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In [[physical]] [[cosmology]], the '''large-scale structure''' of the [[universe]] refers to the characterization of [[observable]] [[distributions]] of [[matter]] and [[light]] on the largest scales (typically on the order of billions of [[light-years]]). Sky surveys and mappings of the various [http://en.wikipedia.org/wiki/Wavelength wavelength bands] of [http://en.wikipedia.org/wiki/Electromagnetic_radiation electromagnetic radiation] (in particular 21-cm emission) have yielded much [[information]] on the [[content]] and [[character]] of the universe's [[structure]]. The [[organization]] of structure appears to follow as a [[hierarchical]] model with organization up to the scale of [[superclusters]] and filaments. Larger than this, there seems to be no continued structure, a [[phenomenon]] which has been referred to as the ''End of Greatness''.

In [[physical]] [[cosmology]], the '''large-scale structure''' of the [[universe]] refers to the characterization of [[observable]] [[distributions]] of [[matter]] and [[light]] on the largest scales (typically on the order of billions of [[light-years]]). Sky surveys and mappings of the various [http://en.wikipedia.org/wiki/Wavelength wavelength bands] of [http://en.wikipedia.org/wiki/Electromagnetic_radiation electromagnetic radiation] (in particular 21-cm emission) have yielded much [[information]] on the [[content]] and [[character]] of the universe's [[structure]]. The [[organization]] of structure appears to follow as a [[hierarchical]] model with organization up to the scale of [[superclusters]] and filaments. Larger than this, there seems to be no continued structure, a [[phenomenon]] which has been referred to as the ''End of Greatness''.

[[File:Universe_Reference_Map700.jpg|center|frame]]

[[File:Universe_Reference_Map650.jpg|center|frame]]

The [[organization]] of [[structure]] arguably begins at the [[stellar]] level, though most cosmologists rarely address [http://en.wikipedia.org/wiki/Astrophysics astrophysics] on that scale. [[Stars]] are organised into [[galaxies]], which in turn form [http://en.wikipedia.org/wiki/Groups_and_clusters_of_galaxies clusters] and [[superclusters]] that are separated by immense voids, creating a vast foam-like structure sometimes called the "cosmic web". Prior to [http://www.wikipedia.org/wiki/1989 1989], it was commonly assumed that virialized [[galaxy]] clusters were the largest structures in [[existence]], and that they were [[distributed]] more or less [[uniformly]] throughout the universe in every direction. However, based on [http://en.wikipedia.org/wiki/Redshift_survey redshift survey data], in 1989 Margaret Geller and John Huchra discovered the "[http://en.wikipedia.org/wiki/Great_Wall_(astronomy) Great Wall]," a sheet of galaxies more than 500 million light-years long and 200 million wide, but only 15 million [[light-years]] thick. The existence of this structure escaped notice for so long because it requires locating the position of galaxies in three dimensions, which involves combining location information about the galaxies with distance information from redshifts. In April 2003, another large-scale structure was discovered, the [http://en.wikipedia.org/wiki/Sloan_Great_Wall Sloan Great Wall]. In August 2007, a possible supervoid was detected in the constellation Eridanus.[1] It coincides with the '[http://en.wikipedia.org/wiki/WMAP_cold_spot WMAP Cold Spot]', a cold region in the microwave sky that is highly improbable under the currently favored cosmological model. This supervoid could cause the cold spot, but to do so it would have to be improbably big, possibly a billion light-years across.

The [[organization]] of [[structure]] arguably begins at the [[stellar]] level, though most cosmologists rarely address [http://en.wikipedia.org/wiki/Astrophysics astrophysics] on that scale. [[Stars]] are organised into [[galaxies]], which in turn form [http://en.wikipedia.org/wiki/Groups_and_clusters_of_galaxies clusters] and [[superclusters]] that are separated by immense voids, creating a vast foam-like structure sometimes called the "cosmic web". Prior to [http://www.wikipedia.org/wiki/1989 1989], it was commonly assumed that virialized [[galaxy]] clusters were the largest structures in [[existence]], and that they were [[distributed]] more or less [[uniformly]] throughout the universe in every direction. However, based on [http://en.wikipedia.org/wiki/Redshift_survey redshift survey data], in 1989 Margaret Geller and John Huchra discovered the "[http://en.wikipedia.org/wiki/Great_Wall_(astronomy) Great Wall]," a sheet of galaxies more than 500 million light-years long and 200 million wide, but only 15 million [[light-years]] thick. The existence of this structure escaped notice for so long because it requires locating the position of galaxies in three dimensions, which involves combining location information about the galaxies with distance information from redshifts. In April 2003, another large-scale structure was discovered, the [http://en.wikipedia.org/wiki/Sloan_Great_Wall Sloan Great Wall]. In August 2007, a possible supervoid was detected in the constellation Eridanus.[1] It coincides with the '[http://en.wikipedia.org/wiki/WMAP_cold_spot WMAP Cold Spot]', a cold region in the microwave sky that is highly improbable under the currently favored cosmological model. This supervoid could cause the cold spot, but to do so it would have to be improbably big, possibly a billion light-years across.