Francis G. Pease's interferometer at Mount Wilson Observatory is the first to measure the diameter of a star - the Betelgeuse
On December 13, 1920
Saint Celestine V abdicates the papacy after only five months; Celestine hoped to return to his previous life as an ascetic hermit.
On December 13, 1294
- 862 Boudouin Iron Arm & Count of Flanders, elopes with Princess Judith, daughter King Charles of West Francia
- 1951 Future British PM Margaret Roberts (26) weds businessman Denis Thatcher (36) at Wesley's Chapel in City Road, London
- 2003 Italian operatic tenor Luciano Pavarotti (68) weds Nicoletta Mantovani at Modena Italy's Teatro Comunale