August 21 is the 233rd day of the year in the Gregorian calendar and the 234th in leap years. After this date there are 132 days left in a common year. The day sits in late summer in the Northern Hemisphere and late winter in the Southern Hemisphere; in many annual lists it is used as a marker for seasonal activities, commemorations and anniversaries. The day’s position is counted according to the Gregorian calendar and the arithmetic for leap years follows standard rules for adding an extra day in leap years.

Notable historical events

  • 1911 – The theft of Leonardo da Vinci’s Mona Lisa from the Louvre became public when the painting was discovered missing, an incident that later drew worldwide attention.
  • 1831 – Nat Turner’s slave rebellion in Virginia began around this date, an event that had major social and political repercussions in the United States.
  • 1959 – Hawaii was admitted to the United States as the 50th state, an important milestone in modern U.S. history.
  • 1968 – Military action by Warsaw Pact forces entered Czechoslovakia during the Prague Spring period; operations spanned late August and are often associated with the night of August 20–21.
  • 2017 – A total solar eclipse crossed the continental United States, an extensively observed scientific and cultural event.

Observances and cultural notes

Various national and local observances fall on August 21 in different places. For example, the United States recognizes National Senior Citizens Day as a date to honor older adults. The day is also a common choice for anniversaries, public commemorations and community events. In popular culture and astrology, people born on August 21 are typically associated with the zodiac sign Leo, and common August birthstones include peridot and spinel.

Because it sits late in the eighth month, August 21 often appears in planning documents, school calendars, seasonal programming and travel schedules. Historians, journalists and archivists commonly use the date when compiling timelines and anniversary coverage; it also frequently appears in lists of notable births and deaths.

Overall, August 21 is remembered both for specific, well‑documented historical moments and for its routine role as a calendrical reference point used across cultures for scheduling, celebration and remembrance.