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
segregation
  سوایش   
savâyeš

Fr.: ségrégation   

The act or practice of segregating. The state or condition of being segregated. → mass segregation.

Verbal noun of → segregate.

selection rule
  رزن ِ گزینش   
razan-e gozineš

Fr.: règle de sélection   

Any of a set of rules specifying the relationships between the → quantum numbers that characterize the initial and final states of a quantum-mechanical system in a → discrete transition. Transitions that do not agree with the selection rules are called → forbidden and have considerably lower probability. There are several types of selection rules (→ rigorous selection rule, → LS coupling, etc.) for → electric dipole transition (→ permitted), → magnetic dipole (forbidden), electric → quadrupole (forbidden), etc.

Selection, verbal noun of → select; → rule.

selective absorption
  درشم ِ گزینشی   
daršam-e gozineši

Fr.: absorption sélective   

Absorption which varies with the wavelength of radiation incident upon an absorbing substance.

Selective, verbal noun of → select; → absorption.

selenehelion
  ماه‌گرفت ِ افقی   
mâhgereft-e ofoqi

Fr.: selenelion   

Same as → horizontal eclipse.

From Gk. selene "Moon," related to sela "light, brightness, flame," + helion, → sun.

horizontal eclipse.

selenelion
  ماه‌گرفت ِ افقی   
mâhgereft-e ofoqi

Fr.: selenelion   

Same as → horizontal eclipse.

From Fr. selenelion, contraction of → selenehelion.

horizontal eclipse.

selenocentric gravitational constant
  پایای ِ گرانشی ماه‌مرکزی   
pâyâ-ye gerâneši-ye mâh-markazi

Fr.: constante gravitationnelle sélénocentrique   

A parameter representing the product of the → gravitational constant by the → lunar mass. It is 49.03 x 1011 m3 s-2.

selenocentric; → gravitational; → constant.

self-absorption
  خود-درشم   
xod-daršam

Fr.: auto-absorption   

The decrease in the radiation from a material caused by the absorption of a part of the radiation by the material itself.

self-; → absorption.

self-induction
  خود-درهازش   
xod-darhâzeš

Fr.: auto-induction   

The generation of a voltage in a circuit due to self-inductance, the polarity of which tends to oppose the changing current in the circuit.

self-; → induction.

Sellmeier's equation
  هموگش ِ زلمایر   
hamugeš-e Sellmeier

Fr.: équation de Sellmeier   

An empirical relation between the → refractive index of a medium and the wavelength of light passing through the medium: n2 - 1 = Σ (Aiλ2/(λ2 - λi2)), where n is the refractive index at wavelength λ, and Ai and λi are constants.

Named after Wolfgang Sellmeier who derived the equation in 1871; → equation.

semi-forbidden transition
  گذرش ِ نیمه-بژکم   
gozareš-e nime-bažkam

Fr.: transition semi-interdite   

An → atomic transition whose probability is reduced by a factor of the order of 106 because of → selection rules. Same as → interconnection line.

semi-; → forbidden; → transition.

semiconductor
  نیم-هازا، نیمه-رسانا   
nim-hâzâ, nime-rasânâ

Fr.: semi-conducteur   

Any of various solid crystalline substances, such as germanium or silicon, which has conducting properties intermediate between metals and insulators.

semi-; → conductor.

semiconductor junction
  جوهه‌ی ِ نیم-هازا   
juhe-ye nim-hâzâ

Fr.: jonction semi-conducteur   

In a semiconductor device, a region of transition between semiconducting regions of different electrical properties.

semiconductor; → junction.

semiconvection
  نیم-همبز   
nim-hambaz

Fr.: semi-convection   

An instability occurring in the region just outside the → convective core of a → massive star. The instability occurs when a → superadiabatic layer is stabilized by a chemical gradient. In fact, semiconvection takes place if → Schwarzschild's criterion for convection is fulfilled but at the same time → Ledoux's criterion is not fulfilled. The time-scale of semiconvection is the thermal time-scale, which is short compared to the nuclear time-scale in → main sequence stars but long compared to the time-scale of convection. However, semiconvection has a profound influence on the → post-main sequence star evolution. It affects the convective mixing above the hydrogen shell source, determines the appearance and extent of → blue loops in the → Hertzsprung-Russell diagram during core → helium burning, and is essential for defining the extent of the convective cores during core helium burning (See, e.g., N. Langer, 2012, Ann. Rev. Astron. Astrophys. 50, 107).

semi-; → convection.

sensation
  حسّکرد، حسّش   
hess-kard, hesseš

Fr.: sensation   

The perception or awareness of stimuli through the senses.

