Johan George Hagen, 1847-1930
Johann Hagen was director of the Georgetown College Observatory, Washington, D.C., from 1888 to 1906. In 1907 he was appointed Director of the Roman College Observatory, a position he held until his death in 1930. During his directorship numerous improvements were made to the observatory. Hagen is noted for his observations of light and dark nebulae and his unproven theories about the latter.
Selected works by Hagen:
Atlas Stellarum variabilim (Rome, 1890-1908). A catalog of variable stars, stellar bodies that change in brightness.
Synopsis der hoeheren mathematik (Berlin, 1890-1930)