TL;DR: Xuân Phân (春分) is the fourth of the 24 solar terms, beginning when the Sun crosses the celestial equator and day and night are nearly equal. In Vietnam time it begins on 20 or 21 March in almost every year from 1900 to 2100; in 2026 it began at 21:36 on 20 March. Xuân Phân is the principal term of the second lunar month. Hiệp kỷ biện phương thư records its three pentads (swallows return, thunder sounds, lightning appears) and the earth-altar sacrifice on the Mậu day nearest Xuân Phân. In Vietnam, Xuân Phân has no festival of its own; grave visiting belongs to the following term, Thanh Minh.
What is the Xuân Phân solar term and why is it important?
Xuân Phân is the fourth of the 24 solar terms. It begins when the Sun reaches ecliptic longitude 0 degrees, the moment it crosses the celestial equator, when day and night are nearly equal in length. It is the mid-spring term, after Lập Xuân, Vũ Thủy, Kinh Trập and before Thanh Minh, Cốc Vũ. Xuân Phân is the principal term (trung khí) of the second month: the lunar month that contains Xuân Phân is the second month.
Tuế thời quảng ký by Trần Nguyên Tịnh (Song dynasty) describes this term through older books: the Hiếu kinh vĩ says that fifteen days after Kinh Trập the handle of the Big Dipper points to Mão, and that is Xuân Phân; the Tam thống lịch lists Xuân Phân as the principal term of the second month; the Nguyệt lệnh chapter describes the mid-spring month as the time of "日夜分", when day and night are divided equally[1].
When does Xuân Phân begin?
In Vietnam time (UTC+7), over the 201 years from 1900 to 2100, Xuân Phân begins on 20 or 21 March in 193 years; it falls on 22 March only in 1903, 1907 and 1911, and on 19 March in five years from 2080 to 2096. The date shifts because a calendar year has 365 or 366 days, while the span from one Xuân Phân to the next is about 365 days 5 hours 48 minutes: the start time moves about six hours later each year, then jumps back a day after each leap year.
Start times of Xuân Phân for 2025 to 2030, in Vietnam time:
| Year | Date | Start time |
|---|---|---|
| 2025 | 20 March | 15:50 |
| 2026 | 20 March | 21:36 |
| 2027 | 21 March | 03:24 |
| 2028 | 20 March | 09:11 |
| 2029 | 20 March | 15:00 |
| 2030 | 20 March | 20:49 |
What are the three pentads (hậu) of Xuân Phân?
The ancients divided each solar term into three hậu (pentads) of about five days each, each tied to a sign in nature.
Hiệp kỷ biện phương thư records the three hậu of Xuân Phân as follows[2]:
- First hậu, huyền điểu chí: the swallows return.
- Second hậu, lôi nãi phát thanh: thunder begins to sound.
- Third hậu, thủy điện: lightning begins to appear.
Tuế thời quảng ký, quoting the Thời huấn chapter of the Chu thư, records the same three hậu, each five days after the one before[1].
What customs surround Xuân Phân?
The earth-altar sacrifice on the Mậu day near Xuân Phân
Hiệp kỷ biện phương thư, in its entry on the two xã days, quotes the Lịch lệ: "二分前後近戊為社", meaning the Mậu day nearest to Xuân Phân, before or after it, is the spring xã day, and the Mậu day nearest to Thu Phân is the autumn xã day[2]. The xã is a sacrifice to the earth deity, praying for the harvest.
The Kinh Sở tuế thời ký by Tông Lẫm (6th century) describes the xã day in the Jing-Chu region: neighbours on all sides gathered, slaughtered offerings, built a shelter under a tree, sacrificed to the deity first and then shared the offered food.
Spring outings in the seasonal almanacs
Volume 1 of Tuế thời quảng ký collects spring pastimes of Tang and Song China that belong to the spring season as a whole, not to Xuân Phân in particular: the "spring-seeking banquet" held by people of the Tang capital after the fifteenth of the first month, the people of Song Bianjing going out of the city for spring outings after the Thượng nguyên festival, and the "Pear Blossom Spring" wine that people of Hangzhou brewed to mature when the pear trees flowered[1].
