A technique in which two waves, usually of electromagnetic radiation; such as, light or radio waves, are combined to produce an interference pattern.

Radiation from a distant source can be analyzed by this method, and very small angles can be accurately determined.

A technique for obtaining better images of celestial bodies by taking a series of rapid photographic exposures of the object.

This enables the effect of scintillation to be minimized.

The technique of linking together several radio telescopes spaced by hundreds and even thousands of miles to achieve very high resolution observations of distant objects; such as, quasars.