Astronomical interferometer

astronomical interferometryinterferometerinterferometrystellar interferometerinterferometrictelescope arrayArrayinterferometer arrayRadio interferometrybaseline
An astronomical interferometer is an array 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, nebulas and galaxies by means of interferometry.wikipedia
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Very-long-baseline interferometry

very long baseline interferometryVLBIlong-baseline interferometry
In Very Long Baseline Interferometry (VLBI) radio telescopes separated by thousands of kilometers are combined to form a radio interferometer with a resolution which would be given by a hypothetical single dish with an aperture thousands of kilometers in diameter.
Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy.

Radio astronomy

radio astronomerradioradioastronomy
Interferometry is most widely used in radio astronomy, in which signals from separate radio telescopes are combined.
Radio astronomy is conducted using large radio antennas referred to as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis.

Aperture synthesis

aperture synthesis imagingsynthetic apertureinterferometric imaging
A mathematical signal processing technique called aperture synthesis is used to combine the separate signals to create high-resolution images.
Astronomical interferometers are commonly used for high-resolution optical, infrared, submillimetre and radio astronomy observations.

Michelson stellar interferometer

One of the first uses of optical interferometry was applied by the Michelson stellar interferometer on the Mount Wilson Observatory's reflector telescope to measure the diameters of stars.
The Michelson stellar interferometer is one of the earliest astronomical interferometers built and used.

Atacama Large Millimeter Array

ALMAAtacama Large Millimeter/Submillimeter Array (ALMA)Atacama Large Millimeter/submillimeter Array
For the next three decades astronomical interferometry research was dominated by research at radio wavelengths, leading to the development of large instruments such as the Very Large Array and the Atacama Large Millimeter Array.
The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths.

Very Large Array

VLAEVLAD. S. Heeschen
For the next three decades astronomical interferometry research was dominated by research at radio wavelengths, leading to the development of large instruments such as the Very Large Array and the Atacama Large Millimeter Array.
The VLA comprises twenty-seven 25-meter radio telescopes deployed in a Y-shaped array and all the equipment, instrumentation, and computing power to function as an interferometer.

Closure phase

closure phasesclosure-phasemathematical methods
Software packages such as BSMEM or MIRA are used to convert the measured visibility amplitudes and closure phases into astronomical images. A number of other interferometers have made closure phase measurements and are expected to produce their first images soon, including the VLTI, the CHARA array and Le Coroller and Dejonghe's Hypertelescope prototype.
The closure phase is an observable quantity in imaging astronomical interferometry, which allowed the use of interferometry with very long baselines.

Infrared Spatial Interferometer

ISI
The same techniques have now been applied at a number of other astronomical telescope arrays, including the Navy Prototype Optical Interferometer, the Infrared Spatial Interferometer and the IOTA array.
The Infrared Spatial Interferometer (ISI) is an astronomical interferometer array of three 65 inch (1.65 m) telescopes operating in the mid-infrared.

Infrared Optical Telescope Array

IOTA
The same techniques have now been applied at a number of other astronomical telescope arrays, including the Navy Prototype Optical Interferometer, the Infrared Spatial Interferometer and the IOTA array.
The Infrared Optical Telescope Array (IOTA) was a stellar interferometer array.

Angular resolution

spatial resolutionresolutionresolved
The advantage of this technique is that it can theoretically produce images with the angular resolution of a huge telescope with an aperture equal to the separation between the component telescopes.
The highest angular resolutions can be achieved by arrays of telescopes called astronomical interferometers: These instruments can achieve angular resolutions of 0.001 arcsecond at optical wavelengths, and much higher resolutions at x-ray wavelengths.

Astronomical seeing

seeingatmospheric seeingatmospheric turbulence
At optical wavelengths, aperture synthesis allows the atmospheric seeing resolution limit to be overcome, allowing the angular resolution to reach the diffraction limit of the optics.
4) Atmospheric seeing causes the fringes in an astronomical interferometer to move rapidly

Infrared astronomy

infraredinfrared radiationJ, H, and K s bands
At the shorter wavelengths used in infrared astronomy and optical astronomy it is more difficult to combine the light from separate telescopes, because the light must be kept coherent within a fraction of a wavelength over long optical paths, requiring very precise optics.
To achieve higher angular resolution, some infrared telescopes are combined to form astronomical interferometers.

Antoine Émile Henry Labeyrie

Antoine LabeyriehypertelescopeLabeyrie
Instead, most existing arrays use a planar geometry, and Labeyrie's hypertelescope will use a spherical geometry. A number of other interferometers have made closure phase measurements and are expected to produce their first images soon, including the VLTI, the CHARA array and Le Coroller and Dejonghe's Hypertelescope prototype. Current projects will use interferometers to search for extrasolar planets, either by astrometric measurements of the reciprocal motion of the star (as used by the Palomar Testbed Interferometer and the VLTI), through the use of nulling (as will be used by the Keck Interferometer and Darwin) or through direct imaging (as proposed for Labeyrie's Hypertelescope).
He is working with the Hypertelescope Lise association, which aims to develop an extremely large astronomical interferometer with spherical geometry that might theoretically show features on Earth-like worlds around other suns, as its president.

