What Is Đại Tuyết, When Does It Begin, and What Customs Are Observed?

What is Đại Tuyết (Major Snow) and where does it sit among the 24 solar terms?

Đại Tuyết (大雪, Major Snow) is the 21st solar term in the system of 24 solar terms, coming right after Tiểu Tuyết (Minor Snow) and before Đông Chí (Winter Solstice). The name of the term is understood as "thick snow", referring to the period when snow in East Asia typically falls more heavily and accumulates deeper than in the preceding term. Under the modern method of calculation, which takes the point of Xuân Phân (Spring Equinox) as the origin with a solar longitude of 0 degrees, the start of Đại Tuyết corresponds to a solar longitude of 255 degrees^[1].

The Tuế thời quảng ký quotes the Chu thư Thời huấn (Zhou Shu Shixun) on the three pentads (hậu) of Đại Tuyết, five days each: on the day of Đại Tuyết the hạt bird (鶡鳥) stops calling, five days later tigers begin to mate, and five days after that the lệ đĩnh grass (荔挺) sprouts (大雪之日鶡鳥不鳴後五日虎始交後五日荔挺出)^[2]. These signs describe the Yellow River basin, not Vietnam.

It is worth distinguishing two layers of meaning in the name of the term. The first is climatic description: in places where snow falls, this is when it falls heavily. The second is calendrical convention: this is a marker dividing the year, determined by the Earth's position in its orbit around the Sun, independent of whether snow actually falls in any particular locality.

Why are the solar terms tied to the Earth's position rather than to a fixed date on the solar calendar? Because the 24 solar terms divide the ecliptic into 24 sectors of 15 degrees each, and each term lasts about 14 to 16 days depending on the season. Since the solar year is not evenly divisible by this cycle, the starting date of each term usually shifts by a day or two from year to year. That is why almanacs must be calculated separately for each year, rather than applying one fixed date to every year.

On what date does Đại Tuyết begin?

Đại Tuyết begins when the Sun reaches 255 degrees of ecliptic longitude, usually on 7 December in Vietnam time. Between 1900 and 2100 it falls on 8 December in some years (up to 1979) and on 6 December in others (from 2016, such as 2024 and 2028). The term lasts about 15 days, until Đông Chí begins on 21 or 22 December.

The moments Đại Tuyết and Đông Chí begin in recent years, in Vietnam time:

7 December 2025 is the 18th day of the 10th month of the lunar year Ất Tỵ, a Canh Tuất day^[1].

The Tuế thời quảng ký, in its section on the second month of winter (Trọng đông), quotes the Hiếu kinh vĩ: fifteen days after Tiểu Tuyết the handle of the Northern Dipper points to the Nhâm direction, and this is Đại Tuyết (小雪後十五日斗指壬為大雪); it also quotes the Tam thống lịch: Đại Tuyết is the tiết (sectional term) of the 11th month, and Đông Chí is the trung khí (principal term) of the 11th month (大雪為十一月節冬至為十一月中氣)^[2].

For this reason, in Bát Tự (Four Pillars), where months are counted by the sectional terms, Đại Tuyết opens the month of Tý: people born from the moment of the term onward belong to the Tý month, those born before it still belong to the Hợi month. Lunar months are numbered by the moon and do not coincide with this boundary: in 2025 the term begins on the 18th day of the 10th lunar month.

How does Đại Tuyết differ from Tiểu Tuyết?

The difference between Tiểu Tuyết and Đại Tuyết lies in the degree of cold and the amount of snow, not in the kind of phenomenon. The Tuế thời quảng ký quotes the Tam thống lịch to explain the two names: snow is frost and rain congealed, in the 10th month it is still light, and in the 11th month it turns heavy (小雪大雪者以霜雨凝結而雪十月猶小十一月轉大)^[2]. Báo Thanh Niên glosses Tiểu Tuyết as "snow appears" and Đại Tuyết as "thick snow", signalling very cold weather, with heavy snowfall in some places and effects on crops^[1].

Snow is rare in Vietnam. In this season the North may see hoarfrost and ice, and cold spells affect the northern mountains, some of them reaching the South as well^[1]. Hoarfrost and ice occur mainly in the high mountains during severe cold spells; snow falls only rarely on a few high peaks in the North. In the lowlands, what people feel is the cold arriving in waves with the northeast monsoon.

So when reading the names of these two terms, people in tropical regions should not take them literally as "snow will fall where I live". They are better understood as time labels from a calendrical system that originated in a temperate climate and was adopted and shared across East Asia.

How are the customs around Đại Tuyết recorded in old books?

