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: 55 Search : mica
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.

economical
  بومداتی   
bumdâti

Fr.: économique   

1) Avoiding waste or extravagance; thrifty.
2) → economic.

economic; → -al.

geochemical
  زمین-شیمیک، زمین-شیمیایی   
zamin-šimik, zamin-šimiyâyi

Fr.: géochimique   

Of or relating to → geochemistry.

geochemistry; → -al.

Infrared Astronomical Satellite (IRAS)
  ماهواره‌ی ِ اخترشناختی ِ فروسرخ   
mâhvâre-ye axtaršenâxti-e forusorx (#)

Fr.: satellite astronomique infrarouge   

An orbiting infrared telescope (60 cm mirror) which successfully operated from launch in January 1983 until the supply of coolant ran out in November 1983. It was a collaborative mission between NASA, the Netherlands, and the UK, and mapped 95% of the whole sky in the wavelength bands 12, 25, 60, and 100 microns.

infrared; → astronomical; → satellite.

International Astronomical Union (IAU)
  یکایش ِ جهانی ِ اخترشناسی   
Yekâyeš-e Jahâni-ye Axtaršenâsi

Fr.: Union Astronomique Internationale (UAI)   

An astronomical association of astronomers that is the controlling body of world astronomy. It was founded in Brussels in 1919.

international; → astronomical; → union.

mica
  میکا   
mikâ (#)

Fr.: mica   

A shiny silicate mineral composed of varying amounts of → aluminum, → potassium, → magnesium, and → iron. Mica appears as thin, flexible layers in → granite and other rocks, or as → crystals. It is used as a thermal or electrical → insulator.

From L. mica "crumb, grain."

real dynamical variable
  ورتنده‌ی ِ توانیک ِ هسیا   
vartande-ye tavânik-e hasyâ

Fr.: variable dynamique réel   

A → dynamical variable which does not have an → imaginary number part.

real; → dynamical; → variable.

Strasbourg Astronomical Data Center (CDS)
     
CDS

Fr.: Centre de Données astronomiques de Strasbourg (CDS)   

A data center dedicated to the collection and worldwide distribution of astronomical data and related information. It is located at the Strasbourg Astronomical Observatory, France. The CDS has several goals, mainly: collecting all of the useful information regarding astronomical objects in computerized form, including observational data produced by observatories on the ground or in space; upgrading these data by critical evaluations and comparisons; and distributing the results to the astronomical community. Currently the CDS services include: → SIMBAD, Aladin interactive sky atlas, and VizieR catalogues.

CDS, short for Centre de Données astronomiques de Strasbourg.

Terrestrial Dynamical Time
  زمان ِ توانیک ِ زمینی   
zamân-e tavânik-e zamini

Fr.: temps dynamique terrestre   

A uniform atomic time scale for apparent geocentric ephemerides defined by a 1979 IAU resolution, which replaced Ephemeris Time. TDT is independent of the variable rotation of the Earth, and the length of the tropical year is defined in days of 86,400 seconds of international atomic time. In 1991 it was replaced by Terrestrial Time.

terrestrial; → dynamical; → time.

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