Portal:History of science/Selected anniversaries/October 20
- 1616 – Birth of Thomas Bartholin, Danish physician, mathematician, and theologian (d. 1680)
- 1631 – Death of Michael Maestlin, German astronomer and mathematician (b. 1550)
- 1785 – Birth of George Ormerod, English historian and antiquarian (d. 1873)
- 1808 – Birth of Karl Andree, German geographer (d. 1875)
- 1891 – Birth of James Chadwick, English physicist, Nobel Prize laureate (d. 1974)
- 1942 – Birth of Christiane Nüsslein-Volhard, German biologist, recipient of the Nobel Prize in Physiology or Medicine
- 1944 – Birth of Nalin de Silva, Sri Lankan theoretical physicist, philosopher and a political analyst
- 1972 – Death of Harlow Shapley, American astronomer (b. 1885)
- 1984 – Death of Carl Ferdinand Cori, Austrian-born biochemist, recipient of the Nobel Prize in Physiology or Medicine (b. 1896)
- 1984 – Death of Paul Dirac, English physicist, Nobel Prize laureate (b. 1902)
- 1987 – Death of Andrey Kolmogorov, Russian mathematician (b. 1903)