TL;DR: Đại Hàn (大寒) is the twenty-fourth and final solar term in the 24 solar terms system, usually beginning around January 20 in the Gregorian calendar when the Sun reaches 300 degrees of celestial longitude, and lasting about 15 days until Lập Xuân follows. It marks the coldest stretch of the year by the solar term division while also signalling that spring is near. The name and meaning of this term are recorded in old texts such as Tuế thời quảng ký and Mệnh lý tham nguyên.
What Is Đại Hàn?
Đại Hàn (大寒) is the twenty-fourth solar term, and also the final solar term in the 24 solar terms system of the Eastern calendar. The name means "severe cold", referring to the coldest period of the year. In the modern calculation, the vernal equinox is taken as the zero point at 0 degrees of solar longitude, and Đại Hàn begins when the Sun reaches 300 degrees[1].
Within the 24 solar terms system, each term lasts about 15 or 16 days, reflecting the Earth's position along its orbit around the Sun. Đại Hàn follows Tiểu Hàn and ends when Lập Xuân begins, opening a new spring cycle.
Mệnh lý tham nguyên explains the names Tiểu Hàn and Đại Hàn with a line from the ode Thất nguyệt in the Bân phong section of the Book of Songs: 一之日觱發，二之日栗烈, meaning that in the days of the first month (by the Zhou calendar) the wind blows piercingly cold, and in the days of the second month the cold is bitter. The book reads 觱發 as cold wind, hence the name Tiểu Hàn, and 栗烈 as cold air, hence the name Đại Hàn[2].
When Does Đại Hàn Begin?
Đại Hàn usually begins around January 20 in the Gregorian calendar each year, when the Sun reaches 300 degrees[1]. In Vietnam time, from 1900 to 2100 the term begins on January 20 in 127 years, on January 21 in 54 years (spread between 1901 and 2004), and on January 19 in 20 years (spread between 2045 and 2098).
For example, in 2026, Đại Hàn begins on January 20 and lasts until February 3. On February 4, 2026, Lập Xuân will follow, marking the transition into spring[1].
Đại Hàn start times from 2025 to 2030, Vietnam time:
| Year | Start date | Transition time |
|---|---|---|
| 2025 | January 20 | 02:53 |
| 2026 | January 20 | 08:40 |
| 2027 | January 20 | 14:28 |
| 2028 | January 20 | 20:16 |
| 2029 | January 20 | 02:05 |
| 2030 | January 20 | 07:54 |
The table below summarises the position of Đại Hàn within the 24 solar terms and its relationship with neighbouring terms:
| Solar term | Order | Solar longitude | Expected time |
|---|---|---|---|
| Tiểu Hàn | 23 | 285 degrees | Around January 5 to 6 |
| Đại Hàn | 24 | 300 degrees | Around January 20 |
| Lập Xuân | 1 | 315 degrees | Around February 3 to 4 |
| Vũ Thủy | 2 | 330 degrees | Around February 18 to 19 |
Why Is It Called Đại Hàn, and What Does This Term Mean?
According to Mệnh lý tham nguyên, Đại Hàn marks a phase of climatic transformation. The book cites earlier scholars: change is gradual transformation, transformation is the completion of change. After Lập Xuân and Vũ Thủy, cold energy gradually shifts, and by Lập Hạ the cold energy has completely dissipated. Similarly, after Lập Thu and Xử Thử, heat energy gradually shifts, and by Đông Chí the heat energy has fully turned into cold energy. Tiểu Hàn and Đại Hàn express this sequential transformation[2].
Tuế thời quảng ký (歲時廣記) by Trần Nguyên Tịnh of the Southern Song, in its entry for the last month of winter (季冬月), quotes the Tam thống lịch: 小寒為十二月節大寒為十二月中氣, meaning Tiểu Hàn is the tiết and Đại Hàn the trung khí of the twelfth month. The same entry explains the names: 月初寒為小月半寒為大, that is, the cold at the start of the month is called minor and the cold in the middle of the month is called major. It also quotes the Hiếu kinh vĩ: 後十五日斗指丑為大寒, that is, fifteen days after Tiểu Hàn, when the handle of the Big Dipper points to Sửu, it is Đại Hàn[3].
What Customs Are Observed During Đại Hàn?
In Vietnam, Đại Hàn begins within the twelfth lunar month (tháng Chạp), close to Tết Nguyên Đán.
Thanh Niên newspaper reports that by old custom, when Đại Hàn arrives people start busily sprucing up their homes, pickling vegetables, and preparing things for Tết[1].
In its entry for the last month of winter, Tuế thời quảng ký records the three pentads of Đại Hàn after the Chu thư Thời huấn: 大寒之日雞始乳又五日鷙鳥厲疾又五日水澤腹堅, meaning that on the day of Đại Hàn hens begin to brood, five days later birds of prey fly fierce and swift, and five more days later the water of ponds and marshes freezes solid to the bottom[3]. This is a phenological calendar of ancient China, not a Vietnamese custom.
How Does Đại Hàn Affect Health and Daily Life?
In folk belief, Đại Hàn is regarded as the coldest stretch of the year, so people take care to keep warm and avoid cold wind.
The book Đàm thiên, thuyết địa, luận nhân sets out the theory of Ngũ vận Lục khí, in which the last qi of the year has Thái Dương Hàn Thủy as its host qi while the guest qi changes from year to year, so the climate of late winter is described differently in different years. For example, in a year whose guest qi is Quyết Âm Phong Mộc, the book writes: "although it is winter, all things tend to grow, and there is often fog"[4].
Đại Hàn in Calendar Systems and Divination
In Bát Tự, the month pillar changes only at the twelve tiết. Đại Hàn is the trung khí of the Sửu month, so it does not change the month pillar: anyone born from the moment of Tiểu Hàn up to the moment of Lập Xuân has the Sửu month pillar, and the year pillar is still the old year, because the Bát Tự year changes only at Lập Xuân.
In feng shui, the 24 solar terms are distributed over the 24 mountains of the compass. According to feng shui theory, below the Nhị Thập Tứ Sơn the 24 solar terms are distributed, with Lập Xuân beginning from Cấn and Đại Hàn beginning from Sửu. Each solar term is divided into thượng hậu, trung hậu, and hạ hậu, making 72 hậu in total, to understand the principle of Yin Yang waxing and waning[6].
It should be noted that this is an application of solar terms in divination and feng shui, not modern astronomical knowledge. Dividing solar terms by solar longitude is an astronomical basis, while assigning solar terms to compass mountains is a convention of feng shui.
How Can One Look Up the Exact Start Date of Đại Hàn?
To look up the exact start date of Đại Hàn for a specific year, one can use the following methods:
- Consult a printed perpetual calendar or lunar-solar calendar: these calendars usually note the transition date. For example, in 2026, Đại Hàn begins on January 20[1].
- Use the solar longitude formula: Đại Hàn begins when the Sun reaches 300 degrees. Astronomical software or spreadsheets can be used to determine this moment.
- Books on calendrics can provide calculation methods and lookup tables.
Nhật Nguyệt's Suggestions
When studying Đại Hàn, one should clearly distinguish between: (a) calendar facts that can be calculated and verified (start date, solar longitude), (b) folk beliefs about weather and health, and (c) applications in divination and feng shui, which are conventions of each discipline. Understanding the nature of each type of knowledge helps avoid confusion between scientific fact and traditional belief.
If you are interested in applying solar terms in daily life, you can start by looking up the exact transition date for the current year, then learn more about weather characteristics and suitable health advice. Health recommendations should be based on modern medical knowledge, combined with traditional beliefs as part of culture.
