An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < aer dyn law the > >>

Number of Results: 67 Search : dynamic
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.

dynamical variable
  ورتنده‌ی ِ توانیک   
vartande-ye tavânik

Fr.: variable dynamique   

Mechanics: One of the variables used to describe a system in classical mechanics, such as coordinates (of a particle), components of velocity, momentum, angular momentum, and functions of these quantities.

dynamical; → variable.


Fr.: dynamique   

The branch of → mechanics that explains how particles and systems move under the influence of forces.

dynamic; → -ics.

  برقاتوانیک، برقاتوانا   
barqâtavânik, barqâtavânâ

Fr.: électrodynamique   

Referring to electrons in motion.

electro- + → dynamics.


Fr.: électrodynamique   

The phenomena, science, and applications of moving electric charges, as contrasted with → electrostatics. More specifically, the branch of physics concerned with the → interaction of → electric currents with → magnetic fields and → electric fields or with other electric currents.

electro- + → dynamics.

first law of thermodynamics
  قانون ِ نخست ِ گرماتوانیک   
qânun-e naxost-e garâtavânik

Fr.: première loi de la thermodynamique   

The total energy of a → closed system is constant. This means that energy can be changed from one form to another, or transferred from one system to another, but it cannot be created or destroyed. A mathematical formulation of the first law is: δQ = δU + δW, where δQ is the heat transferred to the system, δU the change in internal energy (resulting in a rise or fall of temperature), and δW is the work done by the system.

first; → law; → thermodynamics.

fluid dynamics
  توانیک ِ شاره‌ها   
tavânik-e šârehâ

Fr.: dynamique des fluides   

The branch of → fluid mechanics that deals with the movement of gases and liquids.

fluid; → dynamics.

galactic dynamics
  دینامیک ِ کهکشانی   
tavânik-e kakhešâni

Fr.: dynamique galactique   

The study of the → motions of the → stars, → gas, and → dark matter in a → galaxy to explain the main → morphological and → kinematical features of the galaxy.

galactic; → dynamics.

Hamiltonian dynamics
  توانیک ِ هامیلتون   
tavânik-e Hamilton

Fr.: dynamique hamiltonienne   

The study of → dynamical systems in terms of the → Hamilton's equations.

Hamiltonian function; → dynamics.


Fr.: hydrodynamique   

Of or pertaining to → hydrodynamics.

hydro- + → dynamic.

hydrodynamic equation
  هموگش ِ هیدروتوانیک   
hamugeš-e hirdrotavânik

Fr.: équation hydrodynamique   

Fluid mechanics: A → partial differential equation which describes the motion of an element of fluid subjected to different forces such as pressure, gravity, and frictions.

hydrodynamic; → equation.

hydrodynamic equilibrium
  ترازمندی ِ هیدروتوانیک   
tarâzmandi-ye hirdrotavânik

Fr.: équilibre hydrodynamique   

The state of a star when all its internal forces are in equilibrium. The main forces are gas pressure, radiation pressure due to thermonuclear fusion that tends to disrupt the star, and the opposing gravity. → hydrostatic equilibrium.

hydrodynamic; → equilibrium.


Fr.: hydrodynamique   

The branch of physics dealing with the motion, energy, and pressure of neutral → fluids.

hydro- + → dynamics.

ideal magnetohydrodynamics (MHD)
  مغنات-و-هیدروتوانیک ِ آرمانی، ~ مینه‌وار   
meqnâtohidrotavânik-e ârmâni, ~ minevâr

Fr.: magnétohydrodynamique idéale   

Magnetohydrodynamics of a → plasma with very large (infinite) → conductivity. In this condition, → Ohm's law reduces to E = -v × B, where E represents → electric field, B → magnetic field, and v the → fluid velocity. Ideal MHD is the simplest model to describe the dynamics of plasmas immersed in a magnetic field. It is concerned with → one-fluid magnetohydrodynamics and neglects → resistivity. This theory treats the plasma composed of many charged particles with locally neutral charge as a continuous single → fluid. Ideal MHD does not provide information on the velocity distribution and neglects the physics relating to wave-particle interactions, as does the two-fluid theory as well. It does have the advantage that the macroscopic dynamics of the → magnetized plasma can be analyzed in realistic three-dimensional geometries (K. Nishikawa & M. Wakatani, 2000, Plasma Physics, Springer). See also → non-ideal magnetohydrodynamics.

ideal; → magnetohydrodynamics.

Lagrangian dynamics
  توانیک ِ لاگرانژی   
tavânik-e lâgrânži

Fr.: dynamique lagrangienne   

A reformulation of → Newtonian mechanics in which dynamical properties of the system are described in terms of generalized variables. In this approach the → generalized coordinates and → generalized velocities are treated as independent variables. Indeed applying Newton's laws to complicated problems can become a difficult task, especially if a description of the motion is needed for systems that either move in a complicated manner, or other coordinates than → Cartesian coordinates are used, or even for systems that involve several objects. Lagrangian dynamics encompasses Newton dynamics, and moreover leads to the concept of the → Hamiltonian of the system and a process by means of which it can be calculated. The Hamiltonian is a cornerstone in the field of → quantum mechanics.

Lagrangian; → dynamics.

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