A radio telescope is an instrument, be observed with the astronomical objects that emit electromagnetic waves in the spectral range of the radio waves. Radio telescopes used in the radio astronomy.
After the discovery of the first extraterrestrial radio source by Karl Guthe Jansky in 1932, radio telescopes have been developed for observing the cosmos. The first radio telescope in parabolic shape of Grote Reber was, engineer and radio amateur in Wheaton, Illinois, built since Jansky discovery was initially not observed by the professional astronomy. In Germany the first radio telescope, the Astropeiler Stockert near Bad Münster Eifel, 1956 was established. It is a historical monument since 1999.
Westward German radar systems for air traffic control provided always false when the constellation Cygnus (Cygnus ) appeared on the horizon - caused by the present there radio source Cygnus A. 1946 discovered by a research group at the Royal Radar Establishment in Malvern (England), that of a tiny region in the constellation Cygnus emanates intense radio emission.
Most radio telescopes are parabolic metal surfaces, which concentrate the radio waves of an antenna, which is located at the focal point of the concave mirror. As the antenna is generally also referred to the whole system. Today's radio telescopes often consist of several parabolic antennas (arrays ) as well as the evaluation station. The antennas of the array are coupled together to an interferometer, so that effectively results in an antenna having a larger diameter. This technique can also be extended across the array out to the entire globe: When the whole earth distributed radio telescopes simultaneously observe the same source, can the angular resolution of radio telescopes significantly increase. The biggest investments exceed the resolution of optical telescopes by about a factor of 500, as shown in the picture.
One differentiates radio telescopes between immovable and movable telescopes. Immovable telescopes are rare because they can not be rotated in its orientation. The satellite dish they are often determined on the zenith ( for example, the Arecibo telescope, which is firmly planted in a lowland ). Portable radio telescopes can be turned so that it can "look" in the entire hemisphere.
In addition to the size of a radio telescope, which is a measure of the sensitivity, it also depends on the wavelength range that it can cover. While the big telescopes can only observe wavelengths in the meter and centimeter range, "hear" smaller telescopes, such as the 30 - m telescope of the Institute of Radio Astronomy in the Millimeter Range (IRAM ) in Spain, the 3- m telescope KOSMA in Switzerland millimeter range or the 12 - m telescope APEX ( operated in the Chilean Atacama Desert from the Max Planck Institute for Radio Astronomy, millimeter and submillimeter waves ) at shorter wavelengths. Since these frequencies are outside the atmospheric window, the sensitivity of the overlying air envelope is greatly reduced.
Radio telescopes are in addition to the observation of celestial bodies also used to receive data from remote space probes, or to send commands to this or to search for extraterrestrial intelligence ( SETI See Project ).
Currently the largest radio telescope in the world is the Atacama Large Millimeter / submillimeter Array, abbreviated ALMA. It consists of 66 antennas and is located at about 5000 meters above sea level in the Atacama Desert in the north Chilean Andes.
Other large systems are the Russian RATAN 600 at Selentschukskaja and the Arecibo Observatory. The biggest German ( and world's second largest mobile ) radio telescope is the Effelsberg radio telescope in a valley in the Eifel, a movable telescope with diameter of 100 m, which is operated by the Max Planck Institute for Radio Astronomy in Bonn. The largest steerable radio telescope in the world is the 100 x 110 m wide Robert C. Byrd Green Bank Telescope at Green Bank Observatory in West Virginia, USA. The largest radio telescope for millimeter waves is 50 m wide Large Millimeter Telescope in Puebla, Mexico.
Other large radio telescope arrays are the Giant Metrewave Radio Telescope ( GMRT, 30 individual telescopes of 45 meters, scattered up to 25 km distance, six frequency bands from 50 MHz to 1.5 GHz) in India, 80 km north of Pune in Maharashtra and the Very Large Array (VLA, 27 telescopes each 25 meters in a Y -shaped configuration) in Socorro, New Mexico, USA.
Since 2006, a new radio telescope for the observation of low-frequency radio waves in the Netherlands is built in the meter wave range, the Low Frequency Array ( LOFAR ). To be set up in about 40 stations with a maximum baseline of 1500 km about 10,000 antennas by 2009. Since 2007, the first international LOFAR station operates in addition to the 100-m Effelsberg telescope. More stations to follow in 2008 in Garching, Potsdam, Tautenburg, in England and in France. LOFAR is a prototype for an even bigger radio telescope, the Square Kilometre Array (SKA ).
An important project to explore the universe, which is carried out with the aid of radio telescopes, HIPASS is. Here is distance sensitive search for the signature of hydrogen as an indicator of galaxies. The area of the southern hemisphere has been completed. Most of the data were determined using the Parkes radio telescope in Australia.
The European aerospace group EADS is planning the construction of a radio telescope on the back of the moon. Due to the prevailing silence the sensitivity for the reception of radio waves can be significantly improved. By the absence of an atmosphere, there occurs no wavelength-dependent attenuation, so that a wider range of radio waves can be observed.
The concept of combining more radio telescopes in an array with very high detail resolution resulting forms the basis for the idea of the establishment of such arrays in orbit around the sun. This can be an advantageous positioning of the individual telescopes at the Lagrange points L3, L4 and L5.