Born outside Korea, or unsure of your birth time? How K-SaJu handles it

The textbook picture of a K-SaJu (Korean astrology) reading is someone born in Seoul who knows their birth time to the minute. Lots of people don't fit it. Maybe you were born in Chicago, or your mom only remembers "sometime before lunch". This post explains what changes in those cases, what Rocky Saju does about it, and why two apps can hand you two different charts.

Two clocks inside one chart

Your chart runs on two kinds of time, and it helps to keep them apart.

• The year and month pillars follow the solar markers, twelve points in the year when the sun reaches a set position. Each marker happens at one instant for the whole planet. To place your birth before or after it, we need the exact moment you were born in universal time (UTC).
• The day and hour pillars follow the sun where you were. Your birth day and your two-hour block depend on local sun time, which shifts with longitude.

Getting both right is the whole trick. Your birth city makes it possible.

Step one: your city's clock, back then

When you pick a birth city, we look up its time zone, and not just today's rules. We use the time zone history built into the system, which records when a place used daylight saving time and when its standard time changed. A birth at 11:50 pm in Los Angeles in August 1995 happened on Pacific Daylight Time, so that extra hour comes off before anything else.

From the local clock plus that history, we get the exact UTC moment of your birth. That moment is what gets compared with the solar markers for your year and month pillars. Our list covers 16 places in Korea and 88 cities abroad, from New York, Houston and Toronto to London and Sydney, each with its own time zone and longitude.

Step two: the sun's time where you were born

Clock time and sun time aren't the same thing. A time zone is a wide band that runs on one clock, but the sun reaches its high point earlier on the east side of the band and later on the west side. For your day and hour pillars we use local mean time: the clock you'd get if noon were set by your own city's longitude. We leave out the small seasonal wobble of the sun, which keeps it close to how the Korean custom works.

Here's a case where it really matters. Picture two babies born at the very same instant on August 15, 1995, both at 11:50 pm on the local clock. One is in Los Angeles, the other in Phoenix. Both clocks read UTC-7 that night, because LA was on daylight time and Phoenix doesn't use it.

• Los Angeles sits a little east of its zone's center line, so sun time ran about 7 minutes ahead of standard time. That puts the birth near 10:57 pm sun time, in the 9 to 11 pm block. Hour pillar: 癸亥 (Rain Pig).
• Phoenix sits well west of its zone's center line, so its sun time ran about 28 minutes behind the clock. That's roughly 11:22 pm sun time, in the 11 pm to 1 am block. Hour pillar: 甲子 (Oak Rat).

Same moment. Same clock reading. Different hour pillar. Both babies still share the same year, month and day pillars.

Korea's 30-minute custom

Births in Korea work a little differently. Korea's standard time is set by a line well east of the peninsula. Seoul sits about 8 degrees west of that line, so its sun time runs roughly half an hour behind the clock. Korean practice handles this with one simple rule: shift the clock by 30 minutes for the hour pillar. The first two-hour block, the Rat hour, runs from 11:30 pm to 1:30 am instead of 11 pm to 1 am.

Korea's clock history is messy. It used UTC+8:30 for two stretches, 1908 to 1911 and 1954 to 1961, and it had daylight saving time in years between 1948 and 1960 and again in 1987 and 1988. We take daylight saving out first. For births during the UTC+8:30 years, the wall clock already matched the half-hour shift, so we don't shift it a second time.

Close calls get a heads-up

Some births sit right on a line. Rather than pretend otherwise, we tell you.

• Within 2 hours of a solar marker: your month pillar, and at the start of spring your year pillar too, could flip with a small error in the recorded time. If a marker fell on your birthday, we also show the exact time it arrived.
• Within 15 minutes of an hour boundary: a few minutes either way could change your hour pillar. In the Los Angeles example, 10:57 pm is three minutes from the 11 pm line, so that result comes with this note.

If you see one of these notes, a birth certificate or hospital record is worth digging out. If that's not possible, hold both versions loosely.

No birth time? Here's what happens

Plenty of people don't know their birth time, and that's completely fine. When you tick "I don't know the time", we calculate as if you were born at noon. We leave the hour pillar blank instead of guessing, and the result says so plainly. You still get six of your eight characters, including your birthday type, which comes from the day.

There's one thing to watch for. If a solar marker fell on your birthday, your month pillar depends on whether you arrived before or after it. Without a time we can't tell, so we flag it.

Why apps disagree on the hour

If you've checked your chart on a few apps and got different hour pillars, it usually isn't a bug. Apps make different choices:

• Some use the clock time exactly as written.
• Some shift by 30 minutes, following the Korean custom.
• Some use true sun time, which adds a correction that changes through the year.
• Apps also split the hours around midnight differently. We keep a birth in the first half of the Rat hour, before midnight sun time, on the earlier day for your birthday type. Other apps move it to the next day.

We picked one method and use it for everyone, and every result names the method it used. Our guide to the 60 birthday types touches on the midnight question too.

Already know your 8 characters?

Some people have their chart written down by a grandparent or from an old reading, but not the exact birth date. For them, our form has a third option next to the regular and lunar calendars: Enter my 8 characters. You choose your pillars from lists. The month list only shows pairs that fit your year, and the hour list only shows pairs that fit your day, so impossible combinations can't slip in.

We then search every date from 1900 to today, on a Korean clock, for births that produce exactly those characters. The same eight characters come around again roughly every 60 years, so you might be asked whether you were born in 1942 or 2002. Pick one and the reading runs as usual. Leave the hour out and it's handled just like an unknown birth time.

Curious how your own birth city plays out? The free life reading shows the city and method it used right at the top of your result. If you'd like the bigger picture first, start with what K-SaJu is.