Home › Notes › Where manseryeok results diverge › Korea Standard Time
Korea's Standard Time
Changed Three Times
March 21, 1954 – August 9, 1961
Our clocks ran 30 minutes behind today's.
If you were born in this period, add 30 minutes to the recorded time for a correct hour pillar
What time the clock shows isn't set by nature — it's an agreement made by people. When that agreement changes, so does the time written for the same moment. Korea first set that agreement in 1908 and has changed it three times since.
In this article 7 topics
Timeline
| Period | Standard meridian | Offset from UTC | Correction relative to today |
|---|---|---|---|
| 1908.4.1 ~ 1911.12.31 | 127.5°E | +8:30 | +30 min |
| 1912.1.1 ~ 1954.3.20 | 135°E | +9:00 | None |
| 1954.3.21 ~ 1961.8.9 | 127.5°E | +8:30 | +30 min |
| 1961.8.10 – present | 135°E | +9:00 | None |
What actually matters for Saju calculations is March 21, 1954 to August 9, 1961, because many people alive today were born in that period. Almost no one living was born in the 1908–1911 stretch.
Can 30 minutes change your hour pillar?
Yes. Each hour branch covers two hours, so 30 minutes is a quarter of it. If you're within 30 minutes of a boundary, you cross into the next slot.
Some years also overlap with daylight saving time. In the summers from 1955 to 1960, both corrections apply. The detailed calculations are laid out in a table in Twelve years of daylight saving time.
Why 135°E of all meridians?
Standard time is usually set at 15-degree intervals. The Earth turns 15 degrees an hour, so time differences come out as whole hours.
But the Korean Peninsula lies between 124°E and 132°E. It fits neither 120°E (China) nor 135°E (Japan). Taking the midpoint gives 127.5°E, but that's UTC+8:30, which creates a half-hour time difference.
The reasons given for choosing 135°E in 1961 were that whole-hour offsets are convenient for aviation, shipping and international communications. A practical choice, in other words. The trade-off is that Seoul's clocks now run about 32 minutes ahead of the actual sun.
What is true solar time correction?
It's a calculation that matches clock time to the sun's actual position. It adds up two things.
Put the two together and, for Seoul, the difference can reach about 46 minutes. If you were born in Seoul at 12 noon in mid-February, in true solar time that's around 11:14 a.m.
Should you correct for true solar time?
From here on, it's interpretation, not fact. We'll set out both sides' reasoning as they are.
Both sides have their reasons, and the debate has gone on for centuries. So rather than settling it for you, Mutal Unnie calculates without correction by default, but lets you turn it on and off in the calculator to see how the result changes.
Note — true solar time correction is a different kind of thing from standard time and daylight saving corrections. Standard time and daylight saving time really happened, so they should be applied; true solar time is a choice about which clock to use. If an app doesn't apply the first two, you have reason to doubt its accuracy, but not applying true solar time doesn't make it wrong.
In short
- Born 1954.3.21 – 1961.8.9: +30 minutesThis is a matter of fact. It must be applied.
- Born during daylight saving time: −60 minutesThe summers of 1948–51, 1955–60 and 1987–88. This is also a matter of fact.
- True solar time is optionalAbout −32 minutes for Seoul, plus the equation of time (±16 minutes). Try turning it on and off to compare.
→ Turn the three corrections on and off in the Manseryeok calculator
A manseryeok that handles the corrections
The Mutal Unnie app calculates using the clock time you enter (KST) as is. In the Manseryeok calculator, you can turn standard time and daylight saving corrections on and off to see what changes.
Get the app for iPhone & AndroidFAQ
When did Korea's standard time change?
After it was first set at 127.5°E on April 1, 1908, it changed three times: to 135°E on January 1, 1912, back to 127.5°E on March 21, 1954, and back to 135°E on August 10, 1961. Korea still uses 135°E today.
How do you calculate the hour pillar for people born in 1954–1961?
Add 30 minutes to the recorded time. Clocks back then ran 30 minutes behind today's. A recorded time of 8:45 a.m. becomes 09:15, moving from the Jin (辰) hour to the Sa (巳) hour.
What is true solar time correction?
It's a calculation that matches clock time to the sun's actual position. Seoul lies west of the reference meridian, so it runs about 32 minutes behind, and on top of that comes the equation of time, ±16 minutes, which varies by season. Whether to apply it depends on the school.
Why do Korean clocks use 135°E?
By convention, standard time is set at 15-degree intervals, but the Korean Peninsula spans 124–132°E, so neither fits exactly. In 1961, 135°E was chosen for the convenience of aviation, shipping and international communications. That's why Seoul's clocks run about 32 minutes ahead of the sun.