Natal Chart Casting
Purpose
Turn “when and where someone was born” into a readable natal chart: planets by sign and house, axis points (Ascendant / Midheaven, etc.), and an aspect table. See Natal chart.
Inputs
| Input | Requirements |
|---|---|
| Date | Civil calendar; watch Julian/Gregorian switches for historical dates |
| Time | Prefer minute precision; note time zone or UTC offset |
| Place | Latitude and longitude; disambiguate same-named cities |
| Zodiac | Tropical or sidereal (see Tropical zodiac) |
| House system | e.g. Equal, Placidus (see House systems) |
Step 1: Normalize time
- Convert civil time to UTC (or a single internal time scale).
- Compute Julian Day / sidereal time and other intermediate astronomical quantities.
- About 4 minutes of clock error ≈ 1° on the Ascendant, so minute-level accuracy matters.
Step 2: Planetary longitudes
- Use an ephemeris for the ecliptic longitudes of Sun, Moon, Mercury–Saturn, Uranus, Neptune, Pluto, etc.
- Map each to one of the 12 signs (30° each).
- Optional: retrograde flags, speed, latitude.
Planet meanings: term index.
Step 3: Horizon and axes
- From geographic latitude and local sidereal time, find the Ascendant (ASC) longitude.
- Find the Midheaven (MC) and related axes.
- Descendant and IC follow from opposite-house relationships.
Step 4: Houses
- Choose a house-system algorithm and compute the 12 house-cusp longitudes.
- Assign each planet to its house (mind cusp-boundary “on the degree” rules).
- Quadrant systems and Equal houses can differ sharply — always state the house system on the chart header.
Step 5: Aspects
- Compute pairwise ecliptic longitude differences.
- Match major aspects: conjunction, opposition, square, trine, sextile, etc., plus an orb table.
- Output an aspect list: two bodies, aspect type, exact angle, applying/separating.
See Aspects and the individual aspect entries.
Step 6: Validate output
- Time, time zone, coordinates
- Zodiac, house system, ephemeris version
- Planet table, axes, cusps, aspect table