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: 3079 Search : on
bifurcation
  دوگلش   
dogaleš

Fr.: bifurcation   

1) A branching or division into two parts; a splitting apart.
2) A sudden qualitative change in the behavior of a → dynamical system. The equation describing the evolution of the system finds several solutions for certain values of a parameter. Systems undergoing a bifurcation do not necessarily return to their original state, even if the parameter returns to its nominal value. See also → chaos.

Verbal noun of → bifurcate.

bifurcation point
  نقطه‌ی ِ دوگلش   
noqte-ye dogaleš

Fr.: point de bifurcation   

The point or moment in the evolution of a → dynamical system that occurs if a parameter passes through a critical point. At this point the system branches into any number of qualitatively new types of behavior.

bifurcation; → point.

bifurcation theory
  نگره‌ی ِ دوگلش   
negare-ye dogaleš

Fr.: théorie de bifurcation   

1) A theory which studies how, in certain nonlinear systems, there may be paths and shifts in behavior dependent on small changes in circumstances or the current position of the system.
2) Math.: The study of the behavior of a solution of a nonlinear problem in the neighborhood of a known solution, particularly as a parameter varies.

bifurcation; → theory.

bijection
  دوشانش   
došâneš

Fr.: bijection   

A → mapping  f from a → set  A onto a set B which is both an → injection and a → surjection. More explicitly, for every element b of B there is a unique element a of A for which f(a) = b. Also known as → bijective mapping.

From bi- + → injection.

bimodal star formation
  دیسش ِ دومد ِ ستارگان   
diseš-e domod-e setâregân

Fr.: formation bimodale d'étoile   

A concept of → star formation in which → high-mass stars and → low-mass stars form in different physical conditions involving different → molecular clouds. Following the pioneering suggestion of Herbig (1962), successive investigations have generally supported the idea that star formation proceeds bimodally with respect to stellar mass. The star formation rate appears to differ both spatially and temporally for low mass and → massive stars. This is of considerable importance for galactic evolution, since the low-mass stars lock up mass and are long-lived, low luminosity survivors to the present epoch, whereas massive stars are short-lived, recycle and enrich interstellar gas, and leave dark remnants while producing a high luminosity per unit of mass (Silk, J., 1988, in Galactic and Extragalactic Star Formation, p. 503, eds. R. E. Pudritz and M. Fich).

bimodal; → star; → formation.

binary operation
  آپارش ِ درین   
âpâreš-e dorin

Fr.: opération binaire   

A mathematical operation that combines two numbers, quantities, sets, etc., to give a third. For example, multiplication of two numbers is a binary operation.
A binary operation * on a set S is → commutative if a * b = b * a for all a, bS.
A binary operation * on a set S is → associative if (a * b) * c = a * (b * c) for all a, b, cS.

binary; → operation.

binomial distribution
  واباژش ِ دونامین   
vâbâžeš-e donâmin

Fr.: distribution binomiale   

A probability distribution for independent events for which there are only two possible outcomes i.e., success and failure. The probability of x successes in n trials is: P(x) = [n!/x!(n - x)!] px.qn - x, where p is the probability of success and q = 1 - p the probability of failure on each trial. These probabilities are given in terms of the → binomial theorem expansion of (p + q)n.

binomial; → distribution.

binomial expansion
  سپانش ِ دونامین   
sopâneš-e donâmin

Fr.: expansion binomiale   

A rule for the expansion of an expression of the form (x + y)n. The variables x and y can be any → real numbers and n is an → integer. The general formula is known as the → binomial theorem.

binomial; → expansion.

bioastronomy
  زیست‌اخترشناسی   
zistaxtaršenâsi (#)

Fr.: bioastronomie   

A common branch of astronomy and biology dealing with the study of life throughout the Universe; synonymous with → astrobiology and → exobiology.

Bioastronomy, from → bio- + → astronomy.

Zistaxtaršenâsi, from zist-, → bio-, + axtaršenâsi, → astronomy.

biotic environment
  پرگیر ِ زیستیک   
pargir-e zistik

Fr.: environnement biotique   

Ecology: The environment consisting of living organisms, which interact with each other and with their non-living surroundings.

