Methodology

How Auspex computes

Astrology software disagrees with itself more than it admits. Two apps will give you two ascendants and neither will tell you why. This page is what Auspex does, precisely enough that a disagreement can be traced rather than argued about.

Positions

Planetary positions come from JPL DE440, the ephemeris NASA uses for mission planning, read through Skyfield. That is the full apparent-position pipeline: light-time, aberration, precession and nutation, not a truncated series fitted to the modern era.

Checking

Every position is regression-tested against Swiss Ephemeris, the reference implementation most professional astrology software is built on. The tolerances are asserted in the test suite, over a range from 1550 to 2400:

• Planets and the Moon: agreement to 0.001–0.003 arcseconds in the modern era.
• Mean lunar node: 0.01″. True node: within 25″, a known Swiss-internal residual.
• Solar eclipse type, including hybrids: exact across 2025–2035. Local contact times within 1.3 seconds.
• Heliacal rising dates: median agreement to the day.

Where the two engines differ, the difference is recorded with a reason rather than smoothed over. Delta-T — the drift between atomic time and the Earth's actual rotation — is the largest single lever on historical accuracy, and Auspex interpolates the same table Swiss uses, generated against the tidal acceleration of the kernel it serves. The Moon moves 0.55 arcseconds per second of delta-T error, so this is not a detail.

Houses and angles

Placidus by default, with whole-sign, equal and Porphyry available, and per-tradition defaults where a tradition has one — Hellenistic charts use whole-sign because that is what the sources do. Above the polar circle Placidus is undefined for parts of the year, and Auspex says so rather than returning a number that means nothing.

Interpretation

The written material is a curated corpus, authored and reviewed by hand, keyed to the exact factors a chart produces — this placement in this sign, this transit to this natal body. It is not generated per request, and it is not scraped.

There is an optional layer that assembles longer readings across the corpus. It is constrained to cite only material that was actually retrieved for your chart: a claim it cannot ground in a real snippet is dropped before you see it, and each reading carries the version of the corpus, the model and the decoding settings that produced it. Content that has not yet been through editorial review is labelled as such in the app.

What Auspex does not claim

That the planets cause events. The astronomy is literal and the symbolism is symbolic, and Auspex does not pretend the second follows from the first. Nothing here is advice about your health, your money, or your relationships, and the app will not tell you a day is bad.

Traditions

Western tropical and sidereal, Vedic, Hellenistic and Babylonian each get their own wheel, house system and vocabulary rather than being a relabelling of one chart. Chinese BaZi, Mayan Tzolk'in and the Egyptian decans are calendar systems and are treated as such. Where a tradition's dignity tables or terminology are still under editorial review, the app flags it in place instead of presenting it as settled.

Published tables on this site were computed with skyfield:de440+swissdt.