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: 232 Search : era
degenerate
  واگن   
vâgen (#)

Fr.: dégénéré   

Characterized by or associated with → degeneracy.

L. degeneratus, p.p. of degenerare "depart from one's kind, fall from ancestral quality," from → de- + gener-, stem of genus "race, stock, kind," gignere "to beget," cf. with Gk. genos "race, kind," gonos "birth, offspring," from PIE base *gen-/*gon-/*gn- "to produce, beget, be born," cf. Av. zan- "to bear, give birth to a child, be born," infinitive zazāite, zāta- "born," zana- "race" (in sruuô.zana- "belonging to the race of the horned ones"), O.Pers. zana- "tribe" (in paru-zana- "consisting of many tribes"), Skt. janati "begets, bears," jana- "creature, human being, race, tribe, people."

Vâgen, from vâ-, → de-, + gen "kind," (as in hamgen "of the same kind, like each other; friend, partner," from ham- "together," → com- + gen "kind," O.Pers./Av. zana- "race; tribe," cognate with L. genus, as above). Alternatively, gen may be a variant of Mid./Mod.Pers. gôn/gun "kind, type; manner; color, skin color," from Av. gaona- "hair, hair color, color."

degenerate dwarf
  کوتوله‌ی ِ واگن   
kutule-ye vâgen

Fr.: naine dégénérée   

Same as → white dwarf.

degenerate; → dwarf.

degenerate matter
  ماده‌ی ِ واگن   
mâdde-ye vâgen (#)

Fr.: matière dégénérée   

Highly compressed matter in which the normal atomic structure has broken down and which, because of quantum-mechanical effects, exerts a pressure that is independent of temperature. Bodies with masses less than → Chandrasekhar's limit (1.4 solar masses) are supported by electron → degeneracy pressure and have densities of about 106 kg/m3. In collapsed stars of mass above 1.4 solar masses, gravity will overwhelm electron degeneracy and further collapse ensues. Electrons combine with protons to form neutrons, so producing a → neutron star. Because neutrons, like electrons, are → fermions and therefore subject to the → Pauli exclusion principle, at high enough densities, about 1014 kg/m3, neutron degeneracy pressure prevents further collapse of the star. For masses larger than 2-3 solar masses, even neutron degeneracy cannot prevent further collapse, and a → black hole is formed.

degenerate; → matter.

del operator
  آپارگر ِ دل   
âpârgar-e del

Fr.: opérateur del   

In → vector calculus, a vector → partial derivative represented by the symbol → nabla and defined in three dimensions to be:
∇ = (∂/∂x)i + (∂/∂y)j + (∂/∂z)k.
It appears in the operations → gradient: ∇f, → divergence: ∇ . E, → curl: ∇ x E, and → Laplacian: ∇ . ∇f = ∇2f.

From Gk. alphabet letter delta.

deuterate
  دوتریدن   
doteridan

Fr.: deutérer   

To add → deuterium to a → chemical compound.

From L. deuter(ium), → deuterium, + -ate a suffix forming verbs from L. -atus (masc.), -ata (fem.), -atum (neut.).

Doteridan, infinitive from doteriom, → deuterium.

deuterated
  دوتریده   
doteridé

Fr.: deutéré   

Describing a → chemical compound to which → deuterium is added.

Past participle of → deuterate.

deuterated species
  آرز ِ دوتریده   
âraz-e doteridé

Fr.: espèce deutérée   

A chemical species in which the → deuterium abundance is → enriched with respect to a mean standard value.

deuterated; → species.

deuteration
  دوترش   
dotereš

Fr.: deutération   

The process of introducing → deuterium into a → chemical compound.

Verbal noun of → deuterate.

double-degenerate binary system
  راژمان ِ درین ِ دوبار واگن   
râžmân-e dorin-e dobâr vâgen

Fr.: système binaire doublement dégénéré   

A system of evolved → binary stars in which both → components have ejected their envelopes and evolve toward → white dwarf stage. So far a half dozen double-degenerate → binary systems are known, for example Henize 2-248 (M. Santander-Garcia et al., 2015, 518, 5).

double; → degenerate; → binary; → system.

dust temperature
  دمای ِ غبار   
damâ-ye qobâr

Fr.: température de poussière   

An indication of the heat amount received by → dust grains from the ambient → radiation field. Dust temperature depends on the optical properties and → sizes of grains (i.e., on the way they → absorb and → emit radiation) as well as on the → interstellar radiation field. Most of the visible and → ultraviolet radiation in galaxies from stars passes through clouds of particles and heats them. This heating leads to re-radiation at much longer wavelengths extending to the millimeter.

dust; → temperature.

effective temperature
  دمای ِ ا ُسکرمند   
damâ-ye oskarmand

Fr.: température effective   

A measure of the surface temperature of a star derived from the total emitted energy, assuming that the star is a → blackbody emitter (→ Stefan-Boltzmann law, → Planck's radiation law). See also → brightness temperature; → color temperature.

effective; → temperature.

Einstein temperature
  دمای ِ اینشتین   
damâ-ye Einstein (#)

Fr.: température d'Einstein   

A characteristic parameter occurring in the → Einstein model of → specific heats.

