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Willem de Sitter (May 6 1872 – November 20 1934) was a Dutch
Netherlands

The Netherlands is a country that is part of the Kingdom of the Netherlands. It is a parliamentary democratic constitutional monarchy. The Netherlands is located in North-West Europe, and bordered by the North Sea to the north and west, Belgium to the south, and Germany to the east....
 mathematician, physicist and astronomer.

Born in Sneek
Sneek

Sneek is a municipality and a city in the province of Friesland in the northern Netherlands.Population centres *Lo?nga *Offingawier ...
, De Sitter studied mathematics
Mathematics

Mathematics is the study of quantity, structure, space, change, and related topics of pattern and form. Mathematicians seek out patterns whether found in numbers, space, natural science, computers, imaginary abstractions, or elsewhere....
 at the University of Groningen
University of Groningen

The University of Groningen , located in the city of Groningen , was founded in 1614. It is the second List of oldest universities in continuous operation and one of largest university in the Netherlands....
 and then joined the Groningen
Groningen (city)

||-| |-| |-| |-| |-| |-| |-| |-| |}Groningen is the capital city of the province of Groningen in the Netherlands. With a population of 185,000, it is by far the largest city in the north of the Netherlands....
 astronomical
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
 laboratory. He worked at the Cape Observatory
Observatory

An observatory is a location used for observing terrestrial and/or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed....
 in South Africa
South Africa

The Republic of South Africa, also known by Official names of South Africa, is a country located at the southern tip of the continent of Africa....
 (1897-1899). Then, in 1908, de Sitter was appointed to the chair of astronomy at Leiden University
Leiden University

Leiden University , located in the city of Leiden, is the List of oldest universities in continuous operation#Oldest Universities by Region university in the Netherlands....
. He was director of the Leiden Observatory from 1919 until his death.

De Sitter made major contributions to the field of physical cosmology
Physical cosmology

Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of our universe and is concerned with fundamental questions about its formation and evolution....
.






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Willem de Sitter (May 6 1872 – November 20 1934) was a Dutch
Netherlands

The Netherlands is a country that is part of the Kingdom of the Netherlands. It is a parliamentary democratic constitutional monarchy. The Netherlands is located in North-West Europe, and bordered by the North Sea to the north and west, Belgium to the south, and Germany to the east....
 mathematician, physicist and astronomer.

Born in Sneek
Sneek

Sneek is a municipality and a city in the province of Friesland in the northern Netherlands.Population centres *Lo?nga *Offingawier ...
, De Sitter studied mathematics
Mathematics

Mathematics is the study of quantity, structure, space, change, and related topics of pattern and form. Mathematicians seek out patterns whether found in numbers, space, natural science, computers, imaginary abstractions, or elsewhere....
 at the University of Groningen
University of Groningen

The University of Groningen , located in the city of Groningen , was founded in 1614. It is the second List of oldest universities in continuous operation and one of largest university in the Netherlands....
 and then joined the Groningen
Groningen (city)

||-| |-| |-| |-| |-| |-| |-| |-| |}Groningen is the capital city of the province of Groningen in the Netherlands. With a population of 185,000, it is by far the largest city in the north of the Netherlands....
 astronomical
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
 laboratory. He worked at the Cape Observatory
Observatory

An observatory is a location used for observing terrestrial and/or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed....
 in South Africa
South Africa

The Republic of South Africa, also known by Official names of South Africa, is a country located at the southern tip of the continent of Africa....
 (1897-1899). Then, in 1908, de Sitter was appointed to the chair of astronomy at Leiden University
Leiden University

Leiden University , located in the city of Leiden, is the List of oldest universities in continuous operation#Oldest Universities by Region university in the Netherlands....
. He was director of the Leiden Observatory from 1919 until his death.

