equation of state
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 of state parameter
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 of the equinoxes
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 of time
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.
hamugâr, estevâ (#)
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."
Fr.: plan équatorial
Fr.: système équatorial
Of, pertaining to, or near an equator, especially the equator of the Earth.
Hamugâri, from hamugâr, → equator, + adj. suffix -i.
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
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.
Fr.: coordonnées équatoriales
Celestial coordinates in the → equator system.
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.
Fr.: plan équatorial
The plane containing a celestial object's equator.
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.
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.
M.E., from L. aequi-, combining form representing aequus, → equal.
Hamug-, → equal.
Math.: having three axes of the same length. Also equiaxed.
sebar-e sé-pahlu-barâbar (#)
Fr.: triangle équilatéral
A triangle having three equal sides.
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).
naheš-e tarâzmandi (#)
Fr.: position d'équilibre
The position of an oscillating body at which no net force acts on it.