When I look at a synastry chart, I’m not simply trying to figure out whether two people are "compatible." I look at what draws them to each other, what brings them closer, how they communicate, what they bring out in one another… and also where things can get more complicated. To do that, I overlay their two birth charts: the planets, aspects, houses and angles. But I never draw a conclusion from one element alone.
In this article, I’m going to show you how to read a synastry chart, what to look at first, and how to connect the different pieces to understand the dynamics of a relationship.
Because what really matters is understanding how the relationship works as a whole.
What Is Synastry?
Synastry is what happens when two birth charts meet. We overlay them to see what happens when one person’s chart interacts with the other’s: which planets connect, which houses they fall into, what aspects they form and which angles they activate.
It can make a relationship much easier to understand: why the attraction felt immediate, why you seem to understand each other effortlessly in certain areas, or, on the other hand, why the same tension keeps coming up again and again.
What I love about synastry is that it isn’t about giving a relationship a compatibility score, as we unfortunately see so often. It’s about understanding what is actually happening between two people: what comes naturally, what takes more adjustment, what each person brings out in the other, and how both people function individually and within the relationship.
How Does Synastry Work?
To read a synastry chart, we start by looking at both birth charts separately. The idea is to first understand how each person works on their own: how they love, what they need to feel secure, how they communicate, what drives them and what can make them shut down.
Then we overlay the two charts. That’s when we can see, very concretely, what one person’s planets are touching in the other person’s chart. For example, one person’s Moon may form an aspect with the other person’s Mercury, which tells us something about how emotions and communication interact between them. Venus may fall into the other person’s 7th house, strongly activating themes around partnership. Saturn may contact a personal planet, showing both what gives the relationship structure and where it can sometimes feel heavier.
We look at the aspects between the planets, the houses they fall into in the other person’s chart, the angles they activate, and also the patterns that repeat. When several different elements are telling us the same thing, we know we’re looking at something important in the relationship.
That’s why a synastry chart is never read from one aspect alone. We put all the pieces together to understand the relationship dynamic as a whole.
So, what does your synastry say about you two? >
What Are the Most Important Factors in Synastry?
Not every part of a synastry chart tells us the same thing. Some factors tell us more about attraction, others about communication, emotional security, the stability of the bond, or the role each person naturally takes within the relationship.
There isn’t really one planet that matters more than all the others. What matters is understanding what each one is describing and how it fits into the rest of the chart.
The Sun
The Sun represents a very central part of our identity: what we want to express, how we assert who we are, and what makes us feel most like ourselves.
In synastry, contacts to the Sun often show how the other person affects that sense of identity. Some aspects can make us feel seen, encouraged or understood for who we truly are. Others can create more friction, especially when one or both people feel that their way of being or their choices are being challenged.
The Sun can therefore tell us a lot about the way two people support one another, or sometimes challenge each other, in becoming more fully themselves.
The Moon
The Moon is essential when we’re looking at emotional intimacy. It tells us about our emotional needs, our instinctive reactions, what makes us feel safe, what makes us more vulnerable, and how we naturally seek comfort.
When the Moon is strongly involved in synastry, we’re often touching something very intimate. These contacts can create a sense of familiarity, safety or natural emotional understanding. But they can also reveal important differences in the way each person experiences and expresses their feelings.
The Moon often helps explain why someone can make us feel instantly at home… or why certain reactions from them affect us much more deeply than we expected.
Mercury
Mercury is all about communication. We look at how each person thinks, expresses ideas, processes information, asks questions and reacts when there’s a disagreement.
Supportive Mercury contacts can create a real sense of flow: you understand what the other person means quite easily, conversations move naturally and it’s easier to put your thoughts and experiences into words.
More challenging aspects don’t mean two people can’t communicate. They may simply show that each person speaks a slightly different language, interprets things differently or needs to make more of an effort to feel truly understood.
Venus
Venus speaks to the way we love, what we enjoy, what we find beautiful or desirable, and how we give and receive affection.
In synastry, it therefore plays an important role in attraction and in the pleasure two people take in being together.
Contacts between Venus and the Sun, Moon, Mars or Ascendant can create a lot of warmth, chemistry or simply that feeling of genuinely enjoying the other person’s presence.
But Venus alone doesn’t tell us whether a relationship is solid. You can feel a lot of attraction or tenderness for someone without necessarily working well together emotionally or in everyday life.
Mars
Mars speaks to desire, drive and action, but also to the way we assert our needs and react when we meet resistance.
