solar term · 節氣
Chunfen 春分 — Spring Equinox
Chunfen (春分), or Spring Equinox, is the fourth of the twenty-four solar terms — the moment the sun reaches 0° of celestial longitude, crossing the celestial equator, which makes it both the midpoint of spring and the zero from which every other term's position is counted.
What the equinox halves, and what it does not start
分 means half, and this term halves two different things at once. It sits at the midpoint of the ninety days of spring — forty-five days after the season opened, forty-five before it closes — and it is the day on which light and darkness are divided evenly. The classical definition below states both readings and then explains why the summer and winter turning points are not called 分: at the solstices one force is at its extreme, whereas here the two are level.
In 2026 it falls on March 20, 2026, and in 2027 on March 21, 2027.
Its position in the solar year is unusual in a way that is easy to miss. Every solar term is defined by a fixed value of the sun's ecliptic longitude, and this term is the one at 0° — the origin of that scale. Start of Spring at 315° and Grain Rain at 30° are both measured from here. So the sequence of the twenty-four begins at Start of Spring while the measurement they are all defined by begins at the equinox, which is one reason the two get confused.
They are confused for a second reason, which is worth stating plainly: the March equinox is where the Western tropical zodiac starts its year, at 0° Aries. The Chinese solar year does not start here. It started roughly six weeks earlier, and by the equinox the second month of the Chinese calendar's solar half is already half over. Two systems use the same astronomical event for entirely different purposes, and neither is borrowing from the other.
The claim that day and night are exactly equal is very nearly true and not quite. Sunrise and sunset are measured to the upper edge of the sun's disc rather than its centre, and the atmosphere refracts the image of the sun upward so that it is visible when it is geometrically below the horizon. Both effects lengthen the day, so the date of exactly twelve hours of daylight falls a few days before the equinox in the northern hemisphere. At the equinox itself, day is longer than night by several minutes almost everywhere. The classical text says day and night have no difference in length, which is what an unaided observer sees; the small correction comes from instruments the text did not have.
The three pentads are, unusually, all about the sky. The dark bird arrives — the swallow, which the commentary pairs with its departure at the autumn equinox, making the two birds a single annual bracket. Then thunder begins to sound. Then lightning.
Those last two are where this entry stops describing and starts arguing, and it is the most philosophical stretch of the whole book. Three of the four passages here spend most of their length on the fine points: what the particle 乃 implies about the difficulty of qi emerging, and whether light is yang or yin. The text quotes an earlier scholar holding that thunder is yang and lightning yin, and rejects him — on the observational grounds that high summer produces lightning on nights with no thunder at all. A reader expecting a nature almanac finds an argument about physics conducted by citation, and the pentads about swallows and weather are the smaller half of the entry.
Its customs are solar and, in the imperial period, official. The spring equinox was when the emperor sacrificed to the sun at the Altar of the Sun in the eastern suburb of the capital, paired with a sacrifice to the moon at the autumn equinox — a symmetry the calendar made obvious. Away from the court the day is kept with lighter things: standing an egg upright, eating the season's first wild greens, and in southern villages sending out printed spring-ox almanacs door to door.
What the classical text says
The four passages below are the entry for the equinox in Collected Explanations of the 72 Pentads — its definition, then the three pentads that fill the fifteen days.
The first pentad is printed here as 元鳥至 where the Yueling has 玄鳥至. The bird is the same one; the character 玄 was routinely replaced with 元 in later printings, and the edition this archive quotes carries the replacement.
春分，二月中。分者，半也。此當九十日之半，故謂之分。秋同義。夏、冬不言分者，蓋天地閒二氣而已。方氏曰：陽生于子，終于午，至卯而中分，故春為陽中，而仲月之節為春分，正陰陽適中，故晝夜無長短云。
Spring Equinox: the middle month of the second month. "Fen" means half. This falls at the midpoint of the ninety days, and so it is called "fen." The autumn term carries the same meaning. The summer and winter terms do not use "fen" because between heaven and earth there are only two qi at those points. Fang says: Yang is born at the zi position and ends at the wu position; at mao it reaches the midpoint. Therefore spring is the midpoint of yang, and the node of the middle month is the Spring Equinox — precisely when yin and yang are in balance, so day and night have no difference in length.
元鳥至。元鳥，燕也。高誘曰：春分而來，秋分而去也。
The dark bird arrives. The dark bird is the swallow. Gao You says: it comes at the Spring Equinox and departs at the autumn equinox.
雷乃發聲。陰陽相薄為雷，至此，四陽漸盛，猶有陰焉，則相薄乃發聲矣。乃者，《韻會》曰：象氣出之難也。註疏曰：發，猶出也。
Thunder begins to sound. Yin and yang pressing against each other produces thunder. By this point, the four yang have grown gradually stronger, yet yin is still present, so they press against each other and thunder sounds. Regarding the word "nai" (meaning "then" or "thereupon"): the Yunhui says it represents the difficulty of qi emerging. The commentary says: "fa" is like "to come out."
始電。電，陽光也，四陽盛長，值氣泄時而光生焉，故《歷解》曰：凡聲陽也，光亦陽也。《易》曰：雷電合而章。《公羊傳》曰：電者，雷光是也。《徐氏》曰：雷陽陰電，非也。蓋盛夏無雷之時，電亦有之，可見矣。
Thunder begins. Lightning is the light of yang. The four yang forces grow strong, and when the qi finds release, light is produced. Therefore the Lijie says: all sound is yang, and light is also yang. The Yi says: thunder and lightning come together and make things manifest. The Gongyang zhuan says: lightning is the light of thunder. Xu says: thunder is yang and lightning is yin — this is wrong. In the height of summer there are times when there is no thunder, yet lightning still occurs; this makes it clear.
Collected Explanations of the 72 Pentads · 元 吳澄《月令七十二候集解》 · 維基文庫 · text retrieved 2026-07-30
The Chinese is reproduced as printed in that edition, including the modern punctuation its editors added. Interlinear notes in the original are the author's own. The English is our own translation, made for this archive.
Spring Equinox at fengshuiHQ
In the traditional calendar this is the middle term of the second month, and its position gives it the official half of its character: the state sacrifice to the sun at the eastern altar was fixed to this date, as the sacrifice to the moon was fixed to the equinox in autumn. The household customs — the upright egg, the first greens — sit alongside that, not under it.
At fengshuiHQ the equinox is a day the almanac names and a day no chart notices. The solar-term line on the daily card at /huangli carries this term on the day it begins, from the same engine table that decides where the months of a chart start. But the equinox is a middle term: the month turned at Awakening of Insects and will not turn again until Clear and Bright, so a birthday on either side of the equinox carries the same month pillar. The most visible day in the season is, for the pillars, an ordinary one.
Related concepts
The month containing the equinox was opened by Jingzhe (惊蛰) and closed by Qingming (清明). The year that the equinox sits a quarter of the way into began at Lichun (立春). The autumn equinox, its counterpart, has no page yet; the ones that exist are on the Learn index.
See today's almanac
The almanac carries the equinox on the day it falls, next to the day's own stem and branch.
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