01/01/2025
The year 2025 has begun. January 1st is New Year's Day in Japan, but Japan did not start using the Western calendar (Gregorian calendar) until the 19th century. Until then, the lunar calendar had been used.
If you open this link (https://www.benri.jp/calendar/kyuureki/?year=2025), you can see the difference between the solar calendar and the lunar calendar in 2025. (English translation can be chosen from the top right corner.) If you look at the first day of the lunar calendar on this website, you can see that it is January 29th. In other words, today is January 1st in the solar calendar, but if Japan was still using the lunar calendar, it would still be the beginning of December in Japan.
When did Japan start using the solar calendar? The Meiji government decided that the day after December 2nd, 1872, would be January 1st, 1873.
Incidentally, in the lunar calendar, the months of January to March are considered spring, April to June are summer, July to September are autumn, and October to December are winter, and the first day of each month is always a new moon. In other words, each month starts with a new moon, reaches full moon after about 15 days, and then starts the next month when it becomes a new moon. It's easy to understand because it's linked to the waxing and waning of the moon. Furthermore, the number of days in a month is also different from the solar calendar. There are months with 30 days and months with 29 days, and the months with 30 days are called “dai-no-tsuki (large months)” and the months with 29 days are called “sho-no-tsuki (small months)”. This is because the cycle of the waxing and waning of the moon is 29.5 days. If a month is 29 days long, it is too short, and if a month is 30 days long, it is too long.
In order to catch up with the Western powers, the Meiji government changed the calendar rather forcefully, and this has led to various inconveniences in modern Japan.
For example, in January you will often see banners and signs advertising “New Spring Sales (新春セール)”. It is cold in Japan in January. So why is it called “New Spring”? Because, in the lunar calendar, spring begins in January. The day after December 2nd in the 5th year of Meiji (1872) was declared to be January 1st in the 6th year of Meiji (1873). In the lunar calendar, the day was still the beginning of December, but January suddenly began. The impacts of this abrupt change are still present in modern Japan.
In modern Japan, the days of “Vernal Equinox” and “Autumnal Equinox” are written in the calendar in the same way as in the West. In addition to this, the lunar calendar terms “Risshun (First Day of Spring)” and “Rittou (First Day of Winter)” are sometimes written in small letters. Why is that? For example, “Risshun (立春)” in 2025 is February 3rd in the solar calendar. This is January 6th in the lunar calendar, so it is perfect for the “First Day of Spring” in old Japan.
There is also an old Japanese phrase called “Chūshū no Meigetsu” (中秋の名月; the full moon of the middle of autumn). The word “Chūshū” literally means the middle of autumn. In the solar calendar, “Chūshū no Meigetsu” in 2025 will be on October 6th. However, in the lunar calendar, it will be on August 15th. There is quite a difference. In the lunar calendar, the months of July to September are autumn, so it is also exactly in the middle of autumn.
In old Japanese documents, you will find many seasonal terms such as “Risshun” and “Chūshū no Meigetsu”. If you don't know about the lunar calendar, you won't understand the meanings and the context correctly.
Converting from the lunar calendar to the solar calendar is a difficult process. As mentioned above, the government suddenly switched over. Therefore, when translating Edo-period census records into English, it is normal not to convert them to the solar calendar.
Image from https://jpnculture.net/kyuureki-shinreki/
