William Parsons, 3rd Earl of Rosse, Anglo-Irish astronomer, naturalist, and engineer, is born in York, England on June 17, 1800. He is President of the Royal Society (UK), the most important association of naturalists in the world in the nineteenth century. He builds several giant telescopes. His 72-inch telescope, built in 1845 and colloquially known as the “Leviathan of Parsonstown,” is the world’s largest telescope, in terms of aperture size, until the early 20th century. From April 1807 until February 1841, he is styled as Baron Oxmantown.
Parsons is the son of Lawrence Parsons, 2nd Earl of Rosse, and Alice Lloyd. He is educated at Trinity College, Dublin and Magdalen College, Oxford, graduating with first-class honours in mathematics in 1822. He inherits an earldom and a large estate in King’s County (now County Offaly) in Ireland when his father dies in February 1841.
Parsons marries Mary Field, daughter of John Wilmer Field, on April 14, 1836. They have thirteen children, of which four sons survive to adulthood: Lawrence, 4th Earl of Rosse, Rev. Randal Parsons, the Hon. Richard Clere Parsons, and the Hon. Sir Charles Algernon Parsons.
In addition to his astronomical interests, Parsons serves as a Member of Parliament (MP) for King’s County from 1821 to 1834, president of the British Science Association in 1843–1844, an Irish representative peer after 1845, president of the Royal Society (1848–1854), and chancellor of Trinity College, Dublin (1862–1867).
During the 1840s, Parsons has the Leviathan of Parsonstown built, a 72-inch telescope at Birr Castle, Parsonstown, County Offaly. He has to invent many of the techniques he uses for constructing the Leviathan, both because its size is without precedent and because earlier telescope builders had guarded their secrets or had not published their methods. Details of the metal, casting, grinding and polishing of the 3-ton ‘speculum’ are presented in 1844 at the Belfast Natural History Society. His telescope is considered a marvelous technical and architectural achievement, and images of it are circulated widely within the British commonwealth. Building of the Leviathan begins in 1842 and it is first used in 1845, with regular use waiting another two years due to the Great Famine. Using this telescope he sees and catalogues a large number of nebulae, including a number that would later be recognised as galaxies.
Parsons performs astronomical studies and discovers the spiral nature of some nebulas, today known to be spiral galaxies. His telescope Leviathan is the first to reveal the spiral structure of M51, a galaxy nicknamed later as the “Whirlpool Galaxy,” and his drawings of it closely resemble modern photographs.
Parsons dies at the age of 67 on October 31, 1867 at Monkstown, County Dublin.
Parsons’s son publishes his father’s findings, including the discovery of 226 New General Catalogue of Nebulae and Clusters of Stars (NGC) objects in the publication Observations of Nebulae and Clusters of Stars Made With the Six-foot and Three-foot Reflectors at Birr Castle From the Year 1848 up to the Year 1878, Scientific Transactions of the Royal Dublin Society Vol. II, 1878.