Planetary positions
The Sun, the Moon and the planets (Mercury through Pluto) are calculated from the DE421 ephemeris of NASA's Jet Propulsion Laboratory — the same family of ephemerides that guides space probes. The apparent geocentric ecliptic longitude (true equinox and ecliptic of date, with light-time, aberration, gravitational deflection and nutation, the same quantity used by the Swiss Ephemeris) is tabulated in Chebyshev polynomials per decade, with a maximum error of 0.02 arcseconds at the test points and below 0.05 arcseconds in use.
The tables cover 1900 to 2053 and are downloaded on demand, only the decade needed; the calculation runs on your own device and is the same for the birth chart, the solar return, synastry and the horoscope transits. As a fallback, if a table cannot be loaded, the engine uses the VSOP87 theory (planets) and ELP (Moon), with an accuracy of a few arcseconds.
Nodes, Chiron and Lilith
We use the true Lunar Node (calculated from the Moon's real orbit via DE421), with the mean Node as an alternative where indicated. Chiron is obtained by numerical integration from Minor Planet Center orbital elements with planetary perturbations from DE421, validated to the arcminute against reference ephemerides between 1950 and 2026. Lilith is mean Lilith, the mean apogee of the lunar orbit, following Jean Meeus's algorithms.
Houses, time and place
Every chart uses Placidus houses. At latitudes above the polar circle, where Placidus is undefined, we let you know gently and apply a suitable alternative system. The Ascendant and the Midheaven are calculated from local sidereal time and the obliquity of the ecliptic of date.
The birth time is converted to Universal Time using the historical time zone of the place, including any daylight saving time in force on that date — the largest source of error in online charts. Coordinates come from the city you enter; the more precise the city, the more exact the houses.
Interpretation
The texts are generated by Celeste, Austral.Zodiac's artificial intelligence, from the calculated data — positions, houses, aspects with orb, dignities. Celeste never invents positions; she interprets what the engine calculated, with explicit guidance toward warmth, specificity and practical usefulness. Texts are continuously revised based on feedback from readers.
Limits and corrections
Precision is astronomical between 1900 and 2053, the range covered by the app's DE421 tables; outside it the engine uses the VSOP87/ELP fallback and tells you so. If you find a difference compared with another ephemeris, write to contato@australzodiac.com with the date, time and place: we check it and, if there is an error, we fix it and record it here.