Put two people in the same kitchen and within ten minutes you learn things no questionnaire could tell you: who opens the window, who closes it again, and who quietly moves the salt back to where it "belongs". Synastry is the astrological version of that kitchen. It takes two birth charts, sets them side by side, and measures what each person's planets do to the other's.

Nothing is averaged and nothing is merged. Your chart stays your chart, theirs stays theirs, and what is being read is the traffic between them. That is the difference between synastry and the two relationship charts, the composite and the Davison, which build one chart for the pair and read the relationship as a thing in itself. Synastry keeps both people in the room.

Interaspects: the angles between two charts

An interaspect is an aspect between a planet in one chart and a planet in the other: your Moon against their Venus, their Saturn against your Sun. The angles are the familiar ones, the conjunction, sextile, square, trine and opposition, but each one now connects two people instead of two parts of the same person.

Because both charts stay whole, synastry can show that a contact runs mostly one way. Imagine one partner's Saturn sitting on the other's Moon. For the Moon person it can feel like being steadied, or like being gently corrected every time a feeling comes out. For the Saturn person it feels like being needed as the sensible one. Same aspect, two experiences, and a single merged chart could never show you that.

A few of the classic contacts, to give the idea:

Sun and Moon is the oldest marker of ease between two people. One person's sense of self lands on the other's emotional needs, and daily life tends to fit together without much negotiation.

Venus and Mars describe attraction, and the particular energy that makes two people want to do things together, including disagree.

Moon and Moon describes how alike the two of you are when nobody is watching. With the Moons in harmony, both people want a quiet evening on the same evening. With the Moons square, one wants to talk a problem through tonight and the other wants to sleep on it, and each is privately certain that the other's method is the strange one.

Mercury and Mercury is conversation. A square here does not mean you cannot talk. It means you will describe the same trip in two completely different orders, and both of you will feel that the other skipped the important part.

House overlays: where you land in each other's lives

This is the half of synastry people tend to skip, and it is often the more revealing half. Each person's planets also fall into the houses of the other's chart, and the house says which area of life the contact is felt in.

Their Jupiter in your second house can feel like someone who makes you better off, in money or in confidence. Their Saturn in your seventh can feel like someone who makes partnership serious work. Their Mercury in your third is someone you never run out of small talk with; the same Mercury in your tenth is someone whose opinion of your career you cannot stop asking for. Interaspects tend to describe the feel of a first meeting. House overlays often describe the shape of a life together.

How our report reads them

Our synastry report reads the two charts in two runs of question and answer cards. The first run is the interaspects. The second is the house overlays, in both directions: your planets in their houses, and theirs in yours. Above each run there is a button that asks the AI astrologer to synthesise the whole run in about 400 words. It is not a rewrite of the cards, but the picture they make together, built only from the placements you can see on the page.

Under the readings you will find the chart wheels for the pair, the aspect grid, the most important astrological elements between the two of you, and the full list of planet positions and aspects. A section called Areas of Mutual Attraction is an AI analysis of where the connection is strongest: emotional, romantic, spiritual, intellectual and professional. Members also see Pair Traits and Dynamics, a set of relationship trait scores calculated from the aspects between the two charts and in their composite.

Synastry is not only for couples. The same report reads a friendship, a parent and child, two business partners or two siblings who have shared a bathroom for far too long. In a relationship that is not romantic, read the romantic side as love in a broader sense, and as a shared taste for what is beautiful.

What to read first

Start with the personal planets: the Sun, Moon, Mercury, Venus and Mars, plus the Ascendant. They carry most of what is felt day to day. Contacts between the slow planets, Jupiter out to Pluto, are often shared by everyone born within a few years of each other, so they say much less about the two of you than a single Moon contact does.

Then look at the orb, the distance from exact. A contact two degrees from exact says more than one nine degrees away, whatever its name. A tight square between two personal planets will be felt; a loose trine between two outer planets mostly will not.

The site also has articles on individual contacts, such as Moon to Moon synastry, Saturn in synastry, or each planet in the other person's houses, if you want to go deeper into one of them.

Birth times

Birth times matter here in a particular way. Without them, the planets are still reliable, so the list of interaspects stands. But the Moon can be several degrees out, and the Ascendant and the houses are unknown, which removes the whole house overlay half of the reading. With one time missing you get a real synastry of aspects, plus the overlays into the chart whose time is known. With both times, you get all of it.

Hard aspects are not bad news

Squares and oppositions between two charts describe friction that keeps coming back. That is uncomfortable, and it is also what keeps two people interested in each other. Trines describe what will always be easy, which is pleasant and can be a little sleepy. Long relationships are usually made of both, and a comparison with nothing difficult in it is rarer than people expect.

That is why there is no score in our report and no verdict. 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 use rather than a judgement you have to accept.

When you are ready, compare two birth charts here, then follow the questions it raises: the composite chart of the relationship, its Davison chart, or what the sky is doing to the two of you this month.

Frequently asked questions

What is synastry?
A comparison of two birth charts that measures the aspects between them, one person's planets against the other's, and places each person's planets in the other's houses. Both charts stay intact, 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 chart describes the relationship as a thing in itself. Most astrologers start with synastry and then read the pair chart.

Do we both need a known birth time?
For the aspects between the planets, no. For the houses, and for a precise Moon, yes. Without times you get a real reading that is missing one of its two halves: where each person's planets fall in the other's life.

Which synastry aspects matter most?
The tightest ones, 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.

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 can describe a relationship that never quite gets started.

Can I use it for a friend or a colleague?
Yes. The method is the same for any two people. In a relationship that is not romantic, read the romantic contacts as affection and shared taste rather than courtship.