Birth-Time Accuracy
A chart states where the sky stood at one minute over one place, and it is worth exactly as much as that minute is. This series covers what the clock controls, what an unknown hour still leaves standing, and which zero point the degrees are measured from. It is the part of the site where the answer is sometimes that a thing cannot be known, which is why it earns a series rather than a footnote under the calculator.
What this series claims
The claims here are narrow and checkable: given a date, an hour, and a place, these are the quantities that move and roughly how far. What the series does not claim is that a precise chart is a better one to live with, or that a solar chart is a consolation prize. It also declines to settle tropical against sidereal. That fork is philosophical, both frames are computed correctly by the calculator, and a piece that declared a winner would be inventing a result nobody has.
Start here if…
- You have your birth time to the minute.What that precision buys you, layer by layer, and what a rounded time quietly costs.What the clock controls
- Nobody wrote it down.The solar chart, what it is good for, and the four habits that make one read well.The unknown-time guide
- You are still hunting for the hour.Five places to look, in rough order of how often they work.Where birth times turn up
- A headline told you your sign changed.Two coordinate systems, one slow wobble, and nothing broken.Tropical and sidereal
In this series
- Pillar
Why Your Birth Time Matters (Down to the Minute)
The pillar, and the piece with the numbers in it. What each degree of error costs the Ascendant, the houses, and the Moon, followed by a ranked list of where a recorded time is actually found.
- Companion
No Birth Time? Here's What You Can Still Know
The method for the data you have rather than the data you wish you had. What a solar chart is, why it is a real instrument with centuries behind it, and which parts of it to hold loosely.
- Companion
Tropical vs. Sidereal: Why Your Sign Didn't Change
A headline that resurfaces every few years, answered once and properly. Precession without the panic, and a plain statement of which zero point this site measures from and how to change it.
The words these three lean on
Every entry is astronomy or convention. None of it is interpretation, which is why it can be defined in a line.
- Ascendant
- The degree of the zodiac climbing over the eastern horizon at the birth moment. It needs an hour and a place, and nothing else in a chart moves faster.
- Midheaven
- The highest crossing of the ecliptic at that same moment, and the cusp of the 10th house. It turns with the Ascendant, so it goes when the hour goes.
- Ingress
- The moment a body crosses out of one sign into the next. Born on an ingress date and that placement depends on the hour.
- Orb
- The allowance around an exact aspect angle. Half a degree of it and the aspect runs a life; seven degrees of it and the aspect is background weather.
- Precession
- The wobble of Earth’s axis, one full circuit in about 25,800 years. It is what slides the two zodiacs apart at roughly a degree every 72 years.
- Ayanamsha
- That accumulated offset, about 24 degrees today, subtracted from every position when a chart is read sidereally.
- Solar chart
- The planets for the day with whole-sign houses counted from the Sun rather than from the horizon. The standard instrument when the hour is unknown.
- Rectification
- Working backwards from dated life events to a probable birth time. A hypothesis, and never a record.