Navy Precision Optical Interferometer

NPOI is a collaborative effort between the U.S. Naval Observatory, the Naval Research Laboratory, and Lowell Observatory.

With the world’s largest baseline among optical interferometers, the Navy Precision Optical Interferometer (NPOI) can record images of stars that show them as disks, and it can 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 U.S. Naval Observatory uses as a reference system for the determination of positions on Earth and in space and for global positioning systems (GPS) and monitoring time-keeping.

Instead of using a single primary mirror, NPOI combines the light from an array of up to six mirrors spaced tens of meters apart by precisely directing all the beams of light to a single focus. NPOI is aligned in a 3-armed “Y” pattern, with each arm extending for 250 meters (820 feet). Each arm contains a network of mirrors and associated equipment for collecting light, which is then directed through pipes that have been evacuated of air. The light is eventually carried to a facility where the collected light from each mirror is combined to form a single image. Extraordinary stellar image detail can be derived from the resulting data, called an interference pattern.

See How It Works