An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 902
Alcor
  سها   
Sohâ (#)

Fr.: Alcor   

A 4th magnitude star lying in the constellation → Ursa Major (also called 80 Ursae Majoris) which forms a visual pair with the brighter star → Mizar (Zeta Ursae Majoris). Alcor is separated by about 11.5 minutes of arc from Mizar. It is a → main sequence star of type A5 with a mass of 1.8 Msun. Recent observations show that Alcor is a → spectroscopic binary, whose → companion has M-band (λ = 4.8 μm) magnitude 8.8 and projected separation 1''.11 (28 AU) from Alcor. The companion is most likely a low-mass (~ 0.3 Msun) active star which is responsible for Alcor's → X-ray emission detected by → ROSAT (LX ~ 1028.3 erg/s). Alcor is a nuclear member of the → Ursa Major star cluster (distance ~ 25 pc, age ~ 0.5 Gyr). The Alcor binary is probably → gravitationally bound to the Mizar star system, making them a → sextuplet with physical separation 0.36 pc, or 74,000 → astronomical units (Mamajek et al., 2010, AJ 139, 919).

Alcor, perhaps from Ar. al-khawr "the low ground."

Sohâ, from Ar. Suhâ.

Alcyone (η Tauri)
  الکویءون، نیر ِ ثریا، رخشان ِ پروین   
Alkuone, Nayyer-e Sorayyâ, Raxšân-e Parvin

Fr.: Alcyone   

The brightest star in the → Pleiades, located in the constellation → Taurus. → Apparent visual magnitude 2.87, → spectral type B7 III.

In Gk. mythology, a daughter of Aelous who, with her husband, Ceyx, was transformed into a kingfisher.

Nayyer-e Sorayyâ "the bight of the Pleiades," from Ar. nayyir "luminous" + Thorayyâ "the Pleiades".
Raxšân-e Parvin "the bight of the Pleiades," from Mod.Pers. raxšân "bright, luminous" + Parvin "the Pleiades".

Aldebaran (α Tauri)
  دَبَران، گاو‌چشم   
Dabarân, Gâvcašm

Fr.: Aldébaran   

The brightest star in the constellation → Taurus (visual magnitude about 0.9), Aldebaran is an orange K-type giant that lies 60 → light-years away. It has a faint M2 V companion. It is slowly and irregularly variable.

Ar. Aldebaran "the follower" (of the Pleiades, which rise shortly before it does), from al "the" + dabaran "follower," from dobur "to follow". Gâvcašm "the bull's eye," from Mod.Pers. Gâv "bull, cow" + cašm "eye," corresponding to the alternative Ar. name of the star Ayno 's Sowr.

aldehyde
  آلدهید   
âldehid (#)

Fr.: aldéhyde   

Any of a class of organic compounds containing the -CH=O group, that is a double-bonded oxygen and hydrogen bonded to the same terminal carbon atom.

From N.L. al(cohol) dehyd(rogenatum) "alcohol deprived of hydrogen."

Alderamin (α Cephei)
  ذراع ِ یمین   
Zerâ'-e Yamin

Fr.: Alderamin   

The brightest star in → Cepheus and a → subgiant star of apparent visual magnitude 2.44. Its → spectral type is A7 and distance 49 → light-years.

Alderamin, from Ar. al dhirâ' al-yamin "right arm" (of Cepheus), from Ar. dhirâ' "arm" + yamin "right".

Zerâ'-e Yamin, from Ar. al dhira al-yamin.

aleph
  الف   
alef (#)

Fr.: aleph   

1) The first letter of the Hebrew alphabet (ℵ).
2) A → cardinal number representing an uncountable set. For example, ℵ0 (pronounced aleph-null, aleph-nought, or aleph-zero) is the smallest infinite cardinal and ℵ1 is the smallest cadinal larger than ℵ0.

Hebrew and Phoenician letter, from Semitic languages.

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.

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