The Sydney University Stellar Interferometer (SUSI) was an optical long baseline

interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

owned by The

University of Sydney The University of Sydney (USYD) is a public university, public research university in Sydney, Australia. Founded in 1850, it is the oldest university in both Australia and Oceania. One of Australia's six sandstone universities, it was one of the ...

. It was located in the

Paul Wild Observatory The Paul Wild Observatory, also known as the Narrabri Observatory and Culgoora Observatory, is an astronomical research facility located about 24 km west of Narrabri, New South Wales, Australia. It is the home of the Australia Telescope Compa ...

, 20 km west of

Narrabri Narrabri ( ) is a locality and seat of Narrabri Shire Local government in Australia, local government area in the North West Slopes, New South Wales, Australia on the Namoi River, northwest of Sydney. It sits on the junction of the Kamilaroi Hi ...

town in

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. SUSI was initially proposed by Australian astronomer John Davis in 1985, who led the project through to completion in 1993 and past his retirement in 1996 until his death in 2010. From then until its closure in 2017 it was led by Peter Tuthill, and used as a test facility for instruments for the

CHARA Array The CHARA (Center for High Angular Resolution Astronomy) array is an optical interferometer, located on Mount Wilson, California. The array consists of six telescopes operating as an astronomical interferometer. Construction was completed in ...

. The

had several

siderostats A heliostat () is a device that reflects sunlight toward a target, turning to compensate for the Sun's apparent motion. The reflector is usually a plane mirror. The target may be a physical object, distant from the heliostat, or a directi ...

, which collected and reflected starlight into the optical laboratory for interferometry via two vacuum pipes. Although mirrors at the siderostats were 20 cm in diameter, the effective aperture size was 14 cm as they operated at angles of about 45°. By selecting the different siderostats at different distances, the baseline of the interferometer could be varied between 5m and 640m. With beam-combining instruments that operated at visible wavelengths (~550-850 nm), SUSI had an

angular resolution Angular resolution describes the ability of any image-forming device such as an Optical telescope, optical or radio telescope, a microscope, a camera, or an Human eye, eye, to distinguish small details of an object, thereby making it a major det ...

of up to ~0.7mas (

milliarcseconds A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

References

Interferometers Optical telescopes {{observatory-stub