Irishastronomer. In 1845 he completed a 72-inch (1.8-m) reflector in the grounds of his family seat at Birr Castle, Parsonstown, in Ireland. This was by far the largest telescope in the world, and its success helped set the trend for large reflectors. With it Rosse detected, in 1845, spiral structure in M51 (the Whirlpool Galaxy) and embarked on a programme to study the shapes of other ‘nebulae’. Some he was able to resolve into star clusters; others, which we now know to be galaxies, remained nebulous. He gave the Crab Nebula its name, from its appearance in the 72-inch. Among his assistants were his son Laurence Parsons (1840–1908), the fourth earl, and J. L. E. Dreyer.
Subjects: Astronomy and Astrophysics.