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

A measure of variability of a star (such as Welch-Stetson variability index) which combines the information from two passbands assuming that changes in the star's luminosity occur nearly simultaneously at all optical wavelengths.

→ variability; → index.

Something that may or does vary. → variable star.
Math.: A symbol, usually a letter, which in a mathematical or logic expression represents any member of a set of possible values or possible objects.

M.E., from O.Fr. variable, from L. variabilis "changeable," from variare "to change," → vary.

Vartandé agent noun from vartidan "to change," → vary.

A star whose luminosity changes over periods of time; there are many reasons and many types. → cataclysmic variable; → Cepheid; → pulsating star; → nova; → long-period variable; → short-period variable; → Luminous Blue Variable (LBV); etc.

→ variable; → star.

A set of conventions used for naming → variable stars. Stars with existing → Bayer designations are not given new designations. Alternatively, the letters R through Z are used followed by the Latin genitive of the name of the hosting constellation. Otherwise, two letters of alphabet are used (334 combinations) with the Latin genitive of the name of the constellation. Finally, the letter V (variable) is used followed by numbers 335, 336, and so on. Some examples are: → P Cygni, → T Tauri, → FU Orionis, → EX Lupi, and → V2052 Oph.

→ variable; → star; → designation.

A measure of the scatter of the values of a random variable (X) about its mean (μ). Var(X) = E(X -μ)². The positive square root of the variance is called the → standard deviation.

M.E., from O.Fr. variance, from L. variantia, from variare "to change," → vary.

Vartâyi quality noun from vartâ agent noun from vartidan, → vary.

1) Liable to or displaying variation.
2) Something that differs from a standard or type. For example, a different form of the same word.

→ vary.

A quantity which may take any of the values of a specified set with a specified relative frequency or probability. The variate is therefore often known as a → random variable.

L. variatus, p.p. of variare, → vary, + → -ate.

→ variable; → random.

1) General: An instance of changing, or something that changes.
2) Astro.: The periodic inequality in the Moon's motion that results from the combined gravitational attraction of the Earth and the Sun. Its period is half the synodic month, that is 14.77 days, and the maximum longitude displacement is 39'29''.9.
See also: → calculus of variations, → annual variation, → secular variation.

M.E., from O.Fr. variation, from L. variationem (nominative variatio) "difference, change," from variatus, p.p. of variare "to change," → vary.

Varteš, verbal noun from vartidan, → vary.

Of or describing a → variation.

→ variation; → -al.

Any of the physical principles that indicate in what way the actual motion of a state of a mechanical system differs from all of its kinematically possible motions or states. Variational principles that express this difference for the motion or state of a system in each given instant of time are called → differential. These principles are equally applicable to both → holonomic and → nonholonomic systems. Variational principles that establish the difference between the actual motion of a system during a finite time interval and all of its kinematically possible motions are said to be → integral. Integral variational principles are valid only for holonomic systems. The main differential variational principles are: the → virtual work principle and → d'Alembert's principle.

→ variational; → principle.

1) The quality or state of having different forms or types.
2) A number or collection of different things especially of a particular class.
3) Something differing from others of the same general kind.
4) Any of various groups of plants or animals ranking below a species (Merriam-Webster.com).

M.Fr. variété, from L. varietatem (nominative varietas) "difference, diversity; a kind, variety, species, sort," from varius, → various.

Vartiné, from vartin, → various, + noun/nuance suffix -é.

The → moment of the resultant of a → coplanar system of → concurrent forces about any center is equal to the algebraic sum of the moments of the component forces about that center.

Named after Pierre Varignon (1654-1722), a French mathematician, who outlined the fundamentals of statics in his book Projet d'une nouvelle mécanique (1687).

1) Of different kinds, as two or more things; differing one from another.
2) Marked by or exhibiting variety or diversity (Dictionary.com).

M.Fr. varieux and directly from L. varius "changing, different, diverse," → vary.

Vartin, from vart "change," present stem of vartidan, → vary, + adj. suffix -in.

1) To undergo change in form, substance, appearance, etc.
2) To change or alter. → covariance.

M.E. varien, from O.Fr. varier, from L. variare "change, alter, make different," from varius "variegated, different, spotted."

Vartidan "to change," from Mid.Pers. vartitan "to change, turn" (Mod.Pers. gardidan "to turn, to change"); Av. varət- "to turn, revolve;" cf. Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend."

Any physical quantity which requires a direction to be stated in order to define it completely, for example velocity. Compare with → scalar.

From L. vector "one who carries or conveys, carrier," from p.p. stem of vehere "carry, convey;" cognate with Pers. vâz (in parvâz "flight"); Av. vaz- "to draw, guide; bring; possess; fly; float," vazaiti "guides, leads" (cf. Skt. vah- "to carry, drive, convey," vahati "carries," pravaha- "bearing along, carrying," pravāha- "running water, stream, river;" O.E. wegan "to carry;" O.N. vegr; O.H.G. weg "way," wegan "to move," wagan "cart;" M.Du. wagen "wagon;" PIE base *wegh- "to drive").

Bordâr "carrier," agent noun from bordan "to carry, transport" (Mid.Pers. burdan; O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive);" Skt. bharati "he carries;" Gk. pherein "to carry;" L. ferre "to carry;" PIE base *bher- "to carry").

The study of → vectors and → vector spaces.

→ vector; → analysis.

Of a rotating body, a vector of magnitude ω (→ angular velocity) pointing in the direction of advance of a right-hand screw which is turned in the direction of rotation.

→ vector; → angular; → velocity.

In nuclear physics, a → boson with the spin quantum number equal to 1.

→ vector; → boson.

The study of vector functions between vector spaces by means of → differential and integral calculus.

→ vector; → calculus.

A → tensor density of → order 1.

→ vector; → density.