How this experience calculates and interprets

What are the Sabian Symbols?

The Sabian Symbols are a set of 360 symbolic images, one associated with each degree of the zodiac. They were first published in 1925 by the clairvoyant Elsie Wheeler with the astrologer Marc Edmund Jones, and later re-imagined by Dane Rudhyar in his 1973 book The Astrological Mandala. Each image — “A woman rises from the sea,” “A bridge being built” — is a small picture meant for contemplation rather than prediction.

The zodiac and conventions used

• Zodiac: Tropical zodiac (equinox-anchored, IAU standard positions).
• House system: Placidus (Placidus is the MVP default. The choice is isolated in lib/chart/houses.ts behind the chart provider so it can be swapped without touching the rest of the application.)
• Sabian degree convention: Degree-to-next convention. A position within a degree corresponds to the NEXT numbered Sabian degree. A position at exactly the boundary (0°00′00″ of a sign) corresponds to that sign's first degree (degree 1) — the leading edge convention.
• Boundaries: 0°00′00″ of a sign → Sabian degree 1 of that sign (leading edge). 0°00′01″ of a sign → Sabian degree 1 of that sign (within the first degree). 29°59′59″ of a sign → Sabian degree 30 of that sign. 360.0000° (exactly 0° Aries) → global index 360, which is the same as Aries 1 via the 360≡1 boundary.
• Ephemeris: astronomy-engine v2 — MIT License (Don Cross). https://github.com/cosinekitty/astronomy — a deterministic, VSOP87-based geocentric ephemeris.
• North Node: the instantaneous osculating ascending node at the birth instant, derived from the Moon’s position and velocity vectors — never the descending node, and never a value sampled from a nearby node-crossing event.
• Historical time: The local birth time is converted to UTC using the IANA time-zone database’s historical offsets for the exact birthplace and date — never a modern or assumed offset. DST gaps are rejected; ambiguous fall-back times expose both offset choices.

Deterministic calculation vs. AI interpretation

Every astronomical fact in a reading — the Sun’s longitude, the Moon’s degree, the Ascendant, the houses, the resulting Sabian degree — is calculated by deterministic code from a documented ephemeris. No AI model ever computes a planetary position, converts a time zone, or assigns a Sabian number.

AI (or, in demo mode, a deterministic mock) is used only for interpretation: reading the validated chart JSON and the symbol texts into reflective prose, story chapters, prompts, and artwork. It receives only the validated placements and symbol data, and its output is validated against a strict schema. The calculated facts are shown alongside every interpretation so the two can never be confused.

When the birth time is unknown

The Ascendant, Midheaven, and houses depend on the exact time of birth. When that time is not known, this application does not calculate or display them as facts, and never substitutes noon or any other assumed time. The Moon may be marked as potentially uncertain if it changes sign or Sabian degree during the local calendar day. The reading is then reduced to the placements that do not depend on the time of day.

Limitations and purpose

This is a testing-phase product. In demo mode the interpretation and artwork come from deterministic local fixtures and are clearly labeled as such. The Sabian symbol dataset currently contains a small development fixture, not an authorized complete set of 360 texts. Nothing in this experience is a medical, legal, or financial opinion, and nothing predicts your future. Its purpose is reflection and entertainment: a contemplative way to meet your own images.