125th Anniversary of Observatory's Grubb Telescope

Grubb 10 inch

July 28th marks the 125th anniversary of the erection of the 10-inch Grubb refracting telescope at the Armagh Observatory. The refractor was commissioned from Howard Grubb of Dublin. Following some adjustments to the telescope, including the addition of a rack and pinion for rotating the eyepiece, the first night the telescope could be used was on the 8th October 1885.

Dr J.L.E. Dreyer, who had been appointed as Director of Armagh Observatory on 12 June 1882 following the death on 28 February 1882 of his predecessor the Revd Dr T.R. Robinson, had initiated a fund to build the instrument in memory of his illustrious predecessor. Dreyer collected enough finances from subscribers to build the dome to house the telescope and according to Dreyer's Observatory report (1896), the Treasury contributed a further grant in 1884 of £2,000, the interest from which was to be spent on scientific instrumentation. With the approval of the Treasury, the Observatory allocated £1,000 for the new memorial telescope, and invested the remainder, with the annual interest to be used by the Observatory as directed by the Observatory Governors.

Dreyer used the telescope extensively over the next thirty years, especially while confirming some of the details of nebulae and star clusters for his venerable NGC catalogue, that is, A New General Catalogue of Nebulae and Clusters of Stars, published in 1888 by the Royal Astronomical Society. In his observing notebook, Dreyer also made sketches of certain of his NGC objects as well as other celestial bodies, such as Jupiter (1891) and sunspots (1897). He also observed a number of comets with the telescope, including Comet Halley on a number of nights between 23rd and 29th May 1910, but he remarked that he had never once seen it with the naked eye. His last observation was a timing of the Transit of Mercury on 7 November 1914, which was published in the Monthly Notices of the Royal Astronomical Society, Vol.75.

In the 1920s, the telescope was used by Mervyn Ellison, a son of the then Director Revd William F.A. Ellison, to measure aspects of binary stars, that is, stars that revolve around each other orbiting about their common centre of gravity. Such observations are used to determine the masses of the stars. In the course of this work, in 1925 and 1926, Ellison discovered six new systems, currently located in the constellations Leo, Lyra and Pegasus. Three of the systems were included in Robert Aitken's famous New General Catalogue of Double Stars (Carnegie Institution, 1932) and all six systems appear in the Index Catalogue of Visual Double Stars, 1961.0 (Lick Observatory, 1963).

During the 1960s, Patrick Moore, the first Director of the Armagh Planetarium, and local astronomers including Patrick Corvan and Terry Moseley used the instrument to carry out planetary observations, especially of Saturn and Jupiter.

David Andrews, a former staff member of the Observatory, and a few local astronomers used the Grubb 10-inch refractor to discover one of the brightest stellar flares ever recorded on 19 January 1969, as part of an international observing campaign. The flare occurred on the relatively nearby cool dwarf star YZ Canis Minoris causing the star's visual light output to increase by about five times at peak brightness. The flare lasted for a total of 30 minutes. It is believed that the flare was seen also by the radio astronomers at Jodrell Bank, in Cheshire.

In July 1994, the telescope was used to view the results of the collision of Comet Shoemaker-Levy 9 with Jupiter. More recently asteroid occultations - that is, the shadows of asteroids cast by starlight falling on Armagh - have been observed with the instrument in order to determine the sizes of these minor planets.

FOR FURTHER INFORMATION PLEASE CONTACT: John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; jmfat signarm.ac.uk.

Examples of observations made with the Grubb telescope

Orion Nebula

Jupiter

Sunspots

Last Revised: 2010 July 19th