# correlation function

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## correlation function

A measure of the clustering on extragalactic scales obtained from redshift surveys. It is the probability for a galaxy to have another neighbor within a given distance of separation, in excess of the probability expected from a uniform random distribution of galaxies, expressed as a function of that distance. Galaxy positions are highly correlated, with the probability decreasing approximately as the inverse square of the galaxy separation. The*correlation length*for clusters of galaxies is the radius within which the chance of finding another galaxy is double the chance expected from a uniform random distribution of galaxies. Galaxies cluster into groups and clusters on a length-scale of around 30 megaparsecs, whereas superclusters have correlation lengths nearer 130 megaparsecs.

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