List of largest optical telescopes in Ireland and the United Kingdom is a list of the largest optical telescopes in the British Isles, including in the United Kingdom and Ireland.
Some of the most famous telescopes would be Herschel's reflector, which he discovered Georgium Sidus, the Leviathan of Parsontown which at 1.8 meters (72 inches) was for decades the largest aperture telescope in the World, and in the 20th century many older telescopes are popular tourist attractions such as at Royal Observatory in Greenwich, London. There is also number of modest instruments at universities used for various astronomical projects or education.
The biggest optical telescope was the Isaac Newton Telescope at Herstmonceux, with a 98 inch mirror (~249 cm); it was there from 1965 to 1980; a lot of astronomy moved to off-site telescopes in space or distant mountains, with data transmitted electronically. The void left for public outreach is filled in part by planetariums and various museum pieces.
The list is not really representative of the largest telescopes operated by the United Kingdom or Ireland, which by the 20th century were building large telescopes overseas or in the southern hemisphere for better weather or other reasons.
The following is a non-comprehensive list of optical telescopes currently located in the British Isles with an aperture of 24" or greater:
| Name | data-sort-type="number" | Location | Operator | Comments | |||
|---|---|---|---|---|---|---|---|
| Rosse Six Foot Telescope (reconstructed) [1] | 72sigfig=3NaNsigfig=3 | Newtonian reflector | Birr, Leinster, Ireland | 1999 | Largest optical telescope in the British Isles | ||
| The 38-inch Congo Schmidt [2] | 38sigfig=3NaNsigfig=3 | Reflector | Herstmonceux, East Sussex, England | 1960 | Largest optical telescope in UK, but never used due to flawed optics | ||
| James Gregory Telescope[3] | 37sigfig=3NaNsigfig=3 | Cassegrain reflector | St Andrews, Fife, Scotland | 1962 | Largest operational optical telescope in the UK | ||
| Cambridge 36-Inch telescope[4] | 36sigfig=3NaNsigfig=3 | Reflector | Cambridge, Cambridgeshire, England | 1955 | Largest optical telescope still in use in England | ||
| 36-inch Yapp telescope[5] | 36sigfig=3NaNsigfig=3 | Reflector | Herstmonceux, East Sussex, England | The Observatory Science Centre | 1932 | ||
| Edinburgh 36-inch telescope [6] | 36sigfig=3NaNsigfig=3 | Reflector | Edinburgh, Scotland | 1930 | No longer operational | ||
| The 34-inch Hewitt Camera [7] | 34sigfig=3NaNsigfig=3 | Reflector | Herstmonceux, East Sussex, England | The Observatory Science Centre | 1950s | ||
| Perren Telescope [8] | 31.5sigfig=3NaNsigfig=3 | Ritchey–Chrétien reflector | Mill Hill, London, England | 2019 | |||
| John Wall refractor [9] | 30sigfig=3NaNsigfig=3 | Refractor | Hanwell, Oxfordshire, England | Hanwell Community Observatory | 1999 | Largest refractor in the British Isles | |
| 30" Dobsonian [10] | 30sigfig=3NaNsigfig=3 | Reflector | Todmorden, West Yorkshire, England | The Astronomy Centre | 1986 | ||
| The Thompson 30-inch Reflector [11] | 30sigfig=3NaNsigfig=3 | Reflector | Herstmonceux, East Sussex, England | The Observatory Science Centre | 1896 | ||
| Greenwich 28 inch refractor[12] | 28sigfig=3NaNsigfig=3 | Refractor | Greenwich, London, England | 1893 | |||
| Moses Holden Telescope [13] | 27.6sigfig=3NaNsigfig=3 | Reflector | Preston, Lancashire, England | 2015 | |||
| The Thompson 26-inch Refractor [14] | 26sigfig=3NaNsigfig=3 | Refractor | Herstmonceux, East Sussex, England | The Observatory Science Centre | 1897 | ||
| 24 / 17" Schmidt Camera [15] | 24sigfig=3NaNsigfig=3 | Reflector | Knighton, Powys, Wales | The Spaceguard Centre | 1950 | Largest optical telescope in Wales | |
| Thornton Telescope [16] | 24sigfig=3NaNsigfig=3 | Reflector | Keele, Staffordshire, England | 1975 | |||
| 24" Telescope [17] | 24sigfig=3NaNsigfig=3 | Reflector | Bayfordbury, Hertfordshire, England | 2021 |
A noted accomplishment of the biggest telescope at the time, Ross's "six foot" leviathan, was the observation of the spiral structure of M51, which was presented at Cambridge in the summer of 1845.[23] Herschel was quite prolific discovering a planet and many moons of the Solar system also with his reflectors.