The calculation is math. The reading is interpretation.

Astrology.ac calculates geocentric apparent true-ecliptic-of-date positions for the Sun through Pluto with the MIT-licensed, version-pinned Astronomy Engine. Local birth date and time are converted through the selected IANA timezone to an actual UTC instant.

Reference frame

Geocentric apparent positions

Zodiac

Tropical, 12 equal 30° signs

Angles

Ascendant from horizon rotation geometry

Houses

Whole Sign, anchored to the Ascendant sign

The calculator never substitutes noon and presents it as exact. If the time is unknown, the Ascendant and houses are omitted. Exact natal aspects are omitted because the fast-moving Moon and angles cannot be treated as certain.

The engine checks the beginning and end of the local birth date. Any planet that crosses a sign boundary is marked uncertain and is excluded from compatibility scoring. The result says what can be known and leaves the rest blank.

Interpretive copy is original to Astrology.ac and maintained as product content, not scraped or stitched from third-party horoscopes. It separates placement, house, and aspect evidence, avoids a single deterministic personality verdict, and makes room for context and choice.

• No medical, fertility, death, crisis, legal, or financial predictions.
• No guaranteed outcomes, fear prompts, or derogatory sign stereotypes.
• No claim that a human astrologer manually reviews an automated chart.
• No fake precision such as a universal soulmate percentage.

Deterministic tests lock planetary positions against JPL Horizons reference fixtures, Ascendant examples, unknown-time behavior, compatibility symmetry, share-payload privacy, and zodiac route integrity. Lint, type checking, unit tests, a production build, and a browser walkthrough run before release.

Calculation settings and the pinned engine version appear on chart results. A change to the zodiac, house system, ephemeris, or uncertainty rules requires a visible methodology update.

Reference pages are published and maintained by Astrology.ac. The visible byline links here so readers can inspect the calculation and editorial rules behind the page.

To report a factual, calculation, accessibility, or wording issue, send the page URL and the specific correction to hello@astrology.ac. Do not email private birth details; use a reproducible non-sensitive example where possible.

For the boundary between symbolic reflection and professional advice, read the terms of use.