Synastry is the astrological technique of comparing two birth charts to understand the dynamics of a relationship. It reveals why certain people feel magnetic, why some relationships flow effortlessly while others are characterized by intense friction, and what the long-term potential of a connection actually looks like — beyond initial chemistry.
Most synastry calculators compare natal charts and give you a list of aspects. ERA does something fundamentally different: it compares progressed charts. Because both people in a relationship are evolving, the most relevant compatibility picture comes from where they are now, not just where they started.
Synastry works by overlaying one person's chart onto another's and examining how their planets interact. When your Venus falls on your partner's Mars, there is a strong physical and romantic attraction. When your Saturn squares their Moon, there is a tendency toward emotional restriction in the relationship. When your Jupiter conjuncts their Sun, you expand each other's sense of possibility.
These interactions — called aspects — paint a detailed picture of the relationship's strengths, challenges, and growth points. Good synastry does not mean a relationship without tension. It means a relationship where the tensions are productive and the harmonies are genuine.
ERA examines the full spectrum of synastry aspects between two charts, weighing each interaction within the context of the transmitted methodology that guides all of ERA's interpretations. This is not a computer-generated compatibility score — it is a nuanced reading of how two specific people interact at the planetary level.
Here is the problem with standard synastry: it only compares natal charts. Your natal chart is fixed — it was set at your birth and will never change. But you are not the same person at 35 that you were at 22. Your partner is not the same person either. The relationship that worked beautifully five years ago may be experiencing strain now, and standard synastry cannot explain why because the natal charts have not changed.
ERA's methodology addresses this by comparing progressed charts. Both you and your partner have progressed planets that have moved into new signs since birth. Your progressed Venus may have shifted into a completely different sign than your natal Venus, fundamentally changing what you desire in a relationship. Your partner's progressed Mars may have changed signs, altering how they express desire and take action.
By comparing progressed charts, ERA reveals the real-time compatibility dynamics — not just the original blueprint of the connection, but how it is actually functioning right now. This is why ERA can explain relationship shifts that standard synastry cannot: because the progressed charts have moved, even though the natal charts have not.
No other synastry calculator does this. It requires both the calculation power of Swiss Ephemeris and the interpretive framework to make sense of progressed synastry — both of which ERA possesses through its unique transmitted methodology.
ERA analyzes a comprehensive set of synastry interactions between your chart and your partner's. The most significant include:
Sun-Moon contacts, which reveal emotional compatibility and the degree to which partners feel fundamentally understood. Venus-Mars contacts, which show the chemistry, attraction dynamics, and how desire flows between two people. Mercury contacts, which reveal communication compatibility — whether two people naturally understand each other's way of thinking.
Saturn contacts deserve particular attention because they reveal where the relationship gets serious — and where it gets restrictive. A well-placed Saturn contact adds commitment and longevity. A difficult Saturn contact can make one partner feel controlled or limited by the other.
ERA also examines Moon-Moon compatibility (emotional rhythm), Jupiter contacts (where the relationship expands and brings joy), and Pluto contacts (where the relationship triggers transformation and power dynamics). All of these are interpreted through the lens of the progressed chart, not just the natal chart.
To calculate synastry with ERA, you need birth data for both people: date of birth, time of birth (if known), and place of birth. Enter your own data during onboarding, then ask ERA to compare your chart with another person by providing their birth details in the conversation.
ERA will calculate both natal charts and both progressed charts using Swiss Ephemeris, then analyze the cross-chart aspects through the transmitted methodology. You can ask specific questions — about romantic chemistry, communication dynamics, long-term potential, or areas of challenge. ERA will respond with direct, chart-grounded guidance.
ERA gives you 5 free messages per day. Paid subscribers get 30 messages per day, which allows for deeper exploration of synastry dynamics and follow-up questions about specific aspects of the compatibility.
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