Portal:History of science/Selected anniversaries/September 20
- 1633 - Galileo Galilei is tried before the Congregation for the Doctrine of the Faith for teaching that the Earth orbits the Sun
- 1815 - Death of Nicolas Desmarest, French geologist (b. 1725)
- 1842 - Birth of James Dewar, Scottish chemist (d. 1923)
- 1884 - Death of Leopold Fitzinger, Austrian zoologist (b. 1802)
- 1996 - Death of Paul Erdős, Hungarian mathematician (b. 1913)