Guide

The clock and the sky keep different time

A birth certificate records clock time. Clock time is an agreement between people. It holds across a whole zone, and a zone can run more than a thousand miles wide. The sky keeps no such agreement. It is local to a longitude.

So this page converts before it calculates. It takes your date, your clock time, and the coordinates of the city, and it finds where the sun actually stood. Two corrections do the work.

The first is longitude. Every degree away from your zone's reference meridian moves solar noon by four minutes. In a wide zone that can add up to more than an hour.

The second is the equation of time, the running gap between a sundial and a clock. It swings about sixteen minutes each way across the year, because Earth's orbit is an ellipse and its axis is tilted. On your date it has one specific value, and that value is printed above.

Both corrections are shown for your birth rather than as general figures. You can check them against any ephemeris.

This matters most for the houses. The whole chart turns about one degree every four minutes. The Ascendant crosses a full sign in roughly two hours. An error of twenty minutes can leave the Ascendant where it was, or move it into the next sign and carry six houses with it. A chart built from a rounded time is a different chart, not a slightly blurred one.

Time zones also move. Cities have changed their offset, adopted daylight saving, dropped it, and adopted it again. A chart for Seoul in 1954 does not use the offset Seoul uses now. This page reads the IANA time zone database, which records those changes with the dates they took effect, and applies the rule that was in force on your date.

The remaining choices are named rather than assumed. The house system is printed above. So is the ephemeris the positions come from. Those two choices account for most of the disagreement between one site and another, and a site that hides them leaves you no way to find out why its numbers differ from somewhere else.

Where this page says a placement is uncommon, that is measured. The figure comes from a modeled sample of 100,000 births spread across 1940 to 2010, weighted toward Europe and North America. It is a sample, so it has edges. The number is a frequency within that sample rather than a claim about everyone alive.

Nothing here is interpreted. The positions, the pillars, and the frequencies are all calculation, and we publish them in full. The arithmetic is not the part worth selling. A reading built on a chart you cannot check is a reading you cannot argue with.

Four pillars, four boundaries that are easy to cross by accident

A BaZi chart is four pairs of characters. Each pair comes from a boundary, and every one of those boundaries is set by the sun rather than by a calendar. Most of the disagreement between one site and another comes from crossing one of them in the wrong place.

The year does not turn on January 1, and it does not turn on Lunar New Year either. It turns at Start of Spring, the solar term that begins the moment the sun reaches 315 degrees of ecliptic longitude. That falls in the first days of February, and both the date and the hour move from year to year. Two people born a day apart in early February can carry different year pillars, and someone born on the day it turns cannot be answered at all without the time of day. A site that uses Lunar New Year as the boundary places several weeks of births in the wrong year, every year.

The month works the same way. Twelve solar terms divide the year, each beginning at a fixed ecliptic longitude, and the month pillar changes partway through the calendar month rather than on the first.

The day pillar changes at local solar midnight. That is the same correction the birth chart page applies, and it moves the boundary away from 00:00 on the clock by a few minutes in some places and by more than an hour in others, once summer time and a wide time zone are counted. Anyone born in the two hours either side of midnight sits close enough to that line for it to decide their day pillar, which is the pillar most schools read first.

The hour pillar is a two-hour block, and the first block straddles midnight rather than starting at it. This is why an approximate time does not produce an approximate fourth pillar. It produces a wrong one or none. When the hour is unknown we say so and leave the pillar out. We do not substitute noon, and we do not sell a reading that depends on a pillar we had to invent.

Where this page says a combination is uncommon, that is measured against a separate sample from the one used for the chart figures: 200,000 births spread evenly across 1930 to 2020. The two samples are built differently, so the two sets of frequencies are not directly comparable with each other.

Everything above is calculation, published in full. You can take these four pillars to any other calculator and compare. If a number differs, the boundary that produced it is named here, which is the only way to find out which of the two is wrong.

