An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < D l dar dat day dea dec dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dod Dop dou Dra dry dus dwa dyn Dys > >>

Number of Results: 763
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.

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.

tavânzâ (#)

Fr.: dynamo   

An electric generator, i.e. a machine that converts mechanical energy into electrical energy by virtue of the → electromagnetic induction.

From Ger. dynamoelektrischemaschine, coined (1867) by the German inventor Werner von Siemens (1816-1892), from Gk. dynamis "power," → dynamics.

Tavânzâ, from tavân "power," → dynamics + -zâ "generator," from zâdan "to give birth," Mid.Pers. zâtan, Av. zan- "to bear, give birth to a child, be born," infinitive zazâite, zâta- "born," cf. Skt. janati "begets, bears," L. gignere "to beget," PIE base *gen- "to give birth, beget."

dynamo effect
  اسکر ِ دینامو   
oskar-e dinâmo

Fr.: effet dynamo   

The generation of magnetic fields by movements within a → plasma, such as the → convective cores and → convective envelopes of stars. The magnetic field is intensified by the motion of the plasma in much the same way as in a dynamo. The generated magnetic field is not static, but evolves over time.

dynamo; → effect.

dynamo model
  مدل ِ توانزا   
model-e tavânzâ

Fr.: modèle dynamo   

A theory for the generation of a star's or planet's magnetic field by the circulation of conducting fluids inside it. → solar dynamo.

dynamo; → model.

dynamo theory
  نگره‌ی ِ توانزا   
negare-ye tavânzâ

Fr.: théorie de la dynamo   

Branch of magnetohydrodynamics concerned with self-excitation of magnetic fields in any large rotating mass of conducting fluid in motion (usually turbulent). Self-exciting dynamo action is believed to account for magnetic fields at the planetary, stellar, and galactic scales.

dynamo; → theory.

  توان سنج   
tavânsanj (#)

Fr.: dynamomètre   

A device for measuring mechanical force; specifically, one that measures the output or driving torque of a rotating machine.

Dynamometer, from → dynamo + → -meter.

Tavânsanj, from tavân "power," → dynamics + -sanj, → -meter.

din (#)

Fr.: dyne   

The centimeter-gram-second (cgs) unit of force (symbol dyn) that imparts an acceleration of 1 cm s-2 to a mass of 1 gram. 1 dyn = 10-5 → newton.

From Fr., from dynamis "power," → dynamics.

dinod (#)

Fr.: dynode   

An electrode that performs electron multiplication by means of secondary emission.

From dyn(a)- a combining form meaning "power," → dynamics + -ode a combining form meaning "way, road," used in the formation of compound words (anode; electrode), from Gk. hodos "way."

As above.

  دش-، دژ-   
doš- (#), dož- (#)

Fr.: dys-   

prefix meaning "bad, ill, abnormal."

From Gk. dys- "bad, hard, unlucky," cognate with O.Pers. duš-, Av. duž- (see below), Skt. dus- "bad, wrong, difficult, un-, -less," PIE *dus- "bad, ill."

Doš-, dož- "bad, ill, abnormal," from Mid.Pers. duž-, duš-, O.Pers. duš- (dušiyâr- "bad year, famine"), Av. duž-, duš- "bad" (duž-mainnyav- "evil-minded, enemy," Mod.Pers. došman "enemy"); PIE *dus-, as above.

Dysnomia (136199 Eris I)
Dusnomiya (#)

Fr.: Dysnomia   

A → satellite of the → dwarf planet → Eris.

Dysnomia in Gk. mythology is the daughter of Eris and the goddess of lawlessness.

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