What Is Bạch Lộ (White Dew), When Does It Begin, and What Customs Come With It?

What is Bạch Lộ?

Bạch Lộ (白露) is the 15th solar term in the system of 24 solar terms, coming right after Xử Thử and before Thu Phân. The name is made up of two Han characters: "bach" means white, "lo" means dew, the water droplets that condense at night. The ancients observed that around this time, the temperature difference between day and night increases, and water vapour in the air meets the cold and condenses into white dew drops on grass and branches in the early morning, so they named the term Bạch Lộ.

In the current method of calculation, the 24 solar terms divide the year into 24 segments, each corresponding to 15 degrees of solar longitude on the ecliptic and lasting about 15 days. Bạch Lộ begins when the Sun's longitude reaches 165 degrees.

In 2026, Bạch Lộ begins at 21:41 on 7 September (Vietnam time), closing Xử Thử, which began at 09:21 on 23 August.

When does Bạch Lộ begin and how long does it last?

The start date of Bạch Lộ is not fixed in the Gregorian calendar, but fluctuates within the first few days of September, usually 7 or 8 September in Vietnam time. The end date of Bạch Lộ usually falls around 22 or 23 September, when Thu Phân begins. Each solar term lasts about 15 days, but because the Earth's orbit is elliptical, the actual length can differ by about one day.

The start date of a solar term is determined by the Sun's position on the ecliptic, not by the ordinary lunar or Gregorian calendar. Therefore, in the same year, the date of Bạch Lộ can shift by one day compared to the previous year. To look it up accurately, one needs a table calculating solar terms by solar longitude or a perpetual calendar that records solar terms.

Bạch Lộ start times from 2025 to 2030, in Vietnam time (UTC+7):

Why is it called "Bạch Lộ" and not another name?

The way the ancients named solar terms usually describes the characteristic natural phenomenon of that period. Bạch Lộ describes dew, Xử Thử describes the heat gradually receding, Hàn Lộ describes cold dew, Sương Giáng describes frost. Bạch Lộ, Hàn Lộ and Sương Giáng all describe condensed water vapour, at increasing levels of cold.

Tuế thời quảng ký, under the mid-autumn month (仲秋月), quotes the Nguyệt lệnh: "殺氣浸盛陽氣日衰" (the killing qi gradually grows, the yang qi weakens day by day), and the Tam thống lịch: "白露為八月節" (Bạch Lộ is the solar term of the eighth month) and "白露者隂氣漸重露濃色白" (at Bạch Lộ the yin qi grows heavier, and the dew thickens and turns white)^[3]. This is an interpretation according to yin-yang theory, not a meteorological description in the modern scientific sense.

What customs are there for Bạch Lộ?

It is important to distinguish clearly: Bạch Lộ is a calendrical marker, not a festival with fixed rituals like Tet Nguyen Dan or Doan Ngo. The customs attached to this term are mainly seasonal living habits, and most were recorded in books on seasonal ordinances of ancient China, then spread to countries influenced by Han culture.

Seasonal eating and drinking

In some regions of China, folk custom has it that people drink Bạch Lộ tea, picking tea leaves in the early morning of Bạch Lộ, believing that tea picked at exactly this term has a fresh taste and is better for health than tea picked at other times. This custom is not widespread in Vietnam.

In the northern plains of Vietnam, this period is close to Tet Trung Thu (the 15th day of the eighth lunar month). People often mention Bạch Lộ together with the cool early-autumn air, the season of green rice flakes, the season of persimmons, and autumn cakes and fruits. However, this is a folk notion about the harvest season, not a ritual specific to Bạch Lộ.

Taboos according to the perpetual calendar

Thanh Nien newspaper on 7 September 2026, the first day of Bạch Lộ that year, noted that the day was a Giáp Thân day and, according to the perpetual calendar, a Kim Thổ day, which folk belief considers unsuitable for travel or starting major undertakings^[1]. That taboo is tied to that particular Giáp Thân day, not to Bạch Lộ: in other years the first day of the term has a different can chi.

Bạch Lộ in the 24 solar terms and in feng shui

In the system of 24 solar terms, Bạch Lộ is the 15th term, belonging to autumn according to the traditional division. The autumn terms include: Lập Thu, Xử Thử, Bạch Lộ, Thu Phân, Hàn Lộ, Sương Giáng.

In Tam Hop feng shui, the 24 solar terms are placed on a ring of the compass, each term tied to a certain mountain direction, including Bạch Lộ. This placement is a convention of the Tam Hop school, used to choose days and directions according to feng shui theory, not an astronomical datum.

In Qi Men Dun Jia, the 24 solar terms are divided into two halves, yin and yang: the half from Đông Chí to Mang Chủng belongs to yang dun, the half from Hạ Chí to Đại Tuyết belongs to yin dun. Bạch Lộ therefore belongs to the yin dun half. This is a rule for calculating the ju of the Qi Men school, not a weather description.

Bạch Lộ in the book Tue thoi quang ky

Tue thoi quang ky (歲時廣記) is a book by Tran Nguyen Tinh of the Southern Song dynasty, gathering anecdotes about the seasonal ordinances of the year month by month. According to the introduction of the Si Ku Quan Shu edition, the book is divided into four volumes for the four seasons, and the autumn section has 32 entries recording matters related to autumn terms^[3].

Under the mid-autumn month, the book quotes the Hiếu kinh vĩ: "處暑後十五日斗指庚為白露" (fifteen days after Xử Thử, the handle of the Northern Dipper points to the Canh direction, and that is Bạch Lộ), and the Chu thư Thời huấn on the term's three pentads: "白露之日鴻雁來後五日𤣥鳥歸後五日羣鳥養羞" (on the day of Bạch Lộ the wild geese arrive, five days later the swallows return south, five days after that the flocks of birds store up food). The entry Cảnh hạc minh (警鶴鳴) cites the Phong thổ ký on the white crane: "此鳥性警至八月白露降即鳴而相警" (this bird is watchful by nature; in the eighth month, when the white dew falls, it cries out to warn the others)^[3]. These are Chinese anecdotes; the book does not record Vietnamese customs.

Are Bạch Lộ and Tet Trung Thu the same thing?

No. Bạch Lộ is a solar term according to the Gregorian calendar, usually falling in early September. Tet Trung Thu is the 15th day of the eighth lunar month, usually falling between mid-September and early October. These two markers are close together but belong to different calendar systems: one is calculated by the Sun's position, the other by the Moon's cycle.

Because the two calendar systems differ, the gap between the two markers changes by year: from 1990 to 2040, Trung Thu falls anywhere from the first day of Bạch Lộ itself to 29 days after it. In 2014 the two coincided on 8 September; in 2025 Trung Thu (6 October) came 29 days after the first day of the term.

Suggestions from Nhật Nguyệt

If you are interested in Bạch Lộ because you want to choose a day for an important task, look up the specific date in the year you need, rather than relying on the name of the term. Factors such as the day's can chi, auspicious hours, and good or bad stars change from day to day and from school to school. For health care, the transition from hot to cold often makes the body tired, so pay attention to keeping warm in the early morning and late at night. This is general advice and does not replace medical consultation.