Hagen, Johannes Georg (yōhäˈnəs gāˈôrk häˈgən) [key], 1847–1930, American astronomer and mathematician, b. Austria. A Jesuit, he came in 1880 to the United States to teach. In 1888 he was made director of the astronomical observatory at Georgetown Univ., Washington, D.C., where he remained until 1905. In 1906 he was called to Rome to be at the head of the Vatican Observatory. Much of his research and writing was devoted to the variable stars and to nebulae and cosmic clouds.