An Etymological Dictionary of Astronomy and Astrophysics
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A type of → cosmic defect in the fabric of space-time predicted in some models of the early Universe.

→ cosmic; → texture

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.

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.

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

→ cosmic; → ray; → burst.

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.

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.

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.

Combining form of → cosmos.

→ cosmos.

The study of the chemical composition of the universe and the processes that produced those compositions. Cosmochemistry is an interdisciplinary science that overlaps with geochemistry, geology, astronomy, astrophysics, and geophysics.

→ cosmo-; → chemistry.

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.

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.

The branch of → cosmology concerned with the dimensional structures of the → Universe and their measurement.

→ cosmo-; → -graphy.

Pertaining or relating to → cosmology.

→ cosmology; → -al.

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 distance to a remote galaxy based on its redshift assuming that the redshift is caused by the → Doppler effect and reflects the general expansion of the Universe.

→ cosmological; → distance .

→ cosmological; → epoch.

A mathematical description of the Universe, based on observation, which tries to explain its current aspect, and to describe its evolution during time.

→ cosmological; → model.

The → hypothesis that on → large scales the → Universe is → isotropic and → homogeneous, that is, it appears the same at all places and, from any one place, looks the same in all directions. See also → perfect cosmological principle.

Introduced by E.A. Milne in 1933; → cosmological; → principle.

The → redshift of a remote object (galaxy, quasar, supenova) due to the expansion of the Universe.

→ cosmological; → redshift.