A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects, just as optical telescopes are the main observing instrument used in traditional optical astronomy which studies the light wave portion of the spectrum coming from astronomical objects. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observations have identified a number of different sources of radio emission. These include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers. The discovery of the cosmic microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy.
Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. The distance between the radio telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.
The Multi-Element Radio Linked Interferometer Network (MERLIN) is an interferometer array of radio telescopes spread across England. The array is run from Jodrell Bank Observatory in Cheshire by the University of Manchester on behalf of Science and Technology Facilities Council (STFC).
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 orientation, the lobe-pattern of the interferometer produces an output which is one component of the Fourier transform of the spatial distribution of the brightness of the observed object. The image of the source is produced from these measurements. Astronomical interferometers are commonly used for high-resolution optical, infrared, submillimetre and radio astronomy observations. For example, the Event Horizon Telescope project derived the first image of a black hole using aperture synthesis.
Onsala Space Observatory (OSO), the Swedish National Facility for Radio Astronomy, provides scientists with equipment to study the Earth and the rest of the Universe. The observatory operates two radio telescopes in Onsala, 45 km south of Gothenburg, and takes part in several international projects. Examples of activities:
The Joint Institute for Very Long Baseline Interferometry European Research Infrastructure Consortium (JIVE) was established by a decision of the European Commission in December 2014, and assumed the activities and responsibilities of the JIVE foundation, which was established in December 1993. JIVE's mandate is to support the operations and users of the European VLBI Network (EVN), in the widest sense.
The Westerbork Synthesis Radio Telescope (WSRT) is an aperture synthesis interferometer built on the site of the former World War II Nazi detention and transit camp Westerbork, north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands.
ASTRON is the Netherlands Institute for Radio Astronomy. Its main office is in Dwingeloo in the Dwingelderveld National Park in the province of Drenthe. ASTRON is part of the institutes organization of the Dutch Research Council (NWO).
Haystack Observatory is a multidisciplinary radio science center, ionospheric observatory, and astronomical microwave observatory owned by Massachusetts Institute of Technology (MIT). It is located in Westford, Massachusetts (US), approximately 45 kilometers (28 mi) northwest of Boston. Haystack was initially built by MIT's Lincoln Laboratory for the United States Air Force and was known as Haystack Microwave Research Facility. Construction began in 1960, and the antenna began operating in 1964. In 1970 the facility was transferred to MIT, which then formed the Northeast Radio Observatory Corporation (NEROC) with a number of other universities to operate the site as the Haystack Observatory. As of January 2012, a total of nine institutions participated in NEROC.
The Hartebeesthoek Radio Astronomy Observatory (HartRAO) is a radio astronomy observatory, located in a natural bowl of hills at Hartebeesthoek just south of the Magaliesberg mountain range, Gauteng, South Africa, about 50 km west of Johannesburg. It is a National Research Facility run by South Africa's National Research Foundation. HartRAO was the only major radio astronomy observatory in Africa until the construction of the KAT-7 test bed for the future MeerKAT array.
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, nebulas and galaxies by means of interferometry. 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 main drawback is that it does not collect as much light as the complete instrument's mirror. Thus it is mainly useful for fine resolution of more luminous astronomical objects, such as close binary stars. Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array.
The Dominion Radio Astrophysical Observatory is a research facility founded in 1960 and located at Kaleden, British Columbia, Canada. The site houses four radio telescopes: an interferometric radio telescope, a 26-m single-dish antenna, a solar flux monitor, and the Canadian Hydrogen Intensity Mapping Experiment (CHIME) — as well as support engineering laboratories. The DRAO is operated by the Herzberg Institute of Astrophysics of the National Research Council of the Government of Canada. The observatory was named an IEEE Milestone for first radio astronomical observations using VLBI.
Spektr-R was a Russian scientific satellite with a 10 m (33 ft) radio telescope on board. It was launched on 18 July 2011 on a Zenit-3F launcher from Baikonur Cosmodrome, and was designed to perform research on the structure and dynamics of radio sources within and beyond the Milky Way. Together with some of the largest ground-based radio telescopes, the Spektr-R formed interferometric baselines extending up to 350,000 km (220,000 mi).
In optical astronomy, interferometry is used to combine signals from two or more telescopes to obtain measurements with higher resolution than could be obtained with either telescopes individually. This technique is the basis for astronomical interferometer arrays, which can make measurements of very small astronomical objects if the telescopes are spread out over a wide area. If a large number of telescopes are used a picture can be produced which has resolution similar to a single telescope with the diameter of the combined spread of telescopes. These include radio telescope arrays such as VLA, VLBI, SMA, LOFAR and SKA, and more recently astronomical optical interferometer arrays such as COAST, NPOI and IOTA, resulting in the highest resolution optical images ever achieved in astronomy. The VLT Interferometer is expected to produce its first images using aperture synthesis soon, followed by other interferometers such as the CHARA array and the Magdalena Ridge Observatory Interferometer which may consist of up to 10 optical telescopes. If outrigger telescopes are built at the Keck Interferometer, it will also become capable of interferometric imaging.
The OVRO 40 meter Telescope is a radio telescope at the Owens Valley Radio Observatory near Big Pine, California, US. It is owned and operated by Caltech. The telescope is easily visible from the section of US highway 395 just north of Big Pine.
The Event Horizon Telescope (EHT) is a large telescope array consisting of a global network of radio telescopes. The EHT project combines data from several very-long-baseline interferometry (VLBI) stations around Earth, which form a combined array with an angular resolution sufficient to observe objects the size of a supermassive black hole's event horizon. The project's observational targets include the two black holes with the largest angular diameter as observed from Earth: the black hole at the center of the supergiant elliptical galaxy Messier 87, and Sagittarius A* at the center of the Milky Way.
KAT-7 is a radio telescope situated in the Meerkat National Park, in the Northern Cape of South Africa. Part of the Karoo Array Telescope project, it is the precursor engineering test bed to the larger MeerKAT telescope, but it has become a science instrument in its own right. The construction was completed in 2011 and commissioned in 2012. It also served as a technology demonstrator for South Africa's bid to host the Square Kilometre Array. KAT-7 is the first Radio telescope to be built with a composite reflector and uses a stirling pump for 75 K cryogenic cooling. The telescope was built to test various system for the MeerKAT array, from the ROACH correlators designed and manufactured in Cape Town, now used by various telescopes internationally, to composite construction techniques. With the short baselines the telescope is suited to observing diffuse sources, but will begin VLBI observation in 2013.
The Korean VLBI Network (KVN) is a radio astronomy observatory located in South Korea. It comprises three 21-meter radio telescopes that function as an interferometer, using the technique of very-long-baseline interferometry (VLBI).
Johann Anton Zensus is a German radio astronomer. He is director at the Max Planck Institute for Radio Astronomy (MPIfR) and honorary professor at the University of Cologne. He is chairman of the collaboration board of the Event Horizon Telescope (EHT). The collaboration announced the first image of a black hole in April 2019.
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