Historical events on the 21st of November
- 1676 – The Danish astronomer Ole Rømer presents the first quantitative measurements of the speed of light.
- 1861 – American Civil War: Confederate President Jefferson Davis appoints Judah Benjamin Secretary of War.
- 1902 – The Philadelphia Football Athletics defeated the Kanaweola Athletic Club of Elmira, New York, 39–0, in the first ever professional American football night game.