A reconfigurable eye on the cosmos
On the Plains of San Agustin, 50 miles west of Socorro, New Mexico, is a collection of giant mechanical sunflowers. This is the Karl G. Jansky Very Large Array (VLA), a radio telescope comprised of 27 individual antennas. Each dish measures 25 meters (82 feet) in diameter and weighs 209 metric tons (230 short tons). Together, they operate as a single instrument. Authorized by Congress in 1972 with a budget of $78.5 million, the facility was officially inaugurated in 1980.
The VLA is an interferometer, a device that combines signals from multiple telescopes to achieve the resolution of a much larger one. The 27 antennas are arranged along a Y-shaped configuration, with three arms made of double railway tracks. Each arm stretches 21 kilometers (13 miles). A specially designed lifting locomotive, known as "Hein's Trein," can pick up and move the massive dishes along these tracks to various prepared positions. This reconfigurability is the VLA's main feature. Astronomers can change the array's size, acting as a zoom lens for radio waves. The observatory cycles through four standard configurations—designated A, B, C, and D—every 16 months. In the largest "A" configuration, the antennas are spread out over 36 kilometers (22 miles), providing an angular resolution as fine as 0.04 arcseconds. This is sharp enough to distinguish a golf ball from 150 kilometers (100 miles) away. In the most compact "D" configuration, all antennas are clustered within a 600-meter area, which maximizes sensitivity to faint, diffuse objects.