John Dreyer
John Louis Emil Dreyer (February 13 1852 – September 14 1926) was a Danish-Irish astronomer.He was born Johan Ludvig Emil Dreyer in Copenhagen. In 1874, at the age of 22, he went to Ireland to work as the assistant of Lord Rosse (the son and successor of the Lord Rosse who built the "Leviathan of Parsonstown" telescope). In 1878 he went to Dunsink Observatory and in 1882 to Armagh Observatory, where he served as director until 1916.
His major contribution was the monumental New General Catalogue of Nebulae and Clusters of Stars, whose catalogue numbers are still in wide use today, as well as two supplementary Index Catalogues.
He wrote a biography of Tycho Brahe.
A lunar crater is named after him.