Interferometry is the use and analysis of superimposed electromagnetic radiation waves. The patterns produced by waves from slightly different directions or wavelengths include information about relative directions and wavelengths. A device carrying out this function is called an interferometer.
Radio astronomy makes much use of interferometry (radio interferometry), using multiple radio telescopes (dishes) to achieve a higher angular resolution. Keck Observatory and other twin/multiple telescopes can be used for interferometry of visible light (optical interferometry). A type of imaging spectrograph, the imaging Fourier transform spectroscopy makes use of a type of interferometry.
Gravitational-wave detectors such as LISA also use interferometry to measure the extremely short distances involved.