Xiǎoxuě

Xiaoxue, Minor Snow, is the twentieth solar term, at the sun's longitude of 240 degrees, around the twenty-second of November. It is a principal (zhongqi) term. Its name signals the first light snows in the north as the cold sets in, though the snowfall is still slight. In the farming almanac it is a time of storing and preserving, the making of pickled and cured foods for winter, the salting of vegetables and meats, as fresh produce grows scarce. The land settles into its dormant season. 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 division of the tropical year into twenty-four solar terms of fifteen degrees each along the ecliptic.

Xiaoxue, Minor Snow, falls at 240 degrees, around 22 November, and is a qi, or major, term, whose name signals the traditional expectation of the year's first light snowfall across northern China, distinguished from the heavier snow expected at Daxue roughly two weeks later. As with several other terms named for expected precipitation, the actual likelihood of snow at Xiaoxue varies considerably by region and by year, and the name records a traditional agricultural expectation calibrated to the North China Plain rather than a guaranteed meteorological event. Traditional practice in some regions treats this period as the point to begin preparing preserved and pickled vegetables for the winter months ahead.

The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 240 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 terms have not always been spaced the same way. Until the seventeenth century they were reckoned by equal intervals of time, dividing the year into twenty-four equal parts, a method called pingqi. The Shixian calendar, prepared with Jesuit assistance and promulgated in 1645, redefined them by equal intervals of the sun's apparent longitude instead, fifteen degrees apart, which is the definition still used. Because the Earth's orbit is elliptical the sun does not move at a uniform apparent rate, so the intervals between terms now vary by about a day between the shortest and the longest.

Xiaoxue, minor snow, is the first of the two snow terms. Like the paired heat and cold terms it divides a single condition into a lesser and a greater stage, and like them it describes the climate of northern China; in the south of the country neither snow term corresponds to anything a farmer would observe, which is one of the standing limitations of a system fixed to one region and applied across many.