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The UK Schmidt Telescope

A brief History

When the AAT project was already well underway in 1970, the British decided to build a 1.2 metre Schmidt telescope on Siding Spring Mountain. The Schmidt type of telescope is named after its inventor, Bernhard Schmidt, who discovered in the early 1930s that it was possible to build a telescope with a very wide field of view by a suitable combination of a spherical mirror and corrector-plate lens. The first large telescope of this type was the 48 inch Schmidt on Palomar Mountain, which carried out a complete photographic survey of the sky accessible from Palomar, from the north pole to -33_ declination, during the early 1950s. This survey was reproduced as a set of photographs, and the resultant sky survey quickly became a fundamental database for northern hemisphere astronomers. The Palomar Schmidt was the perfect tool to act as a 'scouting telescope' for the 5-metre Hale Telescope on the same site.

In 1971, the then Science Research Council (SRC) established the UK Schmidt Telescope Project as an independent venture with the design, construction and operation under the direction of V C Reddish. The SRC set up a special Unit at the Royal Observatory, Edinburgh (ROE). Sir Howard Grubb Parsons & Company Limited of Newcastle-upon-Tyne, which also fabricated the AAT mirror and tube assembly, began work on the Schmidt Telescope in June 1971. In May 1973 the telescope was delivered to Siding Spring, and the first photographic plate was taken in the following month. The telescope was formally opened on 17 August 1973 by Professor Bengt Stroemgren, President of the International Astronomical Union, and after completing initial commissioning it entered service on 3 September, just three days behind schedule. When Professor Reddish became Director of the ROE in 1975, the Schmidt Unit became part of that Observatory.

At about the same time the European Southern Observatory (ESO) built a 1.0-metre Schmidt telescope alongside its new 3.6-metre telescope on La Silla in Chile. As the primary objective of both Schmidt telescopes was to map the southern sky, the SERC and ESO agreed to share the survey work, with the UK Schmidt taking plates in blue light and ESO the corresponding set of red photographs. The ESO/SERC Southern Sky Survey covers the sky from -17_ to the south pole with a mosaic of 606 photographic plates in each colour. The survey plates were copied onto glass and film at the ESO Sky Atlas Laboratory, and the resulting Atlas was distributed to some 170 institutions around the world. This atlas is now also widely available in digital form. The UK Schmidt also carried out several other large-scale photographic survey projects, including red, near infrared and hydrogen-alpha surveys which were distributed both as photographic atlases and in digital form. By means of full-aperture objective-prisms (of which the telescope had two, with differing apex angles), low-dispersion spectroscopic surveys could also be carried out.

In 1988 the SERC concluded negotiations with the AAT Board for the Schmidt Telescope to become part of the Anglo-Australian Observatory, operated like the AAT under the AAO Director, and funded jointly by the two Governments. The Plate Library at ROE remained the ultimate destination of all Schmidt Telescope plates, and still has a unique archive of sky photographs. When the last UKST photographic image was obtained in 2005, the telescope had taken a total of some 19,500 celestial images.

It was in the early 1980s that the UKST's present mode of operation had its gestation. Experiments with optical fibres conducted by Fred Watson, John Dawe and others, soon led to FLAIR, the Fibre-Linked Array Image Reformatter. This 39-fibre instrument was the world's first wide-field multi-fibre spectroscopy system, and also the first multi-fibre instrument at any observatory to feed a stationary spectrograph. FLAIR demonstrated the effectiveness of the technique, and was replaced on the UKST in 1988 by PANACHE (PANoramic Area Coverage with Higher Efficiency), which combined an improved fibre positioning technique with an improved CCD detector in the spectrograph. A third version, paradoxically known as FLAIR II, was introduced in 1992 with 90 fibres and a much-improved spectrograph. All these instruments used manual positioning of the fibres, making for very slow turn-round between fields - a minor drawback when the main work of the telescope remained photographic imaging. The current 6dF system, with its robotic fibre positioner, was introduced in 2001, and survey spectroscopy soon became the main stock-in-trade of the telescope. In 2005, 6dF completed its first main task, the 6dF Galaxy Survey, and is now engaged on the RAVE stellar velocity survey of a million stars.

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