September is the ninth month of the year in both the Julian and Gregorian calendars, the third of four months to have a length of 30 days, and the fourth of five months to have a length of fewer than 31 days. September in the Northern Hemisphere and March in the Southern Hemisphere are seasonally equivalent. In the Northern hemisphere, the beginning of the meteorological autumn is on 1 September. In the Southern hemisphere, the beginning of the meteorological spring is on 1 September.