Synastry in Astrology: How Compatibility Really Works

Synastry is the branch of astrology that compares two birth charts to understand a relationship. It goes far beyond sun sign compatibility - looking at how every planet in one chart interacts with every planet in the other.

If you have ever wondered why you click instantly with some people and clash with others who seem like they should be compatible, synastry has answers.

How Synastry Works

In synastry, you overlay two birth charts and examine how the planets in one chart aspect (form geometric angles to) the planets in the other chart. The core idea: planetary contacts between charts create energetic exchanges between people.

Each type of contact has a different quality:

• Conjunctions (0 degrees): The strongest connection. The two planets merge energy. Can be harmonious or intense depending on the planets.
• Trines (120 degrees): Easy, flowing energy. Natural compatibility in that area of life. Can sometimes be too comfortable.
• Sextiles (60 degrees): Gentle support. Opportunities for connection that require some effort to activate.
• Squares (90 degrees): Friction and tension. Creates challenge but also passion and growth. Many long-lasting relationships have strong squares.
• Oppositions (180 degrees): Magnetic attraction between opposites. Can feel like the other person has what you lack. Requires balance.

The Most Important Synastry Aspects

Not all planetary contacts are created equal. Here are the ones that matter most:

Sun-Moon Contacts

The most classic compatibility indicator. When one person's Sun conjuncts, trines, or sextiles the other's Moon, there is a natural understanding. The Sun person feels seen; the Moon person feels supported. Sun-Moon conjunctions in synastry often indicate couples who feel like they have known each other forever.

Venus-Mars Contacts

The chemistry aspects. Venus-Mars contacts create physical and romantic attraction. A conjunction or opposition between one person's Venus and the other's Mars is one of the strongest indicators of sexual chemistry. Even squares between Venus and Mars create tension that often manifests as desire.

Moon-Moon Contacts

Emotional compatibility. When two people's Moons are in harmonious aspect, they process emotions similarly and feel safe with each other. Moon conjunctions create deep emotional bonding. Moon squares can create misunderstandings around emotional needs.

Saturn Contacts

The commitment indicator. Saturn aspects in synastry are not romantic, but they create staying power. Saturn conjunct someone's Sun or Moon can feel restrictive at first but often indicates a relationship that lasts. Many married couples have strong Saturn contacts.

North Node Contacts

The "pull" feeling. When someone's planet conjuncts your North Node, the relationship often feels significant and hard to ignore. These contacts suggest the relationship has a growth purpose - the other person helps you move toward your life direction.

House Overlays: Where They Impact Your Life

Beyond aspects, synastry looks at which houses of your chart the other person's planets fall in. This reveals which areas of your life the person activates.

• 1st House overlay: They affect your identity and self-image
• 4th House overlay: They feel like home, affect your domestic life
• 5th House overlay: Romance, fun, creativity together
• 7th House overlay: Classic partnership energy, they mirror you
• 8th House overlay: Deep transformation, intensity, shared resources
• 10th House overlay: They affect your career and public image

Sidereal vs Tropical Synastry

Here is where it gets interesting. Since sidereal placements differ from tropical by about 24 degrees, your synastry aspects can be completely different in each system.

A couple might have a Venus-Mars trine in tropical but a Venus-Mars square in sidereal. This does not mean one reading is wrong - it means the relationship has layers:

• Tropical synastry often describes the relationship's conscious dynamic - how it feels day to day, the patterns you are aware of
• Sidereal synastry can reveal the deeper underlying connection - why you are really drawn to each other, what the relationship is fundamentally about

Seeing both systems side by side often explains why a relationship can feel harmonious on the surface but challenging underneath (or vice versa).

Common Myths About Synastry

Myth: Some signs are incompatible. Reality: Sign compatibility is the most superficial level of synastry. A Scorpio and a Leo might have terrible sun sign compatibility but amazing Venus-Moon contacts that make the relationship work beautifully.

Myth: You need mostly trines and sextiles. Reality: Relationships with only easy aspects often lack spark. Some of the most passionate, growth-oriented relationships have significant squares and oppositions. The key is having a mix.

Myth: One bad aspect ruins everything. Reality: No single aspect makes or breaks a relationship. Synastry is about the full picture. A challenging Saturn square matters less if there are strong Venus-Moon trines to provide warmth.

Getting Your Synastry Chart

To do synastry properly, you need accurate birth charts for both people - including birth time (for house overlays and Ascendant contacts) and birth location.

Synthesis Astrology's synastry calculator compares two charts in both Tropical and True Sidereal systems, showing you the full picture of your compatibility - the conscious dynamic and the deeper connection.

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Curious about your compatibility? Try the Synastry Calculator to see how your charts interact in both zodiac systems.