An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < abs act att clu com dif fac Gal gal imp int pac rad ref sub wei > >>

Number of Results: 304 Search : act
subcritical reactor
  واژیرگر ِ زیر-پرژنی   
vâžirgar-e zir-paržani

Fr.: réacteur sous-critique   

A → nuclear reactor in which the rate of production of → fission neutrons is lower than the rate of production in the previous generation, and therefore the number of fissions decreases over time.

subcritical; → reactor.

  زیرکرشیدن، کاهیدن   
zirkaršidan, kâhidan

Fr.: soustraire   

To take one number away from another; deduct. To perform the arithmetic operation of → subtraction.

From L. subtractus, p.p. of subtrahere "to draw from beneath, take away, draw off," from → sub- "from under" + trahere "to pull, draw."

Zirkaršidan, literally "to draw beneath," from zir-, → sub-, + karšidan "to draw, pul, drag," variant of kašidan "to draw, protract, trail, drag, carry;" Av. karš- "to draw; to plow," karša- "furrow;" Proto-Iranian *kerš-/*xrah- "to draw, plow;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base kwels- "to plow."
Kâhidan, → decrease.


Fr.: soustraction   

The operation of finding the difference between two numbers or quantities.

Verbal noun of → subtract.


Fr.: soustractif   

1) Constituting or involving → subtraction.
2) Math.: Indicating or requiring subtraction; having a → minus sign.

subtract; → -ive.

subtractive color
  رنگ ِ زیرکرششی   
rang-e zirkaršeši

Fr.: synthèse soustractive   

Color produced by mixing pigments rather than light. Mixing all of the subtractive colors together results in the color black. See also → additive color.

subtractive; → color.


Fr.: supergalactique   

Of or pertaining to a system composed of nearby groups and clusters of galaxies in the → local Universe. Se also → galaxy cluster.

super-; → galactic.

supergalactic coordinate system
  راژمان ِ هماراهای ابرکهکشانی   
râžmân-e hamârâhâ-ye abarkahkašâni

Fr.: système des coordonnées supergalactiques   

A spherical → coordinate system in which the → equator is the → supergalactic plane. Supergalactic longitude, SGL, is measured → counterclockwise from direction l = 137.37 deg, b = 0 deg (between 0 and 360 deg). The zero point for supergalactic longitude is defined by the intersection of this plane with the → Galactic plane. In the → equatorial coordinate system (J2000) this is approximately 2.82 h, +59.5 deg. Supergalactic latitude, SGB, is measured from the supergalactic plane, positive northward and negative southward. The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates l = 47.37 deg, b = +6.32 degrees, corresponding to the equatorial coordinate system (J2000) 18.9 h, +15.7 deg.

supergalactic; → coordinate; → system.

supergalactic latitude
  ورونای ِ ابرکهکشانی   
varunâ-ye abarkahkašâni

Fr.: latitude supergalactique   

supergalactic coordinate system.

supergalactic; → latitude.

supergalactic longitude
  درژنای ِ ابرکهکشانی   
derežnâ-ye abarkahkašâni

Fr.: longitude supergalactique   

supergalactic coordinate system.

supergalactic; → longitude.

supergalactic plane
  هامن ِ ابرکهکشانی   
hâmon-e abarkahkašâni

Fr.: plan supergalactique   

The symmetry plane of the → Local Supercluster, where density of galaxies in our environment is the largest. The plane passes through the → Virgo cluster of galaxies, about which many of the brightest galaxies in the sky are concentrated. The supergalactic plane was recognized by Gérard de Vaucouleurs (1918-1995) in 1953 from the  → Shapley-Ames catalogue.

supergalactic; → plane.


