Winter Solstice冬至

Winter Solstice (冬至, Dōng Zhì) is the twenty-second of the twenty-four solar terms: the moment the sun reaches 270° of ecliptic longitude and its lowest arc of the year in the northern hemisphere, landing between 21 and 23 December depending on the year. Across Chinese-speaking regions it is widely marked with family gatherings and festive food, and it carries real cultural weight as a turning point in the year.

It is also the point where popular English-language BaZi content most often gets the mechanism wrong. Many sources describe the 子 (Rat) month — or even the whole cycle of month pillars — as beginning at the Winter Solstice. It does not. This site's calculator does not move any pillar in your chart at this instant; the 子 month it sits inside had already opened a fortnight earlier, at Major Snow.

Astronomically the Winter Solstice is unambiguous: it is the sun's lowest point in the sky and the year's shortest day and longest night in the northern hemisphere, the midpoint between Major Snow and Minor Cold. Nothing about that astronomical significance implies anything about where a month boundary falls — the two are separate systems answering separate questions.

Winter Solstice is a 氣 — a mid-month term — so it changes no pillar. This site's engine confirms it precisely for 2026: the month pillar switches to 庚子 on 12-07 at Major Snow, and checking directly either side of the solstice on 12-22 that year shows the pillar reading 庚子 both immediately before and immediately after it. No change happens here at all.

A birth at the instant of the Winter Solstice carries exactly the same 子 month pillar as a birth the week before or the week after — the term marks the sky's turning point, not a boundary in the chart. This is the single most important distinction this glossary makes about the winter terms: the solstice is famous, but Major Snow is the one that actually does the work.

Major Snow (大雪) — The twenty-four solar terms. The term that actually opens the 子 month, a full two weeks before the Winter Solstice. The solstice's fame as a cultural turning point makes it the natural guess for where the month starts; the engine data says otherwise.