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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meridian observation
  نپاهش ِ نیمروزانی   
nepâheš-e nimruzâni

Fr.: observation au méridien   

The observation of a star when it crosses an observer's meridian.

meridian; → observation.

meridional
  نیمروزانی   
nimruzâni

Fr.: méridien   

Of, pertaining to, or resembling a meridian.

meridian + → -al.

From nimruzân, → meridian, + -i adj. suffix.

meridional circulation
  پرهونش ِ نیمروزانی   
parhuneš-e nimruzâni

Fr.: circulation méridien   

The mass motion of material within a → rotating star generated by the star's departure from spherical symmetry. For a rotating star in which → centrifugal forces are not negligible, → radiative equilibrium and → hydrostatic equilibrium cannot be satisfied. In this condition energy transfer is accomplished by means of the physical motion of material. According to → von Zeipel theorem, the heating on an → equipotential surface is generally higher in the polar direction than in the equatorial direction, which drives a large scale circulation current rising at the pole and descending at the equator. As a consequence, → mixing of material takes place in the stellar interior; see also → Eddington-Sweet time scale. The meridional circulation plays an important role in the evolution of → massive stars. The circulation current was first suggested by Arthur S. Eddington in 1926 (The Internal Constitution of the Stars, Dover Pub. Inc., New York) and subsequently quantified by P. A. Sweet (1950, MNRAS 110, 548).

meridional; → circulation.

meridional flow
  تچان ِ نیمروزانی   
tacân-e nimruzâni

Fr.: courant méridien   

Meteo.: A flow between the poles, or between the equator and the poles. A positive value indicates flow away from the equator; a negative value, flow toward the equator.

meridional; → flow.

meridional magnetic field
  میدان ِ مغناتیسی ِ نیمروزانی   
meydân-e meqnâtisi-ye nimruzâni

Fr.: champ magnétiquue méridien   

In the → solar dynamo model, a magnetic field that points from the north to south or south to north.

meridional; → magnetic; → field.

meson
  مسون   
meson

Fr.: méson   

A nuclear particle with a mass intermediate between that of a proton and an electron, which is believed to be responsible for the strong nuclear force. In contrast to the case of baryons or leptons, meson number is not conserved: like photons, mesons can be created or destroyed in arbitrary numbers. Their charge can be positive, negative, or zero.

From mes-, meso-, from Gk. mesos "middle," akin to L. medius, Pers. miyân, → medium, → middle, + -on a suffix used in the names of subatomic particles.

metal-rich environment
  پرگیر ِ پرفلز   
pargir-e porfelez

Fr.: environnement riche en métaux   

An environment (→ galaxy, → nebula) whose → metallicity is larger than that of the → Milky Way galaxy.

metal; → rich; → environment.

metallicity distribution function (MDF)
  کریای ِ واباژش ِ فلزیگی   
karyâ-ye vâbâžeš-e felezigi

Fr.: fonction de distribution de métallicité   

A plot representing the number of stars (or systems) per metallicity interval, usually expressed in [Fe/H] (abundance of → iron relative to → hydrogen).

metallicity; → distribution; → function.

meteoric ionization
  یونش ِ شهاب‌سنگی، ~ ِ آسمان‌سنگی   
yoneš-e šahâbsangi, ~ âsmânsangi

Fr.: ionisation météoritique   

The ionization of air molecules by the heat generated when a meteorite enters the atmosphere.

meteorite, → ionization.

meteorological observation
  نپاهش ِ هواشناختی   
napâheš-e havâšenâxti

Fr.: observation météorologique   

Evaluation or measurement of one or more meteorological elements.

