Western astrology primer

Tropical zodiac

Western astrology (/western) uses the tropical zodiac: 0° Aries is fixed to the March equinox, tied to the seasons rather than the stars. This is why the same birth gets different signs from the Vedic endpoints like /planets (sidereal) and /western (tropical) — both are internally consistent systems, offset by the ayanamsa (~24°). The API keeps them as separate endpoint families precisely so you never mix frames by accident.

The natal chart

/western computes 13 bodies (Sun through Pluto, plus Chiron and the lunar nodes) with sign, degree, element, modality and dignity (/western/planets), 12 houses under a configurable house system (Placidus by default — /western/houses accepts houseSystem), and the ascendant/midheaven angles.

Aspects

Aspects (/western/aspects) are angular relationships between planets: conjunction (0°), sextile (60°), square (90°), trine (120°), opposition (180°). Each has an orb (how far from exact), whether it's applying or separating (tightening or loosening), and a nature (harmonic/tense). Aspect patterns across a whole chart — Grand Trine, T-Square, Yod, Stellium — are detected by /western/patterns.

Synastry — relationship charts

Synastry (/western/synastry) overlays two natal charts and reads the cross-aspects between them — one person's Venus square the other's Moon, and so on. The API scores four continuous themes — love, communication, tension, growth — available standalone at /western/synastry/themes for compatibility widgets. This is the Western counterpart of Vedic /compatibility.

Transits, progressions, returns

• Transits (/western/transits) — where the planets are now (or any date) relative to the natal chart; the basis of daily/weekly horoscope features.
• Secondary progressions (/western/progressions) — the "day for a year" symbolic advancement of the natal chart.
• Solar return (/western/solar-return) — the chart for the Sun's exact annual return to its natal degree (the "birthday chart" used for year-ahead readings).

The wheel

/chart/western-wheel renders any of this as the classic circular chart with aspect lines — see Chart rendering for the gallery and options.