The Very Large Array
[Adapted from the NRAO website, overview]
The Very Large Array (VLA), one of the major instrument facilities managed by the National Radio Astronomy Observatory (NRAO), operated for the NSF by Associated Universities, Inc., is a collection of 27 radio telescopes located on the Plains of San Agustin, west of Socorro, New Mexico at an elevation of about 7000 feet. It is used primarily by astronomers from around the world on a peer-reviewed competitive basis, but it also has done atmospheric/weather studies, satellite tracking, and other miscellaneous scientific applications.
The VLA is an interferometer. This means that it operates by multiplying the data from each pair of telescopes in the 27-dish array to form interference patterns. The structure of those interference patterns, and how they change with time as the earth rotates, reflect the structure of radio sources in space. Astronomers process and interpret these patterns to make maps.
The VLA was approved by Congress as a National Science Foundation initiative in 1972 and was formally dedicated in 1980 at a total construction cost of $78,578,000 (in 1972 dollars). There were no cost overruns and the project was completed early.
Each antenna element is 25 m (82 ft) in diameter and weighs 230 tons. The elements can be respaced in their Y pattern in four configurations: A array, with a maximum antenna separation of 36 km; B array -- 10 km; C array -- 3.6 km; and D array -- 1 km. The telescopes are switched between these configurations every four months or so. The resolution of the VLA is set by the size of the array -- up to 36 km (22 miles) across. At highest frequency (43 GHz) this gives a resolution of 0.04 arc seconds: sufficient to see a golf ball held by a friend 150 km (100 miles) away. Of course, very few golf balls contain high-power radio transmitters.The VLA is now being transformed into a new research instrument: the Expanded Very Large Array (EVLA). By 2012, new state-of-the-art electronics and software will have completely transformed the VLA into the EVLA, a much more capable research tool with more than ten times the VLA's sensitivity. Reinvigorated by new technologies, the EVLA will push the frontiers of science and knowledge for decades to come.