The Navy Precision Optical Interferometer is a highly specialized telescope capable of extremely high-precision measurements.
Interferometers are not like conventional reflecting telescopes such as the DCT or the Perkins. Instead of employing a single primary mirror, NPOI uses an array of up to six mirrors spaced tens to hundreds of meters apart to precisely direct up to six beams of light from a star to a point. Extraordinary image detail can be derived from the resulting data.
NPOI can record images of stars and optically separate distant pairs of stars so close together that they appear as a single star in even the largest conventional telescopes. NPOI has the ability to measure the precise relative positions of stars across the sky which the Naval Observatory uses as a reference system for the determination of positions on earth and in space and for monitoring time keeping. When finished, the interferometer will span the distance of over four football field lengths, 430 meters.