Nativitas · Two birth skies

Synastry

Compare two natal charts in one bi-wheel.

Enter each person’s birth details. The planets are calculated on your device; birth details are not sent to a calculation service.

If a birth time is unknown, select that option. Local noon will be used; that person’s houses and angles are omitted, and their positions are approximate, especially the Moon.

Method and limits

Eleven bodies, five major cross-chart aspects, and house overlays where birth times are known. The chart with a known time goes inside when only one time is known; otherwise the entered order is retained.

Placidus houses require a known time and are unavailable at or beyond the polar circles. Choose “Birth time unknown” only when the time is actually unknown; no alternative house system is silently substituted.

Aspect orbs: 5° for conjunction, square, trine and opposition; 3° for sextile. These follow the Astrodienst convention of halving our natal orbs. Orb sizes vary between astrologers.

The first calculation downloads approximately 60 MB of astronomy files. Later calculations reuse the loaded engine. Positions remain provisional pending independent validation. Astrological interpretations are not scientifically validated; no compatibility score is assigned.

City data: GeoNames, CC BY 4.0. Software and data credits.