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Mark II (radio telescope)
Encyclopedia
The Mark II is a radio telescope
located at Jodrell Bank Observatory, near Goostrey
, Cheshire
, in the north-west of England
. It was built on the site of the 218 ft (66.4 m) Transit Telescope. Construction was completed in 1964. The telescope's design was used as the basis of the 60ft Goonhilly
1 telescope, and the Mark III
telescope is also based on a similar design.
The original dish surface of the telescope was more accurate than the Lovell Telescope's at the time it was made, meaning that it was better suited for observations at higher frequencies. As well as operating as a solo instrument, it has been used as an interferometer with the Lovell Telescope
, which provides a 425m baseline. It is commonly used as part of the Multi-Element Radio Linked Interferometer Network
(MERLIN), and for Very Long Baseline Interferometry
observations.
at the instigation of Bernard Lovell
, with design work starting around September 1960. Funding for the construction of the telescope was requested on the 19 December 1960, and the telescope was operational by the summer of 1964.
The telescope originally intended as a prototype for a larger, "Mark IV" telescope, which was never constructed. As a result, an elliptical dish was used, with a major axis of 125 ft (38.1 m) and a minor axis of 83 ft 4 in (25.4 m). The focal length
is 40 ft (12.2 m). Although an elliptical dish is not the optimal surface shape for astronomical observations, it would have been necessary on a much larger telescope to reduce the telescope's height above the ground.
The base of the telescope is made of prestressed concrete
.. The telescope has an alt-azimuth mount
sitting on 54 steel rollers in a 42 ft (12.8 m) diameter roller track on top of a foundation block. It was the first telescope in the world to be steered by a digital computer. This computer, the Ferranti
Argus 104, had 12 kilobytes of memory; it was upgraded to an Argus 400 in 1971, with the 104 being put to use controlling the upgraded Lovell Telescope
.
A proposal to upgrade the Mark II to a Mark IIA was put forward in 1974. The upgrade would have been to a 100ft circular aperture which could have been used on wavelengths down to 6mm, which would have enabled it to be used as part of the high-frequency component of the original MERLIN
array. It was also planned that the telescope would be used for spectral line work at millimeter wavelengths. However, the upgrade was never approved.
The original surface had an accuracy of ±1/8 inch, which meant that the telescope could observe at higher frequencies than the Lovell Telescope. The surface was upgraded in 1987 to one with an accuracy of 1/3 mm, which was accurately set using a holographic technique, meaning that the telescope can observe at the 22 GHz MERLIN frequency. The new surface is circular and was laid on top of the old, such that the telescope now has ear-like extensions where the old surface still shows.
In the late 1990s, a new, more compact carousel for the receivers was installed at the prime focus of the telescope.
to develop phase stable long baseline interferometers, leading to the development of MERLIN
. The telescope was used as an interferometer with the Lovell Telescope
to provide more accurate positions for radio sources found from a survey done in 1972 and 1973; the position of one radio source was found to coincide with a pair of faint blue stars, and after optical observations were made it was found to be the first gravitational lens
. The majority of the current observational time of the Mark II is spent either on MERLIN
or VLBI observations.
Radio telescope
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...
located at Jodrell Bank Observatory, near Goostrey
Goostrey
Goostrey is an old farming village and civil parish in the unitary authority of Cheshire East and the ceremonial county of Cheshire, England. It is located off Junction 18 of the M6 motorway, near Jodrell Bank Observatory. According to the 2001 Census, the civil parish had a total population of...
, Cheshire
Cheshire
Cheshire is a ceremonial county in North West England. Cheshire's county town is the city of Chester, although its largest town is Warrington. Other major towns include Widnes, Congleton, Crewe, Ellesmere Port, Runcorn, Macclesfield, Winsford, Northwich, and Wilmslow...
, in the north-west of England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. It was built on the site of the 218 ft (66.4 m) Transit Telescope. Construction was completed in 1964. The telescope's design was used as the basis of the 60ft Goonhilly
Goonhilly Satellite Earth Station
Goonhilly Satellite Earth Station is a large telecommunications site located on Goonhilly Downs near Helston on the Lizard peninsula in Cornwall, England, UK. Owned by BT Group plc, it was at one time the largest satellite earth station in the world, with more than 25 communications dishes in use...
1 telescope, and the Mark III
Mark III (radio telescope)
The Mark III was a portable and fully steerable radio telescope located at Wardle, near Nantwich, Cheshire in the north-west of England . Constructed in 1966, it was remotely controlled from Jodrell Bank Observatory, and was mainly used as part of the MERLIN radio telescope network...
telescope is also based on a similar design.
The original dish surface of the telescope was more accurate than the Lovell Telescope's at the time it was made, meaning that it was better suited for observations at higher frequencies. As well as operating as a solo instrument, it has been used as an interferometer with the Lovell Telescope
Lovell Telescope
The Lovell Telescope is a radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire in the north-west of England. When it was constructed in 1955, the telescope was the largest steerable dish radio telescope in the world at 76.2 m in diameter;it is now the third largest, after the...
, which provides a 425m baseline. It is commonly used as part of the Multi-Element Radio Linked Interferometer Network
MERLIN
The Multi-Element Radio Linked Interferometer Network is an interferometer array of radio telescopes spread across England. The array is run from Jodrell Bank Observatory in Cheshire by the University of Manchester on behalf of STFC as a National Facility.The array consists of up to seven radio...
