An astronomical survey is a general map or image of a region of the sky (or of the whole sky) that lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of images, spectra, or other observations of objects that 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.
5-722: The NRAO VLA Sky Survey ( NVSS ) was an astronomical survey of the Northern Hemisphere carried out by the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO), resulting in an astronomical catalogue . It was led by James J. Condon . The survey covers 82% sky, consisting of everything north of declination -40 degrees . The observations were made in 'D' and 'DnC' configuration at 1.4 gigahertz (21 cm), with an angular resolution of 45 arcsec . It
10-495: A hypothesis, a telescope scheduling committee is more likely to approve new, more detailed observations to test it. The wide scope of surveys makes them ideal for finding foreground objects that move, such as asteroids and comets. An astronomer can compare existing survey images to current observations to identify changes; this task can even be performed automatically using image analysis software. Besides science, these surveys also detect potentially hazardous objects , providing
15-587: A service to Spaceguard . For example, the Asteroid Terrestrial-impact Last Alert System (ATLAS) system surveys the entire night sky every night and, like NEOSTEL , is intended to detect objects as they approach. Broader surveys include the Uppsala–DLR Asteroid Survey and the 20th-century U.K. Schmidt–Caltech Asteroid Survey . Old surveys can be reviewed to find precovery images. Similarly, images of
20-643: The production of an astronomical catalog . They may also search for transient astronomical events . They often use wide-field astrographs . Sky surveys, unlike targeted observation of a specific object, allow astronomers to catalog celestial objects and perform statistical analyses on them without complex corrections for selection effects . In some cases, an astronomer interested in a particular object will find that survey images are sufficient to make new telescope time entirely unnecessary. Surveys also help astronomers choose targets for closer study using larger, more powerful telescopes. If previous observations support
25-789: Was proposed at the same time as the Faint Images of the Radio Sky at Twenty-Centimeters , and test observations for both surveys were taken in 1992. Observations were made between September 1993 and October 1996. The Southern Hemisphere was covered by a similar catalogue called the Sydney University Molonglo Sky Survey (SUMSS), generated using the Molonglo Observatory Synthesis Telescope . Astronomical survey Surveys have generally been performed as part of
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