TL;DR: Xử Thử is the 14th of the 24 solar terms, beginning around August 23 when the Sun reaches 150 degrees of ecliptic longitude, marking the retreat of heat and the arrival of autumn. Old texts such as Tuế thời quảng ký record three signs for this term: hawks sacrificing captured birds, heaven and earth turning stern, and rice ripening. In Vietnam, Xử Thử is not a separate festival but a marker in the solar-term calendar used for choosing days, watching the weather, and planning harvests.
What is Xử Thử and when does it begin?
Xử Thử (處暑) is the 14th of the 24 solar terms, coming after Lập Thu and before Bạch Lộ, and is the second term of autumn.
Xử Thử begins when the Sun reaches 150 degrees of ecliptic longitude and ends when it reaches 165 degrees, as Bạch Lộ begins, so it lasts about fifteen and a half days. In Vietnam time, from 1900 to 2100 the term usually begins on 23 August; 24 August occurs only in years from 1901 to 1983, and 22 August occurs from 2016 onwards. In 2026, Xử Thử begins at 9:21 on 23 August and lasts until Bạch Lộ begins at 21:41 on 7 September.
Start times of Xử Thử from 2025 to 2030, Vietnam time:
| Year | Start date | Time |
|---|---|---|
| 2025 | 23 August | 03:35 |
| 2026 | 23 August | 09:21 |
| 2027 | 23 August | 15:08 |
| 2028 | 22 August | 20:55 |
| 2029 | 23 August | 02:42 |
| 2030 | 23 August | 08:30 |
The Tuế thời quảng ký, in its section on the first month of autumn (孟秋月) in juan 3, quotes the Hiếu kinh vĩ: "大暑後十五日斗指坤為立秋後十五日斗指申為處暑", that is, fifteen days after Đại Thử the handle of the Dipper points to Khôn, which is Lập Thu, and fifteen days later it points to Thân, which is Xử Thử[1].
Why is it called Xử Thử and where does this term stand in the year?
The same section quotes the Tam thống lịch to explain the name: "處暑為七月中氣處暑者謂暑將退伏而潛處也", that is, Xử Thử is the middle qi of the seventh month, so named because the heat is about to withdraw, lie low and stay hidden[1]. The character "xử" (處) in the name therefore means to withdraw and stay hidden, not "to handle".
Juan 3 of the Tuế thời quảng ký is devoted to autumn and goes through its six terms in order: Lập Thu, Xử Thử, Bạch Lộ, Thu Phân, Hàn Lộ, Sương Giáng[1].
The Hiệp kỷ biện phương thư records the Sun's position: "處暑日躔巳宮初度是為鶉尾之次", that is, at Xử Thử the Sun enters the first degree of the Tị palace, in the Thuần Vĩ station[2]. The book uses this position as the monthly general of the seventh month: "處暑七月中日躔在巳宫為七月將"[2].
What customs does Xử Thử have in old books?
According to the Siku Quanshu abstract, the Tuế thời quảng ký (歲時廣記) was compiled by Trần Nguyên Tịnh, a man of the Southern Song, in 4 juan; the book takes the Nguyệt lệnh, the Hiếu kinh vĩ and the Tam thống lịch as its framework, then draws on miscellaneous works that record matters related to the seasons, arranged by month[1]. For Xử Thử it only quotes the three pentads of the Chu thư Thời huấn and records no rite attached to this day: "處暑之日鷹乃祭鳥後五日天地始肅後五日農乃登穀", that is, on the day of Xử Thử the hawk lays out the birds it has caught as if offering them, five days later heaven and earth begin to turn stern, and five days after that the farmers bring in the grain[1].
This is a record by phenology, taking natural phenomena as markers, not an act of worship.
What do Vietnamese people use Xử Thử for?
In practice, Xử Thử is used mainly for three things: tracking the weather as the season turns, choosing days by the solar-term calendar, and planning the farming season.
In the daily flying-star calculation of the Tam nguyên Cửu vận (Three Eras, Nine Periods), Xử Thử is a starting marker. The Trạch vận tân án by Thẩm Trúc Nhưng writes: "Or if one wants to calculate the Nhâm Thân day after Xử Thử. Since Xử Thử governs the matters after Hạ Chí, one begins counting Xử Thử from 3"[4], that is, the first Giáp Tý day after Xử Thử starts from star number 3 and the count runs backwards, so that Nhâm Thân falls on star number 4. This is a convention of the Huyền Không school, not an astronomical calculation.
For those who choose days by the traditional calendar, Xử Thử is a middle qi and does not change the month. The Hiệp kỷ biện phương thư counts the whole stretch from Lập Thu to the end of Xử Thử as the month of Thân ("從建申者始立秋終處暑")[2]; the solar month only turns to Dậu when Bạch Lộ begins.
What do old books say differently about Xử Thử?
The main difference is that each book assigns Xử Thử to a different direction, because each method relies on a different marker.
By the handle of the Dipper, Xử Thử is at Thân: besides the Hiếu kinh vĩ line "斗指申為處暑"[1], the Hiệp kỷ biện phương thư, placing the 24 terms on the 24 directions, also writes "立秋坤處暑申白露庚"[2]. By the Sun, Xử Thử is in the Tị palace. The Hiệp kỷ biện phương thư makes clear that the two methods serve two purposes: "月建視節氣斗杓也月將視中氣太陽也", the month branch follows the solar terms and the Dipper's handle, the monthly general follows the middle qi and the Sun[2].
Kỳ Môn Độn Giáp places Xử Thử in the Khôn palace instead. The Kỳ Môn Chỉ Quy writes "Khôn cung thống xử thử nhất tứ thất", meaning the Khôn palace governs Xử Thử and its three eras use configurations 1, 4 and 7[3]; the Yin Dun song recorded in the Hiệp kỷ biện phương thư also reads "處暑一四七"[2].
Summary table of Xử Thử
| Item | Content |
|---|---|
| Chinese characters | 處暑 |
| Position | The 14th of the 24 solar terms, the 2nd term of autumn |
| Start time | Usually 23 August, when the Sun is at 150 degrees of longitude |
| Length | About fifteen and a half days |
| Previous term | Lập Thu |
| Next term | Bạch Lộ |
| Meaning of the name | The heat withdraws and hides itself |
| Three signs according to the Chu thư Thời huấn | The hawk lays out birds as if offering them; heaven and earth begin to turn stern; the farmers bring in the grain |
| Direction of the Dipper's handle | Thân |
| Sun's palace according to the Hiệp kỷ biện phương thư | Tị |
| Palace in Kỳ Môn Độn Giáp | Khôn, configurations 1, 4, 7 |
Suggestions from Nhật Nguyệt
Nhật Nguyệt's suggestion: if you use the solar-term calendar to track the weather, Xử Thử marks the point when the heat begins to recede. In northern Vietnam, by late August the harsh sun has eased but rain and humidity remain high, so drying farm produce or repairing a house should still be planned around each year's actual weather, not the name of the term alone.
