On August 23, 2026, at 02:18 UTC, the Sun crosses 150° of ecliptic longitude and the Chinese solar calendar announces Chu Shu, 处暑 — 'End of Heat'. It is the fourteenth of the year's twenty-four solar terms, the gentle counterpart to Li Qiu's dramatic season-opening two weeks earlier, and the term the tradition trusts to finally send the Autumn Tiger home. This piece gives the exact engine-computed moment, explains why Chu Shu changes nothing in the Ba Zi calendar — the Fire Monkey month keeps running — and follows the week into the Ghost Festival that opens four days later.
What "End of Heat" actually marks
The character 处 (chù) carries the classical gloss 止也 — "it means to stop." 暑 (shǔ) is the summer heat itself. Read together: the heat halts here. Not the warmth — the heat, the oppressive governing force that organized July and August.
Astronomically, the claim is precise. The solar terms divide the Sun's annual path into twenty-four stations of 15° each. Chu Shu's 150° sits exactly two-thirds of the way from the June solstice (90°) to the September equinox (180°). Daylight is now shortening quickly; the Sun's arc drops visibly week over week. The thermometer, as always, lags the light — oceans and continents release their stored heat for weeks — which is why the tradition split the difference into two terms: Li Qiu declares autumn established while the heat still rages, and Chu Shu, sixteen days later, declares the heat itself spent.
Chinese folk tradition even names the gap between the two declarations. The 秋老虎 — the Autumn Tiger, that ferocious hot spell that prowls after Li Qiu — is traditionally trusted to retreat at Chu Shu. Hot afternoons after August 23 are read as leftovers, not the season.
A note on precision, since we computed this rather than copied it: our two independent implementations put the 2026 crossing at 02:18:58 and 02:18:49 UTC — a nine-second spread, which is why we state the minute (02:18 UTC, 10:18 Beijing) and no more. When a calendar runs on an instant, honest calculation shows its error bars.
What does NOT change: the Fire Monkey keeps running
Here is the detail that separates the solar calendar's two kinds of terms — and the one casual astrology sites most often get wrong.
The twenty-four terms alternate between section terms (节, jié) and mid-month terms (中气, zhōngqì). Only the twelve section terms open a new Ba Zi month; the twelve mid-month terms mark the month's center. Li Qiu was a section term — at 11:42 UTC on August 7 the month pillar turned to 丙申, Bing Shen, the Fire Monkey. Chu Shu is that Monkey month's mid-point marker.
So at 02:18 UTC on August 23, nothing in the Ba Zi calendar changes. Everyone on Earth stays in the Fire Monkey month, inside the Fire Horse year (丙午). The month pillar holds until Bai Lu (白露, White Dew) on September 7 at 14:41 UTC, when it turns to 丁酉, Ding You — the Fire Rooster.
What Chu Shu does mark, inside Ba Zi's logic, is the Monkey month reaching full maturity. A month pillar is not uniform across its thirty days: the branch's energy is read as establishing in its first days, peaking at the mid-month term, and handing over near the boundary. Chu Shu is the Fire Monkey's noon. If the month's classical character — Metal season opening, quick hands, sharp plans, stalled things moving — has felt abstract since August 7, the tradition says this is the week it stops being abstract. (Whether that month character helps or challenges your chart specifically depends on your own pillars — which is what a full pillars calculation is for, starting from your Day Master.)
The three pentads: what the old calendar watches for
Each solar term divides into three pentads (候, hòu) of roughly five days — micro-seasons, each named for one observable change. Chu Shu's three, from the classical almanacs:
| Pentad | Chinese | The observation |
|---|---|---|
| First | 鹰乃祭鸟 | "The hawk offers birds" — raptors hunt visibly and lay out prey as autumn's food chain sharpens |
| Second | 天地始肃 | "Heaven and earth turn stern" — the first austerity enters the air; growth stops being generous |
| Third | 禾乃登 | "The grain is presented" — rice and millet come ripe; the harvest formally begins |
The pentads are the calendar's ground truth. The term names describe the Sun; the pentads describe what a farmer, looking up from the field, should be able to confirm. "Heaven and earth turn stern" is the poetic center of Chu Shu: the year's generosity is over, and its discrimination — autumn's Metal-season work of cutting away — begins.
Four days later: the Ghost Festival
Chu Shu 2026 lands on the eleventh day of lunar month seven — which places it four days before one of the lunar calendar's most storied dates. On August 27, lunar 7/15, comes Zhong Yuan Jie (中元节), the Ghost Festival: the full moon of the "ghost month," when tradition holds that the gates between worlds stand open and offerings are made to ancestors.
The pairing is not a coincidence of 2026 — it is structural. The ghost month is always lunar month seven, and Chu Shu always falls inside it. The same stretch of days that turns heaven and earth "stern" is the stretch the lunar calendar devotes to the dead. Two different clocks — one solar, one lunar, running six days apart this month — arriving independently at the same mood.
That is the quiet lesson of the fourteenth term. Nothing flips at Chu Shu; no pillar turns, no month opens. The calendar simply notes that the year has crossed from accumulation into release — and everything else, from the hawks to the harvest to the festival of ancestors, files in behind it.
The full year of term boundaries, eclipses, and transits is charted in the 2026 Almanac.
Frequently asked questions
When is Chu Shu in 2026?
August 23, 2026. The term is exact at the instant the Sun reaches 150° ecliptic longitude — 02:18 UTC, which is 10:18 Beijing time. Like every solar term, Chu Shu is an instant, not a day: the date is simply the day that instant falls on.
What does Chu Shu mean?
Chu Shu (处暑) translates as 'End of Heat' or 'Heat Withdraws'. The classical gloss reads 处 as 'to halt': the heat stops here. It is the fourteenth of the twenty-four solar terms and the second term of autumn — the calendar's declaration that summer's heat is finished as a governing force, even if hot afternoons linger.
Does the Ba Zi month pillar change at Chu Shu?
No — and this is the detail most casual sources get wrong. Ba Zi month pillars change only at the twelve section terms (节), like Li Qiu. Chu Shu is a mid-month term (中气), so the Bing Shen (Fire Monkey) month that opened on August 7 keeps running until Bai Lu on September 7 at 14:41 UTC, when the pillar turns to Ding You (Fire Rooster).
What is the Autumn Tiger?
The 秋老虎 (Autumn Tiger) is the Chinese folk name for the fierce hot spell that prowls the weeks after autumn officially begins at Li Qiu. Chu Shu is the term traditionally trusted to send it home: after End of Heat, hot days are read as leftovers rather than the season itself.
Is Chu Shu the same as the end of summer weather?
Not exactly. The solar terms track the Sun, not the thermometer — Chu Shu marks the Sun reaching 150°, two-thirds of the way from solstice to equinox. Air temperature lags weeks behind the light, so many regions stay warm past Chu Shu. The calendar is describing the trajectory: from this point, the heat is in retreat.
References
- ChushuWikipedia
- Solar termWikipedia
- Ghost FestivalWikipedia