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"nongravitational forces" "niruhâ-ye nâgerâneši" (#) Fr.: "forces non-gravitationnelles" The forces of jets from a comet's nucleus that can cause a rocket-like effect and alter a comet's direction of motion slightly. → non-; → gravitational; → force. |
-tion -eš, -yi Fr.: -tion A suffix used to form abstract nouns from verbs to express action, state, or associated meanings. From L. -tionem, accusative of noun suffix -tio (genitive -tionis). -eš, from Mid.Pers. -išn. |
ab initio calculation afmâr-e hac bon Fr.: calcul ab initio In physics and chemistry, a calculation that relies on basic and established laws without additional assumptions or special models. Experimental input in ab initio calculations is limited to the determination of values of fundamental physical constants. → ab initio; → calculation. |
Abbe sine condition butâr-e sinus-e Abbe Fr.: condition des sinus d'Abbe In → geometric optics, a condition for eliminating → spherical aberration and → coma in an → optical system. It is expressed by the relationship: sin u'/U' = sin u/U, where u and U are the angles, relative to the → optical axis, of any two rays as they leave the object, and u' and U' are the angles of the same rays where they reach the image plane. A system which satisfies the sine condition is called → aplanatic. Named after Ernst Karl Abbe (1840-1905), a German physicist; → sine; → condition. |
aberration birâheš Fr.: aberration 1) An imperfection in the imaging properties of a → lens
or → mirror.
The main aberrations are → chromatic aberration,
→ spherical aberration, → coma,
→ astigmatism, → distortion,
and → field curvature. Aberration, from L. aberrationem, from aberrare "go astray," → aberrate. Birâheš, from birâidan, → aberrate. |
aberration angle zâviye-ye birâheš Fr.: angle d'aberration The angle tilt required by the → stellar aberration phenomenon in order that a moving telescope points directly to a star. → aberration; → angle. |
aberration constant pâyâ-ye birâheš Fr.: constante d'aberration Same as → constant of aberration. → aberration; → constant. |
aberration of light birâheš-e nur Fr.: aberration de la lumière → aberration; → light. |
aberration of starlight birâheš-e nur-e setâré Fr.: aberration de la lumière d'étoile An apparent displacement in the observed position of a star. It is a result of the finite speed of light combined with the relative motion of the Earth through space. Suppose that you walk through a vertically falling rain with an umbrella over your head. The faster you walk, the further you must lower the umbrella in front of yourself to prevent the rain from striking your face. For starlight to enter a telescope, a similar phenomenon must occur, because the Earth is in motion. The telescope must be tilted in the direction of motion by an angle: tan θ =(v/c), where v the Earth velocity and c the speed of light. The aberration of starlight was discovered by the English astronomer James Bradley (1693-1762) in 1729 by observing → Gamma Draconis. The tilt angle is θ = 20''.50, from which the Earth's orbital speed, 29.80 km s^{-1}, can be deduced, using the above equation. See also → annual aberration; → diurnal aberration; → secular aberration. → Special relativity modifies the classical formula for aberration, predicting results which differ substantially from those of classical physics for objects moving at a substantial fraction of the speed of light; → relativistic aberration. → aberration; → star; → light. |
aberration orbit madâr-e birâheš Fr.: orbite d'aberration The apparent path described by a star on the → celestial sphere due → annual aberration. A star at the → ecliptic pole is seen to move around a circle of angular radius about 20".50, once a year. A star on the → ecliptic oscillates to and fro along a line of angular half-length 20".50. At an intermediate → celestial latitude, β, the aberration orbit is an ellipse, with semi-major axis 20".50 and semi-minor axis (20".50) sin β. → aberration; → orbit. |
aberrational birâheši Fr.: aberrationnel Of or pertaining to → aberration. → aberration; → -al. |
aberrational day number šomâre-ye ruz-e birâheši Fr.: nombre de jours d'aberration A → Besselian day number denoted by C or D. → aberration; → -al; → day; → number. |
aberrational ellipse beyzi-ye birâheši Fr.: ellipse d'aberration The → locus of points on the → celestial sphere occupied by a star during the annual → revolution of the → Earth about the → Sun due to → annual aberration. annual aberration. → aberrational; → ellipse. |
ablation farsâb (#) Fr.: ablation The → erosion of a surface through a process such as → vaporization or → friction. L. ablatio, ablation, from ablatus, from ab- "away" + latus "carried." Farsâb from far-, prefix denoting "abundance, excess" + sâb present stem of sâbidan "to rub, wear out," variants sâyidan, pasâvidan "to touch," Khotanese sauy- "to rub," Sogdian ps'w- "to touch," Proto-Iranian *sau- "to rub." |
abortion fagâné, fagâneš Fr.: avortement The stopping of a process; a result of such termination. Verbal noun of → abort. |
absolute acceleration šetâb-e avast Fr.: accélération absolue For a body that moves with respect to a rotating → reference frame, the vector sum of the observed acceleration, the → Coriolis acceleration, and the → centrifugal acceleration. See also the → Coriolis theorem. → absolute; → acceleration. |
absorption daršam Fr.: absorption 1) General: The process or fact of absorbing. |
absorption band bând-e daršami Fr.: bande d'absorption 1) A series of very closely spaced absorption lines in stellar spectra
resulting from the absorption of light by molecules. Bands caused by
titanium oxide (→ TiO bands) and carbon compounds occur
in the spectra of low temperature M and C stars. → absorption; → band. |
absorption coefficient hamgar-e daršam Fr.: coefficient d'absorption The fraction of normally incident light that is absorbed per unit path length or by a unit mass of absorbing medium. → absorption; → coefficient. |
absorption curve xam-e daršam Fr.: courbe d'absorption A graphic representation of the amount of radiant energy absorbed by a material as a function of the wavelength. → absorption; → curve. |
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