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In astronomy
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
, a redshift survey, or galaxy survey, is a survey
Astronomical surveys

Astronomical surveys generally involve imaging or mapping of regions of the sky using Telescopes. In the past,surveys have been usually restricted to one band of wavelengths of electromagnetic radiation or to measurements of the flux of one type of particle , and they were generally performed as part of the...
 of a section of the sky to measure the redshift
Redshift

In physics and astronomy, redshift occurs when electromagnetic radiation?usually visible light?emitted or reflected by an object is shifted towards the red end of the electromagnetic spectrum due to the Doppler effect....
 of astronomical objects. Using Hubble's law
Hubble's law

Hubble's law is the statement in physical cosmology that distant galaxy are receding from us at a velocity Proportionality to their distance from us....
, the redshift can be used to calculate the distance of an object from Earth. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky.






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2dfgrs
In astronomy
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
, a redshift survey, or galaxy survey, is a survey
Astronomical surveys

Astronomical surveys generally involve imaging or mapping of regions of the sky using Telescopes. In the past,surveys have been usually restricted to one band of wavelengths of electromagnetic radiation or to measurements of the flux of one type of particle , and they were generally performed as part of the...
 of a section of the sky to measure the redshift
Redshift

In physics and astronomy, redshift occurs when electromagnetic radiation?usually visible light?emitted or reflected by an object is shifted towards the red end of the electromagnetic spectrum due to the Doppler effect....
 of astronomical objects. Using Hubble's law
Hubble's law

Hubble's law is the statement in physical cosmology that distant galaxy are receding from us at a velocity Proportionality to their distance from us....
, the redshift can be used to calculate the distance of an object from Earth. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky. These observations are used to measure properties of the large scale structure
Large-scale structure of the cosmos

In physical cosmology, the term large-scale structure refers to the characterization of observation distribution s of matter and light on the largest scales ....
 of the universe. The Great Wall
Great Wall (astronomy)

The Great Wall , sometimes specifically referred to as the CfA2 Great Wall, is the second largest known Large-scale structure of the cosmos in the Universe ....
, a vast conglomeration of galaxies over 500 million light-years wide, provides a dramatic example of a large-scale structure that redshift surveys can detect.

The first redshift survey was the CfA Redshift Survey
CfA Redshift Survey

The Center for Astrophysics Redshift Survey was the first attempt to map the large-scale structure of the universe. It began in 1977 with the initial data collection completed in 1982....
, started in 1977 with the initial data collection completed in 1982.

The most notable, recent and low-redshift surveys are the 2dF Galaxy Redshift Survey
2dF Galaxy Redshift Survey

In astronomy, the 2dF Galaxy Redshift Survey , 2dF or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory with the 3.9m Anglo-Australian Telescope between 1997 and 11 April 2002....
 and the Sloan Digital Sky Survey
Sloan Digital Sky Survey

The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-metre wide-angle optical telescope at Apache Point Observatory in New Mexico....
. At high redshift there exist the DEEP2 Redshift Survey
DEEP2 Redshift Survey

The DEEP2 Survey or DEEP2 is a Redshift survey of the Redshift~1 universe. It uses the Keck telescopes to measure the spectra and hence redshifts of approximately 60,000 galaxies....
 and the VIMOS-VLT Deep Survey (VVDS).

Because of the demands on observing time required to obtain spectroscopic redshifts (i.e., true redshifts measured by velocity), it has become commonplace to use photometric redshift
Photometric redshift

A photometric redshift is an estimate for the distance of an astronomical object, such as a galaxy or quasar. The technique uses photometry to determine the redshift, and hence, through Hubble's law, the distance, of the observed object....
s, based on brightness. Such "redshifts" can be used in surveys and to find the space distribution of galaxies, provided the galaxy types are well known, but, obviously they cannot be used to define points on the Hubble curve, because of circular reasoning.

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