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: 664
equation of motion
  هموگش ِ جنبش   
hamugeš-e jonbeš

Fr.: équation de mouvement   

1) Any equation that describes the motion of objects, i.e., variation of velocity, distance covered, acceleration, etc., as a function of time; e.g., V = V0 + at, S = Vt + (1/2)at2.
2) For a fluid, a relation, in its most fundamental form, equating the rate of change of momentum of a selected portion of fluid and the sum of all forces acting on that portion of fluid.
3) In quantum mechanics, an equation that governs the time variation of the → state of the system. → Schrodinger equation. However, in the Heisenberg formulation of quantum mechanics the equation of motion does not involve the states, which in this case is time independent, but rather the → observables of the system.

equation; → motion.

equation of state
  هموگش ِ حالت   
hamugeš-e hâlat

Fr.: équation d'état   

In physics and thermodynamics, the equation that describes the relationship between pressure, density, and temperature, e.g. → ideal gas law, → van der Waals equation, → polytropic process, → virial equation of state.

equation; → state.

equation of state parameter
  پارامون ِ هموگش ِ حالت   
pârâmun-e hamugeš-e hâlat

Fr.: paramètre de l'équation d'état   

In cosmology, a → dimensionless parameter introduced by the → equation of state representing the ratio of the pressure to the energy density of a fluid, such as the → dark energy: w = p/ρ. The → deceleration or → acceleration of an → expanding Universe depends on this parameter (→ accelerating Universe). A number of numerical values of this parameter are as follows: for the → cosmological constant: w = -1, for → non-relativistic matter (present-day → baryons): w = 0, and for → relativistic matter (photons, neutrinos): w = +1/3. Together with Ω(dark energy) and Ω(matter), w provides a three-parameter description of the dark energy. The simplest parametrization of the dark energy is w = constant, although w might depend on → redshift.

equation; → state; → parameter.

equation of the equinoxes
  هموگش ِ هموگانها   
hamugeš-e hamugânhâ

Fr.: équation des équinoxes   

The difference between → apparent sidereal time and → mean sidereal time. It is due to the nutation of the Earth's polar axis of rotation about its precessional motion. It ranges from +0.8 to +1.2 seconds. Also known as → nutation in right ascension.

equation; → equinox.

equation of time
  هموگش ِ زمان   
hamugeš-e zamân

Fr.: équation du temps   

The difference, due to Earth's elliptical orbit and variable orbital velocity, between apparent solar time and mean solar time. It varies throughout the year, and slightly from year to year. At present, it reaches extremes of about -14 minutes in February, and about +16 minutes in November. The equation of time is visually illustrated by an → analemma.

equation; → time.

equator
  هموگار، استوا   
hamugâr, estevâ (#)

Fr.: équateur   

The great circle on the surface of a body formed by the intersection of the surface with the plane passing through the center of the body perpendicular to the axis of rotation. → celestial equator.

From M.L. æquator "equalizer" (of day and night, as when the sun crosses the equator), from æquare "to make equal, equate" + -tor.

Hamugâr, from hamug, → equal + -âr suffix forming agent nous (as in parastâr) or contracted present stem of âvardan "to bring; to cause, to produce."

equator plane
  هامن ِ هموگاری   
hâmon-e hamugâri

Fr.: plan équatorial   

An imaginary plane → perpendicular to the → axis of a → sphere dividing the sphere into two congruent parts.

equator; → plane.

equator system
  راژمان ِ هموگاری   
râžmân-e hamugâri

Fr.: système équatorial   

A set of celestial coordinates based on the celestial equator as the primary great circle. The coordinates are → declination and → right ascension.

equator; → system.

equatorial
  هموگاری   
hamugâri

Fr.: équatorial   

Of, pertaining to, or near an equator, especially the equator of the Earth.

From → equator + -ial, variant of → -al.

Hamugâri, from hamugâr, → equator, + adj. suffix -i.

equatorial bulge
  بر‌آمدگی ِ هموگاری   
barâmadegi-ye hamugâri

Fr.: bourrelet équatorial   

The excess of the Earth's equatorial diameter over the polar diameter.

equatorial; bulge, from O.Fr. bouge "leather bag," from L. bulga "leather bag," of Gaulish origin.

