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: 892
Alexander's dark band
  نوار ِ سیاه ِ الکساندر   
navâr-e siyâh-e Aleksânder

Fr.: bande noire d'Alexandre   

A dark space or band between the primary and secondary rainbows when both are visible. This effect is due to the minimum refraction angle for the → primary rainbow and the maximum for the → secondary rainbow. The only light in the dark region is caused by (a small amount of) scattering, and not the refraction of light in water droplets.

Named for Alexander of Aphrodisias, Greek Peripatetic philosopher and commentator, who first described the effect in 200 AD.

Alfonsine Tables
  زیج ِ آلفونسو   
zij-e Alfonso

Fr.: Tables alfonsines   

A set of tables created in Toledo, under Alfonso X, el sabio, king of Castile and Léon (1252 to 1284) to correct the anomalies in the → Toledan Tables. The starting point of the Alfonsine Tables is January 1, 1252, the year of king's coronation (1 June). The original Spanish version of the tables is lost, but a set of canons (introductory instructions) for planetary tables are extant. They are written by Isaac ben Sid and Judah ben Moses ha-Cohen, two of the most active collaborators of Alfonso X. The Alfonsine Tables were the most widely used astronomical tables in the Middle Ages and had an enormous impact on the development of European astronomy from the 13th to 16th century. They were replaced by Erasmus Reinhold's → Prutenic Tables, based on Copernican models, that were first published in 1551.The Latin version of the Alfonsine Tables first appeared in Paris around 1320, where a revision was undertaken by John of Lignères and John of Murs, accompanied by a number of canons for their use written by John of Saxony. There is a controversy as to the exact relationship of these tables with the work commissioned by the Spanish king.

After the Spanish monarch Alfonso X (1221-1284); → table.

Alfvén Mach number
  عدد ِ ماخ ِ آلفونی   
adad-e Mach-e Alfvéni

Fr.: nombre de Mach alfvénique   

The ratio of the flow velocity to the → Alfvén speed in a medium.

Alfvén wave; → number.

Alfvén radius
  شعاع ِ آلفون   
šo'â'-e Alfvén

Fr.: rayon d'Alfvén   

1) In theories of magnetized → accretion disks, the distance from a non-rotating star where the → free fall of a spherical accretion flow is stopped, which occurs where the → ram pressure of the infalling matter equals the → magnetic pressure of the star.
2) The distance from an accreting or wind-blowing star where the → Alfvén Mach number of the flow (→ inflow or → outflow) is unity.

Alfvén wave; → radius.

Alfvén speed
  تندا‌ی ِ آلفون   
tondâ-ye Alfvén

Fr.: vitesse d'Alfvén   

The speed at which → Alfven waves are propagated along the magnetic field. It is a characteristic velocity at which perturbations of the lines of force travel. Alfvén speed is given by: vA = B/(μ0.ρ)1/2, where B is the → magnetic field strength, μ0 is the → magnetic permeability, and ρ is the density of the plasma. Alfvén speed plays a role analogous to the sound speed in non-magnetized fluid dynamics. Same as Alfvén velocity.

Alfvén wave; → speed.

Alfvén wave
  موج ِ آلفون   
mowj-e Alfvén

Fr.: onde d'Alfvén   

A → magnetohydrodynamic wave in a → magnetized plasma, arising as a result of restoring forces associated with the magnetic field. It is a → transverse wave which propagates in the direction of the magnetic field. Also called magnetohydrodynamic wave.

Named after Hannes Alfvén (1908-1995), Swedish physicist, who developed the theory of → magnetohydrodynamics, and was awarded the Nobel Prize in Physics in 1970; → wave.

Alfvénic
  آلفونیک   
Alfvenik

Fr.: alfvénicité   

Involving → Alfvén waves.

Alfvénic; → -ity.

Alfvénic fluctuation
  افتاخیز ِ آلفونیک   
oftâxiz-e Alfvenik

Fr.: fluctuation alfvénique   

Large amplitude fluctuations in the → solar wind with properties resembling those of → Alfvén waves. A fluctuation is said to be Alfvénic if the following relationship between the velocity fluctuations (Δv) and magnetic field fluctuations (ΔB) is satisfied: Δv = ± ΔB/(μ0ρ)1/2. Also called Alfvénicity.

