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: 3079 Search : on
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.

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.

last contact
  پرماس ِ واپسین   
parmâs-e vâpasin

Fr.: dernier contact   

Same as → fourth contact at an eclipse.

last; → contact.

law of non-contradiction
  قانون ِ ناپادگویی   
qânun-e nâpâdguyi

Fr.: principe de non-contradiction   

Same as → principle of non-contradiction.

law; → non-; → contradiction.

law of reflection
  قانون ِ بازتاب   
qânun-e bâztâb (#)

Fr.: loi de réflexion   

One of the two laws governing reflection of light from a surface: a) The → incident ray, normal to surface, and reflected ray lie in the same plane. b) The → angle of incidence (with the normal to the surface) is equal to the → angle of reflection.

law; → reflection.

law of refraction
  قانون ِ شکست   
qânun-e šekast (#)

Fr.: loi de réfraction   

One of the two laws governing → refraction of light when it enters another transparent medium: a) The → incident ray, normal to the surface, and refracted ray, all lie in the same plane. b) → Snell's law is satisfied.

law; → refraction.

Layzer-Irvine equation
  هموگش ِ لیزر-آیروین   
hamugeš-e Layzer-Irvine

Fr.: équation de Layzer-Irvine   

The ordinary Newtonian energy conservation equation when expressed in expanding cosmological coordinates. More specifically, it is the relation between the → kinetic energy per unit mass associated with the motion of matter relative to the general → expansion of the Universe and the → gravitational potential energy per unit mass associated with the departure from a homogeneous mass distribution. In other words, it deals with how the energy of the → Universe is partitioned between kinetic and potential energy. Also known as → cosmic energy equation. In its original form, the Layzer-Irvine equation accounts for the evolution of the energy of a system of → non-relativistic particles, interacting only through gravity, until → virial equilibrium is reached. But it has recently been generalized to account for interaction between → dark matter and a homogeneous → dark energy component. Thus, it describes the dynamics of local dark matter perturbations in an otherwise homogeneous and → isotropic Universe (P. P. Avelino and C. F. V. Gomes, 2013, arXiv:1305.6064).

W. M. Irvine, 1961, Ph.D. thesis, Harvard University; D. Layzer, 1963, Astrophys. J. 138, 174; → equation.

leap month
  ماه ِ اندرهلی   
mâh-e andarheli

Fr.: mois intercalaire   

An intercalary month employed in some calendars to preserve a seasonal relationship between the Lunar and Solar cycles. → embolismic month.

leap; → month.

leap second
  ثانیه‌ی ِ اندرهلی   
sâniyeh-ye andarheli

Fr.: seconde intercalaire   

A one-second added between 60s and 0s at announced times to keep the Coordinated Universal Time (UTC), counted by atomic clocks, within 0s.90 of mean solar time (UT1). Generally, leap seconds are added at the end of June or December.

leap; → second.

least common multiplier (LCM)
  کوچکترین بستاگر ِ همدار   
kucektarin bastâgar-e hamdâr

Fr.: plus petit commun multiple   

Of two or more → integers, the smallest positive number that is divisible by those integers without a remainder.

least; → common; → multiplier.

least-squares deconvolution (LSD)
  واهماگیش ِ کمترین چاروشها   
vâhamâgiš-e kucaktarin cârušhâ

Fr.: déconvolution des moindres carrés   

A → cross correlation technique for computing average profiles from thousands of → spectral lines simultaneously. The technique, first introduced by Donati et al. (1997, MNRAS 291,658), is based on several assumptions: additive → line profiles, wavelength independent → limb darkening, self-similar local profile shape, and weak → magnetic fields. Thus, unpolarized/polarized stellar spectra can indeed be seen as a line pattern → convolved with an average line profile. In this context, extracting this average line profile amounts to a linear → deconvolution problem. The method treats it as a matrix problem and look for the → least squares solution. In practice, LSD is very similar to most other cross-correlation techniques, though slightly more sophisticated in the sense that it cleans the cross-correlation profile from the autocorrelation profile of the line pattern. The technique is used to investigate the physical processes that take place in stellar atmospheres and that affect all spectral line profiles in a similar way. This includes the study of line profile variations (LPV) caused by orbital motion of the star and/or stellar surface inhomogeneities, for example. However, its widest application nowadays is the detection of weak magnetic fields in stars over the entire → H-R diagram based on → Stokes parameter V (→ circular polarization) observations (see also Tkachenko et al., 2013, A&A 560, A37 and references therein).

least; → square; → deconvolution.

