Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies.
The initial detection of radio waves from an astronomical object (the Milky Way) was made in the 1930s, but subsequent advances (especially post-World War II) 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, Pulsars and Masers. The discovery of the Cosmic Microwave Background Radiation was a particularly significant event. Radio astronomy is conducted using large radio antenna referred to as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis. The latter has allowed radio sources to be imaged with unprecedented angular resolution.
Radio astronomers use different types of techniques to observe objects in the radio spectrum. Instruments may simply be pointed at an energetic radio source to analyze what type of emissions it makes. To “image” a region of the sky in more detail, multiple overlapping scans can be recorded and piece together in an image ('mosaicing'). The types of instruments being used depends on the weakness of the signal and the amount of detail needed.
Observations from the earth's surface are limited to those wavelengths that can pass through the atmosphere. The picture on the right shows the frequencies that pass best through the Earth's atmosphere. Since water vapor is one of the main interefering components of the atmosphere, radio astronomy at higher frequencies must be conducted from very high and dry sites, to minimize the water vapor content in the line of sight. Alternatively, space based receivers could tune to a wider range of frequencies, but are much more expensive and of more limited size.
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A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes. In their astronomical role they differ from optical telescopes in that they operate in the radio frequency portion of the electromagnetic spectrum where they can detect and collect data on radio sources. Radio telescopes are typically large parabolic ("dish") antennas used singly or in an array. Radio observatories are preferentially located far from major centers of population in order to avoid electromagnetic interference (EMI) from radio, TV, radar, and other EMI emitting devices. This is similar to the locating of optical telescopes to avoid light pollution, with the difference being that radio observatories are often placed in valleys to further shield them from EMI as opposed to clear air mountain tops for optical observatories.
Astronomical radio sources are objects in outer space that emit strong radio waves. Radio emission comes from a wide variety of sources. Such objects represent some of the most extreme and energetic physical processes in the universe.
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution. Astronomical interferometers are widely used for optical astronomy, infrared astronomy, submillimetre astronomy and radio astronomy. Aperture synthesis can be used to perform high-resolution imaging using astronomical interferometers. Very Long Baseline Interferometry uses a technique related to the closure phase to combine telescopes separated by thousands of kilometers to form a radio interferometer with the resolution which would be given by a single dish which was thousands of kilometers in diameter. 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 array.
The National Radio Astronomy Observatory (NRAO) is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy. NRAO designs, builds, and operates its own high sensitivity radio telescopes for use by scientists around the world.
The Max Planck Institute for Radio Astronomy is located in Bonn, Germany. It is one of 80 institute in the Max Planck Society (Max Planck Gesellschaft). By combining the already existing radio astronomy faculty of the University of Bonn lead by Otto Hachenberg with the new Max Planck institute the Max Planck Institute for Radio Astronomy was formed. In 1972 the 100 m radio telescope in Effelsberg was opened. The institute was enlarged 1983 and 2002. The southern wing of the whole complex is occupied by the Argelander-Institute of Astronomy of the University of Bonn. The International Max Planck Research School for Radio and Infrared Astronomy is a graduate program offering a Ph.D. The school is run in cooperation with the University of Bonn and University of Cologne.
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