September (pronunciation) is the ninth month of the year in the Gregorian Calendar and one of four Gregorian months with 30 days. In Latin, septem means "seven" and septimus means "seventh"; September was in fact the seventh month of the Roman calendar until 153 BCE, when the first month changed from Kalendas Martius to Kalendas Januarius. In the Northern hemisphere, the beginning of the meteorological autumn is 1 September. September marks the beginning of the ecclesiastical year in the Eastern Orthodox Church. September begins on the same day of the week as December every year, because there are 91 days separating September and December, which is a multiple of seven (the number of days in the week).