Willem de Sitter
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 discussed the implications of cosmological data for the curvature of the universe. 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.
De Sitter (crater)
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. The crater also receives sunlight at a low angle, when it is on the sunlit side.
This crater forms part of an unusual three-crater cluster, with De Sitter overlying the northeast rim of De Sitter L and the southern rim of De Sitter M. All three craters are of comparable dimension, with the largest being De Sitter M. Where De Sitter overlies the other two craters, its outer rim appears slumped. The rim is more sharply formed along the east-southeast side. Lying next to this part of the rim is De Sitter G, a small formation of two merged craters.
The interior floor of De Sitter is somewhat irregular and hummocky, with a slender central ridge near the midpoint. There are several small and tiny craterlets across the interior floor. There are some rilles near the inner wall, possibly volcanic in origin.
