An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1326
Secchi classification
  رده‌بندی ِ سکی   
radebandi-ye Secchi

Fr.: classification de Secchi   

A pioneering work in → spectral classification conducted in the 1860s. Secchi divided stars into four main groups based on the visual observation of spectra. Class I: The white and bluish stars with a continuous spectrum crossed by hydrogen bands, the metallic bands being absent or weak. Examples, → Sirius, → Vega. Class II: Yellow stars, with spectra in which the hydrogen bands were less prominent and the metallic lines more strong. Examples, Sun, → Capella. Class III: Red or orange stars, showing bands or flutings. Examples, → Antares, → Betelgeuse. Class IV: Red stars, showing bands similar to Class III, but with the sharp edge of the flutings toward the other end of the spectrum. Secchi's scheme was superseded by the photographic → Harvard classification system.

Pietro Angelo Secchi (1818-1878), Italian astronomer and Jesuit priest; → classification.

  ۱) دوم، دومین؛ ۲) ثانیه   
1) dovom (#), dovomin (#); 2) sâniyé (#)

Fr.: seconde   

1) Next after the first in place, time, or value.
2) The unit of time in the International System since 1967. The SI second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133.

M.E., from O.Fr. second, from L. secundus "following, next in order," from root of sequi "to follow;" PIE base *sekw- "to follow;" cf. Pers. az from; Mid.Pers. hac "from;" Av. hac-, hax- "to follow," hacaiti "follows" (O.Pers. hacā "from;" Av. hacā "from, out of;" Skt. sácā "with"); Skt. sácate "accompanies, follows;" Gk. hepesthai "to follow;" Lith. seku "to follow."

1) Dovom, dovomin "ordinal number of do, two" (Mid.Pers. do; Av. dva-; cf. Skt. dvi-; Gk. duo; L. duo; (Fr. deux; E. two; Ger. zwei).
2) Sâniyé, from Ar. sâniyat (feminine) "second."

second approximation
  نزدینش ِ دوم   
nazdineš-e dovom

Fr.: deuxième approximation   

Math: In calculus, limiting an equation to its → second derivative, for example: ex≅ 1 + x + x2/2. Also called linear approximation. → first approximation.

second; → approximation.

second collapse
  رمبش ِ دوم   
rombeš-e dovom

Fr.: deuxième effondrement   

An early evolutionary period in the process of star formation which succeeds the → first collapse. When the mass of the → first core has increased by about a factor 2 and the radius has decreased by a similar factor, the central temperature of the core reaches about 2000 K. At this point the → molecular hydrogen begins to dissociate into atoms. This reduces the → adiabatic index (γ) below the critical value 4/3, with the result that the material at the center of the core becomes unstable and begins to collapse. Most of the gravitational energy generated by this collapse goes into the → dissociation of H2 molecules, so that the temperature rises only slowly with increasing density. In this second collapse phase, as in the first, the density distribution in the collapsing region becomes more and more sharply peaked at center, and the time scale becomes shorter and shorter with increasing central density. The central collapse of the core continues until the hydrogen molecules are nearly all dissociated and γ again rises above 4/3. The central pressure then rises rapidly and once again becomes sufficient to decelerate and stop the collapse at the center. A small core in the → hydrostatic equilibrium then arises, bounded by a shock front in which the surrounding infalling material is suddenly stopped. The initial mass and radius of the second core are about 3 x 1030 g (1.5 x 10-3Msun) and 9 x 1010 cm (1.3 Rsun) respectively, and the central density and temperature are about 2 x 10-2 g cm-3 and 2 x 104 K, respectively. The second core will evolve into a → young stellar object (R. B. Larson, 1969, MNRAS 145, 271).

second; → collapse.

second contact
  پرماس ِ دوم   
parmâs-e dovom

Fr.: deuxième contact   

The beginning of the total phase of a solar eclipse when the leading edge of the Moon touches the eastern edge of the Sun completely obscuring the Sun.

second; → contact.

second core
  مغزه‌ی ِ دوم   
maqze-ye dovom

Fr.: deuxième cœur   

A hydrostatic object predicted to result from the → second collapse of a → molecular cloud in an early stage of star formation.

second; → core.

second derivative
  واخنه‌ی ِ دوم   
vâxane-ye dovom

Fr.: dérivée seconde   

In → calculus, the → derivative of a → first derivative. It is usually written as f''(x), d2y/d2x, or y''.

second; → derivative.

second derivative test
  آزمون ِ واخنه‌ی ِ دوم   
âzmun-e vâxane-ye dovom

Fr.: test de la dérivée seconde   

A method, used in → calculus, for determining whether a given → stationary point of a → function is a → local minimum or → local maximum.

second; → derivative; → test.

