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Willem de Sitter (6 May 1872 – 20 November 1934) was a Dutch mathematician, physicist and astronomer.

Life and work

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 argued that there might be large amounts of matter which do not emit light, now commonly referred to as dark matter. 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 planet Jupiter.

Aernout de Sitter

His son, Aernout de Sitter, was director of the Bosscha Observatory in Lembang, Indonesia (then the Dutch East Indies), where he studied the M4 globular cluster. He died after a brief illness in November 1944 [1][2][3].



* James Craig Watson Medal (1929)
* Bruce Medal (1931)
* Gold Medal of the Royal Astronomical Society (1931)

Named after him

* The crater De Sitter on the Moon
* Asteroid 1686 De Sitter


* On the bearing of the Principle of Relativity on Gravitational Astronomy, 1911, Monthly Notices of the Royal Astronomical Society, Vol. 71, p. 388-415
* A proof of the constancy of the velocity of light, 1913, Proceedings of the Royal Netherlands Academy of Arts and Sciences, 1913, 15 II: 1297-1298
* Ein astronomischer Beweis für die Konstanz der Lichtgeschwindigkeit, 1913, Physikalische Zeitschrift, 14: 429
* On the constancy of the velocity of light, 1913, Proceedings of the Royal Netherlands Academy of Arts and Sciences, 1913, 16 I: 395-396
* Über die Genauigkeit, innerhalb welcher die Unabhängigkeit der Lichtgeschwindigkeit von der Bewegung der Quelle behauptet werden kann, 1913, Physikalische Zeitschrift, 14: 1267


1. ^ Obituary Notes of Astronomers at
2. ^ 1947BAN....10..287D Page 287 at
3. ^ Adriaan, Blaauw (2004). "MY CRUISE THROUGH THE WORLD OF ASTRONOMY" (full text). Annual Review of Astronomy and Astrophysics 42 (1): 1. doi:10.1146/annurev.astro.42.053102.134020.

See also

* de Sitter universe
* de Sitter space
* de Sitter effect

External links

* 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)


* AN 253 (1934) 495/496 (one line)
* JRASC 29 (1935) 1
* MNRAS 95 (1935) 343
* Obs 58 (1935) 22
* PASP 46 (1934) 368 (one paragraph)
* PASP 47 (1935) 65
* Eleanor Kanegis Levin, artist and gallery owner, dies at 82 - The Boston Globe at (Eleanor Kanegis Levin)


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