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Date of visit:
September 12, 2000

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 Location of VLA Site ...

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Site Highlights:
 Situated on a plain
 Open to the public
 No entry fees
 Visitor center
 Self guided tours
 Get close to dishes
 Few visitors
 Learn astronomy
 Photo opportunities


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The National Radio Astronomy Observatory (NRAO)
Radio Astronomy and Radio Telescopes
The VLA Observatory
Visitor Center
Welcome to the VLA

The VLA is the world's most powerful radio telescope. It is not one large structure but an array of 27 antennas which are connected electronically to synthesize a single radio telescope 20 miles in diameter. Astronomers need such a large device to produce radio photographs of celestial objects that have the same detail and resolution as photographs made with the biggest optical telescopes.

Radio astronomy is a young science. In 1933 faint radio noise which interfered with transatlantic communications was first identified as cosmic radio waves from our Milky Way. The science grew up after World War 11 with new radio and radar technology, and it matured in the 1960's and 70's as astronomers detected radio waves from many unusual objects such as pulsars and quasars. In order to study these and other fascinating aspects of the universe, larger and more sensitive telescopes were needed. These developments led to the construction of the VLA.
The VLA Site

Although open to the public, there are no guided tours. All visitors are encouraged to take a self-guided tour that encompasses all of the observatory except the array arms and the inside of the facilities.
[ walking tour ]    [ map 1 ]    [ map 2 ]

Radio Astronomy and Radio Telescopes
The National Radio Astronomy Observatory (NRAO) was founded in Green Bank, West Virginia in 1956 to provide scientists with large radio telescopes necessary for the continued advancement of radio astronomy. Until that time, most observatories were operated by universities; NRAO was the first to be funded directly by the National Science Foundation through congressional appropriations.
The first site was chosen deep in the Allegheny Mountains where it was relatively free from terrestrial radio interference. In the 1960's the stream of scientists who used the telescopes at Green Bank established NRAO as a major world center for radio astronomical research. The NRAO has expanded its facilities to four locations in order to provide astronomers with the most modern telescopes, electronics and computers.

Besides the telescopes at Green Bank, NRAO operates a 12-meter telescope on Kitt Peak, near Tucson, Arizona; a laboratory in Charlottesville, Virginia; and the Very Large Array (described here) near Socorro, New Mexico. NRAO is presently constructing the Very Long Baseline Array, with ten telescopes spread across the USA from Hawaii to the Virgin Islands, to simulate a telescope nearly 5000 miles in diameter.

The Observatory staff at these sites includes astronomers who use and test the telescopes, engineers who design and build the telescopes and receivers, computer scientists who write the data analysis software and other support personnel. Use of the telescopes is awarded to qualified scientists who propose meritorious programs of research in radio astronomy. Since its founding the facilities of the National Radio Astronomy Observatory have been used by thousands of scientists from all over the world.

Among the predecessors that led to the development of the VLA were: the first radio telescope, the first modern parabolic radio telescope, the largest equatorially mounted telescope, the three-element interferometer, and the 12-meter telescope, the Owens Valley interferometer, and the Cambridge Array.

Light and Radio Waves
Horsehead NebulaThrough the ages people have looked in awe at the night sky: the myriad of stars, the planets which wander through the constellations and the Milky Way's band of light. After the invention of the telescope in 1609, astronomers began to collect and analyze light from the heavens but it took breakthroughs in physics in the early 1900's before astronomers began to fathom how stars are born, how their energy is produced, and how they die. Astronomers also discovered that the space between stars is filled with hot and cold matter and that our own Milky Way is a typical galaxy with hundreds of billions of stars in a universe filled with hundreds of billions of galaxies.
Most of the universe is filled with plasma - a mixture of charged particles, electrons, protons, light elements and simple molecules - incessantly moving. The energy of motion is provided by thermonuclear reactions in the center of stars, by gravitational collapse of massive objects and by magnetic fields. When these charged particles are accelerated either in near collisions with other particles or while spiraling around the magnetic force fields, they emit electromagnetic waves. From gentle accelerations, low frequency radio waves are produced; from violent collisions high frequency waves are produced. This spectrum of electromagnetic waves is commonly divided by wavelength into the groups shown on the previous page. Because all waves travel at 300,000 km/second (186,000 miles/second) in a vacuum, the separation be-tween two consecutive crests in a wave varies inversely with the wave frequency and this separation is called the wavelength. Radio waves have the longest wavelength; light waves are a million times smaller.

