Ryle Telescope

{{Infobox telescope cmglee Cambridge MRAO AMI Large Array

The Ryle Telescope (named after

Martin Ryle Sir Martin Ryle (27 September 1918 – 14 October 1984) was an English radio astronomer who developed revolutionary radio telescope systems (see e.g. aperture synthesis) and used them for accurate location and imaging of weak radio source ...

, and formerly known as the 5-km Array) was a linear east-west

radio telescope 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 ...

array at the

Mullard Radio Astronomy Observatory The Mullard Radio Astronomy Observatory (MRAO) is located near Cambridge, UK and is home to a number of the largest and most advanced aperture synthesis radio telescopes in the world, including the One-Mile Telescope, 5-km Ryle Telescope, an ...

. In 2004, three of the telescopes were moved to create a compact two-dimensional array of telescopes at the east end of the

interferometer Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...

. The eight antennas have now become the Arcminute Microkelvin Imager Large Array. The Ryle Telescope was an eight-element interferometer operating at 15 GHz (2cm wavelength). The elements were equatorially mounted 13-m Cassegrain antennas, on an (almost) east-west baseline. Four aerials were mounted on a 1.2 km

rail track A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleepers, ...

, and the others were fixed at 1.2 km intervals. Baselines between 18 m and 4.8 km were therefore available, in a variety of configurations. For high-resolution imaging, the mobile aerials were arranged along the track, to give uniform baseline coverage to 4.8 km; for low-brightness astronomy (e.g. the Sunyaev-Zel'dovich effect) the mobile aerials were arranged in a 'compact array', with a maximum baseline of about 100 m. All antenna pairs were correlated, so some long baseline data were always available, even in the 'compact array' configuration. As the telescope was an east-west instrument, most imaging observations involved 12-hour observations in order to fill the synthesised aperture (

calibration In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of know ...

observations are routinely interleaved). Another consequence of the geometry was that it is not practical to image sources near the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...

, or in the south. The two-dimensional Large Array overcomes this problem with its new north-south baselines. Although the telescope was not designed as a common user instrument, the operators were happy to accept proposals for observing time on the instrument from outside observers, provided that they did not overlap substantially with existing observing programmes, on a 'best efforts' basis. Monitoring variable sources was possible using short observations which could often be inserted between longer 'standard' observations. The telescope had three main scientific programs: study of the Sunyaev-Zel'dovich effect in

galaxy clusters A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second-la ...

, particularly in determining the

Hubble constant Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving ...

; surveying for radio sources that would contaminate degree-scale

observations Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instrument ...

of the

cosmic microwave background In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...

made with the

Very Small Array The Very Small Array (VSA) was a 14-element interferometric radio telescope operating between 26 and 36 GHz that is used to study the cosmic microwave background radiation. It was a collaboration between the University of Cambridge, Univers ...

, and flux monitoring of galactic variable sources. Radio telescopes Cavendish Laboratory Interferometric telescopes