Portal:History of science/Selected anniversaries/March 21
- 1762 - Death of Nicolas Louis de Lacaille, French astronomer (b. 1713)
- 1768 - Birth of Joseph Fourier, French mathematician (d. 1830)
- 1772 - Death of Jacques-Nicolas Bellin, French cartographer (b. 1703)
- 1795 - Death of Giovanni Arduino, Italian geologist (b. 1714)
- 1844 - The Baháʼí calendar begins. This is the first day of the first year of the Baháʼí calendar. It is annually celebrated by members of the Baháʼí Faith as the Baháʼí New Year or Náw-Rúz
- 1859 - Zoological Society of Philadelphia, 1st in US, incorporated
- 1932 - Birth of Walter Gilbert, American chemist, Nobel Prize laureate
- 1980 - Death of Peter Stoner, American mathematician, astronomer and Christian apologist (b. 1888)