Biotic adj. of → biotics; of → environment.

birth binary population (BBP)
  پرینش ِ دورین‌ها هنگام ِ زادمان   
porineš-e dorinhâ hengâm-e zâdmân

Fr.: population binaire à la naissance   

In star formation models, the population of binary components formed via random pairing of stars distributed according to the → canonical IMF.

birth; → binary; → population.

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.

blackbody radiation
  تابش ِ سیه‌جسم   
tâbeš-e siyah-jesm (#)

Fr.: rayonnement de corps noir   

The radiation emitted by a blackbody at a given → temperature. The → distribution of radiation with → wavelength is given by → Planck's blackbody formula or → Planck's radiation law.

blackbody; → radiation.

blue continuum
  پیوستار ِ آبی   
peyvastâr-e âbi

Fr.: continuum bleu   

The → continuum emission of an astronomical source with wavelengths between about 492 and 455 nm.

blue; → continuum.

blue horizontal branch star
  ستاره‌ی ِ آبی ِ شاخه‌ی ِ افقی   
setâre-ye âbi-ye šâxe-ye ofoqi

Fr.: étoile bleue de la branche horizontale   

A member of a population of blue stars appearing on the → horizontal branch in the → Hertzsprung-Russell diagram of the Galactic → halo populations and → globular clusters. Belonging to → spectral types B3 to A0, they have evolved past the → red giant stage and are burning helium in their core.

blue; → horizontal; → branch, → star.

blue Moon
  ماه ِ آبی   
mâh-e âbi

Fr.: lune bleue   

The second full moon in a calendar month. For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month. Full moons are separated by 29 days, while most months are 30 or 31 days long; so it is possible to fit two full moons in a single month. This happens every two and a half years, on average.

The folkloric term blue Moon for the calendrical event is new, and apparently goes back to the Maine Farmers' Almanac for 1937. But its original meaning in that work was the third full Moon in a season when there were four full Moons in that season. Some have related the term to the much older English expression moon is blue, which goes back to a couplet from 1528, interpreting it as "something that occurs rarely." However in that poem the expression had a meaning of "something that was absurd." Alternatively, the term blue Moon may have been borrowed from the Chinese lunar calendar particularly in its usage among American Chinese community. In fact in that calendar when there are two full Moons in a month they use the term "blue Moon" and add a thirteenth intercalary month. → blue; → moon.

blue region
  ناحیه‌ی ِ آبی   
nâhiye-ye âbi

Fr.: région bleue   

The portion of the → visible spectrum lying between 455 and 492 nm.

blue; → region.

blueshifted component
  همنه‌ی ِ آبی-کیب   
hamneye âbikib

Fr.: composante décalée vers le bleu   

A constituent of a composite astronomical object which has a motion directed towards the observer, as revealed by its spectrum.

blueshift; → component.

Boeshaar-Keenan classification
  رده‌بندی ِ بوسهار-کینان   
radebandi-ye Boeshaar-Keenan

Fr.: classification de Boeshaar-Keenan   

A system for the classification of → S-type stars. The system involves the designations of a C/O index and a temperature type. Moreover, when possible, it uses intensity estimates for → ZrO bands, the → TiO bands, the → Na I D-lines, the YO bands, and the Li I 6708 line.

Philip C. Keenan & Patricia C. Boeshaar, 1980, ApJS, 43, 379; → classification.

Bohr magneton
  مگنتون ِ بؤر   
magneton-e Bohr (#)

Fr.: magnéton de Bohr   

A fundamental constant, first calculated by Bohr, for the intrinsic → spin magnetic moment of the electron. It is given by: μB = eħ/2me = 9.27 x 10-24 joule/tesla = 5.79 x 10-5 eV/tesla, representing the minimum amount of magnetism which can be caused by the revolution of an electron around an atomic nucleus. It serves as a unit for measuring the magnetic moments of atomic particles.

Bohr; magneton, from → magnet + → -on.

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