1. The Pilgrims landed in Plymouth - December 21, 1620 is the day the Pilgrims landed in Plymouth, Massachusetts. This event marked the beginning of the Plymouth Colony and the establishment of the first permanent European settlement in New England.

2. The Boston Tea Party - On December 21, 1773, a group of colonists disguised as Native Americans boarded three British tea ships and dumped over 300 chests of tea into Boston Harbor. This event later became known as the Boston Tea Party and was a significant event that led to the American Revolution.

3. The Battle of Savannah - On December 21, 1778, American and French troops attempted to capture the British-held city of Savannah, Georgia. The battle resulted in a major defeat for the Americans and French and led to the deaths of many soldiers.

4. Massachusetts ratifies the US Constitution - On December 21, 1787, Massachusetts became the sixth state to ratify the United States Constitution, helping to pave the way for the adoption of the federal document.

5. First manned spaceflight to orbit the Moon - On December 21, 1968, the Apollo 8 mission became the first manned spacecraft to orbit the Moon. The three-man crew, consisting of Frank Borman, James Lovell, and William Anders, conducted several scientific experiments and famously took the iconic Earthrise photo. The command module for the mission is on display at the Museum of Science in Boston.