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

A → forbidden line in → emission.

→ forbidden; → emission; → line.

A transition between two quantum mechanical → states that → violates the quantum mechanical → selection rules.

→ forbidden; → transition.

The oscillation of a system or object induced by an external periodic force. See also → free oscillation.

→ forced; → oscillation.

Loss of radiant energy received from an astronomical object due to the presence of absorbing matter situated between the object and observer.

→ foreground; → absorption.

1) The act of giving something a form or structure by introducing rules and procedures.
2) The act of formalizing.

→ formalize; → -tion.

1) The act or process of forming or the state of being formed, such as → star formation.
2) Geology: A laterally continuous rock unit with a distinctive set of characteristics that make it possible to recognize and map from one → outcrop or well to another. The basic rock unit of stratigraphy.

Verbal noun of → form, + -ate + -ion.

Diseš, verbal noun of disidan, → from dis-, → form, + -eš.

1) The act or process of formulating.
2) A particular expression of an idea, thought, or theory.
3) Something prepared according to a → formula.

→ formulate; → -tion.

An operator defined as: ▫ = (∂/∂x, ∂/∂y, ∂/∂z, 1/(jc∂/∂t).

→ four; → dimensional; → operator.

The end of a solar eclipse marked by the disk of the Moon completely passing away from the disk of the Sun.

From M.E. fourthe, O.E. féowertha, from four, from O.E. feower, from P.Gmc. *petwor- (cf. Du. and Ger. vier, O.N. fjorir, Dan. fire, Sw. fyra), from PIE *qwetwor (cf. Mod.Pers. cahâr, Av. caθwar-, catur-, Skt. catvarah, Gk. tessares, L. quattuor) + -th a suffix used in the formation of ordinal numbers, from M.E. -the, -te, O.E. -tha, -the; cf. O.N. -thi, -di; L. -tus; Gk -tos; → contact.

Parmâs, → contact; cahârom cardinal form from cahâr "four," cognate with E. four, as above.

A rational number of the form a/b where a is called the numerator and b is called the denominator.

From L.L. fractionem (nom. fractio) "a breaking in pieces," from frangere "to break," from PIE base *bhreg- "to break" (cf. Goth. brikan, O.E. brecan "to break;" Lith. brasketi "crash, crack").

Barxé, from barx "lot, portion," variant bahr, from Mid.Pers. bahr "lot, share, portion," Av. baxəδra- "portion."

1) Math.: Pertaining to fractions; constituting a fraction.
2) Chemistry: Of or relating to any process by which parts of a mixture are separated by exploiting differences in their physical properties, such as their boiling points, solubility, or other characteristics.

→ fraction; → -al.

The portion of the 4π → steradians of the sky that a radiotelescope can observe from a given location on Earth over a 24-hour time interval.

→ fractional; → sky; → coverage.

1) To break something up into smaller parts.
2) To separate a mixture into ingredients or portions having different properties, as by distillation or otherwise.

From → fraction + -ate a suffix forming verbs or nouns, from L. -atus, -ata, -atum.

Barxândan, from barx, barxé, → fraction, + -ândan suffix of transitive verbs.

1) Any of various methods of separating the components of a mixture into fractions of different properties.
2) → isotope fractionation

Verbal noun from → fractionate.

Generally, the process of breaking up into smaller parts. In particular, the splitting of a large molecular cloud into smaller, denser clumps. → cloud fragmentation.

From → fragmenta + -ation, a combination of -ate and -ion, used to form nouns from stems in -ate.

Latpâreš, verbal noun from latpâridan, → fragment.

The succession of physical events that results in the breaking of a → molecular cloud into several → fragments.

→ fragmentation; → process.

An electron that is not attached to an → atom, → molecule, or → ion and is free to move under the influence of a present electric or magnetic field.

→ free; → electron.

The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy  E_SN is transformed into → kinetic energy of the ejected gas, the ejection velocity v_e can be estimated from E_SN by using E_SN = (1/2) M_ev_e², which leads to v_e = (2E_SN / M_e)^(1/2), where M_e is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, R_SW, is defined by M_e = (4π/3) R_SW³ρ₀, that is R_SW = (3M_e / 4πρ₀)^(1/3), where ρ₀ is the initial density of the ISM. This radius is reached at the sweep-up time t_SW = R_SW/v_e. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.

→ free; → expansion; → phase.

Oscillation of any system in stable equilibrium under the influence of internal forces only, or of a constant force originating outside the system, or of both.

→ free; → oscillation.

The radiation emitted when a → free electron is captured by an → ion. See also: → free-free emission; → bound-free transition.

→ free; → bound; → emission.