Synastry is the branch of astrology that studies the bond between two people by comparing their two full birth charts, not just their Sun signs. In practice, you lay the two charts over each other and look at the angles, called aspects, that one person’s planets form with the other’s: one Sun touching the other’s Moon, their Venus and Mars in conversation, their two Moons in echo or in friction. You also notice which houses one person’s planets fall into when placed on the other’s chart, because that shows the areas of life each one lights up in the other. The word comes from the Greek and means "with the stars." Synastry doesn’t score a couple out of ten: it maps a dynamic, the points where two people pull together and the points where they snag, like a chart of the ground they share. It’s a language for understanding each other better, never a pass-or-fail test.

Synastry or sign compatibility: what’s the difference?

Sign compatibility compares two Sun signs, one point out of the ten that make up a chart. It’s a simple way in, perfect for grasping the idea that two temperaments talk to each other, but it stays a shortcut. Synastry compares the two whole charts: each person’s ten planets, their signs, their houses, and every aspect that crosses between them. Two people who share the same pair of Sun signs can live wildly different bonds depending on their Moons, their Venus, their Mars, and their rising signs. Compatibility says "Leo and Aquarius, here’s the general tone"; synastry says "your Mars touches her Venus, your Moon reaches for his Saturn, and your rising signs face each other." One gives you an atmosphere, the other a detailed dynamic. Starting with sign compatibility is a fine idea; synastry is the step after, when you want to understand one specific bond rather than an average tendency.

Do you need both people’s birth times for a synastry?

For a full synastry, yes, ideally both birth times. The time sets the rising sign and the placement of the houses, and that’s exactly what lets you see in which areas of life one person lights up the other, say a Venus that lands in the house of home or in the house of shared work. Without a time, those layers turn hazy and the rising sign, a very telling meeting point, drops out. Even so, a partial reading is still possible and worth doing with only one known time, or none: the aspects between the slow planets and between the personal planets (Sun, Moon apart from time-zone drift, Venus, Mars, Mercury) can largely be worked out from the dates alone. You read the planetary conversation without the map of the houses. It’s less precise, but it isn’t empty: a synastry that’s honest about what it can’t see beats an invented time that skews everything else.

Astrology

Synastry: what two whole charts reveal about a bond, far beyond Sun signs

Synastry compares two whole birth charts, planet by planet, to describe the dynamic of a bond. Comparing two Sun signs tells you almost nothing: your sign is one point out of ten. What synastry actually reads are the aspects between the two charts (Sun-Moon, Venus-Mars, Moon-Moon), the houses each person lights up in the other, and the way the rising signs meet. A tool for understanding the bond, never a compatibility verdict.

By Jade Nohemia 7 min read June 18, 2026

You know your sign. Maybe the sign of the person on your mind. And you’ve probably already searched to see whether “you two are compatible.” The honest answer fits in one line: comparing two Sun signs tells you almost nothing about a real bond. Synastry looks at something else entirely. This page explains what, and why it’s a far truer way to talk about what happens between two people.

Why doesn’t Sun-sign compatibility tell you much?

When a quiz says “Aries and Cancer, moderately compatible,” it’s holding one point of your chart up against one point of theirs. But your birth chart holds ten planets, twelve houses, and dozens of angles between them. The Sun sign is one detail in a whole score. Reducing a bond to that single point is like judging a novel by its first sentence.

Take two people born the same day: same Sun sign, to the minute. If one has the Moon in Scorpio and the other the Moon in Libra, their inner lives have almost nothing in common. One reaches for intensity and secrecy, the other for harmony and conversation. Pair each of them with the same third person and you get two completely different stories, even though “sign compatibility” would hand you the very same verdict for both.

That’s the whole trouble with the shortcut by sign: it erases what makes a bond one of a kind. Synastry does the opposite. It doesn’t compare two labels, it compares two full charts, point by point.

Sign compatibility still has its place: it’s a great way in, playful, instant, and it points to the right hunch, that two temperaments are in conversation. If you haven’t explored that first step yet, go take a look at sign compatibility: it’s the right place to begin. Just know you’re stopping at the doorway. The whole house is behind it.

What synastry actually reads: the cross aspects

The heart of synastry is its inter-chart aspects: the angles that one chart’s planets form with the other’s. To follow how this works, you first have to know what an angle between planets is; the page on aspects in astrology walks through it. In synastry, you take the two charts, lay them over each other, and measure these angles from one to the other. That’s where the dynamic of the bond shows up.

Three meetings come up over and over, and they almost always tell you the heart of it.

Sun-Moon: being seen, being held

When one person’s Sun touches the other’s Moon, something tender and deep happens. The Sun is identity, who the person is in full light. The Moon is the private need, the place of emotional safety. A lovely Sun-Moon contact often feels like being seen and held at once, without ever having to ask. Liz Greene, who reread relationship astrology through depth psychology, makes this point: these contacts don’t spell out a destiny, they describe a resonance between an identity and a need, with everything healing and everything repetitive that can carry.

Venus-Mars: desire and the way you love

Venus speaks of how you love, what draws you in, the way you offer tenderness. Mars speaks of how you want, how you act, how you move toward someone. When one person’s Venus meets the other’s Mars, you’re in the territory of attraction, magnetism, chemistry. It’s often what people are quietly chasing when they talk about “alchemy.” A smooth Venus-Mars contact makes desire feel obvious; a tense one brings fire, sometimes fertile, sometimes draining. Either way, it describes a kind of attraction, not a promise of how long it lasts.

Moon-Moon: the shared emotional weather

When the two Moons are in conversation, the inner weather you share starts to show. Two Moons in easy accord, and you feel “at home” with each other, you read one another without words where feelings are concerned. Two Moons at odds, and the needs pass each other without meeting: one wants closeness at the very moment the other wants space. It’s neither good nor bad. It’s precious information about the emotional rhythms you’ll learn to live with together.

