Introduction
To compute a Saju correctly, the Month Pillar (月柱) must be determined by the 24 Solar Terms (二十四節氣) — not by the moment when a lunar calendar month turns over. Why is that? This column outlines the astronomical principle of the 24 Solar Terms and their significance within Meongri.
1. What Are the 24 Solar Terms?
The 24 Solar Terms divide one year into 24 equal parts based on the position of the sun. Each new term begins when the sun, as viewed from the Earth, moves 15° along the ecliptic (黃道).
- 1 year = 360° (the sun's full circuit along the ecliptic)
- 24 solar terms = 360° ÷ 24 = 15°
The names and starting points (the sun's positions on the ecliptic) of the 24 Solar Terms can be briefly summarized as follows.
| Solar Term | Ecliptic Longitude | Approximate Date | Seasonal Meaning |
|---|---|---|---|
| Ipchun (立春) | 315° | Around Feb 4 | Beginning of spring; start of the Meongri year |
| Chunbun (春分) | 0° | Around Mar 21 | Day and night equal |
| Ipha (立夏) | 45° | Around May 6 | Beginning of summer |
| Haji (夏至) | 90° | Around Jun 21 | Longest day |
| Ipchu (立秋) | 135° | Around Aug 8 | Beginning of autumn |
| Chubun (秋分) | 180° | Around Sep 23 | Day and night equal |
| Ipdong (立冬) | 225° | Around Nov 7 | Beginning of winter |
| Dongji (冬至) | 270° | Around Dec 22 | Longest night |
2. Jeolgi (節氣) and Junggi (中氣)
The 24 Solar Terms are further divided into 12 Jeol (節, nodes) and 12 Jung (中, mid-terms).
- Jeol (節): the starting point of each month — Ipchun, Gyeongchip, Cheongmyeong, Ipha, Mangjong, Soseo…
- Jung (中): the midpoint of each month — Usu, Chunbun, Gogu, Soman, Haji, Daeseo…
In Meongri, Jeol (節) marks the boundary of the month. The moment Ipchun (立春, around February 4) arrives, In-wol (寅月, Tiger month) begins; the moment Gyeongchip (驚蟄, around March 6) arrives, it shifts to Myo-wol (卯月, Rabbit month).
3. Why a Solar Basis — Not the Lunar Calendar
This is a common point of confusion. Because Korea and China traditionally used the lunar calendar, it is easy to assume Saju also follows the lunar calendar. In fact, the Month Pillar and the Year Pillar of a Saju strictly follow the position of the sun — that is, the 24 Solar Terms.
The reason is simple. The foundational premise of Meongri is that the state of natural energy at the moment of birth influences the person. Yet the natural change of seasons is determined not by the phases of the moon (the lunar calendar) but by the geometry of the sun and the Earth.
- The lunar New Year can drift by more than 11 days depending on region and year
- On the solar calendar, Ipchun falls within about one day of February 4 every year
- The natural shift of climate tracks the solar calendar far more closely
The rule that the Month Pillar follows the Solar Terms was therefore a reasonable decision reached by ancient astronomers through observation.
4. Month Branches and Their Five-Element Assignments
Based on the 24 Solar Terms, the twelve Month Branches (月支) are set, and each carries its own Five-Element attribute.
| Month Branch | Corresponding Terms | Approximate Period | Five Element |
|---|---|---|---|
| In (寅) | Ipchun – Gyeongchip | Feb 4 – Mar 5 | Wood (木) |
| Myo (卯) | Gyeongchip – Cheongmyeong | Mar 6 – Apr 4 | Wood (木) |
| Jin (辰) | Cheongmyeong – Ipha | Apr 5 – May 5 | Earth (土, spring earth) |
| Sa (巳) | Ipha – Mangjong | May 6 – Jun 5 | Fire (火) |
| O (午) | Mangjong – Soseo | Jun 6 – Jul 6 | Fire (火) |
| Mi (未) | Soseo – Ipchu | Jul 7 – Aug 7 | Earth (土, summer earth) |
| Sin (申) | Ipchu – Baekro | Aug 8 – Sep 7 | Metal (金) |
| Yu (酉) | Baekro – Hallo | Sep 8 – Oct 7 | Metal (金) |
| Sul (戌) | Hallo – Ipdong | Oct 8 – Nov 6 | Earth (土, autumn earth) |
| Hae (亥) | Ipdong – Daeseol | Nov 7 – Dec 6 | Water (水) |
| Ja (子) | Daeseol – Sohan | Dec 7 – Jan 5 | Water (水) |
| Chuk (丑) | Sohan – Ipchun | Jan 6 – Feb 3 | Earth (土, winter earth) |
The fact that Earth (土) appears four times is because Earth is placed at the transitional periods between seasons. This reflects the practical wisdom that the Five Elements do not divide neatly into four seasons.
5. The Boundary of the Year Pillar — Ipchun
"Is everyone born in 2025 born in an Eulsa year?" The answer depends on whether Ipchun has passed.
In Meongri, the Year Pillar (年柱) does not change on January 1 of the solar calendar but on Ipchun (around February 4). A person born on February 2, 2025 still belongs, in Meongri terms, to the Gapjin year, while someone born on February 5, 2025 belongs to the Eulsa year.
Unfamiliarity with this rule sometimes produces errors in which the Year Pillar is off by a year. The Manseryeok (萬歲曆, perpetual calendar) used by Saju Works handles this boundary automatically, based on accurate solar-term calculations.
6. Precision and Limits of Time Calculation
Saju calculation depends on accurate birth time. A few practical constraints, however, apply.
- Regional difference: Korea Standard Time follows 135° East longitude (the Akashi meridian in Japan). Seoul, at about 127° East, runs roughly 32 minutes behind in true solar time. Strict analyses may correct for this offset.
- Daylight Saving Time: Korea observed DST in certain years (parts of 1948–1960 and 1987–1988). Those born during such periods require a time correction.
- Recording error: Birth times are rarely accurate to the minute. If the Hour Pillar (時柱) falls on a boundary (for example, O-si to Mi-si), interpretation can shift.
Closing Thoughts
The 24 Solar Terms constitute a solar-based timekeeping system arrived at by ancient astronomers through observation. Meongri relies on this system not out of divinatory mysticism, but because it is the most accurate reflection of the seasonal changes of nature.
Saju Works follows the calculation formulas used by international astronomical institutions to determine the 24 Solar Terms precisely and, from them, the Month and Year Pillars. This is the most basic scientific foundation that supports the accuracy of any Meongri analysis.