Why Birth Time and Place Matter in Saju and Astrology
A birth date alone is enough for a Sun sign, but a fuller chart needs the time and the place. Both Saju and Western astrology treat the hour of birth as important, and both need the place to turn a clock time into a real position of the Sun and sky. This guide explains what each piece of information adds, what happens when something is unknown, and why a calculator has to be careful with clocks.
What the date gives you
A date is enough to find the Sun sign in Western astrology. It is also enough to find the year pillar and the month pillar in Saju, as long as the date is not very close to a solar term, and enough to find the day pillar, which holds the Day Master. For many readers this is the heart of the chart.
Dates close to a boundary need extra care. The Western Sun changes sign on a different day each year, and the Saju year changes at the Start of Spring, around February 4. If you were born within a day of one of those moments, the time of day can decide which side of the boundary you fall on.
What the time adds
In Saju, the time gives the fourth pillar, the hour pillar. The day is divided into twelve double-hours, each named for one of the twelve animals, and the stem of the hour pillar depends on the day. Without the time, a chart has three pillars and a reader works with six characters out of eight.
In Western astrology, the time gives the rising sign and sharpens the Moon sign. The rising sign changes about every two hours, so a few hours of error can change it. The Moon changes sign about every two and a half days, so the time matters only when the Moon crossed into a new sign on the day of birth.
What the place adds
A clock time means little without a place, because the same instant is a different hour of the day in different cities. The place also gives the latitude and longitude that fix the horizon, and the horizon decides the rising sign. Someone born at the same moment in Oslo and in Singapore will have different rising signs.
In Saju, the place matters because the traditional hour pillar is based on the Sun, not on the clock. A birth at 12:00 on a clock in the far west of a time zone is earlier in solar terms than a birth at 12:00 in the far east of the same zone.
Local solar time
Local solar time is the time shown by a sundial at the birth place, where noon is the moment the Sun is highest. Time zones are wide bands, so the clock and the sundial can differ by half an hour or more. The difference has two parts. One is the distance of the place from the centre of its time zone, which adds four minutes for every degree of longitude. The other is the equation of time, a seasonal drift of up to about sixteen minutes, caused by the tilt of the Earth's axis and the shape of its orbit.
When you give a birth time and city, our calculator corrects the clock time to local solar time before it finds the Saju hour pillar. A birth at 11:40 pm by the clock may fall in the next day's rat hour or not, depending on where it took place, which is why some charts shift by a pillar after the correction.
Time zones and daylight saving
Time zone rules have changed many times, and so have the dates on which daylight saving time began and ended. A birth in 1985 and a birth in 2005 in the same city may have been recorded on different clock rules. The calculator uses a time zone database that keeps the history, so that the clock time is turned into the correct moment in universal time.
Daylight saving can also create impossible or doubled clock times. When the clocks jump forward, one hour does not exist, and when they fall back, one hour happens twice. If you enter a time in that window, the calculator will ask which one you mean and will not guess.
When the time is unknown
Many people do not know their birth time. A birth certificate or hospital record is the best source, and a parent's memory is the next. If the time is truly unknown, the honest answer is a partial chart. For Saju, that means three pillars. For Western astrology, it means the Sun sign and perhaps the Moon sign, and no rising sign.
NamesByStars handles this by using only what is known and by saying what has been left out. A reading with less information is less specific, and the site tells you so. You can come back and add the time later if you find it.
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If you would like to see how the system works before entering your own details, try it with a sample birth date, and compare the Saju and astrology paths.
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