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

An equation with surprising simplicity that expresses a fundamental result relating several apparently unassociable elements. For example, → Euler's formula for the particular case of θ = π, and the → mass-energy relation.

→ elegant; → equation.

1) General: A component or constituent of a whole or one of the parts into which a whole may be resolved by analysis.
2) Astro.: Any of the data required to define the precise nature of an orbit and to determine the position of a planet in the orbit at any given time. → orbital element.
3) Chemistry:: One of the 117 presently known substances that cannot be decomposed by chemical reaction into a simpler substance.
4) Math.:a) Of a cylinder or cone, the generating line of the surface, taken in any position. b) Of a set, any member of the set.

From O.Fr. élément, from L. elementum "rudiment, one of the four elements, first principle," origin unknown.

Bonpâr, from bon "basis; root; foundation; bottom;" Mid.Pers. bun "root; foundation; beginning," Av. būna- "base, depth," cf. Skt. bundha-, budhná- "base, bottom," Pali bunda- "root of tree" + pâr contraction of pâré "piece, part, portion, fragment;" Mid.Pers. pârag "piece, part, portion; gift, offering, bribe;" Av. pāra- "debt," from par- "to remunerate, equalize; to condemn;" PIE *per- "to sell, hand over, distribute; to assign;" cf. L. pars "part, piece, side, share," portio "share, portion;" Gk. peprotai "it has been granted;" Skt. purti- "reward;" Hitt. pars-, parsiya- "to break, crumble." Onsor from Ar.

An important physical process occurring in stars, which is the relative separation of the various → chemical elements. It is caused by → gravitational settling and → thermal diffusion, on the one hand, and → radiative levitation on the other. This process, which was described by Michaud (1970) to account for the abundance anomalies observed in → chemically peculiar  → A star, is now recognized as occuring in all types of stars. Its influence on the observed → chemical abundances is extremely variable, however, due to competing macroscopic motions like → convective  → mixing or rotation-induced → turbulence. In the Sun, no observable abundance anomalies are expected from element diffusion, as the time scale of the process is longer than the solar lifetime. However the small induced → depletion of → helium and → heavy elements by about 20% is detectable through → helioseismology. Such detections are more difficult in stars, as only global → oscillation modes can be detected, in contrast to the Sun, where local oscillations of the surface can be analyzed (Théado et al., 2005, A&A 437, 553).

→ element; → diffusion.

Emission nebulae: The relative amount of a given → chemical element in an ionized nebula with respect to another element, usually → hydrogen. Elemental abundance ratios of → emission nebulae are obtained either by adding the observed → ionic abundances of the element or by using → ionization correction factors. Same as → total abundance.

Elemental, from M.L. elementalis, → element + -al; abundance, from O.Fr. abundance, from L. abundantia "fullness," from abundare "to overflow," from L. ab- "away" + undare "to surge," from unda "water, wave;" → abundance.

A particle which cannot be divided into other constituents. More specifically, a particle whose field appears in the fundamental field equations of the unified field theory of elementary particles, in particular in the Lagrangian. For example, the → electron, the → photon, and the → quark are elementary particles, whereas the proton and neutron are not. The elementary nature of a particle can be revised depending on new observations or theories. Also called → fundamental particle.

Elementary, M.E. elementare, from M.F. élémentaire, from L. elementarius, from → element + adj. suffix -arius; → particle.

Bonyâdin, from bonyâd "basis, foundation," variant of bonlâd, from bon "basis; root; foundation; bottom" → element + lâd "root; foundation; reason, cause; wall" + adj. suffix -in.

The time required for → light to cross the classical radius of the electron (→ electron radius): t_e = r_e/c ≅ 10^-23 s.

→ elementary particle; → time.

→ orbital element.

→ element; → orbit.

An elongated structure of → interstellar dust and gas which absorbs the radiation from background stars in an → H II region. These structures are the denser remnants of → molecular clouds from which → massive stars are formed. Elephant trunks are eventually dissipated by the action of the → ionizing radiation and → stellar wind of the associated massive stars. A remarkable example of these structures is displayed by the → HST image of the → Eagle Nebula as → pillars of obscuring matter protruding from the interior wall of a dark molecular cloud. Some → Bok globules may represent the remaining densest fragments of elephant trunks.

