An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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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 xamidegi

Fr.: 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 bonâqâzin

Fr.: 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 Riemann

Fr.: 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-zamân

Fr.: courbure de l'espace-temps   

curvature of space-time.

space; → time; → curvature.