In synastry, it can play a major role in physical and sexual attraction, especially when it forms aspects with Venus, the Sun or the Ascendant.
But Mars also shows how two people handle their energy together. Do they energize each other? Push each other into action? Or do their ways of doing things regularly clash?
Mars can bring a lot of movement into a relationship, both through desire and through conflict.
Saturn
Saturn becomes especially interesting when we’re trying to understand what gives a relationship structure.
It speaks to commitment, responsibility, boundaries, time and what two people are able to build together over the long term.
Strong Saturn contacts with personal planets can make a relationship feel serious or stable. There may be a real desire to stay, make an effort or build something together.
But Saturn can also feel more demanding. Depending on the aspects and the rest of the synastry chart, it can point to areas where one person feels restricted, judged or weighed down by expectations.
So Saturn is an important planet when we’re looking at longevity, but its presence alone never guarantees that a relationship will last.
The Ascendant and Descendant
The Ascendant and Descendant are two particularly important angles in synastry.
The Ascendant represents, among other things, the way we meet the world, how we naturally present ourselves and a very visible part of our personality.
The Descendant, directly opposite the Ascendant, is closely connected to relationships and to the qualities we tend to seek or encounter in a partner.
When one person’s planets touch the other person’s Ascendant or Descendant, the effect can feel very immediate. The other person may feel familiar, especially attractive, or instinctively fit something we associate with partnership.
Contacts to the Descendant are therefore particularly interesting when we’re looking at how naturally someone may come to occupy the role of partner in another person’s life.
Synastry Aspects
Aspects show how two people’s planets interact with each other. In other words, they describe what happens when two different energies meet: does it flow easily, does it create stimulation, does it bring tension, or a mix of all three?
In synastry, we mainly look at conjunctions, oppositions, squares, trines and sextiles. A trine or sextile can point to a natural sense of ease between two planets. A square or opposition may create more friction, but also plenty of movement, attraction or stimulation. A conjunction strongly intensifies the two planets involved: depending on which planets they are, it can feel very natural or much more challenging.
But one aspect never tells us very much on its own. A Venus-Mars square, for example, doesn’t simply mean there’s strong attraction. We also need to look at the signs the planets are in, the houses they rule or activate, the other aspects they receive and whether the same theme appears elsewhere in the synastry chart.
So I’m less interested in whether an aspect is labelled positive or negative than in what it tells us within the relationship as a whole.
Planets in Houses in Synastry
We also need to look at the houses. Which houses in the other person’s chart do the planets fall into?
This is very tangible because houses show us which areas of life the other person activates in us.
For example, someone’s Venus falling into your 5th house can awaken pleasure, flirtation, playfulness or creativity. A personal planet falling into your 7th house can make that person feel naturally significant in your relationship life. A planet falling into your 8th house can create something much more intense, intimate or transformative.
And once again, we need to avoid shortcuts. A planet falling into a particular house isn’t enough to sum up a relationship. We always look at which planet is involved, the aspects it forms, the sign it’s in and what the rest of the synastry chart is showing us.
Houses mainly help us understand where the relationship affects us most directly: love, security, communication, family, intimacy, shared plans or the way we imagine a future with the other person.
Love and Attraction in Synastry
When we’re trying to understand attraction in synastry, we pay particular attention to Venus, Mars and a few houses that are strongly connected to love and relationships: the 5th, 7th and 8th houses.
Venus
Venus speaks to the way we love, what we enjoy, what we find attractive and how we give and receive affection. In synastry, its contacts with the other person’s planets can create a lot of warmth, pleasure in being together and a very natural sense of attraction. But Venus isn’t only about desire: it also shows what we genuinely appreciate about the other person and how we try to create harmony within the relationship.
Mars
Mars is more closely connected to desire, drive, physical attraction and the way we pursue what we want. In synastry, its aspects with Venus, the Sun or the Ascendant can be highly stimulating and create strong sexual chemistry. But Mars also tells us how two people deal with frustration, disagreements and the way they take action together. It can fuel desire just as easily as it can fuel friction.
The 5th House
The 5th house is closely connected to flirting, pleasure, playfulness, seduction and romantic excitement. When someone’s planets fall into another person’s 5th house, they can awaken something very lively and spontaneous: the desire to flirt, have fun together, break out of routine or simply enjoy being around each other. It’s an important house for understanding what keeps romance playful and what fuels that initial spark.
