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

The reciprocal force between two or more → charged particles according to → Coulomb's law.

→ coulomb; → interaction.

A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction.

→ decimal; → fraction.

The difference between the deuterium (D)/hydrogen (H) → abundance → ratio in an object with respect to that representing a standard or mean value for that type of objects. Same as → isotope fractionation of deuterium. In the gas phase chemistry many of the D fractionation reactions produce an excess of D atoms relative to → hydrogen atoms. Deuterium fractionation in → interstellar cloud cores, → protostars, and → Solar System bodies is frequently used to infer important aspects of their physical and chemical histories. For example, the → deuterium enhancement in the Earth's sea water, with respect to the cosmic abundance, has been interpreted as being due to → enrichment by → comet-like → planetesimals colliding with the young Earth.

→ deuterium; → fractionation.

A problem encountered in astronomical spectroscopy, which consists of a loss of light from some wavelengths due to → atmospheric dispersion. In simple terms, differential refraction means that at nonzero → zenith distances an object cannot be simultaneously placed at the same position within a → slit at all wavelengths. This problem becomes more important for increasing → airmass, larger → spectral range, and smaller → slitwidths. To remedy this drawback, the slit should always be oriented along a direction perpendicular to the horizon, since differential refraction occurs in that direction.

→ differential; → refraction.

A wave property of light which allows it to curl around obstacles whose size is about that of the wavelength of the light. As a → wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating at that edge. These secondary wavefronts will interfere with the primary wavefront as well as with each other to form a → diffraction pattern.
Related terms: → diffusion; → dispersion; → distribution; → scatter; → scattering.

From Fr. diffraction, from Mod.L. diffractionem, from L. diffrac-, stem of diffringere "break in pieces," from → dis- "apart" + frangere "to break."

Parâš "dispersion, scattering," variant of pâš, pâšidan, → dispersion.

An optical device containing thousands of very fine parallel grooves which produce interference patterns in a way which separates out all the components of the light into a spectrum.

→ diffraction; → grating.

A series of concentric rings of dark and light color produced by interference.

→ diffraction; → pattern.

Olgu, loanword from Turkish; parâš→ diffraction.

One of several light rays emanating from a bright light source in images taken with → reflecting telescopes. They are artifacts caused by light diffracting around the support or → spider vanes of the → secondary mirror.

→ diffraction; → spike.

The quality of an → optical system that is capable of producing images with angular resolution as small as the theoretical limit of the → Airy disk.

→ diffraction; limited, adj. of → limit.

Karânmand "bounded, limited," from karân→ boundary + -mand possession suffix; parâš→ diffraction.

Formation of two refracted rays of light from a single incident ray; property of certain crystals, notably calcite.

→ double; → refraction.

In → general relativity, the → action that yields → Einstein's field equations. It is expressed by:
S_{EH = (1/2κ)∫d⁴x (-g)^1/2R + S^m,
where κ ≡ 8πG and S^m is the matter part of the action.}

→ Einstein; → Hilbert space; → action.

A diffraction phenomenon resulting from the passage of electrons through matter, analogous to the diffraction of visible light. This phenomenon is the main evidence for the existence of waves associated with elementary particles; → de Broglie wavelength.

→ electron; → diffraction.

The unified description of two of the four fundamental interactions of nature, → electromagnetism and the → weak interaction which would merge into a single force under conditions of extreme temperature (above 10¹⁶ degrees, 10² GeV) prevalent in the early history of the → Universe.

→ electroweak; → interaction.

1) The act of extracting or the condition of being extracted.
2) Something obtained by extracting; an extract (FreeDictionary.com).

→ extract; → -tion.

An old explanation, proposed by Enrico Fermi, of the → weak interaction.

→ fermi; → interaction.

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.