For a few decades in the 19th century, the largest telescope in the world stood in a castle garden in Offaly. Ireland's astronomy is older and wider than that one instrument: an archbishop's observatory in Armagh, a Trinity College observatory at Dunsink that kept Ireland's clock, a private observatory in Sligo with what was for a time the largest refractor in the world, and a line of Irish astronomers, several of them women, whose work outlasted the instruments.
The observatories, oldest first · 7
Dunsink Observatory · 1785 · Dunsink, north-west of Dublin · Dublin Founded with £3,000 left in the will of Francis Andrews, Provost of Trinity College Dublin, who died in 1774. From 1791 it was run by the Royal Astronomer of Ireland. William Rowan Hamilton was its director from 1827 until his death in 1865. Dublin Mean Time, Ireland's official time from 1880 until the move to GMT in 1916, was the local mean time at Dunsink. Trinity stopped maintaining it in 1936; since 1947 it has belonged to the Dublin Institute for Advanced Studies. Now: Part of DIAS; public open nights with the 1868 Grubb South Telescope · Map ↗
Armagh Observatory · 1789 · Armagh · Armagh Founded in 1789 by the 1st Baron Rokeby, Church of Ireland Archbishop of Armagh. Its director Thomas Romney Robinson invented the cup anemometer. Its weather records go back to 1794, and in 2018 the World Meteorological Organization recognised 224 years of unbroken records. The Armagh Planetarium beside it opened in 1968 with Patrick Moore as its first director. Now: Research institute, around 25 astronomers; Astropark open to visitors · Map ↗
Markree Observatory · 1830 · Markree Castle, near Collooney · Sligo Set up by Edward Joshua Cooper MP. In 1831 he bought a 13.3-inch lens from Cauchoix of Paris for £1,200, mounted by Thomas Grubb of Dublin in 1834; Wikipedia says that for a number of years this was the largest refractor in the world. Cooper's assistant Andrew Graham discovered the asteroid 9 Metis there in 1848, and the observatory produced a star catalogue of some 60,000 objects in the 1850s. The Royal Astronomical Society in 1851 called it ‘undoubtedly the most richly furnished private observatory known’. Now: No longer operating; active until 1902 · Map ↗
The Leviathan of Parsonstown, Birr Castle · 1845 · Birr Castle demesne, Birr · Offaly William Parsons, 3rd Earl of Rosse, built a reflecting telescope with a 72-inch (1.83 m) metal mirror weighing almost 3 tons, in a tube about 54 feet long slung between two great walls. Wikipedia says it was the largest telescope in the world from 1845 until the 100-inch Hooker Telescope in California was finished in 1917. With it Rosse saw that some nebulae had a spiral shape, the best known being Messier 51. It was used until about 1890; one mirror went to the Science Museum in London in 1914. Now: Rebuilt 1996–97, with a new aluminium mirror in 1999; open to visitors · Map ↗
Daramona · 1871 · Daramona House, Streete · Westmeath William Edward Wilson set up a 12-inch reflector in a dome in the garden of the family house in 1871, replaced in 1881 by a 24-inch Grubb reflector with an electric clock drive, in a tower with its own laboratory and darkroom. With P. L. Gray he measured the temperature of the Sun, arriving at 6,590 °C against a modern value of 6,075 °C. His son gave the telescope to London University. Now: The telescope ended up in a Liverpool museum
Crawford Observatory · 1878 · University College Cork · Cork Built in 1878, paid for in part by £1,000 from William Crawford of the Beamish and Crawford brewery. Its 8-inch Grubb equatorial telescope won a gold medal at the 1878 Paris Exposition Universelle. Light pollution in Cork left it disused, until a €500,000 restoration reopened it in 2006. Now: Used for UCC teaching and outreach; tours in Cork Heritage Week
I-LOFAR, Birr Castle · 2017 · Birr Castle demesne, Birr · Offaly Station IE613 of the European LOFAR radio telescope, built in the castle grounds in 2017: the westernmost station in a network that reaches Latvia. It has 96 low-band and 96 high-band antennas and on its own is the Irish Low Frequency Array. In 2018 it observed the flare star CN Leo, 7.9 light years away. Now: Run by Trinity College Dublin at the Rosse Observatory
The astronomers
William Rowan Hamilton· 1805–1865 Made Royal Astronomer of Ireland and director of Dunsink in 1827, while still an undergraduate. On 16 October 1843, by his own account, walking with his wife along the Royal Canal in Dublin, he hit on the algebra of quaternions and cut the equation into Broom Bridge with a penknife. No trace of the carving survives; a plaque was unveiled in 1958, and the Hamilton Walk from Dunsink to the bridge has been held since 1989.
