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

Any steady movement of material in space. In particular, any movement of electric charge. → stream; → flow; → flux.

From O.Fr. corant "running," pr.p. of courre "to run," from L. currere "to run," from PIE *kers- "to run" (cf. Gk. -khouros "running," Lith. karsiu "go quickly," O.N. horskr "swift," Welsh carrog "torrent").

Jarayân from Ar.

The → Universe at the → redshift z = 0.

→ current; → cosmological; → epoch.

The electric current per unit of cross-sectional area perpendicular to the direction of current flow. It is a vector quantity and represented by symbol J. Electric current density is usually expressed in amperes per square meter.

→ current; → density

A movable, sometime blinking, indicator on a computer screen identifying the point that will be affected by input from the user (OxfordDictionaries.com).

From L. cursor "runner," also "errand-boy," from curs-, p.p. stem of currere "to run," → current.

Jâbân, literally "position/place keeper," or "position/place maker," from jâ, → place, + -bân a suffix denoting "keeper, guard," sometimes forming agent nouns or indicating relation, → host.

A hypothetical → scalar field that is used to explain the → primordial curvature perturbation in the Universe. It is generally supposed that the primordial perturbation originates during → inflation, from the → quantum fluctuation of the inflation field. The curvaton model is an attempt to account for the primordial perturbation by a completely different origin, namely the quantum fluctuation during inflation of a light scalar field which is not the assumed slowly-rolling inflation. In this model, the curvaton field is an energetically sub-dominant component during inflation. As the energy density of the Universe drops after inflation, the fraction of this component becomes significant. At this time the curvaton perturbation is converted into an adiabatic curvature perturbation of the Universe. The amplitude of the final perturbation, which should match observations, depends on both how long the curvaton oscillates before it decays, and on the shape of the potential. The first curvaton model was proposed by D. H. Lyth & D.Wands and in 2002 (Physics Letters B524).

From curvat-, from → curvature, + → -on. Although not related, the term curvaton exists in Fr. meaning "small curve" with variants curvatone, courbaton, and corbatone (A. Jal, 1848, Glossaire nautique).

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.

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.

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.

A line that deviates from straightness in a smooth, continuous fashion. A line representing a variable on a graph.

From L. curvus "crooked, curved, bent;" cf. Av. skarəna- "round," Gk. kirkos, krikos "a ring;" PIE base *sker- "to turn, bend."

Xam, variant kamân "arc," Mid.Pers. kamân, probably from PIE *kamb- "to bend, crook," cf. Breton kamm "curved, bent."

Construction of mathematical functions whose graphs are curves that "best" approximate a given collection of data points.

→ curve; → fitting.

A plot showing how the → equivalent width of an → absorption line, or the radiance of an → emission line, increases as a → function of the → number of → atoms that produce the line.

→ curve; → growth.

Not straight.

Adj. from → curve.

Consisting of, represented by, or bound by curved lines. → rectilinear.

From → curve + → linear.

1) General: Pointed end. A point of transition. → polar cusp.
2) Either point of a → crescent moon.
3) A steep power-law representing the number density of stars in the central region of a galaxy. Cusps are characteristic of low-mass ellipticals. They are thought to result from the gravitational attraction of a central → supermassive black hole.
4) A peaked concentration of dark matter in the center of galaxies, as predicted by the → cold dark matter (CDM) model of galaxy formation. See also → cusp problem.
5) Math: A tooth-like meeting of two branches of a curve, with sudden change of direction.

L. cuspis "point, spear, pointed end."

Tizé, noun from tiz "sharp, pointed," from Mid.Pers. tēz, tēž, tigr "sharp," O.Pers. tigra- "pointed," Av. taēža-, tighra- "pointed," Skt. taējas- "the sharp edge (of a knife), piercing (flame)", from tij- "to be sharp, to pierce," Gk. stizein "to prick, puncture," stigma "mark made by a pointed instrument," L. instigare "to goad," P.Gmc. *stik- "to pierce, prick, be sharp," O.H.G. stehhan, Ger. stechen "to prick," O.E. stician "to pierce, stab," E. stick "to pierce;" PIE *st(e)ig- "to stick; pointed".

A problem encountered by the → cold dark matter (CDM) model of galaxy formation. The numerical simulations with CDM predict a large concentration of dark matter in the center of galaxies, with a peaked density distribution, in contrast to the real, observed galaxies. See also: → angular momentum catastrophe; → missing dwarfs.

→ cusp; → problem.

To penetrate or divide something, as with a sharp-edged instrument.

M.E. cutten, kytten, kitten; O.E. *cyttan, cognate with O.Swed. kotta "to cut;" O.N. kuti "little knife," or from O.Fr. couteau "knife."

Boridan "to cut off;" Mid.Pers. brin-, britan, brinitan "to cut off," brin "cut, delimitation, determined;" Av. (pairi-) brī- "to shave, shear;" cf. Skt. bhrī- "to hurt, injure," bhrinanti "they hurt."

1) A designated limit beyond which the passage of something must be stopped.
2) A device that cuts off a transmission of photons.

→ cut; → off.

Boré, from bor- present stem of boridan "to → cut" + noun suffix -é.

Filter rejecting all light with wavelengths on one side of the cutoff wavelength.

→ cutoff; → filter.

The electrode voltage which reduces the value of a dependent variable, e.g. anode current, to a specified low value.

→ cutoff; → voltage.

Wavelength at which the transmittance of a filter, or the detectivity of a detector, has fallen to one-half its peak value.

→ cutoff; → wavelength.