from the Sun. The disk is not symmetric, one side is brighter than the other. Moreover, it has an inner clear zone about the size of our solar system (some 30 A.U.). Recently a probable giant → exoplanet lying in the disk has been imaged.

Beta (β), the second letter of the Gk. alphabet; → Pictor.

beta plus decay
  تباهی ِ بتا بیشن   
tabâhi-ye betâ bišan

Fr.: désintegration bêta plus   

beta particle.

beta particle; → plus; → decay.

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