Correlation function (astronomy)
 Correlation function (astronomy)

In astronomy, a correlation function describes the distribution of galaxies in the universe. By default, correlation function refers to the twopoint autocorrelation function. For a given distance, the twopoint autocorrelation function is a function of one variable (distance) which describes the probability that two galaxies are separated by this particular distance. It can be thought of as a lumpiness factor  the higher the value for some distance scale, the more lumpy the universe is at that distance scale.
The following definition (from Peebles 1980) is often cited:
 Given a random galaxy in a location, the correlation function describes the probability that another galaxy will be found within a given distance.
However, it can only be correct in the statistical sense that it is averaged over a large number of galaxies chosen as the first, random galaxy. If just one random galaxy is chosen, then the definition is no longer correct, firstly because it is meaningless to talk of just one "random" galaxy, and secondly because the function will vary wildly depending on which galaxy is chosen, in contradiction with its definition as a function.
The npoint autocorrelation functions for n greater than 2 or crosscorrelation functions for particular object types are defined similarly to the twopoint autocorrelation function.
The correlation function is important for theoretical models of physical cosmology because it provides a means of testing models which assume different things about the contents of the universe.
References
See also
Wikimedia Foundation.
2010.
Look at other dictionaries:
Correlation function (disambiguation) — Correlation function may refer to: Correlation function, correlation between random variables at two different points in space or time Correlation function (quantum field theory), matrix element computed by inserting a product of operators… … Wikipedia
Correlation function — For other uses, see Correlation function (disambiguation). A correlation function is the correlation between random variables at two different points in space or time, usually as a function of the spatial or temporal distance between the points.… … Wikipedia
astronomy — /euh stron euh mee/, n. the science that deals with the material universe beyond the earth s atmosphere. [1175 1225; ME astronomie ( < AF) < L astronomia < Gk. See ASTRO , NOMY] * * * I Science dealing with the origin, evolution, composition,… … Universalium
Radio astronomy — is a subfield of astronomy that studies celestial objects at radio frequencies. The field originated from the discovery that many astronomical objects emit radiation in the radio wavelengths as well as optical ones. The great advances in radio… … Wikipedia
List of mathematics articles (C) — NOTOC C C closed subgroup C minimal theory C normal subgroup C number C semiring C space C symmetry C* algebra C0 semigroup CA group Cabal (set theory) Cabibbo Kobayashi Maskawa matrix Cabinet projection Cable knot Cabri Geometry Cabtaxi number… … Wikipedia
cosmos — /koz meuhs, mohs/, n., pl. cosmos, cosmoses for 2, 4. 1. the world or universe regarded as an orderly, harmonious system. 2. a complete, orderly, harmonious system. 3. order; harmony. 4. any composite plant of the genus Cosmos, of tropical… … Universalium
Weak gravitational lensing — While the presence of any mass bends the path of light passing near it, this effect rarely produces the giant arcs and multiple images associated with strong gravitational lensing. Most lines of sight in the universe are thoroughly in the weak… … Wikipedia
The Dark Energy Survey — DES logo The Dark Energy Survey (DES) is a survey that aims to probe the dynamics of the expansion of the universe and the growth of large scale structure. The collaboration is composed of research institutes and universities from United… … Wikipedia
William G. Tifft — is Emeritus Professor/Astronomer at the University of Arizona. His main interests are in galaxies, superclusters and what Tifft calls redshift problems (see redshift quantization). [ [http://www.as.arizona.edu/department/faculty/tifft.html… … Wikipedia
Coherence (physics) — In physics, coherence is a property of waves that enables stationary (i.e. temporally and spatially constant) interference. More generally, coherence describes all properties of the correlation between physical quantities of a wave. When… … Wikipedia