TL;DR: Hạ Chí is the 10th of the 24 solar terms, beginning when the Sun reaches 90 degrees of ecliptic longitude and falling on 20 to 22 June in the Gregorian calendar; from 2012 to 2043 it falls on 21 June every year, Vietnam time, at 15:19 in 2026. It is the longest day of the year in the Northern Hemisphere. Hạ Chí is the middle term of the 5th lunar month and corresponds to the Cấu hexagram; old books record its three signs as deer shedding antlers, cicadas singing and the bànxià plant sprouting.
What Is Hạ Chí and When Does It Begin?
Hạ Chí is the 10th of the 24 solar terms, beginning when the Sun reaches 90 degrees of ecliptic longitude. From 1900 to 2100 this moment falls on 20, 21 or 22 June in the Gregorian calendar, Vietnam time; from 2012 to 2043 it falls on 21 June every year. Start times for the coming years:
| Year | Gregorian date | Start time (Vietnam time) |
|---|---|---|
| 2025 | 21 June 2025 | 09:34 |
| 2026 | 21 June 2026 | 15:19 |
| 2027 | 21 June 2027 | 21:05 |
| 2028 | 21 June 2028 | 02:52 |
| 2029 | 21 June 2029 | 08:39 |
| 2030 | 21 June 2030 | 14:27 |
Hiệp kỷ biện phương thư, a date-selection manual compiled by order of the Qing court, records the three pentads of Hạ Chí: "夏至 鹿角解 蜩始鳴 半夏生"[2], that is, deer shed their antlers, cicadas begin to sing, and the bànxià plant (Pinellia) sprouts. These are the natural signs the ancients used to recognise the solar term.
Why Is Hạ Chí the Longest Day of the Year?
Hiệp kỷ biện phương thư explains that after Xuân Phân the Sun travels north of the celestial equator and reaches its northernmost point at Hạ Chí ("春分以後日行赤道内至夏至而極"), so the day is long and the night short, which is called "the long day" ("故晝長夜短所謂日永也")[2].
After Hạ Chí, the Sun begins to move south, and daylight in the Northern Hemisphere shortens until Đông Chí.
What Customs Does Hạ Chí Have in the Book Tuế thời quảng ký?
The book Tuế thời quảng ký by Trần Nguyên Tịnh of the Song dynasty gathers lore on each month and each term of the year from Nguyệt lệnh and many other books. This is a Chinese-language source, not a Vietnamese custom. In its section on the midsummer month, the book quotes Chu thư thời huấn, which says the three signs of the term come five days apart: "夏至之日鹿角解後五日蟬始鳴後五日半夏生"[3].
The book records two customs about rain around Hạ Chí. Quoting Phong thổ ký: "夏至雨名黄梅雨霑衣服皆敗黤"[3], that is, rain at Hạ Chí is called "plum rain", and clothes it touches are spoiled and stained dark. Under the entry on the Phân long festival, the book says the people of Min held the period after Hạ Chí to be "the parting of the dragons", when rain falls in a different quarter for each place: "閩人以夏至後為分龍雨各有方"[3].
The Qing-era Hiệp kỷ biện phương thư records two more practices reckoned from Hạ Chí: on the day of Hạ Chí the court held the grand sacrifice to Earth at the Altar of the Square Pool ("夏至大祀"), and the count of the three fu periods: "夏至後三庚為初伏四庚為中伏"[2], that is, the third Canh day after Hạ Chí starts the first fu and the fourth Canh day starts the middle fu.
How Is Hạ Chí Related to the Ly and Cấu Hexagrams?
In the hexagram-and-qi system of the I Ching, Hạ Chí corresponds to the Cấu hexagram (姤), the 44th of the 64 hexagrams. Cấu means "meeting"; it has one yin line beneath five yang lines, symbolising yin qi beginning to arise again after the period of yang prosperity. The section Quái khí đệ thập nhất in Chu Dịch thệ thuật (周易筮述) by Vương Hoằng Soạn assigns the 5th month, the month of Ngọ, to the Cấu hexagram, placing Mang Chủng at the start of the Ngọ month and Hạ Chí at its middle: "芒种午之初 夏至午之半"[1].
Another interpretation in Thuật số Lạc Thư holds that Đông Chí and Hạ Chí are the two starting points for two opposing climatic periods, corresponding to the Khảm and Ly hexagrams[4].
How Does the Hạ Chí Solar Term Differ from the Hạ Chí Day in Folk Belief?
In folk belief, many people confuse "Hạ Chí solar term" with "Hạ Chí day". In fact, the Hạ Chí solar term is the whole period from the start of Hạ Chí to the start of Tiểu Thử. The Hạ Chí day is only the first day of this term. In modern life, people usually remember only the Hạ Chí day as the longest day of the year, and pay little attention to the whole solar term.
Table Comparing the Features of the Hạ Chí Solar Term
| Feature | Description |
|---|---|
| Position among the 24 solar terms | 10th term |
| Start time | 20 to 22 June in the Gregorian calendar; 21 June every year from 2012 to 2043 |
| Solar longitude | 90 degrees |
| Corresponding hexagram | Cấu (姤) |
| Astronomical feature | Longest day of the year in the Northern Hemisphere |
| Climatic feature | Midsummer, before the Tiểu Thử and Đại Thử terms |
| Three pentads | Deer shed antlers, cicadas sing, bànxià sprouts |
| Practices reckoned from Hạ Chí | Sacrifice to Earth at the Square Pool altar (Qing), counting the three fu |
How Is the Hạ Chí Solar Term Calculated in the Old Calendar?
Tuế thời quảng ký quotes two ways of fixing the term. Hiếu kinh vĩ reckons by the handle of the Big Dipper: fifteen days after Mang Chủng, when the handle points to the Ngọ direction, it is Hạ Chí ("後十五日斗指午為夏至"). Tam thống lịch makes Hạ Chí the middle term of the 5th month: "夏至為五月中氣"[3].
Hiệp kỷ biện phương thư reckons by the Sun's passage through the twelve palaces: on the day of Hạ Chí the Sun enters the first degree of the Mùi palace, called the Thuần thủ station: "夏至日躔未宮初度是為鶉首之次"[2]. The book therefore places the monthly general of the 5th month in Mùi ("五月在未").
Today's calendar defines Hạ Chí as the moment the Sun reaches 90 degrees of ecliptic longitude. Solar terms vary in length: the shortest is Đông Chí, at about 14 days 17 hours, and the longest is Hạ Chí, at about 15 days 17 hours. In 2026 it runs from 15:19 on 21 June to 08:49 on 7 July.
Nhật Nguyệt's Suggestion
Nhật Nguyệt's suggestion: Hạ Chí marks midsummer in the old Eastern calendar. Understanding this solar term helps you recognise natural rhythms and adjust your daily life accordingly. However, folk customs and taboos should only be taken as reference, not applied rigidly. The most important thing is to stay healthy in the sweltering heat by drinking enough water, eating cool and light food, and avoiding excessive activity under the harsh sun.