Fr.: syntactique   

The study of the grammatical relationships among signs, independently of their meaning (→ semantics. See also → syntax.

syntax; → -ics.

tensor contraction
  ترنگش ِ تانسور   
terengeš-e tânsor

Fr.: contraction de tenseur   

An operation of tensor algebra that is obtained by setting unlike indices equal and summing according to a summation convention.

contraction; → tensor.

thermonuclear reaction
  واژیرش ِ گرماهسته‌ای   
vâžireš-e garmâhaste-yi (#)

Fr.: réaction thermonucléaire   

A nuclear reaction in which two or more atomic nuclei fuse into a single heavier nucleus by a collision of the interacting particles at extremely high temperatures. Chains of thermonuclear reactions, such as the → proton-proton chain and the → CNO cycle, account for the energy radiated from the Sun and more massive stars.

thermo- + → nuclear; → reaction.

third contact
  پرماس ِ سوم   
parmâs-e sevom

Fr.: troisième contact   

The end of the total phase of a solar eclipse marked by the trailing edge of the Moon first revealing the Sun.

third; → contact.

threshold of reaction
  آستانه‌ی ِ واژیرش   
âstâne-ye vâžireš

Fr.: seuil de réaction   

The minimum energy, for an incident particle or photon, below which a particular reaction does not occur.

threshold; → reaction.

ultracompact H II region
  ناحیه‌ی ِ H IIی ِ اولتر-همپک   
nâhiye-ye H II-ye ultar hampak

Fr.: région H II ultracompacte   

A very young → H II region fully embedded in its natal molecular cloud. Ultracompact H II regions are distinguished from classical H II regions by their small sizes (diameter ≥ 0.1 pc), high densities (Ne ≥ 105 cm-3), and high emission measures (EM ≥ 107 pc cm-6). Their typical ionized gas content is about 10-2  → solar masses, in contrast to classical H II regions with a mass of about 105 solar masses. Due to very important extinction, ultracompact H II regions are not accessible to visible wavelengths.

ultra-; → compact; → H II region.

vena contracta
  شاره‌گذر ِ ترنگیده   
šâre-gozar-e terengidé

Fr.: veine contractée   

The location in a → fluid stream where the → cross section of the → stream is at a minimum, and fluid velocity is the highest, such as in the case of a → jet issuing out of a → nozzle.

L. vena "channel;" contracta, "contracted," → contract.

Šâre-gozar "fluid passage," → fluid; → passage, terengidé, → contracted.

vulgar fraction
  برخه‌ی ِ همدار   
barxe-ye hamdâr

Fr.: fraction d'entiers   

Same as → common fraction.

M.E., from L. vulgaris, from vulgus "the common people," + -aris, → -ar.

common; → fraction.

warm-hot intergalactic medium
  مدیم ِ اندر-کهکشانی ِ گرم-داغ   
madim-e andar-kahkašâni garm-dâq

Fr.: milieu intergalactique chaud   

The space containing a cluster of galaxies filled with a tenuous gas of temperature 105 to 107 K and density 10-6 to 10-4 cm-3. WHIM has been continuously shock-heated during the process of structure formation. It is so highly ionized that it can only absorb or emit far-ultraviolet and soft X-ray photons, primarily at spectral lines of highly ionized C, O, Ne, and Fe. WHIM is thought to be the main reservoir of missing baryons.

warm; → hot; → intergalactic medium.

weak interaction
  اندرژیرش ِ نزار، ~ کمزور   
andaržireš-e nezâr, ~ kamzvr

Fr.: interaction faible   

One of the fundamental forces of nature that accounts for some particle interaction, such as → beta decay (→ radioactivity), the decay of free → neutrons, → neutrino interactions, and so forth. It is short-ranged, dominating at distances of 10-16 cm and occurs at a rate slower than that of the → strong interaction by a factor of about 10-13, hence its name. Although the weak interaction also includes interactions in which no neutrinos are emitted, neutrino emission accompanies all weak interactions of interest to astrophysics. Weak interaction plays an important role in the evolution of the stars from birth to death. For example, the → proton-proton reaction is a weak interaction. Also called → weak force or → weak nuclear force.

weak; → interaction.

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