The 7th House
The 7th house is connected to partnership, committed relationships and the way we relate to another person as a partner. When someone strongly activates this house, they may naturally feel like someone we could genuinely be in a relationship with. There can be a sense that they instinctively fit something we look for in a partner. The 7th house therefore isn’t just about attraction: it shows the kind of place the other person may naturally take in our relationship life.
The 8th House
The 8th house is connected to intimacy, sexuality, vulnerability, deep sharing and everything a relationship can transform within us. When it’s strongly activated, the connection can feel much more intense, sometimes with an attraction that is difficult to ignore. But that intensity isn’t always easy to handle: it can also bring up fears, control issues, jealousy or very deep emotional reactions.
Emotional Compatibility
When we’re trying to understand emotional compatibility in synastry, the Moon is central because it speaks to our emotional needs, our instinctive reactions, what makes us feel safe, what tends to hurt us more easily and how we naturally seek comfort.
In synastry, we look at the aspects the Moon forms with the other person’s planets, but also at the houses it activates. A Moon in a harmonious aspect with the Sun or Venus can create a sense of warmth, understanding or emotional safety. More challenging contacts with Mars, Saturn or Mercury can show that emotions aren’t always expressed or received in the same way.
But emotional compatibility doesn’t mean reacting to everything in exactly the same way. Two people can have very different emotional needs and still work beautifully together if they understand what the other person needs in order to feel heard, supported and secure in the relationship.
This is where the Moon becomes particularly revealing: it tells us less about what we think we should feel and more about how we actually react when something hits us emotionally.
Communication in a Relationship
When it comes to communication, we mainly look at Mercury.
Mercury shows how we think, how we put our thoughts into words, how we process information and how we react during a conversation or disagreement.
Its aspects with the other person’s Mercury, Moon, Sun or Mars can tell us a lot about how communication works between two people. Some contacts make conversation feel very natural: you follow each other’s train of thought easily, you can put things into words and misunderstandings are easier to clear up. Others can reveal differences in pace, tone or the way each person approaches a problem.
For example, a challenging Mercury-Mars contact can make conversations more heated or impulsive, while a Mercury-Moon connection has more to do with the ability to talk about feelings and put emotions into words.
Again, synastry doesn’t simply tell us that a couple communicates well or badly. It helps us understand where communication comes naturally, where it takes more effort and, most importantly, why certain conversations seem to keep running into the same misunderstandings.
Can Synastry Show the Long-Term Potential of a Relationship?
Saturn is one of the first things we look at when we’re interested in the stability and long-term potential of a relationship.
Saturn speaks to time, commitment, responsibility, boundaries and what two people are capable of building together. When it forms important aspects with the other person’s personal planets, it can bring a sense of seriousness, stability or deep attachment to the relationship. It can also show the areas where the couple may need to deal with limitations, frustration or stronger expectations.
But Saturn alone can’t tell us that a relationship is definitely going to last. We also look at the synastry chart as a whole: how well the emotional needs are supported, the quality of communication, contacts to the angles, the houses being activated and, above all, repeated patterns showing that several parts of the chart are telling us the same story.
A relationship can have very strong Saturn contacts and last for years while still being difficult to live in. On the other hand, a synastry chart with less Saturn emphasis can absolutely work long term if the rest of the chart provides enough stability, understanding and ability to adapt.
Synastry can therefore show us what may help a relationship hold together over time, but it can’t predict its lifespan like an expiration date.
Can One Synastry Aspect Define a Relationship?
No. And it’s probably one of the shortcuts I see most often in relationship astrology.
An aspect can be very strong, very noticeable, and sometimes explain an important part of the attraction or tension between two people. But it never tells the whole story.
A Venus-Mars square doesn’t sum up your chemistry. A beautiful Moon-Venus connection doesn’t guarantee perfect emotional compatibility. And a strong Saturn contact doesn’t automatically mean a couple is destined to last.
To understand a relationship, we need to look at how all the different pieces work together: the personal planets, aspects, houses, angles, recurring patterns, but also how each person functions individually.
That’s exactly why I created NOUS, Mode d’emploi.
The idea isn’t to give you a compatibility score or pull three aspects out of context. It’s to read your relationship as a whole: what comes naturally between you, what can create tension, the way you communicate, what you bring out in one another and the patterns that keep showing up in your relationship.
Because ultimately, the most interesting question isn’t really "Are we compatible?" but rather: how do we actually work together?
So, what does your synastry say about you two? >