Beside these three big meetings, you also watch the contacts with Saturn, which speak of commitment, staying power, and sometimes weight; and the contacts with the slow planets, which color a bond over the long haul. None of these aspects is “good” or “bad” on its own. A square, an angle of tension, can be the engine that makes a couple grow; a trine, an angle of ease, can lull you to sleep. What matters is what you do with it.

The houses that get lit up and how the rising signs meet

The aspects are only half the story. The other half is the houses that get lit up. When you place one person’s planets on the other’s chart, each planet lands in an astrological house, an area of life. One person’s Venus settling into the other’s house of home doesn’t color the bond the way the same Venus would falling into the house of work or of travel. The planet says “with what energy,” the house says “in which patch of your life this person makes themselves felt.” That’s often where the real texture of a relationship shows: where the other unsettles you, steadies you, opens you up.

And then there’s the rising sign, the point on the horizon that speaks of how you meet the world. In synastry, the contact between one person’s rising sign and the other’s planets describes a meeting that feels almost physical: the instant impression, the first recognition, that “of course it’s you” of the first glance. A Sun on the other’s rising sign, and the person feels lit up, sometimes dazzled. It’s one reason birth time matters so much: without it, no rising sign and no houses, and that living, embodied layer goes missing from the reading.

Synastry vs. the composite chart: what’s the difference?

People often mix up synastry with the composite chart, and it’s worth telling them apart, because they answer different questions. Synastry compares two charts: it describes what A does to B and what B does to A, two people facing each other. The composite chart builds a third chart from the midpoints of the two: it no longer describes two individuals, but the relationship itself, a separate entity with a temperament of its own.

It was Robert Hand who set the firm groundwork for this technique in Planets in Composite in 1975: the idea that “the relationship” has its own chart, its own Sun, its own Moon, its own tensions, apart from what either person brings to it. Synastry tells you how the two of you touch each other. The composite tells you who this “us” is that you make together. The two go hand in hand: you read the synastry first for the conversation, then the composite for the nature of the bond itself. For most people, synastry is more than enough to throw light on what they’re trying to understand.

A compass for the bond, never a compatibility score

Here’s what’s worth holding on to, and it’s the stance running through this whole site: synastry is a mirror for seeing yourselves more clearly together, never a compatibility verdict. It won’t tell you “this will work” or “run.” It hands you a vocabulary for naming what moves between two people: why it pulls here, why it chafes there, where the supports are and where the lessons are.

Liz Greene puts it well: a couple’s chart doesn’t describe a fate, it describes something to work with. The hardest contacts are often the most fruitful, because they bring to light what each person has to learn from the other. A square between your Moons isn’t a sentence, it’s an invitation to understand your rhythms. Read this way, synastry takes nothing away: it hands power back. It turns “are we made for each other?”, a closed, slightly anxious question, into “what can we understand and build together?”, an open and living one.

Astrology stays a symbolic language: it offers a reading, not a proof, and that’s just as it should be. Its value isn’t in predicting a bond, but in helping you look at one with more nuance and more tenderness.

If you want to start right at the beginning, compatibility by sign is the right first step, and the astrology home page lays out the overall map for where all these pieces come from. The day you want to bring two whole charts together, with the real dates, the real times, and the real cities, that overlaying is exactly the work the app does for you, calmly, chart against chart, to help you read the bond rather than score it.

Frequently asked questions

What is synastry?: Synastry is the branch of astrology that studies the bond between two people by comparing their two full birth charts, not just their Sun signs. In practice, you lay the two charts over each other and look at the angles, called aspects, that one person’s planets form with the other’s: one Sun touching the other’s Moon, their Venus and Mars in conversation, their two Moons in echo or in friction. You also notice which houses one person’s planets fall into when placed on the other’s chart, because that shows the areas of life each one lights up in the other. The word comes from the Greek and means "with the stars." Synastry doesn’t score a couple out of ten: it maps a dynamic, the points where two people pull together and the points where they snag, like a chart of the ground they share. It’s a language for understanding each other better, never a pass-or-fail test.
Synastry or sign compatibility: what’s the difference?: Sign compatibility compares two Sun signs, one point out of the ten that make up a chart. It’s a simple way in, perfect for grasping the idea that two temperaments talk to each other, but it stays a shortcut. Synastry compares the two whole charts: each person’s ten planets, their signs, their houses, and every aspect that crosses between them. Two people who share the same pair of Sun signs can live wildly different bonds depending on their Moons, their Venus, their Mars, and their rising signs. Compatibility says "Leo and Aquarius, here’s the general tone"; synastry says "your Mars touches her Venus, your Moon reaches for his Saturn, and your rising signs face each other." One gives you an atmosphere, the other a detailed dynamic. Starting with sign compatibility is a fine idea; synastry is the step after, when you want to understand one specific bond rather than an average tendency.
Do you need both people’s birth times for a synastry?: For a full synastry, yes, ideally both birth times. The time sets the rising sign and the placement of the houses, and that’s exactly what lets you see in which areas of life one person lights up the other, say a Venus that lands in the house of home or in the house of shared work. Without a time, those layers turn hazy and the rising sign, a very telling meeting point, drops out. Even so, a partial reading is still possible and worth doing with only one known time, or none: the aspects between the slow planets and between the personal planets (Sun, Moon apart from time-zone drift, Venus, Mars, Mercury) can largely be worked out from the dates alone. You read the planetary conversation without the map of the houses. It’s less precise, but it isn’t empty: a synastry that’s honest about what it can’t see beats an invented time that skews everything else.