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

same as → Alfven speed.

→ Alfven wave; → velocity.

→ Alfvénic fluctuation.

→ Alfvénic; → -ity.

→ Alfvénic fluctuation.

→ Alfvénic; → -ity.

A measure of the angular displacement per unit time. Of a particle traveling on a circular path or a rotating body, the ratio of the angle traversed to the amount of time it takes to traverse that angle: ω = dθ/dt. For a rigid body, all lines in it rotate through the same angle in the same time, and the angular velocity is the characteristic of the body as a whole. The angular velocity is related to the linear velocity by the equation v = rω, where r is the distance of the point from the rotation axis. → vector angular velocity.

→ angular; → velocity.

The departure from → isoplanicity.

→ an-; → isoplanicity.

For → stellar winds, same as → terminal velocity.

→ asymptotic; → velocity.

The ratio of the displacement (Δx) of a particle, as it moves from point A to point B, to the corresponding time interval: v = Δx/Δt.

→ average; → velocity.

The state of stratification in a fluid in which surfaces of constant pressure do not coincide with those of constant density, but intersect. Where baroclinicity is zero, the fluid is → barotropic. Same as baroclinity.

→ baroclinic; → -ity.

The velocity of a → rotating star at which the → centrifugal force equals the → gravitational force. Also known as → critical velocity. The simplest expression of the break-up velocity for an OB star, ignoring the → Eddington luminosity, is given by the relation: v = (GM / R)^1/2, where M and R are the mass and radius of the star respectively, and G the → gravitational constant. A more realistic expression takes into account not only the → radiation pressure, but also the non-uniformity of the brightness over the stellar surface, as indicated by → von Zeipel theorem. With these conditions, the break-up velocity has a more complicated formula, corresponding to the velocity reached when somewhere on the star the → total gravity becomes zero.

→ break + up; M.E.; O.E. up, uppe, → hyper-; → velocity.

The ability to receive or contain.
Electricity: → capacitance.

From M.Fr. capacité, from L. capacitatem, from capax "able to hold much," from capere "to take, grasp."

Gonjâyeš "capacity, holding, containing," from gonjdan "to be contained; to hold exactly; to be filled;" Mid.Pers. winj- "to be contained;" Proto-Iranian *uiac-/*uic-; cf. Skt. vyac- "to contain, encompass," vyás- "extent, content, extension;" L. uincire "to bind."

The quality of being physically caustic.

→ caustic; → -ity.

The condition of being → chaotic.

→ chaotic; → -ity.

Any large town or populous place.

M.E. cite, from O.Fr. cite "town, city," from L. civitas "citizenry; community," from civis "native, townsman;" related to L. cuna "cradle; bed;" Gk. kome "village;" Skt. śiva- "auspicious, dear;" O.E. ham "dwelling, house, village;" E. home; Ger. Heim (→ hamlet); Iranian dialects kiye "house, home;" Xonsâri ki "house;" Anâraki xiya, Tâti Karingân kâ, Sangesari keh "house, home;" PIE *kei- "to lie; bed."

Šahr "city," from Mid.Pers. šahr "land, country, city;" O.Pers. xša- "to rule," pati-xša- "to have lordship over," Xšyāršan- "hero among kings" or "ruling over heroes" the proper name of the Achaemenid emperor Helenized as Xerxes, upari.xšay- "to rule over," xšāyaθiya- "king;" Mid.Pers. šâh "king," pâdixšâ(y) "ruler; powerful; authoritative;" Mod.Pers. šâh "king," pâdšâh "protecting lord, emperor, monarch, king," šâyestan "to be worth, suit, fit;" Av. xšā(y)- "to rule, have power," xšayati "has power, rules," xšāyô "power;" cf. Skt. ksā- "to rule, have power," ksáyati "possesses;" Gk. ktaomai "I acquire," ktema "piece of property;" PIE base *tkeh- "to own, obtain."

A population of relatively small (typically < 2°) → high-velocity clouds, which are spatially and kinematically isolated from the gas distribution in their environment. They are thought to be located in the → intergalactic medium of the → Local Group.

→ compact; → high-velocity cloud.

The → metallicity of a → star-forming  → molecular cloud when → cooling → rates by → metals dominate the → gravitational  → heating during → protostellar collapse. The minimum → Jeans mass achieved by gravitational → fragmentation depends on the presence/absence of → coolants in the cloud. Since cooling rate in metal lines is more efficient than in primordial molecular lines (H₂ and HD), metals favor fragmentation in gas and formation of → low-mass stars.

→ critical; → metallicity.

1) Velocity of → fluid through a pipe at which the motion changes from → laminar to → turbulent flow.
2) Same as → break-up velocity.

→ critical; → velocity.

The average velocity of a charged particle in a plasma in response to an applied electric field.

→ drift; → velocity.

The amount by which the orbit deviates from circularity: e = c/a, where c is the distance from the center to a focus and a the semi-major axis. If e = 0, the orbit is a circle. If e < 1, the orbit is an ellipse, if e > 1 it is a hyperbola, and if e = 1 it is a parabola. The eccentricity is one of the six → orbital elements that define a → Keplerian orbit.

→ eccentric; → -ity.

The ability of a body which has been → deformed by an applied → force to return to its original shape when the force is removed. Up to a certain point the material obeys → Hooke's law. See also → ductility, → plasticity.

→ elastic + → -ity.

1) The physical phenomena arising from the behavior of → electrons and → protons that is caused by the → attraction of particles with opposite → charges and the → repulsion of particles with the same charge.
2) The → science of electric charges and → currents.
3) A → flow of electrons that is used to generate → light and → power electric devices.

From L. electrum "amber," from Gk. elektron "amber" + -ity a suffix used to form abstract nouns expressing state or condition.

Barq, Pers. term, used also in Ar. and Hebrew (barak "lightening"); variants in Pers.: varq, barx, balk, belak, bala; Lârestâni belak; Tabari, Lahijâni, Semnâni, Sorxeyi, Sangesari belk; Gilaki val; Lori beleyz; Kurd. bilese; Tokharian AB pâlk; Mid/Mod.Pers. bir "lightening," Mid.Pers. brâh "brilliance, splendour," br'z- "to shine, beam," Mod.Pers. barâz "beauty, grace, elegance;" Av. brāz- "to shine, beam; splendour," brazāiti "shines;" cf. Skt. bhrāj- "to shine, beam, sparkle," bhrajate "shines;" Gk. phlegein "to burn;" L. fulgere "to shine," fulmen "lightning," flagrare "to blaze, burn;" O.H.G. beraht "bright;" O.E. beorht "bright;" E. → bright; PIE base *bherəg-; *bhrēg- "to shine; white."