An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A defect in an optical system in which magnification decreases with distance from the optical axis, whereby the image of a square appears barrel-shaped. Opposite of → pincushion distortion.

Barrel, M.E. barel, from O.Fr. baril; → distortion.

Cowlegi, → distortion; celiki, relating to celik "barrel".

1) Extent to which a system, optical, acoustic, or electronic, fails to reproduce accurately at its output the characteristics of the input.
2) Optics: An optical imperfection caused by a → lens or → system of lenses which results in → magnification differences between different points on the → image. The points on the → object are misplaced in the image relative to the → center of the → field. See also → barrel distortion; → pincushion distortion.

Verbal noun of → distort.

An → aberration of a → lens  → system in which → magnification increases with → distance from the → optical axis, whereby → horizontal and → vertical lines bend inward toward the → center of the → field. Opposite of → barrel distortion.

Pincushion, from pin, from M.E. pinne, O.E. pinn "peg;" cf. D. pin, Ger. Pinne; perhaps from L. pinna "feather, quill" + cushion, M.E. cuisshin, O.Fr. coissin (Fr. coussin) a variant of V.L. *coxinum, either from L. coxa "hip, thigh," or from L. culcita "mattress;" → distortion.

Cowlegi, → distortion; bâleštaki, adj. of bâleštak, diminutive of bâlešt, variant bâleš "cushion, pillow," Mid.Pers. bâlišn, bâlên "cushion, pillow;" Av. barəiš- "pillow, cushion;" cf. Skt. barhis- "straw, a bed or layer of kusa grass strewed over the sacrificial ground."

The distortion observed in → redshift space of → galaxy clusters caused by peculiar velocities of the members (→ peculiar velocity). In a perfectly homogeneous → Friedmann-Lemaitre Universe the redshifts would accurately measure radial distances from the observer, and the mapping from real space to redshift space would simply be an identity. In an inhomogeneous Universe the peculiar velocities associated with any inhomogeneous structure will introduce a distortion in this mapping (N. Kaiser, 1987, MNRAS 227, 1). See also: → fingers of God, → Kaiser effect.

→ redshift; → space; → distortion;.

The disruption of the spherical shape of a wavefront due to atmospheric turbulence which makes the adjacent points in the wavefront out of phase.

→ wavefront; → distortion.