Willem de Sitter

Born in Sneek, De Sitter studied mathematics at the University of Groningen 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.

De Sitter made major contributions to the field of physical cosmology. He co-authored a paper with Albert Einstein in 1932 in which they discussed the implications of cosmological data for the curvature of the universe. He also came up with the concept of the de Sitter space and de Sitter universe, a solution for Einstein's general relativity in which there is no matter and a positive cosmological constant. This results in an exponentially expanding, empty universe. De Sitter was also famous for his research on the motions of the moons of Jupiter.[1]

Willem de Sitter died after a brief illness in November 1934.[2][3][4]

In 1912 he became a member of the Royal Netherlands Academy of Arts and Sciences.[5]

• James Craig Watson Medal (1929)
• Bruce Medal (1931)
• Gold Medal of the Royal Astronomical Society (1931)
• Prix Jules Janssen, the highest award of the Société astronomique de France, the French astronomical society (1934)

• The crater De Sitter on the Moon
• Asteroid 1686 De Sitter
• De Sitter universe
• De Sitter space
• Anti-de Sitter space
• De Sitter invariant special relativity
• Einstein–de Sitter universe
• De Sitter double star experiment
• De Sitter precession
• De Sitter–Schwarzschild metric

One of his sons, Ulbo de Sitter (1902 – 1980), was a Dutch geologist, and one of his sons was a Dutch sociologist Ulbo de Sitter (1930 – 2010).

Another son of Willem, Aernout de Sitter (1905 – 15 September 1944[6]), was the director of the Bosscha Observatory in Lembang, Indonesia (then the Dutch East Indies), where he studied the Messier 4 globular cluster.

His great great grandson Jannis Willem Koulman is following in his footsteps and is also studying Maths, Further Maths, Physics and Chemistry at Springwood Sixth Form in King's Lynn.

Einstein, Ehrenfest, Willem de Sitter, Eddington, and Lorentz in Leiden (1923)

• De Sitter, W. (1911). "On the bearing of the Principle of Relativity on Gravitational Astronomy" . Monthly Notices of the Royal Astronomical Society. 71 (5): 388–415. doi:10.1093/mnras/71.5.388. hdl:2027/mdp.39015019246357.
• De Sitter, W. (1913). "A proof of the constancy of the velocity of light" . Proceedings of the Royal Netherlands Academy of Arts and Sciences. 15 (II): 1297–1298. Bibcode:1913KNAB...15.1297D.
  • "Ein astronomischer Beweis für die Konstanz der Lichtgeschwindigkeit"  [An astronomical proof of the constancy of the speed of light]. Physikalische Zeitschrift. 14: 429. 1913.
• "On the constancy of the velocity of light" . Proceedings of the Royal Netherlands Academy of Arts and Sciences. 16 (I): 395–396. 1913.
• De Sitter, W. (1913). "Über die Genauigkeit, innerhalb welcher die Unabhängigkeit der Lichtgeschwindigkeit von der Bewegung der Quelle behauptet werden kann"  [On the accuracy within which the independence of the speed of light from the motion of the source can be asserted]. Physikalische Zeitschrift. 14: 1267. Bibcode:1913PhyZ...14.1267D.

• On Einstein's theory of gravitation and its astronomical consequences:
  1. de Sitter, W. (1916-07-14). "On Einstein's Theory of Gravitation and its Astronomical Consequences. First Paper". Monthly Notices of the Royal Astronomical Society. 76 (9): 699–728. Bibcode:1916MNRAS..76..699D. doi:10.1093/mnras/76.9.699. ISSN 0035-8711 – via Oxford University Press.
  2. de Sitter, W. (1916-12-08). "On Einstein's Theory of Gravitation and its Astronomical Consequences. Second Paper". Monthly Notices of the Royal Astronomical Society. 77 (2): 155–184. Bibcode:1916MNRAS..77..155D. doi:10.1093/mnras/77.2.155. ISSN 0035-8711 – via Oxford University Press.
  3. de Sitter, W. (1917-11-09). "On Einstein's Theory of Gravitation and its Astronomical Consequences. Third Paper". Monthly Notices of the Royal Astronomical Society. 78 (1): 3–28. Bibcode:1917MNRAS..78....3D. doi:10.1093/mnras/78.1.3. ISSN 0035-8711 – via Oxford University Press.

• de Sitter double star experiment
• de Sitter precession
• de Sitter relativity
• de Sitter space
• de Sitter universe
• Anti-de Sitter space
• The Dreams in the Witch House, a story by H. P. Lovecraft featuring de Sitter, and inspired by his lecture The Size of the Universe.

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• O'Connor, John J.; Robertson, Edmund F., "Willem de Sitter", MacTutor History of Mathematics archive, University of St Andrews.
• P.C. van der Kruit Willem de Sitter (1872 – 1934) in: History of science and scholarship in the Netherlands.
• A. Blaauw, Sitter, Willem de (1872–1934), in Biografisch Woordenboek van Nederland.
• Bruce Medal page
• Awarding of Bruce Medal: PASP 43 (1931) 125
• Awarding of RAS gold medal: MNRAS 91 (1931) 422
• de Sitter's binary star arguments against Ritz's relativity theory (1913) (four articles)