An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < abs col den Glo mag per pos rad spe tra > >>

Number of Results: 192 Search : sit
magnetic flux density
  چگالی ِ شار ِ مغناتیسی   
cagâli-ye šâr-e meqnâtisi (#)

Fr.: densité du flux magnétique   

A vector quantity measuring the strength and direction of the magnetic field. It is the → magnetic flux per unit area of a magnetic field at right angles to the magnetic force. Magnetic flux density is expressed in → teslas. Also called → magnetic induction.

magnetic; → flux; → density.

magnetic intensity
  درتنویی ِ مغناتیسی   
dartanuyi-e meqnâtisi

Fr.: intensité magnétique   

Strength of a magnetic field at a point, denoted H. The force which could be exerted on unit north magnetic pole situated at that point. Measured in oersteds. Same as → magnetic field strength.

magnetic; → intensity.

mass density
  چگالی ِ جرمی   
cagâli-ye jermi

Fr.: densité massique   

The mass per unit area of the ring material, integrated through the thickness of the ring. Sometimes called → surface density (Ellis et al., 2007, Planetary Ring Systems, Springer).

mass; → density.

mass-luminosity ratio
  وابر ِ جرم-تابندگی   
vâbar-e jerm-tâbandegi

Fr.: rapport masse-luminosité   

The ratio of the mass of a system, expressed in solar masses, to its visual luminosity, expressed in solar luminosities. The Milky Way Galaxy has a mass-luminosity ratio in its inner regions of about 10, whereas a rich cluster of galaxies such as the Coma Cluster has a mass-luminosity ratio of about 200, indicating the presence of a considerable amount of dark matter.

mass; → luminosity; → ratio.

mass-luminosity relation
  باز‌آنش ِ جرم-تابندگی   
bâzâneš-e jerm-tâbandegi

Fr.: relation masse-luminosité   

A relationship between luminosity and mass for stars that are on the main sequence, specifying how bright a star of a given mass will be. Averaged over the whole main sequence, it has been found that L = M3.5, where both L and M are in solar units. This means, for example, that if the mass is doubled, the luminosity increases more than 10-fold.

mass; → luminosity; → relation.

maximum density of water
  چگالی ِ بیشینه‌ی ِ آب   
cagâli-ye bišine-ye âb

Fr.: densité maximale de l'eau   

The density of pure water occurring at 3.98 °C, which is 1.0000 g cm-3, or 1000 kg m-3. Water when cooled down contracts normally until the temperature is 3.98 °C, after which it expands. Because the maximum density of water occurs at about 4 °C, water becomes increasingly lighter at 3 °C, 2 °C, 1 °C, and 0 °C (→ freezing point). The density of liquid water at 0 °C is greater than the density of frozen water at the same temperature. Thus water is heavier as a liquid than as a solid, and this is why ice floats on water. When a mass of water cools below 4 °C, the density decreases and allows water to rise to the surface, where freezing occurs. The layer of ice formed on the surface does not sink and it acts as a thermal isolator, thus protecting the biological environment beneath it. This property of water liquid is very unusual; molecules pack more closely than in the crystal structure of ice. The reason is that → hydrogen bonds between liquid water are not stable, they are continuously broken and new bonds are created. In the crystal structure of ice molecules have a fixed pattern creating empty space between molecules.

maximum; → density; → water.

mean position
  نهش ِ میانگین   
neheš-e miyângin

Fr.: position moyenne   

Same as → mean place.

mean; → position.

molecular proposition
  گزاره‌ی ِ مولکولی   
gozâre-ye molekuli

Fr.: proposition moléculaire   

In → propositional logic, a → sentence containing at least one → connectives. See also → atomic proposition.

atomic; → proposition.

morphology-density relation
  بازانش ِ ریخت-چگالی   
bâzâneš-e rixt-cagâli

Fr.: relation morphologie-densité   

An observationally determined relationship between the → morphological classification of galaxies and the → environments in which they are located. Specifically, the morphology-density relation indicates that early-type galaxies (→ ETG) are preferentially located in high density environments, whereas late-type galaxies (→ LTG) are preferentially found in low density environments. Hence, spiral galaxies are rare in the high densities of clusters and are common in the lower density group environments. Early-type galaxies, on the other hand, are common in clusters and are rarely found in isolation.

morphology; → density; → relation.


