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

A hypothesis proposed by Alfred Wegener (1912) suggesting that the → continents are not stationary, but drift through time. Wegener's hypothesis has since been developed and included in a new theory called → plate tectonics.

→ continental; → drift.

The → redshift of a remote object (galaxy, quasar, supenova) due to the expansion of the Universe.

→ cosmological; → redshift.

The identification of an object in a data base or catalog and matching it with the same object identified in another catalog.

→ cross; → identification.

The process of producing a quantifiable result in a → fuzzy logic system, given → fuzzy sets and corresponding → membership functions. Defuzzification is the last step in a fuzzy logic system. After → fuzzy inferencing, the overall result is a → fuzzy value. This result should be defuzzified to obtain a final → crisp value.

Verbal noun of → defuzzify; → -tion.

To transform a → fuzzy set to a → crisp set in a → fuzzy logic system.

→ de-; → fuzzy; → -fy.

To rid of mystery or obscurity; clarify. The removal of mystery or confusion surrounding a topic or idea.

→ de-; → mystify;

To be unlike, dissimilar, or distinct in nature or qualities.

From O.Fr. différer, from L. differre "to set apart, differ," from → dis- "away from" + ferre "to carry, bear" (cf. Av. baraiti "carries," O.Pers. barantiy "they carry," Mod.Pers. barad "carries," Skt. bharati "carries," Arm. berem "I carry," Gk. pherein "to carry," O.E., O.H.G. beran, Rus. brat' "to take," bremya "a burden").

Degarsân "different," from degar "another, other" (Mid.Pers. dit, ditikar "the other, the second," O.Pers. duvitiya- "second," Av. daibitya-, bitya- "second," Skt. dvitiya- "second," PIE *duitiio- "second") + sân "manner, semblance" (variant sun, Mid.Pers. sân "manner, kind," Sogdian šôné "career") + budan "to be" (Mid.Pers. budan, from O.Pers./Av. bav- "to be; become, take place," Av. buta- perf. ptcpl. pass., bavaiti "becomes," Skt. bhavati "becomes, happens," bhavah "becoming; condition, state," PIE *bheu- "to be, come into being, become;" cf. Gk. phu- "become," phuein "to bring forth, make grow," L. fui "I was" (perf. tense of esse), futurus "that is to be, future," Ger. present first and second person sing. bin, bist, E. to be, O.Ir. bi'u "I am," Lith. bu'ti "to be," Rus. byt' "to be").

The quality or condition of being different.
Math.: the amount by which one quantity is greater or less than another.
Of two sets A and B, the set consisting of all elements of A which do not belong to B.

Noun form of → differ.

Not alike in character or quality; differing; dissimilar.

Adj. of → difference.

Of a mathematical function, the quality of being → differentiable.

Noun from → differentiable.

Capable of being → differentiated. → differentiable function.

From → differentiate + → -able.

Property of a mathematical function if it has a → derivative at a given point.

From → differentiable; → function.

1) Noun.
1a) General: A difference or the amount of difference, as in rate, cost, quantity, degree, or quality, between things that are comparable.
1b) Math.: An infinitesimally small change in a variable; a function of two variables that is obtained from a given function, y = f(x), and that expresses the increment in the given function as the derivative of the function, f'(x), times the increment in the independent variable, written as dy = f'(x) dx.
1c) Electronics: Referring to a circuit, device, or machine whose principle of operation depends on the difference between two opposing effects.
2) Adjective.
2a) General: Of, relating to, or constituting a difference.
2b) Physics: Pertaining to or involving the difference of two or more motions, forces, etc.
2c) Math.: Pertaining to or involving a → derivative or derivatives.

From M.L. differentialis, from differenti(a), → difference, + → -al.

Degarsâné, from degarsân, → different + noun suffix -é.

The two branches of mathematics that make up the → calculus. → differential calculus; → integral calculus.

→ differential; → integral; → calculus.

A branch of calculus which is concerned with the instantaneous rate of change of quantities with respect to other quantities, or more precisely, the local behavior of functions. → integral calculus.

→ differential; → calculus.

An equation expressing a relationship between an → independent variable, x, an unknown → function, y = f(x), and its → derivatives. The general form of a differential equation is: F(x, y, y', y'', ..., y⁽ⁿ⁾) = 0, or F(x,y, dy/dx, d²y/dx², ..., dⁿy/dxⁿ) = 0. See also: → ordinary differential equation; → partial differential equation; → linear differential equation; → exact differential equation; → first-order differential equation; → homogeneous linear differential equation; → nonhomogeneous linear differential equation; → differential equation with separated variables; → differential equation with separable variables.

→ differential; → equation.

A → differential equation of the form: M₁(x) N₁(y) dx + M₂(x) N₂(y) dy = 0, which can be reduced to a → differential equation with separated variables.

→ differential; → equation; → separate; → variable.

A → differentail equation that can be transformed into the form: M(x)dx + N(x)dy = 0.

→ differential; → equation; → separate; → variable.

The study of curved spaces using differential calculus.

→ differential; → geometry.

A device that is commonly used to measure the → seeing at optical astronomical sites. The DIMM delivers an estimate of the → Fried parameter based on measuring the variance of the differential image motion in two small apertures, usually cut out in a single larger telescope pupil by a mask. The DIMM concept was introduced by Stock & Keller (1960, in Stars and Stellar Systems, Vol. 1, ed. G. P. Kuiper & B. M. Middlehurst, p. 138), whereas its modern implementation was first described by Sarazin & Roddier (1990, A&A 227, 294).

→ differential; → image; → motion; → monitor.