TL;DR: Lập Thu is the 13th solar term of the 24, opening autumn in the solar term calendar, usually falling around 7 or 8 August when the Sun reaches 135 degrees of ecliptic longitude. It is fixed by the Sun's position, not by the lunar cycle, so Lập Thu is not tied to the first day of the seventh lunar month. The Tuế thời quảng ký by Trần Nguyên Tịnh, quoting the Chu thư, records its three phenological signs as cool wind arriving, white dew descending, and cold cicadas singing, five days apart.
What Is Lập Thu?
Lập Thu is the 13th solar term in the system of 24 solar terms, opening autumn according to the solar term calendar. The character Lập means beginning, and Thu means autumn, so the name states directly what it marks: the point regarded as the start of autumn.
A distinction must be made between two senses of "autumn". The solar term sense takes Lập Thu as its opening marker. Meteorology in the Northern Hemisphere starts autumn on 1 September, covering September, October and November. The two do not conflict, they are simply two different frames of reference.
When Does Lập Thu Begin?
Lập Thu begins when the Sun reaches 135 degrees of ecliptic longitude, usually on 7 or 8 August in Vietnam time. Between 1900 and 2100 it falls as early as 6 August in some years (such as 2060) and as late as 9 August in others (1903, 1907). The Gregorian date shifts because the length of the year is not a whole number.
The moment Lập Thu begins in recent years, in Vietnam time:
| Year | Gregorian date | Time of the term |
|---|---|---|
| 2025 | 7 August 2025 | 12:53 |
| 2026 | 7 August 2026 | 18:39 |
| 2027 | 8 August 2027 | 00:25 |
| 2028 | 7 August 2028 | 06:12 |
| 2029 | 7 August 2029 | 12:00 |
| 2030 | 7 August 2030 | 17:48 |
Each month has two solar terms, the first called tiết and the second called khí[2]. The table below compares the position of Lập Thu in the counting systems:
| Counting system | Position of Lập Thu | Note |
|---|---|---|
| 24 solar terms | 13th term | After Đại Thử, before Xử Thử |
| 12 tiết (first term of month) | 7th term | Opens the Thân month, the seventh month by solar terms |
| 12 trung khí | Not in this group | The trung khí of the same month is Xử Thử |
| Solar longitude | 135 degrees | Measured from the vernal equinox |
| Gregorian calendar | Usually 7 or 8 August | From 6 to 9 August between 1900 and 2100 |
What Are the Three Phenological Signs of Lập Thu?
The three phenological signs are three natural markers that people of old recorded within each solar term, each sign lasting about five days. The Hiệp kỷ biện phương thư (Tứ khố toàn thư edition, volume 12, section Khí hậu) records the three signs of Lập Thu as "凉風至 白露降 寒蟬鳴", meaning cool wind arrives, white dew descends, cold cicadas sing[1]. That section lists all 72 signs for the 24 terms, three per term[1].
This is a way of observing nature with the naked eye by farming people, not measured meteorological data. These three signs reflect the experience of the North China region, where the solar term system formed. In Vietnam, the timing of cool winds and white dew usually differs from the signs recorded in the books, depending on region.
What Does Tuế thời quảng ký Record About Lập Thu?
The entry for the Mạnh thu month (the seventh month) in volume 3 of the Tuế thời quảng ký quotes three older books on Lập Thu[3]. The Hiếu kinh vĩ says that fifteen days after Đại Thử the handle of the Big Dipper points to Khôn, and that is Lập Thu. The Tam thống lịch says Lập Thu is the tiết of the seventh month and Xử Thử its trung khí. The Chu thư, chapter Thời huấn, says "立秋之日涼風至後五日白露降後五日寒蜩鳴": on the day of Lập Thu cool wind arrives, five days later white dew descends, five days after that cold cicadas sing. It then reads each sign as an omen: if the cool wind does not come, the state lacks strict government; if white dew does not descend, many people fall ill with coughs; if the cold cicadas do not sing, ministers struggle for power[3].
