Geocentric
Planetary positions are calculated from Earth's frame.
CALCULATION METHODOLOGY
Astronomy establishes the facts. Interpretation explains them.
Selyune is designed around a strict boundary: deterministic code calculates the chart, while the narrative layer can only interpret a structured, versioned subset of those results.
THE CALCULATION PROFILE
A defined Western tropical system, not a mix of methods.
Every result carries engine, calculation, settings, zodiac, and house-system metadata so it can be reproduced and invalidated when needed.
Tropical zodiac
Longitudes are mapped to the seasonal tropical zodiac.
Placidus default
Known-time charts use Placidus houses by default.
Versioned results
Inputs and settings are hashed for lifecycle control.
QUESTIONS ABOUT THE METHOD
What Selyune calculates, and what it leaves out.
The short answers below describe the current production calculation profile. Version metadata is stored with results so a future engine or settings change does not silently rewrite an older chart.
DATE + TIME + PLACE
How does Selyune calculate a birth chart?
Selyune resolves the birth record to a real instant and coordinates, calculates geocentric planetary longitudes, maps them to the tropical zodiac, and then derives supported houses, angles, and aspects.
WESTERN TROPICAL
Which zodiac model does Selyune use?
Selyune uses the Western tropical zodiac. It does not mix tropical and sidereal positions inside one chart.
PLACIDUS DEFAULT
Which house system does Selyune use?
Known-time charts use Placidus houses by default. At latitudes where Placidus cusps cannot be calculated reliably, Selyune uses Whole Sign houses and records that fallback in the result.
RESOLVED LOCATION
How are birthplace and timezone handled?
A selected place supplies validated coordinates and an IANA timezone. The local date and time are converted with that named zone, allowing the runtime's timezone data to apply the relevant historical UTC offset and daylight-saving rule.
NO INVENTED ANGLES
What happens when birth time is unknown?
The date is anchored at local noon only to calculate supported date-level planetary positions. Selyune omits the Ascendant, angles, houses, and Moon aspects, and it reports both possible Moon signs if the Moon crossed a boundary that day.
MEASURED SEPARATION
How are aspects and orbs calculated?
The engine measures the shortest angular separation, compares it with the five supported aspect angles, and accepts a contact only when it falls inside the configured natal, transit, or synastry orb for that aspect.
The current orb tables are published on the Aspects page. Phase is derived from whether the measured relationship is moving toward or away from exactness.MOVING + NATAL
How are transits calculated?
Current planetary positions are compared with supported natal placements. Aspect type, orb tightness, moving body, duration proxy, natal luminaries, and reliable angular-house context contribute to deterministic priority.
TWO COMPLETE CHARTS
How is synastry calculated?
Selyune calculates supported cross-chart aspects, maps them to relationship dimensions, and derives scores from versioned weights. Missing birth time removes unsupported Moon, angle, and house evidence and limits confidence.
NO
Does AI calculate planetary positions?
No. Chart facts, transits, synastry contacts, and deterministic scores exist before a narrative request. AI may explain selected structured evidence, but it cannot add a placement or change a calculation.
REPRODUCIBLE RESULTS
What version metadata is stored?
A chart records engine, engine version, calculation version, ephemeris version, settings version, zodiac mode, house system, capabilities, calculation settings, and input hashes used for invalidation.
THE DETERMINISTIC PIPELINE
From local birth record to a structured chart.
Each step produces typed data for the next. A later description cannot rewrite an earlier calculation.
Resolve the civil moment
Local date, local time, and an IANA timezone are converted to a precise instant. Coordinates are validated separately.
Calculate geocentric positions
Sun through Pluto receive tropical longitude, degree, minute, daily longitude speed, and retrograde state; mean lunar nodes are added.
Build local chart geometry
With reliable time, the engine calculates ASC, DSC, MC, IC, then Placidus cusps or a recorded Whole Sign fallback.
Detect relationships
Major aspects, phase, chart patterns, and weighted dominance are derived from the calculated placements.
Create time-based evidence
Current transits, aspect windows, ingresses, stations, and New and Full Moons are calculated against the natal chart.
Constrain the narrative
A relevance mapper selects factual evidence for the question. The language layer receives those facts plus explicit limitations.
UNCERTAINTY IS DATA
Missing precision changes the output, not just the disclaimer.
Selyune omits calculations that the input cannot support and records why. It does not fill a missing time with a plausible-looking chart.
Known and recorded
- Calculation, engine, ephemeris, and settings versions
- Tropical zodiac and selected house system
- Input and context hashes for invalidation
- Evidence identifiers used by a narrative
Explicit limitations
- Unknown time uses local noon only as a labeled date reference
- No Ascendant, houses, or Moon aspects without time
- Approximate time marks angles and houses as approximate
- High-latitude Placidus failure triggers Whole Sign with a warning
TEST THE METHOD WITH YOUR DATA
Start with a transparent, calculated result.
Your chart shows the available facts and the limits created by your birth-time accuracy.