An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < B r bac Bal Bar bar bea bel Bet bia Big bin bio bis bla ble blu Boe Bol bor bou bra bri bro buo > >>

Number of Results: 471
bel (B)
bel (#)

Fr.: bel   

A dimensionless unit to measure sound. One bel designates a ratio 10:1 between two quantities, P1 and P0, which have the dimension of a power: n [B] = log (P1/P0), in Bel units, with → natural logarithm. If one sound is 2 bels louder than another, this means the louder sound is 100 times more intense than the fainter one. It is also common to use this definition for quantities that are proportional to a power, such as energy, work, intensity, or voltage. The bel was too large for everyday use, so the → decibel (dB), equal to 0.1 bel, is more commonly used.

This unit was put forward by engineers of the Bell telephone network in 1923 and named in honor of the inventor of the telephone, Alexander Graham Bell (1847-1922), who also invented techniques for teaching speech to the deaf.

Belinda (Uranus XIV)

Fr.: Belinda   

One of the small satellites of → Uranus discovered from the Voyager 2 photographs taken during its encounter with the planet in 1986.

Named after the heroine in Alexander Pope's The Rape of the Lock.

Bell's inequality
  ناهموگی ِ بل   
nâhamugi-ye Bell

Fr.: inégalité de Bell   

Any of a large number of inequality relations developed to study the → hidden variable hypothesis suggested in the → EPR paradox. Using Bell's inequalities, the → Aspect experiment showed that no local hidden variable theory can make predictions in agreement with those of quantum mechanics. If, in a measurement, the inequality is violated, the measurement is in agreement with the predictions of the quantum theory. If the equality is satisfied, it suggests that a classical, causal, and local model is adequate to explain the outcome of the measurements. See also → quantum entanglement.

John Stewart Bell (1928-1990); → inequality.

Bellatrix (γ Orionis)
  بلاتریکس، مرزم   
Bellatriks, Merzam

Fr.: Bellatrix   

A bright, blue → giant star ( → spectral type B2 III), one of the main stars of the constellation → Orion. With a visual magnitude of 1.64, it is about 1000 times more luminous than the Sun, and lies at a distance of 243 → light-years.

From L. bellatrix "a female warrior," fem. of bellator, from bellum "war."

Merzam, Ar. name of the star; its other name is Nâjed.


Fr.: appartenir   

1) (With preposition to) To be the property of.
2) (With preposition to) o be a part or adjunct of.

M.E. belongen, from be- intensive prefix, + longen "to go," from O.E. langian "pertain to, to go along with;" akin to Du. belangen, Ger. belangen; of unknown origin.

Pargetidan, literally "to surround, to relate with" (on the model of L. pertinere "pertain," Skt. parigraha- "surrounding; relation to"), from parget "to hold, seize, take around," from par- "around," → peri-, + get "to take, sieze," as in Tâleši gate "to take," Târi gata, Sorxeyi, Lâsgardi, Semnâni, Šâhmerzâdi -git- "take, seize," variants of gereftan "take, hold," → concept.

kamarband (#)

Fr.: ceinture   

A strip of leather or cloth worn around the waist. Something that resembles this type of band, e.g. → Gould's Belt, → Belt of Venus.

O.E. belt, from P.Gmc. *baltjaz, from L. balteus "girdle;" → Orion.

Kamarband "belt," from kamar "waist" (Mid.Pers. kamar "waist; belt, girdle," Av. kamarâ- "belt") + band "a band, tie, belt."

Belt of Orion
  کمربند ِ شکارگر، ~ اریون   
kamarband-e Šekârgar, ~ Orion

Fr.: Baudrier d'Orion   

The three stars Delta (δ, → Mintaka), Epsilon (ε, → Alnilam), and Zeta (ζ, → Alnitak) Orionis which form the belt of the mythological figure of the constellation → Orion. See also: → Orion's Belt.

belt; → Orion.

Belt of Venus
  کمربند ِ ناهید   
kamarband-e Nâhid

Fr.: Ceinture de Vénus   

A pink to brownish border above the horizon separating the Earth's dark shadow on the sky from the sky above it. The Belt of Venus appears during a cloudless twilight just before sunrise or after sunset. It is due to scattered red sunlight in the atmosphere. Also called anti-twilight arc.

belt, → Venus.

Berenice's Hair

Fr.: Chevelure de Bérénice   

Coma Berenices.

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.

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."

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