Major Heat

Meaning

Major Heat, Dashu, is the twelfth of the twenty-four solar terms: the Sun at 120°, about 23 July. It names the hottest weeks of the year in most of China, when the heat of the long days has piled up in the land and the sea, the air is heavy with moisture, and the afternoon storms are frequent. The middle of the dog days falls in its fortnight.

It is a principal term, the middle of the Goat month, and it names the sixth lunar month. It is the last term of summer: the next, Liqiu, opens autumn, even if the heat lingers well past it.

Its three pentads are among the most poetic of the year: rotting grass turns into fireflies, as the ancients believed of the insects that rose glowing from the damp meadows; the earth is wet and the air steaming; and great rains fall in their season, the storms that water the ripening crops.

In practice

• In BaZi nothing turns at Major Heat: the month pillar stays the Goat month’s until Liqiu. A birth near it is no nearer a change of pillar.
• In the Chinese calendar it names the sixth lunar month.
• The Calendar marks it on its day, with the Sun at 0° Leo, as the middle of the Goat month; astrology marks the same instant as the Sun’s entry into Leo.
• In the zodiac and Feng Shui the month animal and the month’s star are those of the Goat month, from Xiaoshu to Liqiu.

Across traditions

• In Western astrology the Sun enters Leo at this very moment, the sign it rules, at the height of the summer heat: two traditions put the hottest weeks under the Sun’s own sign.
• In Japan the Day of the Ox of the summer doyō, when many people eat grilled eel against the heat, falls in these days; the term is taisho, in Korea daeseo, in Vietnam đại thử.
• In the Mediterranean the same weeks are those of the dog days and the canicule, named for the Dog Star, and of the long midday rest.

Origin and history

The term’s three pentads are already in the Monthly Ordinances of the Book of Rites: the fireflies, the damp heat and the great rains of the sixth month, with the ruler’s rites of the season. The Huainanzi, in 139 BC, sets the name among the twenty-four, and the old seasonal instructions assign each sign its five days.

Coastal Zhejiang has kept a festival of its own for Major Heat. In the fishing villages of Taizhou, a boat is built and decorated, carried in procession and sent out to sea on the day of Dashu, with the people’s wishes for a safe and healthy summer; the custom is now protected as part of China’s intangible heritage. Elsewhere, families drink cooling teas and rest through the hottest hours.

How Ulune calculates it

Ulune takes Major Heat as the instant the Sun’s apparent longitude reaches 120°, from its table of the solar terms computed with the Swiss Ephemeris for 1800 to 2200. As a principal term it changes no pillar; the Calendar shows it on the reader’s own date. In 2026 it fell on 22 July at 19:13 UT, already 23 July in China.

Correspondences