Data quality for calculation
core.chart is only as correct as the birth instant, coordinates, and options you pass. This note is a checklist before calling calculate or calculate_sidereal.
Required fields
| Field | Quality checks |
|---|---|
instant (UTC) |
Converted from local civil time with correct time-zones and DST rules; not “floating” local time |
latitude |
Decimal degrees, north positive; plausible for stated birthplace |
longitude |
Decimal degrees, east positive; sign errors (E/W) flip houses dramatically |
Optional but impactful
| Field | Default / note |
|---|---|
house_system |
Defaults to Placidus; set explicitly when comparing house-systems-comparison |
bodies |
Omit for standard set (Sun–Pluto + nodes); add asteroids only if ephemeris supports them |
ayanamsa |
Matters for calculate_sidereal only; default Fagan–Bradley in VSOP config |
Common failure modes
- Wrong UTC offset — one-hour DST error → wrong ASC (birth-time-accuracy).
- Rounded or unknown birth time — use noon/midnight conventions consciously; document uncertainty.
- Wrong city coordinates — using capital instead of hospital suburb shifts angles slightly.
- Mixing tropical and sidereal — use the right operation (sidereal-vs-tropical).
- Expecting Swiss/JPL arcseconds — see ephemeris-uncertainty for VSOP/Moon limits.
Validation habits
- Compare Sun/Moon sign against a trusted almanac for the same UTC.
- If angles matter, bracket time ±10 minutes and see if ASC sign is stable.
- Restart the graph server after note changes so knowledge upserts — unrelated to chart math but relevant for UI tooltips.
References
- Birth certificate — common time source (Wikipedia)
See also birth-input, natal-chart, vsop87.