Willem de Sitter

Willem de Sitter (May 6 1872, Sneek –  November 20 1934, Leiden [1]) was a Dutch mathematician, physicist and astronomer. Born in Friesland, De Sitter studied mathematics at Groningen University and then joined the Groningen astronomical laboratory. He worked at the Cape Observatory in South Africa (1897-1899) then, in 1908, de Sitter was appointed to the chair of astronomy at Leiden University. He was director of the Leiden Observatory from 1919 until his death.
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Noun
1. Dutch astronomer who calculated the size of the universe and suggested that it is expanding (1872-1934)
(synonym) Sitter
(hypernym) astronomer, uranologist, stargazer