An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -le Lag lam Lan Lar las law lea lem lep Li- lig lim lin lin lio lit loc lod lon Lor low Lum lun Lup Lyn > >>

Number of Results: 506
Larmor frequency
  بسامد ِ لارمور، فرگی ِ ~   
basâmad-e Larmor (#), feregi-ye ~ (#)

Fr.: fréquence de Larmor   

The frequency of precession of a charged particle describing a circular motion in a plane perpendicular to the magnetic induction in a uniform magnetic field.

Named after Joseph Larmor (1857-1942), an Irish physicist, the first to calculate the rate at which energy is radiated by an accelerated electron, and the first to explain the splitting of spectrum lines by a magnetic field; → frequency.

Larmor radius
  شعاع ِ لارمور   
šoâ'-e Larmor (#)

Fr.: rayon de Larmor   

The radius of the circular motion of a → charged particle moving in a → uniform magnetic field. Same as → gyroradius, → radius of gyration, → cyclotron radius. The Larmor radius (rL) is obtained by equating the → Lorentz force with the → centripetal force: qvB = mv2/rL, which leads to rL = p/(ZeB), where p is → momentum, Z is → atomic number, e is the → electron charge, and B is → magnetic induction. The frequency of this circular motion is known as the → gyrofrequency.

Larmor frequency; → radius.

Larmor's theorem
  فربین ِ لارمور   
farbin-e Larmor

Fr.: théorème de Larmor   

If a system of → charged particles, all having the same ratio of charge to mass (q/m), acted on by their mutual forces, and by a central force toward a common center, is subject in addition to a weak uniform magnetic field (B), its possible motions will be the same as the motions it could perform without the magnetic field, superposed upon a slow → precession of the entire system about the center of force with angular velocity ω = -(q/2mc)B.

Larmor frequency; → theorem.

Larson relation
  بازانش ِ لرسون   
bâzâneš-e Larson

Fr.: relation de Larson   

An → empirical relationship between the internal → velocity dispersion of → molecular clouds and their size. The velocity dispersions are derived from molecular → linewidths, in particular those of → carbon monoxide. It was first established on star forming regions and found to be: σ (km s-1) = 1.10 L (pc)0.38, where σ is the velocity dispersion and L the size. The relation holds for 0.1 ≤ L ≤ 100 pc. More recent set of cloud data yield: σ (km s-1) = L (pc)0.5. This relation indicates that larger molecular clouds have larger internal velocity dispersions. It is usually interpreted as evidence for → turbulence in molecular clouds. Possible sources of interstellar turbulence include the following processes operating at various scales: galactic-scale (→ differential rotation, → infall of extragalactic gas on the galaxy), intermediate-scale (expansion of → supernova remnants, → shocks, → stellar winds from → massive stars), and smaller-scale processes (→ outflows from → young stellar objects).

First derived by Richard B. Larson, American astrophysicist working at Yale University (Larson, 1981, MNRAS 194, 809). See Falgarone et al. (2009, A&A 507, 355) for a recent study; → relation.

Larson-Penston solution
  لویش ِ لرسون-پنستون   
luyeš-e Larson-Penston

Fr.: solution de Larson-Penston   

The analytical solution to the → hydrodynamic equations describing the → collapse of an → isothermal sphere. The Larson-Penston solution is → self-similar for a purely dynamical isothermal collapse with spherical symmetry. It corresponds to the collapse prior to the formation of a → protostar, and thus is suitable for the study of → pre-stellar cores. The Larson-Penston solution was extended by Shu (1977) to obtain a whole family of solutions for this problem.

Named after R. B. Larson (1969, MNRAS 145, 271) and M. V. Penston (1969, MNRAS 144, 425), who simultaneously, but independently, did this study.

hanjare-yi (#)

Fr.: laryngé   

1) Of, pertaining to, or located in the larynx.
2) Phonetics: articulated in the larynx (

larynx; → -al.

laryngeal consonant
  هم‌آوای ِ حنجره‌ای   
hamâvâ-ye hanjare-yi

Fr.: son laryngé   

A consonant generated in the → larynx with the → vocal cords partly closed and partly vibrating. It is hypothesized that the → Proto-Indo-European language contained some laryngeal consonants (denoted by H).

laryngeal; → consonant.

hanjaré (#)

Fr.: larynge   

A muscular and cartilaginous structure lined with mucous membrane at the upper part of the → trachea in humans, in which the → vocal cords are located (

From M.Fr. larynx, from M.L. from Gk. larynx (genitive laryngos) "the upper windpipe," probably from laimos "throat," influenced by pharynx "throat, windpipe."