How close counts as close

A planetary lines map draws lines where a planet stood on the horizon or on the meridian at the moment you were born. The projection itself is settled. The same birth data produces the same lines anywhere.

The open choice is the radius: how near a place has to be before it counts as on a line. This map uses 400 kilometers.

That number is chosen rather than measured. Nothing has been recorded fading with distance from one of these lines, so a radius is a convention, and a convention deserves to be stated out loud rather than applied quietly. Figures between 800 and 1,100 kilometers are in common use.

A wide radius is worth looking at directly. A thousand kilometers covers most of Western Europe. At that reach nearly every populated place sits near several lines at once, and a statement that holds everywhere cannot be tested anywhere. The honest version of a convention is the tightest one that still leaves the lines readable.

There is a second reason to keep it tight, and it comes from the clock. Earth turns fifteen degrees an hour, so twenty minutes of error in a birth time shifts every meridian line by five degrees of longitude. At middle latitudes that is close to four hundred kilometers, which is the entire radius this map allows. A birth time rounded to the nearest half hour does not blur these lines. It relocates them by about as far as the lines reach.

So the map is drawn from the same corrected time as the chart. Longitude and the equation of time are applied first, the time zone rule in force on the date is used rather than the current one, and the correction is printed with the chart so the two can be checked against each other.

What the map marks is narrow and worth stating plainly. It shows where, at your moment of birth, a given planet was rising, setting, or overhead. That is a fact about the sky and your clock, and it holds whether or not you have been to any of these places. It is not a forecast about those places, and this page makes no claim about what happens in them.

A line also says nothing about how strong it is. Lines are drawn for every planet, so everyone has them everywhere, and a map covered in lines is the normal result rather than a notable one. What can be compared is how many lines fall near one place and which planets drew them, and both of those are printed rather than summarized. The map hands you the geometry. Whether a place has meant anything to you is something you already know, and this page does not pretend to find it out from a birth time.

A number with nothing to compare it to

A compatibility report usually arrives as a set of counts. You have forty-one aspects with this person. Four of their planets fall in your seventh house. The counts are real, and on their own they say nothing, because nothing tells you what two strangers score.

We measured that. Twenty thousand randomly formed pairs of charts, with births spread across 1960 to 2010, drawn from thirty-five cities weighted toward Europe and North America.

Two strangers average 39.51 aspects at standard orb. The middle of the range is 39. One pair in ten comes in at 31 or lower, and one in ten reaches 48 or more. So a pair with 35 aspects is below average for two people who have never met, and a pair with 48 sits at the ninetieth percentile and is still perfectly ordinary.

The count also moves with a setting rather than with the people. Narrow the orb and the average drops to 28.49. Apply natal orbs without narrowing them at all and it rises to 74.5. The same two charts can nearly double their total when one parameter changes, and nothing about the two people has changed.

House overlays behave the same way. Three or more of one person's planets landing in a single house of the other's chart happens in 97 percent of random pairs. Four or more happens in about half. Five or more happens in 14.6 percent, which is the first point on that scale where the word unusual is doing any work.

What separates one pair from another is which combination appears, not how many. The single most common aspect pairing shows up in only 7.2 percent of random pairs, and 975 distinct pairings occur often enough to measure. That is where the information sits. A specific pairing in the bottom few percent is a fact about these two charts. A total of forty-one is a fact about orbs.

So this page prints the comparison group next to your figures rather than behind them. Where a number lands above or below what strangers produce, it says so and by how much.

The sample has edges worth naming. Twenty thousand pairs places a common pairing precisely and says little about the rarest ones. The births are weighted toward two continents, so the planetary distributions follow those birth rates rather than the world's. Every figure is a frequency inside that sample.

The BaZi side and the astrology side are reported separately, and we do not blend them into a single number. They rest on different boundaries and different samples, and one figure made by averaging them would hide which side produced it.

None of this is interpretation. It is counting, with the comparison group shown.