An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 694
dwarf star
  ستاره‌ی ِ کوتوله   
setâre-ye kutulé (#)

Fr.: étoile naine   

A star that burns its hydrogen content to produce its energy and therefore belongs to the main-sequence luminosity class.

dwarf; → star.


Fr.: dynamique   

1) Involving or relating to force related to motion.
2) Pertaining to the science of → dynamics.

From Fr. dynamique, from Ger. dynamisch, introduced by Leibnitz in 1691, from Gk. dynamikos "powerful," from dynamis "power," from dynasthai "be able to have power" + → -ic.

Tavânik, from tavân "power, strength," tavânestan "to be powerful, able," + Pers. suffix -ik; → -ics. The first component from Mid.Pers. tuwan "power, might," from O.Pers./Av. base tav- "to have power, to be strong, to be able," Av. tavah- "power," təviši- "strength," Mod.Pers. tuš, tâb "power, ability," O.Pers. tauman- "power, strength," tunuvant- "powerful," Skt. tu- "to be strong, to have authority," tavas-, tavisa- "strong, energetic," tavisi- "power, strength" + -ik-ic.

dynamic equilibrium
  ترازمندی ِ توانیک   
tarâzmandi-ye tavânik

Fr.: équilibre dynamique   

Mechanics: The condition of a moving mechanical system when the accelerating force is balanced by an imaginary kinetic reaction according to → d'Alembert's principle. See also → static equilibrium; → thermodynamic equilibrium.

Dynamic, adj. from → dynamics; → equilibrium.

dynamic oblateness
  پخی ِ توانیک   
paxi-ye tavânik

Fr.: aplatissement dynamique   

A measure of the extent to which mass has been shifted from the polar regions of a (spinning) body toward its equator (Ellis et al., 2007, Planetary Ring Systems, Springer).

dynamic; → oblateness.

dynamic pressure
  فشار ِ توانیک   
fešâr-e tavânik

Fr.: pression dynamique   

A property of a moving → fluid defined by (1/2)ρv2 in → Bernoulli's law, where ρ is → density of fluid and v is → velocity. Dynamic pressure is the difference between → total pressure and → static pressure. Also called → velocity pressure. → ram pressure.

dynamic; → pressure.

dynamic range
  برد ِ توانیک   
bord-e tavânik

Fr.: dynamique   

The ratio of the maximum to minimum signal levels present in an image. For instance, a true 12-bit digital camera is capable of providing a dynamic range of 4096 to 1.

Adj. of → dynamics; → range.

dynamic viscosity
  وشکسانی ِ توانیک   
vošksâni-y tavânik

Fr.: viscosité dynamique   

Same as → viscosity and → absolute viscosity.

dynamic; → viscosity.


Fr.: dynamique   

Of or pertaining to force or power; of or pertaining to force related to motion.
Pertaining to the science of dynamics. Same as dynamic.

Adj. from → dynamics.

dynamical age
  سن ِ توانیک   
senn-e tavânik

Fr.: âge dynamique   

Age based on dynamical properties of a system. For example, the time derived for a system to evolve from an initial state to its present state, based on velocity and dimension (size) measurements.

dynamical; → age.

dynamical disruption
  گسیخت ِ توانیک   
gosixt-e tavânik

Fr.: rupture dynamique   

The process whereby a → bound system, such as a → binary system or a → globular cluster, is broken apart.

dynamical; → disruption.

dynamical equilibrium
  ترازمندی ِ توانیک   
tarâzmandi-ye tavânik

Fr.: équilibre dynamique   

Of a physical system, a condition in which the parts of the system are in continuous motion, but they move in opposing directions at equal rates so that the system as a whole remains in equilibrium.

dynamical; → equilibrium.

dynamical friction
  مالش ِ توانیک   
mâleš-e tavânik

Fr.: frottement dynamique   

The gravitational interaction between a relatively massive body and a field of much less massive bodies through which the massive body travels. As a result, the moving body loses → momentum and → kinetic energy. An example of dynamical friction is the sinking of massive stars to the center of a → star cluster, a process called → mass segregation. Dynamical friction plays an important role in → stellar dynamics. It was first quantified by Chandrasekhar (1943).

dynamical; → friction.

dynamical law
  قانون ِ توانیک   
qânun-e tavânik

Fr.: loi dynamique   

A law that describes the motion of individual particles in a system, in contrast to → statistical laws.

dynamical; → law.

dynamical mass
  جرم ِ توانیک   
jerm-e tavânik

Fr.: masse dynamique   

The mass of an object derived indirectly from theoretical formulae based on the laws governing the behavior of a → dynamical system.

dynamical; → mass.

dynamical parallax
  دیدگشت ِ توانیک   
didgašt-e tavânik

Fr.: parallaxe dynamique   

A method for deriving the distance to a binary star. The angular diameter of the orbit of the stars around each other and their apparent brightness are observed. By applying Kepler's laws and the mass-luminosity relation, the distance of the binary star can be calculated.

dynamical; → parallax.

dynamical relaxation
  واهلش ِ توانیک   
vâheleš-e tavânik

Fr.: relaxation dynamique   

The evolution over time of a gravitationally → bound system consisting of N components because of encounters between the components, as studied in → stellar dynamics. Due to this process, in a → star cluster, → low-mass stars may acquire larger random velocities, and consequently occupy a larger volume than → high-mass stars. As a result, massive stars sink to the cluster centre on a time-scale that is inversely proportional to their mass. See also → mass segregation.

dynamical; → relaxation.

dynamical stream
  رابه‌ی ِ توانیک   
râbe-ye tavânik

Fr.: courant dynamique   

A group of stars pervading the Solar neighbourhood and travelling in the → Galaxy with a similar spatial velocity, such as the → Ursa Major star cluster, The term dynamical stream is more appropriate than the traditional term supercluster since it involves stars of di fferent ages, not born at the same place nor at the same time. A possible explanation for the presence of young groups in the same area as those streams is that they have been put there by the → spiral wave associated with their formation place, while kinematics of the older stars of the sample have also been disturbed by the same wave. The seemingly peculiar chemical composition of the Hyades-Pleiades stream suggests that this stream originates from a specific galactocentric distance and that it was perturbed by a spiral wave at a certain moment and radially pushed by the wave in the solar neighbourhood. This would explain why this stream is composed of stars sharing a common metallicity but not a common age (Famaey et al. 2005, A&A 430, 165).

dynamical; → stream.

dynamical system
  راژمان ِ توانیک   
râžmân-e tavânik

Fr.: système dynamique   

A system composed of one or more entities in which one state develops into another state over the course of time.

dynamical; → system.

dynamical time
  زمان ِ توانیک   
zamân-e tavânik

Fr.: temps dynamique   

The independent variable in the theories which describe the motions of bodies in the solar system. The most widely used form of it, known as Terrestrial Time (TT) or Terrestrial Dynamical Time (TDT) uses a fundamental 86,400 Systeme Internationale seconds (one day) as its fundamental unit. → Terrestrial Time; → Terrestrial Dynamical Time; → Barycentric Dynamical Time.

dynamical; → time.

dynamical time scale
  مرپل ِ زمانی ِ توانیک   
marpel-e zamâni-ye tavânik

Fr.: échelle de temps dynamique   

1) The characteristic time it takes a protostellar cloud to collapse if the pressure supporting it against gravity were suddenly removed; also known as the → free-fall time.
2) → crossing time for a stellar system like a galaxy.

dynamical; → time-scale.

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