An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A stream of atomic or subatomic particles.

Corpuscular, adj. from → corpuscle; → radiation.

1) The act or process of correcting.
2) A quantity added to a calculated or observed value to obtain the true value.
3) Something that is substituted or proposed for what is wrong or inaccurate.

Noun form of → correct.

General: The degree to which two or more attributes or measurements on the same group of elements show a tendency to vary together; the state or relation of being correlated.
Statistics: The strength of the linear dependence between two random variables.

From M.Fr. corrélation, from cor- "together," → com- + → relation.

Hambâzâneš , from ham-→ com- + bâzâneš→ relation.

A number between -1 and 1 which measures the degree to which two variables are linearly related.

→ correlation; → coefficient.

To be in agreement, harmony, or conformity; to be similar or equivalent in character, quantity, origin, structure, or function.

From O.Fr. Fr. correspondre, from M.L. correspondere from cor-, → com-, + respondere "to answer," → response.

Hampatvâzidan, from ham-, → com-, + patvâz "response" [Mo'in], from Mid.Pers. patvâc "response," Av. paitivak- + -idan infinitive suffix.

The act, fact, or state of agreeing or conforming.

Verbal noun from → correspond.

The principle first put forward by N. Bohr according to which the behavior of quantum mechanical laws reduce to classical laws in the limit of large quantum numbers.

→ correspondence; → principle.

→ accelerating Universe.

→ cosmic; → acceleration.

→ cosmic microwave background radiation (CMBR).

→ cosmic; → background; → radiation.

Same as the → Layzer-Irvine equation.

→ cosmic; → energy; → equation.

Same as the → expansion of the Universe.

→ cosmic; → expansion.

The → observable region of the → Universe, limited in extent by the distance → light has traveled during the time elapsed since the beginning of the Universe (→ Big Bang). No signal from the objects lying beyond the cosmic horizon can be received because light has not yet had enough time to travel the distance. The cosmic horizon can be defined in two ways:
1) The size of the → observable Universe as derived from ct, where c is the → speed of light and t is the → age of the Universe, 13.8 billion years, hence 13.8 billion → light-years.
2) The → comoving distance. The distance given above corresponds to the size Universe had 13.8 billion years ago. Since then the Universe has been growing at a rate of 3.52c. Therefore, the current radius of the observable Universe is about 48 × 10⁹ light-years. Same as → particle horizon, → Hubble distance, → Hubble radius, and → Hubble length. See also → sound horizon.

→ cosmic; → horizon.

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.

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.

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.

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.

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.

A term introduced by Einstein into his gravitational → field equations in order to allow a solution corresponding to a → static Universe. The cosmological constant is physically interpreted as due to the → vacuum energy of quantized fields. See also → dark energy.

→ cosmological; → constant.

The impressive discrepancy of about 120 orders of magnitude between the theoretical value of the → cosmological constant and its observed value. → Quantum field theory interprets the cosmological constant as the density of the → vacuum energy. This density can be derived from the maximum energy at which the theory is valid, i.e. the → Planck energy scale (10¹⁸ GeV). The theoretical vacuum → energy density is (10¹⁸ GeV)⁴ = (10²⁷ eV)⁴ = 10¹¹² erg cm^-3. On the other hand, the observed vacuum energy density is estimated to be about (10^-3 eV)⁴ = 10^-8 erg cm^-3. There is, therefore, a discrepancy of about 120 orders of magnitude.

→ cosmological; → constant; → problem.

The Russian term for → astronaut.

Cosmonaut, from → cosmo- + naute, from Gk. nautes "sailor," from naus "ship" (cognate with Pers. nâv "ship," Av./O.Pers. *nāv-, O.Pers. nāviyā- "fleet," Skt. nau-, nava- "ship, boat," Gk. naus, neus, L. navis; PIE *nâu- "ship").