An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 155 Search : ratio
stellar aberration
  بیراهش ِ ستاره‌ای   
birâheš-e setâre-yi

Fr.: aberration stellaire   

Same as → aberration of starlight .

stellar; → aberratio.

Strehl ratio
  وابر ِ اشترل   
vâbr-e Strehl

Fr.: rapport Strehl   

The ratio of the peak intensity of the central core of the image of a point source to the corresponding intensity contained in an image obtained in the absence of aberration. An optically perfect system has a Strehl ratio of unity. The ratio may be computed by integrating the area under a → modulation transfer function (MTF) curve and dividing it by the integral over the diffraction-limited MTF.

In honor of Karl Strehl (1864-1940), the German physicist and mathematician who introduced the concept; → ratio.


Fr.: super-saturation   

The process whereby the amount of → water vapor in the air exceeds that needed to → saturate. In other words, the condition of air in which the → humidity is above the level required for saturation at a given temperature (i.e. the → relative humidity is greater than 100%). When the temperature drops below freezing, this can lead to a situation where more water vapor is present in the air than the air can hold. At every temperature, there is a maximum amount of water vapor that can be supported in the air. The higher the temperature, the more water vapor can be accommodated. But if the air that is already at 100% relative humidity is cooled then it becomes supersaturated, and this situation is unstable. As a result, the excess water vapor crystallizes out, either into water droplets or directly into ice.

super-; → saturation.


Fr.: trilatération   

A geometrical method in land surveying for the determination of the relative position of points. In contrast to → triangulation, trilateration involves measuring the lengths of the three sides of touching or overlapping triangles and not their angles.

tri-; → lateral; → side; → -tion.

Type I migration
  کوچ ِ گونه‌ی ِ I   
kuc-e gune-ye I

Fr.: migration de type I   

An → orbital migration of low-mass → planets in which no gap is created in the → protoplanetary disk. According to planetary models, beyond a critical core mass for the forming planet, a gap in the protoplanetary disk is created. The critical mass depends on the mass and → metallicity of the disk and therefore it does not have a singular value, but has been shown to be between about 10-30 Earth masses. Compare with → Type II migration.

type; → migration.

Type II migration
  کوچ ِ گونه‌ی ِ II   
kuc-e gune-ye II

Fr.: migration de type II   

The → orbital migration of forming → planets that → accrete enough disk material to exceed the critical mass. This type migrates in a gap created in the → protoplanetary disk. Compare with → Type I migration.

type; → migration.

šiveš (#)

Fr.: vibration   

1) The act of vibrating. The state of being vibrated.
2) A continuing → periodic  → oscillation relative to a fixed reference point or → equilibrium state.

Verbal noun from → vibrate.

šiveši (#)

Fr.: vibrationnel   

Of or pertaining to → vibration. → vibrational mode.

vibration; → -al.

vibrational energy
  کاروژ ِ شیوشی   
kâruž-e šiveši

Fr.: énergie de vibration, ~ vibratoire   

The energy due to the vibration of the molecules making up atoms (→ molecular vibration). A molecule in space can have energies in various forms: → rotational energy, vibrational energy, or electronic energy. These energies of molecules are → quantized and a particular molecule can exist in different rotational and vibrational → energy levels. The molecules can move from one level to another level only by a jump involving a finite amount of energy. → Quantum mechanics predicts that any molecule can never have zero vibrational energy, that is atoms can never be completely at rest relative to each other. The harmonically oscillating molecules can undergo vibrational changes determined by simple selection rules obtained from → Schrödinger equation.

vibrational; → energy.

vibrational frequency
  بسامد ِ شیوشی   
basâmad-e šiveši (#)

Fr.: fréquence de vibration, ~ vibrationnelle   

The frequency at which the atoms in a molecule vibrate. The frequencies of → molecular vibrations in diatomic molecules are in the order of 10-12 to 10-14 Hz. In such molecules, the only → vibrational mode available is along the bond. More complicated molecules have many types of vibration and stretching modes.

vibrational; → frequency.

vibrational mode
  ترز ِ شیوشی   
tarz-e šiveši

Fr.: mode de vibration, ~ vibratoire   

Any of the ways in which a → molecule vibrates. Each vibrational mode has a different → frequency frequency. The number of vibrational modes of a molecule is determined by the number of atoms in it. The number of vibrational modes for a non-linear molecule is 3N - 6, where N is the number of atoms making up the molecule. For a linear molecule it is 3N - 5.

vibrational; → mode.

vibrational transition
  گذرش ِ شیوشی   
gozareš-e šiveši

Fr.: transition vibrationnelle   

A transition between two → quantized  → levels of a → molecule that have different vibrational energies.

vibrational; → transition.

vibrational-rotational transition
  گذرش ِ چرخشی-شیوشی   
gozareš-e carxeši-šiveši

Fr.: transition vibrationnelle-rotationnelle   

A slight change in the → energy level of a → molecule due to → vibrational transition and/or → rotational transition.

vibrational; → rotational; → transition.

weight concentration
  دبزش ِ وزنی   
dabzeš-e vazni

Fr.: concentration en poids   

of a gas included in the composition of a → gas mixture, the ratio of mass of this gas to the mass of the whole mixture. Same as → weight fraction and → weight-fraction concentration.

weight; → concentration.

weight-fraction concentration
  برخه‌ی ِ وزنی ِ دبزش   
barxe-ye vazni-ye dabzeš

Fr.: concentration en poids   

Same as → weight concentration.

weight; → fraction; → concentration.

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