The summer solstice is the longest day of the year, and the shortest night. In the Northern Hemisphere it takes place between June 20 and 22, depending on the year. (The reverse is true in the Southern Hemisphere, where the longest day of the year occurs between December 20 and 22.) Humans may have observed the summer solstice as early as the Stone Age. Cultures around the world still celebrate the day with feasts, bonfires, picnics and songs.