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: 73 Search : bra
Libra
  ترازو   
Tarâzu (#)

Fr.: Balance   

The Scales. An inconspicuous constellation in the southern hemisphere and a sign of the → Zodiac, at 15h 30m right ascension, 15° south declination. Abbreviation: Lib; genitive: Librae.

L. libra "balance," of obscure origin.

Tarâzu "balance, scales," Mid.Pers. tarâzên-, taraênidan "to weigh," Proto-Iranian *tarāz-, from *tarā- "balance, scale" (cf. Skt. tulā- "scales, balance, weight," from tul- "to weigh, make equal in weight, equal," tolayati "weighs, balances," L. tollere "to raise," Gk. talanton "balance, weight," Atlas "the Bearer" of Heaven," Lith. tiltas "bridge;" PIE base telə- "to lift, weigh") + Av. az- "to convey, conduct, drive," azaiti drives" (cf. Skt. aj- "to dive, sling," ájati "drives," ajirá- "agile, quick," Gk. agein "to lead, guide, drive, carry off," L. agere "to do, set in motion, drive," from PIE root *ag- "to drive, move," → act).

libration
  هلازان، رخگرد   
halâzân, roxgard (#)

Fr.: libration   

Small oscillations of a → celestial body about its mean position. The term is used mainly to mean the Moon's libration caused by the apparent wobble of the Moon as it orbits the Earth. The Moon always keeps the same side toward the Earth, but due to libration, 59% of the Moon's surface can be seen over a period of time. This results from three kinds of libration working in combination: → libration in longitude, → libration in latitude, and → diurnal libration. See also: → geometrical libration, → physical libration.

L. libration- "a balancing."

Halâzân "to and fro motion, oscillation," literally "a swing: a seat suspended by ropes on which a person may sit for swinging," from Gilaki halâcin "a swing," Ilâmi harazân "a swing," variants (Dehxodâ) holucin, holu "a swing," probably from Proto-Ir. *harz- "to send, to set."
Roxgard, literally "turning the face," from rox, variant ru(y) "face, surface; aspect; appearance" (Mid.Pers. rôy, rôdh "face;" Av. raoδa- "growth," in plural form "appearance," from raod- "to grow, sprout, shoot;" cf. Skt. róha- "rising, height") + gard "turning, changing," from gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend").

libration in latitude
  هلازان ِ ورونایی   
halâzân-e varunâ-yi

Fr.: libration en latitude   

A tiny oscillating motion of the Moon arising from the fact that the Moon's axis is slightly inclined relative to the Earth's. More specifically, the Moon's polar axis is tilted nearly 7° with respect to the plane of its orbit around Earth. Hence for half of each orbit we see slightly more of the north pole when its tipped toward us, and for the other half we see slightly more of its south pole. Libration in latitude displaces the mean center of the Moon north-south by between 6°.5 and 6°.9.

libration; → latitude.

libration in longitude
  هلازان ِ درژنایی   
halâzân-e derežnâyi

Fr.: libration en longitude   

A tiny oscillating motion of the → Moon arising from the fact that the Moon's orbit is not a precise circle but rather an → ellipse. Therefore, Moon is sometimes a little closer to the Earth than at other times, and as a result its → orbital velocity varies a bit. Since the Moon's rotation on its own axis is more regular, the difference appears as a slight east-west oscillation. Libration in longitude is the most significant kind of libration. It varies between about 4°.5 and 8°.1 because of gravitational perturbations in the Moon's orbit caused by the Sun.

libration; → longitude.

magnetic braking
  لگامش ِ مغناتیسی   
legâmeš-e meqnâtisi

Fr.: freinage magnétique   

The process whereby a star which loses mass slows down under the action of its → magnetic field. The stellar material follows the → magnetic field lines extending well beyond the stellar surface. The material gain → angular momentum and the underlying object is slowed down. Magnetic braking is an efficient mechanism for removing angular momentum from the the rotating object. See also → disk locking.

magnetic; → braking.

magnetic braking catastrophe
  نگونزار ِ لگامش ِ مغناتیسی   
negunzâr-e legâmeš-e meqnâtisi

Fr.: catastrophe du freinage magnétique   

The failure of numerical star formation calculations to produce rotationally supported → Keplerian disks because of the → magnetic braking effect, when → magnetic fields of strengths comparable to those observed in → molecular clouds are accounted for. The formation and early evolution of disks is a long-standing fundamental problem in → star formation models. Early work in the field had concentrated on the simpler problem of disk formation from the → collapse of a rotating dense core in the absence of a magnetic field. However, dense star-forming cores are observed to be significantly magnetized. There is increasing theoretical evidence that disk formation is greatly modified, perhaps even suppressed, by a dynamically important magnetic field. This has been found in analytic studies, axisymmetric numerical models and in 3D calculations using → ideal magnetohydrodynamics. By contrast, recent observations suggest the presence of massive, 50-100 AU disks and evidence for associated → outflows in the earliest (→ class 0) stages of star formation around both low and high mass stars. Two primary solutions have been proposed: → turbulence and → non-ideal magnetohydrodynamics. Calculations of the collapse of a massive 100 Msun core have shown that 100 AU scale disk formation in the presence of strong magnetic fields was indeed possible, with some argument over whether this is caused by turbulent reconnection or another mechanism. Studies, using simulations of collapsing 5 Msun cores, have found that turbulence diffuses the strong magnetic field out of the inner regions of the core, and that the non-zero → angular momentum of the turbulence causes a misalignment between the rotation axis and the magnetic field. Both of these effects reduce the magnetic braking, and allow a massive disk to form (Wurster et al. 2016, arxiv/1512.01597 and references therein).

magnetic; → braking; → catastrophe.

