An Etymological Dictionary of Astronomy and Astrophysics
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In a → syllogism, a → proposition or statement that deals with inclusion or exclusion of members of → subject classes in → predicate classes. Categorical propositions are of four basic forms, see → Aristotelian form.

→ categorical; → proposition.

Chemistry: A → positively charged → ion that is attracted to the → cathode in electrolysis. Any positively charged atom or group of atoms (opposed to → anion).

From cat-, → cathod, + → ion.

A relationship between the → refractive index (n) and the wavelength of light (λ) passing through a medium. It is commonly stated in the following form: n = A + B/λ² + C/λ⁴, where A, B, and C are constants characterizing the medium. The two-component Cauchy equation is n = A + B/λ², from which the dispersion becomes dn/dλ = -2B/λ³ showing that dispersion varies approximately as the inverse cube of the wavelength. The dispersion at 4000 A will be about 8 times as large as at 8000 Å.

Named after Augustin Louis Cauchy (1789-1857), French mathematician and physicist who found the first equation of dispersion in 1836; → equation.

1) The act or process of causing; the act or agency which produces an effect.
2) The relation of → cause to → effect.

Verbal noun from → cause.

A point toward which a force on a body is always directed.

→ center; → attraction.

Of a point rotating in a circle round a central point, the outward acceleration away from the rotation axis. It corresponds to → centrifugal force. The centrifugal acceleration is given by ω x ω x r, or v²/r, where ω is → angular velocity, r the distance to the rotating axis, and v the → tangential velocity. The centrifugal and → centripetal accelerations are equal and opposite.

→ centrifugal; → acceleration.

The rate of change of the → tangential velocity of a body moving along a circular path. The direction of centripetal acceleration is always inward along the → radius vector of the → circular motion. The magnitude of the centripetal acceleration is related to the → tangential velocity (v) and → angular velocity (ω) as follows: a_c = v²/r = rω². According to → Newton's second law, an object undergoing centripetal acceleration is experiencing a → centripetal force.

→ centripetal; → acceleration.

A succession of → nuclear fissions when the neutrons released by previous fissions produce other nuclear fissions which themselves cause other reactions and the reactions goes on increasing exponentially.

→ chain; → reaction.

Physics: An analytical relationship between a set of physical variables that determines the state of a physical system.
Math.: The equation which is solved to find a matrix's eigenvalues, also called the characteristic polynomial.

→ characteristic; → equation.

1) The act of describing the character or qualities of someone or something.
2) The artistic representation (as in fiction or drama) of human character or motives (Merriam-Webster.com).

→ characterize; → -tion.

In particle physics, an operation that changes a particle to its antiparticle in equations describing subatomic particles or, equivalently, reverses its charge and magnetic moment.

→ charge; → conjugation.

The way a number of → electric charges are arranged in space with respect to the point of observation.

→ charge; → distribution.

A charge-transfer device that passes along stored charges positioned at predetermined locations; it is used as an image sensor in which the image points are accessed by reference to their horizontal and vertical coordinates.

→ charge; → injection; → device.

Same as → chemisorption.

→ chemical; → adsorption.

The identities, and relative abundances of the → chemical elements or → compounds that make up a substance.

→ chemical; → composition.

The symbolic representation of a chemical reaction where the formulae of the → reactants are placed on the left and the formulae of → products on the right of an arrow.

→ chemical; → equation.

A cumulative change in the chemical properties, or more specifically, the relative abundances of chemical elements in an astrophysical system.

→ chemical; → evolution.

A → change or → transformation in which a → substance → decomposes, → combines with other → substances, or interchanges constituents with other substances.

→ chemical; → reaction.

The physical processes that can cause certain elements to migrate in a → stellar atmosphere. These processes are thought to be important in creating the chemical peculiarities seen in → Am stars and → Ap stars.

→ chemical; → separation.

A kind of → adsorption in which the forces involved are → valence forces of the same kind as those operating in the formation of → chemical compounds. Same as → chemical adsorption. See also → physisorption.

Chemi-, from → chemical; → sorption.