Portal:History of science/Selected anniversaries/June 20
- 1800 - death of Abraham Gotthelf Kästner, German mathematician (b. 1719)
- 1861 - birth of Frederick Hopkins, English biochemist and Nobel laureate (d. 1947)
- 1877 - Alexander Graham Bell installs world's first commercial telephone service in Hamilton, Ontario, Canada.
- 1889 - birth of John S. Paraskevopoulos, Greek-South African astronomer (d. 1951)
- 1894 - birth of Lloyd Hall, American chemist (d. 1971)
- 1941 - birth of Ulf Merbold, German physicist and astronaut
- 1958 - death of Kurt Alder, German chemist and Nobel laureate (b. 1902)
- 1963 - death of Raphaël Salem, Greek mathematician (b. 1898)
- 1990 - Asteroid Eureka discovered.
- 2002 - death of Erwin Chargaff, Austrian biochemist (b. 1905)
- 2005 - death of Jack Kilby, American electrical engineer and Nobel laureate (b. 1923)