An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1234
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.

cosmic radio noise
  نوفه‌یِ رادیوییِ کیهانی   
nufe-ye râdioyi-ye keyhâni

Fr.: bruit radio cosmique   

Radio waves emanating from extraterrestrial sources.

cosmic; → radio; → noise.

cosmic rays
  پرتوهای ِ کیهانی   
partowhâ-ye keyhâni (#)

Fr.: rayons cosmiques   

Extremely energetic atomic nuclei, mostly protons, which travel through the Universe at practically the speed of light and strike the Earth from all direction. Their energy ranges from 109 to 1020 electron-volts.

cosmic; → ray.

cosmic scale factor
  کروند ِ مرپل ِ کیهانی   
karvand-e marpal-e keyhâni

Fr.: facteur d'échelle cosmologique   

A quantity, denoted a(t), which describes how the distances between any two galaxies change with time. The physical distance d(t) between two points in the Universe can be expressed as d(t) = R(t).x, where R(t) is the → scale factor and x the → comoving distance between the points. The cosmic scale factor is related to the → redshift, z, by: 1 + z = R(t0)/R(t1), where t0 is the present time and t1 is the time at emission of the radiation. The quantity (1 + z) gives the factor by which the → Universe has expanded in size between t1 and t0. It is also related to the → Hubble parameter by H(t) = R.(t)/R(t), where R.(t) is the time → derivative of the scale factor. In an → expanding Universe the scale factor increases with time. See also the → Friedmann equation.

cosmic; → scale; → factor.

cosmic shear
  کرن ِ کیهانی   
karn-e keyhâni

Fr.: cisaillement cosmique, ~ gravitationnel   

The distortion of images of distant galaxies due to → weak gravitational lensing by → large-scale structures in the → Universe (see, e.g., Kilbinger, M., 2015, arXiv:1411.0115).

cosmic; → shear.

cosmic star formation peak
  چکاد ِ کیهانی ِ دیسش ِ ستارگان   
cakâd-e keyhâni-ye diseš-e setâregân

Fr.: pic de formation stellaire cosmique   

A crucial period in the history of the → Universe, when the bulk of stars in massive galaxies were likely formed. Observations of young stars in distant galaxies at different times in the past have indicated that the → star formation rate peaked at the → redshift of z ~ 2, some 10 billion years ago, before declining by a factor of around ten to its present value (P. Madau & Dickinson, 2014, arXiv:1403.0007).

cosmic; → star; → formation; → peak.

cosmic string
  ریسمان ِ کیهانی   
rismân-e keyhâni

Fr.: corde cosmique   

A hypothetical → cosmic defect predicted to be infinitesimally small in cross section but enormously long and massive. Cosmic strings should not be confounded with → subatomic strings predicted by → string theory.

cosmic; → string.

cosmic texture
  بافت ِ کیهانی   
bâft-e keyhâni

Fr.: texture cosmique   

A type of → cosmic defect in the fabric of space-time predicted in some models of the early Universe.

cosmic; → texture

cosmic web
  وپ ِ کیهانی   
vap-e keyhâni

Fr.: toile cosmique   

The entire, large-scale structure of the → Universe in which → galaxy clusters are connected by → cosmic filaments (made up of → dark matter and → baryons) in a spongelike geometry, while the low-density → voids are connected to each other by low-density tunnels. The term cosmic web was coined in 1996 by J. Richard Bond et al. (Nature, 380, 603).

cosmic; → web.

cosmic-ray burst
  بلک ِ پرتوهای ِ کیهانی   
belk-e partowhâ-ye keyhâni

Fr.: sursaut de rayons cosmiques   

An intense beam of cosmic rays coming from any direction on the sky, which originates outside the solar system.

cosmic; → ray; → burst.

cosmic-ray event
  رویداد ِ پرتوهای ِ کیهانی   
ruydâd-e partowhâ-ye keyhâni

Fr.: événement des rayons cosmiques, un cosmique   

Spurious signals in CCD frames caused by ionizing radiation which appear as a set of pixels with intense values sparsely scattered over the CCD frame. High energy particles generate muons, which deposit around 80 electrons per micron in silicon. With a collection depth of 10-20 microns, a cosmic-ray event is seen on a CCD frame as having a signal of up to a few thousand electrons, usually concentrated in one or two pixels. Although attributed to cosmic-ray hits, they may also be due to background terrestrial radiation.

cosmic rays; → event.

cosmic-ray ionization
  یونش ِ پرتوهای ِ کیهانی   
yoneš-e partowhâ-ye keyhâni

Fr.: ionisation par rayons cosmiques   

The ionization of → interstellar medium (ISM) gas by → cosmic rays. Cosmic rays are a primary source of ionization, competing with stellar → ultraviolet photons and → X-rays produced by embedded → young stellar objects. Cosmic rays play a key role in the chemistry and dynamics of the interstellar medium. The ionization fraction in turn drives the chemistry of → molecular clouds and controls the coupling of the gas with the Galactic → magnetic field. Moreover, cosmic rays represent an important source of → heating for → molecular clouds because the energy of primary and secondary electrons produced by the ionization process is in large part converted into heat by → inelastic collisions with ISM atoms and → molecules (see, e.g., Padovanit et al., 2009, arXiv:0904.4149).

cosmic; → ray; → ionization.

cosmic-ray shower
  تندبار ِ پرتوهای ِ کیهانی، رگبار ِ ~   
tondbâr-e partowhâ-ye keyhâni, ragbâr-e ~

Fr.: gerbe cosmique   

An extensive (many kilometres wide) → cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary → cosmic ray collides with atmospheric nuclei creating many → secondary cosmic rays.

cosmic; → ray; → shower.

keyhân- (#)

Fr.: cosmo-   

Combining form of → cosmos.


cosmogenic neutrino
  نوترینوی‌ ِ پرتو ِ کیهانی، ~ کیهانزاد   
notrino-ye partow-e keyhâni, ~ keyhânzâd

Fr.: neutrino cosmogénique   

A type of neutrino generated by → UHECRs during their journey from distant sources to the Earth. Also called → ultra high energy neutrino.

Constructed from cosmo-, from → cosmic rays + -genic, → cryogenic.


Fr.: cosmogonie   

A philosophical, religious, or mythical story of the creation or origin of the → Universe, usually referring to the → solar system.

From → cosmo- + -gony, from L. -gonia, from Gk. -goneia, from gonos, offspring; cf. Av. zan- "to bear, give birth to a child, be born," infinitive zizâite, zâta- "born," Pers. zâdan "give birth, be born", Skt. janati "begets, bears," Gk. gignesthai "to become, happen" L. gignere "to beget," gnasci "to be born," PIE base *gen- "to give birth, beget").

Keyhânzâyeš, from keyhân, → cosmo-, + zâyeš verbal noun from zâdan "be born; give birth," as above.


Fr.: cosmographie   

1) A literal description of the world or of the Universe.
2) Cosmology: Mapping the time evolution of the cosmic expansion; measurement of the cosmic distances.

cosmo- + → -graphy.

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