molecular vibration
  شیوش ِ مولکولی   
šiveš-e molekuli

Fr.: vibration moléculaire   

The dynamical motion of chemically bound atoms which constantly change their position with each other. The vibration of molecules is treated within → quantum theory. Therefore, the energy of molecular vibration can only take → discrete values. To a first approximation, molecular vibrations can be approximated as → simple harmonic oscillator assigned to each mode.

molecular; → vibration.

non-algebraic function
  کریای ِ ناجبری   
karyâ-ye nâjabri

Fr.: fonction non algébrique   

A → transcendental function. Examples are: exponential, logarithmic, and trigonometric functions.

non-; → algebraic + → function.

penumbra
  نیمسایه   
nimsâyé (#)

Fr.: pénombre   

1) The portion of a shadow in which light from an extended source is partially but not completely cut off by an intervening body; the area of partial shadow surrounding the umbra.
2) The lighter part of a shadow during an eclipse. An observer standing in the penumbra of a Solar eclipse will see a partial eclipse.
3) The lighter zone surrounding the dark area (→ umbra) of a → sunspot. It consists of fine, light filaments which are approximately radial for sunspots with circular outline, but irregular for complex spots.

N.L., from L. pæne "almost" + → umbra "shadow."

Nimsâyé, from nim "mid-, half" (Mid.Pers. nêm, nêmag "half;" Av. naēma- "half;" cf. Skt. néma- "half") + sâyé, → shadow; →umbra.

penumbral
  نیمسایه‌ای   
nimsâye-yi (#)

Fr.: pénombral   

Of or relating to a → penumbra.

penumbra; → -al.

penumbral lunar eclipse
  مانگ‌گرفت ِ نیمسایه‌ای   
mânggereft-e nimsâye-yi

Fr.: éclipse de lune pénombrale   

A lunar eclipse that occurs when the Moon passes through the Earth's → penumbra, but misses the darker umbral shadow. Because the Moon is only partially dimmed, a penumbral eclipse is not impressive. Total penumbral eclipses are rare, and when these occur, that portion of the Moon which is closest to the umbra can appear somewhat darker than the rest of the Moon.

penumbral; → eclipse.

photometric calibration
  کبیزش ِ شید-سنجیک، ~ سنور-سنجیک   
kabizeš-e šidsanjik, ~ nursanjik

Fr.: calibration photométrique   

A calibration which converts the measured relative magnitudes into an absolute photometry.

photometric + → calibration.

physical libration
  هلازان ِ فیزیکی، رخگرد ِ ~   
halâzân-e fiziki, roxgard-e ~

Fr.: libration physique   

A real periodic variation in the rotation rate of a celestial object, as distinct from a → geometrical libration. In particular, slight oscillations in the → Moon's rotation caused by the → gravitational attraction of the Earth on the → equatorial bulge of the Moon's near side. The Moon's physical libration is about 0.03° in longitude and about 0.04° in latitude.

physical; → libration.

plane of vibration
  هامن ِ شیوش   
hâmon-e šiveš

Fr.: plan de vibration   

In a → linearly polarized light, a plane perpendicular to the → plane of polarization and containing the direction of propagation of light. It is also the plane containing the direction of propagation and the electric vector (E) of the electromagnetic light wave.

plane; → polarization.

post-asymptotic giant branch star (post-AGB)
  ستاره‌ی ِ پسا-شاخه‌ی ِ غولان ِ ناهمساوی   
setâre-ye pasâ-šâxe-ye qulân-e nâhamsâvi

Fr.: étoile post-asymptotique   

A star in a short-lived evolutionary stage evolving from the → asymptotic giant branch toward higher → effective temperatures. The majority of low and intermediate mass stars (1 to 8 → solar masses) are believed to pass through this stage on their way to becoming → planetary nebulae.

post-; → asymptotic giant branch.

radiative braking
  لگامش ِ تابشی   
legâmeš-e tâbeši

Fr.: freinage radiatif   

The slowing down of a star's rotation due to radiative momentum transfer caused by emission of electromagnetic radiation.

radiative; → braking.

red giant branch (RGB)
  شاخه‌ی ِ غولان ِ سرخ   
šâxe-ye qulân-e sorx

Fr.: branche des géantes rouges   

The evolutionary path of a star that has exhausted its available hydrogen content in the core, between the → main-sequence turnoff and the → helium flash.

red giant; → branch.

red horizontal branch star
  ستاره‌ی ِ سرخ ِ شاخه‌ی ِ افقی   
setâre-ye sorx-e šâxe-ye ofoqi

Fr.: étoile rouge de la branche horizontale   

A star found on the red part of the → horizontal branch. According to theoretical models, these stars result from the evolution of stars with a mass around 0.8 Msun, higher than that giving rise to → BHB stars. Upon helium burning in their cores, the remnant envelope of the red giant collapses.

red; → horizontal; → branch; → star.

rotation-vibration spectrum
  بیناب ِ چرخش-شیوش   
binâb-e carxeš-šiveš

Fr.: spectre rotation-vibration   

The spectrum of a molecule resulting from the simultaneous rotation and vibration of its constituent atoms.

rotation; → vibration; → spectrum.

secondary calibrator
  کبیزنده‌ی ِ دومان   
kabizande-ye dovomân

Fr.: calibrateur secondaire   

An indicator of extragalactic distances that relies on → primary calibrators in our Galaxy. Secondary calibrators of the distance scale depend on statistical measures of the properties of a class of objects, such as the brightness of H II regions, globular clusters, red and blue stars, or the neutral hydrogen 21-cm line width or velocity dispersion (of spiral galaxies), etc. Same as secondary distance indicator.

secondary; → calibrator.

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