Hanjaré, from Ar. Hanjarah.

leyzer (#)

Fr.: laser   

1) A device that generates an intense directional beam of → monochromatic and → coherent light by exciting atoms to a higher energy level and causing them to radiate their energy in phase. The high degree of collimation arises from the fact that excited atoms are are situated in a cavity bounded by two parallel front and back mirrors. A first photon stimulates an atom which emits a second photon, and so on thanks to the mirrors. The resulting photons are all identical. They have the same energy which gives them the same color and a unique direction. The first working laser, a pulsed ruby device, was developed by T. Maiman in 1959. See also → gas laser, → stimulated emission; → maser.
2) The light produced in this way.

Acronym for light amplification by stimulated emission of radiation, on pattern of → maser.

laser cooling technique
  تشنیک ِ سردش ِ لیزری   
tašnik-e sardeš-e leyzeri

Fr.: technique de refroidissement par laser   

A technique that uses a suitable arrangement of → laser beams and magnetic fields to capture → cesium (133Cs) atoms from a thermal vapor and slow the motion of the atoms, cooling them to just a few micro-kelvins above the → absolute zero. The technique allows trapping some 107 cesium atoms in a cloud a few millimeters in diameter in a few tenths of a second. At a temperature of 2 μK, the average thermal velocity of the cesium atoms is of the order of 1 cm s-1, so they stay together for a relatively long time. The laser cooling technique is the key tool which enabled the operation of an → atomic fountain clock.

laser; → cooling; → technique.

laser interferometer
  اندرزنش‌سنج ِ لیزری   
andarzaneš-sanj-e leyzeri

Fr.: interféromètre laser   

An optical instrument using laser → beams to form → interference pattern. There are two types of laser interferometers: → homodyne and → heterodyne. A homodyne interferometer, like → Michelson interferometer, uses a single-frequency laser source. A → heterodyne interferometer uses a laser source with two close frequencies.

laser; → interferometer.

Laser Interferometer Gravitational-Wave Observatory (LIGO)
  نپاهشگاه ِ موجهای ِ گرانشی با اندرزنش‌سنجی ِ لیزری   
nepâhešgâh-e mowjhâ-ye gerâneši bâ andarzaneš-sanji-ye leyzeri

Fr.: Observatoire d'ondes gravitationnelles par interférométrie laser   

A facility dedicated to the detection and measurement of cosmic → gravitational waves. It consists of two widely separated installations, or detectors, within the United States, operated in unison as a single observatory. One installation is located in Hanford (Washington) and the other in Livingston (Louisiana), 3,000 km apart. Funded by the National Science Foundation (NSF), LIGO was designed and constructed by a team of scientists from the California Institute of Technology, the Massachusetts Institute of Technology, and by industrial contractors. Construction of the facilities was completed in 1999. Initial operation of the detectors began in 2001. Each LIGO detector beams laser light down arms 4 km long, which are arranged in the shape of an "L." If a gravitational wave passes through the detector system, the distance traveled by the laser beam changes by a minuscule amount -- less than one-thousandth of the size of an atomic nucleus (10-18 m). Still, LIGO should be able to pick this difference up. LIGO directly detected gravitational waves for the first time from a binary → black hole merger (GW150914) on September 14, 2015 (Abbott et al., 2016, Phys. Rev. Lett. 116, 061102). The Nobel Prize in physics 2017 was awarded to three physicists (Rainer Weiss, Barry C. Barish, and Kip S. Thorne) for decisive contributions to the LIGO detector and the observation of gravitational waves. LIGO had a prominent role in the detection of → GW170817, the first event with an → electromagnetic counterpart.

laser; → interferometer; → gravitational; → wave; → observatory.

