page_title: Telescope
section_title: Radio telescopes
hierarchical_section_title: Telescope / Types / Radio telescopes
caption_attribution_description: The Very Large Array at Socorro, New Mexico, United States.
context_page_description: A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses. They were used for both terrestrial applications and astronomy.
  The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope. In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s. The word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.
context_section_description: Radio telescopes are directional radio antennas that typically employ a large dish to collect radio waves. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed.
  Unlike an optical telescope, which produces a magnified image of the patch of sky being observed, a traditional radio telescope dish contains a single receiver and records a single time-varying signal characteristic of the observed region; this signal may be sampled at various frequencies. In some newer radio telescope designs, a single dish contains an array of several receivers; this is known as a focal-plane array.
  By collecting and correlating signals simultaneously received by several dishes, high-resolution images can be computed. Such multi-dish arrays are known as astronomical interferometers and the technique is called aperture synthesis. The 'virtual' apertures of these arrays are similar in size to the distance between the telescopes. As of 2005, the record array size is many times the diameter of the Earth — utilizing space-based Very Long Baseline Interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite.
  Aperture synthesis is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and aperture masking interferometry at single reflecting telescopes.
  Radio telescopes are also used to collect microwave radiation, which has the advantage of being able to pass through the atmosphere and interstellar gas and dust clouds.
  Some radio telescopes are used by programs such as SETI and the Arecibo Observatory to search for extraterrestrial life.
caption: The Very Large Array at Socorro, New Mexico, United States.
exif: {"Image XResolution": "120", "Image YResolution": "120", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "GIMP 2.10.14", "Image DateTime": "2020:08:08 02:17:08", "Image ExifOffset": "136", "Thumbnail ImageWidth": "256", "Thumbnail ImageLength": "192", "Thumbnail BitsPerSample": "[8, 8, 8]", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail PhotometricInterpretation": "6", "Thumbnail SamplesPerPixel": "3", "Thumbnail JPEGInterchangeFormat": "262", "Thumbnail JPEGInterchangeFormatLength": "8461", "EXIF ColorSpace": "sRGB"}