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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Number of Results: 9 Search : expansion
accelerating expansion of the Universe
  گسترش ِ شتابنده‌ی ِ گیتی   
gostareš-e šetâbande-ye giti

Fr.: expansion accélérée de l'Univers   

accelerating Universe.

accelerating; → expansion; → Universe.

binomial expansion
  گسترش ِ دونامین   
gostareš-e donâmin

Fr.: expansion binomiale   

A rule for the expansion of an expression of the form (x + y)n. The variables x and y can be any → real numbers and n is an → integer. The general formula is known as the → binomial theorem.

binomial; → expansion.

cosmic expansion
  گسترش ِ کیهانی   
gostareš-e keyhâni

Fr.: expansion cosmique   

Same as the → expansion of the Universe.

cosmic; → expansion.

expansion
  گسترش   
gostareš (#)

Fr.: expansion   

1) General: The act or process of expanding; the state or quality of being expanded.
2) Math.: The process of expressing a quantity, or a quantity expressed, as a sum of a series of terms. For example the expression (2x - 1)(x + 3) can be expanded to: 2x2 + 5x - 3. See also → binomial expansion.

Noun from → expand.

expansion of the Universe
  گسترش ِ گیتی   
gostarš-e giti (#)

Fr.: expansion de l'Univers   

The receding of galaxies from one another at a speed proportional to their separation, as inferred by Edwin Hubble from the observed Doppler shift of distant galaxies. → Hubble constant describes the local rate of the expansion.

expansion; → universe.

expansion parameter
  پارامون ِ گسترش   
pârâmun-e gostareš

Fr.: paramètre d'expansion   

A → scale factor that relates the size of the Universe R = R(t) at time t to the size of the Universe R0 = R(t0) at time t0 by R = aR0. The expansion parameter represents the history of expansion of the Universe.

expansion; → parameter.

free expansion phase
  فاز ِ گسترش ِ آزاد   
fâz-e gostareš-e âzâd

Fr.: phase d'expansion libre   

The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy  ESN is transformed into → kinetic energy of the ejected gas, the ejection velocity ve can be estimated from ESN by using ESN = (1/2) Meve2, which leads to ve = (2ESN / Me)(1/2), where Me is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, RSW, is defined by Me = (4π/3) RSW3ρ0, that is RSW = (3Me / 4πρ0)(1/3), where ρ0 is the initial density of the ISM. This radius is reached at the sweep-up time tSW = RSW/ve. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.

free; → expansion; → phase.

post-Newtonian expansion
  گسترش ِ پسا-نیوتنی   
gostareš-e pasâ-Newtoni

Fr.: développement post-newtinien   

post-Newtonian formalism.

post-; → Newtonian; → expansion.

thermal expansion
  گسترش ِ گرمایی   
gostareš-e garmâyi

Fr.: expansion thermique   

The change in dimensions of a material resulting from a change in temperature.

thermal; → expansion.