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

The → state of being → unconscious.

→ unconscious; → -ness.

A wave; the motion of waves.
A wavelike motion in any medium.

From L.L. undulatus "wavy, undulated," from undula "wavelet," diminutive of L. unda "wave."

Mowješ, verbal noun of mowjidan "to undulate," from mowj→ wave.

1) The process of unifying or uniting; union.
2) The state or condition of being unified (Dictionary.com).

Verbal noun of → unify.

The motion of an object around a fixed point at a constant angular speed, and at constant radius.

→ uniform; → circular; → motion.

Motion at a constant → velocity. The state of rest is a special case of uniform motion. → accelerated motion; → inertial motion.

→ uniform; motion.

General: The act of uniting two or more things.
A number of persons, organizations, states, etc., joined or associated together for some common purpose, e.g. → International Astronomical Union (IAU).
Math.: A set containing all the elements of two or more sets being combined. It is represented by ∪.

M.E. from O.Fr. union from L.L. unionem (nominative unio) "oneness, unity," from unus, → one, cognate with Pers. yek, as below.

Yekâyeš, from yek, → one, + -ây- epenthetic vowel, + -eš verbal noun suffix, → -tion.

A transformation whose reciprocal is equal to its Hermitian conjugate.

→ unitary; → transformation.

Same as → gas constant.

→ universal; → gas; → constant.

Same as → superior culmination.

→ upper; → culmination.

A chemical process converting the → yellowcake to → uranium hexafluoride. The uranium hexafluoride is heated to become a gas and loaded into cylinders. When it cools, it condenses into a solid.

→ uranium; → conversion.

The act or process of utilizing.

Verbal noun of → utilize.

A quantum field theory a process in which an electromagnetic field gives rise to virtual electron-positron pairs that in turn exert electromagnetic fields of their own, in a manner similar to classical dielectric polarization.

→ vacuum; → polarization.

An electron of an atom lying farthest from the nucleus. Valence electrons are shared when atoms combine to form molecules.

→ valence; → electron.

An → equation of state that satisfactorily describes the behavior of → real gass over a wide range of temperatures and pressures. It is derived from considerations based on kinetic theory, taking into account to a first approximation the size of a molecule and the cohesive forces between molecules: (P + a / V²) (V - b) = RT, where P, V, and T are pressure, volume, and temperature and R the gas constant. a and b are characteristic constants for a given substance. For a = b = 0, the van der Waals equation reduces to the characteristic equation of an → ideal gas. See also → Dieterici equation.

Named after Dutch physicist Johannes Diderik van der Waals (1837-1923), Nobel Prize in Physics 1910; → equation.

The act of vaporizing. The state of being vaporized.
The rapid change of water into steam.

Verbal noun of → vaporize.

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.

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.

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).