From birth date to astronomical instant
The form receives date, local time, latitude, longitude and IANA time zone. The historical conversion to UTC uses the PHP zone base. We reject non-existent and ambiguous times during time changes to avoid choosing an arbitrary instant. The catalog incorporates GeoNames coordinates and zones; we do not infer an area from the nearest city.
The admitted births range from 1900 to today. Cycle scanning works within 1900–2099, with additional margin at the extremes to look for complete returns. Without time we use a reference of the day and omit astrological houses, Ascendant and Midheaven.
Planets, nodes and astrological houses
The built-in PHP engine uses VSOP87 and Meeus formulas via the Astronomy Bundle. The Sun, Moon and planets are expressed in tropical geocentric coordinates; Pluto uses the Meeus series with precession and light time. The nodes are middle nodes. Chiron is interpolated from a daily apparent geocentric ephemeris obtained from JPL Horizons and Lilith represents the mean lunar apogee.
With a known time we also calculate the Part of Fortune and the Vertex. The Part of Fortune uses the day or night formula according to the actual height of the Sun; The Vertex is obtained from the geometry of the vertical circle. They are omitted when the time is missing because they depend on the local horizon.
The default system is astrological houses by whole signs; There is also support for equal astrological houses in the engine. The Ascendant and Midheaven are calculated from sidereal time, obliquity and coordinates. Placidus requires a vendor to implement it - we don't quietly replace one system with another.
What we validate and what that validation does not mean
We contrast ten bodies on seven dates distributed between 1900 and 2099 against Astronomy Engine. In this sample of 70 lengths the maximum difference was less than 0.01°. Chiron's daily interpolation was also verified against an independent JPL Horizons instant, with a difference of less than 0.001°. They are regression checks on samples, not a universal guarantee or certification of all points and angles of the chart.
The returns numerically seek the crossing of the natal solar or lunar longitude. The resolution of the search is less than a second, but the physical accuracy depends on the position model and birth data. We do not confuse numerical resolution with observational accuracy.
Moon and interpretations
The lunar phase is obtained from the angular separation between the calculated Sun and Moon. Lighting is a geometric approach; it does not describe cloudiness, horizon or local visibility. Daily calendars refer to UTC noon when no other time is specified.
Sources and visible decisions
Astronomy Bundle PHP, Astronomy Engine, JPL Horizons and GeoNames allow us to review the technical bases. GeoNames is used with CC BY 4.0 attribution.
Free interpretations are editorial texts combined with calculated positions. Generative conversation, when configured, requires consent to send the chosen context to OpenAI. A precise astronomical calculation does not validate psychological or predictive claims of astrology.