Electromagnetic waves propagate in all directions from a source, like ripples from a pebble dropped in the middle of a serene pond. After traveling for millions of years the waves reach the earth, but the atmosphere and ionosphere absorb all of the energy in the electromagnetic spectrum, except for light and radio waves. Before 1950 all that was known about the cosmos was limited to light detected by optical telescopes. With the development of radio receivers after World War 11 and the launching of scientific instruments into earth-orbit, astronomers began to study the non-visible waves from the sky. They discovered many new kinds of objects in the universe that were previously unknown.

The Radio Sky
An image of the radio skyThe image on the right shows the radio sky as if viewed from the North Pole of the earth. At first glance it looks similar to that of the night sky. You might imagine thousands of individual "radio stars" forming their own pattern of constella-tions and a radio Milky Way. These ''radio constellations'', however, would be com-pletely different from those seen with the naked eye. The sun, although the brightest source of radio waves, would not dominate the day-time sky, and the moon and planets would appear as bright radio stars moving among fixed radio stars.
Astronomers originally were puzzled by the nature of these radio stars. What celestial objects were producing the radio energy? Were the waves from nearby cool, dying stars, from clouds of hot gas, from particles of cold dust, from distant galaxies or from objects completely invisible with an optical telescope? Initially, measured positions of radio stars were so imprecise that on a corresponding photograph of the sky, made with the largest telescopes, it was impossible to tell which, if any of these objects, was the source of the radio emission. So unsure were astronomers about the origin of radio waves, they began using the term "radio source'' rather than "radio star".

Radio engineers and astronomers in Australia and Great Britain realized in the 1950' s that combining signals from several telescopes separated by many miles could simulate the resolution of a large radio telescope. These early arrays of two or three telescopes obtained more accurate positions of the strongest radio sources and some were finally identified with optical counterparts. Surprisingly, they were coincident with giant, distant galaxies, some more than one thousand million light years away. (One light year is about 6 million million miles). Many of these "radio galaxies", as they were named, were barely visible using the largest optical telescopes. In the 1960's more identifications were made, and some radio sources were coincident with star-like objects with peculiar properties. Astronomers soon discovered that these "Stars" were not stars, but the bright nuclei of very distant galaxies. These objects became known as ''quasars'', for quasi-stellar radio sources.

These first arrays showed that most of the radio emission from radio galaxies and quasars was emitted many thousands of light years outside of their parent galaxies, from regions which contained no stars and emitted no visible. What was producing the enormous quantities of radio waves in these dark regions outside the galaxies? To answer these questions, a large array had to be constructed.

THE VLA: The Most Powerful Radio Telescope
Shiva/ShiwanaIn 1961 the National Radio Astronomy Observatory began planning for a large array capable of producing ''photographs" of the radio sky which would provide as much detail as the best optical telescopes. Preliminary designs of this instrument, the Very Large Array (VLA), were studied in the 1960's, and a telescope array was built at the NRAO facility in Green Bank, West Virginia to test the technical designs. With the expertise of engineers and astronomers from many institutions around the world, NRAO submitted a formal proposal in January 1967 to the National Science Foundation for construction of the VLA.
In 1972 Congress authorized construction and appropriated initial funding. The preliminary stages of the project (detailed design of the telescope and electronics, bidding and contracting for materials, survey and preparation of the site) occupied most of 1973 and 1974. Major work at the site on the 7000-foot elevation Plains of San Agustin, 50 miles west of Socorro, NM, began in early 1975 and the first telescope was completed in September 1975. By the middle of 1977 five telescopes were opera-tional, and useful astronomical observations began. These early scientific observations were crucial to progress of the project since they provided severe performance tests of the telescopes, the electronics and supporting computer software. Engineers, computer scientists, and astronomers worked hand-in-hand during the mid-construction phase to refine the instrument.

The 28th, and last telescope, was constructed in 1979, and the fully completed VLA was dedicated on October 10, 1980. Even during the ceremony the VLA was produc-ing radio images of unparalleled quality and in record time. When the VLA was approved in 1972 its estimated cost was 76 million dollars. Even though it was built during an era of double-digit inflation and its performance has exceeded specifications in every way, the VLA was completed essentially within its original budget at a total cost of 78.6 million dollars.

Our Milky Way Galaxy
From afar our galaxy looks like a flat pancake with prominent spiral arms. It contains about 100 billion stars, glowing hydrogen gas, and small, dense cold clouds which con-tain simple molecules and grains of dust. Most of the stars are similar to the sun but are too distant to be detected by existing radio telescopes. Strong radio signals in our galaxy do come from interacting binary star systems, huge clouds of gas, stars in their infancy or stars that explosively complete their evolution. Near the center of our galaxy there is something which emits a large amount of radio energy. Its nature is still unknown; it may be a black hole or a compact cluster of a million stars.