One point should be made clear first: Đại Tuyết is not a major festival with fixed rituals like Tết Nguyên Đán or Đoan Ngọ. The customs attached to it are mainly observations of weather and folk omens, recorded here and there in almanacs and encyclopaedic works.

One source for this layer of material is the Tuế thời quảng ký (歲時廣記) by Trần Nguyên Tịnh (Chen Yuanjing) of the Southern Song, in a Siku Quanshu edition of 4 volumes. According to the abstract of the Siku edition, the book takes the Nguyệt lệnh (Monthly Ordinances), the Hiếu kinh vĩ and the Tam thống lịch as its framework, then files what other books record about the seasons under each month; the winter section has 38 entries^[2]. The winter section records no custom specific to the day of Đại Tuyết. Its entries on snow are anecdotes, such as the Tang magnate Vương Nguyên Bảo (Wang Yuanbao), who whenever heavy snow fell in winter had his servants sweep a path, stood at the gate of his ward to greet guests and laid out wine and roast meat, calling it the "noãn hàn hội" (gathering to warm the cold), which the book quotes from the Khai Nguyên di sự (Kaiyuan Yishi)^[2]. This is Chinese-language material from China, not a Vietnamese custom.

Another source for the layer of beliefs about snow is the Khai Nguyên chiêm kinh (開元占經), a work of 120 volumes compiled by Cù Đàm Tất Đạt (Gautama Siddha) in the Tang dynasty, collecting divinatory pronouncements about the heavens and natural phenomena^[3]. Its section on snow in volume 101 quotes many earlier works: the Nguyên mệnh bao writes that yin and yang congeal to become snow (陰陽凝為雪), and the Phiếm Thắng thư writes that snow is the essence of the five grains (雪者，五穀之精)^[3].

These statements need to be placed on their proper level. This is divinatory text, that is, a record of how people in the past explained natural phenomena as omens, not a scientific conclusion about the relationship between snow and harvests.

Why did old books regard snow as a good omen?

In the same section on snow, the Khai Nguyên chiêm kinh quotes the Mục Thiên Tử truyện (Mu Tianzi Zhuan): when snow lies several feet deep, the year will be bountiful (雪盈數尺，年豐), and the Bát tiết chiêm: when there is lying snow in winter, the year is good and people live in harmony (冬有積雪，歲美人和). It also quotes Đổng Trọng Thư (Dong Zhongshu): in an age of great peace, snow does not cover the branches (太平之世，雪不封條), and only serves to dispel harmful things^[3]. This is an interpretation of the divinatory art, not a verified meteorological rule.

On another level, the book quotes Kinh Phòng (Jing Fang), who saw snow as a sign of flourishing yin and tied its depth to drought and flood: thick snow means drought, thin snow means flood (雪厚，為旱；薄，則為水)^[3]. This is the yin-yang correlative reasoning characteristic of ancient divination, and should not be read as a modern weather forecast.

What is distinctive about the customs in Vietnam?

In Vietnam, solar terms in general are known mainly through printed calendars and agricultural experience, not through a separate ritual system for each term.

As for customs recorded in writing, the Gia lễ giản yếu by Dương Bá Trạc (1932), in its section on festivals, holds that festival days without meaning such as Đoan ngũ, thượng nguyên, trung nguyên and trung thu should all be dropped, keeping only Tết Nguyên Đán, Tết Thanh minh and Tết cơm mới (the new rice festival) for ceremonies to ancestors^[4]. Among the festivals the book keeps is Tết Thanh minh, which also bears the name of a solar term, while Đại Tuyết is not mentioned.

Do Vietnamese people observe any taboos during Đại Tuyết?

There is no separate, unified system of taboos for Đại Tuyết in Vietnamese texts. What people actually care about when this term arrives is the deepening cold, its effects on the health of the elderly and small children, and on crops and livestock. This is a practical concern, not a religious taboo.

The fact that a day falls within Đại Tuyết carries no instruction about whether or not to do anything. Choosing good or bad days by solar term is a convention of the divinatory arts, not part of calendrical science itself.

What does Đại Tuyết mean in life today?

The greatest practical value of Đại Tuyết today is as a seasonal reminder. For farmers, this is the period to pay attention to protecting crops and livestock from the cold in the North. For those whose work depends on the weather, this is a marker for anticipating intensified cold spells. For those interested in calendrical science, this is one of the 24 points evenly dividing the ecliptic, helping to convert between the lunar calendar, the solar calendar and the solar terms.

Culturally, solar terms in general and Đại Tuyết in particular show that people in the past observed weather cycles long enough and carefully enough to divide the year into 24 segments of practical meaning. This division is still used because it is useful, not because it is sacred, and it says nothing about any individual's fate.