December 20 Holidays

December 20 is the 354th day of the year. More than 5 holidays and observances fall on the date. Cathode-Ray Tube Day marks December 20, 1897, when Karl Ferdinand Braun demonstrated the first cathode-ray tube oscilloscope — the technology that became the foundation of television, radar, and the computer monitor for most of the 20th century. Mudd Day celebrates Dr. Samuel Mudd — the Maryland doctor who treated John Wilkes Booth’s broken leg after Lincoln’s assassination and was controversially convicted of conspiracy — whose name entered the language in the phrase “your name is mud.” Sacagawea Day celebrates Sacagawea, the Shoshone woman who guided the Lewis and Clark Expedition from 1804 to 1806 — serving as interpreter, cultural liaison, and living proof of the expedition’s peaceful intentions to the Indigenous nations they encountered. This page is refreshed each year as new observances are added.