 The Orion Nebula - Optical View   The Orion Nebula - Radio View

On a clear winter's night, the Orion Nebula can be seen just below Orion's belt. The red light is produced by a hydrogen cloud which is heated by four young stars within it. The cloud is shrinking under its own gravity, and it will continue to form stars over the next million years. Filaments and loops at the edge of the Nebula are caused by shock waves moving through the gas. These shocks are produced by strong winds from embryonic stars.

The radio photograph of the Nebula has a similar form to that of the optical photograph, because hot hydrogen gives off both light and radio waves. The colors represent the intensity of radio emission from red (brightest) to yellow, green, blue and black. From a comparison of the two images, astronomers can estimate the temperature in the cloud, its thickness, density, and dust content.

The Birth of a Star
Astronomers believe that supernovae are associated with the violent death of very massive stars. When thermonuclear reactions in the center of these stars exhaust their fuel (mostly hydrogen and helium), stellar material can no longer support itself, and within a matter of minutes, the star collapses under its own gravity. This infall heats up the interior to 100 million degrees and heavy elements are quickly produced in nuclear reactions. As a result, shock waves are created which move outwards from the interior expelling most of the material into space, contaminating the cosmic environment. This material is rich in heavy elements and metals (e.g. oxygen, sulfur, silicon, and iron) which will be eventually recycled into new stars. All of the material in the universe, except hydrogen and helium, was created billions of years ago in supernovae.

Supernova Remanant - Optical   Supernova Remnant - Radio

The brightest radio source in the sky, Cassiopeia A, was produced by ejected material of a supernova which occurred in 1680 and which has now expanded to 12 light years in diameter. New clues to understanding the cataclysmic death of massive stars are captured in the supercomputer-processed radio image. A powerful explosion blew off the star's outer layers and as the material moves outward in an expanding shell at 4000 km/s, it emits radio energy when it collides with clumpy interstellar material. The regions where the most energetic collisions are occurring also emit light as well as radio waves. The optical photograph contains many faint stars, which are in the direction of the supernova; none of them are a relic of the catastrophe.

Questions Commonly Asked About The VLA
   Who owns and operates the VLA?
   What is the purpose of NRAO?
   Who uses the VLA?
   Why is the VLA located on the Plains of San Augustin?
   When does the VLA operate?
   How does an astronomer use the VLA?
   Why are the telescopes moved to different locations?
   Do the telescopes always point in the same direction?
   Is the VLA listening for extra-terrestrial signals?
   What is NRAO's relationship with NASA and the space program?
   Technical Information!
   Antenna Configuration!
   Antenna Specifications!
The Very Long Baseline Array
Very Long Baseline ArrayIn order to probe into the heart of the nucleus of a radio galaxy where massive objects produce enormous amounts of energy and spew out matter at nearly the speed of light, a resolution of more than a hundred-fold over that of the VLA is needed. Such resolution requires telescopes to be many thousands of miles apart. Although experiments of this type, called Very Long Baseline Interferometry (VLBI), have been carried out since 1967 on existing telescopes around the world, there is no dedicated array which is routinely used for this purpose.

The NRAO is in process of building a dedicated VLBA of ten telescopes, exclusively for the high resolution imaging of radio sources. The center for operations of the VLBA will be in Socorro, NM and its operation will be combined with that of the VLA in the Array Operations Center, recently built on the campus of the New Mexico Institute of Mining and Technology. Although it would be possible to use satellite or other continental networking systems to transport the data from each telescope to a central location for processing, the data rate will be so large that 20,000 continuous inter-continental telephone lines would be required. Instead, the radio signals will be recorded on videotape, similar to that used to record TV programs, then shipped to the NRAO in Socorro, where the tapes will be played back to produce, ultimately, a radio image of unprecedented resolution and detail.

Site Gallery - Aerial View of VLA
Center view Looking South North Arm
Overhead Tight Center View Tres Mont
Twilight Wide View
Images courtesy of NRAO
Site Gallery - Ground View of VLA
Approaching the dish At the dish Front of dish
Back of dish Side view of dish Moving a dish
Dishes inline At sunset Wintertime
For More Information
NRAO VLA Home Page
Visiting the VLA
Magdalena, NM Home Page

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