Ledoux's criterion
  سنجیدار ِ لو‌دو   
sanjidâr-e Ledoux

Fr.: critère de Ledoux   

An improvement of → Schwarzschild's criterion for convective instability, which includes effects of chemical composition of the gas. In the Ledoux criterion the gradient due to different molecular weights is added to the adiabatic temperature gradient.

After the Belgian astrophysicist Paul Ledoux (1914-1988), who studied problems of stellar stability and variable stars. He was awarded the Eddington Medal of the Royal Astronomical Society in 1972 (Ledoux et al. 1961 ApJ 133, 184); → criterion.

Legendre equation
  هموگش ِ لوژاندر   
hamugeš-e Legendre

Fr.: équation de Legendre   

The → differential equation of the form: d/dx(1 - x2)dy/dx) + n(n + 1)y = 0. The general solution of the Legendre equation is given by y = c1Pn(x) + c2Qn(x), where Pn(x) are Legendre polynomials and Qn(x) are called Legendre functions of the second kind.

Named after Adrien-Marie Legendre (1752-1833), a French mathematician who made important contributions to statistics, number theory, abstract algebra, and mathematical analysis; → equation.

Legendre transformation
  ترادیسش ِ لوژاندر   
tarâdiseš-e Legendre

Fr.: transformation de Legendre   

A mathematical operation that transforms one function into another. Two differentiable functions f and g are said to be Legendre transforms of each other if their first derivatives are inverse functions of each other: df(x)/dx = (dg(x)/dx)-1. The functions f and g are said to be related by a Legendre transformation.

Legendre equation; → transformation.

legislation
  قانونگذاری   
gânungozâri (#)

Fr.: législation   

1) The act of making or enacting laws.
2) A law or a body of laws enacted (Dictionary.com).

From Fr. législation, from L.L. legislationem, from legis latio, "proposing (literally 'bearing') of a law," → legislator.

Qânungoz&acric;ri "act or process followed by the qânungoz&acric;r", → legislator.

length contraction
  ترنگش ِ درازا   
terengeš-e derâzâ

Fr.: contraction de longueur   

Same as → Lorentz contraction.

length; → contraction.

Leonids
  شیریان   
Širiyân (#)

Fr.: Léonides   

A → meteor shower emanating from an apparent point in the constellation → Leo that occurs from November 14-20, with a maximum on November 17-18. It is due to the annual passage of the Earth through the orbit of the comet → Tempel-Tuttle and encounter with the dust debris from the comet.

From L. Leon, → Leo, + → -ids.

lepton
  لپتون   
lepton (#)

Fr.: lepton   

An → elementary particle that does not participate in the → strong interaction. The Lepton family includes → electrons, → muons, tau leptons, → neutrinos and their → antiparticles. The lepton is a → fermion.

From Gk, lepto-, combining form of leptos "small, slight" + -on a suffix used in the names of subatomic particles (gluon; meson; neutron), quanta (photon; graviton), and other minimal entities or components.

lepton degeneracy
  واگنی ِ لپتون   
vâgeni-ye lepton

Fr.: dégénérescence des leptons   

Postulate that the magnitude of the lepton number density is comparable to or larger than the thermal radiation photon number density, so relaxation to equilibrium produces a degenerate sea of neutrinos. Degenerate neutrinos would suppress the number of neutrons relative to protons in the very early Universe; degenerate antineutrinos would suppress the number of protons relative to neutrons. Either case would affect BBNS (Peebles, P. et al., 2009, Finding the Big Bang, Cambridge: UK, Cambridge Univ. Press).

lepton; → degeneracy.

lepton era
  دوران ِ لپتونی   
dowrân-e leptoni (#)

Fr.: ère leptonique   

The era following the hadronic era, when the Universe consisted mainly of leptons and photons. It began when the temperature dropped below 1012 degrees kelvin some 10-4 seconds after the Big Bang, and it lasted until the temperature fell below 1010 degrees kelvin, at an era of about 1 second.

lepton; → era.

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