Question 1

What is a synastry chart and how do you read it?

Accepted Answer

A synastry chart overlays two birth charts so an astrologer can read the aspects each person's planets form with the other's. Trines and sextiles describe natural flow; squares and oppositions describe tension that can become growth. No couple is astrologically perfect — every configuration reads as a conversation between two planetary archetypes, observed without verdict and worked with consciously over time.

Question 2

How accurate is the synastry calculator on Stars.expert?

Accepted Answer

Stars.expert runs every calculation on Swiss Ephemeris, the astronomical library used by professional astrologers, with planetary positions sourced from the NASA JPL DE431 archive. Accuracy is arc-second-precise from 13 000 BCE through 17 000 CE. The aspects your chart surfaces carry the same scientific footing as a chart calculated by hand from astronomical tables.

Question 3

Which planets matter most in synastry?

Accepted Answer

Venus and Mars define the erotic-affective tone, Sun and Moon describe how two people mirror each other in everyday life, Mercury rules communication and Saturn anchors the long arc of the bond. Hellenistic practice — recovered through Robert Hand and Project Hindsight — adds aspects involving the lunar nodes, read as the karmic remit of the relationship and the direction of shared growth.

Question 4

Can I run synastry without a precise birth time?

Accepted Answer

Yes, with a real limit: no birth time means no ascendant and no house placements. The synastry compatibility calculator still produces a solid reading on the faster planets (Sun, Mercury, Venus, Mars) and the slower ones (Jupiter through Pluto) that barely move over a single day. Stars.expert flags which house-based readings sit out of reach when the exact time is missing.

Question 5

Does synastry predict whether a relationship will last?

Accepted Answer

No synastry forecasts specific events. The synastry chart returns a map of the likely dynamics: where energy will flow, where productive tension will build, which knots will need conscious work. Vettius Valens framed astrology as a discipline of orientation, not divination — a 'difficult' chart can work beautifully when both partners know the friction points and walk them together.

Question 6

How much does the synastry calculator cost?

Accepted Answer

The core synastry chart is free and asks for no signup: enter date, time and place of birth for both people and the synastry compatibility calculator returns the chart with every major aspect. Advanced AI-led interpretation is part of the Premium plan, but the astronomical chart itself and the technical aspect reading stay accessible with no hidden paywall.

Synastry — Free Couple Compatibility Birth-Chart Calculator

First Person

Second Person

Complete Guide to Synastry

Key Aspects in Synastry

Beyond Sign Compatibility

Understanding Planetary Aspects in Synastry

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