From White Dew to Autumn Equinox: The Fifteen or Sixteen Days When Temperature Swings Widen
At three in the morning, I was woken up by the cold.
Fumbling for a blanket in the dark, I was still thinking: wasn't I running the air conditioner just last week? The next morning, the sun was strong enough to make you want short sleeves; coming home at night, I jogged along with my neck tucked down into my collar. My mother sent just one line on WeChat: where are the long johns?
If you too have been living through this "two seasons in one day" lately, then you are standing in one of the stretches of the year when the day-night temperature difference widens sharply — from White Dew to the Autumn Equinox.
In 2026, White Dew arrives at 22:41 on September 7, and the Autumn Equinox at 08:05 on September 23 — just over half a month apart (dates are subject to that year's solar-term table).
Why This Particular Half-Month
Put plainly, the sun has gotten lazy.
The point of direct sunlight moves steadily south, the days grow shorter and the sunlight weaker, and the nights are often clear and cloudless, so the little warmth the ground stored up during the day dissipates in a rush. The daytime residual warmth and the nighttime chill are thus brought to their closest distance, and the temperature difference suddenly opens up.
According to a September 2025 solar-term report in People's Daily, night temperatures fall markedly after White Dew, and in some areas the day-night temperature difference can reach 10 degrees Celsius. Xinhua also noted in its "The Beauty of the Seasons · White Dew" that at this time cold air "switches from defense to offense," the daylight is still hot, and temperatures drop quickly after nightfall.
Our forebears had no instruments, but they wrote this felt experience into folk sayings:
A White Dew, Autumn Equinox night: each night cooler than the last.
At White Dew don't bare your body; at Cold Dew don't bare your feet.
Both say the same thing: the cold begins at night, and people are usually frozen by their own carelessness.
It should be noted that the degree to which the temperature difference widens varies by region — conditions in the northwest and on the Qinghai-Tibet Plateau differ from those in central and eastern China; the "sharp widening" here mainly refers to what most people feel across central and eastern China.
The Ancients Put Three Shifts on Duty for This Half-Month
Wu Cheng of the Yuan dynasty, in his Monthly Ordinances and the Seventy-Two Seasonal Indicators Explained (Yueling Qishi'er Hou Jijie), wrote of White Dew: "The damp qi of water and earth congeals into dew; autumn belongs to metal, the color of metal is white, white is the color of dew, and the qi now begins to turn cold." The "white" in the name is the color of autumn.
It also assigned three seasonal indicators (hou) to White Dew:
| Indicator | Phenological sign | What it means |
|---|---|---|
| First hou | Wild geese arrive | The wild geese begin flying south |
| Second hou | The dark bird returns | The swallows head back south |
| Third hou | Flocks of birds store food | Birds of every kind begin hoarding food for winter |
Interestingly, according to Xinhua, White Dew is the solar term among the twenty-four whose three phenological features are all related to birds. Birds sense the season switching tracks before people do, so the ancients simply used birds as a calendar.
Autumn Is for "Gathering In," Not for "Pushing Hard"
In the Huangdi Neijing (The Yellow Emperor's Inner Classic), "Basic Questions," "The Great Treatise on Regulating the Spirit in Accordance with the Four Qi," autumn's keyword is a single word:
The three months of autumn are called "receiving and leveling." The heavenly qi becomes urgent, the earthly qi becomes clear; go to bed early and rise early, arising together with the rooster; keep the will calm and peaceful so as to soften autumn's severity; gather in the spirit and qi so that the autumn qi stays level; let not the will turn outward, so that the lung qi is clear. This is the response to the autumn qi, the way of nourishing the "gathering in."
In today's words: go to bed early, don't get wildly elated or devastated, and gather back the mind and spirit you have scattered outward.
By traditional health-cultivation accounts, autumn belongs to metal, governs the lungs, and governs descending and subduing. Everything you sent outward in summer — enthusiasm, energy, the credit of late nights — has now come due for settlement. So the last thing you should do in this stretch is precisely to "make one more push."
A Few Small Things I Do During This Half-Month
- When to change the blanket: change it the moment White Dew arrives — don't wait for a cold to remind you
- Don't sleep facing the window at night: autumn wind is called "thief wind," and it picks on people who are asleep
- Take care of your feet first: as the folk saying goes, "at Cold Dew don't bare your feet" — the feet are one stop ahead
- Less pungent, more moistening: autumn is dry; eat too much chili and barbecue, and the next day your throat and skin will protest on your behalf
- Give yourself a stretch of "no deciding": no changing jobs, no major decisions — just sleep enough first
In the end, these are all common sense. But common sense needs to be repeated precisely because we always think we can tough out a season.
If the change of season has lately left you sleeping poorly and feeling pent up inside, without being able to say exactly what the problem is, don't rush to draw conclusions about yourself — if insomnia or low mood persists for more than two weeks, please see a doctor or a counselor. If you simply want another angle on your own state, you can describe your specific situation on 占卜迷指, let the system recommend a suitable method, and produce a chart and reading that you can also export to keep and revisit.
The season doesn't ask whether you're ready. It simply grows a little cooler each night, and cooler still.
Sources
- Original text of "The Great Treatise on Regulating the Spirit in Accordance with the Four Qi" from the "Basic Questions" of the Huangdi Neijing
- Monthly Ordinances and the Seventy-Two Seasonal Indicators Explained (Yueling Qishi'er Hou Jijie), by Wu Cheng (Yuan dynasty), Wikisource
- People's Daily, "What Does the 'White' of White Dew Refer To?" (2025-09-06)
- Xinhua, "The Beauty of the Seasons · White Dew"
- Xinhua Net, "Culture China Tour · Sounding the Twenty-Four Solar Terms · White Dew" (2026-09-06)
- China Weather Network: Twenty-Four Solar Terms feature
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