Major Heat大暑

Major Heat (大暑, Dà Shǔ) is the twelfth of the twenty-four solar terms and, by name, the hottest of them all. It is an astronomical instant, not a day: the moment the sun reaches 120° of ecliptic longitude, which falls somewhere between 22 and 24 July depending on the year.

It follows Minor Heat by roughly two weeks and completes the pair the naming sets up: 小 (lesser) building to 大 (greater). Whether the single hottest day of a given year actually lands on Major Heat is a matter of local weather, not of the solar term — the term marks a point in the sun's path, not a temperature reading.

It falls at the midpoint of the 未 month that Minor Heat opened roughly two weeks earlier, and it is followed roughly two weeks later by the next 節, Beginning of Autumn. In the agricultural calendar it names the stretch when heat and humidity both sit at their highest, a period farming traditions associate with fast growth for some crops and real risk of heat damage for others.

Major Heat is a 氣 — a mid-month term — and a 氣 changes no pillar at all. The month pillar's branch was already set to 未 when Minor Heat opened this month, and it stays 未 straight through to the next 節, Beginning of Autumn. A birth at Major Heat and a birth a week before or after it can carry the same month pillar with nothing about Major Heat itself moving it.

This site's calculator treats every 氣, this one included, as a marker with no effect on the four pillars: it is useful for describing where in the solar year a birth falls, but the year, month, day and hour pillars are computed from the 節 boundaries and the calendar, not from Major Heat.

Minor Heat (小暑) and End of Heat (處暑) — The twenty-four solar terms. All three English names carry the word "heat", and it is easy to assume they all work the same way. They do not: Minor Heat is the one 節 among the three and opens a month pillar; Major Heat and End of Heat are both 氣 and change nothing.