On the Plains of San Agustin in New Mexico, 27 dishes each weighing 230 tons sit on railroad tracks in a giant Y with 13-mile arms, and they move. This episode explores the Karl G. Jansky Very Large Array and the technique of aperture synthesis interferometry that lets separate antennas act as one enormous instrument. We explain how measuring tiny time delays across 351 antenna pairs builds an image, why the array is reconfigured every three to four months between its A and D layouts, and what a resolution of 0.04 arcseconds actually means.

We then cover what the VLA sees at centimeter wavelengths that optical telescopes cannot: magnetic filaments at the galactic center, protoplanetary disks, synchrotron radiation from black hole jets, the faint 1989 transmission from Voyager 2 at Neptune, a SETI search of nearby galaxies, and the VLA Sky Survey expected to catalog 10 million new objects. We trace the history from David Heeschen’s 16-year effort and the 1972 congressional approval through the 2001 to 2012 expansion that replaced the electronics and correlator, and look ahead to the proposed 2 billion dollar Next Generation VLA with over 260 antennas spanning multiple states, countries, and a peak in Germany.

• How linking dishes and measuring arrival-time differences creates a virtual city-sized telescope
• Configurations A through D and the tradeoff between fine resolution and broad sensitivity
• Why radio waves pass through cosmic dust and what that reveals about star formation and black holes
• The EVLA upgrade that expanded capability by a factor of up to 8,000 without new dishes
• Visiting the site off US Route 60, from the self-guided tour to the Bracewell radio sundial