- Technique in which interferometers are used for astronomical observation. Radio and optical astronomy both make use of interferometry. In radio astronomy, interferometry can be practised on a massive scale by combining the signals from radio telescopes hundreds or even thousands of kilometres apart. This is known as Very Long baseline Interferometry or VLBI. It has even been tried with one antenna in orbit, on the former Soviet Union’s Salyut space station. The Very Large Array (VLA) in the US is the world’s largest purpose-built VLBI system.