An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1259
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 which travel through the Universe at practically the speed of light and strike the Earth from all direction. Almost 90% of all the incoming → primary cosmic rays are → protons, about 9% are helium nuclei (→ alpha particles) and about 1% are → electrons (beta minus particles). Some cosmic rays come from the Sun (mainly due to → solar flares), most come from galactic → supernovae, and a few with the highest energy are suspected to originate from outside the → Milky Way. As for their flux, about 1 charged particle per second per cm2 impacts the Earth. The typical kinetic energy of these particles is about 10 MeV/nucleon to several GeV/nucleon, although there are some at higher energies. In fact, the cosmic ray with the highest energy has been measured above × 1020 eV. These → ultra-high energy cosmic rays are suspected to be extragalactic, as there is no plausible mechanism of acceleration to these energies by a supernova, for example. Again, compare these energies to those of solar neutrinos that have only 0.26 MeV. Cosmic rays may be divided into → primary cosmic rays and → secondary cosmic rays. Their energy ranges from 109 to 1020  → electron-volts.

cosmic; → ray; The term "ray" is a misnomer, as cosmic particles arrive individually, not in the form of a ray or beam of particles.

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 time
  زمان ِ کیهانی   
zamân-e keyhâni

Fr.: temps cosmique   

The time as measured by a clock that is at rest relative to the expanding space, and that has been set to zero at the very beginning, the time of the hypothetical → Big Bang singularity. The cosmic time is interpreted as the → age of the Universe (Einstein-online).

cosmic; → time.

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 rays collides with atmospheric nuclei creating many → secondary cosmic rays. Also known as → air shower.

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.

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