M.E. elephant, from O.Fr. olifant, from L. elephantus, from Gk. elephas "elephant, ivory," probably from a non-I.E. language, likely via Phoenician; trunk, from M.E. trunke, O.Fr. tronc, from L. truncus "stem, trunk, stump."

Xortum "the proboscis of an elephant," loanword from Ar. xartum; fil, pil "elephant," from Mid.Pers. pil "elephant;" O.Pers. piru- "ivory."

An elongated dark structure of gas and dust in the → H II region IC 1396. It spans about 5 degrees on the sky in the constellation → Cepheus, about 2400 → light-years from the Earth. The Elephant Trunk Nebula is believed to be site of star formation, containing several very young stars. It is an example of → elephant trunks associated with star forming regions.

→ elephant trunk; → nebula.

1) To move or raise to a higher place or position; lift up.
2) To raise to a higher state, rank, or office; exalt; promote (Dictionary.com).

From L. elevatus, p.p. of elevare "to lift up, raise," from → ex- "out" + levare "lighten, raise," from levis "light" in weight, → lever.

Bâlâyidan, from bâla "up, above, high, elevated, height," related to boland "high," borz, "height, → magnitude."

The floor below a telescope used to lift observers to the level of the telescope's eyepiece, since the telescope is tilted at varying angles when it is in use.

Elevating, adj. of → elevate; → floor.

1) The height to which something is elevated or to which it rises.
2) An elevated place, thing, or part; an eminence (Dictionary.com).

Verbal noun of → elevate; → -tion.

A → chemical reaction on solid surfaces in which one atom or molecule is → adsorbed on the catalyst surface, and another reacts directly from the gas phase. This type of mechanism may occur preferentially on very small → dust grains, where transient heating events prevent weakly bound species from remaining and in larger grains at high temperatures. Compare with the → Langmuir-Hinshelwood mechanism.

Proposed in 1938 by D. D. Eley (1914-2015), a British chemist and Professor of Physical Chemistry and E. K. Rideal (1890-1974), an English physical chemist.

1) To remove or get rid of, especially as being in some way undesirable.
2) Math.: To remove (an unknown variable) from two or more simultaneous equations (Dictionary.com).

L. eliminatus, p.p. of eliminare "to thrust out of doors, expel," from ex limine "off the threshold," from → ex- "off, out" + limine, ablative of limen "threshold."

Osândan, from Tabari uzitan, huzənniyən, hozənniyan "to expel," from os- "out," → ex-, + -ândan suffix of transitive verbs.

1) The act of eliminating; the state of being eliminated.
Math.: The process of solving a system of simultaneous → equations by using various techniques to remove the → variables successively (Dictionary.com).

Verbal noun of → eliminate; → -tion.

The locus of a point the sum of whose distances from two fixed points is constant.

From O.Fr. ellipse, from L. ellipsis "ellipse," also, "a falling short, deficit," from Gk. elleipsis "an omission," from el-, variant of en-, + leip-, stem of leipein "to leave" + suffix -sis.

Beyzi, from Ar.

A three-dimensional geometric figure resembling a flattened sphere. It is generated by rotating an ellipse around one of its axes.

From → ellipse + → -oid.

Relating to or having the form of an → ellipse. Same as → elliptical.

From Gk. elleiptikos "pertaining to an ellipse," from elleipein "to fall short, leave out," from en- "in" + leipein "to leave," + → -ic.

Beyzigun, from beyzi, → ellipse, + -gun, from gun "resembling; manner, fashion; color" (Mid.Pers. gônak "kind, species;" Av. gaona- "color").

That part of → annual aberration proportional to the → eccentricity of the Earth's orbit.

→ elliptic; → aberration.

Pertaining to or having the shape of a geometric ellipse.

→ elliptic; → -al.