An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 14 Search : background
  پس-زمینه، زمینه   
paszaminé, zaminé (#)

Fr.: fond   

General: That part of a view or scene that serves as a setting for the main objects, persons, etc.
Astro.: The part of an observed field which is not physically related to the objects of interest and lies behind them.

Background, from → back + ground, from M.E., from O.E. grund; akin to O.H.G. grunt "ground."

Paszaminé, from pas-, → back, + zaminé "ground," from zamin "ground," → earth.


background noise
  نوفه‌ی ِ پس-زمینه، ~ زمینه   
nufe-ye paszaminé, ~ zaminé

Fr.: bruit du fond   

An unwanted signal in a system which is producing or recording a signal. For instance, a randomly fluctuating signal superimposed on the signal from a cosmic radio source.

background; → noise.

background radiation
  تابش ِ پس-زمینه، ~ زمینه   
tâbeš-e paszaminé, ~ zaminé

Fr.: rayonnement du fond   

The isotropic residual microwave radiation in space left from the primordial → Big Bang. Same as → cosmic microwave background (CMB) radiation.

background; → radiation.

Cosmic Background Explorer (COBE)
  پویشگر ِ زمینه‌ی ِ کیهانی   
puyešgar-e zamin-ye keyhâni

Fr.: Satellite COBE   

NASA's satellite, designed to measure the diffuse infrared and → cosmic microwave background radiation from the early → Universe. It was launched on November 18, 1989 and carried three instruments: DIRBE (the Diffuse InfraRed Experiment), DMR (Differential Microwave Radiometers), and FIRAS (Far-InfraRed Absolute Spectrophotometer). The COBE observations showed that the cosmic microwave background spectrum matches that of a → blackbody of temperature 2.725 ± 0.002 K. COBE also found anisotropies in the cosmic microwave background at a level of a part in 100,000 (→ cosmic microwave background anisotropy). These tiny variations in the intensity of the CMB over the sky show how matter and energy was distributed when the Universe was still very young. Later, through a process still poorly understood, the early structures developed into galaxies, galaxy clusters, and the large scale structure that we see in the Universe today. Two of COBE's principal investigators, George Smoot and John Mather, received the Nobel Prize in Physics in 2006 for their work on the project.

cosmic; → background; → explorer.

cosmic background radiation
  تابش ِ پس‌زمینه‌ی ِ کیهانی   
tâbeš-e paszaminé-ye keyhâni

Fr.: rayonnement du fond cosmique   

cosmic microwave background radiation (CMBR).

cosmic; → background; → radiation.

cosmic infrared background (CIB)
  پس‌زمینه‌ی ِ فروسرخ ِ کیهانی   
paszamine-ye forusorx-e keyhâni

Fr.: le cosmique infrarouge   

A diffuse radiation which consists of the cumulative infrared emission from all galaxies throughout cosmic history. It is about 50 times weaker than the → cosmic microwave background radiation (CMBR). Since the CIB is produced by the dust within such galaxies, it carries a wealth of information about the processes of star formation therein.

cosmic; → infrared; → background.

cosmic microwave background anisotropy
  ناهمسانگردیِ تابشِ ریزموجِ پس‌زمینه‌یِ کیهانی   
nâhamsângardi-ye tâbeš-e rizmowj-e paszaminé-ye keyhâni

Fr.: anisotropies du rayonnement du fond cosmique microonde   

Tiny fluctuations in the intensity of the → cosmic microwave background radiation (CMBR) as a function of angular position over the sky, first discovered in the → Cosmic Background Explorer (COBE) observations. At a level of 1 part in 100,000, these temperature variations trace the distribution of matter and energy when the Universe was very young, about 380,000 years old. Since the CMB spectrum is described to a high precision by a → blackbody law with temperature T0, it is usual to express the anisotropies in terms of temperature fluctuations ΔT/T0 and expand them on the sky in → spherical harmonic series ΔT/T0 (θ,φ) = Σ almYlm(θ,φ), where θ and φ are the → spherical polar coordinates, Ylm is the spherical harmonic functions with → multipole index l, and the sum runs over l = 1, 2, ..., ∞, m = -l, ..., l, giving 2l + 1 values of m for each l, and alm is the multipole moment of the decomposition. The power spectrum of the anisotropies is defined as Cl≡ mean | alm |2 = 1/(2l + 1) Σ mean | alm |2. See also → CMB angular power spectrum.

cosmic; → microwave; → background; → anisotropy.

cosmic microwave background polarization
  قطبش ِ زمینه‌ی ِ ریزموج ِ کیهانی   
qotbeš-e zamine-ye rizmowj-e keyhâni

Fr.: polarisation du rayonnement du fond cosmique microonde   

The polarization of the → cosmic microwave background radiation due to → Thomson scattering by → free electrons during the → recombination era. The polarization can greatly enhance the precision with which the parameters associated with → acoustic oscillations are derived; because it carries directional information on the sky. When an → electromagnetic wave is incident on a free electron, the scattered wave is polarized perpendicular to the incidence direction. If the incident radiation were → isotropic or had only a → dipole variation, the scattered radiation would have no net polarization. However, if the incident radiation from perpendicular directions (separated by 90°) had different intensities, a net → linear polarization would result. Such → anisotropy is called → quadrupole because the poles of anisotropy are 360°/4 = 90° apart.

