January 15 is the 15th day of the year in the Gregorian calendar, which is used by most of the world. It falls in the middle of winter in the Northern Hemisphere and summer in the Southern Hemisphere. This date is often associated with various events and observances, including the celebration of Martin Luther King Jr. Day in the United States, which honors the civil rights leader's contributions to social justice. On this day, people may reflect on the importance of equality and community service. January 15 is also notable for being the birthday of several famous individuals, including Martin Luther King Jr. himself, who was born on this date in 1929.