Mount Wilson Observatory

Mount WilsonMt. WilsonHooker Telescope
One of the first uses of optical interferometry was applied by the Michelson stellar interferometer on the Mount Wilson Observatory's reflector telescope to measure the diameters of stars.
In 1919 the Hooker telescope was equipped with a special attachment, a 6-meter optical astronomical interferometer developed by Albert A. Michelson, much larger than the one he had used to measure Jupiter's satellites.

Cambridge Optical Aperture Synthesis Telescope

COASTan array of separate optical telescopesCambridge Optical Aperture Synthesis Telescope (COAST)
In 1995 this technique was demonstrated on an array of separate optical telescopes for the first time, allowing a further improvement in resolution, and allowing even higher resolution imaging of stellar surfaces. Notable 1990s results included the Mark III measurement of diameters of 100 stars and many accurate stellar positions, COAST and NPOI producing many very high resolution images, and Infrared Stellar Interferometer measurements of stars in the mid-infrared for the first time.
COAST, the Cambridge Optical Aperture Synthesis Telescope, is a multi-element optical astronomical interferometer with baselines of up to 100 metres, which uses aperture synthesis to observe stars with angular resolution as high as one thousandth of one arcsecond (producing images with much higher resolution than can be obtained using individual telescopes such as the Hubble Space Telescope).

Mark III Stellar Interferometer

Mark III
Notable 1990s results included the Mark III measurement of diameters of 100 stars and many accurate stellar positions, COAST and NPOI producing many very high resolution images, and Infrared Stellar Interferometer measurements of stars in the mid-infrared for the first time.
The Mark III Stellar Interferometer was a long-baseline optical astronomical interferometer, located at the Mount Wilson Observatory, California, United States.

Very Large Telescope

VLTNACOVLTI
A number of other interferometers have made closure phase measurements and are expected to produce their first images soon, including the VLTI, the CHARA array and Le Coroller and Dejonghe's Hypertelescope prototype. Current projects will use interferometers to search for extrasolar planets, either by astrometric measurements of the reciprocal motion of the star (as used by the Palomar Testbed Interferometer and the VLTI), through the use of nulling (as will be used by the Keck Interferometer and Darwin) or through direct imaging (as proposed for Labeyrie's Hypertelescope).
The VLT consists of an arrangement of four large (8.2 metre diameter) telescopes (called Unit Telescopes or UTs) with optical elements that can combine them into an astronomical interferometer (VLTI), which is used to resolve small objects.

Darwin (spacecraft)

DarwinDarwin14
Current projects will use interferometers to search for extrasolar planets, either by astrometric measurements of the reciprocal motion of the star (as used by the Palomar Testbed Interferometer and the VLTI), through the use of nulling (as will be used by the Keck Interferometer and Darwin) or through direct imaging (as proposed for Labeyrie's Hypertelescope).
The most recent design envisaged three free-flying space telescopes, each three to four metres in diameter, flying in formation as an astronomical interferometer.

Interferometry

interferometerinterferometricoptical interferometry
An astronomical interferometer is an array 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, nebulas and galaxies by means of interferometry.
An astronomical interferometer consists of two or more separate telescopes that combine their signals, offering a resolution equivalent to that of a telescope of diameter equal to the largest separation between its individual elements.

European Southern Observatory

ESOEuropean Southern Observatory (ESO)ESO Countries
Engineers at the European Southern Observatory ESO designed the Very Large Telescope VLT so that it can also be used as an interferometer.
APEX is a precursor of ALMA (the Atacama Large Millimeter Array), an astronomical interferometer which ESO and its international partners is building on the Chajnantor plateau.

Navy Precision Optical Interferometer

NPOIOutrigger TelescopesNavy Optical Interferometer
The same techniques have now been applied at a number of other astronomical telescope arrays, including the Navy Prototype Optical Interferometer, the Infrared Spatial Interferometer and the IOTA array. Notable 1990s results included the Mark III measurement of diameters of 100 stars and many accurate stellar positions, COAST and NPOI producing many very high resolution images, and Infrared Stellar Interferometer measurements of stars in the mid-infrared for the first time.
The Navy Precision Optical Interferometer (NPOI) is an American astronomical interferometer, with the world's largest baselines, operated by the Naval Observatory Flagstaff Station (NOFS) in collaboration with the Naval Research Laboratory (NRL) and Lowell Observatory.

Martin Ryle

Sir Martin RyleRyleM. Ryle
M. Ryle & D. Vonberg, 1946 Solar radiation on 175Mc/s, Nature 158 pp 339
In 1946 Ryle and Derek Vonberg were the first people to publish interferometric astronomical measurements at radio wavelengths.

Fast Fourier Transform Telescope

Max Tegmark and Matias Zaldarriaga have proposed the Fast Fourier Transform Telescope which would rely on extensive computer power rather than standard lenses and mirrors.
He noted that by using an array of small instruments it would be possible to measure the diameter of a star with the same precision as a single telescope which was as large as the whole array — a technique which later became known as astronomical interferometry.

Aperture masking interferometry

aperture maskaperture maskingAperture masks
This array of holes acts as a miniature astronomical interferometer.

Radio telescope

radio telescopesradiotelescoperadio-telescope
Interferometry is most widely used in radio astronomy, in which signals from separate radio telescopes are combined. An astronomical interferometer is an array 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, nebulas and galaxies by means of interferometry.