From M.L. sensationem (nominative sensatio), from L.L. sensatus "endowed with sense, sensible," from L. sensus "feeling," → sense.

Hess-kard, hesseš, verbal nouns of hess kardin, hessidan, → sense.

sensible horizon
  افق ِ حسّ-پذیر، ~ حسّیدنی   
ofoq-e hess-pazir, ~ hessidani

Fr.: horizon sensible   

The great circle of the celestial sphere whose poles are the nadir and zenith. Same as astronomical horizon.

sensible; → horizon.

separation
  جدایی   
jodâyi (#)

Fr.: séparation   

General: The act or process of separating. The place at which a division or parting occurs.
Astro.: The angular distance between the two components of a visual binary or optical double star.

M.E., from O.Fr. separation, from L. separationem, from separare "to pull apart," from se- "apart" + parare "make ready, prepare."

Jodâyi state noun of jodâ "separate," from Mid.Pers. yut "separate, different;" Av. yuta- "separate, apart."

separation energy
  کاروژ ِ جدایی   
kâruž-e jodâyi

Fr.: énergie de séparation   

The energy required to remove a particle (a proton or a neutron) from a particular atomic nucleus.

separation; → energy.

sequential star formation
  دیسش ِ پی‌آیه‌ای ِ ستاره   
diseš-e peyâye-yi-e setâré

Fr.: formation séquentielle d'étoiles   

The formation of second-generation stars in a → molecular cloud, as triggered by the presence of → massive stars. The observation that some nearby → OB associations contain distinct, spatially separate subgroups of → OB stars in a sequence of monotonically changing age led Blaauw (1964, ARA&A 2, 213) to suggest that star formation in fact occurs in sequential bursts during the lifetimes of the corresponding molecular clouds. The first quantitative model of this mechanism was presented by Elmegreen and Lada (1977, ApJ 214, 725), who showed that the powerful ultraviolet photons of the massive star create an → ionization front which advances in the molecular cloud and is preceded by a → shock front. The compressed neutral gas lying between the ionization and shock fronts is gravitationally unstable and collapses in time-scales of a few million years to form a new generation of massive stars. The propagation of successive births of OB groups would produce a chain of associations presenting a gradient of age. Elmegreen and Lada estimated the propagation velocity to be 5 km s-1. For a region with a length larger than 100 pc, this would imply an age difference of the order of 20 million years between the extremities. See also → stimulated star formation, → triggered star formation; → collect and collapse model.

sequential; → star formation.

set partition
  پرکش ِ هنگرد   
parkeš-e hangard

Fr.: partition d'un ensemble   

A collection of → nonempty subsets of a set A such that every element of A is in exactly one of the subsets. In other words, A is the → disjoint  → union of these subsets.

partition; → set.

Shack-Hartmann wavefront sensor
  حسگر ِ پیشان ِ موج ِ شک-هارتمان   
hessgar-e pišân-e mowj-e Shack-Hartmann

Fr.: analyseur de front d'onde   

An optical device, a modern version of the → Hartmann test, used for analyzing the wavefront of light. Theses sensors can be used to characterize the performance of optical systems. Moreover, they are increasingly used in real-time applications, such as → adaptive optics to remove the wavefront distortion before creating an image. It consists of a microlens array placed in front of a CCD array. A planar wavefront that is transmitted through a microlens array and imaged on the CCD array will form a regular pattern of bright spots. If, however, the wavefront is distorted, the light imaged on the CCD will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wavefront that was incident on the microlens array.

Named after the German astronomer Johannes Hartmann (1865-1936), who first developed the method, and R. V. Shack, who in the late 1960s replaced the screen by a microlens array; → wavefront; → sensor.

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