William Parsons, Third Earl of Rosse (1800-1867)

British astronomer. Born on 17 June 1800 in York, England. Parsons graduated with first class honours in mathematics from Magdalen College, Oxford, in 1822.

His main contribution to astronomy was the design and construction of large telescopes. Parsons set about finding an appropriate material for use in casting large mirrors and developed techniques for casting solid discs as well as improvements in mirror grinding and polishing. In 1842 he cast the first 72 inch disc which he had mounted between two brick walls nearly 60 feet high. This mirror became known as the “Leviathan of Parsonstown”. The telescope, completed in 1845 had a focal length of 54 feet and a tube about 7 feet in diameter. The mirror itself weighed almost four tonnes.

One of Parson’s most important discoveries was the spiral nature of some nebulae, now known as spiral galaxies. Parsons was president of the British Association at its 1843 meeting in Cork and was president of the Royal Society from 1848 to 1854. He died at Monkstown, Ireland on 31 October 1867.

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