A group of 27 radio telescopes, each 25 meters (82 feet) in diameter, spaced as much as 13 miles apart from each other in Socorro, New Mexico, is known as the Very Large Array (VLA). The signals from this group of radio telescopes are combined by a computer. Constructive and destructive interference between the signals allows the array to make very accurate measurements of the location and size of objects.

Larger still are Very Long Baseline Interferometry radio telescopes. These radio telescopes are located around the world. Cables can’t be used to combine the signals, so each telescope needs a very precise clock to determine the arrival time of the signals. Hydrogen masers, whose frequency is stable one part in a million billion, are used. Again, although the signal strength is small, the wide spacing increases the effectiveness of using interference to measure very fine details of the shape, size, and location of stars and galaxies.