Portal:History of science/Selected anniversaries/October 21
- 1505 – Death of Paul Scriptoris, German mathematician
- 1520 - Ferdinand Magellan discovers a strait now known as Strait of Magellan
- 1660 – Birth of Georg Ernst Stahl, German scientist (d. 1734)
- 1687 – Birth of Nicolaus I Bernoulli, Swiss mathematician (d. 1759)
- 1821 – Birth of Eduard Heine, German mathematician (d. 1881)
- 1833 – Birth of Alfred Nobel, Swedish inventor and founder of the Nobel Prize (d. 1896)
- 1872 – Death of Jacques Babinet, French physicist (b. 1794)
- 1914 – Birth of Martin Gardner, American mathematician and writer
- 1952 – Death of Hans Merensky, South African geologist and philanthropist (b. 1871)
- 1957 – Birth of Wolfgang Ketterle, German physicist, Nobel laureate
- 1965 - Comet Ikeya-Seki approaches perihelion, passing 450,000 kilometers from the sun
- 1969 – Death of Waclaw Sierpinski, Polish mathematician (b. 1882)
- 2003 - Images of the dwarf planet Eris are taken and subsequently used in its discovery by the team of Michael E. Brown, Chad Trujillo, and David L. Rabinowitz