De Sitter, Willem: see Sitter, Willem de.

Sitter, Willem de, 1872-1934, Dutch astronomer and mathematician. He was professor from 1908 at the Univ. of Leiden and in 1919 became director of its observatory. His early work on the motions of Jupiter and its satellites contributed to the downfall of the pre-Einstein celestial mechanics. Using Einstein's formulation of relativity, he theorized that space cannot be in a stable equilibrium, and he concluded that the universe is expanding. He suggested a dynamic universe in which there is motion but no matter, in contrast to Einstein's static universe containing matter but no motion. In the combined Einstein-de Sitter model, the universe is expanding at a decreasing rate that approaches zero. De Sitter's works in English include Kosmos (1932) and The Astronomical Aspect of the Theory of Relativity (1933).

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

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 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.

De Sitter died November 20, 1934 in Leiden.

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 was captured by the Japanese when they invaded at the outset of World War II, and died in a Sumatra labour camp in September 1944 .

Honours

Awards

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

Named after him

• De Sitter crater on the Moon
• Asteroid 1686 De Sitter

Notes

See also

• De Sitter universe
• De Sitter space
• De Sitter effect

External links

• 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)

Obituaries

• 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 www.boston.com (Eleanor Kanegis Levin)