Astronomer (astrophysics, solar system). Professor of Astrophysics, University of Maryland; Astronomer, Armagh Observatory (1948-1981); Fellow & Instructor, Moscow University & Observatory (1916-1919); Head of Astronomy Department, Turkestan University, Tashkent (1919-1921); Astronomer/Associate Professor, Tartu University (1921-1944); Research Associate/Visiting Lecturer, Harvard University & Observatory (1930-1934); Professor of Astronomy/Rector, Baltic University (1945-1948). See Irish Astronomical Journal, 10, Special Issue, 1972 and Irish Astronomical Journal, 17, 411-442, 1986 for biographical notes.