Ephemeris

Ephemeris is the runtime-neutral service contract used by chart generation. It keeps astronomical calculations separate from chart projection and allows applications to provide a different ephemeris implementation.

Service contract

interface Ephemeris {
  dateToJulianDay(date: DateTime): Effect.Effect<JulianDay, EphemerisError>;

  calculatePosition(
    julianDay: JulianDay,
    body: CelestialBody,
    ayanamsa: Ayanamsa,
  ): Effect.Effect<PlanetaryPosition, EphemerisError>;

  calculateHouses(
    julianDay: JulianDay,
    latitude: number,
    longitude: number,
    houseSystem: HouseSystem,
    ayanamsa: Ayanamsa,
  ): Effect.Effect<HouseData, EphemerisError>;
}

The service is available as the Ephemeris Effect context tag. Implementations should return EphemerisError rather than silently substituting astronomical values.

Models

CelestialBody supports Sun, Moon, Mars, Mercury, Venus, Jupiter, Saturn, and TrueNode. Ketu is derived by Ascendant from Rahu's exact opposition.

PlanetaryPosition contains longitude, latitude, distance, the three corresponding speeds, and ephemeris flags. HouseData contains the twelve cusps, ascendant, MC, ARMC, vertex, equatorial ascendant, two co-ascendants, polar ascendant, and the selected house system.

JulianDay is a branded finite number. Use the service's date conversion method instead of constructing one from an unverified timestamp.