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

De Sitter may also refer to:

• De Sitter (crater), a lunar crater
• 1686 De Sitter, an asteroid

• Ulbo de Sitter (1902–1980), Dutch geologist
• Ulbo de Sitter (sociologist) (1930–2010), Dutch sociologist whose work has been further developed by Jan in 't Veld

• De Sitter space and anti-de Sitter space, models of spacetime
• De Sitter universe, a solution to general relativity
• De Sitter effect (disambiguation)
• Sitter (disambiguation)

This disambiguation page lists articles associated with the title De Sitter.
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