The technique of diagnosing the properties of two or more waves by studying the pattern of interference, which is the superposition of two or more waves that results in a new wave pattern. Astronomers use this technique to combine the signals from two or more telescopes to produce images that are much sharper than those obtained by a single telescope. The technique is most often applied to radio astronomy, in which up to 30 or more radio dishes are combined into a single array. Optical interferometers, which are more difficult to align and operate, are also becoming more common.