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

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 mean element   بن‌پار ِ میانگین   bonpâr-e miyânginFr.: élément moyen   An element of an adopted reference orbit that approximates the actual, perturbed orbit. Mean elements may serve as the basis for calculating perturbations.→ mean; → element. mean equator   هموگار ِ میانگین   hamugâr-e miyânginFr.: équateur moyen   The orientation the Earth's equator would have if the nutation was subtracted.→ mean; → equator. 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.