William Parsons, 3rd Earl of Rosse· 1800–1867 Builder of the Leviathan. He worked out how to cast, grind and polish large speculum-metal mirrors, with steam-powered grinding machines, and cast his first 6-foot mirror in 1842. He became president of the Royal Society in 1848.
Mary Rosse· Countess of Rosse Wife of the 3rd Earl and an early photographer. Her photographs of the telescope helped its reconstruction in the 1990s, and her darkroom, shown at Birr, is believed to be the oldest surviving example in the world.
Mary Ward· 1827–1869 Naturalist, microscopist and astronomer from Ferbane, Co. Offaly, and a cousin of Lord Rosse. Her sketches of each stage of the Leviathan's building were used to restore it. She wrote Telescope Teachings (1859) as well as books on the microscope. She was killed at Birr in 1869 when she fell under an experimental steam car built by her cousins, and is the first person known to have been killed by a motor vehicle.
Agnes Mary Clerke· 1842–1907 Born in Skibbereen, Co. Cork, and taught at home, she began writing a history of astronomy at 15. Her Popular History of Astronomy during the Nineteenth Century (1885) became a standard account of the new astrophysics. The lunar crater Clerke is named after her, and since 2017 the Royal Astronomical Society has awarded an Agnes Clerke Medal.
J. L. E. Dreyer· worked at Birr 1874–1878 He worked with the Leviathan from 1874 to 1878 and began there the compilation of his New General Catalogue of Nebulae and Clusters of Stars.
Jocelyn Bell Burnell· born 1943 Born in Lurgan, Co. Armagh; the staff of Armagh Observatory encouraged her towards astronomy. As a Cambridge research student she noticed the ‘bit of scruff’ on her chart that, on 28 November 1967, proved to be the first known pulsar. The 1974 Nobel Prize for the discovery went to Antony Hewish and Martin Ryle, not to her, which is still debated. In 2018 she gave her $3 million Special Breakthrough Prize to set up a fund helping female, minority and refugee students to become research physicists.
Mary Ward, Agnes Clerke and Jocelyn Bell Burnell also appear among Irish women in history.
World Heritage
In 2025 Dunsink, Birr Castle and Armagh Observatory were added together, as the Irish Historic Astronomical Observatories, to the UNESCO World Heritage Tentative List: a step towards World Heritage status, not the status itself.
Quick answersWas the largest telescope in the world in Ireland?
Yes. The Leviathan of Parsonstown at Birr Castle, with a 72-inch mirror, was the largest telescope in the world from 1845 until the 100-inch Hooker Telescope was completed in California in 1917, according to Wikipedia.
What is the oldest observatory in Ireland?
Of those on this page, Dunsink, near Dublin, established in 1785. Armagh followed in 1789.
What was Dublin Mean Time?
The local mean time at Dunsink Observatory, which was Ireland's official time from 1880. Ireland moved to Greenwich Mean Time in 1916.
Can you visit Irish observatories?
The Leviathan stands in the grounds of Birr Castle, which are open to the public. Armagh has its Astropark and planetarium, Dunsink holds public open nights, and Crawford Observatory in Cork gives tours in Cork Heritage Week. Check each site before travelling.
Each name links to the Wikipedia article it is drawn from; claims such as ‘largest in the world’ are given with the dates and wording the articles use.
Gaps and differences: the Rosse article says the Leviathan was the largest telescope ‘until the early 20th century’, the Leviathan article says until 1917. Daramona House has no article of its own, and Wilson's article does not say what became of the observatory buildings. Map points are those given in the articles; Daramona, Crawford and I-LOFAR have none.
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