second dredge-up
  برونکشید ِ دوم   
borunkašid-e dovom

Fr.: deuxième dragage   

A → dredge-up process that occurs after core helium burning, in which the convective envelope penetrates much more deeply, pushing hydrogen burning shell into close proximity with the helium burning shell (→ first dredge-up). This arrangement is unstable and leads to burning pulses. The reason is that the hydrogen shell burns out until there is enough helium for the helium combustion to occur and all the helium is rapidly burnt. Afterward the hydrogen shell again burns outward and the process repeats.

second; → dredge-up.

second generation star
  ستاره‌ی ِ آزانش ِ دوم   
setâre-ye âzâneš-e dovom

Fr.: étoile de deuxième génération   

A star whose formation is induced by an older star itself formed previously in the same region. See also → stimulated star formation, → sequential star formation, → triggered star formation.

second; → generation; → star.

second law of black-hole mechanics
  قانون ِ دوم ِ مکانیک ِ سیه‌چال   
qânun-e dovom-e mekânik-e siyah-câl

Fr.: deuxième loi de la mécanique des trous noirs   

The surface area of a black hole's horizon can never decrease.

second; → law; → black hole; → mechanics.

second law of thermodynamics
  قانون ِ دوم ِ گرماتوانیک   
qânun-e dovom-e garmâtavânik

Fr.: deuxième loi de la thermodynamique   

1) Heat cannot be transferred from a colder to a hotter body without some other effect, i.e. without → work being done. Expressed in terms of → entropy: the entropy of an → isolated system tends toward a maximum and its available energy tends toward a minimum.
2) In language of → statistical physics, an isolated physical system will tend toward an equilibrium → macrostate with as large a total → entropy as possible, because then the number of → microstates is the largest. See also → Kelvin's postulate, → Clausius's postulate.

second; → law; → thermodynamics.

second quantization
  کو‌آنتومش ِ دوم   
kuântomeš-e dovom

Fr.: deuxième quantification   

In quantum mechanics, the quantization of the field that replaces potential in Newtonian mechanics, whereby the field variables become operators from which the creation (of particle) operators and destruction operators can be constructed.

second; → quantization.

second-order logic
  گوییک ِ رایه‌ی ِ دوم   
guyik-e râye-ye dovom

Fr.: logique du seconde ordre   

An n extension of → first-order logic that quantifies not only → variables that range over → individuals, but also quantifies over → relations.

second; → order; → predicate; → logic.


Fr.: secondaire   

1) Derived or derivative; not primary or original.
2) Belonging or pertaining to a second order, division, stage, period, rank, grade, etc.
3) → secondary body.
See also:
secondary atmosphere, → secondary calibrator, → secondary cell, → secondary cosmic rays, → secondary crater, → secondary eclipse, → secondary electrons, → secondary emission, → secondary mirror, → secondary star.

From → second + -ary a suffix occurring on adjectives (elementary; honorary; stationary) and nouns denoting objects, especially receptacles or places (library; rosary; glossary).

Dovomân, from dovom, → second.

secondary atmosphere
  جوّ ِ دومان، هواسپهر ِ ~   
javv-e dovomân, havâsepehr-e ~

Fr.: atmosphère secondaire   

An atmosphere of a planet that forms after primordial gases had been lost or had failed to accumulate. A secondary atmosphere develops from internal volcanic outgassing, or by accumulation of material from comet impacts. It is characteristic of terrestrial planets, such as Earth, Mercury, Venus, and Mars. → primordial atmosphere.

secondary; → atmosphere.

secondary body
  جسم ِ دومان   
jesm-e dovomân

Fr.: corps secondaire   

A body that revolves around a more massive body under the → gravitational attraction of the latter is called the → primary body.
The less massive component in a → binary system.

secondary; → body.

secondary calibrator
  کبیزنده‌ی ِ دومان   
kabizande-ye dovomân

Fr.: calibrateur secondaire   

An indicator of extragalactic distances that relies on → primary calibrators in our Galaxy. Secondary calibrators of the distance scale depend on statistical measures of the properties of a class of objects, such as the brightness of H II regions, globular clusters, red and blue stars, or the neutral hydrogen 21-cm line width or velocity dispersion (of spiral galaxies), etc. Same as secondary distance indicator.

secondary; → calibrator.

secondary cell
  پیل ِ دومان   
pil-e dovomân


An electric cell that can be charged by passing a current through it in reverse direction to its discharge. Same as → accumulator. See also → primary cell.

secondary; → cell.

secondary cosmic rays
  پرتوهای ِ کیهانی ِ دومان   
partowhâ-ye keyhâni-ye dovomân

Fr.: rayons cosmiques secondaires   

A burst of secondary charged and neutral particles arising when → primary cosmic rays collide with the atmospheric oxygen or nitrogen nuclei in the upper atmosphere. The collision produces mostly → pions (π), along with some → kaons (K), → antiprotons, and → antineutrons. Neutral pions very quickly decay, usually into two → gamma rays. Charged pions also decay but after a longer time. Therefore, some of the pions may collide with yet another nucleus of the air before decaying, which would be into a → muon and a → neutrino. The fragments of the incoming nucleus also interact again, also producing new particles.

secondary; → cosmic; → ray.

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