December 21

The Roman Senate proclaims Vespasian emperor, concluding the chaotic Year of the Four Emperors.

Vespasian's proclamation as emperor concluded the chaotic Year of the Four Emperors, a period of civil war and rapid political turnover following Emperor Nero's death the previous year. His subsequent decade-long reign restored stability to the empire and founded the Flavian dynasty, whose most enduring physical legacy remains the Colosseum, completed by his son Titus.

Mapuche warriors achieve a major victory against Spanish colonial troops at the Battle of Curalaba in Chile.

The Mapuche victory at Curalaba, in which Spanish colonial forces suffered a devastating defeat including the death of the Spanish governor, triggered a prolonged uprising that pushed Spanish settlement out of much Mapuche territory in southern Chile for generations. The Mapuche would maintain effective independence from Spanish and later Chilean control longer than almost any other Indigenous group in the Americas.

Pilgrims aboard the Mayflower disembark near what would become Plymouth, Massachusetts.

The Pilgrims' landing at Plymouth followed weeks of scouting the Massachusetts coastline after their initial arrival further north than intended, ultimately settling at a site with a natural harbor and previously cleared land, abandoned following a devastating epidemic among the local Wampanoag population. Their first winter proved catastrophic, killing roughly half the colonists before spring.

The Rochdale Society of Equitable Pioneers opens its cooperative shop in England, establishing the modern cooperative movement.

The Rochdale Pioneers' cooperative shop, founded by a group of weavers and skilled tradesmen seeking an alternative to exploitative retail practices, established core principles of democratic member ownership and profit-sharing that became the foundation for the modern cooperative movement worldwide. Their model has since been replicated across countless industries, from agriculture to banking to retail.

HMS Challenger departs Portsmouth, England to conduct a groundbreaking global oceanographic survey.

HMS Challenger's four-year global oceanographic expedition, covering nearly 70,000 nautical miles, fundamentally established the modern science of oceanography, cataloging thousands of previously unknown marine species and gathering extensive data on ocean depths, temperatures, and currents. The voyage's findings filled dozens of scientific volumes and remained a foundational reference for oceanographers for decades afterward.

Apollo 8 launches toward the Moon, marking humanity's first crewed journey beyond low Earth orbit.

Apollo 8's launch sent the first humans beyond low Earth orbit toward the Moon, a mission whose crew famously read from the Book of Genesis during a Christmas Eve broadcast while orbiting the lunar surface, an event watched by hundreds of millions of people worldwide. The mission's success, achieved despite it being only the third crewed Apollo flight, paved the way for the subsequent lunar landing.

A terrorist bomb destroys Pan Am Flight 103 over Lockerbie, Scotland, killing 270 people.

The bombing of Pan Am Flight 103 over Lockerbie, Scotland, killed all 259 people aboard along with eleven residents on the ground, making it the deadliest terrorist attack in British history until the 2017 Manchester Arena bombing. A Libyan intelligence officer was eventually convicted for the bombing, though questions about the full extent of responsibility persisted for years afterward.

Soviet republics sign the Alma-Ata Protocol, formally establishing the Commonwealth of Independent States.

The Alma-Ata Protocol formally expanded the earlier agreement establishing the Commonwealth of Independent States to include eight additional former Soviet republics, effectively finalizing the dissolution of the Soviet Union as a unified state. The protocol addressed practical matters including the fate of Soviet nuclear weapons and the country's UN Security Council seat, which passed to Russia.

The Palestinian Authority assumes administrative control of Bethlehem from Israel.

The Palestinian Authority's assumption of control over Bethlehem, part of a broader transfer of West Bank territories under the Oslo Accords, represented one of the first instances of Palestinian self-governance in a significant Palestinian population center. The transfer carried particular symbolic weight given Bethlehem's religious significance as the traditional birthplace of Jesus.

Jupiter and Saturn reach their closest planetary conjunction observed from Earth since 1623.

The 2020 Great Conjunction of Jupiter and Saturn, appearing so close together in the night sky that some observers described them as forming a single bright point of light sometimes called the "Christmas Star," represented the closest such alignment visible from Earth in nearly 400 years. The rare astronomical event drew widespread public interest in stargazing during a challenging pandemic year.