Synastry: what gets looked at when two charts are compared

Synastry is the technical word for something fairly simple: laying one chart over the other and seeing what touches what.

It does not compare people or decide compatibility. It compares two maps and describes the relationship that forms between them.

How it is done

Both full birth charts are calculated and overlaid. Then the aspects between a body of one and a body of the other are located: your Venus to their Mars, your Moon to their Saturn, and so on through every combination.

Each contact describes a concrete channel between the two people. A soft one marks where the relationship flows without effort; a hard one, where the same argument keeps coming back.

The contacts that weigh most

Sun to Moon. The classic of couples who last. One brings direction and the other support, and they tend to feel at home with each other from day one.

Venus to Mars. Attraction. It is the contact noticed fastest and the one that guarantees least: it ignites, but it does not sustain on its own.

Moon to Moon. Habits and sensitivity. When they agree, living together is easy even if they argue about everything else.

Saturn to anything. The most misunderstood contact. It gives duration, seriousness and commitment, and also weight and a sense of duty. It sits in a great many long marriages, happy and unhappy alike.

Uranus, Neptune or Pluto on a personal planet of the other. Intensity. They fascinate and destabilise. These tend to be the relationships people remember as the strongest, and not always as the best.

The other half: the houses

Besides the aspects, you look at which house of one chart the other's planets fall in. That says what role each occupies in the other's life.

Your planets in their fourth house make you family. In their tenth, someone tied to their work and public image. In their twelfth, someone who appears in the most private part of their life, the part almost nobody sees. All twelve are in this guide.

What you need

Both dates, both times and both cities. Aspects between planets come out without the hour, but houses do not: if one time is missing, the more concrete half of the reading is lost.

If you do not have it, this guide explains what survives and where the hour is usually written down.

Synastry and the composite chart are not the same

There is a second technique sometimes confused with this one. The composite chart averages the two charts into a third, which stands for the relationship itself.

Synastry says what happens to each person with the other. The composite describes the couple as if it were one person. They are used together, and they answer different questions.

And the usual reminder holds: none of this says whether it is a good idea. It describes how it works, which is far more useful information. Why the sign table falls short is in the previous guide.

The short version

• Synastry overlays two charts and reads the contacts between them.
• Sun-Moon sustains, Venus-Mars attracts, Saturn gives duration and weight.
• The house the other's planets fall in says what role they play in your life.
• Without both birth times the houses are lost, and that is the concrete half.
• The composite chart is a different technique: it describes the relationship as a third party.

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