Nagatsuki is a Japanese traditional name for September on the old calendar. The word is however used for September on the new calendar today. It falls on the period from October through November on the new calendar.

There are a lot of theories as to its origin. Some of them state that it is a shortened form of Yonaga-tsuki (a long night month), a pun for Nagame-tsuki (a long rain month) or a pun for Nagori no tsuki, which means a month when a remnant of the full moon can be seen. Still another states that as it is the month for rice harvest and the 長 character has the meaning of swelling, people named the month to cerebrate the swollen ears of rice plants. September on the old calendar is also called Nezametsuki, which means a month of waking up in the morning.

September 1st is the National Disaster Prevention Day, when disaster-preparedness drills are conducted all over the country. The day was established to mark Great Kanto Earthquake, which attacked Japan on this day in 1923. The national holidays in September are Aged People’s Day on the 3rd Monday and Autumnal Equinox Day on the 23rd.