De Sitter made major contributions to the field of physical cosmology
Physical cosmology

Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of our universe and is concerned with fundamental questions about its formation and evolution....
. 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
Dark matter

In astronomy and physical cosmology, dark matter is Hypothesis matter that is undetectable by its emitted electromagnetic radiation, but whose presence can be inferred from gravity effects on visible matter....
. He also came up with the concept of the de Sitter space
De Sitter space

In mathematics and physics, n-dimensional de Sitter space, denoted , is the Lorentzian analog of an n-sphere . It is a maximally symmetric, Lorentzian manifold with constant positive scalar curvature, and is simply-connected for n at least 3....
 and de Sitter universe
De Sitter universe

A de Sitter universe is a solution to Albert 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 correspond to dark energy....
, a solution for Einstein's general relativity in which there is no matter and a positive cosmological constant
Cosmological constant

In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a Einstein's universe....
. 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
Leiden

Media:Nl-Leiden.ogg is a city and municipality in the province of South Holland in the Netherlands and has 118,000 inhabitants. It forms a single urban area with Oegstgeest, Leiderdorp, Voorschoten, Valkenburg, Rijnsburg and Katwijk, with 254,000 inhabitants....
.

Aernout de Sitter

His son, Aernout de Sitter, was director of the Bosscha Observatory
Bosscha Observatory

Bosscha 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 Lembang
Lembang

Lembang is a town in the province of Jawa Barat in Java , Indonesia. The population is 183,300....
, Indonesia
Indonesia

The Republic of Indonesia , is a transcontinental country in Southeast Asia and Oceania. Comprising Islands of Indonesia, it is the world's largest Archipelago state....
 (then the Dutch East Indies), where he studied the M4
Messier 4

Messier 4 or M4 is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Ch?seaux in 1746 and catalogued by Charles Messier in 1764....
 globular cluster
Globular cluster

A globular cluster is a sphere collection of stars that orbits a Galactic Center 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....
. He was captured by the Japan
Japan

Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south....
ese when they invaded at the outset of World War II
World War II

World War II, or the Second World War , was a global military conflict which involved a Participants in World War II, including all of the great powers, organised into two opposing military alliances: the Allies of World War II and the Axis powers....
, and died in a Sumatra
Sumatra

Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the list of islands by area in the world ....
 labour camp in September 1944 .

Honours

Awards
  • James Craig Watson Medal
    James Craig Watson Medal

    The James Craig Watson Medal was established by the bequest of James Craig Watson, and is awarded by the U.S. United States National Academy of Sciences for contributions to astronomy....
     (1929)
  • Bruce Medal
    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....
     (1931)
  • Gold Medal of the Royal Astronomical Society
    Gold Medal of the Royal Astronomical Society

    The Gold Medal is the highest award of the Royal Astronomical Society....
     (1931)
Named after him
  • The crater De Sitter
    De Sitter (crater)

    De Sitter is a Moon Impact 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
    Moon

    The Moon is Earth's only natural satellite and the List of natural satellites by diameter satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is km, about thirty times the diameter of the Earth....
  • Asteroid
    Asteroid

    Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, smaller than planets but larger than meteoroids....
     1686 De Sitter
    1686 De Sitter

    1686 De Sitter is a Main-belt Asteroid discovered on September 28, 1935 by Van Gent, H. at Johannesburg .External links ...


See also

  • de Sitter universe
    De Sitter universe

    A de Sitter universe is a solution to Albert 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 correspond to dark energy....
  • de Sitter space
    De Sitter space

    In mathematics and physics, n-dimensional de Sitter space, denoted , is the Lorentzian analog of an n-sphere . It is a maximally symmetric, Lorentzian manifold with constant positive scalar curvature, and is simply-connected for n at least 3....
  • de Sitter effect
    De Sitter effect

    In astrophysics, the term de Sitter effect has been applied to two unrelated phenomena.The de Sitter effect was first described by de Sitter in 1913 and used to support the special theory of relativity against a competing 1908 theory by Walter Ritz that postulated a variable speed of light....


External links

  • P.C. van der Kruit in: History of science and scholarship in the Netherlands.
  • A. Blaauw, , in Biografisch Woordenboek van Nederland.
  • (four articles)


Obituaries

  • (one line)
  • (one paragraph)
  • at www.boston.com (Eleanor Kanegis Levin)