An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 285 Search : if
specific density
  چگالی ِ آبیزه   
cagâli-ye âbizé

Fr.: densité spécifique   

Same as → relative density.

specific; → density.

specific gravity
  گرانی ِ آبیزه   
gerâni-ye âbizé

Fr.: gravité spécifique   

The ratio of the density of a substance at the temperature under consideration to the density of water at the temperature of its maximum density (4 °C).

specific; → gravity.

specific heat
  گرمای ِ آبیزه   
garmâ-ye âbizé

Fr.: chaleur spécifique   

1) The quantity of heat required to raise the temperature of 1 gm of a substance through 1 °C. More generally, the → heat capacity of a unit mass of a substance. For a homogeneous body it is expressed as: C = dQ/M dT, where dQ is the quantity of heat transferred to a mass of M to raise the temperature by dT. It is often convenient to use the gram-mole as a unit of mass, → molar heat capacity.
2) For a gas there are two principal specific heats depending on the way in which the temperature is increased: i) that measured at constant pressure, CP, and ii) that measured at constant volume, CV. The specific heat CP is greater than CV, because a gas heated at constant pressure expands, and heat energy must be supplied equivalent to the work done in the expansion. The ratio γ = CP/CV is called the → adiabatic index. It varies from 1.66 for mono-atomic gases to a little over 1 for gases with complex molecules.

specific; → heat.

specific humidity
  نم ِ آبیزه   
nam-e âbizé

Fr.: humidité spécifique   

The dimensionless ratio of the mass of water vapor to the total mass in a particular volume. → humidity

specific; → humidity.

specific intensity
  درتنویی ِ آبیزه   
dartanuyi-e âbizé

Fr.: intensité spécifique   

A measure of the amount of radiation received per unit solid angle per unit time per unit area normally from an element of surface.

specific; → intensity.

specific star formation rate (sSFR)
  نرخ ِ آبیزه‌ی ِ دیسش ِ ستارگان   
nerx-e âbize-ye diseš-e setâregân

Fr.: taux de formation d'étoiles spécifique   

Star formation rate per unit → mass. More specifically, the → star formation rate in a galaxy divided by the → stellar mass of the galaxy. Observations of galaxies over a wide range of → redshifts suggest that the slope of the SFR-M* relation is about unity, which implies that their sSFR does not depend strongly on stellar mass. Specific star formation rates increase out to z ~ 2 and are constant, or perhaps slowly increasing, from z = 2 out to z = 6, though with a large scatter, sSFR ~ 2-10 Gyr-1 (Lehnert et al., 2015, A&A 577, A112, and references therein).

specific; → star; → formation; → rate.

specific volume
  گنج ِ آبیزه   
gonj-e âbizé

Fr.: volume spécifique   

The volume occupied by unit mass of a substance. Specific volume is the reciprocal of density.

specific; → volume.

specification
  آبیزش   
âbizeš

Fr.: précision, spécification   

1) The act of specifying.
2) A particular item, aspect, calculation, etc., in such a description.
3) Something specified, as in a bill of particulars; a specified particular, item, or article (Dictionary.com).

Verbal noun of → specify.

specifity
  آبیزگی   
âbizegi

Fr.: spécifité   

The state or character of being → specific.

specific; → -ity.

specify
  ۱) پرسونیدن؛ ۲) آبیزیدن   
1) parsunidan; 2) âbizidan

Fr.: préciser, spécifier   

1) To mention or name specifically or definitely; state in detail.
2) To give a specific character to; to set forth as a specification (Dictionary.com).

specific; → -fy.

speckle lifetime
  عمر ِ پَکال   
omr-e pakâl

Fr.: durée de vie de tavelures   

The time scale on which a stellar image changes significantly due to → atmospheric turbulence. It is proportional to the ratio r0/Δv, where r0 is the → Fried parameter and Δv the standard deviation of the distribution of wind velocities weighted by the turbulence structure coefficient. Typical lifetimes in the visible range from about 3 to 30 milliseconds.

speckle; → life; → time.