The book also quotes the Yếu lãm of Lục Cơ on Liệt Tử riding the wind: on the day of Lập Xuân he returned to the eight directions, and on the day of Lập Thu he went to the cave of the winds; when the wind came, plants grew, and when it left, plants withered, and this was called the wind of meeting and parting[3].
Trần Nguyên Tịnh, a man of the Southern Song, compiled the Tuế thời quảng ký by taking the Nguyệt lệnh, Hiếu kinh vĩ and Tam thống lịch as its framework, then arranging scattered records on the year's seasonal nodes by month; the autumn part has 32 entries[3]. The book was made mainly for use in writing letters, so it quotes many miscellaneous works[3]. What it records are Chinese allusions and customs, not Vietnamese customs.
Is Lập Thu the First Day of the Seventh Lunar Month?
No. Lập Thu and the first day of the seventh lunar month are two different markers, calculated by two different systems. Lập Thu is calculated from the Sun's position, while the first day of the seventh lunar month is calculated from the lunar cycle. The two coincide only in some years, and when they do it is a coincidence, not a rule.
The Sử dụng la bàn explains the difference: a calendar following the moon has a year of only 354 days, eleven days shorter than the solar year, so it does not accurately reflect the seasons; the Han dynasty lunar calendar divided the year into 24 solar terms of a little over 15 days each[2]. This is why Lập Thu falls on different days of the lunar calendar, in the sixth month in some years and in the seventh in others.
In 2025 Lập Thu fell on the 14th day of the leap sixth lunar month; in 2026 it falls on the 25th day of the sixth month; in 2027 on the 7th day of the seventh month.
Folk Customs Around Lập Thu
In Vietnamese folk belief, some hold Lập Thu to be an occasion to make offerings to ancestors and to visit a pagoda to pray for peace[4]. This is a belief, not a calendar rule, and the day of Lập Thu itself has no healing or exorcising power.
Lập Thu in Divination Systems
In day selection, the solar terms are markers for fixing the month and calculating spirits and influences. The Hiệp kỷ biện phương thư classes the day just before Lập Thu as a Tứ tuyệt day, and the ninth day after Lập Thu, counted from the day the term begins, as a Vãng vong day[1]. The book also discusses "bình khí", the method of dividing the year evenly into 24 terms of slightly more than 15 days each[5].
In Lục Nhâm, the day a solar term begins is used as a marker for measuring the time in which a hexagram's outcome will manifest. The book Lục Nhâm, volume 1: Nhập môn explains: if a hexagram has as its Sơ truyền the Can thần or Chi thần of the day the current solar term began, then the matter of the hexagram will occur within the time of that solar term or within no more than 15 days[6]. This is a convention of the Lục Nhâm school, not a scientific forecast.
In Kỳ Môn Độn Giáp, each solar term governs three nguyên, thượng, trung and hạ, each of five days; because độn giáp emphasises the nguyên, each nguyên has 60 hours, exactly one hoa giáp[7]. The Hiệp kỷ biện phương thư records that Lập Thu belongs to the Khôn palace and uses yin arrangement number 2[1]. This division belongs to the conventions of the Kỳ Môn school, not official calendar science.
Why Is Lập Thu Important in Agriculture?
Because Lập Thu is calculated from the Sun's position, it arrives on nearly the same Gregorian date every year, so farmers could rely on it to time the crop season more surely than on lunar dates, which shift with the moon.
The Sử dụng la bàn notes that the names of the 24 solar terms appear earliest in the Hoài Nam Tử, chapter Thiên văn huấn, and that these names reflect the changing seasons and the growth stages of crops[2].
Nhật Nguyệt's Suggestion
Lập Thu is a calendar marker, not a good or bad day. Readers looking up the date of Lập Thu should treat it as information about the Sun's position and the crop season, not as a day with special power. If you wish to use Lập Thu to choose a working day, remember that choosing days by solar term is a convention of divination, not a scientific law.
