Gǔyǔ

Guyu, Grain Rain, is the sixth and last solar term of spring, at the sun's longitude of 30 degrees, around the twentieth of April. It is a principal (zhongqi) term. Its name marks the season of steady, warm rains that swell the newly sown grain, the moisture on which the young crops depend. In the farming almanac it is the last call for late spring planting before summer, and it is closely tied in tradition to tea, the leaves picked around Guyu are especially prized, and to the sowing of cotton and rice seedlings. Being a solar marker, it falls near the same Gregorian date each year. These are the observances of the East Asian agricultural tradition, resting on the twenty-four-fold division of the tropical year into equal solar arcs.

Guyu, the Grain Rain term, falls at 30 degrees, around 20 April, and is a qi, or major, term, the last of the six solar terms assigned to spring before summer's terms begin with Lixia. Its name reflects the traditional expectation that rainfall at this point in the year is sufficient to nourish newly sown grain, and the term closes the spring sowing period in the traditional agricultural calendar of the North China Plain. In some regional folk traditions Guyu is associated with the god Cangjie, legendary inventor of Chinese writing, said in one account to have caused millet to rain from the sky in celebration when writing was created, a story linking the term's name to a mythic register distinct from its literal agricultural meaning.

The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 30 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.

Guyu, grain rain, closes the spring group of six terms and is the major term of the third month. Its name belongs to the agricultural family among the twenty-four, alongside the two terms of grain in early summer, and these names are the clearest evidence that the system was built as a farming instrument. A lunisolar calendar cannot tell a farmer when to sow, because its months drift against the sun; the solar terms can, because they do not.