(MERLIN), and for Very Long Baseline Interferometry
Very Long Baseline Interferometry
Very Long Baseline Interferometry is a type of astronomical interferometry used in radio astronomy. It allows observations of an object that are made simultaneously by many telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.Data...
observations.
Design and construction
The telescope was designed by Charles HusbandCharles Husband
Sir Henry Charles Husband was a leading architect and consulting engineer in Great Britain. His offices were based in Sheffield, England. He designed bridges and major civil engineering works and had a role in designing the Jodrell Bank radio telescope.- Biography :Husband was educated at King...
at the instigation of Bernard Lovell
Bernard Lovell
Sir Alfred Charles Bernard Lovell OBE, FRS is an English physicist and radio astronomer. He was the first Director of Jodrell Bank Observatory, from 1945 to 1980.-Early Life:...
, with design work starting around September 1960. Funding for the construction of the telescope was requested on the 19 December 1960, and the telescope was operational by the summer of 1964.
The telescope originally intended as a prototype for a larger, "Mark IV" telescope, which was never constructed. As a result, an elliptical dish was used, with a major axis of 125 ft (38.1 m) and a minor axis of 83 ft 4 in (25.4 m). The focal length
Focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...
is 40 ft (12.2 m). Although an elliptical dish is not the optimal surface shape for astronomical observations, it would have been necessary on a much larger telescope to reduce the telescope's height above the ground.
The base of the telescope is made of prestressed concrete
Prestressed concrete
Prestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...
.. The telescope has an alt-azimuth mount
Altazimuth mount
An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...
sitting on 54 steel rollers in a 42 ft (12.8 m) diameter roller track on top of a foundation block. It was the first telescope in the world to be steered by a digital computer. This computer, the Ferranti
Ferranti
Ferranti or Ferranti International plc was a UK electrical engineering and equipment firm that operated for over a century from 1885 until it went bankrupt in 1993. Known primarily for defence electronics, the Company was once a constituent of the FTSE 100 Index but ceased trading in 1993.The...
Argus 104, had 12 kilobytes of memory; it was upgraded to an Argus 400 in 1971, with the 104 being put to use controlling the upgraded Lovell Telescope
Lovell Telescope
The Lovell Telescope is a radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire in the north-west of England. When it was constructed in 1955, the telescope was the largest steerable dish radio telescope in the world at 76.2 m in diameter;it is now the third largest, after the...
.
A proposal to upgrade the Mark II to a Mark IIA was put forward in 1974. The upgrade would have been to a 100ft circular aperture which could have been used on wavelengths down to 6mm, which would have enabled it to be used as part of the high-frequency component of the original MERLIN
MERLIN
The Multi-Element Radio Linked Interferometer Network is an interferometer array of radio telescopes spread across England. The array is run from Jodrell Bank Observatory in Cheshire by the University of Manchester on behalf of STFC as a National Facility.The array consists of up to seven radio...
array. It was also planned that the telescope would be used for spectral line work at millimeter wavelengths. However, the upgrade was never approved.
The original surface had an accuracy of ±1/8 inch, which meant that the telescope could observe at higher frequencies than the Lovell Telescope. The surface was upgraded in 1987 to one with an accuracy of 1/3 mm, which was accurately set using a holographic technique, meaning that the telescope can observe at the 22 GHz MERLIN frequency. The new surface is circular and was laid on top of the old, such that the telescope now has ear-like extensions where the old surface still shows.
In the late 1990s, a new, more compact carousel for the receivers was installed at the prime focus of the telescope.
Scientific use
During the 1970s, the telescope was used in conjunction with the Mark IIIMark III (radio telescope)
The Mark III was a portable and fully steerable radio telescope located at Wardle, near Nantwich, Cheshire in the north-west of England . Constructed in 1966, it was remotely controlled from Jodrell Bank Observatory, and was mainly used as part of the MERLIN radio telescope network...
to develop phase stable long baseline interferometers, leading to the development of MERLIN
MERLIN
The Multi-Element Radio Linked Interferometer Network is an interferometer array of radio telescopes spread across England. The array is run from Jodrell Bank Observatory in Cheshire by the University of Manchester on behalf of STFC as a National Facility.The array consists of up to seven radio...
. The telescope was used as an interferometer with the Lovell Telescope
Lovell Telescope
The Lovell Telescope is a radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire in the north-west of England. When it was constructed in 1955, the telescope was the largest steerable dish radio telescope in the world at 76.2 m in diameter;it is now the third largest, after the...
to provide more accurate positions for radio sources found from a survey done in 1972 and 1973; the position of one radio source was found to coincide with a pair of faint blue stars, and after optical observations were made it was found to be the first gravitational lens
Gravitational lens
A gravitational lens refers to a distribution of matter between a distant source and an observer, that is capable of bending the light from the source, as it travels towards the observer...
. The majority of the current observational time of the Mark II is spent either on MERLIN
MERLIN
The Multi-Element Radio Linked Interferometer Network is an interferometer array of radio telescopes spread across England. The array is run from Jodrell Bank Observatory in Cheshire by the University of Manchester on behalf of STFC as a National Facility.The array consists of up to seven radio...
or VLBI observations.