Báilù

Bailu, White Dew, is the fifteenth solar term, at the sun's longitude of 165 degrees, around the eighth of September. It is a sectional (jie) term. Its name comes from the dew that now condenses in glistening white beads on grass and leaves as the nights turn cool and the temperature swings between day and night widen. In the farming almanac it is a time of harvest and of gathering the fruits of autumn, and it is associated in some regions with the picking of tea and the making of seasonal wines. 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, each term naming a precise step of the sun along the ecliptic.

Bailu, White Dew, falls at 165 degrees, around 7 or 8 September, and is a jie, or sectional, term, whose name refers to the traditional observation that overnight temperatures have cooled enough for dew to condense visibly on plants by early morning, an early and comparatively gentle sign of autumn's approach before the more marked cooling of the equinox and later terms. The term sits at the midpoint of the six terms traditionally assigned to autumn, following Liqiu and Chushu and preceding Qiufen, the autumn equinox, and in some regional customs it is associated with drinking tea, since the season's tea harvest, particularly for certain white and oolong varieties, is traditionally timed close to this point in the year.

The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 165 degrees of the sun's apparent longitude. It is a sectional term, a jie, one of the twelve that fall in the odd positions of the twenty-four and open the twelve solar months. The sectional terms and the major terms alternate strictly around the year, so a jie is always followed by a zhong 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.

Bailu, white dew, is the first of two dew terms, with Hanlu, the cold dew, a month later. Dew forming on the ground in the morning is an observable and unambiguous sign, and the two dew terms are among the clearest examples of the principle behind the whole system: a solar term names a point in the sun's course, and its name records what that point looked like from the ground in the region where the calendar was fixed.