| Radcliffe Telescope | |
| Organization: | South African Astronomical Observatory |
| Location: | Sutherland, Northern Cape, South Africa |
| Wavelength: | Optical/near-infrared |
| Built: | 1938-1948 |
| First Light: | 1948 |
| Website: | SAAO Homepage |
| Style: | Ritchey-Chrétien Cassegrain, Coude or Newtonian reflector |
| Mounting: | Cross-axis equatorial |
| Dome: | Turret |
The Radcliffe Telescope is a optical/near-infrared reflecting telescope located at the South African Astronomical Observatory in Sutherland, Northern Cape, South Africa.[1]
When construction was completed in 1948, the Radcliffe was the largest telescope in the Southern Hemisphere, and the joint-fourth largest in the world.[2] It is currently the second largest in Africa.[3]
The telescope is equipped with a range of instruments operating for photometry, spectroscopy and polarimetry. These are used by professional astronomers to conduct a wide range of astronomical research.
When he died in 1714, the English physician and Member of Parliament John Radcliffe bequeathed much of his large fortune to a charitable trust because he had never married and had no natural heirs. This Radcliffe Trust funded a number of public projects in and around Radcliffe's alma mater of Oxford, including the Radcliffe Camera and the Radcliffe Infirmary. On the advice of Thomas Hornsby, in 1773 the trust established the Radcliffe Observatory in the then northern outskirts of Oxford; it was the second observatory to be established in Britain. This observatory carried out astronomical research, initially under the leadership of the University of Oxford's Savilian Professor of Astronomy. In 1839 the Radcliffe Trust began funding a Radcliffe Observer to run the observatory, and observing in Oxford continued productively for most of the next century.[4]
In 1924 Harold Knox-Shaw became Radcliffe Observer. By this time the observatory was struggling to remain at the forefront of astronomical research, for a number of reasons. The largest telescope in Oxford was a refractor, but this was no longer a state-of-the-art instrument and had long been eclipsed by large new reflecting telescopes. In particular, astronomers in America now had access to much larger instruments—such as the Hale Telescope (completed 1908) and the Hooker Telescope (1917).[5]
Because the city had expanded considerably since the observatory had been established, and there was now significant light pollution and poor seeing, it could no longer be located in Oxford. The British weather was also an impediment, with many nights lost to cloud. The neighbouring Radcliffe Infirmary was keen to expand its buildings, and there was no room for the large enclosure which would be required for the new telescope.[6]
In addition to undertaking routine observations, Knox-Shaw began planning for a new telescope and observatory. Before becoming Radcliffe Observer, Knox-Shaw had served at the Helwan Observatory in Egypt, where he came to appreciate the benefits of siting a telescope in an arid area.
In 1928 funding for the Hale Telescope was approved, which was to be built at Palomar Observatory, California. This telescope would have four times the collecting area of the next largest in the world, and would easily outperform anything that the Radcliffe Observatory could construct. This effectively settled the argument in favour of erecting the new telescope in the Southern hemisphere.[7]
Although the case for building a new large telescope in the Southern hemisphere was compelling, initially no funds were available to Knox-Shaw. In 1929, the millionaire philanthropist Sir William Morris, owner of Morris Motor Company and a patron of the Radcliffe Infirmary, offered to buy the grounds and buildings of the Observatory so the Infirmary could expand into them. Morris offered the sum of £100,000 (equivalent to £ million in), which would be sufficient to fund the new Southern observatory.
With the offer of funding in place, in 1929 the Radcliffe Trust asked the Astronomer Royal, Sir Frank Dyson, to assess Knox-Shaw's proposal. Dyson was in favour, and convinced the Trustees of the merits of the plan. Later in that year, Knox-Shaw, Dyson and Sir Arthur Eddington attended a meeting of the British Association in South Africa. They took this opportunity to examine several possible sites in the country for the new observatory, deciding that the most favourable was one located on a range of hills near the city of Pretoria. The local Municipality of Pretoria was heavily in favour, and offered to donate the land and connect it to the water and electricity distribution systems for free. The site occupied an area of on the Kiapperkop ridge of hills 4.5miles south-east of the city. From February to June 1930 detailed testing of the weather and seeing conditions at the site was carried out by William Herbert Steavenson on Knox-Shaws instructions and with logistical support from the municipality, the site was adjudged to be favourable.
Harold Knox-Shaw retired as Radcliffe Observer in 1950, and was succeeded by A. David Thackeray, who had joined the observatory in 1948 as Chief Assistant to Knox-Shaw. Thackeray had previously worked at the Solar Physics Laboratory, Cambridge and the Mount Wilson Observatory, California, and had collaborated closely with Arthur Eddington. At the time of Thackeray's appointment, there was only one other astronomer on the staff of the Radcliffe Observatory, the Second Assistant David Stanley Evans. Michael Feast was appointed as the new Chief Assistant in 1951, at which point Evans left and was replaced by Adriaan Jan Wesselink.
In its early years of operation, the telescope suffered from a lack of scientific instrumentation. For over a year the only observations possible were direct photography, and spectroscopy did not become available until 1951. The first spectrograph was a dual-prism medium-resolution instrument which was mounted at the Cassegrain focus, which quickly became the main instrument for observing. In 1959 it became possible to aluminise the primary mirror, which had previously been coated with silver. This enabled observations to be taken at near-ultraviolet wavelengths. Around 1960 the telescope was equipped with a high-resolution spectrograph housed in the Coudé room, and in 1970 another spectrograph was acquired: an image tube spectrograph optimised for low-resolution observations of faint objects.
The main cause of these problems was a lack of funding, which had also limited staff numbers and the amount of observing which could be undertaken. These problems were alleviated in 1951, when the Radcliffe Observatory entered into an agreement with the British Admiralty (who owned the Royal Observatory at the Cape of Good Hope, Cape Town). The Admiralty bought a one third share of the observing time on the Radcliffe Telescope, for the use of astronomers from the Royal Observatory. Some technical staff were also transferred to Pretoria from the Royal Greenwich Observatory, to provide support for visiting astronomers. In 1967, the UK Science Research Council took over the Admiralty's astronomical responsibilities and increased the UK share of the telescope to 50%, which was made available to all UK-funded observers (not just those based in Cape Town).
After he retired, Knox-Shaw had continued to live in South Africa, but died in 1970 at the age of 85. His ashes were scattered on the observatory grounds. In recognition of his leading role in the construction of the telescope, a bronze memorial plaque was installed on the north pier of the telescope.[8] It reads:
IN MEMORIUMHAROLD KNOX-SHAW1885-1970RADCLIFFE OBSERVER, 1924-1950. THROUGH WHOSE LABOURSTHE RADCLIFFE OBSERVATORY AND THIS TELESCOPEWERE SET UP UNDER THE SOUTHERN SKIESTO THE LASTING BENEFIT OF ASTRONOMY. HE HAS LOVED THE STARS TOO TRULYTO BE FEARFUL OF THE NIGHT