Barâmadegi, from barâmadan "to grow out; to emerge," from bar- "on, upon, up" (Mid.Pers. abar, O.Pers. upariy "above; over, upon, according to," Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + âmadan "to come" (Mid.Pers. âmadan; O.Pers. gam- "to come; to go;" Av. gam- "to come; to go," jamaiti "goes;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").

equatorial coordinate system
  راژمان ِ هماراهای ِ هموگاری   
râžmân-e hamârâhâ-ye hamugâri

Fr.: système de coordonnées équatoriales   

An astronomical → coordinate system for indicating the positions of → celestial objects on the → celestial sphere. The system consists of two components, → right ascension and → declination. Right ascension is the angle between the → vernal equinox and the point where the → hour circle intersects the → celestial equator. The right ascension is always measured eastward from the vernal equinox, in the units of hours, minutes, and seconds. Declination is the angle between the celestial equator and the position of the star measured along the star's hour circle. It is measured in degrees, minutes, and seconds north or south of the celestial equator. By definition, the vernal equinox is located at right ascension 0h and declination 0°. Equatorial coordinates change with time due to the → precession of the Earth's → rotation axis.

equatorial; → coordinate; → system.

equatorial coordinates
  هماراها‌ی ِ هموگاری   
hamârâhâ-ye hamugâri

Fr.: coordonnées équatoriales   

Celestial coordinates in the → equator system.

equatorial, → coordinate.

equatorial mounting
  برنشاند ِ هموگاری   
barnešând-e hamugâri

Fr.: monture équatoriale   

A telescope mounting consisting of a polar axis pointed toward the celestial pole, and a declination axis supporting the instrument at right angles to the polar axis.

equatorial; → mounting.

equatorial plane
  هامن ِ هموگاری   
hâmon-e hamugâri

Fr.: plan équatorial   

The plane containing a celestial object's equator.

equatorial; → plane.

equatorial radius
  شعاع ِ هموگاری   
šo'â'-e hamugâri

Fr.: rayon équatorial   

Of a planet, the distance from the center to the equator. For Earth it is 6,378.1370 km. Jupiter has an equatorial radius 11.2 times Earth's value.

equatorial; → radius.

equatorial wind
  باد ِ هموگاری   
bâd-e hamugâri

Fr.: vent équatorial   

A slow, dense → stellar wind (high → mass loss rate) emanating from equatorial regions of a → B[e] star. The equatorial and → polar winds are the two main wind components in B[e] stars. The mechanism suggested to explain this wind morphology is the rotationally induced → bistability mechanism.

equatorial; → wind.

equi-
  هموگ-   
hamug-

Fr.: équi-   

A prefix meaning "equal," as in → equinox, → equilibrium, → equipartition.

M.E., from L. aequi-, combining form representing aequus, → equal.

Hamug-, → equal.

equiaxial
  هموگ-آسه   
hamug-âsé

Fr.: équiaxe   

Math.: having three axes of the same length. Also equiaxed.
Physics: A crystal exhibiting similar dimensions in all directions.

equi-; → axis.

equilateral triangle
  سه‌بر ِ سه-پهلو-برابر   
sebar-e sé-pahlu-barâbar (#)

Fr.: triangle équilatéral   

A triangle having three equal sides.

equi-, → lateral, → triangle.

Sé-pahlu-barâbar, from , → three, pahlu, → side, barâbar, → equal.

equilibrium
  ترازمندی   
tarâzmandi (#)

Fr.: équilibre   

A state of balance or rest between the forces operating on or within a physical system. → stable equilibrium; → unstable equilibrium; → dynamical equilibrium.

From L. æquilibrium, from æquus, → equal + libra "a balance, scale."

Tarâzmandi, noun of tarâzmand "in equilibrium," from tarâz "level; a level" + possession suffix -mand. The first component from tarâzu "balance, scales," Mid.Pers. tarâzên-, taraênidan "to weigh;" Proto-Iranian *tarāz-, from *tarā- "balance, scale" (cf. Skt. tulā- "scales, balance, weight," from tul- "to weigh, make equal in weight, equal," tolayati "weighs, balances;" L. tollere "to raise;" Gk. talanton "balance, weight," Atlas "the Bearer" of Heaven;" Lith. tiltas "bridge;" PIE base telə- "to lift, weigh") + Av. az- "to convey, conduct, drive," azaiti drives" (cf. Skt. aj- "to dive, sling," ájati "drives," ajirá- "agile, quick;" Gk. agein "to lead, guide, drive, carry off;" L. agere "to do, set in motion, drive," from PIE root *ag- "to drive, move," → act).

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