Science Fair Project Encyclopedia
Very Large Array
- For other uses of the acronym "VLA" see VLA (disambiguation)
The Very Large Array (VLA) is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles (80 km) west of Socorro, New Mexico, USA. The VLA stands at , at an altitude of 6970 ft (2124 m) above sea level. It is a component part of the National Radio Astronomy Observatory (NRAO).
The observatory consists of 27 independent radio antennae, each of which has a dish diameter of 25 meters and weighs 230 tons. The antennae are arrayed along the three arms of a Y-shape (each of which measures 21 km). Using the railroad tracks that follow each of these arms – and that, at one point, intersect with U.S. Highway 60 at a level crossing – and a specially designed lifting locomotive, the antennae can be physically relocated to a number of prepared positions, allowing aperture synthesis interferometry with a maximum baseline of 36 km: essentially, the array acts like a single antenna with that diameter. The highest angular resolution that can be reached is about 0.05 arcseconds.
There are four commonly used configurations, designated A (the largest) through D (the tightest, when all the dishes are within 600 m of the center point). The observatory normally cycles through all the various possible configurations (including several hybrids) every 16 months: in other words, once the massive efforts needed to move two dozen 230-ton highly sensitive scientific instruments have been made, the antennae are not moved again for a period of three to four months.
The VLA site also currently serves as the control center for the Very Long Baseline Array (VLBA), a VLBI array of ten 25-meter dishes located from Hawaii in the west to the U.S. Virgin Islands in the east that constitutes the world's largest dedicated, full-time astronomical instrument.
Past and future
Congressional approval for the VLA project was given in August 1972, and construction began some six months later. The first antenna was put into place in September 1975 and the complex was formally inaugurated in 1980, after a total investment of USD $78.5 million.
With a view to upgrading the venerable 1970s technology with which the VLA was built, a proposal has been floated for the conversion of the VLA into the Expanded Very Large Array ("EVLA"). The upgrade would enhance the instrument's sensitivity, frequency range, and resolution, and would entail installing new hardware at the San Agustin site and the construction and installation of up to eight additional dishes in other parts of the state of New Mexico, up to 300 km away, connected to the hub via fiber-optic links.
The VLA observatory featured prominently in Carl Sagan's 1985 novel Contact, albeit much expanded (131 dishes!) and renamed the "Argus Array". When the time came for Hollywood to make the motion picture version of the story (Contact, 1997), much outdoor footage was shot at the VLA site. The number of dishes visible on screen was artificially increased by means of Computer-generated imagery, however, and the canyon depicted as being in the vicinity of the VLA is actually Chelly Canyon in neighboring Arizona.
The VLA site is open to visitors year round during daylight hours. A visitor center houses a museum and a gift shop, and a self-guided walking tour is available.
- NRAO VLA – official site.
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