Parsons, William (1800–1867)

Irish astronomer, engineer, and politician. He built the largest telescope then in use. He found 15 spiral nebulae and named the Crab nebula. He was among the first to take photographs of the Moon.

Life Parsons was born in York and educated at Trinity College, Dublin and Oxford. As the eldest son of a titled landowner, he was elected to Parliament while still an undergraduate to represent King's County, a seat he then held for 13 years. In 1831 he became Lord Lieutenant of County Offaly, and in 1841, on the death of his father, he entered the House of Lords. During and after the 1846 potato famine, Parsons worked to improve the living conditions of his tenants.

Observatory Determined to construct a large and powerful telescope, Parsons learned to cast and grind mirrors. His experiments began about 1826, and 14 years later he was able to make a 92-cm/36-in solid mirror. In 1842 he cast the ‘Leviathan of Parsonstown’, a disc 1.8 m/72 in in diameter which weighed nearly 4 tonnes and was incorporated into a telescope with a focal length of 16.2 m/54 ft. It took three years to put together and was installed at the family seat, Birr Castle, at Parsonstown in Ireland. It was used 1845–78, mainly for the observation of nebulae and clusters. He also invented a clockwork drive for the large equatorial mounting of an observatory.

Sons His eldest son, Laurence Parsons, 4th Earl of Rosse, was also an astronomer and used the telescope after his father's death. Another son was Charles Parsons, who invented the steam turbine.