An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 1889 Search : ion
"nongravitational forces"
  "نیروهای ِ ناگرانشی"   
"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
   -ش، -یی   
-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.

25 Orionis
  ۲۵-شکارگر، ۲۵-اریون   
25-Šekârgar, 25-Oryon

Fr.: 25 Orionis   

A blue star of → apparent visual magnitude 4.96 lying in the → Orion constellation. It has other designations, including: ψ1 Orionis, BD+01 1005, HR 1789, and HIP 25302. 25 Ori is a → main sequence star of → spectral type B1 V. It lies at a distance of 1,040 → light-years and has a → luminosity of 9,300 MSun, a radius of 5.5 Rsun, and a mass of about 10 Msun. 25 Ori is in fact a → Be star.

25 Orionis group
  گروه ِ ۲۵-شکارگر، ~ ۲۵-اوریون   
goruh-e 25-Šekârgar, ~ 25-Oryon

Fr.: groupe de 25 Orionis   

A group of nearly 200 low-mass → pre-main-sequence stars, concentrated within ~ 1 of the early → B star  → 25 Orionis, in the component a of the → Orion OB1 Association. The group also harbors the → Herbig Ae/Be star V346 Ori and a dozen other early-type stars. The velocity distribution for the low-mass stars shows a narrow peak at 19.7 km s-1, offset ~ 10 km s-1 from the velocity characterizing the younger stars of the Ori OB1b subassociation, and 4 km s-1 from the velocity of widely spread young stars of the Ori OB1a population. This indicates that the 25 Ori group is a distinct kinematic entity. The low-mass members follow a well-defined band in the → color-magnitude diagram, consistent with an age of ~ 7-10 Myr (Briceno et al., 2007, ApJ 661, 1119).

25 Orionis; → group.

42 Orionis
  ۴۲-شکارگر، ۴۲-اریون   
42-Šekârgar, 42-Oryon

Fr.: 42 Orionis   

A blue star with → apparent visual magnitude 4.59 in → Orion's Sword. Also known as → c Orionis, HD 37018, HR 1892, and HIP 26237. More specifically, it is a → main sequence star of → spectral type B1 V, lying in the → H II regionNGC 1977. 42 Orionis is approximately 900 → light-years away based on parallax. It is the major source for ionizing photons in NGC 1977. 42 Ori is a → mutiple star system. The primary star, Aa, of magnitude 6.3 has a → companion companion Ab at a separation of 0.16'', and a more distant companion B of 7.5 magnitude at 1.6'' separation. An irradiated → circumstellar disk near 42 Ori has been detected by Bally et al. (2012) in the → HST image using Hα filter (F658N). They identified a bent → protostellar jet HH1064 from Parenago 2042 (the Spindle) in NGC 1977 with numerous → bow shock features. They argue that the arc feature in the Hα Spindle is centered on the star and its brightened side of the arc is facing toward 42 Ori, suggesting that it may be a → proplyd (Kim et al., 2016, arXiv::1606.08271).

Number 42 in → Flamsteed designation; Orionis, genitive of → Orion.

ab initio calculation
  افمار ِ هچ بن   
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
  بوتار ِ سینوس ِ آبه   
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
  بیراهش   
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.
2) → aberration of starlight.
See also: → aberration angleaberration constanaberration of starlightaberration orbitannual aberrationchromatic aberrationconstant of aberrationdiurnal aberrationoptical aberrationplanetary aberrationrelativistic aberrationsecular aberrationspherical aberrationstellar aberration.

Aberration, from L. aberrationem, from aberrare "go astray," → aberrate.

Birâheš, from birâidan, → aberrate.

aberration angle
  زاویه‌ی ِ بیراهش   
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
  پایا‌ی ِ بیراهش   
pâyâ-ye birâheš

Fr.: constante d'aberration   

Same as → constant of aberration.

aberration; → constant.

aberration of light
  بیراهش ِ نور   
birâheš-e nur

Fr.: aberration de la lumière   

aberration of starlight

aberration; → light.

aberration of starlight
  بیراهش ِ نور ِ ستاره   
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
  مدار ِ بیراهش   
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
  بیراهشی   
birâheši

Fr.: aberrationnel   

Of or pertaining to → aberration.

aberration; → -al.

aberrational day number
  شماره‌ی ِ روز ِ بیراهشی   
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
  بیضی ِ بیراهشی   
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
  فرساب   
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
  فگانه، فگانش   
fagâné, fagâneš

Fr.: avortement   

The stopping of a process; a result of such termination.

Verbal noun of → abort.

absolute acceleration
  شتاب ِ اوست   
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
  درشم   
daršam

Fr.: absorption   

1) General: The process or fact of absorbing.
2) Physics: The action of energy or matter penetrating or being assimilated into a body of matter with no reflection or emission. → adsorption, → desorption, → sorption.
See also: → absorption band, → absorption coefficient, → absorption curve, → absorption feature, → absorption line, → absorption nebula, → absorption spectrum, → atmospheric absorption, → discrete absorption component, → foreground absorption, → intergalactic absorption, → internal absorption, → interstellar absorption, → mass absorption coefficient, → photoabsorption, → selective absorption, → self-absorption.

Verbal noun of → absorb; → -tion, from L. absorptionem.

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