Solar Term Boundary節入

A Solar Term Boundary, sometimes called the solar term entry time, is the moment one of the twelve month-opening terms, out of twenty-four solar terms, begins. In this system a month turns not on the 1st of a calendar month but when the sun reaches a set point in the sky. Examples are the Start of Spring (Lichun), Awakening of Insects (Jingzhe), and Clear and Bright (Qingming). Tied to the sun's motion, a boundary lands on nearly the same solar date each year, while its clock time shifts by several hours. For a birth on a boundary day, a few minutes can change the Month Pillar, and at the Start of Spring the Year Pillar too.

• 節joint, node (Korean reading: jeol)
• 入to enter (Korean reading: ip)

Entering a joint: crossing the threshold of a term that divides the year.

This service computes the moments when the sun's apparent ecliptic longitude reaches a multiple of 15 degrees, and uses as month boundaries the twelve terms spaced 30 degrees apart from the Start of Spring. Against figures published by astronomical agencies the difference is a matter of seconds, and minutes come from rounding the seconds, as those agencies do. A birth minute equal to or later than the boundary minute counts as the new term, compared on the real moment without the true solar time adjustment.

If your results flag a boundary-day birth, compare that day's boundary time with your birth time once more. A birth slightly before the boundary gets the previous month's pillar, and one slightly after gets the new month's. With the hour unknown on a boundary day, a birth in Korea is judged at noon standard time, so the Month Pillar may differ from the real one. The Luck Pillar number moves with it, as it counts days to the boundary.

The 2026 Start of Spring boundary falls at 05:02 on 4 February. A birth at 05:01 that day gives a 乙巳 (Yi Si) year and 己丑 (Ji Chou) month. At 05:02 it gives a 丙午 (Bing Wu) year and 庚寅 (Geng Yin) month, so both pillars change together.

• A common idea

  Solar terms go by date, so anyone born on a term day belongs to the new month.

  How we read it

  A boundary is a time to the minute, not a date. Even on the Start of Spring day, a birth before the boundary is calculated here with the pairs of the previous year and month.

Old texts have also discussed starting the year at the winter solstice instead of the Start of Spring. By that standard alone, births from the winter solstice up to the Start of Spring would get a different Year Pillar. This service uses the Start of Spring as the year boundary.