The antennas are arrayed along the three
arms of a Y-shape (each of which measures 21 km/13 miles long).
Using the railroad tracks that follow each of these arms – and
that, at one point, intersect with
U.S.
Route 60 at a level
crossing – and a specially designed lifting locomotive, the
antennas can be physically relocated to a number of prepared
positions, allowing
aperture synthesis
interferometry with a
maximum baseline of 36 km (22.3 miles): in essence, the array
acts as a single antenna with that diameter. The smallest
angular resolution that can be reached is about 0.05
arcseconds at a
wavelength of 7 mm.
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; the antennas are moved every three to four months. Moves to smaller configurations are done in two stages, first shortening the east and west arms and later shortening the north arm. This allows for a short period of improved imaging of extremely northerly or southerly sources.
The Array Operations Center (AOC) for the VLA is located on the campus of the New Mexico Institute of Mining and Technology in Socorro, New Mexico. The AOC 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.
The
VLA is a multi-purpose instrument designed to
allow investigations of many astronomical
topics. Objects that are commonly studied
include
radio
galaxies,
quasars,
pulsars,
supernova
remnants,
gamma ray
bursts,
radio-emitting
stars,
the
sun
and
planets,
astrophysical masers,
black holes,
and the
hydrogen
gas that comprises a large portion of the
Milky Way
galaxy as well as external galaxies. In 1989 the
VLA was used to receive
radio
communications from the
Voyager 2
spacecraft as it flew by
Neptune.The VLA site is open to visitors year round during daylight hours. A visitor center houses a small museum and a gift shop. A self-guided walking tour is available, as the visitor center is not staffed continuously. Visitors unfamiliar with the area are warned that there is little food onsite, or in the sparsely populated surroundings; those unfamiliar with the high desert are warned that the weather is quite variable, and can remain cold into April.

With a view to upgrading the venerable 1970s technology with which the VLA was built, recent funding has been allocated for the conversion of the VLA into the Expanded Very Large Array ("EVLA"). The upgrade will enhance the instrument's sensitivity, frequency range, and resolution, and will install new hardware at the San Augustin site. A second phase of this upgrade to add up to eight additional dishes in other parts of the state of New Mexico, up to 300 km away, is currently unfunded.
