Four pillars

Classical East Asian timekeeping tracks more than a calendar date. The year sets your family and social background. The month captures the season: the climate and rhythm of when you were born. That is why most schools give the month pillar heavy weight. The day stands for you through the day element, the element on your day stem. Every comparison is made against it, and it is traditionally called the day master. The hour adds detail about your inner rhythm and later life, when you know your birth time.

Without the hour pillar, the other three pillars still give a reading, but a less exact one. That is why we ask for your birth time when you know it.

Each pillar has two layers. The stem (top) is Wood, Fire, Earth, Metal, or Water. It also carries a ten god label, which says how that stem relates to your day element: peer, output, wealth, authority, or support. The branch (bottom) is one of twelve animal signs, Rat through Pig. It has its own element, and more stems hidden inside it.

On My Chart each card is drawn, not spelled out. It shows a shape for the stem's element, a shape for the branch's animal, and a small yang or yin mark under each. A key to all of them is in marks and symbols. The cards are a picture of the same chart the engine reads.

Top characters can also relate to each other. Five pairs combine: each yang stem with the yin stem of the element it controls. They are yang wood with yin earth, yang fire with yin metal, yang earth with yin water, yang metal with yin wood, and yang water with yin fire. Four pairs clash: two stems of the same polarity whose elements sit opposite each other on the compass, wood against metal and fire against water. Earth sits at the centre and clashes with nothing. We read these between neighbouring pillars only, as the classics do, and show them as a label on My Chart. Some schools count more clashes, or read a pair one pillar apart as a faint combination. We do not. In some readings a combination turns into a third element. We do not apply that, so a combination never changes your element balance or any score.

The third word on each row, such as Peak or Resting, places your day element on a twelve-step life cycle. It is measured against that pillar's animal. Two choices decide where it lands, and both are disputed. We let earth follow fire through the cycle, and we run the cycle backward for yin day elements. Some schools let earth follow water instead. Some reject the backward cycle for yin elements altogether. Either choice would change the word on some rows.

1. Your birthplace sets the timezone. The timezone turns your birth date and time into the local clock time we start from.
2. The year and month pillars follow the saju calendar. Months change at solar terms: points set by the sun's position, not by the first of each calendar month.
3. The day pillar changes at midnight in your timezone. Some schools change it at 11pm instead, which would move a birth in that last hour onto the next day’s pillar. That is a school’s choice rather than a mistake either way. We name ours here so you can tell which one you are reading.
4. The hour pillar uses a two-hour branch window: each animal covers about two clock hours, for example 11pm–1am for the Rat hour. Here a birth between 11pm and midnight keeps its own day’s pillar. It takes the Rat hour that runs on into the next day, which both schools agree on.

A rules-based saju engine, not an AI, works out your pillars and everything read from them.

We say this plainly because a practitioner will notice, and you deserve to know before you take a borderline birth to heart.

We read sun time, not clock time, when we know where you were born. A timezone is a political band. Away from the line of longitude it is named for, the sun and the clock disagree. Seoul keeps UTC+9, whose line runs through the sea east of Japan, so in Seoul the sun is about half an hour behind the clock. We shift the birth moment by that difference before reading the day and hour pillars. That can move a birth near the edge of a two-hour window to the other side. The year and month are different. They turn when the sun reaches a solar term, which is one instant for the whole planet, so we read them from your birth moment, unshifted. The birth time we show you is the one you entered: only the chart moves. Our sun time is mean solar time. Some calculators also apply the equation of time, a seasonal wobble of up to about sixteen minutes. That can change the hour pillar for a birth within minutes of an hour boundary.

Our solar terms are calculated, not dated. This used to be the second rough edge. A month now begins at the moment the sun actually reaches its mark. We solved those moments from a NASA/JPL planetary ephemeris and stored them to the second for 1700 through 2050. So a birth on a boundary day is placed by its hour, not given the whole day's answer. The boundary is also one instant everywhere: the same birth reads the same in Seoul time or Los Angeles time. Outside those years we fall back to the older arithmetic estimate, which is accurate to about a day.

Some birthplaces have no coordinate. 1449 of the 1469 places in the picker have a known longitude. The rest, and any place you type that we cannot match, are read from clock time, and your chart's assumptions say so. We would rather leave a chart uncorrected than correct it by the wrong amount.

Away from these edges, the gap that remains does not matter. This is what the chart in front of you was built from, and we would rather tell you than have you find out.

Four-pillar astrology grew out of the Chinese calendar tradition and is still central to Korean saju. Over centuries, practitioners refined how much each pillar weighs, the ten-god roles (how each stem relates to the day element), and five-element balance.

We do not claim to follow every classical school. This app uses a documented modern engine, and it only describes leanings: patterns to reflect on, not fate or commands.