William Parsons: Great Astronomers

William Parsons, 3rd Earl of Rosse KP PRS ( June 17, 1800 - October 31, 1867 ) was an Anglo-Irish astronomer who had several telescopes built. 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. From 1807 until 1841, he was styled as Baron Oxmantown.

He was born in Yorkshire, England, in the city of York, the son of a future Irish peer. He was educated, as Lord Oxmantown, at Trinity College, Dublin, and Oxford University's Magdalen College, graduating with first-class honours in mathematics in 1822. He inherited an earldom and a large estate in King's County (now County Offaly) in Ireland when his father, Lawrence, 2nd Earl of Rosse, died in 1841.

Lord Rosse performed astronomical studies and discovered the spiral nature of some nebulas, today known to be spiral galaxies. Rosse's telescope Leviathan was 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.