Omr "life-time;" from Ar. 'umr; pakâl, → speckle.

spectral classification
  رده‌بندی ِ بینابی   
radebandi-ye binâbi (#)

Fr.: classification spectrale   

A system that assigns a → spectral type to a star according to characteristics of its spectrum. The earliest attempt to divide stars on the basis of their spectra was the → Secchi classification in the 1860s. This scheme paved the way for the → Harvard classification that led to the current → Morgan-Keenan classification of spectral types. In the Harvard system stars were originally thought to follow an evolutionary sequence from the "early" O and B types to the "late" K and M types. Although this is now known to be wrong, the terms → early-type star and → late-type star are still in use. In the Morgan-Keenan system stars are classified as type O, B, A, F, G, K, or M in order of decreasing → effective temperature, and each type further subdivided into subclasses from 0 (hottest, except for → O-type stars) to 9 (coolest). They are also accompanied by a → luminosity class. In the late 1990s, spectral types L and T were added to the sequence to accommodate the coolest stars and → brown dwarfs (with class Y reserved for the coolest brown dwarfs of all, as yet unobserved).

spectral; → classification.

star drift
  دلک ِ ستارگان   
delek-e setâregân

Fr.: dérive stellaire   

The relative motion of two groups of stars in the Galaxy moving in opposite directions.

star; → drift.

stratification
  چینه‌بندی   
cine-bandi

Fr.: stratification   

A layered structure of sedimentary rocks in which the individual layers can be traced a considerable distance. The layers can be caused by many differences which include materials of different composition, color, grain size or orientation.

Strati-, from → stratum + -fication from L. -ficare "to do, make."

Ciné, → stratum + bandi, from bastan "to bind, shut; to contract, get, acquire; to coagulate," (Mid.Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie," Skt. bandh- "to bind, tie, fasten," PIE *bhendh- "to bind," cf. Ger. binden, E. bind, → band).

test of significance
  آزمون ِ نشاناری   
âzmun-e nešânâri

Fr.: test de significativité   

Same as → significance testing and → rule of decision.

test; → significance.

thermal diffusion
  پخش ِ گرمایی   
paxš-e garmâyi

Fr.: diffusion thermique   

A physical process resulting from → temperature gradients in stellar interiors, whereby more highly charged and more massive chemical species are concentrated toward the hottest region of the star, its center. Therefore, thermal diffusion and → gravitational settling tend to make heavier species sink relative to the light ones.

thermal; → diffusion.

Tholen classification
  رده‌بندی ِ تولن   
radebandi-ye Tholen

Fr.: classification de Tholen   

A fundamental system for the classification of → asteroids based on → albedo and → spectral characteristics. The Tholen scheme includes 14 types with the majority of asteroids falling into one of three broad categories, and several smaller types. → C-type asteroid, → M-type asteroid, → S-type asteroid.

David J. Tholen (1984) Ph.D. thesis, University of Arizona; → classification.

Trifid Nebula
  میغ ِ سه‌پاره   
miq-e sepâré

Fr.: nébuleuse Trifide   

A large luminous → H II region in the constellation → Sagittarius. Also known as M20, NGC 6514. Conspicuous → dust lanes radiating from the center appear to divide the nebula in three → lobes. It is a combined → emission nebula and → reflection nebula, extending for nearly 30' on the sky. Its estimated distance is 4100±200 → light-years (Kuhn et al., 2018, arXiv:1807.02115).

Trifid, from L. trifidus "split in three," from → tri- + fidus "divided," from findere "to split;" → nebula.

Miq, → nebula; sepâré "split in three," from , → three, + pâré "piece, part, portion, fragment;" Mid.Pers. pârag "piece, part, portion; gift, offering, bribe;" Av. pāra- "debt," from par- "to remunerate, equalize; to condemn;" PIE *per- "to sell, hand over, distribute; to assigne;" cf. L. pars "part, piece, side, share," portio "share, portion;" Gk. peprotai "it has been granted;" Skt. purti- "reward;" Hitt. pars-, parsiya- "to break, crumble."

ultra-diffuse galaxy (UDG)
  کهکشان ِ اولتر-پخشیده   
kahkešân-e ultar-paxšide

Fr.: galaxie ultra-diffuse   

A galaxy of low stellar density, defined to have low central → surface brightness (> 24 mag arcsec-2) and an → effective radius (Re) of over 1.5 kpc. The question of whether UDGs represent a separate class of galaxies is still under debate. Currently, known UDGs that have been discovered in clusters, in groups, and in the field can have Re as large as 5 kpc which is comparable to that of giant Milky Way like galaxies. This fact has been used to suggest that UDGs are "failed" giants. As Re captures (at most) the central parts of giant galaxies, whether this radius can be used to fairly compare the sizes of UDGs to the more massive galaxies is questionable (see, e.g., Chamba et al., 2020, A&A 633, L3).

Term proposed by van Dokkum et al. (2015), arXiv: 1410.8141v2; → ultra-; → diffuse; → galaxy.

unclassified B[e] star (unclB[e])
  ستاره‌یِ B[e]ی ِ بی‌رده   
setâre-ye B[e]-ye bi radé

Fr.: étoile B[e] non-classée   

A temporary designation for a → B[e] star that cannot be placed in any of the four known classes.

classification; → B[e] star.

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