Methodology
How we calculate your chart
We keep three layers separate that are often confused: astronomical calculation, astrological interpretation and presentation.
1. Astronomical calculation
Positions of the Sun, Moon and planets come from NASA Jet Propulsion Laboratory's JPL DE440 ephemerides (DE440s file, valid from 1850 to 2149), via the open-source Skyfield library. We use apparent geocentric positions in the tropical zodiac, referred to the true equinox of date. The North Node is the true (osculating) lunar node.
The Ascendant, Midheaven and houses are calculated from sidereal time and the true obliquity of the ecliptic. We offer Placidus (default), whole sign, equal and Porphyry houses. Placidus is undefined at polar latitudes; in that case we use Porphyry and tell you so.
2. Verification
Our engine is automatically checked against Swiss Ephemeris, the professional reference in astrology software: in our tests, differences are below 2 arcseconds for the planets and zero for the houses. We also check that it reproduces every eclipse from 2024 to 2030 in NASA's catalog and the times of new moons, stations and equinoxes to within minutes.
3. Your birth time
We convert your local time to universal time using the IANA time zone database, including historical daylight saving changes. If your time fell on a clock change (a repeated or skipped hour), we tell you. For dates before 1970 historical records may be incomplete: we show you the offset applied and you can correct it.
If you don't know your time, we don't invent your rising sign or houses. We calculate the planets at local noon and tell you if the Moon could have been in two signs that day.
4. Interpretation
Texts were written in advance with AI assistance and editorial supervision, and are combined by deterministic rules: the same calculation always produces the same report. Each report stores the engine and text versions it was generated with.
5. What astrology is and isn't
Astrology is not an empirical science and does not predict events. We offer it as a symbolic language for personal reflection and entertainment.