Astronomer (stellar spectra and distances). On the astronomy faculty at Universität Göttingen (1909-1919); and Rijksuniversiteit te leiden 91920-1944); on the staff of the observatory at Leiden (1914-1944), director, (1935-1944).
Astronomer (steller spectra and distances). On the astronomy faculty at Universität Göttingen, 1909-1919; and Rijksuniversiteit te Leiden, 1920-1944; on the staff of the observatory at Leiden, 1914-1944, director, 1935-1944.