Miscellaneous (4)

Suddenly, do you know on which day of February “Setsubun” is held?
I suspect that most people would answer, “February 3.”

It is true that “this year’s” Setsubun is February 3. …… Actually, the date of Setsubun is not fixed and can be on the 2nd or 4th! Here is some trivia about the date of Setsubun.

What is “Setsubun” in the first place?

Setsubun originally means the day before Risshun, Risshatsu, Risshakyu, and Risshwinter, when the spring, summer, autumn, and winter seasons begin. The name “Setsubun” is also derived from the seasonal “Setsubun” (division of the seasons).

In the olden days, it was believed that evil spirits tended to enter the country when the seasons changed, and thus, Setsubun was held to ward off evil spirits. During the Edo period (1603-1867), when the old calendar was used, Risshun was regarded as the beginning of the new year, so Setsubun in February, the day before Risshun, became particularly important, and it seems to have taken root in modern times as a seasonal event.

Are the seasons gradually shifting?

Seasonal divisions, such as Risshun, are determined by the Earth’s orbit, or the “24 seasonal divisions,” which divide the Earth’s orbit around the sun into 24 equal segments of 15 degrees each. However, the orbital period is not exactly 365 days, but rather “365 days plus a little less than 6 hours,” resulting in an error of about 6 hours per year.

As you probably know, once every four years, the month of February is increased by one day to 29 days. However, there is still a small margin of error that cannot be fully eliminated, so the leap year is reduced three times in every 400 years.

The reason why the date of Setsubun comes and goes

Due to such adjustments to the calendar, the 24th day of the month, which is based on the actual movement of the celestial bodies, may change by about one day from year to year. If the day of Risshun changes, the day before Risshun, Setsubun, also changes.

Two years ago, in 2021, the Setsubun was on February 2. This was the first time in 124 years. For the next 30 years, “February 2 Setsubun” will come every four years. Incidentally, the last “February 4 Setsubun” was in 1984, about 40 years ago. The next one will not come until 2104.

How was it? Even though the date of Setsubun is not fixed, I thought it was quite rare since it had not been more than 30 years until 2021 that Setsubun was not on a day other than February 3.

I am again impressed by the fact that people in the past, when there were no computers, were able to discover the 24 solar terms, which were not so different from the modern calendar, and enjoyed seasonal festivals.

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