Construction of the Very Large Array begins on New Mexico’s Plains of San Agustin

Story: 1973 C.E.  |  Last updated: January 1, 1973

In April 1973 C.E., workers broke ground on a remote stretch of high desert in New Mexico, beginning one of the most ambitious scientific construction projects in American history. The Very Large Array — 27 radio telescopes arranged in a giant “Y” across 23 miles of the Plains of San Agustin — would become humanity’s most powerful radio telescope and reshape what we know about the cosmos.

Key facts

• Very Large Array: Construction officially began in April 1973 C.E., following congressional approval in August 1972 C.E., with formal dedication completed in 1980 C.E.
• Radio telescope array: The VLA’s 27 active antennas — each an 82-foot dish — work together to function as a single telescope with an effective aperture of up to 23 miles across.
• Plains of San Agustin: The site’s remote desert location, ringed by mountains, was chosen to shield the antennas from human-made radio interference and atmospheric moisture that distorts faint cosmic signals.

A decade of groundwork before the groundbreaking

The road to construction had started well over a decade earlier. Astronomers at the National Radio Astronomy Observatory (NRAO) recognized in the early 1960s C.E. that single-dish telescopes, however large, had fundamental limits. To map faint cosmic structures with real precision, they needed an array — a coordinated group of antennas that could simulate a telescope miles wide.

NRAO built the Green Bank Interferometer as a stepping stone, using a four-element array throughout the 1960s and early 1970s C.E. to develop the communications, signal correlation, and atmospheric correction techniques a much larger array would require. That decade of patient, unglamorous engineering work made 1973 C.E. possible.

The site selection was as important as the engineering. Cosmic radio waves are billions of times fainter than the signals used in everyday broadcasting. Even a distant city’s radio emissions can overwhelm them. The Plains of San Agustin sit far from major population centers, and the surrounding mountains act as a natural barrier, blocking radio interference from cities hundreds of miles away. The region’s dry desert climate addressed another critical problem: water molecules distort radio waves and emit their own interference at certain frequencies, so low humidity was not a convenience — it was a scientific requirement.

Engineering the “Y”

The VLA’s iconic shape is pure function. Each of three arms holds nine antennas, giving the array three long baselines pointing in different directions simultaneously. The wider the array, the finer the detail it can resolve — so the “Y” maximizes both coverage and flexibility.

The antennas themselves don’t stay put. Three times a year, specially built transporters — 90-ton vehicles running on four railroad rails — pick up each 230-ton dish and carry it to a new position along the arms. Over 16 months, the VLA can stretch its legs from two-thirds of a mile to 23 miles, effectively zooming in or out on the universe depending on what astronomers need to study. The first antenna was placed on September 22, 1975 C.E., and the first interferometric observation followed in February 1976 C.E.

Lasting impact

The VLA was formally dedicated in 1980 C.E. and has since produced some of the most consequential observations in modern astronomy. It has mapped the center of the Milky Way, detected supermassive black holes, traced the structure of distant galaxies, and contributed to nearly every major branch of radio astronomy. The dataset it has generated underpins thousands of peer-reviewed studies.

Beyond its own discoveries, the VLA pioneered the technical and institutional frameworks that made even larger arrays conceivable. The techniques refined at the Plains of San Agustin informed the development of Very Long Baseline Interferometry (VLBI) and, eventually, global collaborations like the Event Horizon Telescope, which in 2019 C.E. produced the first direct image of a black hole. The VLA also played a role in early studies that shaped our understanding of cosmic ray sources and pulsar timing.

The observatory remains operational and scientifically productive. A major upgrade completed in 2012 C.E. expanded its frequency range and sensitivity by orders of magnitude, transforming it from a landmark instrument into a current-generation one. The Next Generation VLA (ngVLA), currently in development, is designed to extend that legacy further into this century.

Blindspots and limits

Radio astronomy — and the VLA specifically — developed primarily within a framework of U.S. federal funding and Cold War-era scientific priorities, which shaped what questions were asked and who had access to the tools. The observatory sits on land with deep ties to Indigenous peoples of New Mexico, including the Pueblo communities of the region, and the history of land use in the San Agustin basin deserves acknowledgment alongside the scientific achievement. Like all large-scale infrastructure science, the VLA also concentrates observational power in the hands of institutions with the resources to apply for telescope time — a structural inequality that the field has been slow to address.

A window that had always been open

The universe has been broadcasting radio waves for 13.8 billion years. It took humanity until the 1930s C.E. to realize it, and until 1973 C.E. to begin building an instrument large enough to truly listen. What the Very Large Array revealed — jets of plasma from distant galaxies, the magnetic structure of star-forming regions, the precise locations of objects billions of light-years away — was not created by the telescope. It was always there. The VLA simply gave us ears big enough to hear it.

Construction that April in the New Mexico desert was, in that sense, less a beginning than a culmination: of a decade of engineering preparation, centuries of curiosity about the sky, and the very long human habit of building better tools to understand a universe that keeps surprising us.

Read more

For more on this story, see: National Radio Astronomy Observatory — The VLA

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