Spring Equinox春分

Spring Equinox (春分, Chūn Fēn) is the fourth of the twenty-four solar terms, marking the moment the sun's ecliptic longitude returns to 0° — the same instant recognised worldwide as the astronomical start of spring in the northern hemisphere. It usually falls on 20 or 21 March, with day and night close to equal length everywhere on Earth.

It is also the midpoint of the 卯 month that Awakening of Insects opened two weeks earlier. That timing is easy to misread as significant for a chart, precisely because the equinox itself is such a well-known astronomical marker elsewhere — but inside the BaZi system it carries no special weight beyond being a mid-month waypoint.

Spring Equinox is one of the four cardinal points of the solar year, alongside the summer solstice, autumn equinox and winter solstice, each spaced 90° apart in ecliptic longitude and each classed as a 氣 rather than a 節. In the agricultural calendar it traditionally marks the season in full swing — sustained growth, longer daylight, and the point past which the risk of a hard frost has usually passed in much of the temperate zone.

It sits at the centre of the traditional "mid spring" pairing with Awakening of Insects, the same position Rain Water holds within "early spring".

Spring Equinox is a 氣 — a mid-month term — so it does not change the month pillar, the year pillar, or any other pillar in the chart. A birth on Spring Equinox carries 卯 (Mǎo) in the month pillar, the same branch that has applied to every birth since Awakening of Insects opened the month two weeks earlier.

Running this site's engine across 2026 bears this out for the full set of twelve 氣: not one of them coincides with a month-branch change. All twelve of that year's pillar changes land on the twelve 節 instead, and Spring Equinox is simply the fourth term overall and the second 氣 in the sequence, sitting on the quiet half of that split.

This is worth stating plainly because the equinox is unusually prominent outside BaZi — it is a genuine, widely marked astronomical event in its own right. Inside a chart, though, it is a date like Rain Water: informative about where in the month a birth falls, but not a boundary the four pillars respond to.

The astronomical vernal equinox — Global solar calendar / seasons. Same instant, different weight. Outside BaZi the equinox is a genuinely significant marker — the conventional start of astronomical spring and the point of equal day and night. Inside a chart it is simply the mid-point of the 卯 month, no more structurally important than any other 氣.