An earthquake, likely originating along a fault in the lower Tagus Valley, struck Lisbon and its surroundings, killing an estimated 30,000 people and toppling churches and homes across the city. Contemporary chroniclers described buildings collapsing across Portugal, and the event stood for over two centuries as the country's worst natural disaster until it was eclipsed by the catastrophic 1755 Lisbon earthquake.

Mao Zedong was born in the village of Shaoshan in Hunan province, the son of a relatively prosperous peasant farmer. He would go on to co-found the Chinese Communist Party, lead the Long March, defeat the Nationalists in China's civil war, and rule the People's Republic of China from 1949 until his death in 1976, reshaping the country through campaigns including the Great Leap Forward and the Cultural Revolution.

The Melbourne Cricket Ground hosted its first Boxing Day Test between Australia and England, beginning what would become one of cricket's most cherished fixtures. The tradition of playing a Test match starting on December 26 grew steadily through the twentieth century, eventually drawing crowds exceeding 80,000 and becoming a fixed centerpiece of the Australian sporting calendar.

Astronauts Frank Borman, James Lovell, and William Anders splashed down safely in the Pacific Ocean, completing history's first crewed lunar orbital mission. Their flight, which included ten orbits of the Moon and a famous Christmas Eve broadcast reading from Genesis, restored American confidence after the Apollo 1 fire and proved the hardware and trajectory needed for a lunar landing the following year.

In a brief, almost anticlimactic session, the Council of Republics of the Supreme Soviet issued Declaration No. 142-Н, formally dissolving the USSR and acknowledging the independence of the twelve remaining republics. It ended nearly 70 years of Soviet rule and closed the Cold War era, replacing the superpower with fifteen independent states and the loosely organized Commonwealth of Independent States.

The third-largest earthquake ever recorded ruptured the seafloor off Sumatra, unleashing waves up to 30 meters high that struck coastlines from Indonesia to Somalia within hours. Entire villages in Aceh vanished; resort beaches in Thailand and Sri Lanka were scoured clean. The disaster exposed the absence of any Indian Ocean tsunami warning system and prompted a global overhaul of early-detection networks.