LunarOtter calculation conventions, version 2
Updated November 1, 2026

This public fact sheet explains the geometry and input policies used in the product. A saved reading's reference names its actual engine and numerical settings; reopening a saved purchase does not recalculate it with a later engine or content edition.

Coordinates and bodies
- astronomy-engine 2.1.19 (MIT), pure JavaScript without external data files.
- True equinox and ecliptic of date, including light-time and aberration.
- Longitude speed uses a symmetric difference with a 0.001-day half-step.
- UTC approximates UT1; TT uses the library's Espenak-Meeus Delta T model.
- Western tropical zodiac, twelve equal 30-degree sectors from the March equinox point.
- Geocentric apparent ecliptic positions for Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
- Latitude/longitude are geodetic decimal degrees, north/east positive.
- Whole Sign houses: house one is the complete Ascendant sign. Each following sign is the next house.
- Ascendant and Midheaven are computed independently. The MC's Whole Sign house is reported and is not assumed to be ten.
- A negative longitude speed marks retrograde motion.
- Signs, houses, and aspects are classified from full precision before formatting for display.

Aspects
- Conjunction: 0 degrees, orb 8 degrees.
- Opposition: 180 degrees, orb 8 degrees.
- Square: 90 degrees, orb 7 degrees.
- Trine: 120 degrees, orb 7 degrees.
- Sextile: 60 degrees, orb 5 degrees.
- The same orb applies to all included points. Ascendant-Midheaven aspects are excluded.
- Every accepted aspect is listed in the complete reference table. The wheel draws twelve selected relationships for legibility.
- Aspects solely among Jupiter through Pluto are identified as slower shared context and are not selected for personalized interpretation.

Time and eligibility
- Birth dates: January 1, 1900 through today in the selected birth zone.
- Complete-reading latitude limit: 66 degrees north or south.
- The city lookup supplies an IANA zone identifier. Its current offset is not applied to historical births.
- Bundled historical time-zone rules supply the birth-date offset. Before 1970 the confirmation explicitly identifies historical rules.
- Repeated and nonexistent local times require an explicit user choice.
- Known time: the entered local hour and minute. No default time is supplied.
- Approximate: entered center time plus/minus 15, 30, 60, or 120 minutes. Every body's sign and house, Ascendant sign, MC sign and house, aspect membership, and retrograde flags must be certified stable throughout the window for a complete purchase.
- Matching interval endpoints is insufficient. A change and return inside the interval must be detected. If the interval cannot be certified, the purchase is unavailable.
- Unknown: the entire local calendar day, supported Sun/Moon signs only. No angles, houses, or complete-reading sale.
- Unsupported latitude: supported free Sun/Moon information, without the advertised complete-reading purchase.

Reading and snapshots
- Versioned deterministic content and selection rules, with no live generative AI in the reading pipeline.
- Each major section identifies its chart basis. The free offer gives structural counts, never paid interpretations or tables.
- Corrections create a new input revision. The purchased chart and reading remain as purchased.

Astronomical calculation and astrological interpretation are separate claims. Geometry is tested against numerical references; symbolic meanings are drawn from astrological traditions for reflection.
Sources: https://ssd.jpl.nasa.gov/horizons/manual.html and https://www.iana.org/time-zones
Product explanation: https://lunarotter.com/methodology