Willem de Sitter

de Sitter was born in the Netherlands to Lamoraal Ulbo de Sitter and Catharine Theodore Wilhelmine Bertling, whose family had a rich tradition of strictly lawful professions. de Sitter rebelled with his love of mathematics and science. He studied at the University of Groningen, earning a degree in math and studying physics at the same time.  David Gill visited Kapteyn to discuss progress on the southern sky survey, and de Sitter met with him (with the help of a translator as his grasp of the English language was complete. After he recieved his Bachelor's degree, he began study at Cape Town with Gill. He worked at the Cape Observatory in South Africa for two years taking part in photometric and heliometer programmes. He submitted his thesis Discussion of Heliometer Observations of Jupiter's Satellites to the University of Groningen in 1901. He married  Eleonora Suermondt, a schoolteacher, and had a child with her in Cape Town. In 1913 de Sitter produced an argument based on observations of double star systems which proved that the velocity of light was independent of the velocity of the source. It put to rest attempts which had been made up until this time to find emission theories of light which depended on the velocity of the source but were not in conflict with experimental evidence. De Sitter asked "If no matter exists other than the test body, does it have inertia?"- this led to Arthur Eddignton's work on gravitation effect's on photons. de Sitter also refined the fundamental constants of astronomy, most notably ones concerning the composition of the Earth. He received the Watson Gold Medal. He died from pneumonia at sixty-two years.