September 21 is the 264th day of the year in the Gregorian calendar, which means there are 101 days left until the end of the year. It is often associated with the arrival of autumn in the Northern Hemisphere, as the autumn equinox typically occurs around this time. This date is also recognized for various observances, including International Day of Peace, which promotes global ceasefire and non-violence. Additionally, it marks the birthday of notable figures such as H.G. Wells, a famous English author known for his works in science fiction.