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

1) An act or instance of discriminating, or of making a distinction.
2) Unfair treatment of a person, racial group, minority, etc; action based on prejudice (Dictionary.com).

Verbal noun of → discriminate.

An act or instance of discussing; → consideration or → examination by → argument, → comment, etc., especially to explore solutions; informal debate (Dictionary.com).

Verbal noun from → discuss.

The breaking up of a body into fragments. For example, that of an unstable nuclei either spontaneously or as a result of bombardment by fast-moving particles, or the breaking up of a comet.

Disintegration, verbal noun of disintegrate, from → dis- + → integration.

Vâpâši, forupâši, from vâ-, frou-→ de- + pâši, noun of pâšidan→ disperse.

A → proposition of the form "A or B" (A ∨ B), where A and B are themselves propositions. A disjunction is → true when one or the other of its components (called → disjuncts) is true, and false otherwise.

→ dis-; → junction.

An accretion process involving an → accretion disk.

→ disk; → accretion.

A logical division of a hard disk that is treated as a separate unit by operating systems and file systems.

→ disk; → partition.

Of a spiral galaxy, those stars that lie in a flattened disk and move in nearly circular orbits around its centre. They are Population I stars of all ages up to the age of the disk, but in general are younger than stars in → halo population.

→ disk; population, from L.L. populationem "a people, multitude," from populatio, from populare "to inhabit," from populus "people," related to plebes "the common people," cf. Gk. plethos "people, multitude, great number," from PIE base *pel- "to be full;" Mod.Pers. por "full," O.Pers. paru- "much, many," Av. pouru- "much, many," pərəna- "full," par- "to fill," Skt. puru-, Gk. polus, O.E. full "completely, full," from P.Gmc. *fullaz, O.H.G. fol, Ger. voll, Goth. full.

Like Gk., Pers. uses the concepts of "multitude, many, full" to denote "people, group, herd, flock". The following examples are all terms derived from O.Pers. paru- "much, many," Av. par- "to fill," pouru- "much, many," pərəna- "full" (Mod.Pers. por "full"): literary Pers. bâré "herd, flock," parré "a rank or file of soldiers, a circular disposition of troops," Lori, Qâyeni bor "group, tribe, herd," Torbat-Heydariyeyi, Qomi borr "heap, bundle, group," Qomi borreh "group, assemblage of people," Pashtu parrak "flock, herd," Urdu para "flock, herd," Lârestâni baila "group, tribe," Tabari balik "herd, flock." With this introduction, porineš "population," verbal noun of porinidan "to populate," infinitive of porin "populous," from por "mutitude, many, full" + -in attribution suffix.

In models of magnetized → accretion disks, the process whereby the disk is disrupted at a radius where the → magnetic pressure overcomes the → ram pressure of the accreted material. This occurs at a distance typically 3-7 stellar radii, below the → corotation radius.

→ disk; → truncation.

1) The resolution of white light into its component wavelengths, either by → refraction or by → diffraction. Dispersion is actually an effect in which radiations having → different wavelengths travel at different speeds in the medium. Since the → angle of refraction of each radiation vary as a function of its → wavelength, the component waves deviate from each other.
2) The rate of change of → refractive index with wavelength: dn/dλ. → Cauchy's equation shows that dispersion varies approximately as the inverse cube of the wavelength.
3) The selective → retardation of → radio waves when they propagate through a → plasma. As a result, higher → frequency waves from a → pulsar will arrive at the Earth before the lower frequencies due to the presence of → intervening → ionized gas in the → interstellar medium. → dispersion measure.
4) Statistics: The spread of values of a → variable around the → mean or → median of a → distribution.

Verbal noun of → disperse.

A graph displaying the variation of the → refractive index of a substance against the wavelength of the electromagnetic wave passing through the substance.

→ dispersion; → curve.

An equation representing the variation of → refractive index as a function of → wavelength; for example → Cauchy's equation and → Sellmeier's equation.

→ dispersion; → equation.

A parameter used in radio astronomy which describes the amount of dispersion in a radio signal due to its passage through an intervening plasma. It is proportional to the product of the interstellar electron density and the distance to the source.

→ dispersion; → measure.

An equation that describes how the → angular frequency, ω, of a wave depends on its → wave number, k. For the simplest of waves, where the speed of propagation, c, is a constant, ω(k) = ck. If the → phase velocity depends on k, that is for a dispersive medium, the function ω(k) is nonlinear.

→ dispersion; → relation.

An act or instance of disqualifying; the state of being disqualified.

→ disqualify; → -tion.

Forcible division into pieces of an object. → tidal disruption.

From L. disruptio "a breaking asunder," noun of action from p.p. stem of disrumpere "break apart, split, shatter, break to pieces," from → dis- "apart" + rumpere "to break."

Gosixt, past stem of gosixtan "to tear away, to beark off."

The act of dissecting.

→ dissect; → -tion.

The loss of energy over time by a → dynamical system, typically due to the action of → friction or → turbulence. The lost energy is converted into heat, raising the temperature of the system. See also: → Ohmic dissipation. → viscous dissipation.

Noun form of → dissipate.

General: An act or instance of dissociating; the state of being dissociated.
Chemistry: Separation of a molecule into two or more fragments (atoms, ions, radicals) by the absorption of electromagnetic radiation or the action of collisional phenomena.

From → dis- + (as)sociation, → association.

Energy required to dissociate a molecule. → dissociate.

→ dissociation; → energy.

A process where a positive molecular ion recombines with an electron, and as a result it dissociates into two neutral products. For example, AB⁺ + e^-→ A + B, where e^- is an electron, AB⁺ is a diatomic or polyatomic molecular ion, and A and B are the neutral fragmentation products. Dissociative recombination is the dominant recombination process in planetary ionospheres and interstellar clouds.

→ dissociative; → recombination.