Astronomical survey

Composite image of the GOODS-South field, result of a deep survey using two of the four giant 8.2-metre telescopes composing ESO's Very Large Telescope.

Gamma-ray pulsars detected by the Fermi Gamma-ray Space Telescope.

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 (e.g. light or radio) or to measurements of the flux of one type of particle (e.g. cosmic rays), and they were generally performed as part of the production of an astronomical catalogue for a specific type of astronomical object (like, for example, all the stars brighter than a certain apparent magnitude). Over the last ten years, taking advantage of technological improvements in the construction of telescopes, and following a general expansion in our understanding of astrophysics at all levels, it has become commonplace to conduct surveys that join together many different observations of a given region in the sky, obtained with different telescopes at different wavelengths. This so-called multi-wavelength approach is now the new standard for surveys, at least in the fields of Extragalactic astronomy and Observational cosmology.

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 the 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

• Optical
  • 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.

• Infrared
  • Infrared Astronomical Satellite did an all sky survey at 12, 25, 60, and 100 μm, 1983
  • The 2-micron All-Sky Survey, 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

• Radio
  • 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 )

• Gamma-ray
  • 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).

• Planned
  • Pan-STARRS - a proposed 4-telescope large-field survey system to look for transient and variable sources
  • Large Synaptic Survey Telescope - a proposed very large telescope designed to repeatedly survey the whole sky that is visible from its location

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