Fr.: nébulosité   

1) A nebulous form, shape, or mass.
2) The state or condition of being nebulous.
3) A fuzzy celestial object, constituted of gas and dust, generally part of a larger → nebula.

nebulous; → -ity.

bâyestegi (#)

Fr.: nécessité   

1) The fact of being necessary or indispensable.
2) Something necessary or indispensable.

necessary; → -ity.

neutral density filter
  پالایه‌ی ِ چگالی ِ نتار   
pâlâye-ye cagâli-ye natâr

Fr.: filtre neutre   

A filter having a flat response over the range of wavelengths of interest. Also called neutral filter or gray filter.

neutral; → density; → filter.

nuclear density
  چگالی ِ هسته‌ای   
cagâli-ye haste-yi (#)

Fr.: densité nucléaire   

The density of an atomic nucleus (about 1014 g/cm3).

nuclear; → density.

nuclear transition
  گذرش ِ هسته‌ای   
gozareš-e haste-yi

Fr.: transition   

A change in the → energy level or state of an atomic → nucleus involving a → quantum of energy.

nuclear; → transition.

number density
  چگالی ِ عددی   
cagâli-ye adadi

Fr.: densité nmérique   

Number of a particular type of object found in each unit volume.

number; → density.

  ۱) رو-به-رو؛ ۲) پادیستین؛ ۳) پادچم   
1) ru-be-ru; 2) pâdistin; 3) pâdcem

Fr.: 1) opposé, d'en face; 2) contraire, opposé; 3) antonyme   

1) Situated, placed, or lying face to face with something else or each other, or in corresponding positions with relation to an intervening line, space, or thing: opposite ends of a room (
2) Contrary or radically different in some respect common to both, as in nature, qualities, direction, result, or significance; opposed (
3) An → antonym.

M.E., from M.Fr., from L. oppositus, p.p. of opponere, → opposition.

1) Ru-be-ru "face to face," → surface.
2) Pâdistin, from pâdist, → opposition, + -in, as in zirin, zebarin, pišin, pasin.
3) Pâdcem, → antonym.

  ۱، ۲) پادیست؛ ۳، ۴) پادیستان   
1, 2) pâdist; 3, 4) pâdistân

Fr.: opposition   

1) The action of opposing, resisting, or combating.
2) A person or group of people opposing, criticizing, or protesting something, someone, or another group (
3) The position of a solar system body having its orbit outside that of the Earth when the Earth is in a line between the Sun and the body. At opposition the body has a solar → elongation of 180°, and is closest to the Earth. It will, in principle, be visible throughout the night. It will rise in the east as the Sun sets in the west and it will set as the Sun rises. This is because, at opposition, the body and the Sun are 12 hours apart. The inner planets can never be in opposition. The opposite of opposition is → conjunction.
4) Two periodic quantities of the same frequency are said to be in opposition when the → phase difference between them is one half of a → period.

Verbal noun of → oppose.

Pâdist "standing against," from pâd- "agaist, contrary to," → anti-, + ist present stem of istâdan "to stand" (Mid.Pers. êstâtan, O.Pers./Av. sta- "to stand; to set;" Av. hištaiti; cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to set, stand").
Pâdistân, from pâdist + -ân suffix of place and time.

optical density
  چگالیِ نوری   
cagâli-ye nuri

Fr.: densité optique   

The transmittance of a point on a photographic negative equal to the log to the base 10 of the reciprocal of the transmittance through the negative at that point.

optical; → density.


Fr.: pallasite   

A class of → iron meteorite containing → olivine crystals.

Named after the German naturalist Peter Pallas (1741-1811), who first studied such a type of meteorites.

peak luminosity
  تابندگی ِ ستیغ   
tâbandegi-ye setiq

Fr.: luminosité du pic   

The → bolometric luminosity of a → supernova corresponding to the highest brightness in its → light curve. The peak luminosity occurs after the → supernova explosion; it is directly linked to the amount of radioactive 56Ni produced in the explosion and can be used to test various explosion models. Following → Arnett's rule, one can derive the 56Ni mass from the peak luminosity of a → Type Ia supernova.

peak; → luminosity.

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