very long baseline interferometry (VLBI)

Very long baseline interferometry (VLBI) is a form of aperture synthesis in which the individual radio telescopes aren't directly connected together, but instead make their observations and record their data separately. At a later time, the data is sent to a central correlator and the signals combined. The advantage of this method is that the telescopes in the array can be arbitrarily far apart, (often on different continents) and so the technique provides the highest resolution images in astronomy, with beamwidths in the range 0.1–10 milliarcsecond (depending on the radio frequency).