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An astronomical survey is a general map or image of a region of the sky which lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of many images or spectra of objects which share a common type or feature. Surveys are often restricted to one band of the electromagnetic spectrum due to instrumental limitations, although multiwavelength surveys can be made by using multiple detectors, each sensitive to a different bandwidth. Surveys have generally been performed as part of the production of an astronomical catalogue.
Scientific value 
Sky surveys, unlike targeted observation of a specific object, allow astronomers to catalogue celestial objects and perform statistical analyses on them without making prohibitively lengthy observations. In some cases, an astronomer interested in a particular object will find that survey images are sufficient to entirely obviate the need for telescope time.
Surveys also help astronomers obtain observation time on larger, more powerful telescopes. If the astronomer can show a telescope scheduling committee that previous observations support his hypothesis, he is more likely to be given a chance to make more detailed observations.
The wide scope of surveys makes them ideal for astronomers searching for moving foreground objects such as asteroids and comets. An astronomer can compare existing survey images to current observations to locate targets which are in motion; this task can even be performed automatically using image analysis software. Similarly, images of the same object taken by different surveys can be compared to detect transient events such as variable stars.
List of sky surveys 
- Pan-Andromeda Archaeological Survey
- National Geographic Society – Palomar Observatory Sky Survey (NGS–POSS) - survey of the northern sky on photographic plates, 1948–1958
- Digitized Sky Survey - optical all-sky survey created from digitized photographic plates, 1994
- Sloan Digital Sky Survey - an optical and spectroscopic survey, 2000-2006 (first pass)
- Photopic Sky Survey - a survey with 37,440 individual exposures, 2010-2011.
- Palomar Distant Solar System Survey (PDSSS)
- Infrared Astronomical Satellite did an all sky survey at 12, 25, 60, and 100 μm, 1983
- The 2-micron All-Sky Survey (2MASS), a ground based all sky survey at J, H, and Ks bands (1.25, 1.65, and 2.17 μm) 1997-2001
- Akari (Astro-F) a Japanese mid and far infrared all-sky survey satellite, 2006–2008
- Wide-field Infrared Survey Explorer was launched in December 2009 to begin a survey of 99% of the sky at wavelengths of 3.3, 4.7, 12, and 23 μm. The telescope is over a thousand times as sensitive as previous infrared surveys. The initial survey, consisting of each sky position imaged at least eight times, was completed by July 2010.
- SCUBA-2 All Sky Survey
- HIPASS - Radio survey, the first blind HI survey to cover the entire southern sky. 1997-2002
- Ohio Sky Survey - Over 19,000 radio sources at 1415 MHz. 1965-1973.
- NVSS - Survey at 1.4 GHz mapping the sky north of -40 deg
- FIRST - Survey to look for faint radio sources at twenty cms.(see http://sundog.stsci.edu/index.html )
- PALFA Survey - On-going 1.4 GHz survey for radio pulsars using the Arecibo Observatory.
- Fermi Gamma-ray Space Telescope, formerly referred to as the "Gamma-ray Large Area Space Telescope (GLAST)." 2008–present; the goal for the telescope's lifetime is 10 years.
- Multi-wavelength surveys
- GAMA - the Galaxy And Mass Assembly survey (see http://gama-survey.org) combines data from a number of ground- and space-based observatories together with a large redshift survey, performed at the Anglo-Australian Telescope. The resulting dataset aims to be a comprehensive resource for studying the physics of the galaxy population and underlying mass structures in the recent universe.
- GOODS - The Great Observatories Origins Deep Survey.
- COSMOS - The Cosmic Evolution Survey
(The latter two surveys are joining together observations obtained from space with the Hubble Space Telescope, the Spitzer Space Telescope, the Chandra X-ray Observatory and the XMM-Newton satellite, with a large set of observations obtained with ground-based telescopes).
Surveys of the Magellanic Clouds 
- The Magellanic Clouds Photometric Survey - UBVI (optical)
- Deep Near Infrared Survey (DENIS) - near-IR
- Surveying the Agents of a Galaxy's Evolution - a Spitzer Space Telescope legacy observation program of the LMC
Further information 
- See astronomical catalogue for a more detailed description of astronomical surveys and the production of astronomical catalogues
- Redshift surveys are astronomical surveys devoted to mapping the cosmos in three dimensions
- Category:astronomical catalogues—List of astronomical catalogues on Wikipedia
- Astrograph for a type of instrument used in Astronomical surveys.
- Timeline of astronomical maps, catalogs, and surveys
- Dr. Pamela Gay, Fraiser Cain: Astronomy Cast Episode #90: The Scientific Method (May 26, 2008).
- Risinger, Nick. "Phototopic Sky Survey". Retrieved 12 May 2011.
- Associated Press (12 May 2011). "Amateur Photographer Links 37,000 Pics in Night-Sky Panorama". Fox News. Retrieved 13 May 2011.
- GAMA: towards a physical understanding of galaxy formation, Astronomy & Geophysics