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

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 5 Search : three
 restricted three-body problem   پراسه‌ی ِ سه‌جسم ِ فروداریده   parâse-ye seh jesm-e forudâridéFr.: problème restreint à trois corps   A special case of the → three-body problem in which the → mass of one of the bodies is negligible compared to that of the two others. If the relative motion of the two massive components is a circle, the situation is referred to as the → circular restricted three-body problem. An example would be a space probe moving in the → gravitational fields of the → Earth and the → Moon, which revolve very nearly in circles about their common → center of mass.→ restrict; → three; → body; → problem. rule of three   رزن ِ سه   razan-e séFr.: règle de trois   Te method of finding the fourth term in a proportion when three terms are given.→ rule; → three. three   سه   sé (#)Fr.: trois   A cardinal number, 2 plus 1.M.E.; O.E. threo, thrib, feminin and neuter of thri(e); cf. O.Fris. thre, M.Du., Du. drie, O.H.G. dri, Ger. drei, Dan. tre), cognate with Pers. sé, as below.Sé, from Mid.Pers. sé; Av. θrayô, θrayas, tisrô, θri; cf. Skt. tráya, tri, trini; Gk. treis, L. tres, Lith. trys, O.C.S. trye, Ir., Welsh tri, O.E. threo, as above; PIE base *trei-. three-body problem   پر‌آسه‌ی ِ سه‌جسم   parâse-ye sé jesmFr.: problème à trois corps   The mathematical problem of studying the positions and velocities of three mutually attracting bodies (such as the Sun, Earth and Moon) and the stability of their motion. This problem is surprisingly difficult to solve, even in the simple case, called → restricted three-body problem, where one of the masses is taken to be negligibly small so that the problem simplifies to finding the behavior of the mass-less body in the combined gravitational field of the other two. See also → two-body problem, → n-body problem.→ three; → body; → problem. three-dimensional flow   تچان ِ سه-وامونی   tacân-e sé-vâmuniFr.: écoulement tri-dimensionnel   A flow whose parameters (velocity, pressure, and so on) vary in all three coordinate directions. Considerable simplification in analysis may often be achieved, however, by selecting the coordinate directions so that appreciable variation of the parameters occurs in only two directions, or even only one (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).→ three; → dimensional; → flow.