willem de sitter bio

Noah McClannahan

Mr. Percival

Astronomy

2/19/2015

Willem De Sitters Astronomer

Willem de sitters parents where named Lamoraal Ulbo de sitter and Catharine Theodore Wilhelmine Bertling. He was born on may 6 1872. The sitters had a family tradition of family members becoming lawyers. Willem decided to take a different route with his love for science and mathematics. Willem attended Secondary school in Arnhem. After he graduated he went to the University of Groningen with hopes of a degree in mathematics. While pursuing his degree he became very interested with physics and physics related experiments. He started working with Jacobus Kapteyn in the laboratory. In 1896 is when Sitters life changed. When David gill discussed the southern sky survey to Kapteyn. Sitters decided to finish his degree before leaving for Cape Town. He got his degree in 1897. He started working in Cape Town South Africa for a couple of years while participating in heliometer and photometric programs. Sitter returned to Groningen in 1899 and became an assistant in the Astronomical Laboratory and also continued to work towards his doctorate in the study heliometer observations of Jupiter's moons. In 1898 sitter married Eleonora Suermondt. Their first child was Lamoraal Ulbo was born in 1899 and died in 1901. The other children they had were Theodora, Lamoraal Ulbo, Aernout, and Agnes. Lamoraal became a geologist. Aernout was part of the Bosscha Observatory. Willem de sitter submitted his thesis on the Discussion of Heliometer Observations of Jupiter's Satellites moons in 1901. In 1913 sitter proved that the velocity of light was independent of the velocity of the source based on his observations of double start systems. In 1916 he suggested a four-dimensional space-time would fit in with cosmological models based on general relativity. Sitter found solutions to Einstein’s field of equations in the absence of matter. Sitters work led to an expedition in 1919 to measure gravitational deflection of light rays passing near the sun. Sitter was elected as President of the International Astronomical Union and served in this capacity from 1925 to 1928. In 1932 Sitter and Einstein joined together for a joint paper where they proposed a model of the universe. In the paper they mentioned dark matter which does not emit light and hasn't been detected. Even today dark matter is still a very mysterious and is a big part of what some people research today. Sitter is best known for his work on relativity. In 1929 he was working on the motions of satellites when he died. His research showed that there was varying tidal friction which affects the moon and earth. De Sitter suffered from chest complaints for several years but seemed to overcome them. However he died from pneumonia at the young age of sixty-two years in in 1934. Willem De sitter dedicated his life to the world of science and his life played a major role in the contributions to modern day physical cosmology.