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Saju guide

Unknown Birth Time, Time Zones, and Why Saju Calculators Disagree

Why two saju calculators can give you different pillars, and what an unknown birth time changes. Solar terms, the Rat hour, longitude and calendars explained.

You type the same birthday into two saju tools and get two different charts. Or you open a calculator and stop at the box asking for your birth time, because nobody in your family remembers it. Both situations are common, and neither means saju is broken. They trace back to a handful of calendar and clock questions that every practitioner, and every calculator, has to settle one way or another. Here they are, one at a time.

What the birth time actually controls

A saju chart, sometimes called sajupalja (四柱八字), "four pillars, eight characters," has one pillar each for the year, month, day and hour of birth. The birth time feeds only the last of these, the hour pillar, or siju. The year, month and day pillars come from the date, apart from the boundary cases covered further down.

So if you do not know your time, you still have six of the eight characters. That includes the day pillar, which most readers treat as the center of the chart, and the month pillar, which sets the season you were born into. What you lose is the hour pillar itself, which tradition usually connects with inner life, later years and children, along with two characters' worth of the five-element count.

Twelve double hours

Saju divides the day into twelve periods of two hours, each named after a zodiac animal. The Rat hour runs from 11 p.m. to 1 a.m., the Ox hour from 1 to 3 a.m., and so on around the clock to the Pig hour from 9 to 11 p.m. Because each period is two hours wide, an approximate time is often enough. Knowing only "early morning" or "just after lunch" can narrow things to one or two candidates, and some people compare the charts for each candidate to see which reads more like them.

The Rat hour and the midnight question

The Rat hour straddles midnight, and that creates a genuine split among practitioners. One view says the new day begins at 11 p.m., when the Rat hour starts, so someone born at 11:30 p.m. gets the next day's pillar. Another view keeps the day change at midnight and treats the first half of the Rat hour as a late-night Rat hour, called yajasi, belonging to the current day, with the early-morning half called jojasi. Under the first approach the day pillar changes; under the second it does not.

Since the day pillar is so central, a birth between 11 p.m. and midnight can produce a noticeably different reading depending on which convention a calculator follows. Neither approach is universally accepted.

Solar terms set the month and year

Saju months do not follow the familiar calendar months. They change at twelve of the twenty-four solar terms, or jeolgi, points along the sun's yearly path, so a new month starts roughly every thirty days. The year itself turns at Ipchun, the start of spring, around February 4.

These boundaries fall at a specific minute, not at midnight. If you were born on the day a solar term begins, whether your month pillar is the old one or the new one depends on your birth time and on how precisely a tool computes the moment of the term. Small differences in astronomical tables or rounding can push a borderline birth to one side or the other.

Clock time versus sun time

Clocks follow standard time zones, which are drawn for convenience across wide areas. The sun, however, reaches its highest point at different clock times depending on longitude. Korea Standard Time is set by a meridian east of the Korean peninsula, so in Seoul the sun is roughly half an hour behind what the clock says.

Some calculators apply a longitude correction to convert clock time into local mean time, the time the sun would suggest at your birthplace. Some go further and use apparent solar time, which also accounts for the slight seasonal wobble in the sun's timing. Others use the clock time as entered. Births near the edge of a two-hour period can land in different hours depending on this choice.

Historical time zones add another layer. Countries have changed their official offsets over the years, and Korea is one of them: from 1954 to 1961 South Korean clocks ran half an hour behind today's standard. A tool therefore needs accurate time-zone history for the place and date of birth. People born abroad face the same question with their own local zone.

Daylight saving periods

When daylight saving time was in effect, clocks ran an hour ahead of standard time. South Korea observed it in a number of years between 1948 and 1960 and again in the summers of 1987 and 1988, and many other countries use it routinely. A birth time recorded during those periods may need an hour subtracted to reflect standard time. Whether a calculator does this automatically, asks you, or ignores it will change the hour pillar for affected births.

Lunar dates and leap months

Many older Koreans know their birthday by the lunar calendar. Converting a lunar date to a solar one is straightforward in most years, but the lunar calendar periodically adds a leap month, called yundal, to stay in step with the seasons. A date in the month that a leap month doubles can therefore refer to two different solar dates; in a year with a leap fourth month, for example, the fourth month and the leap fourth month each have their own fifteenth day. Dates in the other months of that year appear only once. If your birthday is recorded as lunar, it is worth checking whether it falls in a leap month. Hongsil's form lets you choose solar or lunar, and for a lunar date it asks whether the month is a leap month, then shows the converted solar date with the result.

Narrowing down an unknown time

Start with family members, even if they only remember the light outside or a mealtime. Birth certificates, hospital records and baby books often note the time. If you can narrow it to two or three double hours, try each and compare. And if nothing turns up, a reading based on the three date pillars still has plenty to say; on Hongsil you can simply mark the time as unknown.

FAQ

Is a reading without a birth time still meaningful?

Yes. The year, month and day pillars, including the day master that stands for you, do not need the hour unless you were born right on one of the boundaries above. The reading has less to say about the themes tied to the hour pillar, but its main outline is intact.

Which calculator is the correct one?

Usually the difference comes from a convention, not an error. Check how each tool handles the Rat hour, longitude, daylight saving and solar-term timing. If your birth is not near any of these boundaries, most tools will agree.

I was born abroad. Does that change anything?

The method is the same, but the local time zone and its history at your birth date matter. Converting your birth time correctly for the place you were born is the main thing to check.

Related

Part of the dotorium saju guide. Saju readings are for fun and reflection, not for making decisions.