Alfvénic; → fluctuation.

Alfvénicity
  آلفونیکی   
Alfveniki

Fr.: alfvénicité   

Alfvénic fluctuation.

Alfvénic; → -ity.

Alfven Mach number
  عدد ِ ماخ ِ آلفونی   
adad-e Mach-e Alfvéni

Fr.: nombre de Mach alfvénique   

The ratio of the flow velocity to the → Alfvén speed in a medium.

Alfvén wave; → number.

Alfven point
  نقطه‌ی ِ آلفون   
noqte-ye Alfvén

Fr.: point d'Alfvén   

In magnetized disk models, the point where the → poloidal velocity equals the → Alfven speed. Within this point, the magnetic energy density dominates, and the gas is forced to flow along the field lines. Well beyond this point, the kinetic energy acquired by the flowing gas prevails and the field is forced to follow the flow.

Alfven wave; → point.

Alfven radius
  شعاع ِ آلفون   
šo'â'-e Alfvén

Fr.: rayon d'Alfvén   

1) In theories of magnetized → accretion disks, the distance from a non-rotating star where the → free fall of a spherical accretion flow is stopped, which occurs where the → ram pressure of the infalling matter equals the → magnetic pressure of the star.
2) More generally, the distance from an accreting or wind-blowing star where the → Alfvén Mach number of the flow (→ inflow or → outflow) is unity.

Alfvén wave; → radius.

Alfven speed
  تندا‌ی ِ آلفون   
tondâ-ye Alfvén

Fr.: vitesse d'Alfvén   

The speed at which → Alfven waves are propagated along the magnetic field. It is a characteristic velocity at which perturbations of the lines of force travel. Alfvén speed is given by: vA = B/(μ0.ρ)1/2, where B is the → magnetic field strength, μ0 is the → magnetic permeability, and ρ is the density of the plasma. Alfvén speed plays a role analogous to the sound speed in non-magnetized fluid dynamics. Same as Alfvén velocity.

Alfvén wave; → speed.

Alfven surface
  رویه‌ی ِ آلفون   
ruye-ye Alfvén

Fr.: surface d'Alfvén   

In a magnetized wind, the geometric loci of the points where the magnetic pressure equals the flow pressure. See also → Alfven point.

Alfven wave; → surface.

Alfven velocity
  تندای ِ آلفون   
tondâ-ye Alfvén

Fr.: vitesse d'Alfvén   

same as → Alfven speed.

Alfven wave; → velocity.

Alfven wave
  موج ِ آلفون   
mowj-e Alfvén

Fr.: onde d'Alfvén   

A → magnetohydrodynamic wave in a → magnetized plasma, arising as a result of restoring forces associated with the magnetic field. It is a → transverse wave which propagates in the direction of the magnetic field. Also called magnetohydrodynamic wave.

Named after Hannes Alfvén (1908-1995), Swedish physicist, who developed the theory of → magnetohydrodynamics, and was awarded the Nobel Prize in Physics in 1970; → wave.

Alfvenic
  آلفونیک   
Alfvenik

Fr.: alfvénicité   

Involving → Alfvén waves.

Alfvénic; → -ity.

Alfvenic fluctuation
  افتاخیز ِ آلفونیک   
oftâxiz-e Alfvenik

Fr.: fluctuation alfvénique   

Large amplitude fluctuations in the → solar wind with properties resembling those of → Alfvén waves. A fluctuation is said to be Alfvénic if the following relationship between the velocity fluctuations (Δv) and magnetic field fluctuations (ΔB) is satisfied: Δv = ± ΔB/(μ0ρ)1/2. Also called Alfvénicity.

Alfvén wave; → fluctuation.

Alfvenicity
  آلفونیکی   
Alfveniki

Fr.: alfvénicité   

Alfvénic fluctuation.

Alfvénic; → -ity.

alga
  جلبک   
jolbak (#)

Fr.: algues   

A single-celled or multicellular plant living in water or moist conditions, which contain chlorophyll and other pigments but has no true root, stem, or leaf. Algae include seaweeds and pond scum.

From alga (singular), from L. alga "seaweed," of uncertain origin.

Jolbak "alga."

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