Meteorological, of or pertaining to → meteorology; → observation.

method of small perturbations
  روش ِ پرتورش‌های ِ کوچک   
raveš-e parturešhâ-ye kucak

Fr.: méthode des petites perturbations   

The linearization of the appropriate equations governing a system by the assumption of a steady state, with departures from that steady state limited to small perturbations. Also called perturbation method.

method; → small; → perturbation.

method of successive approximations
  روش ِ نزدینش‌های ِ پیاپی   
raveš-e nazdinešhâ-ye payâpey

Fr.: méthode d'approximations successives   

The solution of an equation or by proceeding from an initial approximation to a series of repeated trial solutions, each depending upon the immediately preceding approximation, in such a manner that the discrepancy between the newest estimated solution and the true solution is systematically reduced.

method; → successive; → approximation.

Metonic cycle
  چرخه‌ی ِ متون   
carxe-ye Meton

Fr.: cycle de Méton   

A time interval lasting 235 → lunations, or about 19 → tropical years (235 = 19 x 12 + 7), after which → lunar phases recur on the same days of the year.

Named after Meton of Athens, a Gk. mathematician, astronomer, geometer, and engineer who used it in 432 B.C., but it was known to the Babylonians by around 500 B.C. and to the Chinese around 600 B.C.; → cycle.

MHD condition
  بوتار ِ MHD   
butâr-e MHD

Fr.: condition MHD   

ideal magnetohydrodynamics.

magnetohydrodynamics (MHD); → condition.

Michelson interferometer
  اندرزنش‌سنج ِ مایکلسون   
andarzanešsanj-e Michelson

Fr.: Interféromètre de Michelson   

An apparatus that produces interference fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are brought back together, an interference pattern results. It is used to measure very precise lengths, such as the wavelength of light, and for high-resolution spectroscopy.

Named after Albert Abraham Michelson (1852-1931), German-American physicist, who built the interferometer for the → Michelson-Morley experiment of 1887; → interferometer.

Andarzanešsanj, → interferometer.

Michelson-Morley experiment
  آزمایش ِ مایکلسون-مورلی   
âzmâyeš-e Michelson-Morley (#)

Fr.: expérience de Michelson-Morley   

An experiment performed in 1887 to establish the presence or absence of an → ether, a medium through which light was supposed to travel. The experiment aimed to measure the speed of light coming from different directions. However no → ether drift was found. The null results obtained showed that the ether hypothesis was incorrect. Consequently, the theory of → special relativity, with its hypothesis that the speed of light is the same in all → inertial frames, reconciled the results of the Michelson-Morley experiment with the rest of physics.

Michelson interferometer; Michelson received the Nobel Prize in 1907 for his work, the first American to receive the Prize in science. Edward Williams Morley (1838-1923), an American chemist; → experiment.

micro Moon
  ریز ماه   
riz mâh

Fr.: pleine lune d'apogée   

Same as → apogee full Moon.

micro-; → Moon.

micron
  میکرون   
mikron (#)

Fr.: micron   

A unit of length in the → metric system equal to one millionth of a → meter (10-6 m); symbol μm. Also called → micrometer. The average thickness of a human hair is about 50 μm (30-100 μm). The human eye cannot see anything smaller than 40 μm in size. Other small sizes: white blood cells = 15 μm; red blood cells = 8 μm; bacteria 2 μm.

Coined 1880 in Fr. from Gk. mikron, neutral of mikros "small."

microwave background radiation
  تابش ِ پس‌زمینه‌ی ِ ریزموج   
tâbeš-e paszamine-ye rizmowj

Fr.: rayonnement micro-onde du fond cosmique   

Thermal radiation with a temperature of 2.73 K that is apparently uniformly distributed in the Universe. It is believed to be a redshifted remnant of the hot radiation that was in thermal equilibrium with matter during the first hundred thousand years after the Big Bang. Same as → cosmic microwave background (CMB) radiation.

microwave; → background; → radiation.

microwave radiation
  تابش ِ ریزموج   
tâbeš-e rizmowj (#)

Fr.: rayonnement micro-onde   

Electromagnetic radiation carried by → microwaves.

microwave; → radiation.

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