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

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 mean equinox   هموگان ِ میانگین   hamugân-e miyânginFr.: équinoxe moyen   A fictitious equinox whose position is that of the vernal equinox at a particular epoch with the effect of nutation removed.→ mean; → equinox. mean free path   پویش ِ آزاد ِ میانگین   puyeš-e âzâd-e miyângin (#)Fr.: libre parcours moyen   The mean distance which a particle moves between two successive collisions with other particles of the medium. Mean free path is inversely proportional to the number of particles per cm3 (n), and the collision → cross section (σ). In the case of a gas with molecules having a diameter of d, the cross section is equal to the area of a circle of radius d, i.e. σ = πd2, and the mean free path is given by: l = 1/(nσ). Taking into account the relative velocity distribution of the colliding molecules, l = 1/(√2 . nσ). For a gas at one atmosphere pressure and room temperature, the average distance between molecules is roughly 3.5 × 10-7 cm, that is some 35 times the diameter of a molecule. Taking the gas density n = 2.4 × 1014 molecules cm-3, and a typical diameter d = 2 × 10-8 cm for a molecule, the mean free path is 3.3 × 10-5 cm. This means that the average distance between collisions is about 95 times the average distance between molecules.→ mean; → free; → path.Puyeš, verbal noun of puyidan "to run, trot; wander," from Mid.Pers. pôy-, pwd- "to run;" cf. Gk. speudein "to hasten;" Lith. spudinti; âzâd, → free; miyângin, → mean. mean life   زیست ِ میانگین   zist-e miyânginFr.: vie moyenne   The average amount of time an unstable radioisotope exists before it decays, It is equal to 1.44 times the half-life.→ mean; → life. mean molecular weight   وزن ِ مولکولی ِ میانگین   vazn-e molekuli-ye miyângin (#)Fr.: poids moléculaire moyen   The total atomic or molecular weight divided by the total number of particles. For instance, the mean molecular weight of a plasma of pure ionized 4He would be 4 (the atomic mass number) divided by 3, the total number of particles (1 nucleus plus 2 electrons), i.e. 4/3.→ mean; → molecular; → weight. mean moon   ماه ِ میانگین   mâh-e miyângin (#)Fr.: lune moyenne   A fictitious Moon that has the same average motion as the true Moon but that is not subject to any gravitational perturbations by other bodies.→ mean; → moon. mean motion   جنبش ِ میانگین   jonbeš-e miyângin (#)Fr.: mouvement moyen   The average angular velocity of a satellite in an elliptical orbit.→ mean; → motion. mean parallax   دیدگشت ِ میانگین   didgašt-e miyânginFr.: parallaxe moyenne   The parallax, derived by means of statistical studies of brightness and motions, for a large group of stars whose individual parallaxes cannot be measured.→ mean; → parallax. mean place   جای ِ میانگین   jâ-ye miyânginFr.: position moyenne   An object's celestial position as determined for a given mean equator and equinox. → mean position.→ mean; → place. mean pole   قطب ِ میانگین   qotb-e miyânginFr.: pôle moyen   The direction of the Earth's axis at a particular epoch if the nutation is ignored.→ mean; → pole. mean position   نهش ِ میانگین   neheš-e miyânginFr.: position moyenne   Same as → mean place.→ mean; → position. mean profile   فراپال ِ میانگین   farâpâl-e miyânginFr.: profil moyen   The shape of a pulsar's pulse as determined by averaging several pulses.→ mean; → profile. mean sidereal day   روز ِ اختری ِ میانگین   ruz-e axtari-ye miyânginFr.: jour sidéral moyen   The average time interval between two successive → upper transits of the → mean equinox.→ mean; → sidereal; → day. mean sidereal time   زمان ِ اختری ِ میانگین   zamân-e axtari-ye miyângin (#)Fr.: temps sidéral moyen   The hour angle of the mean equinox for a given observer.→ mean; → sidereal; → time. mean solar day   روز ِ خورشیدی ِ میانگین   ruz-e xoršidi-ye miyângin (#)Fr.: jour solaire moyen   The average length of the apparent solar day. In other words, the interval between successive transits of the mean Sun for a given observer.→ mean; → solar; → day. mean solar time   زمان ِ خورشیدی ِ میانگین   zamân-e xoršidi-ye miyângin (#)Fr.: temps solaire moyen   The time since the mean Sun crossed the meridian with 12 hours added to make the day begin at midnight.→ mean; → solar; → time. mean spectrum   بیناب ِ میانگین   binâb-e miyânginFr.: spectre moyen   A plot of the mass-to-charge ratio of elementary particles, sorted by their isotopic mass.→ mean; → spectrum. mean Sun   خورشید ِ میانگین   xoršid-e miyângin (#)Fr.: Soleil moyen   A hypothetical Sun that moves along the ecliptic at a uniform rate equal to the average motion of the real Sun.→ mean; → sun. mean term   ترم ِ میانی   tarm-e miyâniFr.: terme moyen   In → syllogism, the term which is common to both → premises and is excluded from the → conclusion.→ mean; → term. mean value theorem   فربین ِ ارزش ِ میانگین   farbin-e arzeš-e miyânginFr.: théorème des accroissements finis   1) If f(x) is a continuous function on the interval from a to b, then: ∫ f(x) dx = f(c)(b - a) (summed from a to b) for at least one point in that interval. 2) More generally, If f(x) and g(x) are continuous functions on the interval from a to b and g(x)≥ 0, then: ∫ f(x)g(x) dx = f(c) ∫ g(x) dx (both integrals summed from a to b).→ mean; → value; → theorem. meaning   چمار   cemâr (#)Fr.: sens, signification   The sense or significance of a word, sentence, symbol, etc. The study dealing with meanings is called → semantics. See also → semiotics.M.E., from mean; O.E. mænan "to mean, intend, signify" (cf. O.Fris. mena "to signify," O.S. menian "to intend, signify," M.Du. menen, Du. meenen, Ger. meinen "think, suppose"), related to Pers. maneš "disposition, temperament," mênidan "to think, consider," → idea; + → -ing.Cemâr, from cem or cim "meaning, signification;" Mid.Pers. cim "meaning, reason, cause;" ultimately from Proto-Ir. *cahmāt "wherefore?" cf. Skt. kasmāt "why, where from? whence?," kim "what? how? why?" + âr short form of âvar present stem of âvardan "to cause or produce; to bring," → production, as in bonâr, → cause, used also as a nuance suffix; see also the verb → mean.