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.
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, Astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space–what they are, rather than where they are." Among the subjects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.
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. The array has been constructed on the 5,000 m (16,000 ft) elevation Chajnantor plateau – near the Llano de Chajnantor Observatory and the Atacama Pathfinder Experiment. This location was chosen for its high elevation and low humidity, factors which are crucial to reduce noise and decrease signal attenuation due to Earth's atmosphere. ALMA provides insight on star birth during the early Stelliferous era and detailed imaging of local star and planet formation.
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 Large Millimeter Telescope (LMT), officially the Large Millimeter Telescope Alfonso Serrano, is the world's largest single-aperture telescope in its frequency range, built for observing radio waves in the wave lengths from approximately 0.85 to 4 mm. It has an active surface with a diameter of 50 metres (160 ft) and 1,960 square metres (21,100 sq ft) of collecting area.
The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength radio telescope at Mauna Kea Observatory in Hawaii, US. The telescope is near the summit of Mauna Kea at 13,425 feet (4,092 m). Its primary mirror is 15 metres across: it is the largest single-dish telescope that operates in submillimetre wavelengths of the electromagnetic spectrum. Scientists use it to study the Solar System, interstellar dust and gas, and distant galaxies.
The Submillimeter Array (SMA) consists of eight 6-meter (20 ft) diameter radio telescopes arranged as an interferometer for submillimeter wavelength observations. It is the first purpose-built submillimeter interferometer, constructed after successful interferometry experiments using the pre-existing 15-meter (49 ft) James Clerk Maxwell Telescope and 10.4-meter (34.1 ft) Caltech Submillimeter Observatory as an interferometer. All three of these observatories are located at Mauna Kea Observatory on Mauna Kea, Hawaii, and have been operated together as a ten element interferometer in the 230 and 345 GHz bands. The baseline lengths presently in use range from 16 to 508 meters. The radio frequencies accessible to this telescope range from 194–408 gigahertz (1.545–0.735 mm) which includes rotational transitions of dozens of molecular species as well as continuum emission from interstellar dust grains. Although the array is capable of operating both day and night, most of the observations take place at nighttime when the atmospheric phase stability is best.
Owens Valley Radio Observatory (OVRO) is a radio astronomy observatory located near Big Pine, California (US) in Owens Valley. It lies east of the Sierra Nevada, approximately 350 kilometers (220 mi) north of Los Angeles and 20 kilometers (12 mi) southeast of Bishop. It was established in 1956, and is owned and operated by the California Institute of Technology (Caltech). The Owens Valley Solar Array portion of the observatory has been operated by New Jersey Institute of Technology (NJIT) since 1997.
The Combined Array for Research in Millimeter-wave Astronomy (CARMA) was an astronomical instrument comprising 23 radio telescopes, dedicated in 2006. These telescopes formed an astronomical interferometer where all the signals are combined in a purpose-built computer to produce high-resolution astronomical images. The telescopes ceased operation in April 2015 and were relocated to the Owens Valley Radio Observatory for storage.
Institut de Radioastronomie Millimetrique (IRAM) is an international research institute and Europe's leading center for radio astronomy at millimeter wavelengths. Its mission is to explore the universe, study its origins and its evolution with two of the most advanced radio facilities in the world:
The Atacama Pathfinder Experiment (APEX) is a radio telescope 5,064 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert in northern Chile, 50 km east of San Pedro de Atacama built and operated by 3 European research institutes. The main dish has a diameter of 12 m and consists of 264 aluminium panels with an average surface accuracy of 17 micrometres (rms). The telescope was officially inaugurated on September 25, 2005.
The Plateau de Bure Interferometer (PdBI) was a six-antenna interferometer on the Pic de Bure (2550 m) in the French Alps, operated by the Institut de radioastronomie millimétrique. In 2014, it has been replaced by the Northern Extended Millimeter Array. It was specifically designed for millimetre-wave observations and specialises in studies of line emission from molecular gas and radio continuum of cold dust.
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, called baseline, 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.
Rainer Mauersberger is a German astronomer. His main field of interest is observational molecular spectroscopy of the interstellar matter in galactic and extragalactic star forming regions; millimeter and sub-millimeter astronomy. He is the scientific coordinator of the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics, a collaboration between the Max Planck Institute for Radio Astronomy in Bonn and the Universities of Bonn and Cologne. He teaches as a Privatdozent (lecturer) at Bonn University. He received his PhD from the University of Bonn using the Max Planck Institute for Radio Astronomy Effelsberg 100-m Radio Telescope to measure ammonia throughout the galaxy. The galactic and extragalactic cold interstellar medium remained his main field of investigation while he was working at the Sub-mm Telescope Observatory in Arizona and Pico Veleta Observatory in Granada (Spain), where he served as the station manager for nine years.
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.
The Large Latin American Millimeter Array (LLAMA) is a single-dish 12 m Nasmyth optics antenna which is under construction in the Puna de Atacama desert in the Province of Salta, Argentina, next to the Qubic experiment. The primary mirror accuracy will allow observation from 40 GHz up to 900 GHz. After installation it will be able to join other similar instruments to perform Very Large Base Line Interferometry or to work in standalone mode. Financial support is provided by the Argentinian and Brazilian governments. The total cost of construction, around US$20 million, and operation as well as the telescope time use will be shared equally by the two countries. Construction planning started in July 2014 after the formal signature of an agreement between the main institutions involved.
The Northern Extended Millimeter Array (NOEMA) is one of the largest astronomical facilities on European ground and the most powerful radio telescope in the Northern Hemisphere operating at millimeter wavelengths. It consists of a large array of twelve 15-meter antennas that can spread over distances of up to 1.7 kilometers, working together as a single telescope.
Related media on Commons 
