The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 300 degrees of the sun's apparent longitude. It is a major term, a zhongqi, one of the twelve that fall in the even positions of the twenty-four. The major terms are the ones that anchor the lunar months, and they alternate strictly with the sectional terms, so a zhong is always followed by a jie fifteen degrees later.
The system travelled with the Chinese calendar. Japan, Korea and Vietnam all adopted the twenty-four terms and kept their own readings of the same names, and the terms remain in use in each. In 2016 the twenty-four solar terms were inscribed on the UNESCO Representative List of the Intangible Cultural Heritage of Humanity, on the ground that they remain a living framework for agricultural and everyday practice rather than an obsolete scheme.
Dahan, major cold, is the twenty-fourth and last of the terms, and the sun's arrival at 315 degrees immediately afterwards returns the cycle to Lichun. The list therefore closes at the coldest point and opens at the establishment of spring, which places the boundary of the solar year at a climatic low rather than at an astronomical event, a choice that distinguishes the Chinese scheme from calendars that begin at a solstice or an equinox.