Customs in Vietnam
In Vietnam, Xuân Phân has no festival of its own like Tết Nguyên Đán or Mid-Autumn. The list of yearly festivals in Việt Nam phong tục (Phan Kế Bính, 1915) has none for this term; the book records the custom of the following term, Thanh Minh: Vietnamese people do not celebrate it as a festival, but many take the occasion to visit family graves, clear the grass, add soil to the mounds, and then return home to make offerings to their ancestors.
Nam Kỳ phong tục nhơn vật diễn ca by Nguyễn Liên Phong (1909), in a passage about the silversmiths of Chợ Lớn, has the line "In spring the rites are held with solemn order; flowers are offered and hát bội opera resounds day and night"[3]. The verse describes spring rites and theatre in general and does not mention Xuân Phân.
Xuân Phân in divination systems and feng shui
Hiệp kỷ biện phương thư (volume 2) states that the four Lập terms, the two Phân terms and the two Chí terms correspond to the eight trigrams, are called the eight nodes (bát tiết), and that the nine configurations of Kỳ Môn Độn Giáp all start from them; Xuân Phân corresponds to the Chấn trigram. Volume 8 of the book places Xuân Phân in the Chấn palace, using yang configuration 3.
Thanh Thủy's book Sử dụng la bàn has a table pairing the 24 solar terms with the 24 mountains, reading "Thái âm xuân phân đáo mão sơn": at Xuân Phân, Thái âm reaches the Mão mountain. This is a convention of the feng shui school, used when choosing directions and dates.
In Hà Lạc numerology, Hoàng Tuấn's book Lý thuyết tượng số calculates Hóa Công by the solar terms of the four seasons: a person born from Xuân Phân to before Hạ Chí has Hóa Công in the Chấn trigram, a period when Wood flourishes and Earth declines. This is a convention of that numerological school, not an astronomical datum.
Distinguishing Xuân Phân from other markers
The table below compares Xuân Phân with markers that are easily confused with it, with solar dates in Vietnam time for the years 1900 to 2100:
| Marker | Solar date | Meaning |
|---|---|---|
| Lập Xuân solar term | 3 to 5 February | First solar term, start of spring in the solar-term calendar |
| Xuân Phân solar term | 19 to 22 March, in most years 20 or 21 March | Mid-spring, day and night nearly equal in length |
| Thanh Minh solar term | 4 to 6 April | Fifth solar term, time for grave visits |
| Astronomical spring equinox | Same moment as the start of Xuân Phân | When the Sun crosses the celestial equator; today's solar terms are set to exactly this moment |
Points to note when looking things up
The Vietnamese calendar calculates solar terms in Hanoi time (UTC+7), the Chinese calendar in Beijing time (UTC+8). When the start time falls between 23:00 and midnight Vietnam time, the two calendars give different dates: in 2018, Xuân Phân began at 23:12 on 20 March Vietnam time, which was 00:12 on 21 March Beijing time.
Tuế thời quảng ký, Kinh Sở tuế thời ký and Hiệp kỷ biện phương thư record Chinese customs and calendar rules, not Vietnamese ones. When speaking of Vietnamese customs, one should rely on sources about Vietnam, or state clearly which region a custom belongs to.
Suggestions from Nhật Nguyệt
If you want to use Xuân Phân to choose a day for work, marriage or groundbreaking, treat it as one reference marker in the solar term system, not the sole basis. Day-selection books such as Hiệp kỷ biện phương thư or Vạn sự bất cầu nhân have their own good and bad star tables for each day; the solar term is only one layer within that.
If you are interested in customs, you can learn about the spring festivals in your own locality, because most Vietnamese customs are tied to villages and regions rather than to the solar term alone.
