Restoration Programme for Telescopes and Domes

DCAL

Armagh Observatory has been fortunate in receiving a substantial grant from the Heritage Lottery Fund for the restoration of three of its telescopes and domes.

Armagh Observatory is the oldest scientific institution in Northern Ireland and following the closure of the RGO is now the oldest working observatory in the UK. Its principal buildings are of considerable architectural merit as the work of the 18th century native-born Irish architect, Francis Johnston (known as Ireland's Wren) who later was responsible for many fine buildings in Dublin. In their original designation, the buildings comprise: a residence for the Astronomer, a meridian room, a library and several telescope domes.

The interior of the residence is one of only a handful of 18th century domestic interiors to survive in Northern Ireland and is remarkable for the quality of its joinery and fittings. It houses an historic collection of astronomical clocks, scientific instruments and archives alongside the day to day requirements of modern astronomical research.

Four Domes The telescope domes include the following: (1) The 1790 dome which is believed to be the second earliest surviving astronomical dome in the world and the earliest to survive with its original equipment in situ (The Troughton Equatorial Telescope). (2) The 1827 dome, built originally for a Herschel telescope and shortly thereafter converted for the 15-inch Grubb Reflector. (3) The Robinson Memorial Dome which was built to house the 10-inch Grubb Refractor. (4) A utility dome built circa 1950 to house a late 19th century reflector by Calver.

The restoration of the 1790 dome and the Troughton Equatorial Telescope was completed in 1994. A programme of restoration of the six 18th century astronomical regulators (clocks) belonging to the Observatory has also been largely completed and provision made for their conservation and display to the public. A number of other items of scientific equipment were reassembled and restored for the Bicentenary Exhibition held under the auspices of the Ulster Museum and the National Museum of Ireland in 1990-1991. Several of these are now on permanent display at the Observatory. In general, the policy has been to place the restored instruments in their original location in the building, as far as is possible, so that the public may more clearly understand the context of their use.

The total project cost of á¸381,000, is to be financed by á¸286,000 from the HLF and á¸95,000 from DCAL and elsewhere. It will support the restoration of the 1827 Dome, the Robinson Dome, the Calver Dome and the three telescopes that they will contain: the 1834 Grubb Equatorial Reflector, the 1885 Grubb Refractor and the late 19th century Calver Reflector. All three of these telescopes are of historical interest.

15-inch Grubb Reflector and the 1827 Dome

The 15-inch Equatorial was the first telescope made by Thomas Grubb for a professional observatory. It incorporated several innovations which subsequently became standard in telescope design. Firstly, it had a Cassegrain rather than Newtonian or Heschelian focus as had most large reflecting telescopes at that time; secondly, it was the first large reflecting telescope to be mounted on a polar axis with a clock drive and, lastly, it had a novel lever support system for the primary mirror. The telescope was dismantled in the early 20th century, some of the parts dispersed and others placed in store. Some of the major missing parts, including the mounting and the drive clock, were returned to the Observatory in the late 1980s after they were found in the basement of the Royal School, Armagh. The original stone pier had rested throughout this period in the 1827 Dome. It is proposed to restore the telescope as close to the original design as possible with a new glass mirror by David Sinden to replace the original speculum (now broken). Unfortunately, nothing of the original tube and no drawings or photographs of the telescope have survived that we are aware of. However, Robinson wrote several accounts of his experience with the telescope in which he gave the basic optical dimensions. This information, together with the surviving mechanical and optical parts will enable us to restore the instrument, if not to its original form, to something very similar. The telescope was influential in its design and was frequently referred to by Robinson during the planning of the Great Southern Telescope, later built by Thomas Grubb for Melbourne, Australia.

The 1827 Dome which has not been used since early in this century, was sealed in the 1980s following storm damage. We propose to remove the sealing and to return the dome to its original working order. A dehumidifier system will be installed to prevent corrosion of the telescope by excess humidity. In addition the staircase rising to the dome will be renovated to provide wall space for display material relating to the telescope.

10-inch Grubb Refractor and the Robinson Dome

The Grubb Refractor was built by Howard Grubb as a memorial to Thomas Romney Robinson who died in 1882. It was used by J.L.E. Dreyer for checking some of the clusters and nebulae included in his famous NGC catalogue and later by Ellison to measure the orbits of binary stars. In the 1960s it was employed by David Andrews for some pioneering observations of flare stars which were monitored optically at Armagh and simultaneously at radio wavelengths by the Lovell Radio Telescope at Jodrell Bank. The telescope is currently in need of some cleaning and restoration of its mechanical parts. The original objective lens has suffered from etching by condensation over the years since its manufacture. We are faced with two alternatives: either we repolish the lens and thereby destroy its original figure, or we remove the original lens for safe keeping and replace it with a modern lens. Following the report by Sinden Optical Company, we propose to remove the original objective lens and to place it in a display case where it will be properly conserved for examination by future specialists in scientific instruments. The restored telescope will be fitted with a new objective lens with a similar design to the original.

The Robinson Dome which was built for the 10-inch Grubb Refractor is a listed building with some very unusual architectural features. Basically, it consists of a circular iron frame supporting a ring girder on which rests the moveable part of the dome. It is an early prefabricated building which in concept resembles a tent, with some elements under compression and others in tension. The design may derive from prefabricated buildings used in the Crimean War. The dome needs extensive restoration following decay caused by wet rot and percolation of water through the roof.

18-inch Calver Telescope

This telescope, which was extensively modified in the mid 20th century to a Schmidt design will be returned to its original Newtonian configuration, fitted with a new drive, and rehoused in a new dome. Though the telescope has some claim to fame as an early Schmidt-type system in the UK, it was never very successful in this form and if restored to this configuration would be badly affected by the increasingly bright sky background in Armagh. The existing dome is in very bad condition, of utility construction, and of no historical or architectural value. The original Calver mirror for the telescope will be tested by the Sinden Optical Company and, if found satisfactory, will be coated with a high reflectivity material to allow the use of the telescope by future students of astronomy. Access to wheelchairs will be provided and a dehumidifier installed to reduce the risk of corrosion.

Last Revised: 2009 November 5th