How does the Very Large Array use 27 dishes to make high-resolution images?

The Very Large Array (VLA) achieves high-resolution imaging through a process known as aperture synthesis or radio interferometry. By using 27 independent parabolic dishes, the system functions as a single, massive telescope with an effective diameter of up to 36 km (22 miles).123

The process works as follows:

• Interferometry: Each pair of antennas acts as an interferometer, measuring a specific "Fourier component" of the radio source's brightness distribution. As the Earth rotates, the changing orientation of the antennas relative to the source allows the array to sample a sufficient number of these components to reconstruct a complete image.1
• Data Integration: The radio signals recorded by the 27 dishes are integrated by high-speed computers. These computers perform complex mathematical calculations, specifically the fast Fourier transform (FFT), to convert the interference data into high-resolution images.21
• Configuration: The dishes are mounted on transporters and can be moved along a Y-shaped rail pattern. By changing the physical spacing of the antennas, astronomers can adjust the array's resolution to suit different observational needs.2

This technique allows the VLA to achieve an angular resolution better than a tenth of an arc second, providing image quality that is impossible to obtain with a single, smaller dish.21