Willem de Sitter

Dutch mathematician, physicist, and astronomer.

The genealogy of the noted De Sitter family dates back to 1300. Many PhD academics and regents were born in it. His father was the judge Lamoraal Ulbo de Sitter (5 May 1846, Groningen - 6 September 1908, Arnhem). On 15 July 1871 he married in Assen, Catharina Theodore Wilhelmine Bertling (3 February 1846, Assen - 16 April 1909, Groningen). In 1871 he became substitute clerk (in Sneek), in 1879 Judge (in Assen) and in 1908 President of the court of Arnhem. Here a son Ernst Karel Johan de Sitter (22 November 1879, Arnhem - 19 September 1949, Haren, Groningen) was born. A sister, Wobbine Catharine de Sitter was born 8 August 1876 at 7h30 PM in Assen, when her father was a judge.

The parents of his mother were the judge Ernst Karel Johannes Bertling (19 January 1817, Veendam - 4 December 1889, Assen) and Wobbina Catharina van der Scheer (11 January 182, Coevorden - 27 April 1900, Arnhem). Catharina was first of six children. The parents of his father were Willem de Sitter (9 November 1820, Groningen - 13 January 1889, Groningen) and Wilhelmina Petronella Rengers (18 April 1823, Groningen - 16 November 1895, Groningen). They married 22 November 1843 in Groningen. Lamoraal Ulbo was the second of six children.

Willem de Sitter followed the Gymnasium in Arnhem. On 21 September 1891, Willem de Sitter studied mathematics and physics at the University of Groningen under Kapteyn and then joined the Groningen astronomical laboratory. He worked at the Cape Observatory in South Africa (1897–1899). Back in Leiden 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. From 1925-1926 he was Rector Magnificus in Leiden. From 1925 till 1928 he was President International Astronomical Union.