Know the calculation · Starry Bodies
Birth Time and Astrocartography Accuracy
A map can be calculated precisely while its input time remains uncertain. Keeping those two kinds of accuracy separate makes the result more useful and easier to question.
Starry Bodies guide · Updated
Explore your own mapA small clock difference can move a line.
Earth turns through approximately 360 degrees in a sidereal day, about 23 hours 56 minutes. Four minutes therefore correspond to approximately one degree of rotation. That is a longitude relationship, not a universal kilometre error for every line.
The distance represented by a degree of longitude changes with latitude. Rising and setting lines also have curved geometry, and planetary coordinates evolve with time. Read the four-minute rule as an orientation rather than an exact displacement formula.
Local time needs its historical offset.
A birth record usually gives a civil clock time. To calculate the birth instant, the software must resolve the time zone and any daylight-saving rule that applied at that date and location. Today’s offset can be wrong for a historical birth.
Some local times occurred twice when clocks moved back; others never occurred when clocks moved forward. The Studio asks which occurrence you mean for an ambiguous time and reports an invalid local time instead of silently changing it.
Keep the provenance of the time.
A recorded time, a family recollection and a rounded estimate are different kinds of input. Note where your time came from and any reason to think it was rounded. Apparent precision in a printed chart cannot repair missing information.
Astrological rectification is an interpretive practice. It does not turn an estimated time into a verified historical record. Preserve the original uncertainty when comparing charts or places.
Use the information you actually have.
With an unknown time, the Studio analyses the local civil date and reports planetary ranges and possible sign changes. It omits the Ascendant, time-dependent houses and precise astrocartography lines.
If you later find a reliable time, recast the chart and compare the result. Choose a method you can inspect: a clearly labelled range is more useful than an unlabelled assumed time.
Common questions
A little more clarity.
Does four minutes always move a line by 111 km?
No. Four minutes are roughly one degree of Earth rotation. Geographic distance depends on latitude and line geometry, so a fixed kilometre rule is misleading.
Is a chart without a time useless?
No. Date-based planetary ranges can establish stable placements and show uncertainty. Angles, houses and exact angular maps require a time.
Keep exploring.
- Tropical vs Sidereal Astrocartography ↗
- How to Read an Astrocartography Map ↗
- Moon Lines in Astrocartography ↗
- Calculation methods & sources ↗
- Public validation report ↗
Planetary meanings are symbolic material for reflection. They are not validated predictions about a place or a person. These are original Starry Bodies guides; calculation references are documented on the methods page.