The Solar Terms at which the month and year pillars change, and why a day begins at 23:30.
The 24 Solar Terms come from taking the path the earth travels around the sun (the ecliptic) and dividing it into 24 parts of 15 degrees each. They have nothing to do with the shape of the moon and are set by the position of the sun, so they line up almost exactly with solar-calendar dates (varying by about a day from year to year).
The 24 alternate between two kinds.
Jeol (節) 12 of them — like Start of Spring, Awakening of Insects and Clear and Bright, they are the point where the month changes. The month pillar changes at this moment.
Junggi (中氣) 12 of them — like Rain Water, Spring Equinox and Grain Rain, they fall at the middleof a month. They have nothing to do with the month pillar.
| Jeol (節) | Month it opens | Approximate date | Season |
|---|---|---|---|
| Start of Spring 立春 | 寅 | Around February 4 | Start of spring |
| Awakening of Insects 驚蟄 | 卯 | Around March 6 | Spring |
| Clear and Bright 淸明 | 辰 | Around April 5 | End of spring |
| Start of Summer 立夏 | 巳 | Around May 6 | Start of summer |
| Grain in Ear 芒種 | 午 | Around June 6 | Summer |
| Minor Heat 小暑 | 未 | Around July 7 | End of summer |
| Start of Autumn 立秋 | 申 | Around August 8 | Start of autumn |
| White Dew 白露 | 酉 | Around September 8 | Autumn |
| Cold Dew 寒露 | 戌 | Around October 8 | End of autumn |
| Start of Winter 立冬 | 亥 | Around November 7 | Start of winter |
| Major Snow 大雪 | 子 | Around December 7 | Winter |
| Minor Cold 小寒 | 丑 | Around January 6 | End of winter |
At every turn of the seasons, Earth (土)is placed (辰·未·戌·丑), gathering in the season before and opening the one after. A year starting in the 寅 month (Start of Spring) is likewise because spring is taken to be the beginning of a year.
| Solar Term | Type | Entry time (KST) | Month |
|---|
— these four pillars each change at a different moment. This differs from the calendar's notion of a date, so it is worth knowing.
| Pillar | When it changes | Cycle |
|---|---|---|
| Hour Pillar | every 2 hours, with the boundary at XX:30 (Ja Hour: 23:30) | 12 times a day |
| Day Pillar | 23:30 (when the Ja Hour begins) | One day |
| Month Pillar | Jeol (節) Entry time | About one month |
| Year Pillar | Start of Spring Entry time | One year |
In metaphysics a day begins not at midnight but at 23:30 the previous dayand ends at 23:29 that day. If you were born at 11:40 p.m., the date may be yesterday but the day pillar is the next day's.
The reason it is 23:30 and not 23:00 is the difference in longitude . Korea Standard Time is based on 135°E (near Akashi in Japan), while Seoul sits at about 127.5°E. A 7.5-degree gap equals about 30 minutes, so Seoul's actual solar time runs 30 minutes behind the clock.
A double-hour is one of the twelve divisions of a day. Each is 2 hours long, and the boundaries fall on the half hour, not on the hour.
| Double-hour | Time (KST) | Double-hour | Time (KST) |
|---|---|---|---|
| 子 | 23:30~01:29 | 午 | 11:30~13:29 |
| 丑 | 01:30~03:29 | 未 | 13:30~15:29 |
| 寅 | 03:30~05:29 | 申 | 15:30~17:29 |
| 卯 | 05:30~07:29 | 酉 | 17:30~19:29 |
| 辰 | 07:30~09:29 | 戌 | 19:30~21:29 |
| 巳 | 09:30~11:29 | 亥 | 21:30~23:29 |
Which double-hour it is now is Manse Calendar Clock marked with a yellow outline on the twelve-double-hour row of the screen.