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On this day in 1800 – June 17th – William Parsons, Third Earl of Rosse, was born in York, England.

As well as being a skilled engineer and ingenious scientist, he was a dedicated astronomer who constructed a 72-inch (1.83 metre) diameter reflecting telescope at Birr Castle, Parsonstown in Ireland during the 1840s. Known as the Leviathan of Parsonstown, this huge telescope was larger than any made previously and the largest in the world for several decades, and enabled him to discover the spiral nature of many nebulae.