Ernst Julius Öpik (22 October [O.S. 10 October] 1893 – 10 September 1985) was an Estonian astronomer and astrophysicist who spent the second half of his career (1948–1981) at the Armagh Observatory in Northern Ireland. He is best known for his pioneering work on solar system dynamics, particularly of the Oort cloud and the Yarkovsky effect.
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