Laser Interferometer Space Antenna (LISA)
  آنتن ِ فضایی ِ اندرزنش‌سنج ِ لیزری   
ânten-e fezâyi-e andarzanešsanj-e leyzeri

Fr.: Observatoire d'ondes gravitationnelles par interférométrie laser   

A collaborative project between → NASA and → ESA to develop and operate a space-based gravitational wave detector sensitive at frequencies between 0.03 mHz and 0.1 Hz. LISA detects gravitational-wave induced strains in → space-time by measuring changes of the separation between fiducial masses in three spacecraft 5 million km apart. Ultimately, NASA and ESA decided in 2011 not to proceed with the mission. LISA was not the highest ranked mission in the 2010 Decadal Survey and funding constraints prevented NASA from proceeding with multiple large missions ( → LISA pathfinder.

laser; → interferometer; → space; → antenna.

vâpasin (#)

Fr.: dernier   

Occurring or coming after all others, as in time, order, or place. → last contact, → last quarter

Last, from O.E. latost (adj.) and lætest (adv.), superlative of læt (adj.) and late (adv.); cognate with O.Fris. lest, Du. laatst, O.H.G. laggost, Ger. letzt.

Vâpasin, from vâ-, as intensive prefix, → de-, + pasin, from pas "after, afterward, behind; finally, at last" (Mid.Pers. pas "behind, before, after;" O.Pers. pasā "after;" Av. pasca "behind (of space); then, afterward (of time);" cf. Skt. pazca "behind, after, later;" L. post "behind, in the rear; after, afterward;" O.C.S. po "behind, after;" Lith. pas "at, by;" PIE base *pos-, *posko-) + -in superlative suffix.

last (v.)

Fr.: durer   

To continue in time; go on; endure.

M.E. lasten, from O.E. læstan "to continue, endure;" cf. Goth. laistjan "to follow after," Ger. leisten "to perform, achieve,"), from PIE root *lois- "furrow, track."

Pâyidan "to watch, observe; remain or continue in existence, last," variants pâsidan, pâhidan; Mid.Pers. pây- "to protect, guard;" Sogdian p'y "to observe, protect, watch over;" O.Pers. pā- "to protect," pāta- "protected;" Av. pā- "to protect," pāti "guards," nipā(y)- (with ni-) "to watch, observe, guard," nipātar- "protector, watcher," nipāθri- "protectress;" cf. Skt. pā- "to protect, keep," tanû.pā- "protecting the body," paś.pā- "shepherd;" Gk. poma "lid, cover," poimen "shepherd;" L. pascere "to put out to graze," pastor "shepherd;" Lith. piemuo "shepherd;" PIE base *pā- "to protect, feed."

last contact
  پرماس ِ واپسین   
parmâs-e vâpasin

Fr.: dernier contact   

Same as → fourth contact at an eclipse.

last; → contact.

last quarter
  چارک ِ واپسین   
cârak-e vâpasin

Fr.: dernier quartier   

One of the phases of the Moon that appears when it is 90 degrees west of the Sun. Approximately one week after a full moon, when half of the Moon's disk is illuminated by the Sun. → first quarter.

last; → quarter.

last scattering
  واپسین پراکنش   
vâpasin parâkaneš

Fr.: dernière diffusion   

The epoch in the early evolution of the Universe when matter and photons decoupled. Once atoms formed, light and matter stopped constantly interacting with one another, and photons were able to travel freely. As a result, the Universe became transparent. Light from this period is observed today as the → cosmic microwave background radiation. Same as → decoupling era and → recombination era.

last; → scattering.

last scattering surface
  رویه‌ی ِ واپسین پراکنش   
ruye-ye vâpasin parâkaneš

Fr.: surface de dernière diffusion   

The set of locations in space corresponding to the → last scattering epoch in the early Universe. It is a spherical surface around the present-day observer from which the → cosmic microwave background radiation appears to emanate.

last; → scattering; → surface.


Fr.: dernier né   

Last in order of birth; youngest.

last; → born.

Demâzâ, from Lori, Laki demâzâ, from demâ "last, end, back," related to dom, → tail, + contraction of zâd, → born.

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