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

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

Homepage

Number of Results: 7 Search : curvature
 curvature   خمیدگی   xamidegi (#)Fr.: courbure   A measure of the amount by which a curve, a surface, or any other manifold deviates from a straight line, a plane, or a hyperplane. In particular, The reciprocal of the radius of the circle which most nearly approximates a curve at a given point. See also: → curvature constant, → curvature of space-time, → field curvature, → primordial curvature perturbation.From L. curvatura, from curvatus, p.p. of curvare "to bend," from curvus "curved," → curve.Xamidegi, from xamidé "curved," from xamidag "curved" + noun suffix -i. curvature constant   پارامون ِ خمیدگی   pârâmun-e xamidegiFr.: paramètre de courbure   A parameter occurring in the → Friedmann equations of → general relativity describing the geometry of → space-time. A spatially → open Universe is defined by k = -1, a → closed Universe by k = + 1 and a → flat Universe by k = 0. See also the → Robertson-Walker metric. See also → curvature of space-time.→ curvature; → parameter. curvature of space-time   خمیدگی ِ فضا-زمان   xamidegi-ye fazâ-zamân (#)Fr.: courbure de l'espace-temps   According to → general relativity, → space-time is curved by the presence of → matter. The curvature is described in terms of → Riemann's geometry. In → cosmological models three types of curvature are considered: positive (spherical, → closed Universe), zero (Euclidean, → flat Universe), and negative (hyperbolic, → open Universe). See also → curvature constant.→ curvature; → space-time. field curvature   خمیدگی ِ میدان   xamidegi-ye meydân (#)Fr.: courbure de champ   An aberration in an optical instrument, common in Schmidt telescopes, in which the focus changes from the center to the edge of the field of view. Owing to this aberration, a straight object looks curved in the image.→ field; → curvature. primordial curvature perturbation   پرتورش ِ خمیدگی ِ بن‌آغازین   partureš-e xamidegi-ye bonâqâzinFr.: perturbation de courbure primordiale   In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe.→ primordial; → curvature; → perturbation. Riemann curvature tensor   تانسور ِ خمیدگی ِ ریمان   tânsor-e xamidegi-ye RiemannFr.: tenseur de courbure de Riemann   A 4th → rank tensor that characterizes the deviation of the geometry of space from the Euclidean type. The curvature tensor Rλμνκ is defined through the → Christoffel symbols Γλμν as follows: Rλμνκ = (∂Γλμκ)/(∂xν) - (∂Γλμν)/(∂xκ) + ΓημκΓλην - ΓημνΓληκ.→ Riemannian geometry; → curvature; → tensor. space-time curvature   خمیدگی ِ فضا-زمان   xamidegi-ye fazâ-zamânFr.: courbure de l'espace-temps   → space; → time; → curvature.