The Infrared Spatial Interferometer (ISI) is an

astronomical interferometer An astronomical interferometer or telescope array is a set of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope to provide higher resolution images of astronomical objects such as stars, n ...

array of three telescopes operating in the mid-

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

. The telescopes are fully mobile and their site on Mount Wilson allows for placements as far as apart, giving the resolution of a telescope of that diameter. The signals are converted to radio frequencies through

heterodyne A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called ''heterodyning'', which was invented by Canadian inventor-engineer Reginald Fessenden. Heterodyning is us ...

circuits and then combined electronically using techniques copied from

radio astronomy Radio astronomy is a subfield of astronomy that studies Astronomical object, celestial objects using radio waves. It started in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observat ...

. ISI is operated by the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a Public university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...

Space Sciences Laboratory The Space Sciences Laboratory (SSL) is an Organized Research Unit (ORU) of the University of California, Berkeley. Founded in 1959, the laboratory is located in the Berkeley Hills above the university campus. It has developed and continues to ...

. The longest () baseline provides a resolution of 0.003

arcsecond 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 ...

at a

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

of 11

micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

s. On 9 July 2003, ISI recorded the first

closure phase The closure phase is an observable quantity in imaging astronomical interferometry, which allowed the use of interferometry with very long baselines. It forms the basis of the self-calibration approach to interferometric imaging. The observable ...

aperture synthesis Aperture synthesis or synthesis imaging is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as an instrument the size of the entire collection. At each separation and ...

measurements in the mid infrared.

References

{{Portal, Spaceflight

External links

* https://web.archive.org/web/20071215183003/http://isi.ssl.berkeley.edu/ Infrared telescopes Interferometric telescopes