# an overview of the very large array _vla faq_

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```					                                An Overview of the Very Large Array (VLA FAQ)

History:
1972 August: approved by Congress
1973 April: construction started
1975 September 22: first antenna put in place
1976 February 18: first fringes
1980: formal dedication of the VLA
The total cost was \$78,578,000 (in 1972 dollars), roughly \$1 per taxpayer at the time; the project was
completed nearly one year early, and within the allotted budget.

Location:
Plains of San Augustin, west of Socorro, New Mexico.
latitude = 3404'43.497" north
longitude = 10737'03.819" west
elevation = 2124 m (6970 ft)

Size:
27 antennas. Each antenna is 25 m (82 ft) in diameter, 230 tons.
The Array:
The “Y” shaped Array with 9 antennas on each arm has “Four Configurations” A,B,C,&D:
A Array- maximum antenna separation is 36 km; B Array - 10 km; C Array - 3.6 km; and D Array - 1 km.

Resolution: 0.04 arcseconds
The resolution of the VLA is set by the configuration of the array -- up to 36 km (22 miles) across. Highest
frequency (43 GHz) this gives a resolution of 0.04 arcseconds: 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...

Misc. antenna information:
Slew rates: 40 per minute in azimuth, 20 per minute in elevation
Minimum elevation angle: 8 above the horizon

Frequency coverage:
The VLA can observe at various bands between 74 and 50,000 MHz (400 to 0.7 cm)

How does it work?
The VLA is an interferometer; this means that it operates by multiplying the data from each pair of
telescopes together 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 on the sky: we can take
these patterns and use a mathematical technique called the Fourier transform to make maps.

Who uses it?
The VLA is used primarily by astronomers from around the world. It's also occasionally used for
atmospheric/weather studies, satellite tracking, and other miscellaneous science.

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