# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 equatorial radius   شعاع ِ هموگاری   šo'â'-e hamugâriFr.: 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 hamugâriFr.: 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-âséFr.: 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 sé, → 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). equilibrium partitioning   پرکه‌بندی ِ ترازمند   parkebandi-ye tarâzmandFr.: équilibre de partition   A concept whereby chemical → concentrations among geological or environmental media are at equilibrium, and therefore the partitioning of metals in those media can be predicted based on → partition ratios. equilibrium position   نهش ِ ترازمندی   naheš-e tarâzmandi (#)Fr.: position d'équilibre   The position of an oscillating body at which no net force acts on it.→ equilibrium; → position. equilibrium state   استات ِ ترازمندی، حالت ِ ~   estât-e tarâzmandi, hâlat-e ~Fr.: état d'équilibre   A state in which a → thermodynamic system is in → thermodynamic equilibrium.→ equilibrium; → state. equilux   هموگتاب   hamugtâbFr.: équilux   The date on which the day and night have exactly the same length. Contrary to the widespread statement, the day and night are not equal at the → equinox. The higher the → latitude, the greater the difference. In fact the day and night lengths are equal at the equinox only if the strict theoretical definition is used, according to which sunset and sunrise are the moments when the center of the Sun crosses the → horizon. There are two reasons for this inequality: 1) The Sun is a disk, not a point source. It is about 30 arc minute wide, hence sunrise corresponds to the moment the top of the disk (and not its center) emerges out of the horizon. Similarly, sunset is when the last part of the disk sinks below the horizon. The Sun takes about a minute to move from its center to its edge (the Earth rotates about 1 degree in 4 minutes). This sums to two minutes (a minute for sunset and a minute for sunrise) that adds to 4 minutes in the total difference. 2) The atmosphere acts as a lens, and slightly bends the Sun's rays because of the → atmospheric refraction. When we look at the setting Sun, the fact is that it was already set. Unlike the equinox, which is a fixed date all-over the globe, the date of the equilux is dependent upon the → latitude of the observer. Between the poles and about 20 degrees latitude, it is generally a few days before the → vernal equinox or a few days after the → autumnal equinox .→ equi-; → lux. equinoctial   هموگانی   hamugâniFr.: équinoxial   Of or relating to an equinox or to the equality of day and night.Adjective of → equinox. equinoctial colure   کلدم ِ هموگانی   koldom-e hamugâniFr.: colure d'équinoxe   The great circle of the celestial sphere through the celestial poles and equinoxes; the hour circle of the vernal equinox. → colure.→ equinoctial; → colure. equinoctial points   نقطه‌ها‌ی ِ هموگانی   noqtehâ-ye hamugâniFr.: points équinoxiaux   One of the two points of intersection of the ecliptic and the celestial equator. Same as equinox.→ equinoctial; → point. equinox   هموگان   hamugânFr.: équinoxe   1) One of the two points on the → celestial sphere where the → celestial equator intersects the → ecliptic, that is when the apparent → ecliptic longitude of the Sun is 0° or 180°. 2) Either of the times at which the center of the Sun's disk passes through these points. → autumnal equinox; → vernal equinox. At equinox, the length of the day and the night are equal all over the globe. The equinox is not a fixed point; it moves due to → precession and → nutation. If only precession is considered, we deal with the → mean equinox of date. If nutation is also taken into account, then we are concerned with the → true equinox.M.E., from O.Fr. équinoxe, from M.L. equinoxium "equality of night (and day)," from L. æquinoctium, from æquus, "→ equal" + nox "→ night" (gen. noctis). In Gk. isimeria "equal day," from isos "equal," → iso-, + hemera "day."From hamug, → equal, + -ân suffix denoting time and place. equipartition of energy   هموگپرکش ِ کاروژ   hamugparkeš-e kâružFr.: équipartition de l'énergie   1) General: Equal sharing of the → total energy among all → components of a → system. 2) In the → kinetic theory of gases, the → theorem according to which → molecules in → thermal equilibrium have the same average energy (1/2 kT) associated with each independent → degree of freedom of their motion.→ equi-; → partition. equipotential surface   رویه‌ی ِ هموگ-توند   ruye-ye hamugtavandFr.: surface équipotentielle   An imaginary surface surrounding a body, or group of bodies, over which the gravitational field is of constant strength and, at all points, is directed perpendicular to the surface. For a single star the surface is spherical. In a close binary system the equipotential surface of the components interact to become hourglass-shaped. → Roche lobe; → Lagrangian points.From → equi-; → potential; → surface. equivalence   هموگ‌ارزی   hamug-arzi (#)Fr.: équivalence   The state or fact of being equivalent; equality in value, force, significance, etc. → covalence.From M.F. from M.L. æquivalentia, from L. æquivalent-, → equivalent.Hamug-arzi, noun of hamug-arz, → equivalent. equivalence principle   پروز ِ هموگ‌ارزی   parvaz-e hamug-arziFr.: principe d'équivalence   A fundamental concept of physics, put forward by A. Einstein, that states that gravitational and inertial forces are of a similar nature and indistinguishable. In other words, acceleration due to gravity is equivalent to acceleration due to other forces, and gravitational mass is the same as inertial mass. Same as the → principle of equivalence.→ equivalence; → principle. equivalent   هموگ‌ارز   hamug-arzFr.: équivalent   Equal in value, measure, force, effect, significance, etc.From L.L. æquivalentem (nominative æquivalens) "equivalent," p.p. of æquivalere "be equivalent," from L. æquus, → equal + valere "to be worth; be strong."Hamug-arz, from hamug-, → equi-, + arz stem of arzidan "to be worth," arzân "worthy; of small value, cheap," arj "esteem, honour, price, worth;" Mid.Pers. arz "value, worth," arzidan "be worth," arzân "valuable;" Av. arəjaiti "is worth," arəja- "valuable," arəg- "to be worth;" cf. Skt. arh- "to be worth, to earn," árhant- "worthy person;" Gk. alphanein "to bring in as profit," alphein "to ear, obtain;" Lith. algà "salary, pay;" PIE base *algwh- "to earn; price, value." equivalent depth   ژرفای ِ هم-ارز   žarfâ-ye ham-arzFr.: profondeur équivalente   A measure of the number of particles passing a given point in a → planetary ring per unit time. It is obtained by multiplying the physical width of the ring by its average → optical depth. For the variable-width eccentric rings of → Uranus, equivalent depth remains almost constant around a given ring (Ellis et al., 2007, Planetary Ring Systems, Springer).→ equivalent; → depth.