Synastry: two birth charts read against each other
Synastry compares two birth charts by measuring the angles between them: your Moon against their Venus, their Saturn against your Sun, and so on through both charts. Each of those contacts is an inter-aspect, and together they describe what happens when these two particular people are in a room. Nothing is averaged and nothing is merged — both charts stay exactly what they are, and what is being read is the traffic between them.
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That is what separates synastry from a composite or a Davison chart. Those two make one chart for the pair and read the relationship as a thing in itself. Synastry keeps two people in view and says how each one lands on the other, which is why it can tell you that a contact runs mostly one way: their Pluto on your Moon is not the same experience for both of you, and a single merged chart cannot show that.
Read the personal planets first. Sun, Moon, Venus, Mars and the Ascendant carry most of what is felt day to day: Sun and Moon between two charts is the classic ease, Venus and Mars the attraction, Moon and Moon how alike the two of you are in the unguarded moments. Tight orbs matter more than exact aspect names — a contact two degrees from exact says more than one nine degrees away, whatever it is.
Then look at the houses. Where their planets fall in your chart is where you will feel them: a Jupiter in your second house feels like someone who makes you better off, a Saturn in your seventh like someone who makes partnership serious work. This is the half of synastry that people skip, and it is often the half that describes the shape of a life together rather than the feel of a first meeting.
Hard aspects are not bad news, and easy ones are not a guarantee. Squares and oppositions between two charts describe friction that keeps coming back, which is uncomfortable and also what keeps a pair interested; trines describe what will always be easy, which is pleasant and can be inert. Long relationships are usually made of both, and a chart comparison with nothing difficult in it is rarer than it sounds.
Birth times matter here in a particular way. Without them the planets are still reliable, so the aspect list stands, but the Moon can be several degrees out and the Ascendant and houses are unknown — which removes the whole "where their planets fall in your chart" half. With one time missing you get a real synastry of aspects; with both, you get all of it.
A comparison describes; it does not decide. There is no score here and no verdict, because two charts cannot tell you whether to be with someone — they can tell you what the two of you will keep meeting, which is information you can act on rather than a judgement you have to accept.
Questions people ask
What is a synastry chart?
A comparison of two birth charts that measures the aspects between them — your planets against theirs. It keeps both charts intact rather than merging them, which is how it can show that a contact is felt differently by each person.
Synastry or composite chart — which should I read?
Both, for different questions. Synastry says how two people land on each other; a composite or a Davison says what the relationship is like as a thing in itself. Astrologers usually start with synastry and use the pair chart to describe where the relationship is going.
Do we both need a known birth time?
For the aspects between the planets, no. For the houses — where their planets fall in your chart — and for a precise Moon, yes. Without times you get a real reading that is missing one of its two halves.
Which synastry aspects matter most?
The tightest, and the ones involving the Sun, Moon, Venus, Mars and the Ascendant. Contacts between the slow planets are common to a whole generation and say much less about the two of you than a Moon contact does.
Are hard aspects between two charts a bad sign?
No. They describe friction that will keep recurring, which is work and is also what holds attention. A comparison made only of easy aspects describes a relationship that may never quite start.
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