“Are Leo and Scorpio compatible?” is one of the most searched questions in astrology, but Sun signs tell only a small part of the story. Astrologers use synastry: they lay one person’s whole birth chart over the other’s and study how every planet of one touches every planet of the other. It is the most detailed way astrology looks at a relationship, whether romantic, family or friendship.
An honest note: astrology is a spiritual tradition for reflection and fun, not science or prediction. Every relationship is built by the two people in it.
How synastry works
First, both birth charts are calculated. Then each planet in Person A’s chart is compared with each planet in Person B’s chart. When two planets form a meaningful angle (an aspect), they interact. A trine between her Moon and his Sun feels easy and supportive; a square between his Mars and her Saturn creates friction. The tighter the angle (the smaller the orb), the stronger the effect.
The synastry aspects that matter most in love
- Sun–Moon: the classic “marriage aspect”. One partner’s identity naturally nurtures the other’s emotional needs. Conjunctions, trines and sextiles are especially warm.
- Venus–Mars: the chemistry aspect. Venus shows what someone finds attractive and Mars shows how someone pursues it. Even squares here bring strong sparks.
- Moon–Moon: emotional rhythm. Similar Moons recharge in similar ways, which makes daily life easy.
- Moon–Venus: tenderness and affection; you feel emotionally at home together.
- Mercury contacts: how easily you talk, joke, plan and solve problems.
- Saturn contacts: the “glue” of long-term relationships. Harmonious Saturn aspects bring loyalty and commitment; hard ones can feel heavy but often appear in couples who stay together for decades.
- Ascendant contacts: instant recognition and first-sight attraction.
- Outer planets: Jupiter brings generosity and growth, Uranus excitement and freedom, Neptune a dreamy soulmate feeling (and some illusion), Pluto intensity and transformation.
Are hard aspects bad?
No. Squares and oppositions create tension, but tension is also attraction, passion and growth. A relationship with only easy aspects can feel pleasant yet flat, while many lasting couples share strong hard aspects. What matters is the mix, and how the two of you handle it.
House overlays: where you light each other up
With birth times, you can see where one person’s planets fall in the other’s houses. If your Venus lands in your partner’s 7th house, you activate their sense of partnership; if their Jupiter lands in your 10th, they may support your career. Overlays show which areas of life you bring to each other.
The composite chart: your relationship as its own being
A composite chart blends two charts into one by taking the midpoint of each pair of planets. The composite Sun describes the purpose of the relationship, the composite Moon its emotional climate and the composite Venus its love style. Synastry shows how you affect each other; the composite shows what you create together.
Sun sign compatibility vs synastry
Sun-sign compatibility compares one planet out of ten. Two “incompatible” Sun signs can still share a beautiful Moon–Venus trine or a committed Saturn bond, which is why full synastry is far more nuanced. For a quick overview of each sign’s traditional matches, see our zodiac profiles, such as Aries, Leo or Scorpio.
Try a free synastry reading
Barry’s free synastry and love compatibility calculator does all of this for you. Enter two birthdays (and times and cities if you know them) to get an overall score, five category scores, a bi-wheel of both charts, your strongest bonds and growth edges, Venus–Mars chemistry, house overlays, your composite chart and every synastry aspect explained. It is free, with no sign-up.
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