Synastry Aspects Explained: How Two Charts Actually Interact

Overlay two birth charts and the planets of one person form angles to the planets of the other. Those angles — synastry aspects — are the vocabulary astrology uses to describe how two patterns interact: where they reinforce each other, where they grind, and which of the two tends to initiate the friction.

This guide covers the aspect types, the planet pairs that matter most, and the reason a synastry read in both Tropical and Sidereal can say more than either system alone. Throughout, one rule from our philosophy: aspects describe tendencies in a dynamic, not verdicts about whether two people belong together.

The five major aspects, between two charts#

Conjunction (0°). Your planet sits on theirs. Whatever those two planets do, they now do it together, all the time — the most concentrated form of contact. A Moon-Moon conjunction tends to feel like emotional shorthand; a Mars-Saturn conjunction tends to feel like someone riding the brake on someone else's accelerator.

Square (90°). The planets work at cross purposes and neither can ignore the other. Squares generate the most friction — and the most engagement. Relationships with no cross-chart squares at all often report low charge; the grind is where the aliveness tends to live.

Trine (120°). The planets support each other without effort. Comfortable, low-maintenance — and easy to take for granted, because the dynamic works even when nobody is tending it.

Opposition (180°). The planets face each other across the wheel. In synastry this often reads as complementarity with a tug-of-war inside it: each person holds the end of a pole the other lacks.

Sextile (60°). A softer support than the trine — the dynamic works if someone acts on it. Sextiles describe opportunities in a relationship rather than defaults.

Orb — the distance from exactness — is the volume knob. A square at 0°30′ runs loud in daily life; the same square at 7° hums in the background. When we compute a synastry reading, tight orbs are weighted far more heavily than wide ones, and every aspect we cite is checked against the actual computed positions before it reaches you.

The planet pairs worth reading first#

Sun–Moon. (full guide) The classic. One person's core direction meets the other's emotional metabolism. Harmonious contacts tend to feel like being understood without explaining; hard contacts describe a recurring mismatch between what one wants to do and what the other needs to feel safe.

Moon–Moon. How two emotional systems co-regulate. Same-element Moons tend to default to the same coping style — which doubles both its strengths and its blind spots.

Venus–Mars. (full guide) Attraction mechanics: how one person's way of valuing meets the other's way of pursuing. Easy contacts read as chemistry; hard contacts read as push-pull — magnetic in some pairs, depleting in others, and usually both at different times.

Mercury contacts. How the two of you actually talk. Mercury squares are behind a large share of "we keep having the same argument" reports — not because either person is wrong, but because the two minds sort information differently.

Saturn contacts. (full guide) Where time, structure, and obligation enter. Saturn synastry has a heavy reputation, but tight Saturn contacts show up constantly in relationships that last — the same weight that can feel limiting is also what holds shape under pressure.

Mars–Pluto and other outer-planet contacts. Intensity, will, and power dynamics. These describe the strongest currents in a bond and reward the most honest reading — the question isn't whether the current exists but what each person does with it.

Why we read synastry in two zodiacs#

Most synastry tools use only the Tropical zodiac. The angles between planets barely change between systems — but the signs those planets occupy often do, and sign context changes how an aspect expresses. A Venus-Mars square between fire signs plays differently than the same square shifted into earth signs by the sidereal frame.

Reading both systems side by side does two useful things: dynamics that repeat in both frames are flagged as the most persistent ones, and dynamics that differ between frames get a surface/deeper split — the same layering we use in the five-system natal reading. The systems don't contradict each other; they describe different depths of the same connection.

What the Aspect Grid Asks of You#

An aspect grid is a map of mechanics: where a connection flows, where it grinds, who tends to set off which pattern in whom. What it cannot do is tell you whether to stay, leave, commit, or walk away — that decision the chart always hands back to you. The most useful way to hold a synastry grid is as a description of tendencies you can now name instead of being surprised by. A square you understand is easier to work with than one you keep tripping over. But the grid describes a dynamic between two people, and half of that dynamic is you — your own chart, your own patterns, the aspects you bring into every relationship before the other person's chart ever touches yours. Knowing your own grid first makes every overlay easier to read honestly.

Questions to sit with#

• When you look back at your relationships, which friction shows up again and again — regardless of who the other person is? That repetition usually points at your own chart, not theirs.
• Where do you tend to read intensity as compatibility, and where has that reading served you well or led you astray?
• Run your own chart at /chart and note your tightest inner-planet aspects: which of them describes a pattern you carry into every close relationship?

Growing with Synthesis AI Chat#

The Synthesis AI Chat reads your own chart and remembers what you've explored across conversations, so you can trace the patterns you personally bring to relationships over time. It reads your chart, not a partner's, so keep the questions about your own tendencies:

• "My Venus squares my Mars natally — how does that internal tension show up in how I pursue and receive love?"
• "What relational pattern do I keep repeating, and where in my chart does it live?"
• "How can I work with my Moon-Saturn aspect instead of letting it make me guarded?"

For the actual two-chart comparison, use the synastry reading. Synthesis AI Chat is part of Synthesis AI Chat ($10/mo), and every $28 full reading includes a month of full access. Start a conversation at /chat.

What synastry can't tell you#

An honest limit, stated plainly: no aspect grid can tell you whether to stay, leave, commit, or walk away. Synastry maps the mechanics of a dynamic — where it flows, where it grinds, who tends to initiate which pattern. What you do with the mechanics is a decision the chart hands back to you.

That's also why our synastry reading asks who the other person is to you — partner, parent, coworker, friend — and what you actually want to understand. A Mars square read for a business partnership is a different paragraph than the same square read for a marriage. The free overview shows the aspect grid and compatibility scores across both zodiacs; the full reading writes the pattern up for your specific relationship.