Autumn Equinox, 23 September: The Year’s Most Even Day, and Why It Is Called “Fen”
At half past six in the evening I went downstairs to buy vegetables. The sky was still light, but the sun had already slipped away beyond the next building. Back indoors I looked at the calendar: 23 September 2026, the autumn equinox.
The solar term is called “fen” — the dividing point — and not by accident. Dong Zhongshu, writing in the Han dynasty’s Luxuriant Dew of the Spring and Autumn Annals (Chun Qiu Fan Lu), explained it: on the day of the autumn equinox “yin and yang are in equal halves”, and so “day and night are even and cold and heat are level” — daylight and darkness are much the same length, and so are warmth and chill (the line is often quoted in solar-term features). Only two days in the year are like this: the spring equinox and the autumn equinox. In Japan the day is also a statutory holiday, 秋分の日 (Shūbun no Hi, Autumn Equinox Day), and the meaning the law gives it is “to honour ancestors and remember the departed” (per the Japanese Cabinet Office’s official explanation of the national holidays).
The ancients also split it into three phenological periods, recorded in the Monthly Ordinances and Seventy-two Phenological Periods (Yue Ling Qi Shi Er Hou Ji Jie): the first, “thunder begins to gather in its sound”; the second, “the hibernating insects seal up their burrows”; the third, “water begins to dry up”. The book’s explanation of the first is vivid: thunder sounds in the yang qi of the second month; by the eighth month, amid the yin qi, it “gathers its sound and sinks into the earth”, “and all things follow it down” — from this day, thunder ought to pack up for the season.
The autumn equinox was also once the proper date for worshipping the moon. The Zhou dynasty already had a ritual order in which “the Son of Heaven sacrificed to the sun in spring and to the moon in autumn”, and the line in the Book of Rites, the chapter “Meaning of Sacrifices” (Li Ji, Ji Yi) — “sacrifice to the sun at the altar, sacrifice to the moon at the pit” — describes precisely that arrangement; after the Qin and Han dynasties every age kept a rite of moon sacrifice at the autumn equinox, and by the Ming and Qing the imperial altar for the moon was the site of today’s Moon Altar Park in Beijing (first built in the ninth year of the Jiajing reign, 1530). Later the time for worshipping the moon moved to the Mid-Autumn Festival on the fifteenth day of the eighth month; one widely repeated explanation is that the moon on the equinox itself is not necessarily full, and people preferred the night when the moon was roundest.
What is interesting is that “fen” feels completely unlike “dao”, the character for arrival. The autumn equinox is not “autumn has come” but “autumn is half over”. That makes it the right day for one particular task: checking progress — is the harvest in, is what needed drying dried, is the body still running on a summer schedule. The Yellow Emperor’s Inner Canon (Huang Di Nei Jing) gives the regimen for the three autumn months as “retire early and rise early, keeping the same hours as the chickens”, exactly one step shifted from summer’s “retire late and rise early”.
On 占卜迷指, many people start asking around the autumn equinox how to use what is left of the year. That is a question worth sitting down with: write your situation out clearly and the system will recommend a suitable method, cast the chart, interpret it and export it, laying out the variables for the remaining months so that you can look at them properly.
Sources
- People’s Daily Overseas Edition (Xiao Fang, 24 September 2018: the line “sacrifice to the sun at the altar, sacrifice to the moon at the pit” from the Book of Rites, the historical equinox moon rite, and Beijing’s Moon Altar): http://paper.people.com.cn/rmrbhwb/html/2018-09/24/content_1882922.htm
- Monthly Ordinances and Seventy-two Phenological Periods (Yue Ling Qi Shi Er Hou Ji Jie) — the original text of the three autumn-equinox periods with Bao’s commentary, at Wikisource: https://zh.wikisource.org/wiki/%E6%9C%88%E4%BB%A4%E4%B8%83%E5%8D%81%E4%BA%8C%E5%80%99%E9%9B%86%E8%A7%A3
- Yellow Emperor’s Inner Canon, “Basic Questions” (Su Wen), “Greater Treatise on Regulating the Spirit According to the Four Qi” — the regimen for the three autumn months, at Wikisource: https://zh.wikisource.org/wiki/%E7%B4%A0%E5%95%8F
- Japanese Cabinet Office, official explanation of the national holidays (Autumn Equinox Day, 23 September 2026): https://www8.cao.go.jp/chosei/shukujitsu/gaiyou.html
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