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 opt qua ref str vul > >>

Number of Results: 307 Search : act
strong interaction
  اندرژیرش ِ سترگ   
andaržireš-e sotorg

Fr.: interaction forte   

The interaction between quarks that is transmitted by gluons. The characteristic range of the strong interaction is 10-13 cm, and the time scale over which it operates is on the order of 10-23 second. Also called → strong force.

strong; → interaction.

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.


Fr.: ultracompact   

Extremely compact with respect to a comparison value. → ultracompact H II region, → ultracompact dwarf galaxy.

ultra-; → compact.

ultracompact dwarf galaxy (UCD)
  کهکشان ِ کوتوله‌ی ِ اولتر-همپک   
kahkešân-e kutule-ye ultar-hampak

Fr.: galaxie naine ultracompacte   

A type of very bright compact → stellar system (-14 ≤ MV≥ -12) that is intermediate between → globular clusters (GCs) and → compact elliptical galaxies (cEs). With masses of M > 2 × 106 Msun and radii > 10 → parsecs (pc), UCDs are among the densest stellar systems in the Universe. Nevertheless, the nature and origin of these objects is still widely debated. Early interpretations suggested that UCDs could be the most massive GCs or possibly the → tidally stripped remnants of → dwarf galaxies. However, there is evidence that both formation mechanisms could contribute to the UCD population. → Supermassive black holes (SMBHs) have been confirmed in most UCDs with masses M > 107 Msun. The most massive UCD discovered to date, M59-UCD3 (M* ~ 2 × 108 Msun, radius ~ 25 pc), hosts a SMBH (Ahn et al., 2018, arxiv/1804.02399, and references therein).

ultracompact; → dwarf; → galaxy.

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.

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