cosmic; → microwave; → background; → polarization.

cosmic microwave background radiation (CMBR)
  تابشِ ریزموجِ پس‌زمینه‌یِ کیهانی   
tâbeš-e rizmowj-e paszaminé-ye keyhâni

Fr.: rayonnement du fond cosmique microonde   

The diffuse → electromagnetic radiation in the → microwave band, coming from all directions in the sky, which consists of relic photons left over from the very hot, early phase of the → Big Bang. More specifically, the CMBR belong to the → recombination era, when the → Universe was about 380,000 years old and had a temperature of about 3,000 K, or a → redshift of about 1,100. The photons that last scattered at this epoch have now cooled down to a temperature of 2.73 K. They have a pure → blackbody spectrum as they were at → thermal equilibrium before → decoupling. The CMB was discovered serendipitously in 1965 by Penzias and Wilson (ApJ L 142, 419) and was immediately interpreted as a relic radiation of the Big Bang by Dicke et al. (1965, ApJL 142, 383). Such a radiation had been predicted before by Gamow (1948, Nature 162, 680) and by Alpher and Herman (1948, Nature 162, 774). This discovery was a major argument in favor of the Big Bang theory. In 1992, the satellite → Cosmic Background Explorer (COBE) discovered the first anisotropies in the temperature of the CMB with an amplitude of about 30 µK. See also: → cosmic microwave background anisotropy, → dipole anisotropy, → CMB lensing, → CMB angular power spectrum, → acoustic peak, → baryon acoustic oscillation, → WMAP.

cosmic; → microwave; → background; → radiation.

cosmic neutrino background (CNB)
  نوترینو‌ی ِ پس‌زمینه‌ی ِ کیهانی   
notrino-ye paszamine-ye keyhâni

Fr.: fond cosmologique de neutrinos   

The theoretical → low-energy neutrinos that decoupled from the rest of matter about two seconds after the → Big Bang when the temperature dropped to approximately 2.5 MeV (redshift of z ~ 6 ×109). The CNB is similar to the → cosmic microwave background (CMB), but older. It is estimated that today the CNB has a temperature of Tν = (4/11)1/3Tγ, ~ 1.95 K (or 1.67 × 10-4 eV), where Tγ is the CMB temperature of 2.728 K. Also called the relic neutrinos.

cosmic; → neutrino; → background.

extragalactic background light (EBL)
  نور ِ پس-زمینه‌ی ِ استر-کهکشانی   
nur-e paszimine-ye ostarkahkeši

Fr.: lumière du fond extragalactique   

The integrated intensity of all of the light emitted throughout the history of the Universe across the whole of the → electromagnetic spectrum, including those which are not individually detected. The EBL spectrum includes cosmological backgrounds associated with either primordial phenomena, such as the → cosmic microwave background radiation (CMBR), or photons emitted by stars, galaxies and → active galactic nuclei (AGN) due to → nucleosynthesis or other → radiative processes, including → dust scattering, → absorption and reradiation. The EBL may also contain signals that are diffuse and extended, including high-energy photons associated with dark matter particle decays or annihilation.

extragalactic; → background; → light.

microwave background radiation
  تابش ِ پس‌زمینه‌ی ِ ریزموج   
tâbeš-e paszamine-ye rizmowj

Fr.: rayonnement micro-onde du fond cosmique   

Thermal radiation with a temperature of 2.73 K that is apparently uniformly distributed in the Universe. It is believed to be a redshifted remnant of the hot radiation that was in thermal equilibrium with matter during the first hundred thousand years after the Big Bang. Same as → cosmic microwave background (CMB) radiation.

microwave; → background; → radiation.

sky background
  پس‌زمینه‌ی ِ آسمان   
paszamine-ye âsmân

Fr.: fond du ciel   

The emission of a part of the night sky that does not contain any detectable objects. Sky background results from the combined radiation from faint, unresolved stars and other emitting astronomical objects. The mean brightness of night sky background measured at the → Cerro Tololo Inter-American Observatory (CTIO) for the period 1992 to 2006 are: U = 22.12, B = 22.82, V = 21.79, R = 21.19, and I = 19.85 mag arcsec-2 ( → rms ~ 0.2 mag arcsec-2). See also → sky brightness.

sky; → background..

X-ray background
  پس-زمینه‌ی ِ ایکس، زمینه‌ی ِ ~   
pas-zamine-ye iks, zamine-ye ~ (#)

Fr.: fond de rayons X   

A diffuse background radiation in X-ray wavelengths which has several origins. At very low energies it is due to hot gas in the → Local Bubble. In the → soft X-ray energy band it comes from active galaxies at moderate redshifts. In → hard X-ray range the background is thought to be due to integrated emission from many → quasars at various redshifts.

X-ray; → background.