How synastry works
Instead of reading one chart, synastry overlays two and measures the aspects between one person's planets and the other's. Your Venus touching a partner's Mars, your Moon touching their Sun — these inter-chart contacts describe how two people actually experience each other.
The contacts that matter most
- Sun–Moon — a classic marker of ease and mutual understanding.
- Venus–Mars — attraction, chemistry, desire.
- Moon–Moon and Moon–Venus — emotional comfort and affection.
- Saturn contacts — commitment and longevity, sometimes with a lesson attached.
Browse every combination in the synastry aspect library — each planet-to-planet contact, in every aspect, explained.
Hard aspects aren't dealbreakers
A relationship built only on easy (trine, sextile) contacts can feel pleasant but flat; some friction (squares, oppositions) creates the spark and growth that keep people engaged. Compatibility is about the whole pattern, not a score.
Read your own synastry
AskCelesta can compare two charts and highlight the harmonious and challenging contacts between them. First, it helps to understand a single chart — see how to read your birth chart.
See it in your own chart, free — no signup needed.
Calculate your natal chart →Frequently asked questions
What is synastry in astrology?
Synastry is the comparison of two birth charts to assess relationship compatibility, by reading the aspects formed between one person's planets and the other's.
Which synastry aspects indicate strong compatibility?
Sun–Moon, Venus–Mars, and Moon–Venus contacts are classic markers of attraction and emotional ease. Saturn contacts point to commitment and longevity.
Do challenging synastry aspects mean a relationship won't work?
No. Squares and oppositions add friction, but that friction often creates chemistry and growth. Compatibility depends on the whole pattern, not any single aspect.