William Parsons, 3rd Earl of Rosse KP PRS HFRSE (17 June 1800 - 31 October 1867), was an Anglo-Irish astronomer who had several telescopes built.[1][2] His 72-inch telescope, built in 1845 and colloquially known as the "Leviathan of Parsonstown", was the world's largest telescope, in terms of aperture size, until the early 20th century.[3] From April 1807 until February 1841, he was styled as Baron Oxmantown.