Einstein; → temperature.

electron degeneracy
  واگنی ِ الکترون   
vâgeni-ye elektron (#)

Fr.: dégénérescence des électrons   

A → degenerate matter in which electrons are very tightly packed together, as in a white dwarf, but cannot get closer than a certain limit to each other, because according to quantum mechanics laws (→ Pauli exclusion principle) the lowest energy levels can be occupied by only one electron. Therefore, electrons are forced into high energy states. And the significant pressure created by these high energy electrons supports white dwarf stars against their own gravity.

electron; → degeneracy.

electron temperature
  دمای ِ الکترونی   
damâ-ye elektroni (#)

Fr.: température électronique   

1) The temperature of electrons in an interstellar ionized nebula (e.g. in → H II regions and → planetary nebulae) as determined by characteristic → emission lines (optical → forbidden lines or → radio recombination lines).
2) In the → solar wind, the temperature derived from the mean → thermal agitation of the electrons. More specifically, electric field receivers on board space probes carry out the spectroscopy of the → thermal noise due to the potential fluctuations produced by the thermal agitation of the electrons, yielding the electron temperature in certain conditions (N. Meyer-Vernet, 2007, Basics of the Solar Wind, Cambridge Univ. Press). See also → proton temperature.

electron; → temperature.

electroweak interaction
  اندرژیرش ِ برقانزار   
andaržireš-e barqânezâr

Fr.: interaction électrofaible   

The unified description of two of the four fundamental interactions of nature, → electromagnetism and the → weak interaction which would merge into a single force under conditions of extreme temperature (above 1016 degrees, 102 GeV) prevalent in the early history of the → Universe.

electroweak; → interaction.

energy generation equation
  هموگش ِ آزانش ِ کاروژ   
hamugeš-e âzâneš-e kâruž

Fr.: équation de génération d'énergie   

Of a stellar → nuclear fusion, the equation describing the → energy generation rate as a function of → density and → temperature.

energy; → generation; → equation.

energy generation rate
  نرخ ِ آزانش ِ کاروژ   
nerx-e âzâneš-e kâruž

Fr.: taux de génération d'énergie   

Of a stellar → nuclear fusion, the energy produced per unit mass per unit time, usually denoted ε (erg g-1s-1). The general form of the energy generation equation is: ε = ε0ρλTν, where ε0, ρ, and λ are constants over some efficiently restricted range of → temperature T, → density ρ, and → chemical composition. The temperature exponent ν is about 4, 15, and 40 for → proton-proton chain, → CNO cycle, and → triple alpha process, respectively.

energy; → generation; → rate.

equilateral triangle
  سه‌بر ِ سه-پهلو-برابر   
sebar-e sé-pahlu-barâbar (#)

Fr.: triangle équilatéral   

A triangle having three equal sides.

equi-, → lateral, → triangle.

Sé-pahlu-barâbar, from , → three, pahlu, → side, barâbar, → equal.

era
  دوران   
dowrân (#)

Fr.: ère   

General: A period of time marked by a distinctive character, events, etc.
A system of chronological notation reckoned from a given date.
Geology: A subdivision of geologic time that is longer than a period but shorter than an eon. Precambrian, Paleozoic, Mesozoic, and Cenozoic are the eras of the time scale from oldest to youngest.

From L.L. æra, era "fixed date, era, epoch from which time is reckoned," probably identical with L. æra "counters used for calculation," plural of aes "brass, money," from PIE *aus- "gold" (cf. Av. aiiah- "metal," aiianhaēna- "made of metal;" Skt. áyas- "metal;" O.H.G. ēr "ore;" O.E. ora "ore, unworked metal;" Ger. ehern "brazen").

Dowrân, from Ar. daur "age, time; revolution."

Eratosthenes' method
  روش ِ اراتوستنس   
raveš-e Eratosthenes

Fr.: méthode d'Eratosthène   

A simple way of calculating the Earth's → circumference using two sticks and two theorems of the → Euclidean geometry. Eratosthenes calculated the length of a → meridian arc by measuring the shadow cast by a vertical → gnomon at noon on the → summer solstice. In Cyene (→ tropic of Cancer), no shadow is cast whereas in Alexandria, further north, the shadow is cast at an angle of 1/50 of 360° (measured using a → scaphe), or 7.2°, from the vertical. The circumference is therefore equal to 50 times the distance between the two cities. The distance from Syene to Alexandria was 5,000 stadia, which when multiplied by 50 gives the measure for the Earth's circumference, 250,000 stadia. Estimating the accuracy of this result is not easy because the unit of stadium is not uniquely defined in the ancient world. The most likely reconstruction puts Eratosthenes' stadium in the range 155-185m, implying an error of about 3% below or 15% above the true value. The modern value for the equatorial circumference of the Earth is 40,075 km. As scholars have pointed out, Eratosthenes' experiment was marred by several errors: Syene is not on the Tropic of cancer, it is not on the same meridian as Alexandria, and the distance between the two cities is less than he estimated. But the errors tended to cancel each other out, so his estimate was relatively accurate. See also: → Mamun's method, → Biruni's method.

Eratosthenes (c. 276-194 B.C.), Gk. mathematician, astronomer, and geographer. He studied in Athens and later became a librarian in Alexandria. His treatise On the Measuring of the Earth is lost. The account of his experiment has been preserved in Cleomedes (probably first century A.D.). See also → sieve of Eratosthenes; → experiment.

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