Beginning of Winter立冬

Beginning of Winter (立冬, Lì Dōng) is the nineteenth of the twenty-four solar terms and the point where the BaZi calendar opens its 亥 month. It is an astronomical instant, not a day: the moment the sun reaches 225° of ecliptic longitude, which falls on 7 or 8 November depending on the year.

Like Beginning of Spring, Beginning of Summer and Beginning of Autumn, it sits at a cross-quarter point — the midpoint between an equinox and a solstice, here between the Autumn Equinox and the Winter Solstice. 立 means "to set up" or "to establish", so the term declares winter rather than delivering it: early November in most of the northern hemisphere is only just turning cold.

In the agricultural calendar it traditionally marks the point where the year's growing work is considered finished and the harvest is brought fully in; what remains is storage and preparation rather than fieldwork. Astronomically it is the last of the four cross-quarter month-openers before the year's shortest days arrive at the Winter Solstice.

Beginning of Winter is a 節 — a month-opening term — so at the instant the sun crosses 225° the month pillar's branch becomes 亥 (Hài). It is one of the twelve month-openers that structure the BaZi year, moving the month pillar only; the year pillar turns solely at Beginning of Spring.

This site's engine bears this out directly. Scanning 2026 day by day, the month pillar steps into 亥 by 8 November that year — already showing in the reading taken at noon, since the exact instant of the term can fall a little earlier or later within the same date. Everything from that instant until the next 節, Major Snow, carries an 亥 month pillar because of this term.