Why the calendar matters
节气与月令
In BaZi, the month changes at the solar term, not on the 1st of the calendar month. This is the astronomical clock behind every chart — and one of the easiest places to get a chart wrong.
在八字里，换月看节气，不看到每月 1 号。这是每一张命盘背后的天文时钟——也是最容易排错的地方之一。
What a solar term is
节气是什么
The year is divided into 24 solar terms (节气) by the sun’s position — 12 “jie” (节) that start a month, and 12 “qi” (气) that mark midpoints. The month pillar changes at the jie. So a birth on February 3 might be the previous month, while February 5 is already the next — depending on the year’s exact solar term date.
一年按太阳位置分成 24 个节气——12 个「节」管换月，12 个「气」管月中。月柱在「节」处更换。所以同样是 2 月初，可能还是上个月，也可能已到下个月——取决于当年节气的确切时刻。
The four seasons in terms
四季的节气节点
The year pillar also changes at 立春 (Start of Spring), not on January 1. People born in early January can easily have the “previous” year’s year pillar.
年柱也在立春换年，不是 1 月 1 日。1 月初出生的人，年柱可能还是「上一年」的。
Why precision matters
为什么边界要算准
A chart born an hour on either side of a solar term can have a different month pillar — and the month pillar sets the “climate” of the whole reading. That’s why careful casters flag births near term boundaries (交节±1h) for a human double-check. Sōngyǐn does exactly this in its engine.
交节前后一小时内出生的盘，月柱可能不同——而月柱决定了全盘的「气候」。所以严谨的排盘会标注「交节±1小时」临界盘，引导人工复核。Sōngyǐn 的引擎就是这么做的。
The calendar is a clock, not a verdict
历法是时钟，不是判词
Knowing the solar terms tells you the mechanics behind a chart — when it turns, why it can differ from calendar dates, and where a reading’s assumptions start. It’s astronomy, not fortune.
了解节气，是了解命盘背后的机制——什么时候换柱、为什么和阳历日期不同、解读的假设从哪里来。这是天文，不是算命。
- The month pillar changes at the solar term (jie), not on the 1st.
- 月柱在「节」处换，不看到每月 1 号。
- The year pillar changes at 立春, not January 1.
- 年柱在立春换年，不是 1 月 1 日。
- Births near a boundary deserve a careful double-check.
- 临界盘值得认真复核。
For reflection and curiosity only. BaZi is a classical Chinese practice; readings describe tendencies, not certainties.
仅供自我反思与兴趣参考。八字是传统中国术数体系，解读描述倾向，不构成确定性结论。