Willem de Sitter was a
DutchThe Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
mathematicianA mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....
,
physicistA physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
and
astronomerAn astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
.
Life and work
Born in
SneekSneek is a city southwest of Leeuwarden and seat of the former municipality of Sneek in the province of Friesland . As for 2011 it is part of the municipality Súdwest Fryslân...
, De Sitter studied
mathematicsMathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
at the
University of GroningenThe University of Groningen , located in the city of Groningen, was founded in 1614. It is one of the oldest universities in the Netherlands as well as one of its largest. Since its inception more than 100,000 students have graduated...
and then joined the
Groningen astronomicalAstronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
laboratory. He worked at the Cape Observatory in
South AfricaThe Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
(1897–1899). Then, in 1908, de Sitter was appointed to the chair of astronomy at
Leiden UniversityLeiden University , located in the city of Leiden, is the oldest university in the Netherlands. The university was founded in 1575 by William, Prince of Orange, leader of the Dutch Revolt in the Eighty Years' War. The royal Dutch House of Orange-Nassau and Leiden University still have a close...
. He was director of the Leiden Observatory from 1919 until his death.
De Sitter made major contributions to the field of
physical cosmologyPhysical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...
. He co-authored a paper with
Albert EinsteinAlbert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
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 matterIn astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
. He also came up with the concept of the
de Sitter spaceIn mathematics and physics, a de Sitter space is the analog in Minkowski space, or spacetime, of a sphere in ordinary, Euclidean space. The n-dimensional de Sitter space , denoted dS_n, is the Lorentzian manifold analog of an n-sphere ; it is maximally symmetric, has constant positive curvature,...
and
de Sitter universeA de Sitter universe is a cosmological solution to Einstein's field equations of General Relativity which is named after Willem de Sitter. It models the universe as spatially flat and neglects ordinary matter, so the dynamics of the universe are dominated by the cosmological constant, thought to...
, a solution for Einstein's
general relativityGeneral relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
in which there is no matter and a positive
cosmological constantIn physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...
. 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 ObservatoryBosscha Observatory is the oldest observatory in Indonesia. The observatory is located in Lembang, West Java, approximately north of Bandung. It is situated on a hilly six hectares of land and is above mean sea level plateau...
in
LembangLembang is a town in the province of West Java in Java, Indonesia. The population is 183,300.Lembang is situated between 1,312 and 2,084 above sea level. Its highest point is on top of Tangkuban Perahu Mt...
,
IndonesiaIndonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
(then the Dutch East Indies), where he studied the
M4Messier 4 or M4 is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1746 and catalogued by Charles Messier in 1764. It was the first globular cluster in which individual stars were resolved.-Visibility:M4 is conspicuous in even the smallest of...
globular clusterA globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
. He died after a brief illness in November 1934
.
Honours
Awards
- James Craig Watson Medal
thumb|right|400px|James Craig Watson MedalThe James Craig Watson Medal was established by the bequest of James Craig Watson, and is awarded by the U.S. National Academy of Sciences for contributions to astronomy.The recipients have been:-External links:*...
(1929)
- Bruce Medal
The Catherine Wolfe Bruce Gold Medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. It is named after Catherine Wolfe Bruce, an American patroness of astronomy, and was first awarded in 1898...
(1931)
- Gold Medal of the Royal Astronomical Society
-History:In the early years, more than one medal was often awarded in a year, but by 1833 only one medal was being awarded per year. This caused a problem when Neptune was discovered in 1846, because many felt an award should jointly be made to John Couch Adams and Urbain Le Verrier...
(1931)
Named after him
- The crater De Sitter
De Sitter is a lunar crater that is located near the northern limb of the Moon, to the north of the Baillaud–Euctemon crater pair. Due to its location, this crater appears very foreshortened when viewed from the Earth, limiting the detail that can be viewed...
on the Moon
- Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
1686 De Sitter1686 De Sitter is a main-belt asteroid discovered on September 28, 1935 by Van Gent, H. at Johannesburg .- External links :*...
Publications
- 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
See also
- de Sitter universe
A de Sitter universe is a cosmological solution to Einstein's field equations of General Relativity which is named after Willem de Sitter. It models the universe as spatially flat and neglects ordinary matter, so the dynamics of the universe are dominated by the cosmological constant, thought to...
- de Sitter space
In mathematics and physics, a de Sitter space is the analog in Minkowski space, or spacetime, of a sphere in ordinary, Euclidean space. The n-dimensional de Sitter space , denoted dS_n, is the Lorentzian manifold analog of an n-sphere ; it is maximally symmetric, has constant positive curvature,...
- de Sitter relativity
- de Sitter effect
In astrophysics, the term de Sitter effect has been applied to two unrelated phenomena:* de Sitter double star experiment...
- De Sitter double star experiment
The de Sitter effect was described by de Sitter in 1913 and used to support the special theory of relativity against a competing 1908 emission theory by Walter Ritz that postulated a variable speed of light...
External links
Obituaries