Best Answer: The actual dates vary slightly from year to year, but... Summer-June 21 Autumn-September 21 Winter-December 21 Spring-March 21 The actual dates coincide with specific events in the solar system. Autumn and Spring are the dates (and actually the exact moment) when the sun is directly above the Equator-also known as the equinox. http://answers.yahoo.com/question/;_ylt=...